Projects / Programmes
Patterns, structural self-assembly and multiferroic states in mixtures of nanoparticles and liquid crystals
| Code |
Science |
Field |
Subfield |
| 1.02.00 |
Natural sciences and mathematics |
Physics |
|
| Code |
Science |
Field |
| P250 |
Natural sciences and mathematics |
Condensed matter: structure, thermal and mechanical properties, crystallography, phase equilibria |
mixtures, nanoparticles, liquid crystals, multiferroics, magnetoelectrics, ferrofluids, selfassembly, phase behavior, structural transitions, surface phenomena, disorder, stochastic resonance, topological defects, domain coarsening
Researchers (12)
Organisations (3)
Abstract
We will study, experimentally and theoretically material, the structural and self-assembly properties of mixtures of a variety of nanoparticles (NPs) and thermotropic liquid crystals (LCs). Some NPs will be chemically treated with various functional surfactants. The static structural and phase properties as well as the dynamic properties of the mixtures will be monitored by means of calorimetry, dielectric spectroscopy, transmission electron microscopy, polarized light microscopy, magnetic, and x-ray studies. The theoretical studies will be based on the macroscopic, mesoscopic and semi-microscopic models. We will construct minimal models capable of describing the main qualitative and quantitative properties observed experimentally. Extensive numerical simulations will be carried out. Our Slovenian project team has a depth of experience in these and related topics, covering the synthesis of various NPs, sample preparations, experiments, theoretical modeling, and simulations. In addition, our project activities are strongly linked to several established experimental and theoretical groups abroad, mostly via bilateral projects. Our main objectives will be 1) to find an appropriate combination of NPs+LC to produce quantitatively dramatically enhanced or qualitatively new features that the individual components do not exhibit by themselves; 2) to understand the mixing and phase-separation tendencies of such systems; 3) to investigate the non-equilibrium properties of systems with inherent disorder; 4) to discover combinations of NPs+LCs that are extremely susceptible to changes in the external parameters; 5) to control the geometry, the properties and the surface decoration of NPs; 6) to develop reproducible and simple alignment methods for anisotropic NPs; and 7) to develop new methods for reliably assembling nanoscale building blocks into larger, organized structures. Among other aims we plan to prepare new magnetoelectrics and ferrofluids. We will be the first 1) to synthesize and to study magnetoelectrics in a homogeneous mixture of ferromagnetic NPs and a ferroelectric LC; 2) to study the thermal properties of nano-ferrofluids in a LC host; 3) to study NPs domain coating in a LC host; 4) to study mixtures of uniaxial and biaxial thermotropic LCs; and 5) to investigate stochastic resonance in soft-matter systems. The systems in our study are expected to play an important role in the field of nanotechnology, nano-based microelectronics and computers, low-energy-cost LC devices, extremely sensitive detectors, heat-transfer methods and for composites. In addition we expect to make several important contributions to basic understanding in the field of weak static disorder, domain coarsening dynamics and topological defects.
Significance for science
We were the first to develop experimentally a stable soft magnetoelectric material. This result represents an important first step in the development of future four-bit based computers. Magnetoelectric elements are expected to allow simultaneously both arithmetic operations and data storage. Soft magnetoelectrics have great application potential because of their softness, due to which they could be extremely responsive to weak external driving fields. This feature could enable computer operations at a relatively low energy costs.
We were the first to develop a mesoscopic model to study influence of various parameters on the liquid crystal driven alignment of nanotubes. We showed that one could achieve surprisingly strong alignment effects even in cases where interactions between liquid crystal (LC) molecules and nanotubes are relatively weak. Our model could be in future useful guide for the development of LC-controlled creations of different patterns of nanotubes with specific anisotropy properties. For example, structural arrangement of liquid crystals could be relatively easily controlled by external fields or by appropriately shaped or treated surfaces. A given LC phase could display several different structures. These structures could serve as a template for various configurations of nanotubes.
