A set of special samples for surface anal. were prepared by bonding various functional groups with different polarity on the surface of porous amorphous silica gels. The lifetimes of positrons in these samples were measured. The short lifetime fractions associated with positron annihilation in the bulk phase remain constant for all samples studied, while the long lifetime fractions corresponding to ortho-Ps annihilation in the pores on the surface are different due to the different groups bonded on surface. The longest lifetime fraction was correlated with the polarity and the size of the bonded functional group. The longest lifetimes fraction can characterize the surface polarity and/or chem. properties of the sample. Positron annihilation spectroscopy is a potential technique for qual. surface chem. anal.

Key words: SURFACE CHEMISTRY, SILICA GEL, LIFE, BONDED, POSITRON ANNIHILATION