Journal of Colloid And Interface Science (v.316, #1)
Network structure of collagen layers absorbed on LB film
by Q.B. Qibin Chen; S.H. Shouhong Xu; Rong Li; X.D. Xiaodong Liang; H.G. Honglai Liu (pp. 1-9).
Elucidating the assembly mechanism of the collagen at interfaces is important. In this work, the structures of type I collagen molecules adsorbed on bare mica and on LB films of propanediyl-bis(dimethyloctadecylammonium bromide) transferred onto mica at zero surface pressure was characterized by AFM. On mica, the granular morphologies randomly distributed as elongated structures were observed, which were resulted from the interlacement of the adsorbed collagen molecules. On the LB films, the topographical evolution of the adsorbed collagen layers upon the increasing adsorption time was investigated. After 30 s, the collagen assembled into network-like structure composed of the interwoven fibrils, called as the first adlayer, which was attributed to its adsorption on the LB film by means of a limited number of contact points followed by the lateral association. One minute later, the second adlayer was observed on the top of the first adlayer. Up to 5 min, collagen layers, formed by inter-twisted fibrils, were observed. Under the same conditions after 1 min adsorption on LB film, the AFM image of the layer obtained in the diluted hydrochloric acid solution is analogous to the result of the sample dried in air, indicating that it is the LB film that leads to the formation of the network structure of collagen and the formation of the network structures of collagen layers is tentatively ascribed to the self-assembly of type I collagen molecules on LB film, not to the dewetting of the collagen solution during drying.After the adsorption of 30 s in the diluted collagen acidic solution, the hole-like structures with the diameter of several hundred nm could be observed, as shown in figure, occasionally. The height of the patterns in the holes, indicated by the arrows, is approximately 0.4 nm and the height of the network structure varies from 1.4 to 2.9 nm, while the rims of the hole-like structures are ranged from 3.0 to 6.5 nm higher compared to the network structure.
Keywords: Collagen; Gemini surfactant; LB film; Adsorption; Interface
Adsorption behavior, thermodynamics, and mechanism of phenol on polymeric adsorbents with amide group in cyclohexane
by Jianhan Huang; Yun Zhou; Kelong Huang; Suqin Liu; Qiong Luo; Mancai Xu (pp. 10-18).
Macroporous cross-linked poly( N-methyl- N- p-vinylbenzylacetamide) (PMVBA), poly( N-methyl- N- p-vinylbenzylcaprolactam) (PMVBC), and poly( N-methyl- N- p-vinylbenzylurea) (PMVBU) were synthesized and their adsorption behavior for phenol in cyclohexane was investigated. The results indicated that the adsorption capacities of phenol on the three adsorbents followed the order PMVBU > PMVBA > PMVBC. Adsorption isotherms of phenol on the three polymeric adsorbents were measured and correlated to a Freundlich isotherm. Adsorption enthalpy, adsorption Gibbs free energy, and adsorption entropy were calculated using thermodynamic function relationships. It was found that the adsorption enthalpy of phenol on PMVBU was almost twice that on PMVBA and PMVBC. Analysis of the adsorption mechanism suggested that hydrogen bonding was the primary driving force for phenol adsorbed on the adsorbents in cyclohexane, and multiple hydrogen bonding was involved for PMVBU with phenol.Adsorption isotherms of phenol on PMVBA (a), PMVBC (b), and PMVBU (c) adsorbents in cyclohexane at five different temperatures: 288, 294, 300, 307, and 313 K.
Keywords: Polymeric adsorbents; Phenol; Adsorption; Hydrogen bonding
Investigation of p-hydroxybenzoic acid from a new surface-enhanced Raman scattering system
by Xiaomiao Hou; Yan Fang (pp. 19-24).
In this paper, we developed a new kind of substrate, silver-coated indium tin oxide (ITO), to investigate the character of surface-enhanced Raman scattering (SERS) of p-hydroxybenzoic acid (PHBA). Homogeneous Ag-coated ITO substrate was obtained by decomposing AgNO3 on the surface of ITO. A SERS spectrum of very good quality of “silver nanoparticles/PHBA/silver-coated ITO” was reported by adding PHBA aqueous solution and silver colloid onto the surface of silver-coated ITO repeatedly. PHBA molecules absorbed onto the surface of the silver nanoparticles through ionized carboxyl, and the PHBA molecules tended to tilt on the surface in this system. The rich information obtained from the silver nanoparticles/PHBA/silver-coated ITO system indicates that this is a highly SERS-active system. Not only was the number of the vibrational modes increased, but also were the frequencies of Raman bands shifted. The two SERS mechanisms, the “electromagnetic” and “chemical” mechanism, were mainly responsible for the experimental results. Furthermore, the silver nanoparticles modified on the silver-coated ITO surface play an important role in magnifying the surface local electric field near the silver film surface through resonant surface plasmon excitation.The FT-Raman spectrum of solid PHBA (a), the FT-SERS spectrum of PHBA on the silver-coated ITO (b), on the silver-coated filter paper (c), and in the silver nanoparticles/PHBA/silver-coated ITO system (d).
