Particle interactions mobile liquids

Baker [27] observed mobilization of small particles of several metal oxides on graphite at a temperature (the so-called mobility temperature) that was identical to the Tammann temperature. Thus, at least in systems exhibiting relatively weak interactions between active phase and support surface, particle mobility may be induced at this temperature. The particle migration may perhaps be described as a floating of the active phase particle on the liquid-like surface layer. 

The rheological properties of emulsions are influenced by a number of interacting factors, including the nature of the continuous phase, the phase volume ratio, and to a lesser extent, particle size distributions. A variety of products ranging from mobile liquids to thick semisolids can be formulated by altering the dispersed phase volume and/or the nature and concentration of the emulsifiers. For low internal phase volume emulsions, the consistency of the emulsion is generally similar to that of the continuous phase thus. 

Another interesting experimental stndy of concentrated suspensions of hnman erythrocytes was performed by Znkoski and Saville. Although volume fractions as high as 75% were employed, the electrophoretic mobility changed by the factor (1 - ([)) in the whole concentration range, which was simply explained by the backflow of liquid necessary to conserve the snspension volnme. The electrostatic and hydrodynamic particle-particle interactions apparently canceled each other in these experiments. Note that the electrolyte concentration was relatively high and, contrary to the experiments of Deggelmann et al., " the EDL were thin in comparison with the particle size. 

Different theories exist about the thickening mechanism of fumed silicas. One of the first was the so-caUed chicken wire structure. That means the silica particles interact with each other via their silanol groups and form a three dimensional structure, which reduces the mobility of the hquid molecules. Under mechanical impact like shearing or shaking the structure is destroyed and the viscosity of the system decreases. After the end of the mechanical impact, the three dimensional network re-establishes itself and the viscosity increases again as a function of time. This mechanism may be valid in simple nonpolar liquids. In liquid mixtures or polymer solutions it is much more complicated and the adsorption pattern on the fumed silica surface seems to play an important role [76]. 

The main difference between the three states of matter is the freedom of the parhcles to move past one another. If the average separation of the particles is large, there is hardly any restriction on their mohon, and the substance is a gas. If the particles interact so strongly with one another that they are locked together rigidly, then the substance is a solid. If the particles have an intermediate mobility between these extremes, then the substance is a liquid. We can understand the melting of a solid and the vaporization of a Hquid in terms of the progressive increase in the Hberty of the particles as a sample is heated and the particles become able to move more freely. 

Selection of columns and mobile phases is determined after consideration of the chemistry of the analytes. In HPLC, the mobile phase is a liquid, while the stationary phase can be a solid or a liquid immobilised on a solid. A stationary phase may have chemical functional groups or compounds physically or chemically bonded to its surface. Resolution and efficiency of HPLC are closely associated with the active surface area of the materials used as stationary phase. Generally, the efficiency of a column increases with decreasing particle size, but back-pressure and mobile phase viscosity increase simultaneously. Selection of the stationary phase material is generally not difficult when the retention mechanism of the intended separation is understood. The fundamental behaviour of stationary phase materials is related to their solubility-interaction... 

A wide range of condensed matter properties including viscosity, ionic conductivity and mass transport belong to the class of thermally activated processes and are treated in terms of diffusion. Its theory seems to be quite well developed now [1-5] and was applied successfully to the study of radiation defects [6-8], dilute alloys and processes in highly defective solids [9-11]. Mobile particles or defects in solids inavoidably interact and thus participate in a series of diffusion-controlled reactions [12-18]. Three basic bimolecular reactions in solids and liquids are dissimilar particle (defect) recombination (annihilation), A + B —> 0 energy transfer from donors A to unsaturable sinks B, A + B —> B and exciton annihilation, A + A —> 0. 

The solid phase is considered to be an amorphous pile having a maximum disorder amongst the particles. Such a close-packed assemblage has some similarity with a liquid. But an essential difference from liquids lies in the absence of the supplementary free volume. An amorphous solid phase with interacting particles having a certain degree of mobility is considered to be essential for the diffusion process in plastic materials. 

In preparative liquid-carbon-dioxide-based supercritical flow chromatography (SFC), smaller particles in the 5-10 /tm range are used due to the decreased viscosity of the mobile phase. The pore size of the particles should be large enough to allow the molecules to readily diffuse into and out of the pores. In reversed-phase HPLC, longer alkyl chains provide better load- ability because of the higher volume of interaction be-... 

---