We were the first to create stable suspensions of nanometre-sized ferromagnetic platelets in a nematic liquid crystal and have shown that they order ferromagnetically on quenching from the isotropic phase. Cooling in the absence of a magnetic field produces a polydomain sample exhibiting domains with two opposing states of magnetization, both oriented parallel to the direction of nematic ordering. If the sample is cooled in the presence of an external magnetic field, a monodomain sample is obtained and its magnetization can be switched by domain wall movement on reversal of the applied magnetic field. This ferromagnetic phase responds to very small magnetic fields and is thus very suitable for implementation in magneto-optic devices. Our investigations confirmed more that forty-year-old theoretical prediction on the existence of ferromagnetic liquid crystals and have opened a new area of research. The publication had a large impact both on scientific community and general public, as many reports and interviews with the authors show.
COBISS.SI-ID: 27304231
We created artificial cilia and demonstrated that such cilia successfully pump fluid in a microfluidic chamber. The cilia were assembled from micron-sized superparamagnetic beads and pre-manufactured trenches in a photoresist layer were used to assist the beads to form long chains. The beads were held together by an external magnetic field that was also used to drive the cilia in a periodic but non-reciprocal manner. The non-reciprocity is required since the hydrodynamics in the system is well in the low Reynolds number regime. We were able to detect and observe the generated fluid flow above a ciliated surface and measure the fluid flow velocity. The pumping velocity and the velocity profile were measured as a function of beating parameters. The research was later extended to measurements of a flow field around one beating cilium and to investigations of coupling between neighbouring cilia.
COBISS.SI-ID: 23251239
Many biological systems work with an extremely high energetic efficiency, but at first glance this does not hold for ciliary propulsion, which reaches only about 1%. We numerically determined the optimal beating patterns of cilia according to their energetic efficiency. The problem was studied on both single-cilium level and infinite ciliated surface. We showed that maximising the efficiency of a single cilium leads to curly, often symmetric, and somewhat counter-intuitive patterns. When looking at a densely ciliated surface, the optimal patterns become remarkably similar to what is observed in micro-organisms like Paramecium. Our calculations have shown that the experimentally measured hydrodynamic efficiency of Paramecium reaches about 50 % of the theoretically possible maximum. We also demonstrated that metachronal coordination is essential for efficient pumping and that the highest efficiency is achieved with antiplectic waves.
COBISS.SI-ID: 25073447
We showed for the first time that dynamic light scattering can be used as a probe to detect dynamic soft modes in liquid crystal elastomers and to study the so-called soft elasticity. We measured relaxation rate of thermally excited director fluctuations as a function of applied strain. From these measurements we were able to obtain the visco-elastic constants and confirm the existence of dynamic soft modes, which were predicted by the theory of M. Warner and E. Terentjev. In elastomers, contrary to liquids and gels, movements of molecules are constrained because of crosslinking. Yet, at a certain threshold strain - at the point of elastic instability - a small additional deformation applied perpendicular to the director is completely soft, as in gels and liquids. We have shown that this is a consequence of coupling between the elasticity of the polymer matrix and orientational properties of liquid crystals. Our results are an important contribution to the physics of liquid crystal elastomers as they explain the nature of soft elasticity and reject some of the previous believes regarding the validity of the description of the phenomena related to soft elasticity.
COBISS.SI-ID: 22886183
We performed a comparative study of self-assembling properties of four analogous DNA oligonucleotides in aqueous solution. All investigated oligonucleotides contained the same G-quadruplex forming core sequence (d(GGTG4TGG)) and different number and positions of GC-ends. The investigation was focused on association of quadruplexes into long one-dimensional aggregates known as G-wires. We used circular dichroism to determine the topology and relative orientation of G-quadruplexes, 1H NMR to identify Watson-Crick base pairing, and dynamic light scattering to examine the size of the G-quadruplex assemblies. In contrast to predictions found in the literature, we demonstrated that the longest G-wires are obtained from oligonucleotides with no terminal GC sequences, which assemble via stacking interactions. The presence of d(GC) terminal sequence at the 5' end of the oligonucleotide induces relatively short wire-like structures based on formation of G:C:G:C tetramer, while the presence of d(GC) terminal sequence at the 3' end of the oligonucleotide even hinders the G-wire formation. These insights will be employed to design G-quadruplex-based nanowires and more complex architectures.
COBISS.SI-ID: 2606436