Kinetics of cold crystallization in two liquid crystalline fluorinated homologues exhibiting the vitrified smectic CA∗{C_{A}}^{*} phase

Dielectric relaxation processes in the supercooled antiferroelectric smectic ${C_{A}}^{*}$ phase and crystallization kinetics of two chiral fluorinated 5HF6 and 6HF6 compounds from the same homologous series are investigated. Fragility parameters are determined from the relaxation time of the α-process, including $\tau_{HN}$ from the Havriliak-Negami formula and $\tau_{peak}$ denoting the position of the absorption peak. The coupling coefficient $\xi$ between the characteristic time of isothermal cold crystallization and relaxation time of the α-process is obtained. Despite similar values of the fragility index, the even 6HF6 homologue undergoes cold crystallization much faster than the odd 5HF6 homologue, with significantly different $\xi$ coefficients. Influence of the relaxation time of the $P_{H}$ process (anti-phase phason) in the smectic ${C_{A}}^{*}$ phase on the crystallization kinetics is presumed

Complex magnetic ordering in RE5Pd2In4RE_{5}Pd_{2}In_{4} (RE = Tb-Tm) compounds investigated by neutron diffraction and magnetometric measurements

The RE5Pd2In4 RE Tb Tm compounds crystallize with the orthorhombic Lu5Ni2In4 type crystal structure Pbam space group . In this work we report results of structural and magnetic studies by means of X ray and neutron diffraction as well as dc and ac magnetometric data. Magnetic susceptibility and neutron diffraction data revealed rare earth moments order at low temperatures with complex magnetic structures showing a cascade of temperature induced transitions. The magnetic ordering temperatures are found to be 97, 88, 28.5, 16.5 and 4.3 K for RE Tb, Dy, Ho, Er and Tm, respectively. Magnetic structures related to the propagation vector k [0,0,0] are found just below the magnetic ordering temperatures in majority of the investigated compounds RE Tb Er . Below the Curie temperature TC they have purely ferromagnetic character in Tb5Pd2In4 and Dy5Pd2In4. A ferrimagnetic order finally sets at lower temperatures in Dy5Pd2In4, while in Ho5Pd2In4 two magnetic phases related to k1 are observed the antiferromagnetic one phase I and the ferrimagnetic one phase II, coexisting with phase I at lower temperatures . Er5Pd2In4 is a canted antiferromagnet with additional ferromagnetic component developing at lower temperatures. A purely antiferromagnetic component of magnetic structure with enlarged magnetic unit cell appears with decreasing temperature in Tb5Pd2In4 k [0,1 2,0] and k [0,1 2,1 2] while in Ho5Pd2In4 such component k[,0,0]414 is present within whole temperature range below the magnetic ordering temperature. Magnetic structure of Tm5Pd2In4, exceptionally, has no k1component, but is an antiferromagnetic incommensurate one related to two propagation vectors k5 [0.073 3 ,0.451 1 ,1 2] and k6 [0,0.335 2 ,1 2]. In majority of the compounds RE Tb Er the first rare earth 4g site noted as 4g1 orders at lower temperature than two remaining sites 2a and 4g2 . The direction of the magnetic moments depends on rare earth element involved and indicates an influence of single ion anisotropy in the crystalline electric field CE

Crystal and magnetic structures of R2R_2Ni2_2In compounds (RR = Tb and Ho)

