The photo-induced buckling of axially periodic glassy nematic films with alternating stripped director domains is explored by the F¨oppl-von K′arm′an plate theory along with a modified kinetics approach.The eff...The photo-induced buckling of axially periodic glassy nematic films with alternating stripped director domains is explored by the F¨oppl-von K′arm′an plate theory along with a modified kinetics approach.The effects of domain widths on the critical light intensity as well as the buckling morphology are examined numerically.It is found that in most cases the buckled film forms regularly aligned dimples and protrusions,but shows large scale bending perpendicular to the periodic axis if the widths of the stripes are nearly the same.In addition,change in light intensity is shown to alter the wavenumber of the buckling pattern.These results are expected helpful to the design of shape-shifting structures with glassy nematic films.展开更多
The kinetics of I→N transition of a side chain nematic polymethacrylate has been studied by small angle depolarized light scattering intensity measurements using a charge coupled device linear image sensor. The polym...The kinetics of I→N transition of a side chain nematic polymethacrylate has been studied by small angle depolarized light scattering intensity measurements using a charge coupled device linear image sensor. The polymer shows transition of a liquid crystalline polymer is a spinodal type of phase transition mediated by orientation fluctuation.展开更多
Nematic liquid crystal system of interacting biaxial particles via dispersion forces is studied.The molecular orienting potential form in a magnetic field is given for the first time.Weakly ordered isotropic phase is ...Nematic liquid crystal system of interacting biaxial particles via dispersion forces is studied.The molecular orienting potential form in a magnetic field is given for the first time.Weakly ordered isotropic phase is treated in the two-particle cluster approximation.Taking account of the molecular biaxiality,it is found that the ratio of the lowest supercooling temperature T^(*)to the nematic-isotropic phase transition temperature TC approaches the observed value,and the validity of the mean field theory is clarified.展开更多
The disadvantages of Normally White Twisted Nematic Liquid Crystal Display (NW-TN-LCD) were discussed. The reason that the negative birefringent polyimide thin filmswere used to compensate NW-TN-LCD to decrease off-ax...The disadvantages of Normally White Twisted Nematic Liquid Crystal Display (NW-TN-LCD) were discussed. The reason that the negative birefringent polyimide thin filmswere used to compensate NW-TN-LCD to decrease off-axis leakage, improve contrast ratiosand enlarge viewing angles was explained in this paper. A certain polyimide thin film wastaken as an example to show compensation effect on NW-TN-LCD.展开更多
Semi-rigid liquid crystal polymer is a class of liquid crystal polymers different from long rigidrod liquid crystal polymer to which the well-known Onsager and Flory theories are applied. Inthis paper, three statistic...Semi-rigid liquid crystal polymer is a class of liquid crystal polymers different from long rigidrod liquid crystal polymer to which the well-known Onsager and Flory theories are applied. Inthis paper, three statistical models for the semi-rigid nematic polymer were addressed. They arethe elastically jointed rod model, worm-like chain model, and non--homogeneous chain model.The nematic-isotropic transition temperature was examined. The pseudo-second transition tem-perature is expressed analytically. Comparisons with the experiments were made and the agree-ments were found.展开更多
A schlieren texture with six dark brushes emanating from a point and a closed inversion wall have been observed under polarizing optical microscope in nematic state of a thermotropic aromatic copolyester, which have n...A schlieren texture with six dark brushes emanating from a point and a closed inversion wall have been observed under polarizing optical microscope in nematic state of a thermotropic aromatic copolyester, which have not been reported so far in the field of liquid crystalline polymers (LCPs).展开更多
Basea on the new model and concept of mtramolecular orientational order parameter, a molecular field theory was built up for main chain liquid crystalline polymer (MC-LCPs) with flexible spacers. The theory takes acco...Basea on the new model and concept of mtramolecular orientational order parameter, a molecular field theory was built up for main chain liquid crystalline polymer (MC-LCPs) with flexible spacers. The theory takes account of orientational correlation among all mesogens in a polymer chain and the relationship between the intramolecular orientation and spatial orientation of the mesogens. The free energy, temperature and entropy of the nematic-isotropic transition were determined with the theory and compared with experiments in current work. It was found that many unique transition properties of the MC-LCPs comprising flexible spacer are correctly predicted by the theory and the agreement of the theory with the experiments is impressive.展开更多
