(291a) Exploring the Dispersity-Enhanced Stimulus Response and Bacterial Release in Polyelectrolyte Brushes

Polyelectrolyte brushes attached to surfaces change their conformation when exposed to solutions of varying pH. As responsive materials, polyelectrolyte brushes are used in applications, including drug delivery, enhanced oil recovery, and antifouling coatings. These tunable surfaces are also widely employed to control wettability, adhesion, friction, and biofouling. Despite extensive use across a broad range of applications, the role of polyelectrolyte brush length and dispersity on the pH-responsive behavior is not well understood. Here, we synthesized poly(acrylic acid) (PAA) brushes with controlled brush length and dispersity using the grafting-from approach at a constant grafting density. We identified three key trends in the response of the PAA brushes to changes in pH. First, the thickness of dry brushes decreased as the pH was decreased. Second, the water contact angle measured at low pH increased with dispersity. Finally, disperse brushes exhibited hysteretic memory behavior (i.e. dependent on the direction of pH change) in the contact angle. The origin of hysteresis is consistent with dispersity-driven pH-dependent conformational changes in these polyelectrolyte brushes. Together, these results indicate that increasing brush dispersity significantly alters the pH-response. Next, we used this model system to promote cell detachment via an abrupt change in solution pH (from 4 to 9). In preliminary experiments, we found that bacterial adhesion (at pH 4) increased when brush dispersity decreased. Upon switching to pH 9 the bacteria began to detach from the brushes after a delay time of approximately 5 min, corresponding to equilibration of the brush properties at this pH. The delay time was unaffected by brush length or dispersity.