Direct estimation of the electrostatic interaction between colloidal particle and chemically modified glass surface by the evanescent wave light scattering microscope method

The profile of the interaction potential between polystyrene latex particle and chemically modified glass surface was estimated directly by the evanes cent wave light scattering microscope (EVLSM) method; this enables us to me asure the distance between particle and surface as a function of time in th e order of less than a millisecond. The minimum of the potential profile, w hich is the result of an electrostatic repulsion and an apparent attraction by gravity between the particle and surface, was clearly observed. To chan ge the electrostatic nature, the glass surface was chemically modified by t reatment with a silanization reagent and a vinylmonomer with a sulfonate gr oup. As the absolute value of the zeta potential of the glass surface becam e larger, the position of the potential minimum on the interaction potentia l profile shifted away from the glass surface, reflecting an increase of el ectrostatic repulsion between the particle and the wall. The ionic strength dependence of the potential profile was also clearly observed. In conclusi on, EVLSM is a powerful tool for the quantitative estimation of particle-wa ll interactions.