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Our laboratories have the equipment necessary to measure a wide range of physical properties, and we have developed new methods that are uniquely suited for measuring particular properties and processes.
Surfactant Aggregate Property Measurements
In the study of micelle formation, CMC measurements by surface tensions and conductivity are done routinely. Calorimetry is being used to measure the heats of formation of micelles, heats of formation of admicelles, and the heat of mixing in the formation of mixed micelles or admicelles. Counterion binding is measured using specific ion electrodes, while aggregation numbers can be determined using small-angle x-ray scattering or, if more detailed information is required, our group has experience with neutron scattering at national laboratories. Other methods useful in the study of these phenomena are NMR and density.
We can measure the solubilization of organics by micelles with the greatest accuracy now available. For volatile compounds, a vapor pressure method is employed. For less volatile compounds, a newly developed technique from our laboratory, semi-equilibrium dialysis, is used. Headspace chromatography or micellar-enhanced ultrafiltration are also useful tools for this type of measurement.
Our laboratory can also measure adsorption isotherms for adsorption of surfactants on a variety of solids using HPLC. The co-adsorption or adsolubilization of other constituents can also be measured. Counterion binding on admicelles can be calculated from measured electrophoretic mobilities and zeta potentials can be measured. Column systems are used to study the chromatographic separation of surfactant and other components. Ellipsometry and quartz crystal microbalance measurements are used to characterize adsorbed layers on a flat surface.
We have the capability of measuring properties of a number of other aggregates formed by surfactants. Differential scanning calorimetry is useful in the study of phase transitions in mesomorphic systems. We have developed a variety of methods for determining the phase boundary in precipitating systems, utilizing laser light scattering, spectroscopy, specific ion electrodes, visual methods, and surface tension. The composition and characteristics of coacervate formed above the cloud point of solutions, and microemulsions formed in oil/water systems can also be studied using our instrumentation.
Analytical Capabilities
A number of analytical methods have already been described, but there is an additional need in many projects to measure the concentrations of chemical species in solution. We have four high-performance liquid chromatographs, an ion chromatograph, and several gas chromatographs for the purpose. The HPLC's have UV, conductivity, refractive index, evaporative light scattering and fluorescence detectors. Atomic absorption spectrometry with a graphite furnace is used to determine the concentration of metal ions.
In addition to these chromatographic techniques, we have other spectroscopic methods (Raman, FTIR), a total organic carbon analyzer, wet chemistry methods, conductivity cells, and surface tension apparatus for use in the measurement of surfactant and other chemical concentrations in liquid or gas phase. Tensiometer types include maximum bubble pressure, spinning drop, DuNouy ring, and Wilhelmy plate. We also have a fiber tensiometer that is able to measure both advancing and receding contact angle. A device that uses the Washburn method is able to measure wettability and contact angle of powders. We have torsional rheometers that are able to measure the steady-shear and dynamic viscosity of surfactant systems with high viscosity. The Ross-Miles foam test can be performed along with the Draves wetting test.
IASR operates an atomic force microscope. It is equipped with both contact and non-contact heads and also has an in situ cell. Surface features can be resolved to less than one angstrom. Applicable surfaces include both conducting and nonconducting, flat and complex (e.g., porous powders). We have access to campus-wide scanning electron microscopy and transmission electron microscopy systems. Our group also operates a high-throughput x-ray diffractometry system with area detector.
Consumer Product Testing
We have a Terg-o-Tometer for testing laundry detergency with a Hunter Lab spectrometer for reflectance measurements of resultant fabric. We have flow cells to measure the rate of soap scum dissolution in contact with flowing solutions of detergents. Scrub tests of hard surfaces are also performed routinely.
Separation Techniques and Environmental Applications
After surfactant systems designed for in situ soil remediation applications have been tested in conventional soil columns, they may be tested in a 10 foot-cubed sand tank. The tank can be set up to contain a model aquifer with ground water flow through the aquifer. Probes built into the sides of the tank can be extended into the aquifer to allow determination of the hydrostatic head as a function of position in the aquifer as well as allowing determination of concentration distributions in the aquifer. The tank has been used to test for removal efficiencies for surfactant enhanced remediation of TCE contaminated aquifers.
We have available batch stirred ultrafiltration cells and spiral wound continuous units. These provide the capability of obtaining screening data, as well as results on micellar-enhanced ultrafiltration, which can scale-up to large units. Our laboratory has a number of adsorption columns up to one-inch diameter that can be used to study admicellar chromatography, surfactant-enhanced carbon regeneration, and other adsorption processes of interest. We have continuous liquid-liquid extraction units to study cloud point extractions and multitray foam fractionation units to investigate foam separations to treat wastewaters.