Studies of Electrokinetics and Grain Boundary Phase Transition

摘要

Soft matter is an important subject very relevant to our daily life. It is regarded to be a link connecting physics with chemistry and biology, so the research objects of soft matter is very rich and broad. In this thesis, I will focus on two interesting problems in soft matter, namely electrokinetics and fluctuations of interface.;The study of electrokinetics is a branch with a long history. When a channel is immersed in an electrolyte, the channel surface acquires surface charge. A surface potential trap model is proposed to simplify the understanding on charged surface with only one adjustable parameter. This model gives many reasonable predictions consistent with experiments as described in Chapter 2. In Chapter 3, through experiments of optical tweezers coupled with quadrant photodiode and lock-in amplifier, we have uncovered a complex flow field comprising a ring of vortices around the equatorial plane of the spherical particle, joined by an outer flow field that is well accounted for by previous asymptotic mathematical analysis. The interface between the outer and inner flow fields turns out to be the location where one finds consistency and balance between the Smoluchowski local electroosmotic flow as well as the measured effective charge and non-Stokes drag coefficients.;The study of the dynamics of solid-solid interfaces is presented in Chapter 4. We directly visualize the roughening dynamics of grain boundaries inside bulk thin-film colloidal crystals at the single-particle level by using video microscopy. The thermal fluctuations of grain boundaries share some similarities with capillary waves and exhibit both static and dynamic critical behaviors. The rich phenomenology provides guidance for better control of microstructures in polycrystals and further refinement of theories.