Modeling hydrogen bonding in polymer blends using association models

We present a model to study the phase behavior of polymer blends with hydrogen bonding interactions. In our model, hydrogen bonding groups in A homopolymer and B homopolymer are modeled as sticker groups capable of both self-association and inter-association. We derive an expression for the free energy of such a system in the mean field limit. We use this expression to construct phase diagrams of the blend and explore the effect of strengths of inter-association and self-association, fractions of hydrogen bonding stickers and asymmetry in sticker fractions. Our model is different from the tradtional Flory approach in which a constant negative χ parameter is used to model hydrogen bonding interactions in that our model produces a concentration dependent χ parameter for hydrogen bonding interactions. We subsequently incorporate our model into self-consistent field theory of blends and using it, examine the properties of the A-B interface. We observe that when the net interaction strength between dissimilar stickers is significant, our model predicts lower interfacial tension and a more diffused interface than Flory model with an effective χ parameter corresponding to the same phase boundaries. We rationalize the above observation by analyzing the free energy curves of both models.