Journal of Colloid And Interface Science (v.355, #2)
A facile strategy for synthesis of multilayer and conductive organo-silica/polystyrene/polyaniline composite particles
by Yunxing Li; Zhaoqun Wang; Hao Gu; Gi Xue (pp. 269-273).
A facile strategy is exploited intelligently to fabricate the multilayer and conductive organo-silica/polystyrene/polyaniline (organo-silica/PS/PANi) composite particles with well-defined morphology and a narrow size distribution.Display Omitted► We simplified preparation process without any surface treatments of substrates. ► Organo-silica/PS/PANi composite particles were prepared by distinct SDIPM. ► Multilayer composite particles had good morphology and narrow size distribution.By means of a facilely designed strategy, we successfully fabricated the multilayer and conductive organo-silica/polystyrene/polyaniline (organo-silica/PS/PANi) composite particles. First, organo-silica/PS core/shell composite particles were synthesized by seeded emulsion polymerization and the vinyl groups located on the surface of organo-silica nanoparticles were used to induce in situ polymerization of styrene. The influence of the route of the addition of styrene on the morphology of organo-silica/PS composite particles was investigated. Then, the coating of organo-silica/PS composite particles with PANi was achieved by virtue of the “Swelling–Diffusion–Interfacial-Polymerization Method” (SDIPM). The whole preparation process was monitored by transmission electron microscope, scanning electron microscope, Fourier transform infrared, Raman spectroscopy, dynamic light scattering, and thermogravimetry. As a result, the multilayer and conductive organo-silica/PS/PANi nanocomposites possessed of a uniform size and well-defined morphology, and furthermore, their structure could be well controlled by simply changing the weight ratio of aniline/PS.
Keywords: Multilayer nanocomposites; Conductive polymer; Nanoparticle; Diffusion control; Structure control
UV luminescent organic-capped ZnO quantum dots synthesized by alkoxide hydrolysis with dilute water
by Takahisa Omata; Kazuyuki Takahashi; Shinichi Hashimoto; Yasuhiro Maeda; Katsuhiro Nose; Shinya Otsuka-Yao-Matsuo; Kenji Kanaori (pp. 274-281).
A novel technique to synthesize organic-capped ZnO QDs has been developed. The UV emission intensity is higher than that of the Vis emission and adjustable by the QD size.Display Omitted► Organic-capped and colloidal ZnO quantum dots that are dispersible in various organic solvents have been synthesized by alkoxide hydrolysis based reaction and successive surface capping with oleylamine. ► The ZnO quantum dots exhibit quantum size effect on their UV emission. ► The defect-related visible emission that usually appears for the ZnO was highly depressed by using a high purity zinc alkoxide as a starting material.A novel synthesis route to organic-capped and colloidal ZnO quantum dots (QDs) has been developed. Specifically, zinc-di- t-butoxide and zinc-di- n-butoxide are hydrolyzed by very dilute water (400–600 mass ppm) in hydrophilic benzylamine and polymerized to ZnO by dehydration and/or a butanol elimination reaction. Growth of the ZnO QDs and exchange of the surface capping ligand from the hydroxyl groups and/or benzylamine to the oleylamine occur by heating the colloidal solution after addition of the oleylamine at 100–180°C. The final ZnO QDs with diameters in the range of 3–7nm are highly dispersible in various organic solvents. The ZnO QDs exhibit the quantum size effect upon UV emission; it was controlled between 3.39 and 3.54eV in the present study. The defect-related Vis emission decreased and the UV emission becomes dominant when zinc-di- n-butoxide with a 99.99% zinc purity is used as the starting material. The intensity of the photoluminescence UV emission is 1.5 times higher than that of the Vis emission.
Keywords: Zinc oxide; Quantum dots; Solution process; Colloidal solution; UV emission
Characterization of iron hydroxide/oxide nanoparticles prepared in microemulsions stabilized with cationic/non-ionic surfactant mixtures
by Ali Bumajdad; Sami Ali; Asha Mathew (pp. 282-292).
Stability of iron hydroxide nanoparticles prepared in microemulsions as a function of precipitating agent. NH3-precipitated nanoparticles (right) and TBAH-precipitated particles (left).Display Omitted► Tetrabutylammonium hydroxide, promotes precipitation of nanoparticles out of the microemulsion. ► Tetrabutylammonium cations, block the pores of the powders which are removed by calcination. ► The droplet size and surfactant concentration have no direct effect on the dispersed nanoparticles. ► The droplet size and surfactant concentration have effects on the nanoparticle powders. ► High surfactant concentration and small droplets give the highest surface areas powders.Iron oxide-hydroxide (α-Fe2O3; Fe(OH)3) nanoparticles have been prepared by a microemulsion route using ammonia (NH3) solution or tetrabutylammonium hydroxide (TBAH) as precipitants. The iron oxide–hydroxide nanoparticles obtained were characterized by TGA, N2 sorptiometry, XRD, IR, SEM, HR-TEM, and DLS techniques. Properties such as specific surface area ( SBET), pore sizes and shapes, average particle size and distribution, crystallite structure, and thermal stability were determined. The properties of nanoparticles prepared using NH3 and TBAH were compared after drying at 100°C and after being calcined in the temperature range 250–1100°C. It was found that the suspensions prepared using TBAH suffered immediate separation while those prepared using NH3 resulted in very stable suspensions. Also, it was found that TBAH did not offer any advantage over NH3 either in terms of specific surface area or in particle size of the prepared nanoparticles. Hence, the later part of the study was concentrated on the NH3-precipitated nanoparticles with particular emphasis on finding the most favorable, W (water-to-surfactant ratio) and/or surfactant concentration, S, to obtain the best conditions in terms of higher surface areas and narrower particle size distribution. It was found that the prepared suspension consisted of monodisperse nanoparticles (standard deviations <10%) and after separation and drying, high surface area powders were obtained. The highest surface area (315m2g−1) was obtained when the smallest W (=20) and highest S (=0.20molL−1) were employed.
Keywords: Fe; 2; O; 3; Iron oxide; Haematite; Hematite; Iron oxide nanoparticle; Water-in-oil microemulsion; Surfactant mixture; Cationic surfactant; Non-ionic surfactant; DDAB; Brij 35
Electroless synthesis of multibranched gold nanostructures encapsulated by poly( o-phenylenediamine) in Nafion
by Subramani Thangavel; Ramasamy Ramaraj (pp. 293-299).
Novel P oPD encapsulated cactus like Au nanocomposites materials were synthesized in Nafion film through the electroless synthetic route.Display Omitted ► o-Phenylenediamine ( oPD) acts as a reducing agent and P oPD encapsulates Aunano. ► First report on the preparation of cactus like Aunano@P oPD in Nafion matrix. ► Nafion film acts as a reaction vessel and as the template for Aunano formation. ► Both P oPD and Aunano are electrochemically active.Multibranched gold (Au) nanocomposite materials encapsulated by poly( o-phenylenediamine) (P oPD) (Au@P oPD) were synthesized in a Nafion polymer film through the electroless synthetic route. The micro-heterogeneous structured Nafion film acted as a reaction vessel and as the template for the formation of Au@P oPD nanocomposite materials leading to the formation of highly uniform distribution of high density of the polymer–gold nanocomposite material. The formation of Au@P oPD nanomaterials at the GP/Nf surface was scrutinized by recording in situ absorption spectra and was characterized. The formation of the (111) plane of gold was dominant at the Au@P oPD nanocomposite. The ratio of the benzenoid and quinoid units of the P oPD (ca. 1.65) observed for the Au@P oPD confirmed that the micro-heterogeneous structure of Nf film acted as a reaction vessel and as template for the formation of Au@P oPD nanocomposite material. Both P oPD and Au at the Au@P oPD nanocomposite showed electrochemical activities at the GC/Nf–Au@P oPD modified electrode. The electrocatalytic activity of the GC/Nf–Au@PoPD modified electrode was studied for oxygen reduction reaction (ORR).
