Thickness dependence of structural relaxation in spin-cast, glassy polymer thin films

Abstract

The isothermal structural relaxation of glassy, spin-cast polymer thin films has been investigated. Specifically, the thickness h of freshly cast poly(methyl methacrylate) thin films was measured over time using spectroscopic ellipsometry. The spin-cast films exhibit a gradual decrease in thickness, which is attributed to structural relaxation of the glass combined with simultaneous solvent loss. In all cases, h was found to be greater than the equilibrium thickness h ϱ , which is obtained by cooling slowly from the melt. It is observed that both the rate of the volume relaxation and the fractional departure from h ϱ (referred to as ␦ 0 ) increase with increasing film thickness. In the limit of very thin films, the initial h is close to h ϱ , and ␦ 0 is small, whereas in thick films ͑Ͼ500 nm͒, a plateau value of ␦ 0 of 0.16 is observed, which is close to the volume fraction of the solvent at the vitrification point. This dependence of ␦ 0 on thickness is observed regardless of the substrate, polymer molecular weight, or angular velocity during spin casting. Enhanced mobility near film surfaces could be leading to greater relaxation in thinner films prior to, and immediately after, the vitrification of the polymer during the deposition process.

Adhesion of microorganisms to bovine submaxillary mucin coatings: effect of coating deposition conditions

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Characterization of thick film poly(triarylamine) semiconductor diodes for direct x-ray detection

“…Solvent loss and the accompanying structural relaxation are exceedingly slow in glassy films at sub-T g temperatures. 37 In the preparation of the diodes used here, the PTAA was annealed above its T g to allow any solvent trapped inside the film to escape. To examine the solvent loss from the PTAA films, TGA was employed ͓Fig.…”

Influence of drying procedure on glass transition temperature of PMMA based nanocomposites

“…For an amorphous polymer such as PMMA, with a high glass transition temperature, it was shown that a glassy material is obtained once the solvent fraction in the film is less than 0.19, and the formation of the glass will considerably decrease the evaporation rate of the solvent. 44,45 The amount of retained solvent in different cast films was studied by several groups. 44,45,[47][48][49] García-Turiel and Jé rô me 47 used gas chromatography to study solvent retention in PS films spin cast from toluene.…”

“…44,45 The amount of retained solvent in different cast films was studied by several groups. 44,45,[47][48][49] García-Turiel and Jé rô me 47 used gas chromatography to study solvent retention in PS films spin cast from toluene. They concluded that while in thick films, there are only a few percent of solvents left after annealing at a temperature above the glass transition temperature, the amount of retained solvent can be much higher in thin films.…”