System of measuring mechanical properties of colloidal gels with optical tweezers.

摘要

Due to the unique rheological properties of colloidal gels, gelation of colloidal suspensions has become increasingly important to fundamental investigations, as well as to technological applications. Recent experimental approaches are mainly focused on the bulk properties of colloidal gels, using methods of static and dynamic light scattering and shear rheometry. This thesis describes the development of a system for measuring the mechanical properties of colloidal gels with optical tweezers.;We successfully assembled the main instrument, a time-sharing single beam optical tweezers, and calibrated the lateral stiffness of the optical trap. Our optical tweezers setup is used to study the polystyrene gel and it has many more applications in colloidal samples. The strong 3D optical trapping highlights the optical tweezers as a powerful technique suitable for further investigation of colloidal samples.;We make colloidal gels out of polystyrene beads of two different sizes, diameters of 3.5mum or 62nm respectively. Investigation of the colloidal gels under the light microscope shows the fractal nature of the gel structure while macroscopic study confirms that the gelation process of the smaller polystyrene beads is faster than that of the bigger polystyrene beads. We were also able to generate a phase diagram of the gelation process.