Abstract: | Correlation between the equation of state and the temperature dependence of the self-diffusion coefficient D for polymers such as polystyrene (PS) and polydimethyl siloxane (PDMS) and simple liquids such as argon, methane and benzene and the pressure dependence of D for oligomers such as dimethyl siloxane (DMS) and simple liquids such as cyclohexane and methanol has been examined based on the equation of state derived previously. The experimental data used were published by Antonietti et al. and McCall et al. for polymers, by McCall for linear dimethylsiloxanes and by Jonas et al. and Woolf et al. for simple liquids. The expression for D in this work is given by where A1(M) is a function of molecular weight Mw, C1(T) and P1(T) are functions of temperature and B1, n1 and m1 are constants determined experimentally. For simple liquids, the values of n1 obtained range from 0.3 to 1.2, with an average
, and m1 is in the range 0.5–1.2, with
. For polymers, values of n1 are in the range 2.5–7.0 for PS and 0.5–1.3 for PDMS and m1 for DMS is in the range 0.8–1.0. The relation Dη/T = f(M) is found to be useful for simple liquids over a wide range of temperature including the critical region and for pressures up to ≈5 kbar 1 kbar = 100 MPa There is a close correlation between ln(D/T) and p and βT through ln(D/T) ln Dc? ?1p?β?1T, where Dc is D at the critical temperature and p and βT are the thermal expansion coefficient and compressibility, respectively. The molecular weight dependence of D for polymers and simple liquids is discussed based on the experimental data and recent theory of Doi and Edwards. A new model for the mechanism of self-diffusion in the liquid state is proposed. |