Measuring slow relaxation and stability in vapor deposited stable polymer glasses

Recent work in our lab allows us to create stable polymer vapor deposited glasses of polystyrene with N up to ~12, with kinetic stability observed down to deposition temperatures of ~0.84*T_g.  These stable vapor deposited polymer glasses have fictive temperatures as low as T_g - 20 K relative to the supercooled liquid line for glasses of polystyrene of the same N.  Previous measurements on stable molecular glasses suggests that annealing above the deposition temperature rejuvenates the glass, at least partially, forming a less stable glass apparently similar to a conventional glass formed by cooling an equilibrium liquid.  This rejuvenation behavior of the glasses may be interpreted as the glass moving up through a metabasin of the potential energy landscape.  Physical aging measured by ellipsometry has been used as a direct measurement of stability in conventional polymer glasses, but not stable polymer glasses.  We explore here the physical aging behavior of stable vapor deposited, aged, and rejuvenated polymer glasses (N>9 and a T_g = 308 K).  Slow relaxation dynamics are measured and compared with measurements of stability before and after rejuvenation in vapor deposited PS and PMMA films.