Salt-Responsive Zwitterionic Polymer Brushes with
Tunable Friction and Antifouling Properties
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Abstract
Development
of smart, multifunction materials is challenging but
important for many fundamental and industrial applications. Here,
we synthesized and characterized zwitterionic poly(3-(1-(4-vinylbenzyl)-1<i>H</i>-imidazol-3-ium-3-yl)propane-1-sulfonate) (polyVBIPS) brushes
as ion-responsive smart surfaces via the surface-initiated atom transfer
radical polymerization. PolyVBIPS brushes were carefully characterized
for their surface morphologies, compositions, wettability, and film
thicknesses by atomic force microscopy (AFM), X-ray photoelectron
spectroscopy (XPS), contact angle, and ellipsometer, respectively.
Salt-responsive, switching properties of polyVBIPS brushes on surface
hydration, friction, and antifouling properties were further examined
and compared both in water and in salt solutions with different salt
concentrations and counterion types. Collective data showed that polyVBIPS
brushes exhibited reversible surface wettability switching between
in water and saturated NaCl solution. PolyVBIPS brushes in water induced
the larger protein absorption, higher surface friction, and lower
surface hydration than those in salt solutions, exhibiting “anti-polyelectrolyte
effect” salt responsive behaviors. At appropriate ionic conditions,
polyVBIPs brushes were able to switch to superlow fouling surfaces
(<0.3 ng/cm<sup>2</sup> protein adsorption) and superlow friction
surfaces (<i>u</i> ∼ 10<sup>–3</sup>). The
relationship between brush structure and its salt-responsive performance
was also discussed. This work provides new zwitterionic surface-responsive
materials with controllable antifouling and friction capabilities
for multifunctional applications