A micro-porous membrane Ultrathin 3-layers laminated fabric or coating can be defined as a thin-walled structure having an open spongy morphology of precisely controlled pore size, typically ranging from 0.03 μm to 10 μm in diameter. Micro-porous coatings and membranes rely on an interconnected network of tiny holes pores introduced by various means into an otherwise impermeable polymeric structure.35 Sheets of polymers can be produced with common salt incorporated which is washed out afterwards to leave voids pores. Such holes or pores are too small to allow water droplets to pass through, but are large enough to allow water vapour to pass through. Micro-porous structures work, as do tightly woven structures, because of the large difference in size between individual water molecules present in water vapour and water droplets of rain, each of the latter consisting of many millions of water molecules held tightly together by surface tension forces.
Micro-porous membranes typically weigh and should be durable and resistant to laundering, chemicals and UV degradation.Micro-porous based breathable fabrics usually have a layer of polyurethane or water fluorocarbon or silicone so as to ensure consistent performance and to prevent the pores being contaminated.The first use of a micro-porous membrane to produce a breathable fabric in the , represented a major step forward in the achievement of comfortable breathable fabrics and garments. The membrane μm in diameter) being orders of magnitude smaller than the smallest water droplet and several times larger than a water vapour molecule and able to withstand a water pressure of up to 100 psi.Pore size should preferably be below for optimum balance between waterproofness and breath-ability.
The PTFE membrane is chemically inert, smooth, UV resistant, water repellent, durable and can withstand high temperatures.The most common emulsification membranes are SPG membrane, polymeric membranes, and microsieve membranes. Nanoemulsions comprising soybean oil or MCT oil dispersed in aqueous solutions of SDS or Tween 20 can be prepared by direct ME using SPG membranes with a maximum pore size of 0.2 μm and the ratio of the median drop size to the mean pore size ranges from Due to higher ability to generate nanodrops, premix ME is more convenient process for preparation of nanoemulsions than direct process.
The median drop size can be reduced by decreasing the pore size and increasing the number of extrusion cycles and transmembrane pressure. Track-etched polycarbonate membranes are less efficient in reducing the drop size in premix ME than SPG membranes, due to their rectilinear pores and smaller thickness as compared to SPG membrane . One extrusion of premix through SPG membrane with a pore size of 100–300 nm led to smaller drops than 11 or 21 extrusion cycles through tracked-etched PC membranes with the same pore size. The median drop size in premix ME using polymeric membrane primarily depended on the contact angle between the continuous aqueous phase and the membrane surface. The contact angle between the surfactant solution and the membrane surface must be < 49° to create nanoemulsions with a d50 value smaller than 500 nm after 21 extrusion cycles at the flow rate of through a polymeric membrane filter.
