화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.104, No.3, 451-457, 2000
Dielectric friction and rotational diffusion of hydrogen bonding solutes
Rotational diffusion times (tau(r)) of 4-(hydroxymethyl)stilbene (HMS) have been measured as a function of temperature in seven n-alcohols from ethanol through octanol. Stokes-Einstein-Debye plots (tau(r) versus eta/T, eta = viscosity) indicate substantial friction in excess of that predicted by the Stokes-Einstein-Debye model for mechanical friction. Comparison of HMS with diphenylbutadiene (DPB), a solute of similar size and shape but without the hydroxyl group, suggests that hydrogen bonding interactions influence the HMS rotational diffusion time. Hydrogen bonding is modeled as dielectric friction using the longest solvent Debye relaxation time in the zero-frequency limiting form of the Nee-Zwanzig equation. The longest Debye relaxation time of alcohols is associated with rotational motion of solvent molecules in hydrogen bonded clusters and reflects the time scale for breaking of hydrogen bonds. The HMS results are well represented when the dielectric friction contribution is added to the DPB data. Agreement between model and data suggests that hydrogen bonding is responsible for the additive contribution of dielectric friction to the rotational diffusion time of HMS in n-alcohols.