Initial streaming potential

Addition of the anionic polyelectrolyte Streaming potential Initial streaming potential... 

The oscillation of the piston (A) streams the liquid phase along the walls, gathering counterions in the diffuse layer into a cloud that moves away from the particle-fixed layer system (Figure 10.7b). A difference in potential is thus created between the diffuse layer cloud and the particle-fixed layer system. This is known as the initial streaming potential (PFl). It is measured by the two electrodes built into the vat and expressed in mV. It indicates the charge of the particles under investigation. 

The initial streaming potential of red wine is negative. This indicates that the compounds in wine have an excess of negative surface charges. The titration curve of a red wine with a cationic polyelectrolyte (Figure 10.9) is used to calculate the surface charge density of the wine, expressed in meq/1 (Lagune, 1994). 

The above governing equations are supplemented by initial conditions and boundary conditions on the cluster-macro void interface T js. Denote N the unit normal exterior to Cls. continuity of mass, concentrations, streaming potentials, total flux of the species and the normal component of the stress tensor give (where tpf = (RTtp /F))... 

A is the conductivity of the solution. A streaming potential is established by a confined solution flowing under pressure through small-diameter pores and capillaries. It is believed that the confining walls, typically glass, become charged with OH-, thereby initiating the potential. 

There has been considerable effort directed toward the immobilization of both enzymes and whole cells in a wide array of formats.15 Initial attempts to immobilize enzymes on naturally derived supports such as charcoal were conducted early in the twentieth century and eventually led to the development of more robust biocatalysts immobilized on synthetic resins by the mid-1950s. Immobilization often confers a number of advantages relative to the free biocatalyst including ease of removal from the process stream, potential for reuse, improvements in stability, favorable alterations in kinetic parameters, suitability for continuous production and in some cases the ability to operate in organic solvents. The focus of this section is on the immobilization of enzymes, however, many of the same principles apply to whole cells, the primary difference being the fact that immobilized cells are often less stable than individual enzymes and may contain additional undesired enzyme activities. 

The first results about foam electrokinetics have been reported by Sharovamikov [62,63]. An electroosmotic liquid transport is observed in foams from solutions of ionic surfactants (NaDoS, CTAB, PO-3A, etc.) and it is larger than in systems with solid capillaries (specific transport from 1.6-1 O 6 to 210 6 m3 C 1). The maximum electroosmotic pressure depends on the initial pressure in borders and reaches 1 Pa. The addition of dedecanol to the NaDoS solution sharply decreases the electroosmotic transport but increases the electroosmotic pressure. To reduce the influence of border and film non-homogeneity that originates in a static foam under gravity, the electrokinetic studies have been performed in an advancing foam [62]. The specific electroosmotic transport depends on the capillary pressure and reaches a maximum value at pg = 0.5 kPa. The streaming potential (up to 10 mV)... 

Adsorption isotherms are habitually obtained using the solution depletion method, which consists of comparing the solute concentrations before and after the attainment of adsorption equilibrium. Electrokinetic or zeta potentials are determined by two techniques microelectrophoresis [12,14,17] and streaming potential [13,58,59]. The former is employed to measure the mobility of small particles of chemically pure adsorbents, whereas the latter is adopted to investigate the electrophoretic behaviour of less pure coarser mineral particles. A correlation between the adsorption and electrophoretic results is usually examined with the aim of sheding light on the mechanism by means of which the surfactants are adsorbed at the solution-solid interface. This implies the necessity of maintaining the same experimental conditions in both experiments. For this purpose, the same initial operational procedure is applied. 

Figure 5. Typical example of streaming potential experiment, showing dependence of layer thickness 5h on time during initial deposition (rising part), saturation (horizontal part), followed by desorption (decreasing part) and readsorption (rising part). M = 105 kg/mol, c= 10 g/m and Re= 127.

P 68] No detailed experimental protocol was given [61, 62,142,143]. Two reactant streams, the solution of the reactant in hexane and concentrated sulfuric acid, were fed separately in a specially designed micro reactor by pumping action. There, a bilayer was formed initially, potentially decomposed to a dispersion, and led to rapid mass transfer between the phases. From this point, temperature was controlled by counter-flow heat exchange between the reaction channel and surrounding heat-transfer channel. The reaction was typically carried out at temperatures from 0 to 50 °C and using residence times of only a few seconds. If needed, a delay loop of... 

Fig. 5.17 shows the curves for the potentiometric titration of Ca2f in the range 5 10 3-5 10 2 M with a titrant carrier stream of 5 10 4 M EDTA using a calcium ion-selective electrode each titration is initiated by an abrupt increase in the potential, followed by an S-shaped decrease in which the inflection point marks the end of titration. According to eqn. 5.12, where the titration product is AB , the mixing volume V, the original concentration of A in the sample Cl and the titrant concentration CB, can be calculated. In the experiments in Fig. 5.17 the sample volume was 200/d and/ = 0.84 ml min-1 by... 

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