Keywords: Polymer–metal nanocomposite; Gold nanostructure; Polyelectrolyte; Conductive polymer; Oxygen reduction; Modified electrode
Structural, textural and adsorption characteristics of nanosilica mechanochemically activated in different media
by V.M. Gun’ko; E.F. Voronin; L.V. Nosach; V.V. Turov; Z. Wang; A.P. Vasilenko; R. Leboda; J. Skubiszewska-Zięba; W. Janusz; S.V. Mikhalovsky (pp. 300-311).
Mechanochemical activation of nanosilica, compacting secondary particles, changes adsorption characteristics and bound water structure.Display Omitted► Mechanochemical activation of nanosilica. ► Compaction of nanoparticle aggregates changes textural porosity. ► Adsorption of water increases but adsorption of protein decreases. ► Free surface energy and fractality of treated wetted silica decrease.The structural, textural, and adsorption characteristics of mechanochemically activated (MCA) fumed silica A-300 as dry or water, ethanol, or water/ethanol-wetted powders (0.5g of a solvent per gram of silica) in a ball mill for 1–6h were studied in comparison with those of the initial powder. The MCA treatment enhances bulk density ( ρb) of the powder (from 0.045g/cm3 for the initial silica to 0.4g/cm3 for 6h-MCA-treated water-wetted silica) depending on medium type and MCA time ( tMCA). Stronger effects are observed for the MCA treatment of water-wetted silica than of dry or ethanol- or water/ethanol-wetted samples. The MCA treatment weakly affects the specific surface area ( SBET). However, void (pore) size distribution, porosity, particle aggregation and size distribution in aqueous suspension, behavior of interfacial water, properties of poly(vinyl alcohol)/silica composites and adsorption of gelatin depend more strongly on the tMCA and ρb values. Some of the observed changes in the characteristics (e.g., gelatin adsorption) depend on the ρb value but are independent of the medium type used on the MCA. Other characteristics are nonlinear functions of both tMCA and ρb values.
Keywords: Fumed silica; Mechanochemical activation; Textural characteristics; Aqueous suspension; Particle size distribution; Interfacial water behavior; Gelatin adsorption; PVA/silica film
Fast and facile synthesis of silica coated silver nanoparticles by microwave irradiation
by Newaz Mohammed Bahadur; Takeshi Furusawa; Masahide Sato; Fumio Kurayama; Iqbal Ahmed Siddiquey; Noboru Suzuki (pp. 312-320).
Silica coated silver nanoparticles with different silica shell thickness were prepared by a novel, fast and facile microwave (MW) technique. Prepared particles were functionalized with different groups for many applications.Display Omitted► Silica coated silver nanoparticles were prepared by a novel microwave (MW) irradiation method. ► Without using primer or pre-coating step, silica coating was performed within 2min of MW irradiation. ► Prepared particles were functionalized with different groups for many applications. ► Detailed characterization of the prepared samples was carried out by different techniques.A novel, fast and facile microwave technique has been developed for preparing monodispersed silica coated silver (Ag@SiO2) nanoparticles. Without using any other surface coupling agents such as 3-aminopropyltrimethoxysilane (APS) or polymer such as polyvinyl pyrrolidone (PVP), Ag@SiO2 nanoparticles could be easily prepared by microwave irradiation of a mixture of colloidal silver nanoparticles, tetraethoxysilane (TEOS) and catalyst for only 2min. The thickness of silica shell could be conveniently controlled in the range of few nanometers (nm) to 80nm by changing the concentration of TEOS. Transmission electron microscopy (TEM) and UV–visible spectroscopy were employed to characterize the morphology and optical properties of the prepared Ag@SiO2 nanoparticles, respectively. The prepared Ag@SiO2 nanoparticles exhibited a change in surface plasmon absorption depending on the silica thickness. Compared to the conventional techniques based on Stöber method, which need 4–24h for silica coating of Ag nanoparticles, this new technique is capable of synthesizing monodispersed, uniform and single core containing Ag@SiO2 nanoparticles within very short reaction time. In addition, straightforward surface functionalization of the prepared Ag@SiO2 nanoparticles with desired functional groups was performed to make the particles useful for many applications. The components of surface functionalized nanoparticles were examined by Fourier transform infrared (FT-IR) spectroscopy, zeta potential measurements and X-ray photoelectron spectroscopy (XPS).
Keywords: Silver nanoparticles; Silica coating; Core–shell; Microwave irradiation; Transmission electron microscopy; X-ray photoelectron spectroscopy
Symmetric and asymmetric adsorption of pH-responsive gold nanoparticles onto microgel particles and dispersion characterisation
by Melanie Bradley; Beatriz Sanchez Garcia-Risueño (pp. 321-327).
The influence on the dispersion properties of symmetric and asymmetrically modified microgel particles through the adsorption of carboxylic acid-stabilised gold nanoparticles.Display Omitted► The characterisation of rarely studied pH-responsive microgel particles and carboxylic acid-stabilised gold nanoparticles. ► The influence on microgel dispersion properties, such as particle size and electrophoretic mobility, by the adsorption of gold nanoparticles onto the microgel network. ► The asymmetric modification of microgel particles through adsorption of gold nanoparticles from a particle-stabilised emulsion. ► The effect of pH on the dispersion stability and properties of composite microgel particles.The interaction between carboxylic acid-stabilised gold nanoparticles (AuNP) and pH-responsive microgels is shown. The microgel particles are a copolymer of N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) and N-isopropylacrylamide (NIPAM). The microgel properties are presented by their hydrodynamic diameter and electrophoretic mobility in response to pH. These microgel particles are pH-responsive under neutral conditions decreasing in diameter beyond pH 7. The dispersion characteristics of AuNP adsorbed onto the microgel network are shown with respect to adsorbed amount and the pH-responsive properties of the AuNP. This data is presented between pH 3 and 6 where the microgel properties remain constant. Asymmetric adsorption of AuNP onto poly(DMAPMA-co-NIPAM) microgels is achieved by adsorption of nanoparticles, from the aqueous phase, onto microgel-stabilised oil-in-water emulsions. These asymmetrically modified microgels display very different dispersion behaviour, in response to pH, due to their dipolar nature.
Keywords: Microgel; Adsorption; Asymmetric; Gold nanoparticles
Mesoporous Fe2O3-doped TiO2 nanostructured fibers with higher photocatalytic activity
by Sihui Zhan; Jiangyao Yang; Yu Liu; Nan Wang; Jingjing Dai; Hongbing Yu; Xichao Gao; Yi Li (pp. 328-333).
Mesoporous Fe2O3-doped TiO2 nanostructured fibers were fabricated through electrospinning relevant gel precursors. Compared with different types of photocatalysts, the 1% Fe2O3-doped TiO2 fibers exhibited higher photocatalytic activity.Display Omitted► Long mesoporous Fe2O3-doped TiO2 fibers with high surface areas were prepared by the sol–gel and electrospinning techniques. ► The mesoporous fibers were as long as 20cm with diameters of 0.5–2μm. ► N2 adsorption–desorption isotherms gave a BET surface area of 200–228m2/g and average pore size of 6.5nm. ► These mesoporous 1% Fe2O3-doped TiO2 fibers showed higher photocatalytic activity toward decomposition of MB than many other catalysts. ► In addition, the long composite fibers can be conveniently fixed and reclaimed so that they are good candidates for photocatalytic applications.Mesoporous Fe2O3-doped TiO2 nanostructured fibers were fabricated through electrospinning the relevant gel precursor. The prepared fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and surface analysis, respectively. The photocatalytic activity of these mesoporous composite fibers was evaluated by photocatalytic degradation of methylene blue (MB) in water under UV irradiation. Compared with different types of photocatalysts, the 1% Fe2O3-doped TiO2 fibers exhibited super photocatalytic activity.
