Abstract Sum frequency generation (SFG) vibrational spectroscopy has been used to characterize the interfacial structure of a series of model peptides at the hydrophobic polystyrene-buffer interface. The peptides contain two types of amino acids, one hydrophobic (X) and one hydrophilic (Y). Their sequences are Ac-XYYXXYXXYYXXYX-NH 2 (XY 14) and Ac-XYXYXYX-NH 2 (XY 7), respectively, where the X and Y combinations are: ...