Biomedical subjects

Zdravko Kutnjak

Publications and source records attributed to Zdravko Kutnjak.

10 recordsLinked to original sources

PubMed2006

Two-dimensional Ising model criticality in a three-dimensional uniaxial relaxor ferroelectric with frozen polar nanoregions.

The charge-disordered three-dimensional uniaxial relaxor ferroelectric Sr0.61Ba0.39Nb2O6 splits up into metastable polar nanoregions and paraelectric interfaces upon cooling from above Tc. The frozen polar nanoregions are verified by piezoresponse force microscopy, respond domainlike to dynamic light scattering and dielectric excitation, reveal nonergodicity at T>Tc via global aging, and coalesce into polar nanodomains below Tc. Contrastingly, the percolating system of unperturbed interfaces becomes ferroelectric with two-dimensional Ising-model-like critical exponents alpha=0, beta=1/8, and gamma=7/4, as corroborated by ac calorimetry, second harmonic generation, and susceptometry, respectively.

Journal Article↗

PubMed2006

Soft-stiff regime crossover for an aerosil network dispersed in liquid crystals.

Hydrophilic and hydrophobic aerosil particles immersed in S-(+)-[4-(2-methylbutyl) phenyl 4-n-octylbiphenyl-4-carboxylate] or [p-(n-decyloxy) benzylidene-p-amino-(2-methylbutyl) cinnamate] compound have been studied by employing x-ray diffraction. The aerosil-induced relative layer compression Delta d has been measured in the smectic A phase as a function of aerosil concentration x. Delta d(x) is shown to sensitively monitor the intermediate-rigid transition of the adaptive aerosil network. The dominant mechanism leading to the Delta d(x) profiles is the global establishment of the aerosil-induced molecular tilt in the smectic A phase.

Journal Article↗

PubMed2005

Calorimetric and dielectric studies of ferroelectric sodium nitrite confined in a nanoscale porous glass matrix.

Heat-capacity measurements of the sodium nitrite confined in a nanoscale porous glass matrix show that the intermediate incommensurate phase, present in the bulk, has disappeared and that the first-order ferroelectric transition becomes suppressed and gradual. The ferroelectric transition temperature is shifted considerably to lower temperatures. Two noncritical dielectric modes were observed; however, the observed giant growth of the dielectric constant on heating through the transition temperature TC is shown to be mainly due to the electrode polarization effect.

Journal Article↗

PubMed2005

Calorimetric study of phase transitions in a liquid-crystal-based microemulsion.

A lyotropic inverse micelle phase composed of water, thermotropic liquid-crystal octylcyanobiphenyl (8CB), and surfactant (DDAB) was studied by using high-resolution calorimetry on several mixtures with 3%, 8%, and 15% micelle concentration. Calorimetric results show strong depression of the isotropic to nematic (I-N) phase-transition temperature. Broad heat-capacity anomalies show the existence of a wide coexistence range of isotropic, nematic, and smectic-A phases, which mimics the behavior of a new nearly stable thermodynamic phase. An observation of the rather sharp almost bulklike nematic to smectic-A (N-A) transition at low-temperatures indicates that our heat capacity results are consistent with the phase separation scenario in which significant number of micelles is expelled during I-N conversion leaving almost pure nematic phase at lower temperatures. It was found that micelles get almost completely remixed on heating the mixture back to the isotropic phase.

Journal Article↗

PubMed2005

Electrical conduction in macroscopically oriented deoxyribonucleic and hyaluronic acid samples.

Measurements of the quasistatic and frequency dependent electrical conductivity below 1 MHz were carried out on wet-spun, macroscopically oriented, calf thymus deoxyribonucleic (DNA) and umbilical cord hyaluronic acid (HA) bulk samples. The frequency dependence of the electrical conductivity in the frequency range of approximately 10(-3) - 10(6) Hz of both materials is surprisingly rather similar. Temperature dependence of the quasistatic electrical conductivity above the low temperature saturation plateau can be well described by the activated Arrhenius law with the activation energy of approximately 0.8 eV for both DNA and HA. We discuss the meaning of these findings for the possible conduction mechanism in these particular charged polyelectrolytes.

