纳米SiO_2对PDMS/PIB不相容共混物在低剪切速率下凝聚行为的影响

INFLUENCE OF SILICA NANOPARTICLES ON THE COALESCENCE OF IMMISCIBLE PDMS/PIB BLENDS UNDER LOW-RATE SHEAR FLOW

借助在线剪切-显微装置研究了简单剪切流场下疏水纳米二氧化硅(SiO2)粒子对聚二甲基硅氧烷/聚异丁烯(PDMS/PIB=90 wt%∶10 wt%)不相容共混物实时结构演变过程的影响.研究表明,分散相尺寸的大小及其分布由粒子含量和剪切速率共同决定.少量纳米SiO2的加入能够抑制PIB分散相的凝聚,分散相的尺寸随着纳米SiO2含量的增大而减小,并且呈现出双峰分布.但随着SiO2粒子含量的进一步增加,分散相尺寸的双峰分布现象逐渐消失.SiO2的加入还导致PIB分散相对剪切速率的依赖性降低.当SiO2粒子含量低于2.5wt%时,较高的剪切速率凝聚得到的分散相的尺寸较大;当SiO2粒子含量超过2.5 wt%后,低速和高速剪切速率下凝聚得到的分散相尺寸基本相同.粒子的包覆、分散相的破碎和凝聚是出现以上现象的根本原因.

The effects of hydrophobic SiO2 nanoparticles on the real-time morphology evolution of the immiscible blend of polydimethylsiloxane （PDMS）/polyisobutylene （PIB）（90 wt% ： 10 wt% ） were investigated under simple shear flow with an online optical-shear system. The theoretical predication indicated that SiO2 particles were mainly trapped in the interface between two phases. It was found that the droplet size of PIB dispersed phases was determined by the content of SiO2 nanoparticles and shear rate. The coverage of SiO2 particles on the PIB dispersion droplets suppressed the coalescence of the dispersed phases and decreased their size at low shear rate. A bimodal distribution of the droplet size which originated from the uncompleted coverage of SiO2 on PIB dispersed phase was observed. With the increase in the content of particles, the peak on the droplet size curve which corresponded to those large dispersed phases, shifted gradually towards another peak corresponding to those small dispersed phases, and finally merged into a single one. It was also found that the incorporation of SiO2 nanoparticles in PDMS/PIB blends decreased the dependence of droplet size on the shear rate. The synergetie effects of particle coverage, droplet breakup and coalescence resulted in similar droplet size in PDMS/PIB blends under two different shear rates when the contents of SiO2 particles exceeded 2.5 wt %.