Estimation of polymer/water interfacial tensions: hydrophobic homopolymer/water interfaces

In this study, quantitative models for monomer/water and the corresponding polymer/water interfaces were developed. The monomer/water interface was modeled within the framework proposed by Fu and Li (Chem. Eng. Sci: 44 (1989) 1519) for organic liquid/water interfaces. We took a similar approach with that which others used to simulate micelle formation of surfactants and block polymers in developing the model for the polymer/water interface. In this model, the Gibbs free energy of interfacial formation was decomposed into two components: transfer free energy of a polymer segment to the interface and mixing free energy within the interface. Inter-facial tensions were then estimated using concentration gradient theory. The ratio of the number of total nearest neighbors of a site in a lattice within the interface to that located in each of the adjacent planes was found to be the important correlating factor. It was shown that this ratio for monomer/water interfaces and that for polymer/water interfaces are linearly related. The polymer in the interface is likely to be in the form of short polymer segments (2-4 monomer units) rather than dangling chain ends. The estimation of polymer/water interfacial tension from the models established in this work is in reasonable agreement with experimental observation. (C) 2003 Elsevier Science (USA). All rights reserved.