Complex Mixtures↗

PubMed2005

Confinement-induced orientational order in a ferroelectric liquid crystal containing dispersed aerosils.

The study of the smectic-A to chiral smectic-C(*) phase transition of the liquid crystal S-(+)-[4-(2(')-methyl butyl) phenyl 4(')-n-octylbiphenyl-4-carboxylate] (CE8) containing dispersed hydrophilic aerosils reveals novel properties, important to understanding quenched disorder and confinement in ferroelectric liquid crystals. Smectic layer compression leads to a distribution of transition temperatures inducing smearing of the macroscopic data across the transition. A pronounced confinement-induced pretransitional tilted order is observed.

Journal Article↗

PubMed2004

Ferroelectric smectic- C* liquid-crystal phase: reexamination of the electric-field influence.

Calorimetric and dielectric experiments are presented near the recently proposed Lifshitz point in order to study the nature and properties of the newly suggested phase transitions in the electric-field-temperature (E-T) phase diagram. It was found that both calorimetric and dielectric results obtained across the recently proposed C1 - C2 transition line agree with the predictions of the extended Landau model, showing that the C1 - C2 transition line is not a true phase transition but is merely a continuous evolution similar to a supercritical evolution between two states possessing microscopically the same symmetry. However, it was confirmed in agreement with findings by Ghoddoussi et al. that in samples of finite thickness the extended Landau model cannot adequately describe some features of the E-T phase diagram and some other physical quantities such as the Goldstone mode temperature dependence and the polarization field dependence P (E) . These discrepancies are discussed within the frame of a relaxing mechanism of the helicoidal structure involving annihilation of pairs of +/-2pi disclination lines.

Journal Article↗

PubMed2004

Influence of finite size and wetting on nematic and smectic phase behavior of liquid crystal confined to controlled-pore matrices.

The high-resolution calorimetric study was carried out on octylcyanobiphenyl liquid crystal (LC) confined to various controlled-pore glass (CPG) matrices with silane-treated surface. The diameter of the voids cross section ranged between 23.7 and 395 nm. The results are compared to those obtained previously on CPG voids nontreated with silane. We found a striking similarity between the shifts in the isotropic to nematic and nematic to smectic-A phase transition temperatures as a function of the void radius in which order parameter variations at the LC-void interface play the dominant role. Weaker temperature shifts are observed in silane-treated samples, where surface ordering tendency is larger. In nontreated samples, a finite-size scaling law in the maximum value of the heat capacity at the nematic to smectic-A transition was observed for void diameters larger than 20 nm. In silane-treated samples, this behavior is considerably changed by surface wetting interactions.

Journal Article↗

PubMed2003

Calorimetric study of octylcyanobiphenyl liquid crystal confined to a controlled-pore glass.

We present a calorimetric study of the phase behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass (CPG). We used CPG matrices with characteristic void diameters ranging from 400 to 20 nm. In bulk we obtain weakly first-order isotropic to nematic (I-N) phase transition and nearly continuous character of the nematic to smectic-A (N-SmA) phase transition. In all CPG matrices the I-N transition remains weakly first order, while the N-SmA one becomes progressively suppressed with decreasing CPG pore radius. With decreased pore diameters both phase transition temperatures monotonously decrease following similar trends, but increasing the stability range of the N phase. The heat-capacity response at the weakly first order I-N and continuous N-SmA phase transitions gradually approaches the tricritical-like and three-dimensional XY behavior, respectively. The main observed features were explained using a bicomponent single pore type phenomenological model.

Journal Article↗

PubMed2003

Electrical conduction in native deoxyribonucleic acid: hole hopping transfer mechanism?

Measurements of the quasistatic and frequency dependent electric conductivity below 1 MHz were carried out on wet-spun, macroscopically oriented, calf thymus DNA bulk samples, thus effectively extending previous radio frequency data down to quasistatic time scales. The frequency dependence of the electrical conductivity in the frequency range of approximately 10(-3)-10(15) Hz agrees well with predictions of the hopping hole mechanism. Temperature dependence of the quasistatic electrical conductivity can be rather well described by the activated Arrhenius law with the activation energy of approximately 0.9 eV; however, based on the quality of the fits, the hopping ansatz cannot be ruled out.

Animals↗