Keywords: Mesoporous Fe; 2; O; 3; -doped TiO; 2; Nanostructured fibers; Electrospin; MB
A solid-state NMR study of structure and segmental dynamics of poly(propylmethacryl-heptaisobutyl-pss)-co-styrene nanocomposites
by Qin Zou; Limin Zhang; Shenhui Li; Xiuzhi Gao; Feng Deng (pp. 334-341).
The domain structure of the nanocomposites was investigated by spin-diffusion solid-sate NMR technique. The dispersed POSS domain size was increased with the POSS loading.Display Omitted► The domain structure and mobility of a type of POSS nanocomposites were investigated by various solid-state NMR techniques. ► Increasing POSS content trended to mobilize the chains in PS units. ► The dispersed POSS domain size determined was increased with the POSS loading.The domain structure and mobility of poly(propylmethacryl-heptaisobutyl-pss)-co-styrene nanocomposites with different polyhedral oligomeric silsesquioxane (POSS) contents were investigated by various solid-state NMR techniques in combination with XRD. The NMR relaxation time measurements suggested that increasing POSS content trended to mobilize the chains in PS unit. Although XRD results showed that POSS was well dispersed into the polymer matrix, 2D WISE NMR indicated that the dispersion of POSS into the polymer matrix led to a composite structure composed of rigid and densely packed PS domain and mobile and amorphous POSS domain. This implied that the size of the two domains was very small. 2D HETCOR NMR implied that the distance between PS network and POSS unit gradually decreased when the POSS content successively increased. The dispersed POSS domain size determined by 2D spin-diffusion NMR experiments was increased with the POSS loading, being about 3.0, 3.9, 6.0nm for the POSS15, POSS25 and POSS45 nanocomposites, respectively.
Keywords: Solid-state NMR; Spin diffusion; NMR relaxation; POSS nanocomposites
Interactions between single-walled carbon nanotubes and lysozyme
by F. Bomboi; A. Bonincontro; C. La Mesa; F. Tardani (pp. 342-347).
Schematic representation of single-walled carbon nanotubes and lysozyme.Display Omitted► Single-Walled Carbon Nanotubes stabilization by protein was investigated. ► Interactions were studied as a function of both protein content and pH of the medium. ► Dielectric relaxation, electrophoretic mobility and circular dichroism were used. ► The results show protein binding to saturation and depletion phenomena. ► Stabilization of composite dispersions is controlled by electrostatics and adsorption.Dispersions of single-walled and non-associated carbon nanotubes in aqueous lysozyme solution were investigated by analyzing the stabilizing effect of both protein concentration and pH. It was inferred that the medium pH, which significantly modifies the protein net charge and (presumably) conformation, modulates the mutual interactions with carbon nanotubes. At fixed pH, in addition, the formation of protein/nanotube complexes scales with increasing lysozyme concentration. Electrophoretic mobility, dielectric relaxation and circular dichroism were used to determine the above features. According to circular dichroism, lysozyme adsorbed onto nanotubes could essentially retain its native conformation, but the significant amount of free protein does not allow drawing definitive conclusions on this regard. The state of charge and charge distribution around nanotubes was inferred by combining electrophoretic mobility and dielectric relaxation methods. The former gives information on changes in the surface charge density of the complexes, the latter on modifications in the electrical double layer thickness around them. Such results are complementary each other and univocally indicate that some LYS molecules take part to binding.Above a critical protein/nanotube mass ratio, depletion phenomena were observed. They counteract the stabilization mechanism, with subsequent nanotube/nanotube aggregation and phase separation. Protein-based depletion phenomena are similar to formerly reported effects, observed in aqueous surfactant systems containing carbon nanotubes.
Keywords: Carbon nanotube; Lysozyme; Electrophoretic mobility
Mesoporous silica hybrid membranes for precise size-exclusive separation of silver nanoparticles
by Moataz M. Mekawy; Akira Yamaguchi; Sherif A. El-Safty; Tetsuji Itoh; Norio Teramae (pp. 348-358).
Size-exclusion separation of Ag NPs using hybrid membranes.Display Omitted► Highly ordered mesoporous silicas hybrid AAM membranes were successfully fabricated through a template-guided method with a number of Brij-type surfactants. ► The mesoporous silicas are vertically aligned in the AAM channels, with a predominantly columnar orientation. ► The membranes show promise as a size-exclusive separation system in isolating Ag NPs in both aqueous and organic solution phases. ► The development of size-exclusive membranes composed of mesostructures would be indispensible for the production of uniform Ag NPs with unique properties.One-dimensional (1D) nanomaterials have unique applications due to their inherent physical properties. In this study, hexagonally ordered mesoporous silica hybrid anodic alumina membranes (AAM) were synthesized using template-guided synthesis with a number of nonionic n-alkyl-oligo(ethylene oxide), Brij-type (C xEO y), which are surfactants that have different molecular sizes and characteristics. The hexagonal mesoporous silicas are vertically aligned in the AAM channels with a predominantly columnar orientation. The hollow mesostructured silicas had tunable pore diameters varying from 3.7 to 5.1nm. In this synthesis protocol, the surfactant molecular natures (corona/core features) are important for the controlled generation of ordered structures throughout AAM channels. The development of ultrafiltration membranes composed of silica mesostructures could be used effectively in separating silver nanoparticles (Ag NPs) in both aqueous and organic solution phases. This would be relevant to the production of well-defined Ag NPs with unique properties. To create a size-exclusive separation system of Ag NPs, we grafted hydrophobic trimethylsilyl (TMS) groups onto the inner pores of the mesoporous silica hybrid AAM. The immobilization of the TMS groups allowed the columnar mesoporous silica inside AAM to retain this inner pore order without distortion during the separation of solution-phase Ag NPs in organic solvents that may cause tortuous-pore membranes. Mesoporous TMS-silicas inside 1D AAM channels were applicable as a size-exclusive separation system to isolate organic solution-phase Ag NPs of uniform morphology and size.
Keywords: Mesoporous silica; One-dimensional channels; Membrane; Silver nanoparticles
Fabrication of high-aspect-ratio poly(2-hydroxyethyl methacrylate) brushes patterned on silica surfaces by very-large-scale integration process
by Jem-Kun Chen; Tsung-Yen Chen (pp. 359-367).
A novel fabricated process including electron beam and isotropic oxygen plasma was used to generate signal line patterns of polymerized 2-hydroxyethyl methacrylate (HEMA) with 350nm and 0.27 of resolution and high-aspect-ratio on patterned Si(100) surfaces, respectively.Display Omitted► With E-beam and isotropic oxygen plasma, generated a high aspect ratio of PHEMA brushes. ► The active grafting specie deactivation is quantitatively proved for ATRP system. ► Resolutions of the line patterns of the PHEMA brush are approached to 350nm. ► Good and poor solvent immersion for the PHEMA brushes could greatly affect the aspect ratios.We used a novel fabricated process including electron beam and isotropic oxygen plasma to generate signal line patterns of polymerized 2-hydroxyethyl methacrylate (HEMA) on patterned Si(100) surfaces. Isotropic oxygen plasma was introduced to enhance the resolutions of the line and dots patterns of the PHEMA brush are approached to 350nm and 2μm, respectively. We established the surface grafting polymerization kinetics of the PHEMA chains on silicon surface by to fit the thickness and number-average molecular weight (M n). The propagation rate (k p) and active grafting specie deactivation rate (k d) lies in the range of ∼3.6×10−2 s−1M−1 and 4.8×10−5s−1, respectively. The measured thicknesses by ellipsometer and analyzedM n of “free” PHEMA by gel permeation chromatography (GPC) are fitted well by the polymerization kinetic model. In addition, aspect-ratios (height/width) are used to define the shape of patterned PHEMA brushes. The high-aspect-ratio of the PHEMA brush line with width of 350nm is 0.27. We use a graft polymerization/solvent immersion method for generating various patterns of polymer brushes to investigate the deformation of the PHEMA brush through aspect-ratios.
Keywords: High-aspect-ratio; PHEMA; Polymer brush; Patterns
Influence of assembly pH on compression and Ag nanoparticle synthesis of polyelectrolyte multilayers
by Xiao Gong; Lulu Han; Yanan Yue; Jianrong Gao; Changyou Gao (pp. 368-373).
