Confocal laser scanning microscopy and laser light scattering: applications in soft matter and technological materials

Abstract

The availability of laser light sources and powerful low-cost computer data processing and imaging systems have helped in popularizing the confocal laser scanning microscope because it rejects light that does not come from the focal plane, enabling one to perform optical slicing and construction of three-dimensional (3D) images. Because of this unique feature, CLSM is now finding wider applications in the study of a variety of materials and process such as crystallization and glass transition in colloidal systems, phase separation in polymer blends, fracture toughness in alloys and microvisualization of corrosion. This paper reviews some of these recent applications and also discusses our results in providing evidence for long-range attraction between like-charged particles and for the occurrence of gas-solid transition in highly charged colloidal systems. Apart form colloids, other macromolicular systems (e.g., gels, surfactant systems, membranes etc.) that constitute soft matter are characterized by building blocks essentially causes the materials to be soft (i.e. elastic constants of the order of 10-100 dynes/cm²) and dynamics to be very slow (~ microseconds to several seconds). The information with regard to the structure and dynamics at the lower end of length and time scales in the soft matter can be obtained using laser light scattering (photon correlation spectroscopy) and that at the higher end using CLSM. By combining judiciously the two techniques, we have investigated charged colloidal systems for their structure, dynamics and phase behavior and these results are discussed in this paper.