Keywords: SERS; p; -Hydroxybenzoic acid (PHBA); Adsorption behavior; Silver nanoparticles/PHBA/silver-coated ITO system
Interfacial tension studies of crown ethers at air/water and hexane/water interfaces
by Saeid Azizian; Kaoru Kashimoto; Takashi Matsuda; Hiroki Matsubara; Takanori Takiue; Makoto Aratono (pp. 25-30).
The adsorption of phase transfer catalysts, 18-crown-6 and dicyclohexano-18-crown-6, at the air/water and the hexane/water interfaces were investigated. Interfacial tension σ decreased by increasing concentrations of these compounds and therefore both of these crown ethers are accumulated at interfaces. The variation of σ with concentration for both compounds follows the Szyszkowski equation very well, from which the values of saturated surface densities and interaction parameters have been evaluated. On the basis of occupied surface area of each molecule, the orientation of each of molecules at the air/water and the hexane/water interfaces have been proposed. The present results show that dicyclohexano-18-crown-6 has the higher tendency not only to dissolve into the hexane phase but also to adsorb at the hexane/water interface than 18-crown-6 and that the Starks extraction mechanism was suggested for the present phase transfer catalysis systems.
Keywords: Interfacial tension; Crown ether; Phase transfer catalysis; Hexane/water interface
From simple amphiphilic to surfactant behavior: Analysis of1H NMR chemical shift variations
by Cristiano Andrade-Dias; Sérgio Lima; José J.C. Teixeira-Dias (pp. 31-36).
Analysis of the1H NMR chemical shift variations for the methyl protons of sodium decanoate and decanoic acid in D2O solutions using reduced variables is consonant with a narrow distribution of sizes about the mean aggregation number for decanoate ion micelles, in contrast with decanoic acid polydisperse aggregates which increase their size with concentration, until phase separation is reached. At defined temperatures between 10 and 50 °C, the chemical shift coefficients for the methyl group protons exhibit a negative temperature slope (shielding) for decanoate ion micelles and a positive temperature slope (deshielding) for decanoic acid aggregates. These results suggest that an increase of temperature improves the mobility of the decanoate ion chains in the micelles, thus inducing the methyl groups of the decanoate ion micelles to spend more time near the micelle–water interfaces. In turn, the size of polydisperse decanoic acid aggregates increases with temperature.
Keywords: Sodium decanoate; Decanoic acid; 1; H NMR; Chemical shift; Temperature variation; Aggregate; Micelle; Polydisperse
On relationships between surfactant type and globular proteins interactions in solution
by Elena Blanco; Juan M. Ruso; Gerardo Prieto; Félix Sarmiento (pp. 37-42).
The binding of sodium perfluorooctanoate (C8FONa), sodium octanoate (C8HONa), lithium perfluorooctanoate (C8FOLi), and sodium dodecanoate (C12HONa) onto myoglobin, ovalbumin, and catalase in water has been characterized using electrophoretic mobility. The tendency of the protein–surfactant complexes to change their charge in the order catalase < ovalbumin < myoglobin was observed which was related to the contents of α-helices in the proteins. α-Helices are more hydrophobic than β-sheets. The effect of surfactant on the zeta potentials follows C8HONa < C8FONa < C8FOLi < C12HONa for catalase and ovalbumin; and C8HONa < C8FOLi < C8FONa < C12HONa for myoglobin. The numbers of binding sites on the proteins were determined from the observed increases of the zeta-potential as a function of surfactant concentration in the regions where the binding was a consequence of the hydrophobic effect. The Gibbs energies of binding of the surfactants onto the proteins were evaluated. For all systems, Gibbs energies are negative and large at low concentrations (where binding to the high energy sites takes place) and become less negative at higher ones. This fact suggests a saturation process. Changes in Gibbs energies with the different proteins and surfactants under study have been found to follow same sequence than that found for the charge. The role of hydrophobic interactions in these systems has been demonstrated to be the predominant.
Keywords: Protein; Ligand; Hydrophobic interactions; Fluorosurfactants; Zeta potential
Enhancement of gemcitabine affinity for biomembranes by conjugation with squalene: Differential scanning calorimetry and Langmuir–Blodgett studies using biomembrane models
by Francesco Castelli; Maria Grazia Sarpietro; Dorotea Micieli; Barbara Stella; Flavio Rocco; Luigi Cattel (pp. 43-52).
