Reorientational relaxations in confined PPG by Rayleigh wing studies

We present experimental depolarized light scattering (DLS) results per form ed in propylene glycol (PG) and its oligomers polypropylene glycol (PPG) at different molecular weight 425, 725 and 4000, confined in 25 Angstrom pore s of a sol-gel silica glass. The goal is to study the influence of the conf inement on the molecular mobility of hydrogen-bonded liquids with identical chemical composition but different steric hindrance. Furthermore, eve also studied the behaviour of this kind of intermolecular interaction thanks to the opportunity to control the number of active silanol group (Si-OH) and non-active (Si-OCH3) groups on the porous inner surfaces. In particular the removing of the OH groups in the inner surface represents an important too l to elucidate its role on the confined polymer dynamics. Comparing the obt ained results performed on the hydrogen-bonded liquids in the active and no n-active surfaces, the main role played by the original Si-OH surface an th e studied dynamics is showed. Furthermore the reorientational dynamics in c onfined samples exhibit a noticeable slowing down compared with the corrisp ective in the bulk samples.