Imaging Single Nano-droplets With Surface Plasmon Resonance Microscopy

The optically excited collective electronic oscillation through the interaction between metals and incident light form the propagating surface plasmon resonance(SPR)existing at the interface between any two materials where the real part of the dielectric function changes sign across the interface(e.g.a metal-dielectric interface).Recently SPR-based techniques have been widely used in the label-free imaging of single nanoparticles.The optical contrast depends on the dielectric constant(refractive index)of nanoparticles.As refractive index is an intrinsic physical property of any kind of nanomaterials,SPRM is suitable to image individual nanobubbles and nanodroplets,whose molecular spectroscopy features are often poor.We summarize the major results and conclusion of this thesis below:1.Research on the preparation and properties of decane nano-dropetsSurface nanobubbles have attracted great attentions because of its unique values in surface physical chemistry as well as its important applications in flotation and chemical engineering.In order to clarify the nucleation and dissolution kinetics of nanobubbles,nanodroplets are often considered as an important analog because they are intrinsically similar and it is experimentally feasible to prepare nanodroplets compared with nanobubbles.In Chapter 2,we prepare surface nanodroplets with solvent exchange method,and demonstrate the capability of SPRM to visualize individual nanodroplets.2.Research on the time evolution of surface decane nanodroplets.The evolution of surface nanodroplet strongly depends on the physical chemistry properties of the liquid-substrate interface.After striking onto the substrate,nanodroplet could exhibit different behaviors including adsorption,desorption,dissolution and diffusion.Atomic force microscopy(AFM)has been one of the most powerful technologies to characterize nanodrplet.However,it remains challenging for AFM to monitor the fast dynamical process because of its limited temporal resolution.In Chapter 3,we use SPRM to investigate the influences of surface property on the dynamical behaviors of individual decane nanodroplets in aqueous solution.We were able to measure the diffusion coefficient of decane molecules on a hydrophobic interface.Based on the experimental results,a surface energy accelerated dissolution theory was proposed to understand the influence of surface property on the dissolution kinetics of nanodroplets.