ABSTRACT
There is a major interest in the behavior of amorphous polymers at the nanometer-size scale primarily due to the discovery [1-3] that glass-forming liquids, including polymers [4-9], when constrained to dimensions of approximately 100 nm or less, exhibit strong deviations in the glass transition temperature from the properties observed in the bulk material. There have been different reports concerning the glass transition temperature in confined systems, and it can increase, decrease, or remain the same depending upon the details of the experiment. In the case of liquids in porous media or polymers supported on a substrate, the strength of the interactions between the confining and confined media seems to have a very strong influence. Increases in the Tg relative to the bulk value are related to strong interactions while decreases are related to weaker interactions, though it has been reported that both an increase and a decrease can occur in the same film but from
6.1 Introduction 205
6.2 Viscoelastic response of polymers at the macroscopic-size scale 206
6.2.1 Stress relaxation modulus 206
6.2.2 Dynamic moduli and creep compliance 209
6.3 Membrane inflation 210
6.3.1 Membrane equations 212
6.3.2 Elastic analysis 213
6.3.2.1 Stress-strain approach 213
6.3.2.2 Energy balance approach 215
6.3.3 Viscoelastic analysis 217
6.4 Spontaneous particle embedment 223
6.4.1 Elastic analysis 223
6.4.2 Particle characterization 224
6.4.3 Particle embedment measurements and modulus determinations 224
6.4.4 Viscoelastic analysis 228
6.4.4.1 Isochronal results 229
6.4.4.2 Viscoelastic results 230
6.5 Summary and perspectives 235
Acknowledgments 236
References 236
different measurements, for example, thickness dilatometry versus temperature and inelastic neutron scattering [10,11] on the same samples. In the case of freely standing polymer films, it seems that nearly all, but not all, reports to date suggest a reduction in the glass transition temperature [7-9,12-19], with such reductions being reported [20] to be as much as 122°C, for extremely thin films of polycarbonate.