Assembly pH of the multilayers has a great impact on their compression behavior, resulting in a compression ratio of 70% at pH 4 and 50% at other pHs.Display Omitted► Compression ratio of multilayers depends on their assembly pH. ► Compression of the multilayers reduces Ag NPs amount. ► Multilayer thickness is significantly reduced after Ag NPs synthesis.Influence of assembly pH on compression and Ag nanoparticle synthesis of polyelectrolyte multilayers was studied using poly(diallyldimethylammonium chloride) (PDADMAC) and poly(4-styrenesulfonic acid-co-maleic acid, 1:1SS:MA) sodium salt (PSSMA 1:1) as the building blocks. The thickest multilayers turned out at pH 4. A homogeneous compression by a silicone rubber stamp increased significantly the water contact angle to a same value which was independent on the original assembly pH anymore. The multilayers assembled at pH 4 could be maximumly compressed to a ratio of 70% by a silicone rubber stamp with linear patterns, which was considerably larger than those assembled at other pHs (the compression ratio ∼50%). The Ag nanoparticles were then synthesized inside the multilayers either flat compressed or not. The results showed that the compression reduced significantly the amount of Ag nanoparticles for the multilayers assembled at pH 2 and pH 4. The particle amount was also decreased significantly when the multilayers were assembled at higher pH, pH 6, for example, regardless of the compression. Substantial alteration of the multilayers in terms of the surface morphology, thickness and refractive index was found during the reduction of Ag+ containing multilayers by NaBH4 solution.
Keywords: Compression; Patterns; Multilayers; Polyelectrolytes; Silver nanoparticles
Polyphosphazene nanoparticles for cytoplasmic release of doxorubicin with improved cytotoxicity against Dox-resistant tumor cells
by Cheng Zheng; Jing Xu; Xiaping Yao; Jian Xu; Liyan Qiu (pp. 374-382).
pH-responsive nanoparticles based on novel pH-responsive polyphosphazenes facilitate cytoplasmic release of cargo drugs through membrane disruption, which results in highly improved cytotoxicity against adriamycin-resistant cancer cells.Display Omitted► Novel pH-responsive polyphosphazenes are developed. ► Nanoparticles derived from these polymers exhibit fast pH-responsive drug release. ► pH-responsive polyphosphazenes can disturb endosomal membrane and release cargo drug into cytosol.This study involved the construction of self-assembled nanoparticles from novel pH-sensitive amphiphilic polyphosphazenes. These nanoparticles provide fast pH-responsive drug release and have the capability to disturb endosomal membranes. The polymers were prepared by linking N, N-diisopropylethylenediamine (DPA) onto a backbone of PEGylated polyphosphazene. In vitro cell viability measurements demonstrated the superior efficacy of these pH-responsive nanoparticles over free doxorubicin (Dox): the IC50 was over 60 times lower than that of free Dox against a Dox-resistant cell line. Using flow cytometry and confocal microscopy, the further investigation of the intracellular distribution of Dox and fluorescent probes provided evidence that, upon internalization by cells through endocytic pathways, the pH-sensitive polymer would disrupt membranes of endosomal compartments, releasing the cargo drugs into the cytoplasm in a burst-like manner. This resulted in reduced likelihood of drug efflux via exocytosis, and reversal of the drug resistance of the tumor cells. Generally, the pH-responsive nanoparticles designed in this study have achieved their potential as a drug delivery system for tumor therapy applications.
Keywords: pH-responsive polymer; Polyphosphazene; Nanoparticles; Drug resistance; Tumor therapy
Effects of polymer wrapping and covalent functionalization on the stability of MWCNT in aqueous dispersions
by Susana Addo Ntim; Ornthida Sae-Khow; Frank A. Witzmann; Somenath Mitra (pp. 383-388).
(a) Particle size distribution and (b) zeta potential of the F-CNTs as a function of salt concentration. Based on hydrophobicity index, particle size distribution, zeta potential as well as the aggregation kinetics studied using time-resolved dynamic light scattering, the PVP wrapped CNT was somewhat less prone to agglomeration than the covalently functionalized MWCNT–COOH. However, its long-term stability was lower, and this was attributed to the partial unwrapping of the polyvinyl pyrrolidone layer on the CNT surface.Display Omitted► Aggregation behavior of covalent functionalized and poly wrapped colloidal systems differed. ► MWCNT–PVP agglomerated less based on hydrophobicity index, particle size, zeta potential. ► MWCNT–COOH showed higher attachment efficiencies due to stronger surface charges. ► Long-term stability of MWCNT–PVP lower due to potential partial unwrapping of PVP layer.The colloidal behavior of aqueous dispersions of functionalized multiwall carbon nanotubes (F-CNTS) formed via carboxylation and polymer wrapping with polyvinyl pyrrolidone (PVP) is presented. The presence of polymer on the nanotube surface provided steric stabilization, and the aggregation behavior of the colloidal system was quite different from its covalently functionalized analog. Based on hydrophobicity index, particle size distribution, zeta potential as well as the aggregation kinetics studied using time-resolved dynamic light scattering, the PVP wrapped CNT was somewhat less prone to agglomeration. However, its long-term stability was lower, and this was attributed to the partial unwrapping of the polyvinyl pyrrolidone layer on the CNT surface.
Keywords: Carbon nanotubes; Hydrophobicity; Aggregation; Stability
Two-fluid model for the simultaneous flow of colloids and fluids in porous media
by P.M. Biesheuvel (pp. 389-395).
Simultaneous transport of water, ions and colloids through porous media can be elegantly described by a modified two-fluid model.Display Omitted► Theory for the flow of water and particles such as ions and colloids in solution and in porous media. ► For various membrane processes an elegant and comprehensive modeling framework is presented. ► Extension of the mass transport theory is possible, for instance to include effects of ion volume.To describe the velocities of particles such as ions, protein molecules and colloids dispersed or dissolved in a fluid, it is important to also describe the forces acting on the fluid, including pressure gradients and friction of the fluid with the particles and with the porous media through which the fluid flows. To account for this problem, the use of a two-fluid model is described, familiar in the field of fluid mechanics, extended to include osmotic effects. We show how familiar relationships follow in various situations and give examples of combined fluid/particle transport in neutral and charged membranes driven by a combination of electrostatic, diffusional and pressure forces. The analysis shows how the same modeling framework can be generally used both for multidimensional electrokinetic flow through macroscopic channels and around macroscopic objects, as well as for mean-field modeling of transport through porous media such as gels and membranes.
Keywords: Electrokinetics; Two-phase flow modeling; Porous media; Navier–Stokes equation; Nernst–Planck equation; Ion-exchange membranes
Layer-by-layer composite of anionic and cationic clays by metathesis
by B.R. Venugopal; Michael Rajamathi (pp. 396-401).
A simple route for the preparation of layer-by-layer composite of anionic and cationic clays through delamination followed by solvothermal treatment of the monolayer colloidal dispersions is presented..Display Omitted► Surfactant-intercalated anionic and cationic clays were delaminated in 1-butanol. ► Solvothermal treatment of a mixture of the dispersions of both the clays yield a layer-by-layer composite of the clays. ► The anionic clay component of the composite is thermally more stable compared to the precursor.An alternately stacked layer-by-layer composite of oppositely charged layered solids was obtained by solvothermal treatment of the monolayer colloidal dispersions of dodecylsulfate intercalated nickel aluminum LDH and cetyl trimethylammonium intercalated smectite in 1-octanol. This composite shows altered thermal decomposition behavior compared to the parent solids. On heating the LDH component of the composite decomposes to NiO, while the layer structure of the cationic clay is retained up to 800°C.
Keywords: Layered solid; Delamination; Costacking; Metathesis; Composite; Colloidal dispersion; Clays
Binding of chloroquine–conjugated gold nanoparticles with bovine serum albumin
by Prachi Joshi; Soumyananda Chakraborty; Sucharita Dey; Virendra Shanker; Z.A. Ansari; Surinder P. Singh; Pinak Chakrabarti (pp. 402-409).
