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Issue 32, 2016
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Thermodynamics of the multi-stage self-assembly of pH-sensitive gradient copolymers in aqueous solutions

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Abstract

The self-assembly thermodynamics of pH-sensitive di-block and tri-block gradient copolymers of acrylic acid and styrene was studied for the first time using isothermal titration calorimetry (ITC) and dynamic light scattering (DLS) performed at varying pH. We were able to monitor each step of micellization as a function of decreasing pH. The growth of micelles is a multi-stage process that is pH dependent with several exothermic and endothermic components. The first step of protonation of the acrylic acid monomer units was accompanied mainly by conformational changes and the beginning of self-assembly. In the second stage of self-assembly, the micelles become larger and the number of micelles becomes smaller. While solution acidity increases, the isothermal calorimetry data show a broad deep minimum corresponding to an exothermic process attributed to an increase in the size of hydrophobic domains and an increase in the structure's hydrophobicity. The minor change in heat capacity (ΔCp) confirms the structural changes during this exothermic process. The exothermic process terminates deionization of acrylic acid. The pH-dependence of the ζ-potential of the block gradient copolymer micelles exhibits a plateau in the regime corresponding to the pH-controlled variation of the micellar dimensions. The onset of micelle formation and the solubility of the gradient copolymers were found to be dependent on the length of the gradient block.

Graphical abstract: Thermodynamics of the multi-stage self-assembly of pH-sensitive gradient copolymers in aqueous solutions

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Supplementary files

Article information


Submitted
11 May 2016
Accepted
04 Jul 2016
First published
13 Jul 2016

Soft Matter, 2016,12, 6788-6798
Article type
Paper

Thermodynamics of the multi-stage self-assembly of pH-sensitive gradient copolymers in aqueous solutions

Z. Černochová, A. Bogomolova, O. V. Borisova, S. K. Filippov, P. Černoch, L. Billon, O. V. Borisov and P. Štěpánek, Soft Matter, 2016, 12, 6788 DOI: 10.1039/C6SM01105E

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