Molecular interactions between gemcitabine, alone or conjugated with squalene to form the gem-squalene prodrug, with dimyristoylphosphatidylcholine have been investigated by differential scanning calorimetry and Langmuir film balance techniques to gain information about the interaction of gemcitabine and its prodrug with mammalian cell membranes and to evaluate the potential of liposomes as a delivery system for gemcitabine prodrugs. Phospholipids assembled as multilamellar vesicles or monolayers (at the air water interface) have been used as biomembrane models. Different interactions of gemcitabine, its prodrug, and squalene with the lipid were detected by dispersing the compounds in the MLV and were compared with kinetic experiments carried out to consider the ability of the examined compounds to dissolve in an aqueous medium, to migrate through it, and to be captured by multilamellar vesicles. Their ability to be released from drug-loaded liposomes and be taken up by empty vesicles mimicking biomembranes was also considered. Analysis of the differential scanning calorimetry curves reveals that gemcitabine has very little interaction with multilamellar vesicles whereas the gem-squalene prodrug strongly interacts with multilamellar vesicles. The kinetic experiments suggest that an aqueous medium does not permit the prodrug uptake by the biomembrane models, whereas it is allowed when gem-squalene is gradually released by the liposomes. The molecular area/surface pressure isotherms of the gemcitabine/lipid, gem-squalene/lipid, and pure compound monolayers, in agreement with the calorimetric results, indicate that gem-squalene interacts with the phospholipid monolayer with the squalene moiety in contact with the phospholipid chains and gemcitabine protruding in the aqueous medium.A prodrug of gemcitabine was synthesized by linking its 4-amino group with squalene and its interaction with biomembrane models studied by differential scanning calorimetry and Langmuir–Blodgett techniques.
Keywords: Gemcitabine; Lipophilic gemcitabine derivative; Dimyristoylphosphatidylcholine; Langmuir–Blodgett; Differential scanning calorimetry; Biomembrane models
A general method to synthesis of amphiphilic colloidal nanoparticles of CdS and noble metals
by Guanwei Wei; Fei Wen; Xu Zhang; Wangqing Zhang; Xiaowei Jiang; Peiwen Zheng; Linqi Shi (pp. 53-58).
Amphiphilic colloids of CdS and noble metal nanoparticles, which can be dispersed both in water and organic solvents such as ethanol,N,N-dimethylformamide, chloroform, and toluene, are studied. The amphiphilic colloidal nanoparticles are synthesized by grafting the amphiphilic and thermoresponsive polymer of thiol-terminated poly( N-isopropylacrylamide) to CdS and noble metal nanoparticles. The size and morphology of the PNIPAM-grafted colloidal nanoparticles of CdS@PNIPAM can be tuned by changing the molar ratio of PNIPAM/CdS. The size of CdS@PNIPAM nanoparticles slightly decreases first from 5.5 to 4.4 nm then slightly increases from 4.4 to 6.1 nm with the decrease in the molar ratio from 1/1 to 1/10. Spherical nanoparticles of CdS@PNIPAM are synthesized at a higher molar ratio and worm-like nanoparticles are obtained at a lower molar ratio. The resultant PNIPAM-grafted colloidal nanoparticles of CdS@PNIPAM, Au@PNIPAM, Pd@PNIPAM, and Ag@PNIPAM are thermoresponsive in water and show a cloud-point temperature at about 32.5 °C.Poly( N-isopropylacrylamide) is grafted to CdS and noble metals nanoparticles to synthesize amphibious colloids which can be homogeneously dispersed both in aqueous and organic milieu. The resultant colloids are thermoresponsive in water.
Keywords: Amphiphilic; CdS; Colloidal nanoparticles; Graft; Poly(; N; -isopropylacrylamide)
A study of oil droplet coalescence
by T.K. Boyson; R.M. Pashley (pp. 59-65).
Oil droplets dispersed in water can be readily studied when they are coated with surfactants, which lower their interfacial tension and enhance their stability. Pure oil droplets are more difficult to study because of their high interfacial tension, which facilitates coalescence and the adsorption of contaminants. In this study, we have characterised the surface charging properties of a water insoluble oil, bromododecane, which has a density close to water. The small density difference allows us to study relatively large drops of this oil and to analyse its coalescence behaviour. The results obtained with this simple, surfactant-free, system suggest that an additional attractive force, such as the long range hydrophobic interaction, might be required to explain oil droplet coalescence behaviour.The surface charging properties of a water insoluble oil, bromododecane, which has a density close to water, allows us to predict its coalescence behaviour.
Keywords: Dispersion; Coalescence; Emulsion
Chemical and heating treatments of ionic monolayer-protected clusters (IMPCs) with different surface counter anions
by Hosun Choo; Steven R. Isaacs; Adam Small; Seth Parmley; Young-Seok Shon (pp. 66-71).
This paper shows an in-depth study on the chemical and thermal responses of two ionic monolayer-protected gold clusters (Oct4N+−Br- and Oct4N+−O3SS-IMPCs). Two IMPCs displayed completely different phase-transfer behaviors when the solutions were in contact with the aqueous solution containing N-(2-mercaptopropionyl)glycine (tiopronin). Not Oct4N+−O3SS-IMPCs but Oct4N+−Br-IMPCs experienced a facile phase transfer from the organic layer to the aqueous layer, which was resulted from the displacement of ionic ligands by tiopronin monolayers on the gold nanoparticle surface. When the toluene solution containing Oct4N+−Br-IMPCs was treated with the aqueous solution containing NaCl salts, the UV–vis spectrum of the solution containing Oct4N+−Br-IMPCs undertook a fast spectral evolution caused by decomposition/agglomeration of IMPCs. In contrast, Oct4N+−O3SS-IMPCs exhibited much higher stability against the NaCl treatments. The Oct4N+−O3SS-IMPCs also displayed a superior thermal stability at relatively high temperature of∼110°C. Core size evolutions of Oct4N+−O3SS-IMPCs without a fast decomposition or aggregation of clusters were also observed during solid-state heating treatments at ∼150 and∼200°C. These results support that the presence of different anions clearly affect the overall stability of ionic nanoparticles. The stronger binding property of thiosulfate anions compared to bromide anions with gold nanoparticle surfaces makes Oct4N+−O3SS-IMPCs chemically more inert and thermally more stable.The stronger binding property of thiosulfate anions compared to bromide anions with gold nanoparticle surfaces makes Oct4N+−O3SS-IMPCs chemically more inert and thermally more stable.
