Liquid polymer solutions

Precipitation of the cast liquid polymer solution to form the anisotropic membrane can be achieved in several ways, as summarized in Table 3.1. Precipitation by immersion in a bath of water was the technique discovered by Loeb and Souri-rajan, but precipitation can also be caused by absorption of water from a humid atmosphere. A third method is to cast the film as a hot solution. As the cast film cools, a point is reached at which precipitation occurs to form a microporous structure this method is called thermal gelation. Finally, evaporation of one of the solvents in the casting solution can be used to cause precipitation. In this technique the casting solution consists of a polymer dissolved in a mixture of a volatile good solvent and a less volatile nonsolvent (typically water or alcohol). When a film of the solution is cast and allowed to evaporate, the volatile good solvent evaporates first, the film then becomes enriched in the nonvolatile nonsolvent, and finally precipitates. Many combinations of these processes have also been developed. For example, a cast film placed in a humid atmosphere can precipitate partly because of water vapor absorption but also because of evaporation of one of the more volatile components. 

The Flory equation of state does not reduce to the ideal gas equation of state at zero pressure and infinite volume. Flory and his coworkers derived the equation of state specifically for liquid polymer solutions and were not concerned with the performance of the equation in the vapor phase. Poor vapor phase performance of an equation of state causes considerable difficulty, however, when one tries to apply the equation to higher pressure, higher temperature situations. The Chen et al. equation of state was developed in order to remedy this deficiency of the Flory equation of state. 

Dipcoating. A liquid polymer (solution) is introduced into the monolith channels by dipcoating, and converted into carbon by heating in an inert atmosphere. 

Viscosity Measurement for Liquid Polymers, Solutions, and Dispersions... 

Rheology is the science of describing the flow of liquids. Polymer solutions often follow complex, non-Newtonian... 

Asphaltenes in crude oil are large, bulky molecules which behave like polymer molecules. Thus, liquid-liquid polymer solution theories are used to... 

Gelation TransformatiOTi of a liquid polymer solution or colloidal suspension (a sol) to a solid impregnated with liquid, by continuous formation of an open and porous three-dimensional polymer, uniformly throughout the entire solvent, without any formation of a precipitate... 

Many product specifications call for the use of a rotational viscometer, a simple device that measures the resistance to turning a cylindrical metal spindle dipped in the liquid polymer solution being tested. The higher the viscosity, the greater the resistance. Although this measurement is simple in principle, great care must be taken not to misuse or misinterpret the results. 

Simple liquids such as solvents have the same viscosity no matter how fast they are stirred (Barnes, 2000). These are Newtonian liquids. Polymer solutions differ from simple liquids in the way they react to stirring (Wicks et al., 2007). Polymer molecules impart a structure to the liquid. The structure is disturbed while the solution is stirred vigorously. There are a number of different behaviours on stirring. Viscosity can reduce on stirring (shear thinning) as the molecules line up in the direction of flow, so reducing the viscosity... 

After the cross-linking process is started, it cannot be cancelled or stopped it is controlled only by the initial process conditions. Photopolymerization is the conversion of a liquid polymer solution to gel under the action of photosensitizing additives and light [10] and is the most ideal method for synthesis of cross-linked hydrogels intended for use in medical practice since it allows for the reaction to be carried out with almost 100% efficiency. 

Weissenberg effect A phenomenon that occurs when a spinning rod is placed into a liquid polymer solution. Molecular entanglements within the polymer cause the polymer chains to be drawn towards the rod and appear to climb up the rod instead ofbeing throvm... 

The precipitation of liquid polymer solution to form a solid membrane can be... 

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