Micelle Formation of Amphiphilic Polystyrene-b-poly(N-vinylpyrrolidone) Diblock Copolymer in Methanol and Water-Methanol Binary Mixtures

摘要

The micelle formation by the amphiphilic polystyrene-block-poly(N-vinylpyrrolidone) (PS48-b-PNVP99) copolymer is investigated in methanol and water-methanol binary mixtures of various compositions using H-1 NMR, fluorescence spectroscopy, static/dynamic light scattering (SLS/DLS), and transmission electron microscopy (TEM). Critical micelle concert I rations (cmc) are determined by employing fluorescence spectroscopy and DLS Measurements. The cmc of the PS48-b-PNVP99 block copolymer increases with increasing methanol content in the water-methanol binary mixtures, suggesting that methanol is a better solvent for the PS48-b-PNVP99 block copolymer than water-methanol mixtures or pure water. The amphiphilic PS48-b-PNVP99 diblock copolymer forms spherical micelles of R-b similar to 16 nm in pure methanol Solution as revealed by DLS measurements, In contrast, significantly larger micelles having higher aggregation numbers are formed in water-methanol binary mixtures. Temperature dependent data reveal an increase in aggregation number and radius of gyration (R-g) concomitantly with temperature (10-40 degrees C). In contrast, the overall size (R-b) of the micelles remains almost constant over the same temperature range. An explanation is tendered that PNVP coronas dehydrate/desolvate at higher temperatures counteracting the increase in micelle size (R-b) caused by increased aggregation numbers (N-agg).