Keywords: Nanoparticles; Monolayers; Ionic ligands; Chemical stability; Thermal stability
Synthesis and characterisation of clay-supported titania photocatalysts
by Lisa M. Daniel; Ray L. Frost; Huai Yong Zhu (pp. 72-79).
This study examines the use of laponite, a synthetic smectite, which forms exfoliated silicate layers when dispersed in water, as an inorganic support for titania nanocrystals. Titania nanocrystals are prepared prior to addition to the clay dispersion, by a sol–gel synthesis incorporating a microwave hydrothermal step. The characteristics of the resultant structure such as titania phase, crystallite size, and particulate size are examined via X-ray diffraction (XRD), transmission electron spectroscopy (TEM), and infrared spectroscopy.
Keywords: Titania; Photocatalyst; Laponite; Colloid; Surfactant; Hydrothermal treatment
Effect of UV and visible light on photocatalytic reduction of lead and cadmium over titania based binary oxide materials
by T. Mishra; J. Hait; Noor Aman; R.K. Jana; S. Chakravarty (pp. 80-84).
Uniform sized silica and zirconia mixed titania samples were prepared in presence of a surfactant (CETAB) using controlled hydrolysis of corresponding metal alkoxides. Photocatalytic activity towards reduction of lead and cadmium metal in aqueous solution was evaluated both in UV and visible light in a 100 ml capacity reactor. In particular mixing of 10 wt% silica with titania not only increases the surface area of the material but also increases the photocatalytic activity in UV light. Whereas mixing of zirconia with titania proved to be beneficial for visible light reaction. However, addition of hole scavenger increases the activity many folds and complete removal of Pb2+ and Cd2+ was possible in 60 min of reaction using synthesized catalysts. Among all the organic hole scavengers used, sodium formate is found to be the most active one. Interestingly quite high metal removal (89%) is also observed in presence of visible light within 60 min of reaction. Thus the above study indicates that the presence of certain oxides in low quantity (10 wt%) with titania can facilitates the photocatalytic process selectively in UV as well as visible light.Both UV and visible light mediated complete photocatalytic removal of Cd2+ and Pb2+ (100 ppm) over uniform sized binary oxide materials.
Keywords: Titania mixed oxide; Photoreduction; Lead; Cadmium; UV/visible light
Synthesis and photocatalytic activity of mesoporous TiO2 with the surface area, crystallite size, and pore size
by Dong Suk Kim; Shin Jung Han; Seung-Yeop Kwak (pp. 85-91).
Mesoporous TiO2 materials with various pore-size distributions were synthesized by using diblock copolymers via a sol–gel process in aqueous solution. The properties of these materials were characterized by FE-SEM, HR-TEM, XRD, DRS, BET, and BJH analysis. All particles have spherical morphology with a diameter range of 1–3 μm. The mesoporous TiO2 materials calcined at 400 °C were found to have different specific surface areas—186, 210, and 192 m2 g−1—and average pore sizes depending on the type of diblock copolymer—5.1, 6.1, and 6.4 nm—and their crystallite sizes were found to be 8.1, 8.3, and 8.8 nm. The photocatalytic activity of each sample was investigated by measuring the photodecomposition of methylene blue (MB), and the small crystallite size, large surface area, and small pore size were found to exhibit better photocatalytic activities. In addition, the photocatalytic activities of all the mesoporous TiO2 materials were found to be better than that of commercial TiO2.Various crystallite sizes, surface areas, and pore sizes of mesoporous TiO2 materials were synthesized from diblock copolymers via a sol–gel process in aqueous solution. The mesoporous TiO2 materials with small crystallite sizes, large surface areas, and small pore sizes were found to exhibit better photocatalytic activities. In addition, they show better photocatalytic activity compared to commercial TiO2.
Keywords: Mesoporous TiO; 2; Photocatalytic activity; Calcination temperature; Pore size; Porous structure
Introducing interacting diffuse layers in TLM calculations: A reappraisal of the influence of the pore size on the swelling pressure and the osmotic efficiency of compacted bentonites
by J. Gonçalvès; P. Rousseau-Gueutin; A. Revil (pp. 92-99).
