On relaxation and vibrational dynamics in the thermodynamic states of a chiral smectogenic glass-former.

This article shows the full characteristics (i.e., the phase situation as well as the relaxation and vibrational dynamics) of the (S)-4'-(1-methyloctyloxycarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy)pentyl-1-oxy]-benzoate chiral liquid crystal. Besides two enantiotropic chiral smectic phases (SmC* and ), the compound under study also forms the hexatic smectic phase and two crystal phases (Cr1 and Cr2). The XRD patterns imply a similar structure of both crystal phases. The sample crystallizes upon slow cooling, while the phase undergoes a glass transition during fast cooling. Upon subsequent heating, cold crystallization is observed. Our research reveals the complex relaxation dynamics in the identified thermodynamic states, e.g., two relaxations up to the beginning of cold crystallization, three modes in the crystal phases and seven processes in all smectic phases. The results from the scaling of the dielectric response indicate that the origin of the dynamics and behavior of the dielectric permittivity is the same for all phases, regardless of the change in temperature and/or external biasing field. The high value of the fragility index (mf ≈ 146) indicates that the compound under study is a fragile glass-forming system. The region of the -COO- and -COC- group stretching vibrations is primarily sensitive to the structural changes occurring during phase transitions.

Effect of high pressure on relaxation dynamics and crystallization kinetics of chiral liquid crystal in its smectic phase.

The impact of high pressure on molecular dynamics and the crystallization process in the smectic phase with antiferroelectric properties of partially fluorinated liquid crystal (S)-4'-(1-methyloctyloxycarbonyl)biphenyl-4-yl-4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy)heptyl-1-oxy]-benzoate (3F7HPhH7) was studied by broadband dielectric spectroscopy (BDS). By analyzing dielectric spectra measured under isobaric and isothermal conditions, the changes of the activation volume vs. temperature and the activation enthalpy vs. pressure have been determined to better understand the molecular system's behaviour in terms of its thermodynamic properties. The isothermal and isobar crystallization was studied by a BDS method along the trajectory of constant relaxation time τ on the (T, p) plane. The kinetics of this process was compared to that at ambient pressure, derived from the results of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The melt crystallization depends primarily on the formation of nuclei with the activation energy of approx. 50 kJ mol-1. This energy corresponds with the intramolecular movements of the carbonyl group in the rigid core. The behaviour of the apparent activation energies suggests that this process becomes easier with the progressive crystallized volume fractions. The obtained values of the Avrami exponent nA suggest that the crystal growth is three-dimensional. Additionally, we successfully used the scaling of dielectric response for experimental data. The scaling of the dielectric relaxation processes indicates that the dynamics and the behaviour of dielectric permittivity have the same origin for all phases regardless of the change in temperature and/or pressure.

Molecular Dynamic in Ethosuximide Glass Forming Pharmaceutical as Studied by Dielectric Relaxation Spectroscopy.

Polymorphism and molecular dynamics of ethosuximide with molecules of left- and right-handed chirality have been studied in detail using dielectric spectroscopy. Density functional theory calculations of molecular conformations and dimer formation were performed to aid the interpretation of measurements. Moving window correlation analysis of the imaginary part of dielectric permittivity spectra allowed us to complete the monotropic system of phases found by the differential scanning calorimetry method. Extra transition connected with freezing-in/activation of slow molecular motions was identified in partially ordered crystal CrI phase. In high-temperature orientationally disordered CrIh and in low-temperature conformationally disordered CrIl phases, 2 relaxation processes were detected at frequency range below 105 Hz. In glass of CONDIS CrIl, ß-relaxation was identified.

Dynamics of Dimethylbutanols in Plastic Crystalline Phases by Field Cycling 1H NMR Relaxometry.

