Electrokinetic Measurements Fibers

The glass fibers and fused-silica glass (Thermal American Fused Quartz Co.) were crushed and then dispersed in water. The pH of this near-neutral suspension was varied using KOH or HNO,. In some experiments, a hydrolyzed solution of y-APS was added to this suspension. Here, the initial pH was 10. The electrophoretic mobilities of glass fragments suspended in these solutions were measured without any further treatment except for the addition of electrolyte (10-3 M KNO,). These analyses were performed using a Rank Brothers Particle Micro-Electrophoresis Apparatus Mark II or a Pen Kem System 3000 Automated Electrokinetics Analyzer. 

Electrokinetic mobilities can be measured by direct observation of the particle movement by use of a microscope or of the boundary between suspension and clear electrolyte separated from the suspension by centrifugation (moving boundary method). When electrolyte is forced through a fixed bed, e.g., of carbon fibers, a potential builds up between the ends of the bed. This streaming potential can also be used for the measurement of -potentials. Details of these methods are described in textbooks of colloid chemistry. 

For this purpose, Li s group reported a simple multi-functional particle detection PDMS chip [17]. This chip generates liquid flow and particle motion electrokinetically, and uses two pairs of parallel optical fibers embedded in the chip to measure particle speed and size, and to count particles. More recently, a new microfluidic method was developed to counting the particles flowing through microchannels, not by the optic method as described previously, but by an electric method. This method is called the microfluidic differential resistive pulse sensor method [18]. Figure 6 below illustrates the principle of this method. 

Streaming potential measurements have been used extensively to eharaeterize surfaee properties of fibers (25), and this technique has been applied to analyze the effects of shampoos and conditioners on hair by a number of authors (26-28). Jachowicz and his coworkers developed new instrumentation for this purpose, which permits the simultaneous determination of electrokinetic and permeability parameters on hair fiber plugs. DEPA is... 

The results of the contact force measurements, p, between cellulosic fibers in the presence of PEI are shown in Figure 2.23. The observed trends are similar to those shown in Figure 2.21 for the friction coefficient measurements and are also in good agreanent with the patch model of flocculation by the PEI, and the previously mentioned electrokinetic studies, as reflected by the maximum in the cohesive force at low concentrations of PEI. As expected, after reaching the maximum, the cohesive forces decrease with a further increase in the PEI concentration. This corresponds to the decrease in the fraction of available negatively charged patches for interaction with PEI and the increase in the electrostatic repulsion due to a continued adsorption of PEI. 

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