Nature has optimised polymeric surfactants by selecting precise distributions of hydrophilic and hydrophobic amino acids to build amphiphilic proteins. Protein surfactants are employed in areas including the construction of ultra-stable foam nests, and facilitating the growth of filamentous fungi through high surface tension interfaces. Meanwhile, the most common synthetic polymeric surfactants have block copolymer architecture, such as the ubiquitous Pluronics that are widely used as emulsifiers, stabilizers and dispersants. Such hydrocarbon-based polymeric surfactants are typically unable to match the surface activity of silicone and fluorocarbon surfactants, materials that are environmentally-persistent and have been termed “forever chemicals”. These surfactants outperform hydrocarbon surfactants in a broad range of applications based on non-aqueous formulations, including firefighting, polyurethane synthesis, and hand sanitizers.<br/><br/>We report here that by selecting optimal combinations of hydrophobic and hydrophilic monomers, hydrocarbon surfactants with a statistical distribution of comonomers can outperform their diblock copolymer analogues. These statistical copolymers are prepared by simple one-step free radical polymerization from commercial monomers. A series of predominantly (meth)acrylic-based copolymers were screened for foam stabilization in aqueous ethanol solutions, to identify optimal surface activity in typical hand sanitiser formulations. Statistical copolymers comprising branched hydrophobic monomers and hydrophilic poly(ethylene glycol) pendant groups demonstrated the highest foamability performance. Furthermore, surface tensiometry showed that the statistical copolymers reduce the surface tension of ethanol-water mixtures at much lower concentrations than the analogous block copolymers. Small-angle X-ray scattering analysis revealed that statistical copolymers exist as unimicellar aggregates, suggesting a conformation transition occurs at the interface that resembles behaviour of naturally-occurring amphiphilic proteins.

Hydrocarbon-based statistical copolymer surfactants that outperform block copolymer analogues in ethanol-water foam stabilisation

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