Fillers minimum critical volume

In adding conductive filler to an insulating resin, the volume resistivity changes slowly until a critical level of filler is reached, called the percolation point. The percolation point occurs when the resistivity drops abruptly, then continues to drop slowly (Fig. 2.11). " Almost continuous linkage of metal particles occurs at the percolation point where typical filler volumes for silver flakes are 25-30%. According to the percolation theory, there is a minimum critical volume of filler required for electrical conductivity in a polymer at which each filler particle must contact two other particles. A misconception in the use of silver flakes is that increasing the number of contacts lowers volume resistivity. Actually, the converse is true because, once the percolation point has been reached, each additional contact adds resistance. Thus, increasing the particle size can increase conductivity since the total number of contacts for a fixed volume decreases." ... 

The spherical nature of the pellets provides the minimum surface/volume ratio for the application of a coating, which is usually a polymer. The shape of the pellets was not found to be critical for pellets coated with a solution of a polymer in non-aqueous solvent (114). There was, however, a relationship between the specific surface area of the pellets and the mean dissolution time (MDT) for a series of pellets which had been prepared by different techniques (15) the higher the value of the specific surface area, the lower the value of the MDT. For pellets coated with polymer dispersion, there was a complex relationship between drug, the level of drug and the excipients used as filler (115). For a... 

Interparticle contact is of critical importance to the behavior of lithium batteries. Most lithium-ion electrodes contain 2 to 15 wt% conductive filler, such as carbon black, in order to maintain contact among aU the particles of active material and in order to reduce ohmic losses in the electrodes. Presently, there are few models available for predicting contact resistance, and the effect of the weight fraction of conductive filler on the overall electronic conductivity of the composite electrode must be determined experimentally. Doyle et al. [35] demonstrate how the fuU-cell-sandwich model can be used to determine what minimum value of effective electronic conductivity is needed to make solid-phase ohmic resistance negligible. Then, one need only measure the effective conductivity of the composite electrode as a function of filler content, and one need not run separate experiments on complete cells to determine the optimum filler content. Modeling techniques for predicting effective electroitic conductivities of composite electrodes are under development, and hold promise to aid in optimizing filler shape and volume fraction [85]. 

Level Control Filler. Plastic bottles can be manufactured clear thus for consumer appeal, they are filled to a level. This means the volume may vary but will appear to be equal due to the visually perceived common level in the containers. Flow is by gravity through a nozzle into a sealed container, whereas air equilibrates via a vent tube (Figure 8). When the rising liquid reaches the air vent port, flow stops. There is no overflow of product as in a pressure or pure vacuum filler. Aeration is at a minimum, perceived fill level is extremely accurate, and the filler is relatively simple and easy to maintain. Size consistency of the blow-molded container is critical to control, because this dictates the amount of product being sold. 

Introduction of small amounts of filler of different chemical natrme (0.5-1.0%) into the polymer melts leads to a marked drop in viscosity and only after some critical concentration does the viscosity begin to increase again. The effect of the decreasing viscosity may reach 10-40% of the viscosity of rm-filled melt. The nature and the size of filler particles is of great importance. Increase in the size or as5mimetry of particles diminishes this effect. The decrease in viscosity is not sensitive to the nature of the filler if the comparison is made at a constant shear rate. However, the viscosity changes if we compare the resrdts of measurements at constant shear stress. The latter effect is connected with the influence of shear stress on the thickness of an adsorption layer. The appearance of the minimum viscosity was explained by formation of additional free volume in surface layers of filler particles. 

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