(A) surface hydrodynamics study on soft matter materials

Abstract

Soft matter materials show intermediate mechanical properties which include those of solid and liquid. Their interesting characteristics come from the flexibility of a long chain molecule or amphiphilic nature. These materials constitute our daily environment as well as the human body. This motivates diverse research and applications in petroleum industry, pharmacy, and bio-medical. In this dissertation, the author adopts various soft matter materials and geometry and explores their surface hydrodynamic properties. At first, surface waves on semi-infinite viscoelastic medium were studied from the externally excited surface wave spectroscopy on agarose gels. He observed two coexisting elastic modes in the frequency region of crossover from elastic to capillary mode. The coexistence of two modes was explained based on the theory of elasticity. Moreover, differing from common solid, the viscous loss of soft matter materials enhances the two modes to be comparable. His second topic relates to more realistic cases: confined geometries. He measured surface waves propagating on thin gels with thicknesses less than 1 cm. In the frequency region where the elastic and surface tension forces dominate, multiple harmonics of a surface mode are predicted theoretically for a finite thickness due to a coupling with the normal direction wave to the surface. This result shows the first experimental measurement of the multiple harmonics of a surface mode. He compared the experimental data with the theoretical calculation. Finally, charged monolayers adsorbed by opposite charged macromolecules at an air-water interface were studied. He explored their structure-related thermodynamic and surface hydrodynamic properties. Using the enhanced damping of the capillary wave by energy dissipation due to the presence of an elastic monolayer, the cationic lipid-DNA complex formation could be sensitively observed.