Vitrification and crystallization of organic liquids confined to nanoscale pores

The effect of finite size on the solidification of o-terphenyl and benzyl alcohol confined in model controlled pore glass (CPG) materials is described. These two organic liquids form either amorphous glasses or crystalline solids in the bulk upon cooling, depending on the rate of cooling and other factors. The solidification behavior of the liquid in the pores was studied as a function of pore diameter (4-73 nm), chemical surface treatment of the CPG and the degree of pore filling, by differential scanning calorimetry (DSC). We observe that the glass transition, T_g, shifts to a lower temperature as pore size decreases. This shift is independent of the degree of pore filling for both o-terphenyl and benzyl alcohol, suggesting that a reduction in bulk density or a negative pressure effect is not the cause of the observed shift. The crystallization behavior of o-terphenyl and benzyl alcohol is also altered by confinement and strongly depends on the pore size and degree of pore filling.