论文信息 - Thickness dependence of the dynamics in thin films of isotactic poly (methylmethacrylate)

Thickness dependence of the dynamics in thin films of isotactic poly (methylmethacrylate)

Abstract.The film thickness dependence of both the glass transition temperature (Tg) and the 1 kHz alpha relaxation were studied for thin films of isotactic Poly (methylmethacrylate) (i-PMMA) supported on aluminium substrates. Films in the thickness range 7-200 nm were studied. The ellipsometrically determined Tg was found to show reductions for films thinner than 60 nm, with the largest observed reduction being 12 K for a 7 nm thick film. Measurements of the Tg were also performed on i-PMMA films supported on silicon substrates. Dielectric studies of the temperature dependent 1 kHz alpha relaxation peak, showed that the position (Tα) and shape of the peak have no film thickness dependence. This was shown to hold for films with one free surface and films with a 30 nm thermally evaporated capping layer. Capping the films was shown to have no effect on the thickness dependence of either Tg or Tα. The implications of these results are discussed further and the different film thickness dependencies of Tg and Tα are discussed. This is done within the framework of the Vogel-Fulcher-Tamann (VFT) theory of glass forming materials and also in the context of the existence of a dynamic correlation length ξ.

J. Forrest | J. S. Sharp | J S Sharp | J A Forrest

[1] F. Kremer,et al. How many molecules form a liquid , 1999 .

[2] Forrest,et al. Quantifying glass transition behavior in ultrathin free-standing polymer films , 2000, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[3] Y. Grohens,et al. Some relevant parameters affecting the glass transition of supported ultra-thin polymer films , 2002, The European physical journal. E, Soft matter.

[4] J. Forrest,et al. Dielectric and ellipsometric studies of the dynamics in thin films of isotactic poly(methylmethacrylate) with one free surface. , 2003, Physical review. E, Statistical, nonlinear, and soft matter physics.

[5] P. Nealey,et al. Dependence of the Glass Transition Temperature of Polymer Films on Interfacial Energy and Thickness , 2001 .

[6] F. Kremer,et al. Length Scale of Cooperativity in the Dynamic Glass Transition , 1997 .

[7] Vlachos,et al. Nanoscopic-confinement effects on local dynamics , 2000, Physical review letters.

[8] F. Kremer,et al. Molecular dynamics in thin films of isotactic poly(methyl methacrylate) , 2002, The European physical journal. E, Soft matter.

[9] E. Donth. The size of cooperatively rearranging regions at the glass transition , 1982 .

[10] Richard A. L. Jones,et al. Polymers at Surfaces and Interfaces , 1999 .