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

Glassy dynamics of two poly(ethylene glycol) derivatives in the bulk and in nanometric confinement as reflected in its inter- and intra-molecular interactions

The inter- and intra-molecular interactions as they evolve in the course of glassy solidification are studied by broadband dielectric—and Fourier-transform infrared—spectroscopy for oligomeric derivatives of poly(ethylene glycol) derivatives, namely, poly(ethylene glycol) phenyl ether acrylate and poly(ethylene glycol) dibenzoate in the bulk and under confinement in nanoporous silica having mean pore diameters 4, 6, and 8 nm, with native and silanized inner surfaces. Analyzing the spectral positions and the oscillator strengths of specific IR absorption bands and their temperature dependencies enables one to trace the changes in the intra-molecular potentials and to compare it with the dielectrically determined primarily inter-molecular dynamics. Special emphasis is given to the calorimetric glass transition temperature Tg and Tαβ ≈ 1.25Tg, where characteristic changes in conformation appear, and the secondary β-relaxation merges with the dynamic glass transition (α-relaxation). Furthermore, the impact of main chain conformations, inter- and intra-molecular hydrogen bonding, and nanometric confinement on the dynamic glass transition is unraveled

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

Kinetics of Non-Isothermal and Isothermal Crystallization in a Liquid Crystal with Highly Ordered Smectic Phase as Reflected by Differential Scanning Calorimetry, Polarized Optical Microscopy and Broadband Dielectric Spectroscopy

The kinetics of the non-isothermal and isothermal crystallization of the crystalline smectic B phase (soft crystal B, SmBcr) in 4-n-butyloxybenzylidene-4′-n′-octylaniline (BBOA) was studied by a combination of differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS) and polarized optical microscopy (POM). On cooling, part of the SmBcr phase undergoes conversion to a crystalline phase and the remainder forms a glassy state; after the glass softens, crystallization is completed during subsequent heating. By analyzing the area of the crystal growing in the texture of SmBcr as a function of time, the evolution of degree of crystallinity, D(t), was estimated. It was demonstrated that upon heating, D(t) follows the same Avrami curve as the crystallization during cooling. Non-isothermal crystallization observed during slow cooling rates (3K/min ≤ ϕ ≤ 5K/min) is a thermodynamically-controlled process with the energy barrier Ea ≈ 175 kJ/mol; however, the crystallization occurring during fast cooling (5 K/min > ϕ ≥ 30K/min) is driven by a diffusion mechanism, and is characterized by Ea ≈ 305 kJ/mol. The isothermal crystallization taking place in the temperature range 274 K and 281 K is determined by nucleus formation

Phase Sequence, Kinetics of Crystallization and Molecular Dynamics of the Chiral Liquid Crystalline Compound Forming a Hexatic Smectic Glass

The vitrification of the antiferroelectric hexatic smectic XA* phase and cold crystallization are reported for (S)-4′-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]benzoate. The kinetics of isothermal cold crystallization and melt crystallization are investigated, revealing that both are controlled mainly by diffusion, as indicated by decrease in the characteristic crystallization time with increasing temperature of crystallization, with an activation energy of 114 kJ/mol. A weak relaxation process is detected in a crystal phase, with an activation energy of 38 kJ/mol, implying the conformationally disordered crystal phase. The estimated fragility parameter of the investigated glass former is equal to 94.5, which indicates rather high fragility

Crystallization kinetics of (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[4-(2,2,3,3,4,4,4-heptafluorobutoxy)but-1-oxy]-2-fluorobenzoate

Chiral liquid crystalline compounds belonging to the homologous series of (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[m-(2,2,3,3,4,4,4-heptafluorobutoxy)alk-1-oxy]-2-fluorobenzoates show various behavior on cooling depending on the length of the CmH2m chain. The homologue with m = 2 crystallizes, while for m = 5, 6, 7, and presumably also for m = 3, the glass of the anticlinic smectic CA* phase is formed. The previous results for m = 4 suggest that this homologue may also be a glassformer. This paper presents the study of the crystallization kinetics for the compound with m = 4 in isothermal conditions (by polarizing optical microscopy) and for the 5-40 K/min cooling rates (by differential scanning calorimetry). Microscopic observations enable estimation of the energy barrier for nucleation, which equals 409 kJ/mol. The threshold cooling rate necessary for complete vitrification of the smectic CA* phase, obtained by extrapolating the enthalpy change during crystallization to zero, is equal to 81 K/min or 64 K/min for the linear and parabolic fit, respectively. The structural studies by X-ray diffraction show that crystal phases have lamellar structures both in the pristine sample and after crystallization from the melt but with different layer spacing. A weak relaxation process is detected in the sample after melt crystallization, revealing the presence of the conformational disorder. The dynamic glass transition temperature of the SmCA* phase, estimated from the relaxation time of the PH process (as the {\alpha}-relaxation time could not be registered in a wide enough temperature range), is 244 K.Comment: 20 pages, 16 figure

Magnetic Properties Study of Iron Oxide Nanoparticles-Loaded Poly(ε-caprolactone) Nanofibres

Magnetic nanofibres have attracted more and more attention recently due to their possible applications e.g., in spintronics and neuromorphic computing. This work presents the synthesis and physicochemical characterization of the electrospun nanofibres of poly(ε-caprolactone) (PCL) doped by iron oxide nanoparticles with diameters of 5 nm. PCL is a semi-crystalline, hydrophilic polymer showing controllable biodegradation rates, biocompatibility, and flexible mechanical properties. In the composite material, two different concentrations of magnetic nanoparticles were used: 2 and 6 wt.%. PCL-based composites were investigated using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetry (TGA). Although in the literature one can find many studies on magnetic polymeric composites, the investigation of their magnetic properties is usually limited to measuring the magnetization curve. Detailed analysis of dynamic magnetic susceptibility is rather rare. In this report, special attention was paid to the detailed analysis of magnetic properties, where we followed the evolution of changes in the magnetic behavior of the material depending on the concentration of magnetic nanoparticles

Correction: Deptuch et al. Molecular Dynamics and Kinetics of Isothermal Cold Crystallization in the Chiral Smectogenic 3F7FPhH6 Glassformer. <i>Crystals</i> 2021, <i>11</i>, 1487

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