Department of Chemistry, University of Alabama at Birmingham, 901 S. 14th Street, Birmingham, AL 35294, USA.
Molecules. 2018 Nov 20;23(11):3025. doi: 10.3390/molecules23113025.
The purpose of this study is to highlight the surface and size effects of the nanopores on the thermodynamics and kinetics of gelation. The effects have been probed by applying differential scanning calorimetry to poly(vinylidene fluoride) solutions in tetraethylene glycol dimethyl ether (tetraglyme) and γ-butyrolactone. Nanoconfinement has been accomplished by introducing gels into native and organically modified silica nanopores (4⁻30 nm). Nanoconfinement has produced two major effects. First, the heat of gelation has decreased three to four times compared to that for the bulk systems. Second, the temperature of gelation has increased by ~40 °C (tetraglyme based systems) and ~70 °C (γ-butyrolactone based systems), the increase being stronger in native nanopores. The effects are discussed in terms of acceleration of gelation due to heterogeneous nucleation at the confining surface, and retardation of gelation due to constricted polymer chain mobility in the middle of the pore volume. Calorimetric data have been subjected to isoconversional kinetics analysis. The obtained temperature dependencies of the activation energies of gelation have been interpreted in the frameworks of the nucleation model of Turnbull and Fisher. The results suggest that nanoconfinement leads to a lowering of both the free energy of nucleation and activation energy of diffusion.
本研究旨在强调纳米孔的表面和尺寸效应对凝胶化热力学和动力学的影响。通过应用差示扫描量热法研究聚偏氟乙烯在四甘醇二甲醚（四甘醇二甲醚）和γ-丁内酯中的溶液，探测到了这些影响。通过将凝胶引入天然和有机改性的硅纳米孔（4-30nm）中，实现了纳米限制。纳米限制产生了两个主要影响。首先，与本体体系相比，凝胶化的热减少了三到四倍。其次，凝胶化温度升高了约 40°C（基于四甘醇二甲醚的体系）和 70°C（基于γ-丁内酯的体系），在天然纳米孔中，这种增加更为强烈。这些影响是通过在限制表面的异核成核加速凝胶化，以及在孔体积中间限制聚合物链的迁移率来减缓凝胶化来讨论的。量热数据已进行等转化率动力学分析。凝胶化活化能的温度依赖性是根据特鲁布尔和费舍尔的成核模型来解释的。结果表明，纳米限制导致成核自由能和扩散活化能的降低。
