聚环氧乙烷对PAMPS/PAM双网络水凝胶结构和性能的影响

采用紫外光引发聚合制备了含聚环氧乙烷（PEO）的聚(2-丙烯酰胺-2-甲基丙磺酸)(PAMPS）/聚丙烯酰胺（PAM）双网络（DN）水凝胶。使用扫描电子显微镜（SEM）观察了PAMPS单网络水凝胶的结构;测定了PEO改性前后双网络水凝胶的压缩及拉伸性能。PEO改性DN凝胶的第一网络网孔上由于PEO片晶结构引起不同程度的褶皱,这种褶皱起支撑作用;PEO的分子量达到5万时,褶皱的支撑作用最佳,DN凝胶的力学性能最佳;DN凝胶的力学性能随PEO加入量先提高后下降,在PEO加入量为0.1%时,PEO片晶结构加固了DN凝胶的物理交联点,力学性能达到最大,压缩应力达到31.6 MPa;加入更多的PEO阻碍了第一网络的凝胶化,造成网络结构的不连续,从而使DN凝胶的力学性能下降。     

Superior Mechanical Properties of Double-Network Hydrogels Reinforced by Carbon Nanotubes without Organic Modification

A facile method is developed to fabricate nanocomposite double-network (DN) gels with excellent mechanical properties, which do not fracture upon loading up to 78 MPa and a strain above 0.98, by compositing of carbon nanotubes (CNTs) without organic modification. Investigations of swelling behaviors, and compressive and tensile properties indicate that equilibrium swelling ratio, compressive modulus and stress, fracture stress, Young’s modulus, and yield stress are significantly improved in the presence of CNTs. Scanning electron microscopy (SEM) reveals that the pore size of nanocomposite DN gels is decreased and some embedded micro-network structures are observed on the fracture surface in comparison to DN gels without CNTs, which leads to the enhancement of mechanical properties. The compressive loading-unloading behaviors show that the area of hysteresis loop, dissipated energy, for the first compressive cycle, increases with addition of CNTs, which is much higher than that for the successive cycles. Furthermore, the energy dissipation mechanism, similar to the Mullins effect observed in filled rubbers, is demonstrated for better understanding the nanocomposite DN polymer gels with CNTs.     

Emodin voltammetric sensor based on molecularly imprinted polymer membrane‐modified electrode using a multiple hydrogen bonds strategy

Similar to those in complementary nucleotides' base pairs, we present a novel molecularly imprinted electrochemical sensor for emodin, constructed using a multiple hydrogen bonds strategy. We obtained the sensor by in situ photopolymerization, using allobarbital as a new functional monomer. We optimized the conditions of membrane imprinting and the composition of adsorption solvent. This artificial receptor exhibits high selectivity for the template in comparison with closely related analogs, aloin A and simetryne. The sensor was successfully applied in determination of emodin levels in one of the traditional Chinese medicines, the content of emodin in Sanhuang tablets detected using the voltammetric sensor and high performance liquid chromatography (HPLC) were 0.249 ± 0.009 (mg/tablet) and 0.246 ± 0.007 (mg/tablet), respectively. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Crack propagation in silica from reactive classical molecular dynamics simulations

Mechanistic insight into the process of crack growth can be obtained through molecular dynamics (MD) simulations. In this investigation of fracture propagation, a slit crack was introduced into an atomistic amorphous silica model and mode I stress was applied through far‐field loading until the crack propagates. Atomic displacements and forces and an Irving–Kirkwood method with a Lagrangian kernel estimator were used to calculate the J‐integral of classical fracture mechanics around the crack tip. The resulting fracture toughness (K_IC), 0.76 ± 0.16 MPa√m, agrees with experimental values. In addition, the stress fields and dissipation energies around the slit crack indicate the development of an inelastic region ~30Å in diameter. This is one of the first reports of K_IC values obtained from up‐scaled atomic‐level energies and stresses through the J‐integral. The application of the ReaxFF classical MD force field in this study provides the basis for future research into crack growth in multicomponent oxides in a variety of environmental conditions.     

Hydrogel–hydrogel composites: The interfacial structure and interaction between water and polymer chains

This work examines the interfacial structure and interaction between water and polymer chains in the hydrogel–hydrogel composites with the goal of establishing foundations for further investigation of drug diffusion from one hydrogel to another in the soft contact lens. This is based on the ability of the hydrogel–hydrogel composites to release ophthalmic drugs in a sustained manner. The hydrogel–hydrogel composites were synthesized by immersing the glycerol-swollen particles of crosslinked N-vinyl-2-pyrrolidone (NVP) into the monomer of hydroxyethylmethacrylate (HEMA) containing initiator benzoylperoxide (BPO) that polymerizes to form a matrix in the presence of the first networks. The hydrogel–hydrogel composites were characterized by UV/Vis spectrophotometer, scanning electronic micrography (SEM), and differential scanning calorimetry (DSC). The results showed that the samples of hydrogel–hydrogel composites of the particles of crosslinked NVP and poly-HEMA were transparent and glassy and suitable for soft contact lens. Three types of the interfacial structure, no interpenetrating interface, partly interpenetrating interface, and fully interpenetrating interface, of the hydrogel–hydrogel composites existed, and the type of the interfacial structure was determined by the degree to which the monomer of HEMA penetrated into the first networks before formation of the matrix. Different from poly-HEMA hydrogels, the peaks near 0°C on DSC curves of the hydrogel–hydrogel composites did not split while they were kept acute, and the amount of freezable-bound water was less. This shows that the water incorporated in the hydrogel–hydrogel composites does not strongly interact with polymer matrix, so the hydrogel–hydrogel composites cannot keep their shape during the phase transition of water. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008