School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA.
Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
Phys Rev E. 2017 Jan;95(1-1):012608. doi: 10.1103/PhysRevE.95.012608. Epub 2017 Jan 19.
We investigate microgels synthesized from N-isopropylacrylamide (NIPAM) copolymerized with a large mol% of acrylic acid, finding that when the acid groups are partially ionized at high temperatures, competition between ion-induced swelling and hydrophobic deswelling of poly(NIPAM) chains results in microphase separation. In cross-linked microgels, this manifests as a dramatic decrease in the ratio between the radius of gyration and the hydrodynamic radius to ∼0.2, indicating that almost all the mass of the microgel is concentrated near the particle center. We also observe a concurrent decrease of the polymer network length scale via small-angle neutron scattering, confirming the presence of a dense, deswollen core surrounded by a diffuse, charged periphery. We compare these results to those obtained for a system of charged ultralow-cross-linked microgels; the form factor shows a distinct peak at high q when the temperature exceeds a threshold value. We successfully fit the form factor to theory developed to describe scattering from weakly charged gels in poor solvents, and we tie this behavior to charge segregation in the case of the cross-linked microgels.
我们研究了由 N-异丙基丙烯酰胺（NIPAM）与大量摩尔百分比的丙烯酸共聚合成的微凝胶，发现当酸基团在高温下部分离解时，离子诱导的溶胀与聚（NIPAM）链的疏水性去溶胀之间的竞争导致微相分离。在交联的微凝胶中，这表现为回旋半径与流体力学半径之比急剧下降到约 0.2，表明微凝胶的几乎所有质量都集中在颗粒中心附近。我们还通过小角中子散射观察到聚合物网络长度尺度的同时减小，证实了存在一个密集的、去溶胀的核心，周围是扩散的、带电的外围。我们将这些结果与带电超低交联微凝胶系统的结果进行了比较；当温度超过阈值时，高 q 值处的形状因子出现明显的峰值。我们成功地将形状因子拟合到理论中，该理论用于描述在不良溶剂中弱带电凝胶的散射，并且我们将这种行为与交联微凝胶中电荷分离联系起来。
