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, Tg (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 Tg (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
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- Tg (D, 0) / Tg (∞, 0) ∝ σg2 (∞, 0) / σg2 (D, 0)
where σg is the root of mean squared displacement of surface and interior molecules of glasses at Tg (D, 0), α = σs2 (D, 0) / σv2 (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.
Read more about this topic: Polymer Nanocomposite
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