The idea that rod-like molecules possessing an electric dipole moment could exhibit a ferroelectr... more The idea that rod-like molecules possessing an electric dipole moment could exhibit a ferroelectric nematic phase was suggested more than a century ago. However, only recently such a phase has been reported for two quite different liquid crystals: RM734 (4-[(4nitrophenoxy)carbonyl)]phenyl 2,4-dimethoxybenzoate) and DIO (2.3´,4´,5´-tetrafluoro[1,1´biphenyl]-4-yl 2.6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate). For RM734 a direct ferroelectric nematic (NF) to classical nematic N transition was reported, whereas for DIO an intermediate phase Nx was discovered between the NF and the N phases. Here we present highresolution calorimetric evidence that an intermediate Nx phase also exists in RM734 along a narrow temperature range between the NF and the N phases.
High-resolution calorimetry has played a significant role in providing detailed information on ph... more High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity cp(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl-2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a lowtemperature ferroelectric nematic phase (NF) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (Nx). From the detailed data of h(T) and cp(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (xDIO). The xDIO dependence of the transition temperatures for both the transitions could be well described by a quadratic function. Both these transitions were weakly first-order. The true latent heat of the Nx-N transition of DIO was as low as L = 0.0075 ± 0.0005 J/g and L = 0.23 ± 0.03 J/g for the NF-Nx transition, which is about twice the previously reported value of 0.115 J/g for the NF-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing xDIO. At all the Nx-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the NF to the higher temperature phase exhibits substantial pretransitional behavior, in particular in the high-temperature phase. Power law analysis of cp(T) resulted in an effective critical exponent α = 0.88 ± 0.1 for DIO and this value decreased in the mixtures with decreasing xDIO towards α = 0.50 ± 0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis. Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry
Industrial & Engineering Chemistry Research, Nov 27, 2013
A novel type of nano template was prepared by loading a Ziegler−Natta catalyst on nanosized carbo... more A novel type of nano template was prepared by loading a Ziegler−Natta catalyst on nanosized carbon spheres for ethylene polymerization to form nanosized polyethylene (PE) particles; triethylaluminum (AlEt 3) was used as a co-catalyst. The results revealed that the nano templates were spherical and their average diameter was ∼180 nm. The nano template had a high titanium content of 4.5 wt %, determined by inductively coupled plasma (ICP) emission spectroscopy and high catalytic activity (up to 7.68 × 10 5 g PE /((mol Ti) h) for ethylene polymerization. Polyethylene particles 310 nm in diameter were obtained. The morphology of the polymer particles was spherical and the size distribution is uniform, as confirmed by scanning electron microscopy (SEM).
Nematic–nematic transitions in a highly polar nematic compound are studied, in thick cells in whi... more 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.
We observe chiral domains in the paraelectric nematic phase of a chemically achiral ferronematic.... more We observe chiral domains in the paraelectric nematic phase of a chemically achiral ferronematic. This behaviour is due to spontaneous symmetry breaking arising from saddle splay elasticity and helical segregation, the first example of this observation.
High-resolution calorimetry has played a significant role in providing detailed information on ph... more High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity cp(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl-2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a lowtemperature ferroelectric nematic phase (NF) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (Nx). From the detailed data of h(T) and cp(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (xDIO). The xDIO dependence of the transition temperatures for both the transitions could be well described by a quadratic function. Both these transitions were weakly first-order. The true latent heat of the Nx-N transition of DIO was as low as L = 0.0075 ± 0.0005 J/g and L = 0.23 ± 0.03 J/g for the NF-Nx transition, which is about twice the previously reported value of 0.115 J/g for the NF-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing xDIO. At all the Nx-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the NF to the higher temperature phase exhibits substantial pretransitional behavior, in particular in the high-temperature phase. Power law analysis of cp(T) resulted in an effective critical exponent α = 0.88 ± 0.1 for DIO and this value decreased in the mixtures with decreasing xDIO towards α = 0.50 ± 0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis. Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry
The nematic-nematic transitions in a nematic compound DIO are studied in homogeneously planar and... more The nematic-nematic transitions in a nematic compound DIO are studied in homogeneously planar and homeotropic aligned cells using dielectric spectroscopy in the frequency range 0.1 Hz to 10 MHz over a wide range of temperatures. Three relaxation processes are identified in this material. All the three relaxation processes show large jumps in the dielectric strength and discontinuity in frequency at the NX-NF transition, indicative of it being a first order phase transition. Unlike a conventional nematic liquid crystalline material that usually shows molecular relaxation processes at higher frequencies, this material shows three processes at relatively lower frequencies. The three processes are found to be collective in nature. The least frequency process is proven to be due to the conductivity of ions in the medium and due to the accumulation of charge at the alignment layers unlike mistakenly reported in the literature otherwise. The mode at the highest frequency is proven to be due to the ferroelectric domains in the NF phase. This is evidenced by its dielectric strength two orders of magnitude higher in a homeotropic aligned cell than planar aligned cell. Its mechanism is soft mode like in the N phase. The intermediate frequency mode is proven to be due to the correlation of molecules of the medium as is normally observed in liquid crystalline cybotactic clusters.
