Translational and rotational diffusion in supercooled orthoterphenyl close to the glass transition

Abstract

Self diffusion coefficients in supercooled orthoterphenyl (OTP) have been determined down to Dt=3·10-14 m2s-1 using a1H-NMR technique applying static field gradients up to 53 T m-1 In a range of more than two decades the Dt values agree with those of photochromic tracer molecules of the same size determined by forced Rayleigh scattering down to the glass transition temperature Tg. A change of mechanism is found for translational diffusion at Tc≈1.2 Tg where Dt is proportional to the inverse shear viscosity η-1 at T>Tc but Dt ∼ηξ with ξ=0.75 at T