Ren Chun-Lai, Nap R J, Szleifer I
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208, USA.
J Phys Chem B. 2008 Dec 18;112(50):16238-48. doi: 10.1021/jp8080904.
A molecular theory to study the properties of end-tethered polymer layers, in which the polymers have the ability to form hydrogen bonds with water, is presented. The approach combines the ideas of the single-chain mean-field theory to treat tethered layers with the approach of Dormidontova (Macromolecules, 2002, 35, 987.) to include hydrogen bonds. The generalization includes the consideration of position-dependent polymer-water and water-water hydrogen bonds. The theory is applied to model poly(ethylene oxide) (PEO), and the predictions are compared with equivalent polymer layers that do not form hydrogen bonds. It is found that increasing the temperature lowers the solubility of the PEO and results in a collapse of the layer at high enough temperatures. The properties of the layer and their temperature dependence are shown to be the result of the coupling between the conformational entropy of the chains, the ability of the polymer to form hydrogen bonds, and the intermolecular interactions. The structural and thermodynamic properties of the PEO layers, such as the lateral pressure-area isotherms and polymer chemical potentials, are studied as a function of temperature and type of tethering surface. The possibility of phase separation of the PEO layer at high enough temperature is predicted due to the reduced solubility induced by breaking of polymer-water hydrogen bonds. A discussion of the advantages and limitations of the theory, together with how to apply the approach to different hydrogen-bonding polymers, is presented.
提出了一种分子理论，用于研究末端连接聚合物层的性质，其中聚合物能够与水形成氢键。该方法将单链平均场理论处理连接层的思想与多尔米东托娃（《大分子》，2002年，35卷，987页）的方法相结合，以纳入氢键。推广内容包括考虑位置依赖的聚合物 - 水和水 - 水氢键。该理论应用于模拟聚环氧乙烷（PEO），并将预测结果与不形成氢键的等效聚合物层进行比较。研究发现，升高温度会降低PEO的溶解度，并在足够高的温度下导致层的塌陷。层的性质及其温度依赖性被证明是链的构象熵、聚合物形成氢键的能力以及分子间相互作用之间耦合的结果。研究了PEO层的结构和热力学性质，如横向压力 - 面积等温线和聚合物化学势，作为温度和连接表面类型的函数。由于聚合物 - 水氢键断裂导致溶解度降低，预测了在足够高温度下PEO层发生相分离的可能性。还讨论了该理论的优点和局限性，以及如何将该方法应用于不同的氢键聚合物。
