Polymer properties, liquid media

Strength, brittleness, and solvent permeability properties are limited because of lack of control of the ceramic composition on a macro- and microlevel. Even small particle sizes are large compared with the molecular level. There have been a number of attempts to produce uniform ceramic powders including the sol-gel synthesis in which processing involves a stable liquid medium, coprecipitation in which two or more ions are precipitated simultaneously. More recently, Carraher and Xu have used the thermal degradation of metal containing polymers to deposit metal atoms and oxides on a molecular level. 

The best known property of pectin is that it can gel under suitable conditions. A gel may be regarded as a system in which the polymer is in a state between fully dissolved and precipitated. In a gel system, the polymer molecules are cross-linked to form a tangled, interconnected three-dimensional network that is immersed in a liquid medium (Flory, 1953). In pectin and most other food gels, the cross-linkages in the network are not point interactions as in covalently linked synthetic polymer gels, but involve extended segments, called junction zones, from two or more pectin molecules that are stabilized by the additive effect of weak intermolecular forces. 

Latex is a dispersion of polymer particles in a liquid medium, where the particles will remain suspended indefinitely. This property means that latices are colloidal dispersions. By nature of its origin, latex is classified into natural latex for dispersions obtained from plants, and synthetic latex for dispersions that are man made, typically by a process called emulsion polymerization. Blackley discusses a number of further classifications including artificial latex for dispersions in which the polymer is dispersed after synthesis, and modified latex where a chemical modification of existing latex is made. 

The negative first normal stress difference under a medium shear rate, characterized by liquid crystalline polymers, makes the material avoid the Barus effect—a typical property of conventional polymer melt or concentrated solution, i.e., when a polymer spins out from a hole, or capillary, or slit, their diameter or thickness will be greater than the mold size. The liquid crystalline polymers with the spin expansion effect have an advantage in material processing. This phenomenon is verified by the Ericksen-Leslie theory. On the contrary, the first normal stress difference for the normal polymers is always positive. 

In facilitated transport membranes, the carriers can be dissolved in a liquid solvent or fixed to a solid polymer matrix. When the carriers are dissolved in a liquid medium, the carriers at the upstream interface react with a specific small molecule to form an adduct, which then moves across the membrane and releases the small molecule from the adduct due to a releasing reaction, as shown in Fig. 9-1 la. As such, the separation property depends on the binding and releasing reaction rates as well as the mobility of the adduct in the liquid medium. 

This explains why there is no principal difference between the raw (doped) polyaniline and its dispersions, in whatever medium. The differences to be observed were only of quantitative, and not of qualitative nature, at least not in the direction, which was expected by most of those who still favor the fibril hypothesis. They believe that the chain is the primary active unit, which could also be dissolved and is believed to have conductive properties, even as a single chain. If that were the case, a dispersed (i.e., mechanically separated, in case of assumed fibrillar morphology, even destroyed) conductive polymer would not have the same conductivity and especially not the same transport properties in the dispersion medium above the critical volume concentration or after deposition from a low molecular weight liquid medium and drying. 

The movement of material from cell wall to cell junctions is believed to occur due to perturbations of closed cell geometry from that of perfect sphere. Since the material inside the closed cells (solvent-rich material) has better wetting properties than that around the cells (polymer-rich material), these perturbations are unstable. The tendency of the system is to form larger spherical domains from the smaller solvent-rich spherical cells (as in the case of gas bubble coalescence in a liquid medium). Clearly, as a first step toward this process, closed cells would coalesce with one another the smaller cells tending to coalesce with the bigger ones. During the removal of the solvent to form the solid product, the wall thinning and rupture processes continue to occur. The extent of this second mechanism depends on how efficient is the solvent removal process. 

Fig. 40 Experimental apparatus developed by Murayama and Silverman [44] for measuring viscoelastic properties of a polymer in a liquid medium. The letter A denotes a thermoregulator B, a temperature controller C, clamps and T, transducers.

The properties of LCPs are uniquely dependent on their final physical forms and the mode of processing. Conventional polymers have been processed by the extrusion of the polymer melt into a stream of evaporating gaseous streams, also known as dry spinning, or by precipitation into liquid medium, which is referred to as wet spinning. 

The opposite results are obtained, when polymer-analogous transformation /diffusion copolymerization is accompanied by an increase of refractive index, i.e. when ri > 2 In this case, decrease of the process duration by the sample radius from the periphery to the center produces a medium with properties of a concave lens, and increase gives a medium with properties of a convex lens. In this process, the results mentioned are achieved under conditions of injection of an active medium/diffusate and an inert liquid into the reactor under different regimens. 

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