聚甲基丙烯酸甲酯/聚醋酸乙烯酯/纳米二氧化硅体系的相分离行为研究

Phase Separation Behavior of Poly(methyl methacrylate)/Poly(vinyl acetate)/Silica Blends

研究了聚甲基丙烯酸甲酯/聚醋酸乙烯酯/纳米二氧化硅(PMMA/PVAc/silica)体系的相分离行为.通过傅里叶变换红外光谱和链缠结行为的研究发现PMMA和PVAc间存在较强的分子间相互作用,加入纳米二氧化硅导致2种聚合物在纳米粒子表面吸附,从而改变了分子间相互作用.体系中复杂的分子间相互作用以及纳米粒子-聚合物相互作用使得时温叠加严重失效,因此提出用归一化Cole-Cole图分析该体系的相分离过程.纳米粒子对不同组成体系相分离行为的影响不同,近临界组成中纳米粒子促进相分离并最终分布于两相界面,远临界组成中纳米粒子起成核作用并始终分布于海岛相中,这种由相分离机理决定的纳米粒子选择性分布为调控纳米粒子在聚合物中的组装结构提供了新的思路.

The phase separation of poly(methyl methacrylate)/poly(vinyl acetate)/silica(PMMA/PVAc/SiO)blends was investigated by optical microscope,rheology,morphological observation and Fourier transform infrared spectroscopy.Strong inter-molecular interaction between PMMA and PVAc was found by the shift of the carbonyl peak position compared to the FTIR of pure polymer and the reduction of chain entanglements inferred from the rheological curves.The addition of nano-silica led to the adsorption of chains of both polymers on the particle surfaces,which changed the inter-molecular interaction between pure PMMA and PVAc.The complex inter-molecular interaction and polymer-particle interaction resulted in the failure of time-temperature superposition over the entire temperature range.So the normalized Cole-Cole plot was proposed to analyze the phase separation process of the blend.Due to the inter-molecular interaction,the normalized Cole-Cole plot of the PMMA/PVAc blend deviates from the polymer,and secondary deviation occurs at the end of the curve during the heating process,which is the contribution of the phase interface.The nanoparticles have different influences on the phase separation behavior of the blend,depending on the blend composition.In the near-critical blends,nano-silica promoted the phase separation and was finally located at the interface of the two phases.In the off-critical blends,nano-silica had little effect on phase separation and was finally located in the island domains.The effect of nanoparticles on phase separation of different blends is related to the mechanism of phase separation:the near-critical blends form discontinuous shapes through the decomposition of the spiral nodal line.The phase separation speed is faster than the Brownian motion speed of nanoparticles,which results in the initial distribution of nano-silica in the two phases,and the subsequent movement towards the interface of two phases.The off-critical blends form island shapes through nucleation growth mechanism.Due to the slow phase separation rate,the nano-slica play the role of nuclei during the phase separation.In other words,the phase separation mechanism,Broenian motion of nanoparticles and dynamic adsorption and desorption of polymer chains on the surface of nanoparticles jointly determine the distribution of nanoparticles.Such selective location of nanoparticles determined by the phase separation mechanism supplied a new approach for the control of aggregation of nanoparticles in polymers.