Swelling behavior of responsive amphiphilic gels

We study the equilibrium swelling degrees of an amphiphilic microgel which consists of two different types of constituents: hydrophobic (H) and hydrophilic (P) monomers. Using Flory-type theories, scaling arguments, and variational calculations, we investigate the influence of the number of cross links and cross-linking types on the equilibrium swelling behavior. We show that amphiphilic microgels exhibit discrete swelling degrees which are more pronounced than for homopolymer networks as the fraction of hydrophobic components in the gel changes. The heterogeneous cross links between different types of monomers prevent a complete phase separation and stabilize the gel at relatively high fraction of H monomers. Disorder in the arrangement of the monomers as well as the cross-linking positions is treated in the framework of the variational principle. The method developed here is also applied for designed networks which display well-defined conformational transitions. Such macrogels can be used for drug loading or release under specific environments. We provide scaling results for specifically constructed networks that are confirmed by our variational theory. (C) 2003 American Institute of Physics