Directional thermally induced phase separation

Hydrophilic MF membranes can be made by the dry-wet phase inversion technique, which can also be used to make PVDF membranes. On the other hand, other hydrophobic microflltration membranes are made by the thermally induced phase separation technique. In particular, semicrystalline PE, PP, and PTFE are stretched parallel to the direction of film extrusion so that the crystalline regions are aligned in the direction of stretch, while the noncrystalline region is ruptured, forming long and narrow pores. Hydrophobic membranes do not allow penetration of water into the pore until the transmembrane pressure drop reaches a threshold called the liquid entry pressure of water (LEPw). These membranes can therefore be used for membrane distillation. The track-etching method is applied to make microfiltration membranes from PC. 

Thermally-induced phase separation (TIPS) has been shown to be an excellent way to make microporous polymeric membranes. Microporous membranes are generally prepared by TIPS process, which is based on the phenomenon that the solvent quality decreases when the temperature is decreased. On removing the thermal energy by cooling or quenching, a polymer-diluent solution phase separation occurs. After the phase separation, the diluent is removed, typically by solvent extraction, and the extractant is evaporated to yield a microporous structure. Typically, the TIPS process has been used to produce isotropic structures that is, the pore size does not vary with direction in the membrane. A few studies have been reported on the formation of... 

In the atmospheric gas phase the main reactive species are OH, N03, 03, and sunlight itself which can be involved in direct photolysis processes. In the latter case a sunlight-absorbing molecule reaches an electronically and vibra-tionally excited state after absorption of a photon of appropriate wavelength. The surplus energy can be dissipated by vibrational relaxation (i.e., thermally lost), fluorescence, phosphorescence, or chemical reactivity. The latter is often in the form of bond breaking (photolysis), induced by the excess of vibrational energy that can sometimes increase vibration amplitude beyond the threshold where the atoms involved in the bond (B and C in Equation 17.1) are permanently separated [7]. 

It has been well known for a couple of decades that noncrystalline metallic alloys can be made by vapour- and melt-quenching. Recent results show that an amorphous phase can also be formed directly when a crystalline metallic alloy is subjected to various types of disordering processes. Solid-state amorphization can be induced through a variety of methods including absorption of atomic hydrogen, thermal interdiffusion reaction along the interface separating... 

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