Evaluation of molecular-scale roughness at liquid interfaces

In order to better interpret molecular orientation measurements at interfaces, a method based on thermal excitation of capillary waves is proposed to evaluate the roughness of liquid interfaces at molecular scales. The method is general enough to be applied at essentially any liquid interface in either the absence or presence of a surfactant. Based on calculations using the model, the water/air interface is quite smooth at molecular scales. However, cases are discussed in which the roughness of other liquid interfaces can be considerably greater.