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Issue 15, 2016
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Hysteretic memory in pH-response of water contact angle on poly(acrylic acid) brushes

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Abstract

We investigated the pH-dependent response of flat polyacid brushes of varying length and dispersity in the extended brush regime. Our model system consisted of poly(acrylic acid) brushes, which change from hydrophobic and neutral at low pH to hydrophilic and negatively charged at high pH, synthesized on silicon substrates using a grafting-from approach at constant grafting density. We observed three trends in the pH-response: first, the dry brush thickness increased as the pH was increased for brushes above a critical length, and this effect was magnified as the dispersity increased; second, the water contact angle measured at low pH was larger for brushes of greater dispersity; and third, brushes of sufficient dispersity exhibited hysteretic memory behavior in the pH-dependence of the contact angle, in which the contact angle upon increasing and decreasing pH differed. As a consequence, the pKa of the brushes measured upon increasing pH was consistently higher than that measured upon decreasing pH. The observed pH response is consistent with proposed changes in the conformation and charge distribution of the polyelectrolyte brushes that depend on the direction of pH change and the dispersity of the brushes.

Graphical abstract: Hysteretic memory in pH-response of water contact angle on poly(acrylic acid) brushes

  • This article is part of the themed collection: Polymers
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Article information


Submitted
29 Dec 2015
Accepted
07 Mar 2016
First published
08 Mar 2016

Soft Matter, 2016,12, 3589-3599
Article type
Paper

Hysteretic memory in pH-response of water contact angle on poly(acrylic acid) brushes

V. Yadav, A. V. Harkin, M. L. Robertson and J. C. Conrad, Soft Matter, 2016, 12, 3589
DOI: 10.1039/C5SM03134F

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