(543i) Stranding Amphiphilic Polypeptoids at the Air/Solution Interface with Interfacial Processing

The study of the adsorption of surface-active polymers to fluid interfaces often 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 like surface coverage and elasticity can be related to design properties like block structure and molecular weight. However, the portrait of an equilibrium interface can be distorted by polydispersity which smears adsorption dynamics and large molecular weight which stalls chain reorientation at the interface, making it difficult to determine the impact of subtle changes along the polymer chain on interfacial properties. We have bypassed these difficulties by choosing four sequences of compositionally uniform, amphiphilic polypeptoids (molecular weight ≈ 4000 g/mol). The subtle variations in sequence possessed by these four isomers (so-called 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 acetonitrile/water by volume). In fact, no adsorption is seen from a better solvent (50/50), and adsorption from the selective solvent is only modest. 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 of the bubble.