Mean-Field Study of Poly(methacrylic acid) Shells in Partly Hydrophobically Modified Amphiphilic Block Copolymer Micelles in Polar Solvents

摘要

The structure of poly(methacrylic acid) (PMA) shells in polystyrene-block-poly(methacrylic acid) (PS-PMA), micelles was studied by self-consistent field (SCF) calculations. The PS-PMA micelles can be modified by naphthalene tags immobilized at the core/shell interface and by hydrophobic anthracene tags at the ends of PMA chains. The nonmodified, partly modified, and 100% hydrophobically modified PS-PMA micelles were studied. Special attention was devoted to the distribution of anthracene tags attached at the ends of PMA blocks in aqueous mixtures with 1,4-dioxane (i.e., in nonpolyelectrolyte regime). The study shows that hydrophobic tags try to avoid the polar solvent and force the PMA chains to loop toward the core. We found that in partly modified micelles, the tags return closer to the core than in 100% tagged micelles because the entropy loss due to the looping is compensated by the conformational behavior of nonmodified PMA chains. The nonradiative energy transfer from naphthalene donors to anthracene traps was treated on the basis of distribution functions obtained by SCF method. The donor fluorescence decays were compared with experimental data published in the accompanying paper. The agreement was found to be good at the semiquantitative level.