Positronium annihilation and pore surface chemistry in mesoporous silica films

Lifetimes of ortho-positronium in mesoporous silica films were measured before and after surface trimethylsilylation of –OH groups. Variations of positronium lifetimes in the mesopores upon the surface modification indicate that the interaction between positronium and the pore surface is weakened in the pores, whose surface is covered with –CH3 groups, in comparison with those covered with –OH groups. This is consistent with the authors’ previous observation that positronium slowing down is less efficient in the pores covered with –CH3 groups. The present work demonstrates that in the porosimetric application of positron annihilation lifetime spectroscopy, the interaction between positronium and the pore surface has to be properly taken into consideration.