Tuning the Behaviors of Polymeric Surfactants at Liquid-Liquid Interfaces via Amino Acid Conjugation

Receptor-mediated interactions at liquid-liquid interfaces offer a powerful strategy for detection of trace contaminants. To enable selective sensing, these methods leverage polymeric surfactants to transduce molecular recognitions into measurable changes in interfacial tension (IFT). Therefore, establishing the structure-property relationships of polymeric surfactants under relevant conditions is crucial for advancing practical implementations. To this end, we test the hypothesis that surface-activity of polymeric surfactants is governed primarily by the chemistry of the hydrophilic block. Specifically, we investigate the colloidal properties and interfacial properties of two amphiphilic diblock copolymers (BCPs), poly(styrene)-block-poly(acrylic acid) (PS-b-PAA) and poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP), under different aqueous conditions. We demonstrate that postpolymerization modification of PS-b-PAA with amino acids with varying hydrophilic properties strongly influences the IFT. Our results indicate that the addition of hydrophilic and ionic amino acids leads to larger reduction of interfacial tension and reduction in aggregation but also increases sensitivity to varying pH values and nonspecific interactions with dissolved ions in complex matrices, such as synthetic groundwater (SGW). In contrast, addition of hydrophobic amino acids leads to stable IFT values, indicative of higher tolerance to the presence of dissolved ions. We anticipate that these findings will advance further design of polymeric surfactants for selective interfacial sensing and enable the development of robust sensors for environmental monitoring.