Phase separation polymer-solvent

Wet process Phase separation Polymer + solvent Polymer + solvent -H filler Isotropic film Large pore size High porosity PE PE Asahi, Tonen Asahi... 

The most popular way to synthesize microgel particles is via emulsion polymerization. Each micelle acts as a separate microreactor, preventing macrogelation during the reaction. Another way to obtain microgel particles is the irradiation of phase-separated polymer solutions (Fig. 5). Phase separation can be achieved by heating (for temperature-sensitive polymers) or mixing with non-solvents. 

In the case of polystyrene blends with poly(vinyl methyl ether) two phase behaviour was found for blends from various chlorinated solvents whereas single phase behaviour was found for blends from toluene The phase separation of mixtures of these polymers in various solvents has been studied and the interaction parameters of the two polymers with the solvents measured by inverse gas chromatography It was found that those solvents which induced phase separation were those for which a large difference existed between the two separate polymer-solvent interaction parameters. This has been called the A% effect (where A% = X 2 Xi 3)-A two phase region exists within the polymer/polymer/solvent three component phase diagram as shown in Fig. 2. When a dilute solution at composition A is evaporated, phase separation takes place at B and when the system leaves the two phase region, at overall... 

Phase separated polymer mixtures are important in many practical applications, such as confectionery and low-fat foods. Values of the fraction (x) of a component can be replaced by those of the fraction of solvent (Sx) associated with polymer (Morris, 1998) so that Figure 6-22 may be used also to understand the role of solvent partitioning. A key assumption is that there is complete separation of the two polymers in to their respective phases, so that the relative phase volumes (hence, the polymer concentration in each phase) may be characterized by the p-factor, defined as ... 

Chapter 9 describes the technique of separating polymer-solvent mixtures by adding an SCF additive to the mixture. Chapter 7 notes that the fundamentals of polymer-solution phase-splitting are identical to the fundamentals of propane deasphalting, a process developed more than fifty years ago. 

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.

B. J. P. Jansen, H. E. H. Meijer, andP. J. Lemstra. Processing of (in)tractable polymers using reactive solvents. Part 5 Morphology control during phase separation. Polymer, 40(ll) 2917-2927, May 1999. 

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. 

Similar materials could be obtained by an emulsification method [253]. Nematic liquid crystal is emulsified into an aqueous dispersion of a water-insoluble polymer colloid (i.e., latex paint). An emulsion is formed which contains a droplet with a diameter of a few microns. This paint emulsion is then coated onto a conductive substrate and allowed to dry. The polymer film forms around the nematic droplets. To prepare an electrooptical cell a second electrode is laminated to the PDLC film [253]. In the phase separation and solvent-casting methods the chloroform solutions of liquid crystal and polymer are also used [254, 255]. The solution is mixed with the glass spheres of the required diameter to maintain the desired gap thickness and pipetted onto a hot (140 °C) ITO-coated glass substrate [255]. After the chloroform has completely evaporated another ITO-coated glass cover is pressed onto the mixture and then it is cooled down. Structural characteristics of the PDLC films are controlled by the type of liquid crystal and polymer used, the concentration of solution, the casting solvent, the rate of solvent evaporation, perparation temperature, etc. [254]. 

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. 

The ternary model was established to investigate the effects of a solvent in polymer blends during phase separation. In cases of constant solvent concentration it emerged that, the less solvent that was in solution, the slower was the evolution of the morphology in phase separation. This effect was due to the polymers being immiscible with each other, but both being miscible with the solvent. The addition of a solvent decreased the free energy level in the blend, which in turn slowed down the evolution of phase separation. The mechanism of phase separation with solvent evaporation was further complicated by dynamic solvent evaporation from the ternary system. 

It is important to stress that in spite of the nonselectivity of the solvent, in ordered mesophases, inhomogeneities in A (B) composition are also accompanied by solvent concentration fluctuations. As for the interfaces in phase-separated polymer A - polymer B - solvent systems, this effect is due to the preferential location of solvent at the interfaces between microdomains the solvent screens out unfavorable A-B contacts. Fredrickson and Leibler have shown that solvent inhomogeneities lead to a negligible contribution to the free energy only for very long chains (when < < 1). Also, contrary to the pure... 

The presence of solvent gives the two phase separating polymers an additional means to lower the interface tension between their phase regions, that is, by the accumulation of solvent at the interface. This solvent, though, is extracted from the bulk of the phases. The area far (>D 10 nm) from... 

Gel permeation chromatography, exclusion chromatography. gel filtration chromatography. A technique for separating the components of a mixture according to molecular volume differences. A porous solid phase (a polymer, molecular sieve) is used which can physically entrap small molecules in the pores whilst large molecules pass down the column more rapidly. A solvent pressure up to 1000 psi may be used. 

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