Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA.
Langmuir. 2010 Jun 1;26(11):8709-20. doi: 10.1021/la9044573.
We have studied the effects of particle packing fraction, polymer molecular weight (MW), and polymer-segment-particle-surface affinity on the phase behavior of 44 nm silica dispersions in unentangled, low MW polyethylene oxide (PEO), polyethylene oxide dimethyl ether (PEODME), and polytetrahydrofuran (PTHF) through rheological measurement and small-angle X-ray scattering. Particles are shown to be stable in PEO nanocomposites up to high volume fractions due to an adsorbed layer of polymer segments that stabilizes particles in the melt. Comparison of the PEO nanocomposite to PEODME and PTHF nanocomposites reveals little evidence of an adsorbed layer in the spirit of the PEO nanocomposite. Measurement of the PTHF nanocomposite viscosity reveals evidence of segment slip at the particle surface by the particle intrinsic viscosity being less than Einstein's value. At higher particle volume fractions, the viscosity diverges, yielding an elastic response. The elastic response of the PEO nanocomposite has the signatures of a colloidal glass, while the PEODME and PTHF nanocomposites resemble a gel. Measurement of the particle structure factor reveals a change from overall repulsive particles in PEO to attractive particles in PTHF as the segment-surface interaction is changed.
我们通过流变学测量和小角 X 射线散射研究了颗粒堆积分数、聚合物分子量（MW）和聚合物段-颗粒-表面亲和力对 44nm 二氧化硅在未缠结、低 MW 聚环氧乙烷（PEO）、聚环氧乙烷二甲醚（PEODME）和聚四氢呋喃（PTHF）中的相行为的影响。由于吸附在熔体中的聚合物段稳定了颗粒，因此颗粒在 PEO 纳米复合材料中在高体积分数下仍保持稳定。将 PEO 纳米复合材料与 PEODME 和 PTHF 纳米复合材料进行比较，发现很少有迹象表明存在吸附层，这符合 PEO 纳米复合材料的精神。通过测量 PTHF 纳米复合材料的粘度，发现颗粒内禀粘度小于爱因斯坦值，表明在颗粒表面发生了段滑动。在更高的颗粒体积分数下，粘度发散，产生弹性响应。PEO 纳米复合材料的弹性响应具有胶体玻璃的特征，而 PEODME 和 PTHF 纳米复合材料则类似于凝胶。通过测量颗粒结构因子，发现当改变段-表面相互作用时，PEO 中的整体排斥颗粒转变为 PTHF 中的吸引颗粒。