The experimental investigation on the conformation of a thermotropic main-chain nematic polymer by small-angle X-ray scattering (SAXS) has been carried out. The average radius of gyration of the polymer has been deter...The experimental investigation on the conformation of a thermotropic main-chain nematic polymer by small-angle X-ray scattering (SAXS) has been carried out. The average radius of gyration of the polymer has been determined in nematic and isotropic state respectively. The experiment shows that the boundary between domains is not sharp but diffuse, and the diffuse-boundary thickness of the polymer as a function of temperature has been given.展开更多
The banded texture in films prepared from nematic poly （1,4-benzamide） （PBA）/H<sub>2</sub>SO<sub>4</sub> solution by shearing and without shearing has been studied by using microscopy techn...The banded texture in films prepared from nematic poly （1,4-benzamide） （PBA）/H<sub>2</sub>SO<sub>4</sub> solution by shearing and without shearing has been studied by using microscopy techniques. The kinetic parameters of banded texture formation γ<sub>c</sub> and τ<sub>b</sub> were measured for nematic solution of PBA by using parallel-plate shearing apparatus. The banded texture was also observed in randomly packed domains for nematic solution of PBA on standing without shearing. The properties of banded texture show no difference between the two samples with or without shearing.展开更多
A 90°mixed-mode twisted nematic liquid-crystal-on-silicon(90°-MTN LCoS) with protrusion located between the adjacent pixels is proposed to reduce the effect of fringing field. The influence of the protrusion...A 90°mixed-mode twisted nematic liquid-crystal-on-silicon(90°-MTN LCoS) with protrusion located between the adjacent pixels is proposed to reduce the effect of fringing field. The influence of the protrusion with different widths from0.5 μm to 0.9 μm and different heights from 0.3 μm to 0.7 μm is investigated. The results demonstrate that the invalid pixel region width can be reduced by 31.5% via using the protrusion with the suitable width and height compared with no protrusion case, which provides a higher display quality, such as the higher reflectance and contrast ratio.展开更多
A novel series of chiral dopants synthesized from(S)-1,2-propanediol and mesogenic carboxylic acids were characterized by FT-IR,~1H NMR,elemental analysis and their helical twisting properties were investigated by dop...A novel series of chiral dopants synthesized from(S)-1,2-propanediol and mesogenic carboxylic acids were characterized by FT-IR,~1H NMR,elemental analysis and their helical twisting properties were investigated by doping the chiral dopants into a nematic liquid crystal host(SLC-1717).The results show that,the helical pitch of N~*-LC mixture exhibited a terminal alkyl chain length dependence and the molecular twisting power β also exhibited a temperature dependence(increasing β with increasing temperature...展开更多
The dielectric properties of the nematic mesophase, p-methoxy benzylidene p-decyl aniline(MBDA), measured in planar geometry with a function of frequency and temperature are investigated in detail. The complex dielect...The dielectric properties of the nematic mesophase, p-methoxy benzylidene p-decyl aniline(MBDA), measured in planar geometry with a function of frequency and temperature are investigated in detail. The complex dielectric permittivity(ε' and ε'') is also studied at a bias voltage of 10 V for planar aligned sample cell of nematic mesophase. The dielectric permittivity with bias voltage attains a higher(> 2 times) value than that without bias voltage at a temperature of 56℃,which is due to the fact that the linking group of nematic molecules is internally interacted with an applied bias voltage.This is supported by observing an enhanced dielectric permittivity of nematic liquid crystal(LC) in the presence of bias voltage, which can be fully explained as the increasing of the corresponding dipole moment. The dielectric relaxation behaviors of nematic LC are also demonstrated for planar aligned sample cell. The remarkable results are observed that the relaxation frequency shifts into low frequency region with the increase of the bias voltage applied to the planar aligned sample cells. The dielectric relaxation spectra are fitted by Cole–Cole nonlinear curve fitting for nematic mesophase in order to determine the dielectric strength.展开更多
