Espinosa-Dzib Alejandra, Vyazovkin Sergey
Department of Chemistry, University of Alabama at Birmingham, 901 S. 14th Street, Birmingham, AL 35294, USA.
Soft Matter. 2020 Apr 1;16(13):3285-3293. doi: 10.1039/d0sm00004c.
Differential scanning calorimetry is used to obtain insights into the kinetics and thermodynamics of nanoconfined gelation. Gels of polyacrylonitrile in propylene carbonate, poly(vinyl alcohol) in ethylene glycol, and isotactic polypropylene in o-dichlorobenzene and decalin are studied in silica nanopores. Two major effects are observed for nanoconfined gels: a decrease in the heat of gelation and an increase in the gelation temperature. The smaller heat indicates that nanoconfinement of polymer chains results in the formation of fewer ordered crosslinks. The increased gelation temperature suggests acceleration of the gelation kinetics. The kinetics has been treated by an advanced isoconversional method and interpreted in terms of the Fisher-Turnbull model. It is found that acceleration of gelation in nanopores is associated with a decrease in the free energy barrier to nucleation, as one would expect for a change in the process mechanism from homogenous to heterogenous nucleation.
差示扫描量热法用于深入了解纳米受限凝胶化的动力学和热力学。研究了碳酸丙烯酯中的聚丙烯腈凝胶、乙二醇中的聚乙烯醇凝胶以及邻二氯苯和十氢化萘中的全同立构聚丙烯凝胶在二氧化硅纳米孔中的情况。对于纳米受限凝胶观察到两个主要影响：凝胶化热降低和凝胶化温度升高。较小的热量表明聚合物链的纳米限域导致形成的有序交联较少。凝胶化温度升高表明凝胶化动力学加速。动力学已通过先进的等转化率方法处理，并根据费舍尔 - 特恩布尔模型进行解释。结果发现，纳米孔中凝胶化的加速与成核自由能垒的降低有关，正如从均相成核到异相成核过程机制变化所预期的那样。