We have conjugated chloroquine, an anti-malarial, antiviral and anti-tumor drug, with thiol-functionalized gold nanoparticles and studied their binding interaction with bovine serum albumin (BSA) protein. Gold nanoparticles have been synthesized using sodium borohydride as reducing agent and 11-mercaptoundecanoic acid as thiol functionalizing ligand in aqueous medium. The formation of gold nanoparticles was confirmed from the characteristic surface plasmon absorption band at 522nm and transmission electron microscopy revealed the average particle size to be ∼7nm. Chloroquine was conjugated to thiolated gold nanoparticles by using EDC/NHS chemistry and the binding was analyzed using optical density measurement and Fourier transform infrared spectroscopy. The chloroquine–conjugated gold nanoparticles (GNP–Chl) were found to interact efficiently with BSA. Thermodynamic parameters suggest that the binding is driven by both enthalpy and entropy, accompanied with only a minor alteration in protein’s structure. Competitive drug binding assay revealed that the GNP–Chl bind at warfarin binding site I in subdomain IIA of BSA and was further supported by Trp212 fluorescence quenching measurements. Unraveling the nature of interactions of GNP–Chl with BSA would pave the way for the design of nanotherapeutic agents with improved functionality, enriching the field of nanomedicine.We report the synthesis of chloroquine–conjugated gold nanoparticles and their binding to bovine serum albumin using biophysical and docking studies.Display Omitted► Synthesis and characterization of drug (chloroquine)–conjugated gold nanoparticles (GNP–Chl). ► Binding of GNP–Chl with bovine serum albumin (BSA) using biophysical techniques. ► Docking of drug with BSA.
Keywords: Bovine serum albumin; Gold nanoparticle–chloroquine conjugation; Protein–nanoparticle interaction; Trp fluorescence; Binding constant measurement; Drug docking
Association between branched poly(ethyleneimine) and sodium dodecyl sulfate in the presence of neutral polymers
by Katalin Pojják; Róbert Mészáros (pp. 410-416).
By the addition of a suitable neutral polymer sterically stabilized colloidal dispersions of the poly(ethyleneimine)/sodium dodecyl sulfate nanoparticles can be prepared, which preserve their kinetic stability even at high ionic strengths.Display Omitted► PEO and PVP adsorb considerably onto the surface of PEI/SDS nanoparticles. ► Sterically stabilized PEI/SDS dispersions can be prepared. ► The stabilizing effect of neutral polymers decreases with decreasing pH. ► The kinetic stability of these dispersions can be maintained at high ionic strengths. ► The adsorption and stabilizing effect of dextran is not significant.In the present paper, the effect of different neutral polymers on the self-assemblies of hyperbranched poly(ethyleneimine) (PEI) and sodium dodecyl sulfate (SDS) has been investigated at different ionization degrees of the polyelectrolyte molecules. The investigated uncharged polymers were poly(ethyleneoxide), poly(vinylpyrrolidone) and dextran samples of different molecular mass. Dynamic light scattering and electrophoretic mobility measurements demonstrate that the high molecular mass PEO or PVP molecules adsorb considerably onto the surface of the PEI/SDS nanoparticles. At appropriate concentrations of PVP or PEO, sterically stabilized colloidal dispersions of the polyelectrolyte/surfactant nanoparticles with hydrophobic core and hydrophilic corona can be prepared. These dispersions have considerable kinetic stability at high ionic strengths where the accelerated coagulation of the PEI/SDS nanoparticles results in precipitation in the absence of the neutral polymers. In contrast, the addition of dextran does not affect considerably the kinetic stability of PEI/SDS mixtures because of its low adsorption affinity towards the surface of the polyelectrolyte/surfactant nanoparticles.
Keywords: Polyelectrolyte; Surfactant; Colloidal dispersion; Kinetic stability; Polymer adsorption; Steric stabilization
Effect of retardation in the dispersion forces between spherical particles
by G.Sh. Boltachev; N.B. Volkov; K.A. Nagayev (pp. 417-422).
For particles with a diameter of 3μm the retardation effect reduces about twice the distance, where van der Waals attractive force predominates over the gravitational force.Display Omitted► The model intermolecular potential has been proposed, which takes into account the retardation effect and makes possible to approximate the real intermolecular potentials. ► The generalization of known Hamaker formula for the attractive energy of macroscopic particles, which takes into account the retardation effect, has been derived rigorously. ► It has been found that neglecting the retardation effect can give the energy and force values overestimated more than one order of magnitude.A model potential for intermolecular attractive forces, which takes into account the retardation effect at large distances, is proposed. This potential is shown to be capable of approximating arbitrary empirical potentials of intermolecular interactions. For this model potential, the generalization of the known Hamaker formula for the attractive energy of macroscopic particles is derived. A comparison of the laws of attraction of particles of spherical shapes, when the retardation effect is taken into account as realized in the model discussed, with the classical Hamaker result neglecting such dependence is carried out.
Keywords: Intermolecular potential; Colloids; Hamaker formula; Retardation effect
Size distribution analysis of single and bi-component polymer and inorganic particle systems by comparison of two analysis methods in analytical ultracentrifuge
by V. Mittal; M.D. Lechner (pp. 423-430).
Differential particle size distributions of the mixture of smaller and larger inorganic particles in the weight ratio of 5:95. The particles were analyzed separately at 10,000 and 30,000rpm (solid line: VelXLAI, dotted line: Sedfit). Both the fractions were also analyzed at 10,000rpm alone using VelXLAI program (-□-).Display Omitted► Comparison of two common data analysis programs in analytical ultracentrifugation. ► Both polymer and inorganic suspensions as well as mixtures evaluated. ► Advantages and limitations of programs for data analysis on complex mixtures established.Sedimentation velocity runs were performed on organic and inorganic particles with analytical ultracentrifugation and the diameter and diameter distribution analysis was carried out with Sedfit and VelXLAI data analysis programs. The particles were measured either as pure components or as mixtures of different organic or inorganic particles using different weight ratios of these components. Polymer particles with peak diameters of ≈15 and 32–35nm and inorganic particles with peak diameters of ≈5 and ≈32nm were used and the particles also differed in the extent of polydispersity. The mixtures of particles in the weight ratios of 50:50, 90:10 and 95:5 of smaller to larger particles or vice versa were studied. The aim was to compare the performance of the analysis programs to characterize the various polymer and inorganic particle samples of varying complexity. The analysis programs were compared with each other not only for peak particle diameters and their size distributions, but also for the cumulative fractions of components of the particle mixtures.
Keywords: Size distribution; Cumulative fractions; Data analysis; VelXLAI; Sedfit; Analytical ultracentrifugation; Sedimentation
Characterization of pH-induced changes in the morphology of polyelectrolyte multilayers assembled from poly(allylamine) and low molecular weight poly(acrylic acid)
by Bin Sun; Ryan M. Flessner; Eric M. Saurer; Christopher M. Jewell; Nathaniel J. Fredin; David M. Lynn (pp. 431-441).