Crystal and magnetic structures of $R_2$Ni$_2$In ($R$ = Tb and Ho) have been studied by powder neutron diffraction at low temperatures. The compounds crystallize in an orthorhombic crystal structure of the Mn$_2$AlB$_2$-type. At low temperatures, the magnetic moments localized solely on the rare earth atoms form antiferromagnetic structures. The Tb magnetic moments, equal to 8.65(6) $\mu_B$ and parallel to the $c$-axis, form a collinear magnetic structure described by the propagation vector $\boldsymbol{k} = [\frac{1}{2}, \frac{1}{2}, \frac{1}{2}]$. This magnetic structure is stable up to the N\'eel temperature equal to 40 K. For Ho$_2$Ni$_2$In a complex, temperature-dependent magnetic structure is detected. In the temperature range 3.5-8.6 K, an incommensurate magnetic structure, described by the propagation vector $\boldsymbol{k}_1 = [0.76, 0, 0.52]$ is observed, while in the temperature interval 2.2-3.1 K the magnetic order is described by two propagation vectors, namely, $\boldsymbol{k}_2 = [\frac{5}{6}, 0.16, \frac{1}{2}]$ and its third harmonics $3\boldsymbol{k}_2 = [\frac{5}{2}, 0.48, \frac{3}{2}]$. Below 2 K, a coexistence of all magnetic structures detected at higher temperatures is observed. For all magnetic phases, the Ho magnetic moments are parallel to the $c$-axis. The low temperature heat capacity data confirm a first order transition near 3 K

Investigation of chiral smectic phases and conformationally disordered crystal phases of the liquid crystalline 3F5FPhH6 compound partially fluorinated at the terminal chain and rigid core

Complementary methods are applied to investigate the phase transitions and crystallization kinetics of the liquid crystalline compound denoted as 3F5FPhH6. Two crystal phases are confirmed, and one of them is the conformationally disordered (CONDIS) phase. Complexity of the melt crystallization process is revealed by the analysis with Friedman’s isoconversional method. The melt crystallization of 3F5FPhH6 shows different mechanisms depending on temperature, which is explained by the relation between the thermodynamic driving force and the thermal energy of translational degrees of freedom. The studied compound crystallizes even during fast cooling (30 K/min), unlike similar compounds with different fluorosubstitutions of the benzene ring, which form the smectic glass for moderate cooling rates. The tendency to vitrification of the smectic phase decreases apparently with the decreasing stability width of the $SmC_{A}$* phase and the increasing relaxation time of the collective relaxation process in this phase, at least for homologues differing from 3F5FPhH6 only by the type of fluorosubstitution

Study of crystalline and liquid crystalline phases of nOS5 homologous series by complementary methods.

Przeprowadzono badania przejść fazowych trzech związków z szeregu homologicznego 4-n-alkoksybenzenotiokarboksylanów S-4-pentylofenylu: 7OS5, 8OS5 oraz 10OS5, tworzących termotropowe fazy ciekłokrystaliczne. Wykonano pomiary metodą różnicowej kalorymetrii skaningowej (DSC) i mikroskopii polaryzacyjnej (PM) w celu wyznaczenia temperatur oraz sekwencji przejść fazowych. Wykorzystano metodę dyfrakcji rentgenowskiej (XRD) na próbkach polikrystalicznych do określenia struktury faz krystalicznych oraz podstawowych parametrów charakteryzujących fazy ciekłokrystaliczne i fazę cieczy izotropowej, takich jak grubość warstw smektycznych, średnia odległość między długimi osiami molekuł i długość korelacji.Phase transitions of three thermotropic liquid crystalline compounds denoted as 7OS5, 8OS5 and 10OS5 from 4-n-penthylphenylthiol-4’-n-alkoxythiobenzoate homologous series have been studied. Differential scanning calorimetry and polarizing microscopy have been used to obtain the temperatures and the sequence of phase transitions. X-ray diffraction of polycrystalline samples has given information about the structure of crystalline phases and basic parameters of liquid crystalline phases and isotropic liquid phase, like the thickness of smectic layers, the average distance between long axes of molecules and the correlation length

Molecular Dynamics and Kinetics of Isothermal Cold Crystallization in the Chiral Smectogenic 3F7FPhH6 Glassformer

