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New Zwitterionic Polymers "Low-fouling" Surfaces

Subject Area Preparatory and Physical Chemistry of Polymers
Term from 2015 to 2020
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 279753164
 
Final Report Year 2025

Final Report Abstract

Fouling, i.e., the non-specific adsorption of molecules, matter, pathogens or organisms on surfaces compromises the stability, lifetime, and functional integrity of manmade materials in technological applications such as biomedicine. Particularly, the ubiquitous problem occurs in aqueous environments rich in nutrients, such as body fluids or in maritime applications. As at the start of the project of only few zwitterionic monomers were commercially available, the goal of the proposal was to broaden the types of structural motifs for optimized effective biocideand PFAS-free protective coatings and to develop a fundamental understanding for molecular architectures with superior low-fouling properties. For this purpose, we intended to identify design rules for protective zwitterionic polymer hydrogels. A focus was the development of polyzwitterionic polymers that contained pairs of anionic and cationic compounds which were in sum neutrally charged. In the synthetic approach, multiple sets of zwitterionic monomers and photo-crosslinkable copolymers were synthesized, while systematically varying their chemical structure. With a focus on polysulfo- and polysulfabetaine coatings, the chemical nature of the zwitterionic groups was systematically varied by altering the lengths of the spacer group between zwitterion and polymer chain, and of the spacer between the oppositely charged groups within the zwitterion, the relative orientation of the zwitterions' dipoles against the polymer chain, the density of the photoreactive groups, the chemical structure of the polymer chain, and the balance between hydrophilic and hydrophobic monomers. From the polymers, we prepared 100-200 nm thin hydrogel layers which were thoroughly characterized using several surface analytical techniques. The polymer coatings were investigated in custom developed antifouling assays against a broad range of fouling species (proteins, bacteria, diatoms, algae, barnacle larvae) in laboratory and for selected cases, also in short term field immersion tests in the ocean, and compared against positive and negative references. In most cases, the antifouling performance was strongly enhanced by the presence of the zwitterionic groups in the coatings. Though, even apparently tiny differences in the structural design caused major differences in the antifouling performance. In particular, for the dipole orientation and also for the spacer length, the effect was species dependent, rendering a generalization difficult. For the use in the ocean, the degree of swelling of the hydrogels had to be controlled in order to minimize the absorption of silt. Latter leads to a loss of the hydrophilic properties, and the silt particles act as attachment possibility for the fouling organisms. Thus, a well-designed balance between hydrophilicity, choice of zwitterionic moiety, cross linking density, and amphiphilic properties is needed.

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