Packing material desirable characteristics

Several thousands of different columns are commercially available, and when selecting a column for a particular separation the chromatographer should be able to decide whether a packed, capillary, or monolithic column is needed and what the desired characteristics of the base material, bonded phase, and bonding density of selected column is needed. Commercial columns of the same general type (e.g., CIS) could differ widely in their separation power among different suppliers. Basic information regarding the specific column provided by the manufacturer, such as surface area, % carbon, and type of bonded phase, usually does not allow prediction of the separation or for the proper selection of columns with similar separation patterns. 

To be able to control the PCM properties in the desired direction it is very important to know the relationships between the material composition and properties. Since melt viscosity is one of the most important characteristics of processability of PCM, there have naturally been a large number of equations proposed for describing the viscosity versus filler concentration relationship. For the purpose of this review it may be most interesting to discuss the numerous equations which have in common the use of the value < representing the maximum possible volume filling by filler particles packed in one way or another, as the principal constant. Here are a few examples of such equations. 

To give the particles the required momentum, they should be densely packed and rigid and have a well-defined narrow particle size distribution. Friable and oblique particles are not desirable because the penetration depth will increase if the particle characteristic is more variable (Hickey 2001). Studies have been performed with particles ranging from 20 to 40 J,m in size and 1.1 to 7.9 g/cm3 in density impacting human cadaver skin (Kendall et al. 2000). Velocities of up to 260 m/s were applied to particles of this size range. For many applications, smaller particles of about 1 to 4 j,m diameter may be required for an optimized delivery. To deliver particles of this size into the skin, higher densities and impact velocities are required. For this reason, gold particles are used as a carrier material for the delivery of plasmid DNA vaccines (Kendall et al. 2001). 

Various additives, generally with very low concentrations, have been used to control the characteristics of the feed materials, in order to achieve desired shapes and control the packing uniformity of the green body of ceramics. For some methods, such as tape casting and injection molding, the use of suitable additives is especially important. The additives can be either organic or inorganic materials. 

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