title: Reversible negative thermal expansion of polymer films.
abstract: A basic understanding of the properties of thin polymer films is of fundamental importance for developing applications in nanotechnology. Results of energy and angle dispersive x-ray reflectivity measurements on polymer thin films as a function of temperature exhibit reversible negative thermal expansion below the glass transition temperature T(g). Above T(g), the thickness expansion becomes almost equal to the expected bulk volume expansion. These results could be explained on the basis of evolution of disorder with temperature at the interfaces, chain entanglement and associated entropy changes.
authors.affiliation: Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700 064, India.
authors.forename: M
authors.initials: M
authors.lastname: Mukherjee
authors.forename: M
authors.initials: M
authors.lastname: Bhattacharya
authors.forename: M K
authors.initials: MK
authors.lastname: Sanyal
authors.forename: Th
authors.initials: T
authors.lastname: Geue
authors.forename: J
authors.initials: J
authors.lastname: Grenzer
authors.forename: U
authors.initials: U
authors.lastname: Pietsch