Spontaneous Symmetry Breaking and Linear Electrooptic Response in the Achiral Ferronematic Compound

A compound with the constituent non-chiral molecules, DIO, known to exhibit three nematic subphases namely N, Nx and NF, is studied by polarizing microscopy as function of the alignment layers on one of the substrates, no alignment on any of the substrates, alignment layer on both substrates with parallel and antiparallel rubbing, different cell spacings. The cell with one alignment layer is also studied by electro-optics. N is found to be a conventional nematic phase, but it shows two additional unusual features: chiral domains of opposite chirality and the linear EO response to the applied signal under certain experimental conditions. The emergence of chiral domains is explained by a segregation of the stable helical conformers of the opposite chirality, these preferring to form chiral domains, each with optical rotation power of ± 4o/μm. This is the first example of helical segregation observed in non-chiral molecules in the high temperature nematic phase. The conformers are suggested to arise from the rotations of the aromatic rings either left-handed or right-handed. Unlike the ordinary nematic liquid crystalline phase, linear electrooptical response to the applied electric field (i.e. to its fundamental frequency) is observed, this confirms the polar nature of this phase. The NF is the ferroelectric nematic as reported previously. The strong polar azimuthal surface interaction energy in NF phase stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and in cell rubbed antiparallel, it gives a twisted structure. The transmission spectra simulated using Berreman’s 4 x 4 matrix method for different cell conditions and for different angles between the Polarizer and the Analyzer quantitatively confirm the twisted structures in antiparallel rubbed cells that agree with experimental observations. The twist angle of 170o is found between the directors from the top to the bottom in antiparallel rubbed cells as opposed to 180o observed previously

Spontaneous Mirror Symmetry Breaking and Chiral Segregation in the Achiral Ferronematic Compound DIO

An achiral compound, DIO, known to exhibit three nematic phases namely N, NX and NF, is studied by polarizing microscopy and electro-optics for different surface conditions in confinement. The high temperature N phase assigned initially as a conventional nematic phase, shows two additional unusual features: the optical activity and the linear electro-optic response related to the polar nature of this phase. An appearance of chiral domains is explained by the spontaneous symmetry breaking arising from the saddle-splay elasticity and followed by the formation of helical domains of the opposite chirality. This is the first example of helical segregation observed in calamitic non-chiral molecules in the nematic phase. As reported previously, the ferronematic NF shows strong polar azimuthal surface interaction energy which stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and exhibits a twisted structure in cells with antiparallel buffing. The transmission spectra are simulated using Berreman\u27s 4 × 4 matrix method. The observed agreement between the experimental and the simulated spectra quantitatively confirms the presence of twisted structures in antiparallel rubbed cells

Two mechanisms for formation of ferronematic phase studied by dielectric spectroscopy

A non-chiral ferroelectric nematic compound DIO was studied by dielectric spectroscopy in the frequency range 0.01 Hz to 10 MHz over a wide range of temperatures. The compound exhibits three nematic phases on cooling from the isotropic phase, viz. the ordinary paraelectric nematic N; intermediate nematic NX and ferroelectric NF phases. The lower frequency relaxation process P1 is similar to those observed in other ferronematic compounds. It is a continuation of the molecular flip-flop mode in the isotropic phase and corresponds to the collective movement of dipoles which are strongly coupled with splay fluctuations in the nematic phases. In addition to this process, the studied compound DIO shows another collective relaxation process in both paraelectric nematic phases. The high-frequency P2 originates from the polar/chiral domains which appear due to spontaneous symmetry breaking in achiral system. Both the collective processes, P1 and P2, show soft mode-like behavior on cooling to the NX-NF phase transition and therefore independently contribute to the formation of ferronematic phase

Two mechanisms for the formation of the ferronematic phase studied by dielectric spectroscopy

A non-chiral ferroelectric nematic compound with a 1,3-dioxane unit in the mesogenic core called 2,3′,4′,5′-tetrafluoro-[1,1′-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) was studied by dielectric spectroscopy in the frequency range 0.1 Hz–10 MHz over a wide range of temperatures. The compound exhibits three nematic phases on cooling from the isotropic phase, i.e., the ordinary paraelectric nematic N; the intermediate nematic NX and the ferroelectric NF phase. The least frequency process is due to the dynamics of ions. The middle frequency relaxation process P1 is like as observed in other ferronematic compounds and this mode is a continuation of the molecular flip-flop motion in the isotropic phase to the collective dynamics of dipoles which are strongly coupled with the splay fluctuations in nematic phases. In addition to this process, DIO shows an additional collective relaxation process P2 at higher frequencies both in the N and the NX phases. This mode originates from the polar/chiral molecules of the opposite chirality, these arise from the spontaneous symmetry breaking of achiral mesogens in the N phase. Both collective processes, P1 and P2, show soft mode-like characteristic behavior on cooling from the N to the NX-NF phase transition temperature and are shown to contribute independently to the formation of the ferronematic NF phase

Collective Relaxation Processes in Nonchiral Nematics

Nematic–nematic transitions in a highly polar nematic compound are studied, in thick cells in which the molecules are aligned parallel to the substrates but perpendicular to the applied electric field, using dielectric spectroscopy in the frequency range 1 Hz to 10 MHz over a wide temperature range. The studied compound displays three nematic phases under cooling from the isotropic phase: ubiquitous nematic N; high polarizability NX; and ferroelectric nematic NF. Two collective processes were observed. The dielectric strength and relaxation frequency of one of the processes P2 showed a dependence on the thickness of the cell. The process P1 is the amplitude mode, while the process P2 is the phason mode

INVESTIGATING CHEMICAL PROPERTIES AND COMBUSTION CHARACTERISTICS OF TORREFIED MASSON PINE

To investigate chemical properties and combustion characteristics, masson pine was torrefied using GSL 1600X tube furnance in the argon atmosphere. The properties of torrefied masson pine were respectively determined through thermogravimetry (TGA), fourier transform infrared spectrometer (FTIR) and X-ray diffraction (XRD). Results showed that thermal decomposition of hemicelluloses, cellulose and lignin occurred during torrefaction process. Crystalline region of cellulose was destroyed when temperature was up to 250℃. The effect of torrefaction temperature was more significant than that of residence time. Torrefaction improved combustion characteristics of masson pine. The optimum process was 300℃ of torrefaction temperature and 2.0h of residence time. Combustion process of torrefied masson pine included drying, oxidative pyrolysis and char combustion. Torrefied masson pine had a lower H/C and O/C ratios, peak temperature of oxidative pyrolysis and char combustion and burnout temperature. It had a higher energy density, ignition temperature and activation energy. This data will be significant to understand the torrefied masson pine for energy product to directly combustion