Mobility and glass transition temperature of polymer nanospheres

Recent studies have illustrated a decoupling between cooperative segmental mobility and the glass transition temperature (Tg) of thin polymer films and nanocomposites. Here, we use dielectric spectroscopy to probe the cooperative segmental mobility and capacitive dilatometry to determine the Tg of films of polystyrene nanospheres with diameters (d) less than 400 nm. We find that both capacitive dilatometry and calorimetry revealed nearly identical suppressions in Tg as the size of the nanospheres was reduced. While Tg was impacted by confinement, in the range 130 nm ≤ d ≤ 400 nm, in stark contrast, the cooperative segmental mobility, i.e., the peak position of the α-relaxation process was not. Furthermore, when d ≤ 200 nm, an additional molecular relaxation process, not observed in bulk, was present. We interpret these findings as evidence of a decoupling between Tg and cooperative segmental mobility in nanospheres. That is, the latter may be impacted by confinement under conditions in which the former is not.We acknowledge usage of the PRISM Imaging and Analysis Center, which is supported in part by the NSF MRSEC program through the Princeton Center for Complex Materials (DMR-0819860). C.Z. acknowledges support by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG). R.D.P. acknowledges the donors of the American Chemical Society Petroleum Research Fund (PRF 49903-DNI10) and the 3M-nontenured faculty grant program for partial support of this work. V.M.B and D.C. acknowledge the University of the Basque Country and Basque Country Government (Ref. No. IT-436-07, Depto. Educación, Universidades e investigación) and Spanish Minister of Education (Grant No. MAT 2007-63681) for their financial support. V.M.B. acknowledges CSIC for the JAE-Doc contract, co-financed by the European Social Fund (ESF).Peer Reviewe