Zhou B, Gasser U, Fernandez-Nieves A
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen, Switzerland.
Department of Condensed Matter Physics, University of Barcelona, 08028 Barcelona, Spain; ICREA-Institucio Catalana de Recerca i Estudis Avancats, 08010 Barcelona, Spain; and Institute for Complex Systems (UBICS), University of Barcelona, 08028 Barcelona, Spain.
Phys Rev E. 2023 Nov;108(5-1):054604. doi: 10.1103/PhysRevE.108.054604.
Microgels are of high interest for applications and as model systems due to their volume response to external stimuli. We use small-angle neutron scattering to measure the form and structure factors of poly(N-isopropylacrylamide) microgels in dilute and concentrated suspensions and find that microgels keep a constant size up to a concentration, above which they deswell. This happens before random-close packing. We emphasize suspension polydispersity must be considered to obtain accurate form and structure factors. Our results are compatible with microgel deswelling triggered by the osmotic pressure set by counterions associated to charged groups in the microgel periphery, which sharply increases when the counterion clouds surrounding the microgels percolate throughout the suspension volume.
由于微凝胶对外部刺激的体积响应，它们在应用和作为模型系统方面具有很高的研究价值。我们使用小角中子散射来测量稀悬浮液和浓悬浮液中聚（N-异丙基丙烯酰胺）微凝胶的形状和结构因子，发现微凝胶在达到一定浓度之前保持恒定大小，超过该浓度后它们会发生溶胀收缩。这发生在随机密堆积之前。我们强调，为了获得准确的形状和结构因子，必须考虑悬浮液的多分散性。我们的结果与微凝胶外围带电荷基团所关联的抗衡离子产生的渗透压引发的微凝胶溶胀收缩现象相符，当微凝胶周围的抗衡离子云在整个悬浮液体积中渗透时，渗透压会急剧增加。
