An acoustic continuum model of molecular friction in simple dense fluids

An acoustic model is presented with the aim of calculating an upper bound for the molecular friction constant. Problems arising from the use of macroscopic boundary conditions at molecular surfaces are circumvented by treating the molecule in a continuum as a distributed force centre modifying the propagation of acoustic waves. The computed friction constant is a factor of two larger than experiment. Physical arguments are given for the validity of the relation. with ζ0 and ζ defined by equations (1) and (14). Other acoustic models are briefly discussed.