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Retention forces

The capillary retention forces in the pores of the filter cake are affected by the size and size range of the particles forming the cake, and by the way the particles have been deposited when the cake was formed. There is no fundamental relation to allow the prediction of cake permeabiUty but, for the sake of the order-of-magnitude estimates, the pore size in the cake may be taken loosely as though it were a cylinder which would just pass between three touching, monosized spheres. If dis the diameter of the spherical particles, the cylinder radius would be 0.0825 d. The capillary pressure of 100 kPa (1 bar) corresponds to d of 17.6 pm, given that the surface tension of water at 20°C is 12.1 b mN /m (= dyn/cm). [Pg.389]

Table 4. Effect of Particle Size on Capillary Retention Force... Table 4. Effect of Particle Size on Capillary Retention Force...
Fig. 16 Typical force-time trace from an instrumented Zanasi LZ-64 automatic capsule-filling machine. PC, precompression resulting from dipping of dosator into the powder bed C, compression resulting from actual piston tamping R, retention force Ej, ejection D, drag force developing during retraction of piston. (From Ref. 38.)... Fig. 16 Typical force-time trace from an instrumented Zanasi LZ-64 automatic capsule-filling machine. PC, precompression resulting from dipping of dosator into the powder bed C, compression resulting from actual piston tamping R, retention force Ej, ejection D, drag force developing during retraction of piston. (From Ref. 38.)...
Hydrophobic Effect. The primary retention force in normal phase adsorption is the attraction of solute polar moieties to the polar stationary phase. In contrast, the retention force in RPLC is repulsion from the mobile phase. The stationary phase is a relatively passive surface, the solute attraction for the hydrocarbon stationary phase being weak and non-selective. How does this come about, and what are the resultant selectivity characteristics ... [Pg.45]

The multilayered character of acetonitrile adsorption creates a pseudo-stationary phase of significant volume on the surface, which acts as a suitable phase for the ion accumulation. In the low organic concentration region (from 0 to 20 v/v% of acetonitrile), studied ions show significant deviation from the ideal retention behavior (decrease in ion retention with increase in acetonitrile composition) due to the formation of the acetonitrile layer, and significant adsorption of the chaotropic anions was observed. This creates an electrostatic potential on the surface in which there is an adsorbed acetonitrile layer, which provides an additional retentive force for the enhancement of the retention of protonated basic analytes. When the dielectric constant is lower than 42 [167], this favors the probability of ion pair formation in this organic enriched layer on top of the bonded phase. [Pg.214]

A balance of forces in the direction of the pore permits a quantitative assessment of the conditions under which globule mobilization can occur within that pore. The conditions under which mobilization forces balance retention forces are termed the critical conditions for mobilization. Summation of the pressure and gravity forces acting on the globule along the 1 direction yields... [Pg.303]

Gradual Pore Blocking. This mechanism includes continuous capture of fine particles at the rock walls due to retention forces. For... [Pg.304]

Polar van der Waal s retention forces are a consequence of dipole-dipole interactions and hydrogen bonding between molecules. Only components with dipoles similar to the solvent (stationary phase) will disperse, producing solute-solvent pairs. Dipole induced dipole interactions arise from the charge on one molecule (component or stationary phase) disturbing the electrons in a second associated molecule, producing a shift in charge which then forms the induced dipole. [Pg.23]

An optimised chromatographic separation is achieved by varying the mobile and stationary phase properties and operating parameters to give the required retention of the components in a sample. The overall retention characteristics for each component are related to the kinetics and mass transfer processes, leading to retention forces. [Pg.25]

Adsorption chromatography mode of separation in which a solute or sample components are attracted to a solid surface, the stationary phase, by adsorption retention forces, the mobile phase may be a gas or liquid. [Pg.525]

Adsorption retention forces attraction of a solute onto a solid stationary phase due to microporosity (pores 5-50 nm) and polar character (formation of van der Waal s forces and hydrogen bonding) of the surface, described by Langmuir isotherms (see isotherms). [Pg.525]

Displacement chromatography the separation process where a sample mixture is introduced at the start of the column and is then eluted with a mobile phase that is more strongly attracted to the stationary phase than the sample components. Individual components are therefore displaced by the mobile phase and by each other, in order of retention forces. [Pg.529]

