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Issue 5, 2015
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Hydrophobic effects within the dynamic pH-response of polybasic tertiary amine methacrylate brushes

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Abstract

The solvation and swelling behaviour of three dialkylaminoethyl methacrylate polymer brushes, of varying hydrophobicity, have been investigated using a combination of in situ ellipsometry and a quartz crystal microbalance with dissipation (QCM-D). At low pH the tertiary amine groups of the three polymers are protonated and all three brushes are significantly solvated and swell by adopting an extended conformation. As the pH is increased the weak polybasic brushes become increasingly deprotonated and collapse via solvent expulsion. By employing high temporal resolution measurements we have found that monomer hydrophobicity has a direct influence on the dynamics of this pH-response. The most hydrophobic poly(2-diisopropylamino)ethyl methacrylate (poly(DPA)) brush exhibits the fastest maximum swelling rate. This maximum swelling rate is reduced with decreasing monomer hydrophobicity for the 2-diethylamino, and even further for the 2-dimethylamino analogues. For all three brushes, the corresponding collapse transition is slower and compounded by an induction time that decreases with monomer hydrophobicity. Here also, the maximum collapse rate is greatest for the most hydrophobic polymer. This domination of the pH-response kinetics by monomer hydrophobicity is attributed to attractive hydrophobic forces between polymer segments overcoming the repulsive electrostatic forces between the tertiary amine residues.

Graphical abstract: Hydrophobic effects within the dynamic pH-response of polybasic tertiary amine methacrylate brushes

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Publication details

The article was received on 14 Nov 2014, accepted on 19 Dec 2014 and first published on 19 Dec 2014


Article type: Paper
DOI: 10.1039/C4CP05292G
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Citation: Phys. Chem. Chem. Phys., 2015,17, 3880-3890

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    Hydrophobic effects within the dynamic pH-response of polybasic tertiary amine methacrylate brushes

    J. D. Willott, B. A. Humphreys, T. J. Murdoch, S. Edmondson, G. B. Webber and E. J. Wanless, Phys. Chem. Chem. Phys., 2015, 17, 3880
    DOI: 10.1039/C4CP05292G

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