Polyelectrolyte multilayers fabricated from poly(allylamine) and low molecular weight poly(acrylic acid) undergo large-scale transformations upon exposure to low-pH conditions to yield films with pores as large as 10–15μm.Display Omitted► The molecular weight of PAA plays a role in determining the sizes of pores that form. ► Low MW PAA leads to films with larger pores than films containing high MW PAA. ► Treatment at low pH yields films with pores up to 10–15μm in size. ► Fabrication using fluorescently labeled PAA enables imaging of porous transformations. ► Contact with surfaces influences transformation and leads to larger pore sizes.We report characterization of pH-dependent behavior in polyelectrolyte multilayers (PEMs) fabricated from poly(allylamine) (PAH) and low molecular weight poly(acrylic acid) (PAA) synthesized by living/controlled polymerization. Exposure of these films to solutions of low pH (e.g. pH 2.0–3.2) resulted in transformations from films that were smooth and uniform to films with porous morphologies, as characterized by scanning electron microscopy (SEM). We observed large differences in both the extent of this transformation and the sizes of the pores that resulted compared to films fabricated using higher molecular weight PAA used in past studies. Whereas transformations reported in past studies generally lead to pores with sizes in the range of 0.3–2μm, we observed larger-scale transformations and films with cell-like internal structures comprised of networks of closed pores, interconnected pores, and through-pores with sizes as large as 10–15μm depending on pH and the manner in which the films were incubated. Films fabricated using fluorescently end-labeled samples of PAA permitted real-time imaging of changes in internal structure using confocal microscopy (LSCM). The results of these studies also revealed large differences in the nature of these transformations when films were placed in contact with surfaces as opposed to when dipped into aqueous solutions. Our results reveal approaches that can be used to fabricate films with large pores (e.g., pores with sizes on the order of 10–15μm) and suggest methods that could potentially be used to generate PEMs having controlled gradients in pore size.
Keywords: Thin films; Layer-by-layer; Polymers; Polyelectrolytes; Porous materials
Bioconjugation of the estrogen receptor hERα to a quantum dot dye for a controlled immobilization on a SiO2 surface
by C. Cherkouk; L. Rebohle; W. Skorupa (pp. 442-447).
This paper demonstrated the immobilization of the conjugated estrogen receptor hERα with QDS655 dye on the silanized SiO2 surfaces. The immobilization of the estrogen receptor on the silanized SiO2 surface occurred under a certain angle which makes the binding pocket of the receptor accessible for estrogen docking.Display Omitted► The conjugation of the estrogen receptor hERα to the quantum dots dye QD655 and their immobilization on the three different silanized SiO2 surfaces. ► A higher molarity ratio of 10–20 between the QDs and the receptors leads to the immobilization of the estrogen receptor on the silanized SiO2 surface under a certain angle. ► The binding pocket of the receptor is accessible for estrogen docking. ► Detection of 17ß-estradiol (E2) concentration in waterish solution by use of a second color of dye QD800 at 800nm.We investigated the immobilization of the estrogen receptor hERα on silanized SiO2 surfaces for biosensor applications. The conjugation of the estrogen receptor hERα to the quantum dot dye QD655 was achieved. In order to obtain an optimal immobilization of the estrogen receptor hERα on the functionalized SiO2 surface, the bioconjugate hERα-QD655 (Rcpt-qd655) solution was prepared with a higher molar ratio of 10–15 between the QDs and the receptors. A blue laser with an excitation wavelength of 405nm was used for photoluminescence spectroscopy (PL) investigations to monitor the bioconjugate Rcpt-qd655 immobilization on the silanized SiO2 surfaces with three different functional groups, namely NH2, -COO-, and –SH. Several wash processes were applied to remove the excess receptors from the surface after the immobilization. A Fourier transform infrared spectroscopy (FTIR) was used to control the biofilm background after each wash of the receptor-coated surface which allows the optimization of the immobilization protocol. In order to test its stability a quartz crystal microbalance (QCM) was employed and the receptor density was calculated. Finally the optimal biolayer (silane film+hERα receptor) was tested for measurements of 17ß-estradiol (E2) with a concentration of 1μM in waterish solution. The measurement concept outlined in [L. Rebohle et al., Vacuum 83 (2009) 24–28] was applied. The whole system was investigated by PL, which exhibits two color signals, namely from the receptor and the detected E2 molecules.
Keywords: Estrogen receptor hER; α; Immobilization; Si-based light emitter; Photoluminescence spectroscopy; 17ß-Estradiol; QDs dye
Disruption of reverse micelles and release of trapped ribonuclease A photochemically induced by Malachite Green leuconitrile derivative
by Ryoko M. Uda; Tsuyoshi Nishikawa; Yoshitsugu Morita (pp. 448-452).
Anionic AOT reverse micelles encapsulate ribonuclease A (RNase) A and Malachite Green derivative (MGL) is solubilized into the reverse micelle solutions. After UV irradiation, MGL transforms into a cationic surfactant that interacts with the anionic AOT, which results in the disruption of the AOT reverse micelles. The trapped RNase A is consequently transferred into the aqueous phase, indicating a novel method for targeted delivery.Display Omitted► A Malachite Green derivative undergoes photoionization in reverse micelles. ► The ionized Malachite Green derivative leads to disruption of the reverse micelles. ► Irradiation triggers the release of ribonuclease A trapped in the reverse micelles.Photoinduced disruption of a sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle is triggered by a Malachite Green leuconitrile derivative (MGL). UV irradiation of MGL solubilized in an AOT-water-chloroform mixture creates a cationic surfactant that interacts electrostatically with the anionic AOT. We investigated the disruption of the reverse micelle by using proton nuclear magnetic resonance spectroscopy and found that UV irradiation of MGL decreases the number of water molecules solubilized in the interior of the AOT reverse micelles. Furthermore, the photoinduced disruption of the reverse micelle is shown to release ribonuclease A, which is trapped in the water in the interior of the AOT reverse micelle. This photoinduced release may offer a desirable transport system of biopolymers.
Keywords: Reverse micelle; Disruption; Malachite Green; Photochemical control; Enzyme transfer
Porous microcapsule formation with microsieve emulsification
by Nagesh A. Wagdare; Antonius T.M. Marcelis; Remko M. Boom; Cees J.M. van Rijn (pp. 453-457).
Porous Eudragit microcapsule prepared from 3% polymer and 15% hexadecane in DCM by cross-flow microsieve emulsification.Display Omitted► Microcapsules with a hydrophilic polymeric shell and a hexadecane core were made. ► Microsieve emulsification controls size and size distribution of microcapsules. ► The polymeric shell is stable below pH 7, but dissolves rapidly at alkaline pH. ► The microcapsules were characterized with several optical, SEM and AFM techniques.A simple route is presented to prepare core–shell Eudragit microcapsules through a solvent extraction method with the use of microsieve emulsification. Droplets from a solution of Eudragit FS 30D (a commercial copolymer of poly(methyl acrylate-co-methyl methacrylate-co-methacrylic acid) 7:3:1) and hexadecane in dichloromethane are dispersed into water, using a micro-engineered membrane with well-defined pores, in a cross-flow setting. The dichloromethane is extracted from the droplets, which induces demixing in the droplets, leading to a hexadecane-rich core, and an Eudragit-rich shell. The obtained microcapsules have a narrow size distribution due to the microsieve emulsification process. The capsules have a porous shell as shown by SEM and AFM measurements. Their porosity and pore size is dependent on the ratios of Eudragit and hexadecane in the dispersed phase. At pH 7.1 and above Eudragit (FS 30D) dissolves in water; this pH change is used to release the contents of the microcapsule.
Keywords: Microcapsule; pH trigger; Phase separation; Membrane emulsification; Controlled release
TODGA based w/o microemulsion in dodecane: An insight into the micellar aggregation characteristics by dynamic light scattering and viscometry
by Rajib Ganguly; Joti N. Sharma; Niharendu Choudhury (pp. 458-463).
