Kramb Ryan C, Zukoski Charles F
Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, Illinois 61801, USA.
Langmuir. 2008 Jul 15;24(14):7565-72. doi: 10.1021/la800021h. Epub 2008 Jun 18.
Here we describe a method to create gels where the gel point is decoupled from gel elastic properties. Working with charge stabilized polystyrene latex particles with diameters, D, of 508-625 nm at ionic strengths of 0.1-1 M, the gel volume fraction is varied from 0.10-0.35 through the addition of less than monolayer coverage of hexaethylene glycol monododecyl ether (C6E12). At each surfactant concentration, the gel volume fraction depends on the background ionic strength. The changes in gel point with surfactant concentration suggest the strength of interparticle attraction decreases with increasing surfactant concentration. These changes are not reflected in the gel moduli, which are independent of surfactant concentration and ionic strength. We propose a model to describe this behavior based on gelation due to localization in a shallow truncated van der Waals minimum produced by the surfactant acting as a steric stabilizing layer. The surfactant remains mobile on the surface. Below the gel volume fraction, the time particles spend in the truncated well are not sufficient for the surfactant to be displaced such that the particles can only sample the shallow well. Above the gel volume fraction, particles are localized in the truncated van der Waals minima for sufficient periods of time to displace the surfactant layers with the result being that the particles fall into a primary van der Waals minimum. The result is gel points sensitive to surfactant concentration but moduli that are independent of the gel volume fraction.
在此，我们描述了一种制备凝胶的方法，其中凝胶点与凝胶弹性特性解耦。我们使用直径D为508 - 625 nm的电荷稳定聚苯乙烯乳胶颗粒，在离子强度为0.1 - 1 M的条件下，通过添加少于单层覆盖的六甘醇单十二烷基醚（C6E12），使凝胶体积分数在0.10 - 0.35之间变化。在每个表面活性剂浓度下，凝胶体积分数取决于背景离子强度。凝胶点随表面活性剂浓度的变化表明，颗粒间吸引力的强度随表面活性剂浓度的增加而降低。这些变化并未反映在凝胶模量中，凝胶模量与表面活性剂浓度和离子强度无关。我们提出了一个模型来描述这种行为，该模型基于由于表面活性剂作为空间稳定层产生的浅截断范德华最小值中的定位而导致的凝胶化。表面活性剂在表面上保持可移动状态。在凝胶体积分数以下，颗粒在截断阱中停留的时间不足以使表面活性剂被置换，以至于颗粒只能对浅阱进行采样。在凝胶体积分数以上，颗粒在截断的范德华最小值中定位足够长的时间以置换表面活性剂层，结果是颗粒落入主要的范德华最小值中。结果是凝胶点对表面活性剂浓度敏感，但模量与凝胶体积分数无关。
