Complex aggregation of TPPS and PEG-b-P4VP in confined space

Abstract

To explore the structure and property features of complex aggregates assembled by polymer and organic dye molecules in microcosmic soft confined space, a three-dimensional microconfinement is constructed by W/O inverse emulsion as the site for the complex aggregation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP). It is found that porphyrin molecules exist in emulsion droplets mainly as the deprotonated monomer form, even though the pH of the water phase is much lower than the pK_a of TPPS in bulk (pK_a ≈ 4.7). In spatially confined circumstances, upon blending of the single-component emulsions, complex aggregates are formed due to the thermodynamic collision of emulsion droplets and the subsequent electrostatic interaction between TPPS and polymer. The resultant novel complexes possess a relatively precise structure and homogenous core consisting of a porphyrin and P4VP block. Upon emulsion-breaking, the metastable complex kinetic intermediates generated in original acidic emulsion droplets display a remarkable trend of reaggregation within a certain period of time followed by a disassociation and redispersion. Complex aggregates with some novel morphologies are observed. The final product has a core–shell structure with the electrostatic complex of deprotonized porphyrin molecules homogenously dispersing in the P4VP clew as the core and the soluble PEG as the shell. However, those complexes produced in basic emulsion droplets exhibit a relatively higher stability against further aggregation after breakage of emulsion.