A comparison of the variation of the experimental and the calculated diffusion coefficient plots highlight the presence of an attractive interaction between the TODGA micelles.Display Omitted► TODGA reverse micellar system in dodecane was studied by DLS and viscometry. ► The studies show that the inter micellar interaction in this system is attractive in nature. ► The attractive interaction weakens with increase in the micellar concentration and temperature. ► Such weakening of micellar attraction results in suppression of gas-liquid type phase separation.N,N,N′,N′-tetraoctyl diglycolamide abbreviated as TODGA, is one of the most promising extractant for actinide partitioning from high level nuclear waste. It forms reverse micelles in non polar solvents on equilibration with aqueous HNO3 solutions. This reverse micellar system undergoes phase separation into dilute and concentrated reverse micellar solutions at high aqueous acid concentration. Small angle neutron scattering (SANS) studies reported in the literature explained this phenomenon based on gas–liquid type phase transition in the framework of Baxter adhesive hard sphere theory in the presence of a strong inter-micellar attractive interaction. The present investigation attempts to throw further light on this system by carrying out systematic dynamic light scattering (DLS) and viscometry studies, and their modeling on the TODGA reverse micellar solutions in the dodecane medium. The variation of the diffusion coefficient with the micellar volume fraction observed from the DLS studies is suggestive of the presence of an attractive interaction between the TODGA reverse micelles, which weakens at the high micellar volume fraction due to the increased dominance of the excluded volume effect. It is suggested that this weakened interaction is responsible for the absence of phase separation in this system at high TODGA concentration. The results thus highlight the importance of the presence of an attractive interaction between the TODGA micelles in determining the observed phase separation in the TODGA reverse micellar systems. The modeling of the DLS and viscosity data, however, suggest that the characteristic stickiness parameter of this system could be smaller than the critical value required for inducing a gas–liquid type phase transition.
Keywords: TODGA; Reverse micelle; Viscosity; Hydrodynamic radius; Phase separation
Effect of cobalt precursors on the dispersion, reduction, and CO oxidation of CoO x/γ-Al2O3 catalysts calcined in N2
by Lingling Zhang; Lihui Dong; Wujiang Yu; Lianjun Liu; Yu Deng; Bin Liu; Haiqin Wan; Fei Gao; Keqin Sun; Lin Dong (pp. 464-471).
The CoO from cobalt acetate is highly dispersed on γ-Al2O3 while the Co3O4 from cobalt nitrate prefers to agglomerate, which leads to their different redox and CO oxidation properties.Display Omitted► CoO was obtained from cobalt acetate with its dispersion capacity of 1.50 mmol/(100 m2 γ-Al2O3). ► Co3O4 was obtain from cobalt nitrate with its dispersion capacity of 0.15 mmol/(100 m2 γ-Al2O3). ► CoO/γ-Al2O3 was more difficult to be reduced and easier to desorb oxygen than Co3O4/γ-Al2O3. ► CoO/γ-Al2O3 were more active for CO oxidation than Co3O4/γ-Al2O3. ► A surface model was proposed to explain the dispersion and reduction properties of CoO/γ-Al2O3.The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoO x/γ-Al2O3 catalysts calcined in N2. XRD, Raman, XPS, FTIR, and UV–vis DRS results suggested that CoO/γ-Al2O3 was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al2O3 below its dispersion capacity of 1.50mmol/(100 m2 γ-Al2O3), whereas Co3O4/γ-Al2O3 was obtained from cobalt nitrate precursors and Co3O4 preferred to agglomerate above the dispersion capacity of 0.15mmol/(100m2 γ-Al2O3). Compared with Co3O4/γ-Al2O3, CoO/γ-Al2O3 catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H2-TPR, O2-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al2O3 catalysts.
Keywords: Cobalt precursors; Dispersion capacity; Incorporation model; CO oxidation
Size controlled synthesis of Li2MnSiO4 nanoparticles: Effect of calcination temperature and carbon content for high performance lithium batteries
by V. Aravindan; S. Ravi; W.S. Kim; S.Y. Lee; Y.S. Lee (pp. 472-477).
Pristine and carbon coated Li2MnSiO4 spherical nanoparticles with the size of ∼30nm have been synthesized by adipic acid assisted sol–gel technique, which exhibits good battery performance than other counterparts.Display Omitted► Highly phase pure and mono dispersed Li2MnSiO4 nanoparticles were synthesized. ► EPR study confirms the existence of the Mn2+ ions in the prepared material. ► Carbon coating reveal the improvement in battery performance. ► Higher carbon content leads to decrease in the performance of the cell.Size controlled, nanoparticulate Li2MnSiO4 cathodes were successfully prepared by sol–gel route. Effects of calcination temperature and carbon content (adipic acid) were studied during synthesis process. EPR study was conducted to ensure the formation of phase through oxidation state of manganese. Microscopic pictures indicate spherical shape morphology of the synthesized Li2MnSiO4 nanoparticles. Transmission electron microscopic pictures confirmed the presence of carbon coating on the surface of the particles. Further, the optimization has been performed based on phase purity and its battery performance. From the optimization, 700°C and 0.2mol adipic acid (against total metal ion present in the compound) were found better conditions to achieve high performance material. The Li2MnSiO4 nanoparticles prepared in the aforementioned conditions exhibited an initial discharge capacity of ∼113mAhg−1 at room temperature in Li/1M LiPF6 in EC:DMC/Li2MnSiO4 cell configuration. All the Li2MnSiO4 nanoparticles prepared at various conditions experienced the capacity fade during cycling.
Keywords: Li; 2; MnSiO; 4; nanoparticles; Adipic acid; EPR; Lithium battery
A comparison study between polymeric ligand and monomeric ligand for oligopeptide adsorption
by Jing Feng; Li-Xue Fu; Jun Wang; Wei Wang; Ji-Hong Li; Yi-Tao Qiao; Ping-Chuan Sun; Zhi Yuan (pp. 478-485).
This work compared two types of affinity ligands, i.e. polymeric and monomeric ligands, by investigating their adsorption affinity, capacity and selectivity to the oligopeptide NH2-VVRGCTWW-COOH (VW-8).Display Omitted► Polymeric ligands exhibited better adsorption capacity and affinity than monomeric ligands. ► Polymeric ligands were characterized by its good flexibility. ► Polymeric ligands exhibits better adsorption selectivity than monomeric ligands.This work aimed to compare two types of affinity ligands, i.e. polymeric and monomeric ligands, by investigating their adsorption affinity, capacity and selectivity to oligopeptide. The peptide NH2-VVRGCTWW-COOH (VW-8) was chosen as the target adsorbate, while histidine (His), aspartic acid (Asp), and leucine (Leu) were selected as the ligands, respectively. For each kind of ligand, both monomeric (M) and polymeric (P) forms were introduced onto the Sepharose matrix respectively to obtain the corresponding adsorbents. Both affinity tests using isothermal titration calorimetry (ITC) and adsorption capacities using static adsorption experiments indicated that the adsorbents with polymeric ligands (MX-P) exhibited better adsorption ability for VW-8 than the adsorbents with monomeric ligands (MX-M). In particular, the MX-PHis exhibited its affinity constant of 2.39×106M−1 and its adsorption capacity of 77.4mg/g for VW-8, which was approximately 8–10 times higher than that of MX-MHis. Such distinct adsorption abilities between polymeric and monomeric ligands were interpreted based on nuclear magnetic resonance (NMR) and ITC data, and the results indicated that such better characters of polymeric ligands were ascribed to their good flexibility which facilitated the cooperative effects as well as the accessibility of ligands to the peptide. Additionally, the selective adsorption experiments indicated that all the adsorbents with polymeric ligands exhibited good selectivity to the peptide VW-8.
Keywords: Affinity adsorbent; Monomeric ligand; Polymeric ligand; Oligopeptide
Dielectrophoretic alignment of metal and metal oxide nanowires and nanotubes: A universal set of parameters for bridging prepatterned microelectrodes
by A.W. Maijenburg; M.G. Maas; E.J.B. Rodijk; W. Ahmed; E.S. Kooij; E.T. Carlen; D.H.A. Blank; J.E. ten Elshof (pp. 486-493).
