Chunling Zhang

PNIPAM-MAPOSS Hybrid Hydrogels with Excellent Swelling Behavior and Enhanced Mechanical Performance: Preparation and Drug Release of 5-Fluorouracil

Poly(N-isopropylacrylamide) (PNIPAM) is a widely-studied polymers due to its excellent temperature sensitivity. PNIPAM-MAPOSS hybrid hydrogel, based on the introduction of acrylolsobutyl polyhedral oligomeric silsesquioxane (MAPOSS) into the PNIPAM matrix in the presence of polyethylene glycol, was prepared via radical polymerization. The modified hydrogels exhibited a thick, heterogeneous porous structure. PEG was used as a pore-forming agent to adjust the pore size. MAPOSS reduced the swelling ratios of gels, and decreased the LCST, causing the hydrogels to shrink at lower temperatures. However, its hydrophobicity helped to improve the temperature response rate. The incorporation of rigid MAPOSS into the polymer network greatly increased the compressive modulus of the hydrogel. It is worth noting that, by adjusting the amount of MAPOSS and PEG, the hydrogel could have both ideal mechanical properties and swelling behavior. In addition, hydrogel containing 8.33 wt % MAPOSS could achieve stable and sustained drug release. Thus, the prepared PNIPAM-MAPOSS hybrid hydrogel can serve as drug carrier for 5-fluorouracil and may have potential application in other biomedical fields.

Effects of incorporating acrylolsobutyl polyhedral oligomeric silsesquioxane on the properties of P(N-isopropylacrylamide-co-poly(ethylene glycol) diacrylate) hybrid hydrogels

A novel system for enhancing the properties of P(N-isopropylacrylamide-co-poly(ethylene glycol)diacrylate) (P(NIPAM-co-PEGDA)) temperature-sensitive hybrid hydrogels by incorporating acrylolsobutyl polyhedral oligomeric silsesquioxane (MAPOSS) was developed in this study. Inorganic/organic hybrid P(NIPAM-co-PEGDA) hydrogels based on MAPOSS were synthesized via free radical polymerization. Environmental scanning electron microscopy images showed that hydrogels with different feed ratios exhibited significant changes in the porous structure and average pore size. The heterogeneous and irregular network was caused mainly by MAPOSS aggregation. The rigid cage-like nanostructure of MAPOSS had dual opposite effects on polymer thermal properties; this effect was proven through differential scanning calorimetry and thermogravimetric analysis. The mechanical behaviors of the swollen hydrogels investigated through compression test showed that MAPOSS incorporation enhanced the yield strength. Swelling, deswelling and reswelling behaviors of hydrogels with different feed ratios were systematically examined and compared. The increase in MAPOSS provided the hydrogels with improved deswelling rate because of its cage-like nanostructure and hydrophobicity.

Effect of polyaniline-modified glass flakes on the corrosion protection properties of epoxy coatings

In this study, polyaniline (PANI) and different mass ratios of PANI/glass flake (PANI–GF, PGF) composites were prepared via in situ oxidative polymerization. The chemical structure of the composites was investigated via Fourier transform infrared spectroscopy and X-ray diffraction. PANI, GF, and PGF composites were added as fillers into epoxy coating and then applied on a steel substrate. The corrosion resistance of the coatings was evaluated through electrochemical impedance spectroscopy and salt spray test. The coatings added with PANI, GF, and PGF composites displayed improved corrosion resistance. The greatest improvement in corrosion resistance was exhibited by the coating loaded with PGF composites at a PANI/GF mass ratio of 2:1. This enhancement was attributed to the passivation ability of PANI and the penetration resistance of the GF in the coating. Moreover, PANI was coated uniformly on the GF surface, and the composites were uniformly dispersed in the epoxy resin.

Synthesis and Surface Modification of CdTe Nanocrystals

CdTe nanocrystals were prepared in aqueous solution via the reaction between Cd 2+ and NaHTe in the presence of mercaptoacetic acid. Interactions between CdTe nanocrystals and phenylalanine were formed via electrostatic/coordinate self-assembly. The photoluminescence intensity of CdTe nanocrystals was improved obviously. The interaction mechanism was discussed and was considered to be surface passivation.

Effect of Surface-modified Clay on the Thermal Stability and Insulation of Polyorganosiloxane Foam

Polyorganosiloxane foam(SIF) nanocomposites reinforced with vinyl-modified montmorillonite(Mt-V) and hydroxyl-modified montmorillonite(Mt-OH) were prepared through cross-linking and foaming. The effects of modified Mt on the density, pore morphology, and thermal and compressive properties of the prepared polyorganosiloxane foams were investigated. The structure of the polyorganosiloxane foam was studied by solid-state nuclear magnetic resonance analysis. Clay dispersion in polyorganosiloxane nanocomposites and pore morphology were investigated by X-ray diffraction and scanning electron microscopy analyses. The thermal and mechanical properties of the prepared materials were also evaluated by differential scanning calorimeter, thermogravimetric analysis, thermal diffusivity and compressive strength. The results show that Mt-V exhibits improved cell structure, thermal insulation, and crush compressive than Mt-OH. The addition of modified Mt reduces the density, cell size, and thermal conductivity but increases the high-temperature resistance and compressive strength of the nanocomposite. The amount of the residues of SIF/Mt-OH nanocomposites increases by 9% compared with that of the pure SIF. Furthermore, SIF/Mt-V decreases the thermal conductivity to 0.014 W/mK and the cell size to 98 μm. Those properties give the material potential application value in the aerospace and construction industry.