Distrihution ratio, equilibrium constant K, the term describing the distribution of a solute between the mobile phase and stationary phase and reflects the retention forces. Also known as partition ratio Kp, for partition chromatography. [Pg.529]

Gas chromatography GC, employs a gaseous mobile phase, e.g. nitrogen or helium, and usually a liquid stationary phase, e.g. non-polar Apiezon (alkane grease), OVIOI (polymethyl siloxane) or polar PEG20M (polyethylene glycol). Separation is effected by competition between attraction of the components for the stationary phase and volatility at the column temperature being used, that is, retention forces versus partial vapour pressure in the mobile phase. [Pg.531]

Mobile phase transports the solutes or components to be separated through a column or plate of stationary phase material. The solution properties of a liquid mobile phase compete with the retention forces of the stationary phase to determine the distribution ratio and hence elution time. In GC the gaseous mobile phase transports components in the vapour phase. [Pg.535]

Partition coefficient, describes the distribution of a solute between a liquid or gaseous mobile phase and a liquid stationary phase on an inert support material. The solute molecules are partitioned between the two phases according to the retention forces of the stationary phase and the solvating properties of the mobile phase in LC or vapour pressure in GC. The equilibrium is temperature dependent see distribution ratio ... [Pg.537]

Partition retention forces intermolecular forces that result in attraction of solute molecules to the stationary phase. Polar retention forces include dipole-dipole attractions, van der Waal s forces and hydrogen bonding. Non-polar retention forces consist of London s dispersion forces arising from induced polarity in non-polar molecules, remember that like attracts like . [Pg.537]

Retention forces see polar, non polar and adsorption retention forces. [Pg.540]

Retention time, tg time interval between introduction of a sample and elution. Corrected or relative retention time 4 is a more accurate measure of delay due to retention forces and takes into account the system dead time, the time the mobile phase takes to pass through the system,... [Pg.541]

Retention volume, Fr volume of mobile phase required to elute a component. Corrected or relative retention volume Kr is a more accurate measure of the delay due to the retention forces by allowing for the volume of mobile phase in the system V. Usually a constant mobile phase flow-rate, Fq is maintained hence the more convenient term retention time is used. [Pg.541]

Stationary phase solid material or liquid immobilised on an inert support, which attracts components in the mobile phase according to characteristic retention forces and thus retards their progress through the column or plate see mobile phase. [Pg.543]

The measurement of ultralow interfacial tension has been of continued interest (98, 116-128) both in fundamental research and in industrial applications, particularly in surfactant-based (enhanced) oil recovery - an attempt to recover remaining oil reserves by reducing the oil/water interfacial tension through microemul- sions (117, 120, 125, 129, 130). Typically, oil is recovered in a primary process by the natural energy of a reservoir. However, as much as 40-60% of the original oil can remain trapped in porous rocks due to capillary retention force. A seeondary process of water injection with surfactant is therefore used to facilitate further oil displacement. [Pg.16]

The reduction in the interfacial tension decreases the capillary retention force significantly and enables oil droplets to deform and maneuver easily through pores in the rock medium (117). [Pg.16]

It follows that the remaining dominant retentive forces will be polar or ionic in nature. In the second case, the mobile phase is predominantly water and thus provides very strong polar interactions with the solute but very weak dispersive interactions. It also follows, that the retention forces of the stationary phase, in this case, will be dominantly dispersive... [Pg.245]

A uup break in the drainage curve is noticeable as the drainage force increases (increase in iVc > 0.14) this may be due to breakdown of retention forces leading to a p dular state in the liquor between particles. [Pg.313]


See other pages where Retention forces is mentioned: [Pg.25]    [Pg.138]    [Pg.357]    [Pg.149]    [Pg.138]    [Pg.627]    [Pg.145]    [Pg.169]    [Pg.23]    [Pg.23]    [Pg.24]    [Pg.541]    [Pg.138]    [Pg.602]    [Pg.18]    [Pg.105]    [Pg.190]    [Pg.153]   
See also in sourсe #XX -- [ Pg.21 ]




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