以聚乙烯醇(PVA)作为助纺剂,对疏水改性的海藻酸钠衍生物海藻酸辛酰胺(ACA)进行电纺性能研究。采用透射电镜、激光粒度和zeta电位分析仪、表面张力仪、电导率仪和流变仪对ACA的胶体界面性能进行表征,并采用扫描电镜、红外光谱仪和多晶X...以聚乙烯醇(PVA)作为助纺剂,对疏水改性的海藻酸钠衍生物海藻酸辛酰胺(ACA)进行电纺性能研究。采用透射电镜、激光粒度和zeta电位分析仪、表面张力仪、电导率仪和流变仪对ACA的胶体界面性能进行表征,并采用扫描电镜、红外光谱仪和多晶X射线衍射仪对ACA/PVA电纺纳米纤维膜的形貌、官能团和晶型结构进行测试。结果表明:疏水改性使海藻酸钠(SA)分子灵活性增强,ACA分子可以蜷曲形成水动力学粒径大小为324 nm(PDI=0.38),zeta电位为-43.8 m V的胶束。疏水改性和添加PVA助纺剂可以有效地降低SA溶液的表面张力和电导率,使其有效链缠结增多,ACA/PVA电纺纳米纤维膜的形貌更加规整均一。光谱分析结果表明,ACA和PVA两者间的氢键作用力是其增加链缠结点,实现静电纺丝的主要作用力。展开更多
By preparing homogenous blend samples with different degrees of chain entanglement, we report an anomalous contribution of chain entanglement to phase separation temperature and rate of poly（methyl methacrylate）/pol...By preparing homogenous blend samples with different degrees of chain entanglement, we report an anomalous contribution of chain entanglement to phase separation temperature and rate of poly（methyl methacrylate）/poly（styrene-co- maleic anhydride） （PMMA/SMA） blends presenting a typical lower critical solution temperature （LCST） behavior. The melt- mixed PMMA/SMA blends with a higher chain entanglement density present a lower cloud point （To） and shorter delay time, but lower phase separation rate at the given temperature than solution-cast ones, suggesting that for the polymer blends with different condensed state structure, thermodynamically more facilitation to phase separation （lower Tc） is not necessarily equivalent to faster kinetics （decomposition rate）. The experimental results indicate that the lower Tc of melt-mixed sample is ascribed to smaller concentration fluctuation wavelength （Am） induced by higher entanglement degree, while higher entanglement degree in melt-mixed sample leads to a confined segmental dynamics and consequently a slower kinetics （decomposition rate） dominated by macromolecular diffusion at a comparable quench depth. These results reveal that the chain packing in polymer blends can remarkably influence the liquid-liquid phase separation behavior, which is a significant difference from decomposition of small molecular mixtures.展开更多
Nanoparticle-polymer composites exhibit unusual mechanical properties and chain dynamics when the nanoparticle size is smaller than the entanglement mesh size of the matrix polymer chains, corresponding to the ultrasm...Nanoparticle-polymer composites exhibit unusual mechanical properties and chain dynamics when the nanoparticle size is smaller than the entanglement mesh size of the matrix polymer chains, corresponding to the ultrasmall regime defined by de Gennes.However, the mechanism is still ambiguous due to the lack of suitable model systems. Here, we develop an ultrasmall nanoparticle system by using a bimodal grafting strategy to graft both short alkyl chains and long polystyrene chains onto the polyoxometalate molecular nanoparticles with a tunable repulsive potential between the nanoparticles, thus facilitating their uniform dispersion in polystyrene matrices. Linear viscoelasticity of the resultant nanocomposites changes with increasing the filler content, which shows a decrease in both plateau modulus and terminal relaxation time, indicative of a dilution effect of the nanoparticles. Namely, the entanglement network becomes sparser with increasing the filler content.展开更多
文摘以聚乙烯醇(PVA)作为助纺剂,对疏水改性的海藻酸钠衍生物海藻酸辛酰胺(ACA)进行电纺性能研究。采用透射电镜、激光粒度和zeta电位分析仪、表面张力仪、电导率仪和流变仪对ACA的胶体界面性能进行表征,并采用扫描电镜、红外光谱仪和多晶X射线衍射仪对ACA/PVA电纺纳米纤维膜的形貌、官能团和晶型结构进行测试。结果表明:疏水改性使海藻酸钠(SA)分子灵活性增强,ACA分子可以蜷曲形成水动力学粒径大小为324 nm(PDI=0.38),zeta电位为-43.8 m V的胶束。疏水改性和添加PVA助纺剂可以有效地降低SA溶液的表面张力和电导率,使其有效链缠结增多,ACA/PVA电纺纳米纤维膜的形貌更加规整均一。光谱分析结果表明,ACA和PVA两者间的氢键作用力是其增加链缠结点,实现静电纺丝的主要作用力。
基金financially supported by the National Natural Science Foundation of China(No.51173165)the Fundamental Research Funds for the Central Universities(No.2013QNA4048)
文摘By preparing homogenous blend samples with different degrees of chain entanglement, we report an anomalous contribution of chain entanglement to phase separation temperature and rate of poly（methyl methacrylate）/poly（styrene-co- maleic anhydride） （PMMA/SMA） blends presenting a typical lower critical solution temperature （LCST） behavior. The melt- mixed PMMA/SMA blends with a higher chain entanglement density present a lower cloud point （To） and shorter delay time, but lower phase separation rate at the given temperature than solution-cast ones, suggesting that for the polymer blends with different condensed state structure, thermodynamically more facilitation to phase separation （lower Tc） is not necessarily equivalent to faster kinetics （decomposition rate）. The experimental results indicate that the lower Tc of melt-mixed sample is ascribed to smaller concentration fluctuation wavelength （Am） induced by higher entanglement degree, while higher entanglement degree in melt-mixed sample leads to a confined segmental dynamics and consequently a slower kinetics （decomposition rate） dominated by macromolecular diffusion at a comparable quench depth. These results reveal that the chain packing in polymer blends can remarkably influence the liquid-liquid phase separation behavior, which is a significant difference from decomposition of small molecular mixtures.
基金support by the National Natural Science Foundation of China (Nos. 21622403 and 21474039)support by the National Natural Science Foundation of China (No. 21722407)
文摘Nanoparticle-polymer composites exhibit unusual mechanical properties and chain dynamics when the nanoparticle size is smaller than the entanglement mesh size of the matrix polymer chains, corresponding to the ultrasmall regime defined by de Gennes.However, the mechanism is still ambiguous due to the lack of suitable model systems. Here, we develop an ultrasmall nanoparticle system by using a bimodal grafting strategy to graft both short alkyl chains and long polystyrene chains onto the polyoxometalate molecular nanoparticles with a tunable repulsive potential between the nanoparticles, thus facilitating their uniform dispersion in polystyrene matrices. Linear viscoelasticity of the resultant nanocomposites changes with increasing the filler content, which shows a decrease in both plateau modulus and terminal relaxation time, indicative of a dilution effect of the nanoparticles. Namely, the entanglement network becomes sparser with increasing the filler content.