Improved thermal properties of epoxy resin modified with polymethyl methacrylate-microencapsulated phosphorus-nitrogen-containing flame retardant

Epoxy resin (EP) composites with improved thermal resistance were fabricated. To solve the problem of low thermal resistance derived from phosphazene flame-retardant additives, we designed a system based on flame-retardant microcapsules P(H), with hexaphenoxycyclotriphosphazene as the core and polymethyl methacrylate as the shell. The core–shell structure was characterized and confirmed. The thermal resistance of the cured EP composites containing 1 wt% P(H) microcapsules was improved because of the increased glass transition temperatures. The P(2.75H)/EP composites can reach a limited oxygen index of 30.5% and V-1 rating in UL-94 tests. Heat and gas release rates were reduced during combustion tests. Residual images implied that the P(H) microcapsules may promote the formation of a flame-retardant char layer. Pyrolysis analysis demonstrated that the P(H) microcapsules can decompose in two procedures to produce flame-retardant gas components. Therefore, the flame-retardant mechanism involved the flame inhibition effect in the gas phase, and the charring effect in the condensed phase.

Thermal insulation and stability of polysiloxane foams containing hydroxyl-terminated polydimethylsiloxanes

An effective method was described here to improve the thermal insulation and stability of polysiloxane foam (SIF) by controlling the chain length of hydroxyl-terminated polydimethylsiloxane (OH-PDMS). A series of SIFs were prepared through foaming and cross-linking processes with different cross-linking densities. The morphology of SIF was investigated by environmental scanning electron microscopy. The results demonstrated that increasing the chain length of OH-PDMS reduced the average cell size from 932 μm to 220 μm. Cell density ranged from 4.92 × 106 cells per cm3 to 1.64 × 108 cells per cm3. The thermal insulation capability was significantly enhanced, and the SIF derived from the long-chain OH-PDMSs yielded a minimum thermal conductivity of 0.077 W mK−1. Cell size reduction and an increase in cell density were considered to be the main factors to reduce thermal conductivity. Thermal stability, which was also improved, mainly depended on the free motion rate of the polysiloxane chains and cross-linking density of the polysiloxane networks.

Preparation of dual-functionalized graphene oxide for the improvement of the thermal stability and flame-retardant properties of polysiloxane foam

Polysiloxane foam (PSF) is a foam material with outstanding performance. However, the limiting oxygen index (LOI) of pure PSF is only 22.0 vol%, which can be attributed to combustible materials. In this work, graphene oxide (GO) was functionalized with hexachlorocyclotriphosphazene (HCCP) and 3-aminopropyltriethoxy-silane (APTS). The introduction of the functionalized GO into the PSF matrix has significantly improved the dispersion and flame-retardant properties of the final PSF composite. The char residue of PSF with 1.0 wt% functionalized GO content is 43.04%, which is considerably higher than that of the pure PSF (23.18%). Furthermore, the Tmax of PSF with 5.0 wt% functionalized GO content has increased from 585.9 °C to 668.8 °C. The results of the cone calorimetry test indicate that modification with functionalized GO prolongs the combustion of PSF composites. The LOI value of PSF with 5.0 wt% functionalized GO content has increased from 22.0% to 27.6%. In addition, the peak heat release rate, total heat release, and total smoke production of PSF with 5.0 wt% functionalized GO content were decreased by 49.2%, 14.5%, and 62.2% relative to those of pure PSF. These results can be ascribed to the barrier effect of GO, the condensed-phase and gas-phase mechanisms of HCCP, and the bonding effect of APTS.

Effect of polyaniline-modified glass fibers on the anticorrosion performance of epoxy coatings

Polyaniline (PANI) and different mass ratios of polyaniline/glass fiber (GB) composites (PANI/GB, PGB) were prepared through in situ oxidative polymerization. The chemical structure of composites was investigated via Fourier transform infrared spectroscopy and X-ray diffraction. Epoxy coatings loaded with different mixtures of PANI and GB were applied on steel substrate and exposed to NaCl solution. The morphological properties and corrosion resistance of the coatings were investigated through environmental scanning electron microscopy, electrochemical impedance spectroscopy, and salt spray tests. Results showed that the addition of PANI, GB, and PGB composites caused an improvement in corrosion resistance. The greatest improvement in corrosion resistance was exhibited by the coatings loaded with mass ratio of 1:1 of PANI/GB. This enhancement was attributed to the corrosion resistance of PANI and penetration resistance of GB. Moreover, the uniform distribution of PGB composites in the epoxy resin is an important parameter affecting corrosion resistance of the coatings.