Cors Marian, Wiehemeier Lars, Wrede Oliver, Feoktystov Artem, Cousin Fabrice, Hellweg Thomas, Oberdisse Julian
Department of Physical and Biophysical Chemistry, Bielefeld University, Universitätsstr. 25, 33615 Bielefeld, Germany.
Forschungszentrum Jülich GmbH, Jülich Centre for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum MLZ, 85748 Garching, Germany.
Soft Matter. 2020 Feb 19;16(7):1922-1930. doi: 10.1039/c9sm02036e.
The radial density profile of deuterated poly(N,n-propyl acrylamide) shell monomers within core-shell microgels has been studied by small-angle neutron scattering in order to shed light on the origin of their linear thermally-induced swelling. The poly(N-isopropyl methacrylamide) core monomers have been contrast-matched by the H2O/D2O solvent mixture, and the intensity thus provides a direct measurement of the spatial distribution of the shell monomers. Straightforward modelling shows that their structure does not correspond to the expected picture of a well-defined external shell. A multi-shell model solved by a reverse Monte Carlo approach is then applied to extract the monomer density as a function of temperature and of the core crosslinking. It is found that most shell monomers fill the core at high temperatures approaching synthesis conditions of collapsed particles, forming only a dilute corona. As the core monomers tend to swell at lower temperatures, a skeleton of insoluble shell monomers hinders swelling, inducing the progressive linear thermoresponse.
为了阐明氘代聚（N，n-丙基丙烯酰胺）壳单体在核壳微凝胶中线性热致溶胀的起源，通过小角中子散射研究了其径向密度分布。聚（N-异丙基甲基丙烯酰胺）核单体已通过H2O/D2O溶剂混合物进行对比匹配，因此强度提供了壳单体空间分布的直接测量。简单的建模表明，它们的结构与定义明确的外壳的预期情况不符。然后应用通过反向蒙特卡罗方法求解的多壳模型来提取单体密度作为温度和核交联的函数。结果发现，在接近塌陷颗粒合成条件的高温下，大多数壳单体填充在核中，仅形成稀薄的冠层。随着核单体在较低温度下趋于溶胀，不溶性壳单体的骨架阻碍溶胀，从而引发渐进的线性热响应。
