Natural particles, electrophoretic mobilities

The Penn State workplan is based on five tasks Task 1 to participate in round-robin particle electrophoretic mobility measurements, Task 2 to determine the nature of reactive sites on the silicon nitride surface, Task 3 to modify the chemistry of the silicon nitride interface using organic species, Task 4 to determine the rheological and dispersion properties of the nonaqueous silicon nitride suspensions, and Task 5 to ensure transfer technology to ORNL via meetings and reports. Each task is discussed in detail below. 

Electroultrafiltration (EUF) combines forced-flow electrophoresis (see Electroseparations,electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45—47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Elotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane faciUtates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

The electrophoretic mobility of natural suspended sediments has been measured on the field a few hours after sampling using a Pen Kern s Model 501 Laser Zee Meter which uses a rotating prism design enabling simultaneous measurements of many particles. 

Model particle mobility has been determinated with the Tiselius method (Tiselius, 1937, 1938). This method also allows the integration of the mobility of a large number of particles even if the refractive index is very close to that of the electrolyte medium, allowing to minimize the experimental errors inherent to the classical microelectrophoretic techniques. The electrophoretic mobilities will not be transformed into surface charges because the theoretical relationship between these parameters is highly dependant on the particle radius of curvature and the electrolyte concentration in the vicinity of the particle (Hunter and Wright, 1971). For both methods, the analytical error falls below 5 %, however, it increases up to 10 % for natural composite samples and/or low mobilities. 

We have tried to specify the influence of different physico-chemical parameters upon the electrophoretic mobility, using model particles such as silica (Aerosil 380 - Degussa) which is characterized by a charge very close to that of natural suspended sediment from Loire and Gironde. 

Fig. 4. Electrophoretic mobilities (Ug)of natural (untreated) - curve A - and treated particles as a function of salinity (S°/°<>) for two sets of samples from Keithing Burn (KB 1 open symbols - 31 March 1982 KB 2 closed symbols - 30 dune 1982). Shaded area B indicates the spread of results from other estuaries (redrawn from Fig. 3 of Hunter and Liss 1979). Curve D - suspended particles centrifuged and resuspended in UV- oxidized sample supernatant and then UV-oxidized. Curve C - natural samples (particles plus supernatant) UV-oxidized. Curve E - sample supernatant UV-oxidized to form new particles (UV-PPT). Several UV-PPT samples from KB2 were centrifuged and the particles resuspended in their original untreated sample supernatant. The resulting changes in Ug are indicated by the dashed lines (asterisks - final values). Keithing Burn suspended matter is mostly composed of iron oxides (after Loder and Liss, 1985).

Fig. 5. Plot of the logarithm of the electrophoretic mobility of natural particles in the Gironde, Loire and Conwy estuaries (Date for Conwy from Hunter and Liss, 1982).

Figure 2. Electrophoretic mobilities of particles in seven4on (l t) and natural sea water (right). Tie lines connect values for the same kind of particle. Data from Ref. 15.

Figure 4. Variation of electrophoretic mobilities of natural particles with salinity of the medium. Standard deviations are indicated. Data...

The coefficient of variation of electrophoretic mobilities in the case of natural particles (33%) was greater than that found for immersed test particles all of a single kind in natural water (< 10% ). However, the range of mobilities spanned by the entire population of many kinds of test particles in natural water is quite similar to that found with the natural particles shown in Figure 3. 

That the electrophoretic mobility is independent of the nature and concentration of the above ions, and depends solely on pH, is almost conclusive proof that the charge on L-myosin particles is determined exclusively by the binding (and release) of H ions. This means that the other ions, including sodium and potassium, are not bound, but are free in solution as gegenions. The agreement between the alkali content of salt-free myosin gel and the amount of protons given up on the alkaline side of the I.P. leads to the same conclusion (Hollwede and Weber, 1938) and finally, the pH-mobility curve found by Erdos and Snellman (1948)... 

As illustrated in Figure 9.22, the electrophoretic mobility increased (in the absolute value) together with the temperature, irrespective of the nature of the surface charge. Such behavior is related to the surface charge density versus temperature. The amplitude of the measured transition in the electrokinetic property was more marked for low cross-linked thermally sensitive particles (i.e., high swelling ability). The electrokinetic study of such thermally sensitive particles needs particular attention in order to demonstrate the location of charges implicated in electrophoretic mobility and what is the relationship between the volume phase transition temperature and the electrokinetic transition temperature. 

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