According to Fick's law of diffusion, paicle flux is inversely propoional to the thickness of the membrane and directly propoional to the area of the membrane, the concentration difference across the membrane, and the diffusion coefficient. The diffusion coefficient depends on the physical propeies of the paicle and the membrane through which it is diffusing. In general, the larger the diameter of the paicle, the slower the rate of diffusion. Increasing temperature will increase the rate of diffusion. Ref: Katzung B.G. (2012). Chapter 1. Introduction. In B.G. Katzung, S.B. Masters, A.J. Trevor (Eds), Basic & Clinical Pharmacology, 12e.