Frontiers of Materials Science (v.6, #3)

Resistive switching effects in oxide sandwiched structures by Xiao-Jian Zhu; Jie Shang; Run-Wei Li (183-206).
Resistive switching (RS) behaviors have attracted great interest due to their promising potential for the data storage. Among various materials, oxide-based devices appear to be more advantageous considering their handy fabrication and compatibility with CMOS technology, though the underlying mechanism is still controversial due to the diversity of RS behaviors. In this review, we focus on the oxide-based RS memories, in which the working mechanism can be understood basically according to a so-called filament model. The filaments formation/rupture processes, approaches developed to detect and characterize filaments, several effective attempts to improve the performances of RS and the quantum conductance behaviors in oxide-based resistive random access memory (RRAM) devices are addressed, respectively.
Keywords: resistive random access memory (RRAM); resistive switching (RS); oxide film; filaments; quantum conductance

Crystal structures and magnetic performance of nanocrystalline Sm-Co compounds by Xiao-Yan Song; Zhe-Xu Zhang; Nian-Duan Lu; Hai-Ning Liang; Ding-Peng Li; Xiang-Quan Yan; Jiu-Xing Zhang (207-215).
A variety of intermetallic compounds in the binary Sm-Co system were reviewed, and the contents were focused on the crystal structures, magnetic properties and the nanoscale effects. The representative nanocrystalline Sm-Co compounds were introduced in details, the diagrams for their lattice structures and the atomic sites and occupancies were provided. Moreover, the magnetic properties of the nanocrystalline Sm-Co compounds were compared with those of the conventional polycrystalline counterparts. It showed that the nanocrystalline Sm-Co compounds exhibit special phase stability and remarkably enhanced magnetic performance, which are promising candidates for the matrix phases to develop permanent magnets, particularly the advanced high-temperature magnetic materials.
Keywords: Sm-Co compounds; nanoscale; crystal structure; magnetic performance

Electrical properties of garnet-like lithium ionic conductors Li5+x Sr x La3−x Bi2O12 fabricated by spark plasma sintering method by Yun-Xia Gao; Xian-Ping Wang; Qin-Xing Sun; Zhong Zhuang; Qian-Feng Fang (216-224).
A typical approach involving Pechini method and spark plasma sintering (SPS) method was presented for the preparation of high density Li5+x Sr x La3−x Bi2O12 (x = 0, 1) ceramics. Phase formation, microstructure, grain size and electrical properties of the specimens were examined using XRD, SEM and alternating current impedance spectroscopy (ACIS). Dense Li5La3Bi2O12 and Li6SrLa2Bi2O12 ceramics with pure garnet-like phase, relative density of 97% and average grain size of about 5 μm were fabricated using this approach. The total conductivities at 298 K of Li5La3Bi2O12 and Li6SrLa2Bi2O12 ceramics prepared by the SPS method are 5.1×10−5 and 6.8×10−5 S/cm, respectively, 2 times higher than that of samples prepared by the conventional sintering method.
Keywords: lithium ionic conductor; Li5+x Sr x La3−x Bi2O12 ; Pechini method; spark plasma sintering (SPS); ionic conductivity

Effect of laminate thickness on moisture diffusion of polymer matrix composites in artificial seawater ageing by Ratna Pal; H. N. Narasimha Murthy; M. Sreejith; K. R. Vishnu Mahesh; M. Krishna; S. C. Sharma (225-235).
The influence of laminate thickness of polymer matrix composites on moisture diffusion in seawater immersion, as well as the resulting mechanical property degradation for composites of glass/isopolyester (G/IPE), carbon/isopolyester (C/IPE), glass/vinylester (G/VE) and carbon/vinylester (C/VE), was investigated in this paper. Laminates 3 and 10mm in thickness, fabricated using the wet hand lay-up technique, were characterized for moisture absorption in artificial seawater medium, and their flexural strength and interlaminar shear strength (ILSS) degradations were studied. Moisture diffusion was observed to be anamolous to the Fick’s law for both 3 and 10mm thick samples in the later stage of diffusion. Moisture permeability of 10mmthick samples was two to three order greater than that of 3mm thick ones, while the time to moisture saturation remained unchanged. With the increase of laminate thickness, moisture saturation increased by 1.4% for C/VE and 7% for G/IPE. The residual flexural strength and ILSS were greater in case of 10mm thick specimens after 200 days of exposure. SEM examination of the fractured specimens showed greater levels of fibre/matrix debonding in 10mm thick specimens.
Keywords: polymer matrix composite; diffusion coefficient; Fick’s law; degradation

Gold nanoparticles (AuNPs) were synthesized by sonication using ethanolic leaf extract of Andrographis paniculata. We investigated the optimum parameters for AuNP synthesis and functionalization with polycaprolactone-gelatin (PCL-GL) composites. The AuNPs were characterized with various biophysical techniques such as TEM, XRD, FT-IR and EDX spectroscopy. TEM images showed that nanoparticles were spherical in shape with a size range from 5 to 75 nm. EDX analysis revealed the presence of molecular oxygen and carbon on the surface of AuNPs. The synthesized AuNPs were tested for their effect on HeLa (human cervical cancer) and MCF-7 (human breast cancer) cell lines and found to be nontoxic and biocompatible, which are potential carriers for hydrophobic drugs.
Keywords: sonocatalasis; Andrographis paniculata ; functionalization; crystal growth; biomaterial; PCL-GL composite

