School of Engineering and Applied Sciences and Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
Langmuir. 2010 Mar 2;26(5):3174-8. doi: 10.1021/la903127a.
Mixtures of nonadsorbing polymer and colloidal particles exhibit a range of different morphologies depending on the particle and polymer concentrations and their relative size ratios. These can be very important for technological applications, where gelation can produce a weak solidlike structure that can help reduce phase separation, extending product shelf life. However, industrial products are typically formulated with polydisperse polymers, and the consequences of this on the phase behavior of the mixture are not known. We investigate the role of polymer polydispersity and show that a small amount of larger polymer in a distribution of nominally much smaller polymer can drastically modify the behavior. It can induce formation of a solidlike gel structure, abetted by the small polymer, but still allow further evolution of the phase separation process, as is seen with a monodisperse distribution of larger polymer. This coarsening ultimately leads to gravitational collapse. We describe the full phase behavior for polydisperse polymer mixtures and account for the origin of the behavior through measurements of the structure and dynamics and by comparing to the behavior with monodisperse polymers.
非吸附聚合物和胶体颗粒的混合物会根据颗粒和聚合物的浓度及其相对大小比呈现出一系列不同的形态。这些对于技术应用非常重要，因为凝胶化可以产生一种弱固态结构，有助于减少相分离，延长产品的保质期。然而，工业产品通常是用多分散聚合物来配方的，而这种聚合物的多分散性对混合物的相行为的影响尚不清楚。我们研究了聚合物多分散性的作用，并表明在名义上小得多的聚合物分布中少量较大的聚合物可以极大地改变行为。它可以通过小聚合物促进固态凝胶结构的形成，但仍允许相分离过程进一步演化，就像具有单分散较大聚合物的分布一样。这种粗化最终导致重力坍塌。我们描述了多分散聚合物混合物的全相行为，并通过测量结构和动力学以及与单分散聚合物的行为进行比较，解释了这种行为的起源。
