Fréedericksz Transitions in 6CB Based Ferronematics-Effect of Magnetic Nanoparticles Size and Concentration.

In this paper, results acquired from capacitance measurements performed on composites based on nematic liquid crystal 4-cyano-4'-hexylbiphenyl (6CB) and spherical iron oxide nanoparticles of various sizes are presented. Electric and magnetic Fréedericksz transitions, as well as structural transitions in combined electric and magnetic fields, were investigated. The obtained results showed the lowering of the threshold magnetic field with an increase in the volume concentration of nanoparticles. Estimations based on results obtained from measurements suggest soft anchoring between liquid crystal director and nanoparticles magnetization vector.

Protein Determination with Molecularly Imprinted Polymer Recognition Combined with Birefringence Liquid Crystal Detection.

Liquid crystal-based sensors offer the advantage of high sensitivity at a low cost. However, they often lack selectivity altogether or require costly and unstable biomaterials to impart this selectivity. To incur this selectivity, we herein integrated a molecularly imprinted polymer (MIP) film recognition unit with a liquid crystal (LC) in an optical cell transducer. We tested the resulting chemosensor for protein determination. We examined two different LCs, each with a different optical birefringence. That way, we revealed the influence of that parameter on the sensitivity of the (human serum albumin)-templated (MIP-HSA) LC chemosensor. The response of this chemosensor with the (MIP-HSA)-recognizing film was linear from 2.2 to 15.2 µM HSA, with a limit of detection of 2.2 µM. These values are sufficient to use the devised chemosensor for HSA determination in biological samples. Importantly, the imprinting factor (IF) of this chemosensor was appreciable, reaching IF = 3.7. This IF value indicated the predominant binding of the HSA through specific rather than nonspecific interactions with the MIP.

Pretransitional effects in a mesogenic mixture under an electric field.

Nematogenic liquids are materials that are in high demand for many application purposes. Field-induced nematic order in isotropic liquids can be observed by the enhancement of electric permittivity during dielectric spectroscopy measurements under the bias electric field. For this reason, dielectric measurements were done on a nematogenic mixture of highly polar compounds. This paper presents a discussion on the influence of the bias electric field on the dielectric response. We observed a decrease of electric permittivity in the isotropic phase under the bias electric field. This effect is most likely caused by the field-induced creation of some complex molecular objects. In the paper, relaxation parameters of the molecular modes were analyzed. The field-induced orientational order was determined using a dichroic ratio in a guest-host system. The measurements show the significant order parameter in the isotropic phase under an electric field.

The effect of dopant chirality on the properties of self-assembling materials with a ferroelectric order.

A series of achiral hockey stick-shaped molecules forming a tilted smectic I liquid crystal phase as well as one non-mesogenic chiral bistereogenic analogue were synthesized and characterized. Herein, we report an example of an achiral hockey stick-shaped compound exhibiting a smectic I phase with a direct transition to the isotropic phase for the first time. This occurrence was confirmed via polarized light microscopy, dielectric spectroscopy, and XRD studies. Homologues with an odd number of carbon atoms in the oligomethylene spacer chain exhibit a lower clearing point than members posessing an even number of carbon atoms in this chain; thus, a characteristic odd-even effect has been observed. The influence of the synthesized compounds with different degrees of chirality and similar chemical structures on the properties of the host compound with a chiral smectic C phase was investigated. A chiral compound forming a wide-temperature chiral smectic C phase without any additional mesophase and having a short helical pitch was selected as the host material for the creation of two bicomponent systems. The mesomorphism of each binary mixture was characterized using optical microscopy and differential scanning calorimetry. The helical pitch of every binary mixture, forming a chiral smectic C phase, was studied within its full phase temperature range. As expected, the chiral host compound in the smectic C* phase doped with the hockey stick-shaped mesogen exhibited a longer helical pitch and lower spontaneous polarization than the chiral host material. On the other hand, for the chiral host compound doped with a non-mesogenic analogue containing two chiral centres, the helical pitch was shorter, and the spontaneous polarization was higher. These results should be potentially applicable for the design of advanced functional multi-component mixtures useful for various applications. The mesogenic behaviour of one binary mixture, forming both the chiral smectic I and titled chiral smectic C phases, was deeply studied via X-ray diffraction and dielectric spectroscopy techniques.