The truncation of the Gouy–Chapman diffuse part in compacted clay-rocks and bentonite is introduced into the electrical triple-layer model (TLM) recently developed by P. Leroy and A. Revil [J. Colloid Interface Sci. 270 (2004) 371]. The new model is used to explain the dependence of the osmotic efficiency and the swelling pressure as functions of the mean pore size of the medium, determined from the porosity and the specific surface. The truncation of the diffuse layer introduces a new variable in the system of equations to be solved, the electrical potential at the midplane between adjacent charged surfaces. This new variable is evaluated through a Taylor expansion of the electrical potential. The present model is able to capture the variation of the osmotic efficiency and the swelling pressure with the mean pore size. The partition of counterions between the Stern layer and the diffuse layer as a function of the pore size calculated by the TLM also shows a good consistency with the model. This implies that more than 90% of the counterions are located in the Stern layer.Sketch of the electrical triple-layer model at clay surface with two alternative cases: the infinitely developed diffuse layer and the truncated diffuse layer accounted for in the present paper.
Keywords: Triple-layer model; Truncation; Pore size; Osmotic efficiency; Swelling pressure
A photoluminescent switch based on the hybrid organized molecular films of decatungsteuropate and some amphiphiles
by Min Jiang; Minghua Liu (pp. 100-106).
Hybrid organized molecular films composed of a polyoxometalate, decatungsteuropate (EuW10), and amphiphiles such as hexadecyltrimethylammonium bromide (CTAB), n-octadecylamine (ODA) and 4-hexadecylaniline (HDA) were fabricated by Langmuir–Blodgett (LB) technique and their photoluminescent properties were investigated. The hybrid films, which were formed through in situ complex formation at the air/water interface and subsequently transferred onto the solid substrate, were characterized by UV–vis, FT-IR, fluorescence, and AFM measurements. The transferred hybrid films showed red emission characteristic of the Eu(III) ion upon UV irradiation. The photoluminescence of the hybrid films was sensitive to the acid and base gases. When ODA/EuW10 and HDA/EuW10 hybrid films were exposed to HCl gas, their photoluminescence disappeared completely. Interestingly, the photoluminescence was recovered upon subsequent exposing the same film to NH3 gas. Such process could be repeated many times and a switch based on these hybrid films was proposed. On the other hand, the photoluminescent intensity of CTAB/EuW10 film decreased but never disappeared upon exposing to HCl gas. Similarly, the photoluminescence could also be partially recovered upon exposing to NH3 gas. Detailed investigation on the spectral changes of the films revealed that the interaction between EuW10 and CTAB and was different from EuW10 with ODA or HDA, and protonation of amine group in ODA or HDA induced by HCl gas played an important role in realizing the “on” and “off” photoluminescence switch of the hybrid films.Hybrid organized molecular films containing decatungsteuropate are constructed by LB technique. The hybrid films showed switch-able fluorescence, which could be wiped out by HCl gas and recovered in NH3 gas atmosphere. Protonation of the amine group in amphiphiles was found to play an important role in the luminescent switch.
Keywords: Polyoxometalate; Langmuir–Blodgett films; Photoluminescence; Switch
The influence of the size of the hydrophilic group on the miscibility of zwitterionic and nonionic surfactants in mixed monolayers and micelles
by Paweł Wydro (pp. 107-113).
The aim of this work was to study the surface properties of nonionic and zwitterionic surfactants (namely dodecyl- β-D-glucoside—DG, dodecyl- β-D-maltoside—DM, and dodecylsulfobetaine—DSB) and the miscibility of these compounds in mixed monolayers and micelles. A thermodynamic description of the interactions between surfactants in the mixed aggregates was provided by the Motomura theory. The obtained results indicate that the investigated compounds mix nonideally both in the mixed adsorbed layers and in micelles. The calculated values of the excess free energies of mixing prove that the interactions between molecules, in the mixed monolayers and micelles, are more attractive or less repulsive than those in the respective one-component aggregates. However, the values of the excess free energy of the components mixing in the monolayers and micelles are more negative for the DSB/DG system than for the DSB/DM system. This indicates that the investigated zwitterionic surfactant interacts more strongly with DG than with DM. This results from the difference in the size of the polar heads of nonionic surfactants.
Keywords: Nonionic surfactants; Zwitterionic surfactants; Mixed monolayers; Mixed micelles; Excess free energy of mixing
IGC studies of binary cationic surfactant mixtures
by S.M. Bardavid; P.C. Schulz; E.L. Arancibia (pp. 114-119).
Inverse gas chromatography (IGC) has been used to measure the interaction parameter between two twin-tailed cationic surfactants. Didodecyldimethylammonium (DDAB) and dioctadecyldimethylammonium (DODAB) bromides and their mixtures were used as stationary phases. IGC and DSC techniques have been used for the determination of the temperature zone of working. The activity coefficients at infinite dilution (on a mole fraction basis) were calculated for eleven probe solutes on each pure surfactant column. Values of interaction parameter between surfactants obtained at four weight fractions of the mixtures and at five temperatures are positive and suggested that the interactions is more unfavourable with the increment of DODAB concentration in the mixture. The results are interpreted on the basis of partial miscibility between DDAB and DODAB.Interaction parameters between DDAB and DODAB as a function of weight fraction of DDAB at different temperatures.
Keywords: Cationic surfactant mixtures; IGC; DSC; Interaction parameters
Counterion and composition effects on discotic nematic lyotropic liquid crystals
by Rodrigo Montecinos; Hernán Ahumada; Víctor E. Bahamonde-Padilla; Andrés F. Olea; Boris E. Weiss-López (pp. 120-125).
