We have studied various complex systems from particle and biopolymer gels to concentrated surfactant solutions using classical rheometry and optical microrheology. Optical microrheology uses dynamic light scattering, usually in the multiple scattering regime, to obtain information about the microscopic dynamic properties of complex media. This can be done either by direct investigation or by addition of tracer particles to otherwise transparent systems. Based on the local dynamics the macroscopic viscoelastic properties are predicted. We have implemented several new approaches to extend the range of application for optical microrheology
Taking advantage of the recently developed “two-cell technique” we will show how dynamic multiple light scattering (Diffusing Wave Spectroscopy) can be used to investigate the properties of fluid and solid-like media. Furthermore we have significantly extended the range of accessible correlation times to 10-8>–104> s using a CCD based multispeckle analysis scheme. Our experiments cover such different materials as polystyrene latex dispersions and gels, ceramic green bodies, casein micellar gels (yogurt) and giant micelle solutions. Excellent quantitative agreement is found when comparing the results obtained from DWS to classical rheological measurements. However, compared to classical rheology, we were able to significantly increase the range of accessible frequencies using optical microrheology, thereby opening up a wealth of new possibilities for the study of these fascinating materials.