| dc.description.abstract | Much interest has been shown in recent years in the study of colloidal systems. This is due in part to the fact that the lattice spacing of these spontaneously crystallized systems of charged macromolecules is comparable to the wavelength of visible light. As a result of this, laser light can be used to collect data from these crystalline arrays of suspended particles, as opposed to the x-ray illumination required in probing atomic crystals. Several groups have devoted research to the measurement of the properties of colloidal dispersions, such as polystyrene, polymethyl methacrylate, and silica spheres, in a variety of solvents[1 � 7]. These properties include the shear modulus, as well as dynamic viscocity and sample structure and morphology. Methods of measurement have varied from rheologic measurements for highly concentrated samples, to light scattering rheological techniques for dilute samples. While it is impossible to detail within this paper all of the work done on this subject, it would perhaps be appropriate at this time to mention a few of the developements in the measurement of the elastic moduli of colloidal cryst.als. Theoretical and experimental studies have been done by R. Nossal and M. Jolly to determine the allowable frequencies of the mechanically excited shear waves of soft gels in cylindrical cuvettes[8]. By solving a set of modified elasticity equations, they were able to show how the measured frequencies depended both on the material properties of a sample and on the dimensions of the sample's container. Using the observed resonances during inelastic light scattering, they were able to calculate the transverse sound speed and from that, the shear modulus of a sample. | |