The static fluorescence quenching of pyrene by bromide, at the interface of mixed TTAC/TTAB discotic nematic lyotropic liquid crystals, allowed an estimation of the equilibrium constant for the exchange of chloride by bromide. The affinity of the interface for bromide is much higher than for chloride(KBr−/Cl−=13.2). For a molecular level understanding of the experimental results of this and the preceding paper, 20 ns molecular dynamics (MD) simulations were calculated for samples with TTAB/TTAC molar percent ratios 100/0 (A), 50/50 (B) and 0/100 (C). The increment in the concentration of chloride induces a wider distribution of ammonium headgroups along the axis normal to the bilayer surface, increasing the width of the interface. The charge density profile of simulation B shows that the concentration of bromide is higher than the concentration of chloride in the vicinity the ammonium headgroups. The short range contribution to the electrostatic energy from the ammonium–ammonium repulsion is 291.7 kJ/mol for TTAC and 195.6 kJ/mol for TTAB, and the short range ammonium–halide interaction is−6166kJ/mol for TTAC and−6607kJ/mol for TTAB, from simulations A and C, respectively. These results are in agreement with a more neutralized TTAB interface. Consistently, the electric dipole moments of water are significantly more aligned with the larger electric field of the TTAB interface.
Keywords: Counterion exchange equilibrium constant; Dissociation degree; Discotic nematic lyotropic liquid crystal; Molecular dynamics
Counterion and composition effects on discotic nematic lyotropic liquid crystals
by Rodrigo Montecinos; Hernán Ahumada; Ramiro Araya-Maturana; Andrés F. Olea; Boris E. Weiss-López (pp. 126-131).
Counterion and composition effects on the size and interface dynamics of discotic nematic lyotropic liquid crystals made of tetradecyltrimethylammonium halide (TTAX)–decanol (DeOH)–water–NaX, with X = Cl− and Br−, were investigated using NMR and fluorescence spectroscopies. The dynamics of the interface was examined by measuring deuterium quadrupole splittings from HDO (0.1% D2O in H2O) and 1,1-dideuterodecanol (20% 1,1-dideuterodecanol in DeOH) in 27 samples of each liquid crystal. Aggregation numbers,ND, from 15 samples of each mesophase were obtained using the fluorescence of pyrene quenched by hexadecylpyridinium chloride.ND of TTAB and TTAC are about230±30 and300±20, respectively.ND of TTAC increases with increasing concentration of all mesophase components, whereas TTAB shows no correlation between size and composition. The dimension of these aggregates prevents the occurrence of undulations, previously observed in lamellar phases. The quadrupole splitting of decanol-d2 in TTAC is about 5 kHz smaller than in TTAB, and the splitting of HDO is observed only in TTAB. All results are consistent with a more dynamic TTAC interface. The TTAC aggregate should be more dissociated from counterions and the excess ammonium–ammonium electrostatic repulsions contribute to increase the mobility of the interface components.
Keywords: Interface dynamics; Aggregation number and composition; Discotic nematic lyotropic liquid crystal
Vesicle–micelle transition in aqueous mixtures of the cationic dioctadecyldimethylammonium and octadecyltrimethylammonium bromide surfactants
by Fernanda Rosa Alves; Maria Elisabete D. Zaniquelli; Watson Loh; Elisabete M.S. Castanheira; M. Elisabete C.D. Real Oliveira; Eloi Feitosa (pp. 132-139).
The vesicle–micelle transition in aqueous mixtures of dioctadecyldimethylammonium and octadecyltrimethylammonium bromide (DODAB and C18TAB) cationic surfactants, having respectively double and single chain, was investigated by differential scanning calorimetry (DSC), steady-state fluorescence, dynamic light scattering (DLS) and surface tension. The experiments performed at constant total surfactant concentration, up to 1.0 mM, reveal that these homologous surfactants mix together to form mixed vesicles and/or micelles, depending on the relative amount of the surfactants. The melting temperatureTm of the mixed DODAB–C18TAB vesicles is larger than that for the neat DODAB in water owing to the incorporation of C18TAB in the vesicle bilayer. The surface tension decreases sigmoidally with C18TAB concentration and the inflection point lies aroundxDODAB≈0.4, indicating the onset of micelle formation owing to saturation of DODAB vesicles by C18TAB molecules. WhenxDODAB>0.5 C18TAB molecules are mainly solubilised by the vesicles, but whenxDODAB<0.25 micelles are dominant. Fluorescence data of the Nile Red probe incorporated in the system at different surfactant molar fractions indicate the formation of micelle and vesicle structures. These structures have apparent hydrodynamic radiusRH of about 180 and 500–800 nm, respectively, as obtained by DLS measurements.
Keywords: DODAB; C; 18; TAB; Surfactant; DSC; Tensiometry; Light scattering; Melting temperature; Nile Red; Steady-state fluorescence
Influence of the Stern layer on electrokinetic phenomena in porous media
by A.K. Gupta; D. Coelho; P.M. Adler (pp. 140-159).
