What is PTFE porous film? Microporous PTFE membrane waterproofing mechanism? Principles of PTFE composite fabric waterproof?
A, PTFE microporous membrane of waterproof mechanism
The formation of capillary porous PTFE film, the crescent-shaped surface tension of liquid-gas interface will be attached to the capillary jet, according to La MEP equation, additional pressure P as:
P = YLG (1/p1 1/p2)
Where: YLG liquid and gas interface, surface energy or interfacial tension of liquid to gas, commonly referred to as surface tension, 200C water 0.0725N / M;
P1, P2 curved surface by two half-axial curvature.
For the cylindrical capillary pore, p = P1 = P2 is the following:
P = 2yLG / P
As: p = r / cos
Where: r-half by capillary equivalent;
θ-capillary wall and the contact angle of liquids, PTFE a value of 1180.
P out is positive, so it is:
P = 2yLGcos / r
The resultant film is microporous PTFE simplified formula for the cylindrical capillary model. Formula shows that the capillary wall and the liquid when the contact angle greater than 900 into the capillary water formed by the liquid-gas interfacial tension out of the additional pressure. Therefore, you need to make the water through the porous surface tension than that generated by the resistance force bigger. r = 1um, the calculated P is about 72.5kPa, which requires a minimum of 7.2m water column of the applied pressure to make the water through the capillary pores; that, for the hole by the 1um porous PTFE film, in theory, its resistance to pressure is not 72.5kPa. Taking into account the porous PTFE porous film is not actually a straight on the channel, but the channel in the membrane to form the network structure, so the actual test value should be greater than the theoretical calculated values.
From the above formula can be found, of PTFE porous membrane is the major factor in resistance to pressure micropore by r and the contact angle. When 900 <<1800, the greater the resistance, the higher the water pressure. PTFE porous membrane porous wall and the advancing contact angle of water in 1180, receding contact angle of 910, the contact angle of 1040 is the largest variety of materials; r smaller, the higher the resistance to water pressure. Semi-porous PTFE porous film by a very small, only a few tenths of microns. Therefore, hydrostatic pressure is high, and the hole by less than the minimum can not be directly through the rain.
In addition PTFE porous film surface energy is low, water in the PTFE porous film surface of the contact angle of about 1,200, so the poor wetting; PTFE film itself has a certain mechanical strength, under pressure Microporous broken when pushed hard, these are conducive to increased resistance to water pressure.
Hydrostatic pressure theory has nothing to do with the film thickness, in fact, the thinner film thickness, the lower mechanical strength, can cause water decreased.
The results also shows that the capillary in vertical position, the height of water surface film (PTFE microporous membranes with the thickness of the same order of magnitude) due to the effects of gravity can be ignored.
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