Steady-State Diffusion in Complex Amphiphilic Films

The relation between structure and diffusive transport at steady-state
is investigated theoretically for amphiphilic systems. Amphiphilic
systems typically show a large response to moderate changes in control
parameters, such as temperature, osmotic pressure, and the presence of
cosolvents and cosolutes. Such systems is therefore expected to show a
local response in structure due to the transport process. The structure
of the system is analysed in terms of a local equilibrium description.
The main focus is on systems with the propensity of undergoing an
internal phase separation. In this case there is a particularly strong
coupling between the diffusion process(es) and the local structure of
the system, which can lead to non-linear behaviour.

Specific applications include diffusive transport through the outermost
layer of human skin, the stratum corneum, where the possibility of a
phase change of the stratum corneum lipids could explain experimental
observations of a non-linear behaviour of the water transport. A model
for the formation of a gradient in pH over the stratum corneum is also
presented in terms of the diffusive transport of water and carbon
dioxide. Another application is film formation at the air-liquid
interface of surfactant-water systems undergoing evaporation. A study
showing that the structure of the surfactant layer lining the alveoli is
functionally beneficial for the diffusive transport of oxygen is also
presented.