Tuneable micro- and nano-periodic structures in a free-standing flexible urethane/urea elastomer film |
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Authors: | M H Godinho A C Trindade J L Figueirinhas L V Melo P Brogueira A M Deus P I C Teixeira |
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Institution: | (1) Departamento de Ciência dos Materiais and CENIMAT, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, P-2829-516 Caparica, Portugal;(2) Centro de Fısica da Matéria Condensada, Universidade de Lisboa, Avenida Professor Gama Pinto 2, P-1649-003 Lisbon, Portugal;(3) Departamento de Fısica, Instituto Superior Técnico, Avenida Rovisco Pais, P-1049-001 Lisbon, Portugal;(4) ICEMS, Instituto Superior Técnico, Avenida Rovisco Pais, P-1049-001 Lisbon, Portugal;(5) Departamento de Engenharia de Materiais, Instituto Superior Técnico, Avenida Rovisco Pais, P-1049-001 Lisbon, Portugal;(6) Faculdade de Engenharia, Universidade Católica Portuguesa, Estrada de Talaıde, P-2635-631 Rio de Mouro, Portugal |
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Abstract: | We have studied the control and manipulation of tuneable equilibrium structures in a free-standing urethane/urea elastomer
film by means of atomic force microscopy, small-angle light scattering and polarising optical microscopy. The urethane/urea
elastomer was prepared by reacting a poly(propyleneoxide)-based triisocyanate-terminated prepolymer (PU) with poly(butadienediol)
(PBDO), with a weight ratio of 60% PU/40% PBDO. An elastomer film was shear-cast onto a glass plate and allowed to cure, first
in an oven, then in air. Latent micro- and nano-periodic patterns are induced by ultra-violet (UV) irradiation of the film
and can be “developed” by applying a plane uniaxial stress or by immersing the elastomer in an appropriate solvent and then
drying it. For this elastomer we describe six pattern states, how they are related and how they can be manipulated. The morphological
features of the UV-exposed film surface can be tuned, reproducibly and reversibly, by switching the direction of the applied
mechanical field. Elastomers extracted in toluene exhibit different surface patterns depending upon the state in which they
were developed. Stress-strain data collected for the films before and after UV irradiation reveal anisotropy induced by the
shear-casting conditions and enhanced by the mechanical field. We have interpreted our results by assuming the film to consist
of a thin, stiff surface layer (“skin”) lying atop a thicker, softer substrate (“bulk”). The skin's higher stiffness is hypothesised
to be due to the more extensive cross-linking of chains located near the surface by the UV radiation. Patterns would thus
arise as a competition between the effects of bending the skin and stretching/compressing the bulk, as in the work of Cerda
and Mahadevan (Phys. Rev. Lett. 90, 074302 (2003)). We present some preliminary results of a simulation of this model using the Finite Element package ABAQUS. |
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Keywords: | 61 41 +e Polymers elastomers and plastics 62 25 +g Mechanical properties of nanoscale materials 82 20 Wt Computational modeling simulation |
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