The Stern layer has been included in the description of electrolytes in a charged porous medium, with possibly large zeta potentials. The surface charge density, the conductivity, and the electroosmotic coupling coefficient are calculated for various porous structures and various physico-chemical conditions. The saturation of the Stern layer is analyzed, as well as its consequences for the macroscopic properties of the medium. The discontinuous character of the solid interface has an important influence on the macroscopic conductivity and the electroosmotic coefficient.The dimensionless conductivityσ′ depends on the discontinuous character of the solid interface. Data are for arrays of nontouching (a) and touching (b) spheres for variouspK+: no Stern layer (—);pK+=−1 (⧫), 0 (+), and 2 (×).
Keywords: Stern layer; Charge densities; Zeta potential; Electroosmosis; Surface conduction; Conductivity
Sol–gel synthesis and morphological control of nanocrystalline TiO2 via urea treatment
by Li-Heng Kao; Tzu-Chien Hsu; Hong-Yang Lu (pp. 160-167).
Nanocrystalline TiO2 rods and hollow tubes with an engraved pattern on the surface have been prepared by a novel anionic template-assisted sol–gel synthesis via urea treatment and under hydrothermal condition. X-ray diffractometry (XRD) results indicate that these nanocrystallines consist predominantly of anatase TiO2, with minor amounts of rutile and brookite. Scanning and transmission electron microscopy (SEM and TEM) analyses reveal these rods and hollow tubes may result from the aggregates of nanorods of ∼10 nm in diameter. The crystallographic faceting found from TEM further reveals the polymorphic nature of the nanocrystalline TiO2 thus prepared. A “reverse micelle” formation mechanism taking into account the hydrothermal temperature, the pH effect of the sol–gel system, the isoelectric point, the formation of micelles, and the electrostatic interaction between the anionic surfactant and the growing TiO2 particulates is proposed to illustrate the competition between the physical micelle assembly of the ionic surfactants and the chemical hydrolysis and condensation reactions of the Ti precursors.Formation of nanocrystalline TiO2 rods and hallow tubes is favorable at lower temperatures when the pH value is below IEP of TiO2 (path I); while higher temperatures encourage the formation of a tabular structure of TiO2 (path II).
Keywords: Nanocrystalline TiO; 2; Anionic template-assisted; Sol–gel; Urea; Hydrothermal; Reverse micelle; Isoelectric point; pH effect
Fabrication of photonic crystals with nigrosine-doped poly(MMA- co-DVB- co-MAA) particles
by Shuai Zhang; Xiang-Wei Zhao; Hua Xu; Rong Zhu; Zhong-Ze Gu (pp. 168-174).
A convenient approach was developed to fabricate monodisperse nigrosine-doped poly(methyl methacrylate- co-divinylbenzene- co-methacrylic acid) nanoparticles with different cross-linkage by soap-free emulsion polymerization at boiling status and swelling process. The dye-doped nanoparticles were used for the fabrication of colloidal crystal films and beads. It was found that nigrosine dye in the nanoparticles can efficiently depress the light scattering inside the colloidal crystal films and eliminate the iridescent effect in the photonic beads. These results make the colloidal crystals useful in photonic paper, bioassay, and so on.The bright-field microscopic pictures of photonic beads in methyl silicone oil fabricated by colloidal spheres (G) with and (H) without nigrosine.
Keywords: Colloidal crystal; Structure color; Colloid
Multi-faceted titanium glycolate and titania structures from room-temperature polyol process
by Hyung Kyun Yu; Tai Hee Eun; G.R. Gi-Ra Yi; Seung-Man Yang (pp. 175-182).
Multi-faceted microstructures of titanium glycolate have been produced by room-temperature polyol process in which titanium alkoxide and polymethylene glycol were mixed rigorously and then the mixture was aged to settle down as white precipitate. Depending on types of titanium alkoxides and polymethylene glycols, stirring time, and composition, a variety of polygonal microrods were generated. Unlike unidentified structures produced from polyol process at elevated temperature, the titanium glycolate products obtained at room temperature revealed well-defined rod-like or plate-like structures with polygonal cross sections. Then, as-prepared titanium glycolate microstructures were transformed into higher refractive index titania of anatase or rutile phase by annealing. The characterization of as-prepared and annealed structures was conducted using scanning and transmission electron microscopes, X-ray diffractomer, and thermal analyzer for thermogravimetry and differential scanning calorimetry.Multi-faceted microstructures of titanium glycolate and titania have been produced from room-temperature polyol process. The resulting titanium based products revealed well-defined rod-like or plate-like structures with polygonal cross sections.
Keywords: Titania; Polyol process; Microrods; 1-D structures
Solution synthesis of magnesium hydroxide sulfate hydrate nanobelts using sparingly soluble carbonate salts as supersaturation control agents
by Zhengzhi Zhou; Yulin Deng (pp. 183-188).
