Polymeric materials glassy

In this review we will focus on recent atomistic modeling of gas transport through polymeric materials, glassy solids as well as rubbery liquids, described in atomistic detail. We aim to reveal the probable mechanism of gas moUlity and diffusion in polymers as brought forth through the combined use of Molecular Dynamics (MD) and a Transition-State Approach (TSA). 

Fig. 19. Generalized modulus—temperature curves for polymeric materials showing the high modulus glassy state, glass-transition regions for cured and uncured polymers, plateau regions for cross-linked polymers, and the dropoff in modulus for a linear polymer.

Three factors affect the essential nature of a polymeric material and determine whether it is glassy, rubbery, or fibre-forming under a given set of conditions. These are ... 

The relative magnitudes of these two moduli, Gj and G2, vary according to the state of the polymeric material. In the glassy state, where good elasticity is shown, Gj is high in the rubbery state, where there is a greater contribution from the viscous element, G is low. 

MA Samus, G Rossi. Methanol absorption in ethylene-vinyl alcohol copolymers Relation between solvent diffusion and changes in glass transition temperature in glassy polymeric materials. Macromolecules 29 2275-2288, 1996. 

By the sol-gel-process, inorganic glassy and hybrid polymeric materials are accessible at comparatively low temperatures [1], Therefore, organic molecules or dyes can easily be incorporated into the oxide matrix. This combination is especially attractive for the development of the following devices optical filters, solid-state lasers, optical switches, nonlinear optical laser hosts, optical data storage media, and photoconductive devices and films [2]. 

The group of ion-selective electrodes with fixed ion-exchange sites includes systems with various membrane structures. The membranes are either homogeneous (single crystals, pressed pellets, sintered materials) or heterogeneous, set in an inactive skeleton of various polymeric materials. Important electrode materials include silver halides, silver and divalent metal chalcogenides, lanthanum trifluoride and various glassy materials. Here, the latter will be surveyed only briefly, for the sake of completeness. 

Apicella, A., Nicolais, L., Mikols, J. K., Seferis, J. J. Sorption mechanisms in glassy thermosets in Interrelations between processing structure and properties of polymeric materials , J. C. Seferis and P. S. Theocaris (Eds.), Elsevier 1984... 

Thus, the possibility to regulate effectively the orientation of polymer side groups by varying the parameters of the electric field, together with the possibility to fix the oriented structure in a glassy state enables the use of such LC systems for making polymeric materials with required optical properties. 

Based on their thermal properties, polymeric and glassy molecular PR materials can be classified as high-7 and low-7), materials. The Tg values of polymer composites can be lowered by doping small molecules as plasticizer. Introduction of a long alkyl side chain can effectively reduce the Tg of fully functionalized polymers. The glassy molecular materials usually possess low Tg if they are amorphous. For the high-7 and low-7), materials, the figures of merit of the NLO chromophores are defined by Eqs. (35) and (40), respectively. The latter are obviously enhanced by contributions from the polarizability anisotropy of the NLO chromophore. 

The density or its reciprocal, the specific volume, is a commonly used property for polymeric materials. The specific volume is often plotted as a function of pressure and temperature in what is known as a pvT diagram. A typical pvT diagram for an unfilled and filled amorphous polymer is shown, using polycarbonate as an example, in Figs. 2.10 and 2.11 The two slopes in the curves represent the specific volume of the melt and of the glassy amorphous polycarbonate, separated by the glass transition temperature. 

Figure 2. Schematisation of amorphous polymeric material. Macromolecules are coupled with weak van der Waals forces. At T > Tg, the system is in a fluid state, and the thermal motion makes the macromolecules move besides each other. At T < Tg, the system is in a glassy state, large-scale conformations of the chains are frozen, and a macromolecule can change its neighbours at the deformation of the material only.

Haward RN, "The Nature of the Glassy State in Polymers", in Ledwith A and North AN (Eds), "Molecular behaviour and development of polymeric materials, pp 404—459, Chapman and Hill, London, 1975. 

Einhorn IN, "Fire Retardance of Polymeric Materials", J Macromol Sd, Revs Polymer Technol D1 (2) (1971) 113-184. Haward RN (Ed), "The Physics of Glassy Polymers", Applied Science Publishers, London 1973. 

Thermosets are polymeric materials which when heated form permanent network structures via the formation of intermolecular crosslinks. Whether the final product has a glass transition temperature, Tg, above or below room temperature, and therefore normally exists as an elastomer or a glass, it is, strictly speaking, a thermo-set. In practice, however, thermosets are identified as highly crosslinked polymers that are glassy and brittle at room temperature. These materials typically exhibit high moduli, near linear elastic stress-strain behavior, and poor resistance to fracture. 

The potential application of organic and polymeric materials, especially glassy polymers, is promising as evidenced by the pertinent material properties. A model nonlinear optical glassy polymer system, combining the large nonlinear susceptibilities of the dopant and favorable optical properties of the host polymer glass, was fabricated and evaluated. The nonlinear optical... 

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