Diffusion Through the Water Barrier of Arthropod Cuticles: A Statistical Mechanical Approach to the Analysis of Temperature Effects

We have developed a theoretical model of water diffusion across the cuticle of terrestrial arthropods from blood to the atmosphere. Our treatment is based on the theory of absolute reaction rates and its application to the diffusion process as developed by Glasstone. Using this model, we show that the relationship between transcuticular water flux (J) and vapor pressure can be written in the form J = σ(1 - R.H.) where R.H. is the relative humidity. If the heights of the potential energy barriers within the epicuticle are approximately uniform, then we find that the permeability σ takes the form σ = A exp[-E/kT] where T is the absolute temperature and A has only a very weak temperature dependence compared to the exponential factor. We derive a simple expression for A in terms of the microscopic parameters of this model. iminary analysis of the water conducting properties of a variety of representative man-made and biological membranes, using the model, is presented.