Evaporation from polymer solution

Solution Properties. Typically, if a polymer is soluble ia a solvent, it is soluble ia all proportions. As solvent evaporates from the solution, no phase separation or precipitation occurs. The solution viscosity iacreases continually until a coherent film is formed. The film is held together by molecular entanglements and secondary bonding forces. The solubiUty of the acrylate polymers is affected by the nature of the side group. Polymers that contain short side chaias are relatively polar and are soluble ia polar solvents such as ketones, esters, or ether alcohols. As the side chaia iacreases ia length the polymers are less polar and dissolve ia relatively nonpolar solvents, such as aromatic or aUphatic hydrocarbons. 

Fig. 10. Schematic of casting machine used to make microporous membranes by watervapor imbibition. A casting solution is deposited as a thin film on a moving stainless steel belt. The film passes through a series of humid and dry chambers, where the solvent evaporates from the solution, and water vapor is absorbed from the air. This precipitates the polymer, forming a microporous membrane that is taken up on a collection roU (25).

Photoreceptors are prepared by the sequential application of the various layers onto a web or drum substrate. Vapor-deposition methods can be used for some pigments. Most layers, however, are coated from solution or dispersions in organic solvents. Wicks (1986) has reviewed film formation from polymer solutions. The choice of solvent is determined by such factors as solubility, evaporation rates, surface tension, toxicity, as well as environmental... 

These are usually prepared by casting from polymer solution followed by solvent evaporation. It results in formation of a dense membrane. Membrane may be (1) homogeneous, (2) blend, (3) mixed matrix, (4) polyelectrolyte, or (5) polymer-ceramic composite depending on the type of polymer and other additives used for making the membrane. 

It is also noteworthy, however, that the sample preparation technique also influences PU crystallization, as shown for the case of a dibenzyl PU (DBDI PEA BDO) in Fig. 2.20. The crystallinity of the materials with DBDI is more pronounced when the polymer is obtained as a sheet cast directly as a melt following synthesis (Fig. 2.20, curve 1) than when the same PU has been obtained by evaporation from 10% solution of DMF (Fig. 2.20, curve 2). The crystallinity also changes completely if the solution-cast PU film is stretched to 300% elongation and released (Fig. 2.20, curve 3). 

Soiid Matrices. Most work on synthetic polymers use the solid matrices developed for the biopol5uner analysis. To use these matrices, solutions of polymer, matrix, and cationizing salt are mixed. The solvent is then allowed to evaporate from these solutions deposited onto a sample surface. The mass proportion ratios of the matrix pol5nner salt in the final solid mixture cover the range of 5 1 2 to 2000 1 1. These proportions are often dependent on molecular mass of the polymer (1). The choice of matrix compounds for synthetic polymers with respect to the polarity of the polymer have been discussed (34). As a general rule, matrix polarity should be matched with the polarity of the polymer so that both are soluble in a common solvent. Since the MALDI sample preparation requires intimate... 

This patent deals with proton-conducting membranes having improved resistance to methanol crossover. The membranes are obtained by solution casting followed by solvent evaporation from a solution containing an organic solvent, a polymer (preferably a polyphosphazene), and an oxoacid. It is claimed that a particularly useful application for these polymeric membranes is in methanol fuel cells. 

The film forming process is very different from a solvent soluble resin and is much more difficult to control. From polymer solutions, the polymer chains are already present in a fully interpenetrated network with the molecules of solvent fully solvating the polymer species. On drying, the solvent merely evaporates, leaving the fully interpenetrated network of polymer chain as a concentrated uniform layer. 

The heated polymer solution emerges as filaments from the spinneret into a column of warm air. Instantaneous loss of solvent from the surface of the filament causes a soHd skin to form over the stiU-Hquid interior. As the filament is heated by the warm air, more solvent evaporates. More than 80% of the solvent can be removed during a brief residence time of less than 1 s in the hot air column. The air column or cabinet height is 2—8 m, depending on the extent of drying required and the extmsion speed. The air flow may be concurrent or countercurrent to the direction of fiber movement. The fiber properties are contingent on the solvent-removal rate, and precise air flow and temperature control are necessary. 

Fibers spun by this method may be isotropic or asymmetric, with dense or porous walls, depending on the dope composition. An isotropic porous membrane results from spinning solutions at the point of incipient gelation. The dope mixture comprises a polymer, a solvent, and a nonsolvent, which are spun into an evaporative column. Because of the rapid evaporation of the solvent component, the spinning dope solidifies almost immediately upon emergence from the spinneret in contact with the gas phase. The amount of time between the solution s exit from the spinneret and its entrance into the coagulation bath has been found to be a critical variable. Asymmetric fibers result from an inherently more compatible solvent/nonsolvent composition, ie, a composition containing lower nonsolvent concentrations. The nature of the exterior skin (dense or porous) of the fiber is also controlled by the dope composition. 

Phase Inversion (Solution Precipitation). Phase inversion, also known as solution precipitation or polymer precipitation, is the most important asymmetric membrane preparation method. In this process, a clear polymer solution is precipitated into two phases a soHd polymer-rich phase that forms the matrix of the membrane, and a Hquid polymer-poor phase that forms the membrane pores. If precipitation is rapid, the pore-forming Hquid droplets tend to be small and the membranes formed are markedly asymmetric. If precipitation is slow, the pore-forming Hquid droplets tend to agglomerate while the casting solution is stiU fluid, so that the final pores are relatively large and the membrane stmcture is more symmetrical. Polymer precipitation from a solution can be achieved in several ways, such as cooling, solvent evaporation, precipitation by immersion in water, or imbibition of... 

Solvent Evaporation from Solutions of Thermoplastic Polymers. A solution of a copolymer of vinyl chloride (chloroethene) [75-01-4] C2H2CI, vinyl acetate (acetic acid ethenyl ester) [108-05-4] and a hydroxy-functional vinyl monomer having a number average molecular... 

Ascher and Nemny 495) found that residues of triphenyltin acetate on glass, resulting from the evaporation of acetone solutions thereof, were, on contact to houseflies, less toxic with rising concentration. As triphenyltin acetate is likely to be a self-associated polymer in the solid state [similar to trimethyltin acetate (355)] and in concentrated solutions, it was suggested 495) that the monomer, which exists in dilute solutions, is toxic to insects, and the polymer, nontoxic. Interestingly, in this connection, a triphenyltin methacrylate copolymer has 470) a very low mammalian toxicity (acute, oral LDso for mice >2000 mg/kg). 

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