This dissertation is dedicated to the study of a nano-porous membrane used in pressure-driven composite processes as a surface barrier layer for non-wetting fluids. The membrane allows continuous venting of the surface and reduces overall void content. An overall methodology for membrane selection is developed that relates constituent properties of the membrane and the resins.

First, we investigate the transport of non-wetting fluids into a straight pore to capture the mechanisms at stake in the membrane. It combines capillary and viscous effects and shows that the key to the membrane's success is the balance between pressure applied and the capillary pressure exerted by the pores.

Because the membrane is made of fibrils, its microstructure adds more complexity to the single sized straight pore approximation and a more detailed characterization of the membrane's pores is required. Based on porometry data, statistical means were coupled with transport models to obtain the pore size distribution of any membrane. In parallel, we also characterize the fluids of interest (water and the Cycom 977-20 epoxy resin system). The interactions between membrane and fluids are investigated too by evaluation of the contact angle.

The transport mechanisms of the membranes are then described in terms of permeability, which has a unique pressure dependent behavior. At low pressures, the permeability is several orders of magnitude smaller than a typical carbon fabric. Then, it becomes highly sensitive to slight changes in external pressure. Eventually, at higher pressures, the permeability reaches a steady-state level. A parametric study is conducted to reveal the sensitivity of membrane permeability to surface tension, contact angle and pore size distribution. The pressure capability of a given membrane/resin system was established by recognizing that membrane must limit flow up to the point of resin gelation. To validate this approach, unique experiments are conducted and found to be in good agreement with the predictions.

Exploratory experiments are conducted on the effects of stretching that occurs during processing of complex geometries. Uniaxial stretching experiments show that strain mismatch between the support and the membrane induces biaxial tension loading of the membrane. The pore size distribution shifts to larger pores which reduces the pressure capability of the membrane.