期刊
JOURNAL OF NON-CRYSTALLINE SOLIDS
卷 357, 期 2, 页码 580-586出版社
ELSEVIER
DOI: 10.1016/j.jnoncrysol.2010.06.057
关键词
Langmuir films; Surface rheology; Out of equilibrium mechanical properties; Photosensitive polymers; Azobenzene
We report the details of the construction and calibration of a sensitive surface rheometer, inspired by an instrument described in the literature, adapted to the study of photosensitive polymeric materials. By high resolution video tracking of the motion of a floating magnetized needle we are able to measure the viscoelastic complex shear modulus G of a Langmuir monolayer with an accuracy of 5*10(-6) N/m. This instrument is then employed for the rheological characterization of a Langmuir monolayer of a photosensitive azobenzene polymer, which can be brought out of equilibrium by a suitable photoperturbation. The shear modulus is measured as a function of temperature, illumination power and wavelength. The reversible rheological changes induced in the film by photo-perturbation are monitored during time, observing a transition from a predominantly elastic (G mainly real) to a viscoelastic regime (real and imaginary parts of G comparable). These results are confirmed by a comparison with independent measurements performed using other rheological techniques. Finally a discussion is made, taking into account the results of a recent X-ray photon correlation spectroscopy (XPCS) experiment on the same polymer in equilibrium and out of equilibrium. (C) 2010 Published by Elsevier B.V.
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