Reducing Biofouling with Polymer Brushes

Biofouling in the Marine Environment

A multitude of industries operate in or near the marine environment. They all suffer consequences from the phenomenon of biofouling. Biofouling results from the immense settlement pressure of benthic organisms, which requires a solid substrate for reproduction and proliferation, as well as biofilm-forming microorganisms, such as bacteria and diatoms, which rapidly inhabit the solid-water interface [1], see Figure 1. For the shipping industry, invertebrate macro-fouling, such as barnacles, has great impact on hull drag, leading to increased fuel consumption and cost. For example, it is estimated that fuel consumption has to be increased up to 40 % for a heavily fouled hull, in order to maintain speed [2]. Further, power plants that rely on seawater-based cooling systems suffer from pipe clogging due to macro-fouling, which shortens maintenance intervals, and in severe cases, causes extended plant-shutdown periods. Aquaculture and fishing suffer from the growth of fouling on nets, which increases the need for maintenance periods and thus shortens operation time. Biofouling is ubiquitous in the marine environment, and with an estimated annual cost exceeding 60 billion USD for the shipping industry alone, has great economical as well as environmental significance.

Past and Emerging Biofouling Remedies

The use of biocides have been a successful approach to regulate fouling, and in particular tributyltin (TBT)-containing paint formulations, developed in the 1970s, were so effective at reducing fouling that no further paint development was considered necessary. However, the unspecific toxicity of TBT led to a worldwide ban on the use of these compounds in 2008 [3], which spurred research into alternative and environmentally benign biofouling solutions. Current approaches include non-biocidal and copper-containing, self-polishing paints, fouling-release coatings, and amphiphilic materials. Self-polishing paints have a slow hydrolysis rate upon water immersion, continuously regenerating the interface during their lifetime. Fouling-release coatings consist of low-modulus materials, such as poly (dimethylsiloxane) (PDMS), from which fouling can be removed upon an applied shear stress. Amphiphilic materials are co-polymers having side-chains of an immiscible nature, forming a nano-structured interface, which appears to further increase fouling-release performance combined with a non-fouling action. Apart from these industrially available strategies, research is moving towards non-fouling materials, typically consisting of surface-tethered polymers, where fouling can be inhibited in a passive manner [4, 5]. A common theme amongst these materials is that they are hydrophilic, having a strongly adhered water film that forms a kinetic barrier to fouling. They also resist fouling by steric repulsion from excluded volume effects upon compression. However, more insight is required to further understand the fouling-resistant action of these promising materials, as well as finding mechanically and chemically stable formulations that are effective towards the plethora of fouling organisms in the marine environment.