Role of Interfacially Active Diblock Copolymers toward Controlling the Glass Transition of Thin Polymer Films

We show that small concentrations of polystyrene-b-polymethylmethacrylate (PS-b-PMMA) diblock copolymers significantly alter the thickness, h, dependence of the glass transition of polystyrene (PS) films supported by silicon substrates. The T$_{g}$ can be induced to increase, or decrease, with decreasing h or to be independent of h. T$_{g}$-shifts of as much of 35\r{ }C are obtained for films h $<$ 30 nm. The copolymers form micelles and the critical micelle concentration ($\phi _{cmc})$ of the copolymer in the thin films is considerably larger than for the bulk, larger than 15{\%}. In fact micelles form only beyond a critical film thickness, determined by the size of the chains and by the number of chains required to saturate the interfaces.