Layer-by-layer films of block copolymer micelles with cores exhibiting upper critical solution temperature behaviour

Abstract

We report on preparation of block copolymer micelles with cores exhibiting upper critical solution temperature (UCST) behavior in the range of 40–45°C at pH 7.5 and incorporation of such micelles into layer-by-layer (LbL) films to obtain UCST-type multilayer films. Pyridine units of poly(2-vinylpyridine-b-ethylene oxide) (P2VP-b-PEO) were partially quaternized and its self-assembly into micellar aggregates was achieved in the presence of potassium hexacyanoferrate (K3Fe(CN)6) at pH 7.5 at either 25°C or 37.5°C. The cores of the resulting (QP2VP+[Fe(CN)6]3−)-b-PEO micelles exhibited UCST-type behavior at pH 7.5 and the critical temperature varied in the range of 40–45°C depending on the micellization temperature and amount of K3Fe(CN)6. Our results showed that micellization temperature and K3Fe(CN)6 concentration were highly critical on the UCST of the micellar cores. In case of (QP2VP+[Fe(CN)6]3−)-b-PEO micelles prepared at 25°C, increasing K3Fe(CN)6 concentration during micellization suppressed UCST behavior within a temperature range of 25-50°C. In contrast, increasing K3Fe(CN)6 concentration induced only small shifts in UCST when (QP2VP+[Fe(CN)6]3−)-b-PEO micelles were produced at 37.5°C. Moreover, we showed that (QP2VP+[Fe(CN)6]3−)-b-PEO micelles could be incorporated into LbL films using Tannic Acid (TA) at pH 7.5. Multilayers which partially disintegrate near above 40°C could be assembled by controlling micellization temperature and film deposition temperature. This study contributes to fundamental understanding of salt-induced micellization and structure–property relationship in hydrogen-bonded LbL films.