Hyatt John S, Do Changwoo, Hu Xiaobo, Choi Hong Sung, Kim Jin Woong, Lyon L Andrew, Fernandez-Nieves Alberto
School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA.
Biology and Soft Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Sep;92(3):030302. doi: 10.1103/PhysRevE.92.030302. Epub 2015 Sep 29.
We investigate poly(N-isopropylacrylamide) (pNIPAM) microgels randomly copolymerized with large mol % of protonated acrylic acid (AAc), finding that above the lower critical solution temperature the presence of the acid strongly disrupts pNIPAM's collapse, leading to unexpected new behavior at high temperatures. Specifically, we see a dramatic increase in the ratio between the radius of gyration and the hydrodynamic radius above the theoretical value for homogeneous spheres, and a corresponding increase of the network length scale, which we attribute to the presence of a heterogeneous polymer distribution that forms due to frustration of pNIPAM's coil-to-globule transition by the AAc. We analyze this phenomenon using a Debye-Bueche-like scattering contribution as opposed to the Lorentzian term often used, interpreting the results in terms of mass segregation at the particle periphery.
我们研究了与大量摩尔百分比的质子化丙烯酸（AAc）随机共聚的聚（N-异丙基丙烯酰胺）（pNIPAM）微凝胶，发现高于最低临界溶液温度时，酸的存在强烈干扰了pNIPAM的塌陷，导致在高温下出现意想不到的新行为。具体而言，我们观察到回转半径与流体动力学半径之比急剧增加，超过了均匀球体的理论值，并且网络长度尺度相应增加，我们将此归因于由于AAc阻碍pNIPAM从线圈到球体的转变而形成的非均相聚合物分布的存在。我们使用类似于德拜-比切的散射贡献来分析这一现象，而不是通常使用的洛伦兹项，并从颗粒周边的质量分离角度解释结果。