Controlled release behaviors of chitosan/α, β-glycerophosphate thermo-sensitive hydrogels by Wei-Fang Liu; Chuan-Zhen Kang; Ming Kong; Yang Li; Jing Su; An Yi; Xiao-Jie Cheng; Xi-Guang Chen (250-258).
Chitosan/α, β-glycerophosphate (CS/α, β-GP) thermo-sensitive hydrogels presented flowable solution state at low temperature and semisolid hydrogel when the ambient temperature increased. In this research, different concentrations of metronidazole encapsulated, CS and α, β-GP, as well as different acid solvents, were chosen to evaluate their influences on the drug release behaviors from CS/α, β-GP hydrogels. It was found that there was a sustaining release during the first 3 h followed by a plateau. SEM images showed that drugs were located both on the surface and in the interior of hydrogels. The optimal preparation conditions of this hydrogel for drug release were as follows: 1.8% (w/v) CS in HAc solvent, 5.6% (w/v) α, β-GP and 5 g/L metronidazole encapsulation. Cytotoxicity evaluation found no toxic effect. In order to control the release rate, 2.5 g/L chitosan microspheres with spherical shape and smooth surface were incorporated, and it was found that the initial release process was alleviated, while drug concentration had no obvious effect on the release rate. It could be concluded that the metronidzole release behaviors could be optimized according to practical applications.
Keywords: chitosan (CS); glycerophosphate (GP); thermo-sensitive hydrogel; controlled release; microsphere

β-Cyclodextrin inclusion complex: preparation, characterization, and its aspirin release in vitro by Hui-Yun Zhou; Ling-Juan Jiang; Yan-Ping Zhang; Jun-Bo Li (259-267).
In this work, the optimal clathration condition was investigated for the preparation of aspirin-β-cyclodextrin (Asp-β-CD) inclusion complex using design of experiment (DOE) methodology. A 3-level, 3-factor Box-Behnken design with a total of 17 experimental runs was used. The Asp-β-CD inclusion complex was prepared by saturated solution method. The influence on the embedding rate was investigated, including molar ratio of β-CD to Asp, clathration temperature and clathration time, and the optimum values of such three test variables were found to be 0.82, 49°C and 2.0 h, respectively. The embedding rate could be up to 61.19%. The formation of the bonding between -COOH group of Asp and O-H group of β-CD might play an important role in the process of clathration according to FT-IR spectra. Release kinetics of Asp from inclusion complex was studied for the evaluation of drug release mechanism and diffusion coefficients. The results showed that the drug release from matrix occurred through Fickian diffusion mechanism. The cumulative release of Asp reached only 40% over 24 h, so the inclusion complex could potentially be applied as a long-acting delivery system.
Keywords: β-cyclodextrin (β-CD); aspirin (Asp); saturated solution method; Box-Behnken design; release kinetics

A new type of anionic surfactant with four carboxylates for the preparation of mesoporous materials by Lin-Hao Sun; Song Wang; Wei-Lin Shi; Shuming Zhang; Xi Chen; Qiang Cai (268-277).
In this paper, a new type of anionic surfactant containing four carboxylates was synthesized by a four-step synthetic reaction including bromination reaction and primary amide protective reaction. Intermediates and final products of each step in the whole synthetic process were characterized by 1H NMR and MS. Purification of the anionic surfactant was accomplished through combination of recrystallization and silica gel column chromatography. The structure and the critical micelle concentration (CMC) of this surfactant at different temperatures were also investigated. Unlike traditional monocarboxylate surfactant easy to form lamellar mesostructure, this surfactant has the hexagonal mesophase structure and comparatively low CMC, hopefully to be applied in the preparation of mesoporous metal oxides.
Keywords: surfactant; four carboxylates; hexagonal mesosphase; critical micelle concentration (CMC)

Synthesis of novel thiol-functionalized mesoporous silica nanorods and their sorbent properties on heavy metals by Xi Chen; Qiang Cai; Lin-Hao Sun; Wei Zhang; Xing-Yu Jiang (278-282).
Novel thiol-functionalized mesoporous silica nanorods (MSNRs) were synthesized through a base co-condensation method, in which two organoalkoxysilanes, tetraethoxylsilane (TEOS) and bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), were used as silica precursors simultaneously. TESPT was firstly used for both morphology control and inner surface functionalization of mesoporous silica hybrid materials. The microstructures as well as porous character of the MSNRs were characterized by means of SEM, XRD, TEM and N2 sorption measurements. Infrared spectrum analysis and heavy metal ions (Ag+ and Cd2+) adsorption measurements were carried out to confirm the functionalized framework of MSNRs.
Keywords: nanocomposite; porous material; morphology control; inner surface functionalization; sorbent