A novel type of nano template was prepared by loading a Ziegler–Natta catalyst on nanosized carbo... more A novel type of nano template was prepared by loading a Ziegler–Natta catalyst on nanosized carbon spheres for ethylene polymerization to form nanosized polyethylene (PE) particles; triethylaluminum (AlEt3) was used as a co-catalyst. The results revealed that the nano templates were spherical and their average diameter was ∼180 nm. The nano template had a high titanium content of 4.5 wt %, determined by inductively coupled plasma (ICP) emission spectroscopy and high catalytic activity (up to 7.68 × 105 gPE/((mol Ti) h) for ethylene polymerization. Polyethylene particles 310 nm in diameter were obtained. The morphology of the polymer particles was spherical and the size distribution is uniform, as confirmed by scanning electron microscopy (SEM).
Chiral domains of opposite chirality are observed surprisingly in a nematic phase of an achiral r... more Chiral domains of opposite chirality are observed surprisingly in a nematic phase of an achiral rod-like liquid crystalline mesogen that shows ferroelectric nematic and antiferroelectric smectic phases. The observations of chiral domains of opposite chirality are enabled by application of a weak electric field across a planar-aligned cell. However once domains of opposite chirality are created, these stay permanently even if the field is removed. The observed phenomenon is due to the symmetry breaking of achiral mesogens of rod-shaped molecules. These domains are similarly observed in the Nx phase. However for temperatures close or in the NF, the size of domains is reduced significantly below the wavelength of visible light. There is either a single domain with dipole moments parallel to the surface or domains antiparallel in the NF phase, not possible to determine in this experiment.
The idea that rod-like molecules possessing an electric dipole moment could exhibit a ferroelectr... more The idea that rod-like molecules possessing an electric dipole moment could exhibit a ferroelectric nematic phase was suggested more than a century ago. However, only recently such a phase has been reported for two quite different liquid crystals: RM734 (4-[(4nitrophenoxy)carbonyl)]phenyl 2,4-dimethoxybenzoate) and DIO (2.3´,4´,5´-tetrafluoro[1,1´biphenyl]-4-yl 2.6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate). For RM734 a direct ferroelectric nematic (NF) to classical nematic N transition was reported, whereas for DIO an intermediate phase Nx was discovered between the NF and the N phases. Here we present highresolution calorimetric evidence that an intermediate Nx phase also exists in RM734 along a narrow temperature range between the NF and the N phases.
High-resolution calorimetry has played a significant role in providing detailed information on ph... more High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity cp(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl-2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a lowtemperature ferroelectric nematic phase (NF) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (Nx). From the detailed data of h(T) and cp(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (xDIO). The xDIO dependence of the transition temperatures for both the transitions could be well described by a quadratic function. Both these transitions were weakly first-order. The true latent heat of the Nx-N transition of DIO was as low as L = 0.0075 ± 0.0005 J/g and L = 0.23 ± 0.03 J/g for the NF-Nx transition, which is about twice the previously reported value of 0.115 J/g for the NF-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing xDIO. At all the Nx-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the NF to the higher temperature phase exhibits substantial pretransitional behavior, in particular in the high-temperature phase. Power law analysis of cp(T) resulted in an effective critical exponent α = 0.88 ± 0.1 for DIO and this value decreased in the mixtures with decreasing xDIO towards α = 0.50 ± 0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis. Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry
Industrial & Engineering Chemistry Research, Nov 27, 2013
A novel type of nano template was prepared by loading a Ziegler−Natta catalyst on nanosized carbo... more A novel type of nano template was prepared by loading a Ziegler−Natta catalyst on nanosized carbon spheres for ethylene polymerization to form nanosized polyethylene (PE) particles; triethylaluminum (AlEt 3) was used as a co-catalyst. The results revealed that the nano templates were spherical and their average diameter was ∼180 nm. The nano template had a high titanium content of 4.5 wt %, determined by inductively coupled plasma (ICP) emission spectroscopy and high catalytic activity (up to 7.68 × 10 5 g PE /((mol Ti) h) for ethylene polymerization. Polyethylene particles 310 nm in diameter were obtained. The morphology of the polymer particles was spherical and the size distribution is uniform, as confirmed by scanning electron microscopy (SEM).
