Statistical Mechanics of Thermoreversible Gelation

Grzegorz Szamel获得了理论和计算化学项目的教师早期职业发展奖的支持，旨在从理论上了解热可逆聚合物凝胶化和热可逆凝胶的特性。要研究的具体问题是：1)所观察到的凝胶化转变背后的热力学转变的存在和性质；2)溶胶和凝胶相的结构；3)凝胶相的弹性性质；以及4)溶胶和凝胶相的粘弹性性质。所使用的方法是将最近橡胶硫化(形成永久聚合物网络)的统计力学方法推广到可逆交联的情况。具体地说，化学缔合的统计力学理论将被用来描述沿聚合物链随机分布的特定单体的可逆键合。将使用复制方法来促进对特定单体的位置进行平均。最后，引入序参数场(与冻结密度涨落有关)，得到有效的自由能泛函。自由能泛函将使用与硫化转变研究中使用的方法类似的方法进行分析。该教育计划的目标是向学生传授定量推理在物理化学和一般化学中的价值和意义。特别是在物理化学课程教学中引入背诵课，以提高学生运用相关数学形式主义方法解决化学问题的能力。此外，将为化学家开设一门关于数学和计算方法的新课程，以使学生了解数值方法和模拟方法在化学中的应用。聚合物凝胶因其潜在的实际应用价值而引起了人们的极大兴趣。例子包括药物输送装置、化学阀和传感器以及磁共振监测剂。它们的性质会随着外界刺激如温度、电场或光的变化而发生巨大的变化。Szamel的研究集中在一类聚合物凝胶上，即热可逆凝胶。这些凝胶源于聚合物体系的可逆交联性。这些凝胶是可逆的，即它们在加热时液化，在冷却时再生。

Grzegorz Szamel is supported by a Faculty Early Career Development Award in the Theoretical and Computational Chemistry Program to develop a theoretical understanding of thermoreversible polymer gelation and the properties of thermoreversible gels. The specific problems to be studied are: 1) existence and properties of a thermodynamic transition underlying the observed gelation transition; 2) structure of the sol and gel phases; 3) elastic properties of the gel phase; and 4) viscoelastic properties of the sol and gel phases. The method to be used is a generalization of a recent statistical mechanical approach to rubber vulcanization (formation of a permanent polymer network) to the case of reversible crosslinking. Specifically, a statistical mechanical theory of chemical association will be used to describe reversible bonding of specific monomers distributed randomly along polymer chains. A replication approach will be used to facilitate averaging over the positions of specific monomers. Finally, an order parameter field (related to frozen density fluctuations) will be introduced, and an effective free energy functional will be derived. The free energy functional will be analyzed using methods similar to those used in the study of the vulcanization transition. The goal of the education plan is to teach students the value and significance of quantitative reasoning in physical chemistry, and chemistry in general. In particular, recitation classes will be introduced into teaching the physical chemistry courses in order to improve student's ability to solve chemical problems using the relevant mathematical formalism. Moreover, a new course on mathematical and computational methods for chemists will be instituted in order to expose students to the applications of numerical and simulational methods in chemistry. Polymer gels have attracted a lot of interest because of the wealth of their potential practical applications. Examples include drug delivery devices, chemical valves and sensors, and magnetic resonance monitoring agents. Their properties can change drastically in response to external stimuli such as temperature, electric field, or light. Szamel's research concentrates on one class of polymer gels, thermoreversible gels. These gels originate from reversible crosslinking of polymeric systems. These gels are reversible, i.e. they liquify upon heating, and are regenerated upon cooling.