Sedimentation binary system

A binary suspension consists of equal masses of spherical particles of the same shape and density whose free falling velocities in the liquid are 1 mm/s and 2 mm/s, respectively. The system is initially well mixed and the total volumetric concentration of solids is 0.2. As sedimentation proceeds, a sharp interface forms between the clear liquid and suspension consisting only of small particles, and a second interface separates the suspension of fines from the mixed suspension. Using a suitable model for the behaviour of the system, estimate the falling rates of the two interfaces. It may be assumed that the sedimentation velocity uc in a concentrated suspension of voidage e is related to the free falling velocity u0 of the particles by ... 

Note that for a monodisperse system. Eg, = e and Eq. (134) reverts back to Eq. (131). Both Eqs. (132) and (134) were able to map features of the binary batch sedimentation data of Richardson and Meikle (1961a) for spheres of different sizes and densities having the same value of /q. 

Selim MS, Kothari AC, Turian RM. Sedimentation of binary suspensions. AIChE S5mp Series (Fluidization and Fluid Particle Systems Theories and Applications, Knowlton TM, ed.) 79(222) 103-108, 1983a. 

At elevated concentrations, hydrodynamic and other interactions between sedimenting molecules become important. Two sorts of sedimentation measurement, involving respectively a binary and a ternary system, then suggest themselves. First, s in binary polymer systems may depend on polymer concentration and molecular weight. Second, the sedimentation rate of colloidal particles or probe polymer molecules through a solution of a second polymer, as might occur in ternary systems, may depend on the second polymer s properties. 

Chapter 2 treats the sedimentation of polymer molecules and the sedimentation of probe particles and tagged polymer molecules through a solution of matrix polymers. What generalizations can be obtained from the extant phenomenology First, s c) for polymers in a homogeneous binary polymer solvent system almost always follows a stretched exponential in polymer concentration. For probe colloids or chains sedimenting through a polymer matrix solution, s(c) also has a stretched-exponential dependence on matrix polymer concentration. 

The simultaneous adsorption of poly(vinylpyrrolidone) (PVP) and an anionic hydrocarbon or fluorocarbon surfactant from their binary mixtures on polystyrene latex was studied by Otsuka et al [59]. The bare particles and the particles coated with PVP/surfactant were sized by sedimentation field flow fractionation (SFFF). The adsorption of PVP was enhanced by LiDS or LiFOS at low surfactant concentrations, but decreased at high surfactant concentrations. The conformation of adsorbed PVP changed from loops and trails to trains with the increasing surfactant concentration. However, in the PVP-LiFOS system, the fraction of train segments increased steeply at a lower surfactant concentration and was greater than that in the PVP-LiDS system. The thickness of the adsorbed layer was also determined by photon correlation spectroscopy after prefractionation by SFFF. The thickness of the adsorbed layer decreased with increasing surfactant concentration. (For the characterization of adsorbed surfactant layers, see Ref. 56, pp. 205-216). 

Influence of SDS concentration on relative volume of coacervate phase in the ternary system, and turbidity of the system is shown in Figure 11. Coacervate layer formation appears at the onset of HPMC-SDS interaction. Relative volume of coacervate phase increases with SDS addition, and reaches maximum at the end of HPMC-SDS interaction (i.e. at PSP). The relative volume of coacervate phase increases on addition of SDS due to increased hydrophilic properties of HPMC/SDS complex, as more SDS molecules are bound to HPMC, which results in better solvation of HPMC/SDS complex. At SDS concentrations larger than PSP the coacervate disappears. On increase in SDS concentration turbidity of the ternary mixtures decreases until it reaches constant value, which is the same as is turbidity of binary HPMC/NaCMC mixture (Measured turbidity of the ternary mixtures having lowest SDS concentrations is low due to fast sedimentation of coacervate during the measurement.). The decrease in turbidity is attributed to increase in HPMC/SDS complex solvation as SDS concentration in the ternary system is increased. 

The interpretation of sedimentation and diffusion velocity data for non-electrolytes in binary macromolecular component systems as well as in solutions of more than two components is based on well-tried and familiar equations. Whether the same principles can be extended to multicomponent polyelectrolyte solutions has been the subject of several controversies. 

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