Dielectrophoresis is used for the alignment of metal and metal oxide nanowires and nanotubes between prepatterned microelectrodes.Display Omitted► Universal set of parameters for dielectrophoretic alignment. ► Indirect alignment technique to prevent short circuiting after alignment. ► Low resistivity found for ZnO nanowire, indicating good ohmic contact.Nanowires and nanotubes were synthesized from metals and metal oxides using templated cathodic electrodeposition. With templated electrodeposition, small structures are electrodeposited using a template that is the inverse of the final desired shape. Dielectrophoresis was used for the alignment of the as-formed nanowires and nanotubes between prepatterned electrodes. For reproducible nanowire alignment, a universal set of dielectrophoresis parameters to align any arbitrary nanowire material was determined. The parameters include peak-to-peak potential and frequency, thickness of the silicon oxide layer, grounding of the silicon substrate, and nature of the solvent medium used. It involves applying a field with a frequency >105Hz, an insulating silicon oxide layer with a thickness of 2.5μm or more, grounding of the underlying silicon substrate, and the use of a solvent medium with a low dielectric constant. In our experiments, we obtained good results by using a peak-to-peak potential of 2.1V at a frequency of 1.2×105Hz. Furthermore, an indirect alignment technique is proposed that prevents short circuiting of nanowires after contacting both electrodes. After alignment, a considerably lower resistivity was found for ZnO nanowires made by templated electrodeposition (2.2–3.4×10−3Ωm) compared to ZnO nanorods synthesized by electrodeposition (10Ωm) or molecular beam epitaxy (MBE) (500Ωm).
Keywords: Templated electrodeposition; Dielectrophoresis; Alignment; Nanowires; Nanotubes
In-pore tensile stress by drying-induced capillary bridges inside porous materials
by Majda Bouzid; Lionel Mercury; Arnault Lassin; Jean-Michel Matray; Mohamed Azaroual (pp. 494-502).
The paper describes a mechanico-chemical coupling in a porous material. The sampled pore is deformed after hosting a NaCl precipitate, by a pulling action emanating from the salt-wall capillary bridges.Display Omitted► Salt precipitation in initially homogeneous pores changes their topology. ► The capillary aqueous solution interacts differently with the solids than the bulk. ► Capillary bridges are able to deform the host solid.We present here some evidences that capillary liquid bridges are able to deform micrometric cylindrical pores by tensile stress. Brine-soaked filter membranes are submitted to drying conditions leading to NaCl precipitation inside the 5–10μm pores. A close examination demonstrated that two forms of NaCl crystallites are successively generated. First, primary cubic crystals grow, driven by the permanent evaporation. When this angular primary solid gets near the pore wall, while the evaporation makes the pore volume to be partly invaded by air, capillary liquid can bridge the now-small gap between the halite angles and the pore wall. In a second step, these small capillary bridges are frozen by a secondary precipitation event of concave-shaped NaCl. The proposed interpretation is that the liquid capillary bridges deform the host matrix of the membrane, and the situation is fossilized by the growth of solid capillary bridges. A quantitative interpretation is proposed and the consequences towards the natural media outlined.
Keywords: Unsaturated zone; Liquid water; Tensile strength; Poromechanics; Soluble salts
Influence of substrate stiffness on cell–substrate interfacial adhesion and spreading: A mechano-chemical coupling model
by Jianyong Huang; Xiaoling Peng; Chunyang Xiong; Jing Fang (pp. 503-508).
Schematic illustration of receptor–ligand adhesions between plasma membrane and underlying elastic substrate.Display Omitted► A mechano-chemical model is developed to describe the kinetics between cells and elastic substrates. ► An analytical solution is derived to relate cell adhesion strength to substrate rigidity. ► Dependence of cell specific adhesion and spreading on substrate stiffness is predicted.Cell interactions with extracellular matrix, such as cell adhesion and spreading, are crucial for many biological functions and processes. Recent experimental progresses have demonstrated that substrate rigidities exert a remarkable influence on cell–substrate interfacial adhesion and spreading behaviors. The underlying biophysical mechanism, however, remains elusive. Based on the classical Bell-Dembo’s theory, this paper develops a mechano-chemical coupling model to physically describe cell adhesion and spreading mediated by substrate stiffness. By investigating the competitive nature between cell–substrate specific attraction and non-specific repulsion, the kinetic relation of receptor–ligand interplay is established, in which the influences of receptor–ligand separation, substrate elasticity and non-specific repulsion on cell adhesions are especially addressed. According to mechanical equilibrium conditions between cell membranes and underlying elastic substrates, an analytical expression is then deduced to relate the cell–substrate interfacial adhesion strength to the substrate rigidity. Moreover, by means of the conventional wetting theory, the dependence of steady-state cell spreading on substrate stiffness is also quantitatively studied. Comparisons with the existing experimental data show that the proposed model can be used to explore cell–substrate interactions regulated by substrate rigidities.
Keywords: Cell–substrate interaction; Substrate stiffness; Adhesion strength; Spreading area; Mechano-chemical coupling model
Nano-encapsulation as high pressure devices for folding–unfolding proteins
by A. Steinchen; K. Sefiane; A. Sanfeld (pp. 509-511).
The high pressures in small capsules modifies the reactivity of biological reactions. Variation of the equilibrium constant for the cytochrome c+cytochrome c oxidase reaction, with encapsulation nature, and curvature. Inset is a zoom on smaller scales.This communication focuses on the capillary pressure effect in nano-objects. Indeed the change in pressure inside encapsulated biomaterials due to capillary effects can drastically alter the chemical equilibrium and the kinetics of biological reactions. This can potentially be exploited to design specific encapsulations in hollow solid nano-spheres or nano-tubes as carriers to optimise biochemical processes.
Keywords: Nano-encapsulation; High pressure; Protein unfolding; Reactivity; Drug carriers; Nano-medicine
Synthesis and swelling behavior of temperature responsive κ-carrageenan nanogels
by Ana L. Daniel-da-Silva; Luciana Ferreira; Ana M. Gil; Tito Trindade (pp. 512-517).
The synthesis of thermo-sensitive κ-carrageenan hydrogel nanoparticles using reverse microemulsions is described. Carrageenan nanoparticles undergo reversible volume transitions in response to temperature stimuli.Display Omitted► The size of nanogels varied with biopolymer concentration at constant surfactant concentration. ► κ-carrageenan nanogels are thermo-sensitive and undergo reversible volume transitions in response to temperature stimuli. ► In vitro release rate from nanogels is temperature-controlled.Crosslinked κ-carrageenan hydrogel nanoparticles (nanogels) with an average size smaller than 100nm were prepared using reverse microemulsions combined with thermally induced gelation. The size of the nanogels varied with biopolymer concentration at a constant water/surfactant concentration ratio. The nanogels were found to be thermo-sensitive in a temperature range acceptable for living cells (37–45°C) undergoing reversible volume transitions in response to thermal stimuli. This opens the possibility to explore the application of these nanogels in smart therapeutics such as thermo-sensitive drug carriers. As such, the sustained release of methylene blue from the nanogels was evaluated in in vitro conditions as proof of concept experiments and the release rate was found to be controlled with temperature.
Keywords: Nanogels; κ-Carrageenan; Thermoresponsive; Controlled drug delivery
Analysis of Gibbs adsorption equation and thermodynamic relation between Gibbs standard energies of adsorption and micellization through a surface equation of state
by Carolina Bermúdez-Salguero; Jesús Gracia-Fadrique (pp. 518-519).
Surface saturation, reached at the region where the slope of the surface tension vs. logarithm of concentration curve is maximal, precedes micelle formation as demonstrated by a thermodynamic model..Display Omitted► Calculation of surface molecular areas is valid in the surface saturated region. ► Surface saturation precedes micellization. ► Standard energies of adsorption and micellization differ by a positive constant.The calculation of surface molecular areas through Gibbs adsorption equation has been questioned in some early works on the belief that these areas have been obtained from the apparently constant slope of the surface tension vs. logarithm of concentration curve along the entire region at which surface tension declines rapidly as the concentration increases. This premise leads to consider that Gibbs equation predicts that surface saturation is reached at the beginning of this region. However, through an analysis of the forementioned curve in accordance to Gibbs equation, it can be easily shown that surface saturation is attained at the end of the region. On the other hand, based on a thermodynamic model, it is also shown that the adsorption process, and thus, surface saturation, proceeds before micellization.
Keywords: Gibbs adsorption equation; Surface saturation; Critical micelle concentration; Standard energy of adsorption; Standard energy of micellization; Surface equation of state
by Arthur Hubbard (pp. 520-520).