Influence of Anion Hydrophilicity on the Conformation of a Hydrophobic Weak Polyelectrolyte Brush

• DOI: 10.1021/acs.macromol.6b01897
• Publication Date: 2016-12-13T17:12:57Z
• Authors: Timothy J. Murdoch; Joshua D. Willott; Wiebe M. de Vos; Andrew Nelson; Stuart W. Prescott; Erica J. Wanless; Grant B. Webber
• Keywords: Chaotropic agent; Perchlorate; Potassium thiocyanate; Thiocyanate; Hydrophobic effect

The conformation of a hydrophobic, weak cationic poly(2-diisopropylamino)ethyl methacrylate (PDPA) brush was studied using neutron reflectometry as function aqueous solution pH, ionic strength, and anion identity. In pH 4, 10 mM potassium nitrate the is highly charged, resulting in an extended, dilute conformation; at 9 uncharged collapses to single, dense layer. response added salt constant (4.5) for varying concentrations salts acetate, nitrate, thiocyanate revealed ion-specific conformations brush. At low strength (0.1 mM) collapsed, independent identity, while higher strengths (up 500 dependent on counterion exhibited extended presence kosmotropic acetate counterions, collapsed were retained strongly chaotropic counterions. showed richer set behaviors solutions containing weakly anion, being similar (swollen) intermediate but (collapsed) high concentrations. Numerical self-consistent field (nSCF) simulations indicate that changes dominated by hydrophobicity polymer values near pKa. Furthermore, reveal addition single Flory–Huggins interaction parameter analogous hydrophilicity sufficient replicate observed specific hydrophobic polyelectrolyte