Positron lifetime study of poly(dimethylsiloxane) based polymer-nanoparticle composites

Abstract

Positron annihilation lifetime spectroscopy was employed to study the changes in the size of the local free volume elements (holes) of poly(dimethylsiloxane) (PDMS) based nanocomposites incorporating two different types of nanoparticles, meta-carborane (m-CB) and iso-octyl polyhedral oligomeric silsesquioxane (POSS). Materials were prepared with various loading levels of each nanoparticle and the temperature dependence of the o-Ps lifetime, and thus the free volume, and its distribution were measured from 100-300 K. It was observed that m-CB reduces the size of the local free volume elements while POSS has the opposite effect, in each case the change is only seen in the rubbery state below the so-called "knee temperature" (Tk ∼ 210 K).