Chair of Technical Thermodynamics, RWTH Aachen University , D-52062 Aachen, Germany.
J Phys Chem B. 2017 Apr 6;121(13):2887-2895. doi: 10.1021/acs.jpcb.6b09147. Epub 2017 Mar 24.
Microgels have a wide range of possible applications and are therefore studied with increasing interest. Nonetheless, the microgel synthesis process and some of the resulting properties of the microgels, such as the cross-linker distribution within the microgels, are not yet fully understood. An in-depth understanding of the synthesis process is crucial for designing tailored microgels with desired properties. In this work, rate constants and reaction enthalpies of chain propagation reactions in aqueous N-isopropylacrylamide/N,N'-methylenebisacrylamide and aqueous N-vinylcaprolactam/N,N'-methylenebisacrylamide systems are calculated to identify the possible sources of an inhomogeneous cross-linker distribution in the resulting microgels. Gas-phase reaction rate constants are calculated from B2PLYPD3/aug-cc-pVTZ energies and B3LYPD3/tzvp geometries and frequencies. Then, solvation effects based on COSMO-RS are incorporated into the rate constants to obtain the desired liquid-phase reaction rate constants. The rate constants agree with experiments within a factor of 2-10, and the reaction enthalpies deviate less than 5 kJ/mol. Further, the effect of rate constants on the microgel growth process is analyzed, and it is shown that differences in the magnitude of the reaction rate constants are a source of an inhomogeneous cross-linker distribution within the resulting microgel.
微凝胶具有广泛的应用前景，因此越来越受到关注。尽管如此，微凝胶的合成过程以及一些微凝胶的特性，如微凝胶内的交联剂分布，尚未完全理解。深入了解合成过程对于设计具有所需特性的定制微凝胶至关重要。在这项工作中，计算了水相 N-异丙基丙烯酰胺/N,N'-亚甲基双丙烯酰胺和水相 N-乙烯基己内酰胺/N,N'-亚甲基双丙烯酰胺体系中链增长反应的速率常数和反应焓，以确定导致微凝胶中交联剂分布不均匀的可能原因。气相反应速率常数是根据 B2PLYPD3/aug-cc-pVTZ 能量和 B3LYPD3/tzvp 几何形状和频率计算的。然后，基于 COSMO-RS 的溶剂化效应被纳入到速率常数中，以获得所需的液相反应速率常数。速率常数与实验值的偏差在 2-10 倍以内，反应焓的偏差小于 5 kJ/mol。此外，还分析了速率常数对微凝胶生长过程的影响，结果表明，反应速率常数的大小差异是导致微凝胶内交联剂分布不均匀的一个原因。