Magnesium hydroxide sulfate hydrate (MHSH, 5Mg(OH)2⋅MgSO4⋅3H2O) nanobelts were synthesized under the conditions of ambient pressure and boiling temperature (∼101 °C). Several sparingly soluble carbonate salts were selected based on the hypothesis that the sparingly soluble carbonate salts in aqueous solution can provide OH− ion in a slow and continual manner, which is important to maintain a low supersaturation environment for one-dimensional MHSH nanobelt growth. The results indicated that the concentration of the reaction ions in the solution is one of the critical parameters for nanobelt growth. Scanning electron microscopy (SEM) showed that the nanobelts are about 50 nanometers in thickness, 200–500 nanometers in width and tens to hundreds of micrometers in length. The higher the solubility product constant of the sparingly soluble salt, the faster the reaction occurred. The effect of temperature on the reaction rate was investigated. The chemistry of the reaction was studied and the mechanism of nanobelt growth was proposed.Sparingly soluble carbonate salts could be used to control the supersaturation for solution synthesis of magnesium hydroxide sulfate hydrate nanobelts at ambient pressure and boiling temperature. The method described in this paper can be easily scaled up.
Keywords: Nanobelt; Supersaturation; Magnesium hydroxide; One-dimensional
Disclosure of the imidazolium cation coordination and stabilization mode in ionic liquid stabilized gold(0) nanoparticles
by Henri S. Schrekker; Marcos A. Gelesky; Marcelo P. Stracke; Clarissa M.L. Schrekker; Giovanna Machado; Sergio R. Teixeira; Joel C. Rubim; Jairton Dupont (pp. 189-195).
A surface-enhanced Raman spectroscopy (SERS) study of imidazolium ionic liquid stabilized gold(0) nanoparticles (GNPs) furnished previously unknown knowledge about the coordination and stabilization mode of the imidazolium cation. GNPs were prepared by hydrazine reduction of a chloroauric acid solution in 1-triethylene glycol monomethyl ether-3-methylimidazolium methanesulfonate2 as ether-functionalized room-temperature ionic liquid (RTIL). UV–vis spectroscopy showed the presence of GNP aggregates as absorptions extended to the NIR region. A parallel coordination mode for the imidazolium cation of RTIL2 on the GNP surface was observed by SERS, which occurred without the simultaneous coordination of the 1-triethylene glycol monomethyl ether-functionality. Instead of this, the ether-functionality was directed away from the GNP surface and acted as steric barrier between the GNPs/GNP aggregates, thus preventing further aggregation. These new insights suggest that the imidazolium cation is responsible for electrosteric stabilization.
Keywords: SERS; Transition-metal nanoparticles; Gold; Electrosteric stabilization; Interface; Ether-functionalized imidazolium ionic liquids
Electrical double layer around a spherical colloid particle: The excluded volume effect
by J.J. López-García; M.J. Aranda-Rascón; J. Horno (pp. 196-201).
The influence of the excluded volume effect on both the spatial distribution of ionic species and the electrostatic potential distribution in the neighborhood of a suspended spherical particle is examined on the basis of a modified Poisson–Boltzmann equation, which takes into account the finite ion size by means of a Langmuir-type correction. We find that κa ( κ and a being the reciprocal Debye length and the particle radius, respectively) ceases to be a valid parameter for the characterization of the electrical double layer, and that it is necessary to use both parameters κ and a to characterize adequately the system. We also find that the excluded volume effect considerably increases the surface potential (for a given value of the surface charge density) as compared to the case when ideal ion behavior is assumed. This suggests the use of the particle charge rather than the surface potential in order to characterize the system. Because of this, an approximate equation for the surface charge density of spherical colloid particles, valid for a wide range of system parameter values, is also reported.The excluded volume effect (cmax) considerably increases the surface potentialyS (for a given value of the surface charge density, I) as compared to the case when ideal ion behavior is assumed (PB equation). This suggests the use of the particle charge rather than the surface potential in order to characterize the system.
Keywords: Modified Poisson–Boltzmann equation; Excluded volume effect; Finite ion size
Face preferred deposition of gold nanoparticles on α-cyclodextrin/octanethiol inclusion compound
by S. Rodríquez-Llamazares; P. Jara; N. Yutronic; M. Noyong; J. Bretschneider; U. Simon (pp. 202-205).
The preferred deposition of gold nanoparticles (Au NPs) onto microcrystal faces of α-cyclodextin/octanethiol inclusion compound was obtained. The immobilization of Au NPs is caused by the spatial replacing of the citrate shell of the NPs by the free danglingSH groups of the guest molecule.A preferred deposition of gold nanoparticles onto microcrystal faces of α-cyclodextin/octanethiol inclusion compound was obtained.
Keywords: Gold nanoparticles; Deposition; α; -Cyclodextrin inclusion compound
Wetting behavior of a SiO2–polystyrene nanocomposite surface
by Weixin Hou; Qihua Wang (pp. 206-209).
A SiO2–polystyrene (PS) nanocomposite surface was prepared with a simple method. The wetting behavior of the as-prepared surface was investigated. It was found that the as-prepared surface could be varied from superhydrophilicity to superhydrophobicity just by controlling the drying temperature and the content of SiO2 nanoparticles in the system. In addition, a transition from the Wenzel regime to the Cassie regime was observed.Superhydrophobic surface was prepared when the ratio between polystyrene and silica is 0.1/0.2, and the drying temperature is 180 °C.
Keywords: Superhydrophobicity; Superhydrophilicity