Antipolyelectrolyte Response of Amphiphilic Sulfobetaine Polymer Coatings

Zwitterionic, amphiphilic polymer coatings are an effective strategy to decrease biofouling. Yet their performance strongly depends on the mechanical properties, the degree of swelling, and the structure of the swollen hydrogels. These properties depend on the zwitterionic groups in the polymers and the properties of the surrounding electrolyte. Therefore, the influence of the ions present and their concentrations on the swelling behavior of amphiphilic zwitterionic copolymers is studied. Coatings of 3-[N-2′-(methacryloyloxy)ethyl-N,N-dimethyl]-ammoniopropane-1-sulfonate (SPE) with increasing amounts of butyl-methacrylate (BMA) are compared to the respective homopolymers PSPE and PBMA. Surface plasmon resonance spectroscopy shows a salt concentration-dependent anti-polyelectrolyte behavior. A variation of the salts revealed that the anions dominated the swelling response, while a change of cations has hardly any effect. Small angle X-ray scattering reveals the morphological changes in the polymer films that accompanied the swelling. With increasing salt concentration, the internal structure changed from compact pores in a gel-like network to elongated cylindrical pores at higher salinities. The understanding gained from the presented multi-technique approach allows to understand the behavior of zwitterionic coatings in saline solutions and helps to tailor the swelling response and mechanical properties for future marine and medical low-fouling applications.