An investigation of the glass transition of the antiferroelectric smectic CA* phase and cold crystallization of (S)-4′-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluoro- butoxy)heptyl-1-oxy]benzoate (denoted as 3F7FPhH6) by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy is presented. The fragility index mf = 72, classifying 3F7FPhH6 as a glassformer with intermediate fragility, was obtained from the temperature dependence of the α-process relaxation time, measured upon cooling. Duplication of the α-process was observed exclusively upon heating, before the onset of cold crystallization, and is connected with the pre-transitional effect. The presence of two crystal phases likely influences the kinetics of cold crystallization; the idea stems from a comparison with previous results for the 3F7HPhF6 and 3F7HPhH7 compounds. Additionally, the presence of the smectic Cα* sub-phase in a narrow temperature range was proved based on the differential scanning calorimetry and broadband dielectric spectroscopy results, as well as the fractal dimension analysis of the textures obtained by polarizing optical microscopy

Influence of molecular structure on properties of thermotropic chiral liquid crystals investigated by experimental and computation methods

Dziesięć chiralnych estrów z ciekłokrystalicznych szeregów 3FmXiPhX2 (m = 2, 4, 5, 6, 7; X1, X2 = H, F) przebadano komplementarnymi metodami eksperymentalnymi i obliczeniowymi pod kątem wpływu struktury molekularnej na przemiany fazowe i właściwości fizyczne. W oparciu o obliczenia kwantowo-mechaniczne dla izolowanych molekuł (metodą DFT i pół-empiryczną metodą AM1) zdefiniowano poprawkę na nieliniowy kształt molekuł, przetestowano jej cztery warianty oraz wykazano, że jej wprowadzenie umożliwia wyznaczenie wartości nasycenia kąta pochylenia tego typu molekuł w oparciu o pomiary dyfrakcyjne. Wyniki przeprowadzonych obliczeń DFT wykorzystano również do analizy widm w podczerwieni dla związku 3F2HPhF. Zbadano polimorfizm faz smektycznych i krystalicznych, a dla wybranych homologów (3FmHPhF i 3FmFPhF, m = 5 i 7) przeprowadzono badania kinetyki krystalizacji. Wyznaczono temperaturowe zależności spontanicznej polaryzacji, czasu przełączania, lepkości rotacyjnej, grubości warstw smektycznych, kąta pochylenia molekuł oraz średnią odległość między molekułami i długość korelacji w warstwach smektycznych. Zidentyfikowano procesy relaksacyjne w fazach smektycznych (proces Goldstone'a, proces miękki, fazon ferroelektryczny, fazon antyferroelektryczny, proces domenowy, proces alfa). Na podstawie temperaturowej zależności czasu relaksacji procesu alfa określono wartość parametru kruchości dla homologów 3FmHPhF (m = 5, 6, 7), występujących w zeszklonej fazie SmC*A.An influence of the molecular structure on the phase sequence and physical properties of ten chiral liquid crystalline esters of the 3FmXiPhX2 series (m = 2, 4, 5, 6, 7; X1, X2 = H, F) were studied by complementary experimental and computational methods. Based on quantum-mechanical computations (by DFT and semi-empirical AM1 method) a correction for the nonlinear shape of the molecules was proposed, its four different definitions were tested and it was shown that the saturated values of the tilt angle of molecules can be successfully estimated based on X-ray diffraction as long as the shape-related correction is considered. The DFT results were also used to analyze the FT-IR spectra of the 3F2HPhF compound. Polymorphism of liquid crystalline and crystalline phases were investigated, moreover the kinetics of the crystallization process were studied for chosen homologues (3FmHPhF and 3FmFPhF, m = 5, 7). The temperature dependencies of the spontaneous polarisation, the switching time, the rotational viscosity, the smectic layer thickness, the tilt angle as well as the average distances between molecules and the correlation length within smectic layers were determined. Relaxation processes in the smectic phases were identified (as the Goldstone mode, soft mode, ferroelectric phason, antiferroelectric phason, domain mode and alpha mode). For three 3FmHPhF homologues (m = 5, 6, 7), exhibiting the vitrified SmC*A phase, the fragility parameter was determined based on the temperature dependence of relaxation time of the alpha mode