Separating Sequence-specific from Composition Effects on Adsorption of Amphiphilic Polypeptoids at Fluid-Fluid Interfaces

Adsorption of surface-active polymers to fluid interfaces involves the formulation of stable solutions or suspensions and the subsequent equilibration of an adjacent interface. By measuring adsorption at long times as equilibrium is approached, interfacial properties are related to design properties like block structure and molecular weight. However, polydispersity and large molecular weight making it difficult to determine the impact of subtle changes along the polymer chain on interfacial properties. We avoid these difficulties by choosing four sequences of compositionally uniform, amphiphilic polypeptoids (4 kg/mol). Subtle variations in sequence possessed by these four isomers (tapered, inverse tapered, blocky and distributed) do not manifest in distinct values of surface tension or dilatational modulus at the air/solution interface when adsorbing from a selective solvent (25/75 ACN/water). When the polypeptoid solutions are rinsed out with water, a nonsolvent, while the adjacent polypeptoid-laden bubble is preserved more chains are driven to the interface, and surface pressure increases rapidly. Variation in chain sequence appears in the measurement of dilatational elasticity only after processing has driven the adsorption of additional chains to the surface.