We report on a nearly isothermal, reversible transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. The phase transition phenomenon and the related unidirectional mass-transport effect are caused by optically driven molecular motion of azobenzene-functionalised molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. We also show that the selective excitation of chromophores by linear polarized light induces an anisotropic expanding force, which can be used for polarization-selective opto-mechanical actuators and sensors. Moreover, since the molecular motions can be induced also by spatially confined non-propagating optical fields, we are able to manipulate the state and position of nanoscopic elements of matter using optical near-field approaches.
An increase in stochastic molecular vibrations of a solid due to heating above the melting point leads to a decrease in its
long-range order and a loss of structural symmetry. Therefore conventional liquids are isotropic media. We report on a
light-induced isothermal phase transition of polymer materials from an isotropic solid to an anisotropic liquid state in
which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular polarized
light the materials behave as an isotropic viscoelastic fluid, they display considerable fluidity only in the direction
parallel to the light field vector under linear polarized light. In this case the polymers behave visually as a liquid along
one direction and as a solid in others (one-direction liquid-state), demonstrating thus extraordinarily anisotropic
mechanical properties. The fluidisation phenomenon is related to photoinduced motion of azobenzene-functionalised
molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the
direction of the light polarization. We also show that the selective excitation of chromophores orientated parallel to the
light polarization not only has great influence on the anisotropy of the mechanical properties of the materials, but also
induces an anisotropic expanding force, which can be used for polarization-selective opto-mechanical actuators and
sensors.
We report on a light-induced isothermal transition of a polymer film from an isotropic solid to an anisotropic liquid state in which the degree of mechanical anisotropy can be controlled by light. Whereas during irradiation by circular polarized light the film behaves as an isotropic viscoelastic fluid, it displays considerable fluidity only in the direction parallel to the light field vector under linear polarized light, demonstrating thus extraordinarily anisotropic mechanical properties. The fluidisation phenomenon is related to photoinduced motion of azobenzene-functionalised molecular units, which can be effectively activated only when their transition dipole moments are oriented close to the direction of the light polarization. Along with the phenomenological finding, our work allows us to make a substantial step in understanding the mass transport effect in azobenzene containing systems under conditions of far- and near-field illumination.
KEYWORDS: Near field optics, Near field scanning optical microscopy, Near field, Polymers, Molecules, Glasses, Image transmission, Data storage, Polarization, Atomic force microscopy
In the last few years a range of techniques for opto-mechanical manipulations of organic films and small structures has been developed and significantly improved. Among these techniques a very promising candidate turned out to be the optically induced mass transport. Not only that the physical mechanisms underlying this phenomenon is not yet been fully understood, but in addition, the lateral dimensions of structures created in that way have been limited by the used light wavelength. In order to gain deeper insight into the physical fundamentals of this phenomenon and to open possibilities for applications (lithography, data storage, manipulation of molecules, ...) it is necessary to create and study reproducible, sharply defined single structures not only in a macroscopic but also in nanometer range. SNOM (Scaning Nearfield Optical Microscopy) seemed to us an intriguing method to approach this goal. We report here novel experimental results about the generation of ultra-small structures by optically driven mass transport. We have investigated different ways to generate localized mass transport in azobenzene-containing films by using focused light in far and nearfields. Thus, the dimensions of optically created structures range to 5 μm (lens focusing) and even down to 100 nm (SNOM nearfield). These experiments offer new expectations to manipulate ultra small objects on surfaces by optical means without mechanically touching them.
UV light influence on the surface potential φs of poly(vinylcinnamate) (PVCN) layers widely used for liquid crystal (LC) photoalignment is investigated. In case when PVCN film is spin coated on the ITO electrodes the surface potential changes under irradiation in both PVCN aligning film and ITO coating. The measured increment of the surface potential changes under irradiation in both PVCN aligning film and ITO coating. The measured increment of the surface potential Δφs=400 mV is mainly cuased by the photoconductivity of ITO electrodes, whereas the part caused by PVCN substrate is at least one order of magnitude lower. The relaxation time of Δφs for the ITO-PVCN coatings was estimated to be about 1 h. The induced potential may substantially modify dielectric properties of the aligned LC layers and its anchoring characteristics when the freshly irradiated substrates are used. On the contrary, this influence is weak when the substrates are irradiated several hours before the use for LC alignment.
Conference Committee Involvement (5)
Molecular and Nano Machines V
21 August 2022 | San Diego, California, United States
Molecular and Nano Machines IV
3 August 2021 | San Diego, California, United States
Molecular and Nano Machines III
24 August 2020 | Online Only, California, United States
Molecular and Nano Machines II
13 August 2019 | San Diego, California, United States
Molecular Machines
21 August 2018 | San Diego, California, United States
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