Temperature-induced phase separation TIPS

Phase inversion is a process in which a polymer is transformed from a liquid to a solid state. There are a number of methods to achieve phase inversion. Among others, the dry-wet phase inversion technique and the temperature induced phase separation (TIPS) are most commonly used in the industrial membrane manufacturing. The dry-wet phase inversion technique was applied by Loeb and Sourirajan in their development... 

Solvent selection was also proven to affect the resulting structure in temperature-induced phase separation (TIPS) (Lloyd et al. 1990 Gu et al. 2006 Lu and Li 2009). Diluents such as phthalates promote the formation of irregular fuzzy structures (Lloyd et al. 1990). PVDF membranes prepared from dimethyl phthalate (DMP) as a solvent showed larger spherulite structures compared to that of membranes prepared from DBP, or mixtures of DMP with dioctyl sebacate and dioctyl adipate. It can be ascribed from these differences that the degree of polymer-solvents interactions influences the extent of PVDF crystallization (Lloyd et al. 1990 Gu et al. 2006). Using different types of solvents, the crystallization temperature of PVDF during TIPS can also be changed. A more complex mechanism is indeed expected for a combined solvent system. For instance, in the PVDF/DMAc/TEP system, TEP (weaker solvent) acts as a latent solvent in the immersion precipitation process (Liu et al. 2012). 

Another scaffold fabrication technique is thermally induced phase separation (TIPS) [34,46,84,147-149]. TIPS involves decreasing the temperature of a polymer solution to obtain a polymer-rich and polymer-poor phase. Following phase separation, the solvent is removed using one of a number of methods (freeze drying, evaporation) resulting in the formation of pores in the polymer stracture. TIPS can also be combined with the use of porogens to increase void fraction, have better control over pore size, or improve pore interconnectivity. 

Thermally induced phase separation (TIPS) an increased reaction temperature, or a high concentration, produces a high-connectivity phase structure so that the polymerization surpasses the phase separation using a low-temperature stage, a moderate decrease in phase separation is observed at a lower nucleation temperature (Kim et al. 2016 Padilla et al. 2011 Stieger etal.2003). 

Liquid crystal and polymer dispersions are fabricated using thermally-induced phase separation (TIPS), solvent-induced phase separation (SIPS), or Polymerization-induced phase separation (PIPSX/I)- For TIPS, a homogeneous mixture of a low-molecular weight liquid crystal and thermoplastic polymer is cooled below the critical phase separation temperature to induce phase separation into liquid crystal rich and polymer rich domains. The morphological properties (domain size, number of domains per unit volume, and the composition of the domains) depend primarily on the choice of liquid crystal and thermoplastic polymer, the initial weight fraction of liquid crystal in die initial mixture, and the rate of cooling. 

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... 

Thermally induced phase separation (TIPS) is used to create symmetric membranes and involves the cooling of a homogeneous polymer solution until it reaches a set temperature, at which point it will separate into two phases. 

Thermally Induced Phase Separation In the TIPS process, an initially homogeneous solution consisting of a polymer and solvent(s) phase separates due to a decrease in the solvent quality when the temperature of the casting solution is decreased. After demixing is induced, the solvent is removed by extraction, evaporation, or freeze drying. 

Asymmetric membrane structures have been created from these materials using the diffusion induced phase separation process (DIPS) as well as a thermally induced phase separation process (TIPS) [23] that relies on temperature gradients to produce a gradient in phase separated domain size. Moreover, membranes formed by either process can be further modified by stretching or drawing to alter pore size and porosity. 

Among these various phase separation techniques, pressure-induced phase separation is particularly important since pressure changes can be brought about uniformly and very fast throughout the bulk of a solution. This would not be so in other techniques due to for example heat (in TIPS) and mass transfer (in SIPS) limitations. The technique therefore opens up new opportunities for formation of microstructured materials with potentially more uniform morphologies. It is also important to recognize temperature, solvent, reaction, or field-induced phase separation may all be carried out at elevated pressures if so desired, as such all modes of phase separation methods are of interest when working with near-critical or supercritical fluid systems. 

Recently it has been shown that surface-induced molecular orientation can be determined by atomic force microscopy (AFM), both in the isotropic and nematic phase of thermotropic liquid crystals [6-10]. At separations of several nanometers between the homeotropically modified glass surface and the AFM tip or homeotropically modified glass microsphere, respectively, a temperature-dependent short-range attractive (prenematic) or on average repulsive, but oscillatory, (presmectic) force was observed [6,7,9]. 

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