Solvent-induced phase separation

It is difficult to mix liquid crystals directly with polymers because polymers are usually in solid state at room temperature. A solvent can be added to mix hquid crystals with polymers. We now 

A ternary mixture is specified by the three fractions, xa, xb, and xc, of the three components 

correspond to the three components. For a composite represented by a point P in the triangle, the fraction of a component is equal to the length of the line drawn from P to the side opposite to the comer representing the component, which is parallel to one of the sides from the corner. The fraction of A is PQ = xa, the fraction of B is PR = Xb, and the fraction of C is PS = Xc- It can be shown from geometry that xa + xb + xc=1. The equilateral triangle diagram has the following properties  

All the points on a line drawn from one comer of the triangle to the opposite side represent the composites in which the relative fractions of the two components represented by the other two comers remain unchanged. 

When a mixture represented by point P phase separates into two phases represented by points U and V, the three points, P, U, and V, lie on a straight line, and point P is between points U and V. The percentages of the material in the phases U and V are equal to PUlUV and PV/UV, respectively. 

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In the course of solvent induced phase separation periodic structures can be detected only when tc exceeds tp,tc — tp > 0. 

Figure 1. Schematic plots of polymer/polymer/solvent phase diagrams for (a) two miscible polymers plus a solvent Inducing phase separation, (b) two immiscible polymers. The lines AB and CD show evaporation pathways.

Cellulose and PAN or PA Phase separated morphology Solvent induced phase separation Roeder et al., 1993... 

Removal of the solvent through freeze-drying or extraction can produce porous polymer scaffolds. Phase separation can be induced by changing the temperature or by adding non-solvent to the polymer solution. These are known as thermally induced and non-solvent-induced phase separation, respectively. The scaffolds obtained by... 

Figure 1. Schematic representation of the influence of various factors on the miscibility and phase separation. The shaded areas represent the two-phase regions. The arrows show the paths for phase separation, while the reverse directions would be the paths for miscibility. From left-to-right Temperature-induced phase separation solvent-induced phase separation reaction (i.e. polymerization) -induced phase separation (the two-phase regions are entered with increasing degree of polymerization (DP)) and pressure-induced phase separation. < ) = polymer concentration, S2 and SI solvent and nonsolvent PI andP2 = polymer 1 and polymer 2.

TCA removal was also studied using SBS asymmetric membranes prepared by non-solvent induced phase separation (NIPS), as reported in the US patent by Sikdar et al. (2008). In this work, the temperature and vacuum pressure were varied while the feed concentration ( 120 ppm) was kept constant. TCA, water and total flux increased with increasing the temperature (from 10°C to 35°C) at the constant pressure of 0.05 bar. At a permeate pressure of 0.05 bar and temperature of 34°C, TCA flux was about 0.018 kg m i. Separation factor ((Ztca/Hjo) increased from 900 to 4600 at higher temperature (from 10°C to 35°C) and from 640 to 2300 changing the permeate pressure from 0.01 to 0.05 bar. 

The phase-separation method was developed at Kent State University in the late 1980s. It consists of in sitn segregation of liqnid crystalline microdroplets from a homogeneous mixture of liquid crystal and polymer/prepolymer, indnced by a factor that gave the techniqne its name, as follows (a) polymerization-induced phase separation (PIPS) (b) solvent-induced phase separation (SIPS) and (c) thermally induced phase separation (TIPS). 

Solvent-induced phase separation occurs when both liquid crystal and polymer are combined in a homogeneous solution the liquid crystal grows (as microdroplets) as the solvent evaporates. In such a segregation mechanism, the rate... 

Chen Lu Guang, and Shanks Robert. Thermoplastic polymer-dispersed liquid crystals prepared from solvent induced phase separation with predictions using solubility parameters. Liq. Cryst. 34 no. 12 (2007) 1349-1356. 

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. 

HEL Hellmann, E.H., Hellmann, G.P., and Rennie, A.R., Solvent-induced phase separation in polycarbonate blends PC/TMPC, Colloid Polym. Sci., 269, 343, 1991. 

Malik MK, Bhatia PG, Eteshmukh RR (2012) Effect of nematic liquid crystals on optical properties of solvent induced phase separated PDLC ctunposite films. Ind J Sci Technol 5 3440-3452... 

Binary mixtures of a flexible polymer and a rigid rod-like molecule (nematogen or liquid crystal) play an important role in electro-optical devices, such as light shutters and displays. Since the miscibility or phase separation controls the performance of the materials, the phase behavior and phase separation kinetics have been of fundamental and practical interests. Liquid crystalline domains dispersed in a polymer matrix are called polymer dispersed-liquid crystals (PDLCs), or polymer-stabilized liquid crystals (PSLCs), where the polymer forces the liquid crystals to phase separate into droplets surrounding by the polymer matrix [2]. Practically, there are many ways to create PD LCs by mixing polymers and liquid crystals the emulsion method [37] and phase separation method [38], including polymerization-, thermally-, and solvent-induced phase separations. The reader is referred to text books [1, 2] for details of PDLC and a review [39] for the rheological and mechanical properties. 

S. BonyadL T.S. Chung, W.B. Krantz, Investigation of corrugation phenomenon in the inner contour of hoUow fibers during the non-solvent induced phase-separation process. Journal of Membrane Science, 299 (2007) 200-210. 

Non-solvent induced phase separation (NIPS), or diffusion-induced phase separation, involves dissolution of the polymer in a good solvent in order to obtain a homogeneous solution, followed by the addition of a non-solvent miscible with the first solvent. This will cause precipitation of the polymer when the non-solvent concentration becomes significant. 

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