Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen, Switzerland.
School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
Phys Rev E. 2017 Sep;96(3-1):032609. doi: 10.1103/PhysRevE.96.032609. Epub 2017 Sep 25.
We investigate the phase behavior of suspensions of poly(N-isopropylacrylamide) (pNIPAM) microgels with either bimodal or polydisperse size distribution. We observe a shift of the fluid-crystal transition to higher concentrations depending on the polydispersity or the fraction of large particles in suspension. Crystallization is observed up to polydispersities as high as 18.5%, and up to a number fraction of large particles of 29% in bidisperse suspensions. The crystal structure is random hexagonal close-packed as in monodisperse pNIPAM microgel suspensions. We explain our experimental results by considering the effect of bound counterions. Above a critical particle concentration, these cause deswelling of the largest microgels, which are the softest, changing the size distribution of the suspension and enabling crystal formation in conditions where incompressible particles would not crystallize.
我们研究了具有双峰或多分散尺寸分布的聚（N-异丙基丙烯酰胺）（pNIPAM）微凝胶悬浮液的相行为。我们观察到，根据多分散性或悬浮液中大颗粒的分数，流体-晶体转变会移向更高的浓度。在高达 18.5%的多分散度和高达 29%的大颗粒数分数的双分散悬浮液中观察到结晶。晶体结构为随机密堆积六方，与单分散 pNIPAM 微凝胶悬浮液相同。我们通过考虑结合抗衡离子的影响来解释我们的实验结果。在临界粒子浓度以上，这些离子会使最软的大微凝胶溶胀，从而改变悬浮液的尺寸分布，并在不可压缩粒子不会结晶的条件下实现结晶。
