Sedimentation pressure-change measurement

On the other hand many methods have been devised for measuring pressure changes with time at a given point in the sedimentation tube. These methods are based on the so-called Wiegner (1918) sedimentation tube. This tube consists of a cylinder with relatively large diameter. At a point -distant from the top is attached a smaller tube provided with a stopcock. This tube is bent upward parallel to the sedimentation tube. The smaller tube is filled with sedimentation fluid, free of particles, to the level of the suspension itself in the sedimentation tube. When the stopcock is opened the liquid in the smaller tube rises as sedimentation progresses, the liquid in the smaller tube decreases. 

Due to the high centrifugal fields apphed in the ultracentrifuge, pressure gradients with pressures up to 200 bars are encountered in the cell and change appreciably the viscosity and the density of the solvent and the partial specific volume of the polymer. Thus the sedimentation coefficient, 5, measured at a pressure p differs from the sedimentation coefficient, measured at 0 bar. Application of Eq. (A9) for the calculation of 5 requires the knowledge of ri I (362), p I (given in a number of Handbooks) and V2 (148). More precise equations for the calculation of the pressme influence on the sedimentation have been worked out by several authors (363,364,365,800). The equation of 0th and Desreux (Ref 363)... 

The various physical methods in use at present involve measurements, respectively, of osmotic pressure, light scattering, sedimentation equilibrium, sedimentation velocity in conjunction with diffusion, or solution viscosity. All except the last mentioned are absolute methods. Each requires extrapolation to infinite dilution for rigorous fulfillment of the requirements of theory. These various physical methods depend basically on evaluation of the thermodynamic properties of the solution (i.e., the change in free energy due to the presence of polymer molecules) or of the kinetic behavior (i.e., frictional coefficient or viscosity increment), or of a combination of the two. Polymer solutions usually exhibit deviations from their limiting infinite dilution behavior at remarkably low concentrations. Hence one is obliged not only to conduct the experiments at low concentrations but also to extrapolate to infinite dilution from measurements made at the lowest experimentally feasible concentrations. 

PPTs (Pore Pressure Transducer), made in US, were buried in the sediment to measure the pore pressure. Two sets of digital cameras were used to record the change of sediment s surface during dissociation of gas hydrate. Three laser displacement transducers (LSI, LS2 and LS3) were located over the samples with distances of 5 cm, 25 cm and 45 cm to the top of slopes respectively and all with a distance to one side wall 20 cm. 

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