Poly , transport mobility

Due to the universality in all glasses, physical aging can be theoretically explained in a straightforward way based on the free-volume concept. As proposed by Struik, This is the basic and rather obvious idea that the transport mobility of particles in a closely packed system is primarily determined by the degree of packing of the system or by its inverse measure, viz. the free volume [2]. The idea could date back to 1943 when Alfrey et al. proposed that the isothermal aging below Tg can be attributed to the diffusion of free volume holes from the interior of polymers into the surface [34]. This free volume diffusion model (FVDM) was developed by Curro et al. [35] to quantitatively analyze the volume relaxation experiments of poly(vinyl acetate) [36, 37]. The motion of free volume holes can be described by a diffusion equation ... 

In the example above, a short-chain poly(ethylene glycol) was added to a rigid polyelectrolyte to plasticise the material and thereby increase polymer-solvent motion in the vicinity of mobile ions. This strategy has been widely explored as a means of improving ion transport in electrolytes. 

Poly silanes have a quantum efficiency of >30% and show a hole mobility of 10-4 cm2s-1V-1 at room temperature, independent of the side groups.37,38 Due to sufficient hole mobility, polysilanes are considered to be suitable materials for the hole-transporting layer in injection-type organic EL diodes.36 It is also known that polysilanes themselves can be efficient emission materials in the UV and visible regions. 

Solvent-free polymer-electrolyte-based batteries are still developmental products. A great deal has been learned about the mechanisms of ion conductivity in polymers since the discovery of the phenomenon by Feuillade et al. in 1973 [41], and numerous books have been written on the subject. In most cases, mobility of the polymer backbone is required to facilitate cation transport. The polymer, acting as the solvent, is locally free to undergo thermal vibrational and translational motion. Associated cations are dependent on these backbone fluctuations to permit their diffusion down concentration and electrochemical gradients. The necessity of polymer backbone mobility implies that noncrystalline, i.e., amorphous, polymers will afford the most highly conductive media. Crystalline polymers studied to date cannot support ion fluxes adequate for commercial applications. Unfortunately, even the fluxes sustainable by amorphous polymers discovered to date are of marginal value at room temperature. Neat polymer electrolytes, such as those based on poly(ethyleneoxide) (PEO), are only capable of providing viable current densities at elevated temperatures, e.g., >60°C. 

In crystalline organic solids such as anthracene, in which the mobility is on the order of 1 cm2/Vs, the transport mechanism may still be explained by a band theory formalism. But for most organic solids (especially if disordered), the mobility values are far below the lower limit value and a hopping transport mechanism seems to be more appropriate. Organic polymers are classic examples of hopping transport materials. In poly-iV-... 

Isotactic and syndiotactic poly(9-fluorenyl methacrylate)s have been prepared that are effective as hole mobility charge transport materials and as electrical conductors of charge transport materials. 

Hole transport in polymers occurs by charge transfer between adjacent donor functionalities. The functionalities can be associated with a dopant molecule, pendant groups of a polymer, or the polymer main chain. Most literature references are of doped polymers. The more common donor molecules include various arylalkane, arylamine, enamine, hydrazone, oxadiazole, oxazole, and pyrazoline derivatives. Commonly used polymers are polycarbonates, polyesters, and poly(styrene)s. Transport processes in these materials are unipolar. The mobilities are very low, strongly field and temperature dependent, as well as dependent on the dopant molecule, dopant concentration, and the polymer host This chapter reviews hole transport in polymers and doped polymers of potential relevance to xerography. The organization is by chemical classification. The discussion mainly includes molecularly doped, pendant, and... 

Pai et al. (1983) measured hole mobilities of a series of bis(diethylamino)-substituted triphenylmethane derivatives doped into a PC and poly(styrene) (PS). The mobilities varied by four orders of magnitude, while the field dependencies varied from linear to quadratic. In all materials, the field dependencies decreased with increasing temperature. The temperature dependencies were described by an Arrhenius relationship with activation energies that decrease with increasing field. Pai et al. described the transport process as a field-driven chain of oxidation-reduction reactions in which the rate of electron transfer is controlled by the molecular substituents of the hopping sites. 

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