Glass transition temperature of freely-standing films of atactic poly(methyl methacrylate)

We have used ellipsometry to measure the glass transition temperature T g of high molecular weight (M w =790 × 103), freely-standing films of atactic poly(methyl methacrylate) (a-PMMA), as well as films of the same polymer supported on two different substrates: the native oxide layer of silicon (Si) and gold-covered Si. We observe linear reductions in T g with decreasing film thickness h for the freely-standing PMMA films with 30 nm <h<100 nm, which is qualitatively similar to previous results obtained for freely-standing polystyrene (PS) films. However the magnitude of the T g reductions for PMMA is much less than for freely-standing films of PS of comparable molecular weight and thickness. We also find that for films supported on either substrate, with thicknesses as small as 30 nm, the T g values do not deviate substantially from the value measured for thick films

Dielectric relaxations in ultrathin isotactic PMMA films and PS-PMMA-PS trilayer films

The local and cooperative dynamics of supported ultrathin films (L = 6.4 - 120 nm) of isotactic poly(methyl methacrylate) (i-PMMA, $\overline{M}_n = 118\times10^3$ g/mol) was studied using dielectric relaxation spectroscopy for a wide range of frequencies (0.1 Hz to 106 Hz) and temperatures (250 - 423 K). To assess the influence of the PMMA film surfaces on the glass transition dynamics, two different sample geometries were employed: a single layer PMMA film with the film surfaces in direct contact with aluminum films which act as attractive, hard boundaries; and a stacked polystyrene-PMMA-polystyrene trilayer film which contains diffuse PMMA-PS interfaces. For single layer films of i-PMMA, a decrease of the glass transition temperature T g by up to 10 K was observed for a film thickness L < 25 nm (comparable to R EE ), indicated by a decrease of the peak temperature T α in the loss ε ″(T) at low and high frequencies and by a decrease in the temperature corresponding to the maximum in the apparent activation energy E a (T) of the α-process. In contrast, measurements of i-PMMA sandwiched between PS-layers revealed a slight (up to 5 K) increase in T g for PMMA film thickness values less than 30 nm. The slowing down of the glass transition dynamics for the thinnest PMMA films is consistent with an increased contribution from the less mobile PMMA-PS interdiffusion regions

Elastic and elasto-optic properties of thin films of poly(styrene) spin coated onto Si(001)

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Glass transition reductions in thin freely-standing polymer films : A scaling analysis of chain confinement effects

In this paper we present a new analysis of data on the reduced glass transitions observed in thin freely-standing films. The empirical analysis presented is highly suggestive of the existence of a mechanism of mobility in thin freely-standing films that is inhibited in the bulk and distinct from the usual cooperative motion near the glass transition temperature Tg. A tentative mechanism for Tg reductions in thin freely-standing films is discussed

Light-scattering observation of surface acoustic modes in high-order Brillouin zones of a Si(001) grating

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