Dewetting Rheology for Determining Viscoelastic Properties of Nonequilibrated Thin Polymer Films

Abstract

We performed systematic dewetting experiments on isotactic poly(para-methylstyrene) (iPpMS) films to explore the temperature dependence of the viscoelastic behavior of these films. We quantified the amount of residual stresses σ res induced through film preparation by spin-coating. As anticipated, σ res was found to be independent of the temperature T dew at which dewetting was done. A particular focus was on the temperature dependence of the relaxation time τ of σ res , which was measured with the help of three independent dewetting parameters. Within error, all three values of τ were identical and followed an Arrhenius behavior yielding an activation energy of 60 ± 10 kJ/mol. The initial dewetting velocity, being proportional to the ratio of surface tension of iPpMS and the corresponding viscosity, increased significantly with T dew . Assuming a linear stress−strain response, we deduced that the elastic deformation responsible for the maximum height of the dewetting rim increased with temperature, although σ res did not vary with temperature. Correspondingly, the shear modulus of iPpMS films was found to decrease monotonically with increasing temperature. Using a Maxwell-type model, the corresponding viscosity of the film showed the expected decrease with increasing temperature. Our experiments suggest that preparationinduced residual stresses affect material properties such as elastic modulus or viscosity of iPpMS as a function of temperature.

Dewetting Dynamics of Sheared Thin Polymer Films: An Experimental Study

“…They also have been thoroughly examined both from a theoretical and experimental point of view. [8][9][10][11][12] The effects of viscoelasticity, 13 slip 14 or residual stresses 15 have been considered, as such films find many industrial applications in conformal, protective, optical or functional coatings [16][17][18][19] and electrical films. 20 A case less studied is the stability of multilayer structures, i.e.…”

Rheological Properties of Blends of Isotactic Polystyrene–Isotactic Poly(para-methylstyrene) Films Derived from a Comparative Dewetting Study

“…As in previous dewetting experiments, we used the same iP p MS [weight average molecular weight, M w = 608 kDa, a dispersity D̵ = 2.19, a glass-transition temperature T g ≈ 110 °C, and a nominal melting temperature T m around (220–240 °C)] , and isotactic polystyrene (iPS) [ M w = 400 kDa, D̵ = 2.8, T g ≈ 95 °C, T m = 220 °C]. ,− …”

“…Poly­( para- methylstyrene) differs from polystyrene by a nonpolar methyl group introduced at the para -position (position 4) of the phenyl ring of styrene monomers . The miscibility, crystallization, thermal and structural dynamics of iPS, and blends of iPS with other polymers have widely been investigated, − but only a few studies have focused on iP p MS. , Methylstyrene monomers as opposed to styrene monomers may improve the performance of polymer materials in terms of material strength, chemical modification, and stability. − Although iP p MS can crystallize, its melting temperature has not been clearly identified. ,, Previous dewetting experiments on iP p MS films and related works have revealed an activation energy of molecular relaxation processes that is somewhat lower than the ones observed for both atactic and isotactic PS. , …”

Functional morphology of plants – a key to biomimetic applications

“…Moreover, scientists are currently studying the development, structure and properties of multifunctional complex plant surface structures at a fundamental level and are creating functional polymeric materials and surfaces based on the functional principles of plants. Cuticles are concept generators for the regulation of water permeability (Mulama et al, 2019), structural colours (Moyroud et al, 2017) and sticky or nonfriction surfaces (Bergmann et al,…”

“…Moreover, scientists are currently studying the development, structure and properties of multifunctional complex plant surface structures at a fundamental level and are creating functional polymeric materials and surfaces based on the functional principles of plants. Cuticles are concept generators for the regulation of water permeability (Mulama et al ., 2019), structural colours (Moyroud et al ., 2017) and sticky or nonfriction surfaces (Bergmann et al ., 2020). The moving‐by‐growing abilities of climbing plants have become models for the development of low‐mass and low‐volume robots capable of anchoring themselves, negotiating voids and more generally climbing (Fiorello et al ., 2020; Mazzolai et al ., 2020).…”