(324f) Temperature-Step Dewetting of Ultrathin Polymer Films: A Rapid Means to Tg Determination

The determination of the glass transition temperature of polymer films as a function of film thickness can be tedious and time consuming because the general methods of measurement of the properties of ultrathin polymer films have required a new sample for every determination of Tg as a function of thickness h. Here we show a novel temperature-step rheological method that overcomes this difficulty. We build upon the methods of Bodiguel and Fretigny [1] for determination of the viscoelastic response of ultrathin polymer films to develop a temperature-step dewetting procedure that gives the Tg-h relationship for multiple values of h from a single measurement. In principle, one can make a single measurement that provides the same information as do 10 to 15 individual measurements with current methods. We will demonstrate the method and provide new results for polystyrene and polycarbonate dewetting from glycerol and from an ionic liquid.  The results show that the Tg reduction of films floating on glycerol is greater than that for films floating on the [BMIM][OTf] ionic liquid, but that in both instances the reductions are less than observed for the same materials supported on SiO₂ rigid substrates. The results suggest that the T_g - thickness effects observed in ultrathin films are very subtley dependent on surface energy but not on the surface mobility or rigidity.

[1] H. Bodiguel and C. Fretigny, Phys. Rev. Lett., 97, 266105 (2006).

This work is supported by the J.R. Bradford Endowment at TTU and by the National Science Foundation under grants DMR-0804438 and DMR-1207070.