Amphiphilic Block Copolymer Micelles in Selective Solvents: The Effect of Solvent Selectivity on Micelle Formation.

Labeesh Kumar,Bhanu Nandan,Andriy Horechyy,Petra Uhlmann,Eva Bittrich,Andreas Fery

doi:10.3390/polym11111882

Abstract

We investigated the micellar behavior of a series of asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers in different P4VP-selective alcoholic solvents. The micellar behavior was further correlated with the spectroscopic ellipsometry results obtained on swelling of PS and P4VP polymer films in the corresponding solvent vapors. The time-resolved (in situ) dynamic light scattering (DLS) measurements, in combination with (ex situ) electron microscopy imaging, revealed information about the aggregation state of PS-b-P4VP BCP in different alcohols and the effect of heat treatment. The ellipsometry measurements allowed us to estimate the difference in solvent selectivity toward PS/P4VP pair. Both DLS and ellipsometric studies suggested that less polar alcohols (i.e., 1-propanol, 1-butanol, and 1-pentanol) are likely to be close to each other in terms of their selectivity toward PS/P4VP pair, whereas more polar ethanol and methanol show the highest and the lowest affinity toward P4VP, respectively.

Highlights

Amphiphilic block copolymers (BCP) attract research interest as template materials for the fabrication of various hybrid nanostructures, such as core–shell, yolk–shell particles, vesicles, porous membranes, or nanofibers, which found their application in various fields [1,2,3,4]
We used PS-b-P4VP(59) block copolymer, with a shorter PS block (φ(PS) ≈ 0.33), which self-assembles into cylindrical morphology in bulk (PS cylinders in P4VP matrix)
While our previous reports dealt with functionalization of PS-b-P4VP nanofibers and spherical micelles, the present work is addressed to a fundamental understanding of micellization process taking place upon dispersion of PS-b-P4VP BCPs in P4VP-selective solvents, and the role of temperature and solvent selectivity on micelle formation and their characteristics

Summary

Introduction

Amphiphilic block copolymers (BCP) attract research interest as template materials for the fabrication of various hybrid nanostructures, such as core–shell, yolk–shell particles, vesicles, porous membranes, or nanofibers, which found their application in various fields [1,2,3,4]. Solution self-assembly provides opportunities to regulate size, shape, morphology, or composition of block copolymer structures and subsequent functional materials [5]. Block copolymers consisting of poly(vinyl pyridine) segments in their structure are frequently used for the fabrication of various hybrid nanostructures, and polystyrene-block-poly(4-vinylpyridine). Micellization of symmetric and asymmetric PS-b-P4VP BCP was studied in the past by several research groups, focusing on different aspects of micelle formation and morphological transformation processes [8,9,10,11,12,13,14,15]

Methods

Results

Discussion

Conclusion