Projects / Programmes
Collective and molecular dynamics of photosensitive liquid crystal elastomers
| Code |
Science |
Field |
Subfield |
| 1.02.01 |
Natural sciences and mathematics |
Physics |
Physics of condesed matter |
| Code |
Science |
Field |
| P002 |
Natural sciences and mathematics |
Physics |
| Code |
Science |
Field |
| 1.03 |
Natural Sciences |
Physical sciences |
Elastomers, liquid crystals, photo-isomerization
Researchers (11)
Organisations (2)
Abstract
Liquid crystal elastomers (LCE) are smart materials with extraordinary mechanical and optical properties, which can be in a broad range controlled by external influences and tailored to specific needs with preparation procedures and addition of suitable dopants. Due to the coupling between polymer elasticity and nematic order, LCE samples strongly deform with a change of nematic order. This can happen due to temperature change or other external influence. It can be changed by adding into LCE some dopant that changes conformation under the influence of (usually UV) light. In addition to extraordinary mechanical properties LCE poses similar optical properties as usual liquid crystals.
The molecular kinetics of the absorption processes and transitions among the electronic states leading to the trans to cis isomerization is very important for the understanding of the behavior of photosensitive LCE. The measurements of azobenzene derivatives in low molecular weight solvents show that these processes take place on the timescale of picoseconds. Up till now there have been no reports of such measurements in the LCE. In our laboratory we have a laser system that enables us to generate laser pulses of less than 100 fs duration with wavelengths in visible UV and IR region. This allows us to measure optical processes and molecular dynamics on the timescale of picoseconds.
In the proposed project we intend to do the following research:
1. By observing dynamically scattered light using photon correlation spectroscopy we will measure nematic fluctuations in photosensitive LCE doped with azobenzene derivatives. Measurements will be performed as a function of deformation, UV light irradiation, and temperature. Thus we will determine the dependence of the nematic order, coupling between the nematic order and polymer network and elastic and viscous parameters as a function of the irradiation, i.e. concentration of the cis isomer.
2. We will study spectral properties in Uv, visible and infrared domain for the components of photosensitive LCE, i. e. for the liquid crystal moieties, for the derivatives of azobenzene and similar molecules that change conformation upon irradiation with light and can be incorporated in LCE, and for the polymer chains that determine the mechanical properties of LCE.
3. Using light pulses with the duration around 100 ps we will excite azobenzene derivatives in LCE. With measurements of the time dependence of the resulting fluorescence we will determine the kinetics of the electronic transitions that are involved in the trans to cis transformation. We will also measure the time dependence of IR spectrum and try to determine the temporal evolution of orientation of some molecular bonds. These measurement will also be performed as a function of temperature, i.e. nematic order. In this way we will try to determine how the partially ordered polymer medium influences the molecular kinetics of the azobenzene derivatives and the coupling of the trans and cis isomers with the polymer network of LCE.
4. We will investigate the possibility of writing holographic patterns in photosensitive LCE to obtain specific changes of shape or optical properties. By analysis of diffraction of a test beam on a holographically written diffraction grating we will determine the distribution of cis isomers, its dependence on power and time of irradiation. We will also measure the dependence on polarization of writing and test beams, which will enable us to follow the changes in angular distribution of the trans and cis isomers as a function of irradiation. We will investigate the feasibility of elements that can change shape under holographically patterned illumination and that can be used in micro-mechanical and micro-rheological devices.
Significance for science
In the field of soft matter physics liquid crystal elastomers represent one of the most important new developments in the last two decades and are in the center of international scientific interest. Particularly important are LCE doped with photosensitive additives, like azobenzene derivatives, in which extraordinary thermo-mechanical, opto-mechanical, and potentially electromechanical properties are combined. The results of our research on the mechanism of photo-isomerzation in LCE, together with the search for the best materials, investigation of their material parameters and preparation procedures, and properties of spatially modulated photosensitive LCE by optical holographic patterning, are on the cutting edge of the international research in this field. The results, which are published in the top international research journals, contribute to the understanding of the mechanisms of the interactions of light with photosensitive LCE and the resulting mechanical and optical effects. This will help in designing new material which will be suitable for mechanical actuators – artificial muscles, for example in microrheological devices.
Significance for the country
LCE belong to the category of smart materials which have optical, electrical, and mechanical properties that can be controlled by external influences and mutual interactions. In the future they will certainly find a number of important practical applications in devices and technologies that will be part of a new development cycle. In Slovenia we already have a developed industry of photonic devices (Fotona, Balder, LPKF, Optoteh,…) which work in the field of laser medical systems and laser processing of materials. The results of the research project maz potentially lead to new products that will contribute to the development of this industry and lead to new companies, including direct spin-off of this research. Optically controlled microrheological devices are of particular interest, for example LCE based micro-pumps and valves, that would allow chemical and biochemical processing units that require very small amounts of material and in this way contribute to new sustainable technology. Photosensitive LCE also offer possibilities of cheap and robust elements for optical information systems Applications of LCE in the whole world are still at the beginning, so successful research of LCE can help Slovenia to become a global player in the applications of this segment of smart materials. Through connection with the university education and the program of young researchers the proposed research significantly contributed to the education of experts in the field of materials science. This research did not required big investments into the experimental infrastructure and still is at the international forefront. So it was particularly suitable for a small country like Slovenia. As part of the research we collaborated with the most distinguished scientists in the world and so importantly contributed to the image of Slovenia in the world and to the increase of the knowledge base in Slovenia.
Most important scientific results
Annual report
2011,
2012,
2013,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2011,
2012,
2013,
final report,
complete report on dLib.si
