Polymer Nanocomposite - Size and Pressure Effects On Nanopolymers

Size and Pressure Effects On Nanopolymers

The size- and pressure- dependent glass transition temperatures of free-standing films or supported films having weak interactions with substrates decreases with decreasing of pressure and size. However, the glass transition temperature of supported films having strong interaction with substrates increases of pressure and the decrease of size. Different models like two layer model, three layer model, T_g (D, 0) ∝ 1/D and some more models relating specific heat, density and thermal expansion are used to obtain the experimental results on nanopolymers and even some observations like freezing of films due to memory effects in the visco-elastic eigenmodels of the films, and finite effects of the small molecule glass are observed. To describe T_g (D, 0) function of polymers more generally, a simple and unified model recently is provided based on the size-dependent melting temperature of crystals and Lindemann's criterion

T_g (D, 0) / T_g (∞, 0) ∝ σ_g2 (∞, 0) / σ_g2 (D, 0)

where σ_g is the root of mean squared displacement of surface and interior molecules of glasses at T_g (D, 0), α = σ_s2 (D, 0) / σ_v2 (D, 0) with subscripts s and v denoting surface and volume, respectively. For a nanoparticle, D has a usual meaning of diameter, for a nanowire, D is taken as its diameter, and for a thin film, D denotes its thickness. D₀ denotes a critical diameter at which all molecules of a low dimensional glass are located on its surface.