2,2-Dimethylbutan-1-ol (2,2-DM-1-B), 3,3-dimethylbutan-1-ol (3,3-DM-1-B), and 3,3-dimethylbutan-2-ol (3,3-DM-2-B) show a rich solid-state polymorphism, which includes one or more plastic crystalline phases (also referred to as orientationally disordered crystalline (ODIC) phases) and glass of the liquid or ODIC phases. In this work, the dynamics of the three isomeric alcohols was investigated in the liquid and plastic crystalline phases by fast field cycling 1H NMR relaxometry in the temperature range between 213 and 303 K. The analysis of the nuclear magnetic relaxation dispersion curves (i.e., longitudinal relaxation rate R1 vs 1H Larmor frequency) acquired for the different alcohols at different temperatures gave quantitative information on internal motions, overall molecular reorientations, and molecular self-diffusion. Self-diffusion coefficients were also determined in the liquid phase and in some ODIC phases of the samples from the trends of 1H R1 as a function of the frequency square root at low frequencies. Remarkable changes in the temperature trends of correlation times and self-diffusion coefficients were found at the transition between the liquid and the ODIC phase for 2,2-DM-1-B and 3,3-DM-1-B, and between ODIC phases for 3,3-DM-2-B, the latter sample showing a markedly different dynamic and phase behavior.

Earliest effects of sudden occlusions on pressure profiles in selected locations of the human systemic arterial system.

We have developed a numerical simulation method for predicting the time dependence (wave form) of pressure at any location in the systemic arterial system in humans. The method uses the matlab-Simulink environment. The input data include explicitly the geometry of the arterial tree, treated up to an arbitrary bifurcation level, and the elastic properties of arteries as well as rheological parameters of blood. Thus, the impact of anatomic details of an individual subject can be studied. The method is applied here to reveal the earliest stages of mechanical reaction of the pressure profiles to sudden local blockages (thromboses or embolisms) of selected arteries. The results obtained with a purely passive model provide reference data indispensable for studies of longer-term effects due to neural and humoral mechanisms. The reliability of the results has been checked by comparison of two available sets of anatomic, elastic, and rheological data involving (i) 55 and (ii) 138 arterial segments. The remaining arteries have been replaced with the appropriate resistive elements. Both models are efficient in predicting an overall shift of pressure, whereas the accuracy of the 55-segment model in reproducing the detailed wave forms and stabilization times turns out dependent on the location of the blockage and the observation point.

Protective properties of the arterial system against peripherally generated waves.

An anatomically detailed model consisting of a network of electric transmission lines is developed to simulate propagation of the pulse waves in humans. The simulations show that the real arterial tree geometry, together with the elastic and rheological parameters of particular segments, ensure an efficient protection of vital organs against pulse waves generated at peripheral locations. Because locomotive movements are the most obvious source of such disturbances, additional cyclic perturbations are applied to the model femoral arteries. It is shown that the impact of such peripherally generated pulse waves onto the pressure profiles at the ascending aorta and at other vital locations of the system is surprisingly weak independently of synchronization/desynchronization with the heart action period. This may witness to an intrinsically protective nature of the arterial tree anatomy in addition to its known functionality of the optimal blood supply at possibly low lumen volume. The extent of the protection is also studied in the presence of a complete arterial embolism at the left common carotid artery.

Dynamics of the Chiral Liquid Crystal 4'-Butyl-4-(S)-(2-methylbutoxy)azoxybenzene in the Isotropic, Cholesteric, and Solid Phases: A Fast Field-Cycling NMR Relaxometry Study.

(1)H NMR relaxometry was applied to investigate dynamic processes in the isotropic liquid, cholesteric, and crystalline phases of the chiral mesogen 4'-butyl-4-(S)-(2-methylbutoxy)azoxybenzene (4ABO5*). To this aim, (1)H longitudinal relaxation rates were measured as a function of temperature (between 257 and 319 K) and Larmor frequency (from 10 kHz to 35 MHz by a fast field-cycling relaxometer and at 400 MHz by an NMR spectrometer). The NMR relaxation dispersion (NMRD) curves so obtained were analyzed in terms of models suitable for the description of dynamic processes in the different phases, thus quantitatively determining values of characteristic motional parameters. In particular, internal and overall rotations/reorientations, molecular translational diffusion, and collective motions contribute to relaxation in the isotropic and cholesteric phases, whereas, in the crystalline phase, relaxation is mainly determined by internal motions and molecular reorientations. The results were discussed and compared with those previously obtained on the same compound by dielectric relaxation spectroscopy.