Biofouling, a phenomenon characterized by the accumulation of marine organisms on submerged surfaces, has spurred extensive research into innovative solutions. This study endeavours to assess the effectiveness of phosphonium ion gels, which consist of phosphonium monomers ([P444VB][AOT] and [P888VB][AOT]), as well as free ionic liquid ([P444n][AOT] and [P888n][AOT]) at varying concentrations (ranging from 10% to 50% by weight). Additionally, it explores the impact of altering the length of alkyl chains (with values of n= 8 and 14) and varying the concentration of copper(II) oxide biocide (ranging from 0% to 2% by weight). Another factor under investigation is the role of the docusate anion [AOT] in enhancing hydrophobicity.

To evaluate the efficacy of these formulations, a seachest simulator was employed, positioned in New Zealand coastal waters and shielded from both light and tidal currents. The testing period encompassed the summer and autumn seasons. The performance of these anti-fouling formulations was subsequently correlated with the hydrophobic nature of the submerged surfaces, determined by the water contact angle, which ranged from 14° to 131°, and the concentration of the biocide.

Notably, formulations exhibiting higher levels of hydrophobicity, achieved through a reduction in free ionic liquid content and the incorporation of longer alkyl chain substituents, demonstrated superior anti-fouling performance. Intriguingly, the presence of the copper (II) biocide had an adverse effect on anti-fouling performance by increasing the surface's hydrophilicity. Importantly, no significant correlation was identified between antimicrobial activity and anti-fouling performance in this context.

In summary, this research underscores the potential of phosphonium ion gels as a promising avenue for combining anti-fouling and foul release properties, offering a multifaceted approach to addressing the persistent challenge of biofouling in marine environments.