Nematic–nematic transitions in a highly polar nematic compound are studied, in thick cells in whi... more 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.
We observe chiral domains in the paraelectric nematic phase of a chemically achiral ferronematic.... more We observe chiral domains in the paraelectric nematic phase of a chemically achiral ferronematic. This behaviour is due to spontaneous symmetry breaking arising from saddle splay elasticity and helical segregation, the first example of this observation.
High-resolution calorimetry has played a significant role in providing detailed information on ph... more High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity cp(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl-2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a lowtemperature ferroelectric nematic phase (NF) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (Nx). From the detailed data of h(T) and cp(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (xDIO). The xDIO dependence of the transition temperatures for both the transitions could be well described by a quadratic function. Both these transitions were weakly first-order. The true latent heat of the Nx-N transition of DIO was as low as L = 0.0075 ± 0.0005 J/g and L = 0.23 ± 0.03 J/g for the NF-Nx transition, which is about twice the previously reported value of 0.115 J/g for the NF-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing xDIO. At all the Nx-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the NF to the higher temperature phase exhibits substantial pretransitional behavior, in particular in the high-temperature phase. Power law analysis of cp(T) resulted in an effective critical exponent α = 0.88 ± 0.1 for DIO and this value decreased in the mixtures with decreasing xDIO towards α = 0.50 ± 0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis. Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry
The nematic-nematic transitions in a nematic compound DIO are studied in homogeneously planar and... more The nematic-nematic transitions in a nematic compound DIO are studied in homogeneously planar and homeotropic aligned cells using dielectric spectroscopy in the frequency range 0.1 Hz to 10 MHz over a wide range of temperatures. Three relaxation processes are identified in this material. All the three relaxation processes show large jumps in the dielectric strength and discontinuity in frequency at the NX-NF transition, indicative of it being a first order phase transition. Unlike a conventional nematic liquid crystalline material that usually shows molecular relaxation processes at higher frequencies, this material shows three processes at relatively lower frequencies. The three processes are found to be collective in nature. The least frequency process is proven to be due to the conductivity of ions in the medium and due to the accumulation of charge at the alignment layers unlike mistakenly reported in the literature otherwise. The mode at the highest frequency is proven to be due to the ferroelectric domains in the NF phase. This is evidenced by its dielectric strength two orders of magnitude higher in a homeotropic aligned cell than planar aligned cell. Its mechanism is soft mode like in the N phase. The intermediate frequency mode is proven to be due to the correlation of molecules of the medium as is normally observed in liquid crystalline cybotactic clusters.
A novel type of nano template was prepared by loading a Ziegler–Natta catalyst on nanosized carbo... more A novel type of nano template was prepared by loading a Ziegler–Natta catalyst on nanosized carbon spheres for ethylene polymerization to form nanosized polyethylene (PE) particles; triethylaluminum (AlEt3) was used as a co-catalyst. The results revealed that the nano templates were spherical and their average diameter was ∼180 nm. The nano template had a high titanium content of 4.5 wt %, determined by inductively coupled plasma (ICP) emission spectroscopy and high catalytic activity (up to 7.68 × 105 gPE/((mol Ti) h) for ethylene polymerization. Polyethylene particles 310 nm in diameter were obtained. The morphology of the polymer particles was spherical and the size distribution is uniform, as confirmed by scanning electron microscopy (SEM).
Chiral domains of opposite chirality are observed surprisingly in a nematic phase of an achiral r... more Chiral domains of opposite chirality are observed surprisingly in a nematic phase of an achiral rod-like liquid crystalline mesogen that shows ferroelectric nematic and antiferroelectric smectic phases. The observations of chiral domains of opposite chirality are enabled by application of a weak electric field across a planar-aligned cell. However once domains of opposite chirality are created, these stay permanently even if the field is removed. The observed phenomenon is due to the symmetry breaking of achiral mesogens of rod-shaped molecules. These domains are similarly observed in the Nx phase. However for temperatures close or in the NF, the size of domains is reduced significantly below the wavelength of visible light. There is either a single domain with dipole moments parallel to the surface or domains antiparallel in the NF phase, not possible to determine in this experiment.
Uploads
Papers by Wanhe Jiang