We were the first to calculate the core structure of a surface topological defect (boojum), which can not leave the surface. The physics of topological defects is rather universal, and therefore our results are of interest also to other fields of physics (Note that the first theory of topological defects was developed in cosmology.). In addition, we showed under what conditions nanoparticles could be efficiently trapped in cores of defects. This trapping mechanism could be in future exploited for controlled positional placement of nanoparticles by using topological defects.
For the general progress of science is also important our experimental and theoretical work in which we have proved that appropriate surface treated nanoparticles could increase temperature stability of blue phases for an order of magnitude. These phases are extremely interesting for various applications due to their exceptional electro-optical properties. In addition, we showed that the temperature stability regime of blue phases could be driven towards room temperatures by adding appropriate nanoparticles. Our findings may lead to development of robust displays based on blue phases, which operate at ambient temperatures. The major advantage of such displays would be relatively simple treatment of surfaces surrounding the working liquid crystal phase material.
We were the first to show under what conditions randomly perturbed systems obey the Imry-Ma theorem, which represents one of a pivotal stone of statistical thermodynamics of disorder. The theorem was originally derived to describe behavior of magnetic systems. But its validity is highly universal, because it only requires the existence of a Goldstone mode. Goldstone mode type of excitation is a necessary consequence of continuous symmetry breaking in the phase transition, via which long range order is established in absence of the random field. The latter phenomenon is extremely common in nature and consequently our results are of universal validity.
We were the first to demonstrate that a source of static disorder in a soft systems could be exploited for amplification of input signals using stochastic resonance. This knowledge could lead to the development of sensitive detectors that exploit combined high sensitivity of both stochastic resonance and soft materials.
We were the first to show that an appropriate mixture of liquid crystals and nanoparticles could be used as a memory element. In addition, we demonstrated that impact of nanoparticles on a liquid crystal structure could be similar to an impact of external quenched random field. The latter analogy has not yet been known.
Significance for the country
Many firms in Slovenia are engaged in nanotechnology. In particular are of interest ferrofluids. Our studies provide an insight under which circumstances stable mixtures of different isotropic or anisotropic fluids and nanoparticles could be realized. In addition, our research suggests a number of new potential applications (liquid crystal driven alignment of nanotubes, development of sensitive detectors based on soft materials and stochastic resonance, soft memory elements), which could be developed in Slovenia.
The project involved many young researchers (Marko Jagodič and Sašo Gyergyek, in some research activities participated also Brigita Rozic, Dalija Jesenek, Matej Cvetko and Marko Gosak) who have gained diverse experiences in the field of physics, mathematics, computer science and chemistry. The project was highly interdisciplinary and inter-institutional. Among the participating institutions stronger collaboration has been established both in research and education activities.
New knowledge gained within the project has been included in the content of several university courses and doctoral studies. Examples are subjects Complex mixtures, Modeling in soft matter physics, Overview of Modern Physics, Modern Aspects of Physics on doctoral studies at the Faculty of Science and Mathematics University of Maribor and the subjects Liquid Crystals and Soft Matter at the Jožef Stefan International Postgraduate School in Ljubljana.
The project involved a number of reputable research groups abroad (Leuven, Pavia, Bucharest, Athens). The collaboration within the project has strengthen integration of Slovenian researchers in international research networks.
Project members organized the 11th European Conference on Liquid Crystal which was held in Maribor in the period between 6-11 February 2011. The conference was led by the project leader S. Kralj. The conference was held under the patronage of the President of the Republic of Slovenia Dr Danilo Türk. It was attended by 250 researchers from around the world. Majority of the conference contributions considered composites of different liquid crystal phases and nanoparticles, which testifies the relevance of the project topics. In addition, the project members organized within the conference the educational section for the first time in the history of liquid-crystal conferences. In this section several top researchers presented hot research topics in soft matter physics to Slovenian secondary school teachers. In this way we transferred some of the modern knowledge in the field of soft matter to the general audience. The conference was a success and has contributed to already established outstanding reputation of Slovenian researchers in the field of liquid crystal research.
Most important scientific results
Annual report
2008,
2009,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2008,
2009,
final report,
complete report on dLib.si
