Confinement effects on the glass transition of hydrogen bonded liquids

The glass transition behavior of glycerol and propylene glycol confined in nanoporous glass is investigated using differential scanning calorimetry. Both silanized and unsilanized porous glasses are used to confine the liquids with nominal pore sizes ranging from 2.5 to 7.5 nm, and the glass transition temperature (T(g)) and the limiting fictive temperature (T(f )') are measured on cooling and heating, respectively. The effect of pore fullness is also examined. We find that differences in T(g), DeltaC(p), and the enthalpy overshoot behavior observed on heating are significant between partially and completely filled pores for the case of the unsilanized controlled pore glasses (CPGs) but that the effect of pore fullness is insignificant for the silanized CPGs. In general, the behavior in the silanized CPGs is similar to the behavior in the completely filled unsilanized pores. For glycerol, this includes a small depression in T(f )' on the order of 5 K at 2.5 nm. For propylene glycol, similar behavior is found except that an additional glass transition is observed in both silanized and unsilanized systems approximately 30 K higher than the bulk and a slightly smaller depression on the order of 3 K at 2.5 nm is observed in the completely filled unsilanized pores and in partially and completely filled silanized pores. The results are compared to those in the literature, and the confinement effects are discussed.