Nematic phase intertwines closely with high-Tc superconductivity in iron-based superconductors.Its mechanism,which is closely related to the pairing mechanism of superconductivity,still remains controversial.Comprehen...Nematic phase intertwines closely with high-Tc superconductivity in iron-based superconductors.Its mechanism,which is closely related to the pairing mechanism of superconductivity,still remains controversial.Comprehensive characterization of the electronic state reconstruction in the nematic phase is thus crucial.However,most experiments focus only on the reconstruction of band dispersions.Another important characteristic of electronic state,the spectral weight,has not been studied in details so far.Here,we studied the spectral weight transfer in the nematic phase of FeSe0.9S0.1 using angle-resolved photoemission spectroscopy and in-situ detwinning technique.There are two elliptical electron pockets overlapping with each other orthogonally at the Brillouin zone corner.We found that,upon cooling,one electron pocket loses spectral weight and fades away,while the other electron pocket gains spectral weight and becomes pronounced.Our results show that the symmetry breaking of the electronic state is manifested by not only the anisotropic band dispersion but also the band-selective modulation of the spectral weight.Our observation completes our understanding of the nematic electronic state,and put strong constraints on the theoretical models.It further provides crucial clues to understand the gap anisotropy and orbital-selective pairing in iron-selenide superconductors.展开更多
In this paper,we consider the short time classical solution to a simplified hydrodynamic flow modeling incompressible,nematic liquid crystal materials in R^3. We establish a criterion for possible breakdown of such so...In this paper,we consider the short time classical solution to a simplified hydrodynamic flow modeling incompressible,nematic liquid crystal materials in R^3. We establish a criterion for possible breakdown of such solutions at a finite time. More precisely,if(u,d)is smooth up to time T provided that ∫_0~T||▽×u(t,·)||_(BMO)(R^3)+||▽d(t,·)||_(L^4(R^3))~8dt<∞.展开更多
The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped i...The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe_(1-x)Co_(x))_(2)As_(2),suggesting a strong interplay between nematicity and superconductivity.Since the long-range spin order is absent in FeSe superconductor,whether a similar strain effect could be also observed or not is an interesting question.Here,by utilizing a flexible film as substrate,we successfully achieve a wide-range-strain tuning of FeSe thin flake,in which both the tensile and compressive strain could reach up to~0.7%,and systematically study the strain effect on both superconducting and nematic transition(T_(c)and Ts)in the FeSe thin flake.Our results reveal a predominant A1g-type strain effect on T_(c).Meanwhile,Ts exhibits a monotonic anti-correlation with T_(c)and the maximum T_(c)reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe_(1-x)Co_(x))_(2)As_(2),the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity.In addition,our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.展开更多
A theoretical treatment of photo-refractive effect and experimental verifications of the associated nonlinear-optical processes in the nematic phase of liquid crystals are presented. The effect is attributed to the dc...A theoretical treatment of photo-refractive effect and experimental verifications of the associated nonlinear-optical processes in the nematic phase of liquid crystals are presented. The effect is attributed to the dc space charge fields induced by the photo-charges which may come from the photoionization impurities. The phenomenon is analyzed and a theoretical modeI of photorefractivity in nematic liquid crystals is developed. New experimental results are found to be in good agreement with the theory.展开更多
The elastic pair potential model of liquid crystal molecules was described. On the basis of Poniewiersky-stecki statistical theory of the elastic constants of nematic liquid crystals, the effects of non-ideal rigid re...The elastic pair potential model of liquid crystal molecules was described. On the basis of Poniewiersky-stecki statistical theory of the elastic constants of nematic liquid crystals, the effects of non-ideal rigid repulsion between molecules on the elastic constants of nematics were studied.展开更多
Director field in a bipolar configured nematic droplet is analyzed numerically. Results of the calculation are expressed as the tilted angle of the director in the droplet, which balance between torque by elastic ener...Director field in a bipolar configured nematic droplet is analyzed numerically. Results of the calculation are expressed as the tilted angle of the director in the droplet, which balance between torque by elastic energy and the torque by external electrical field. The tilted angle is expressed as the function depending on latitude angle and relative radius r / R in the spherical droplet. The result shows that the maximum difference of the tilted angle happens at 0.87 R, where the tilted angle varies 12°C before applying external field (0 V/μm.) and after applying electrical field (0.62 V/μm). If nematic droplet would be applied as a micro lens, its focus would vary because the refractive index changes due to the change of tilted angle. According to the calculation, maximum modification of refractive index is 0.036, if E7 would be adapted as the nematic phase in the droplet.展开更多
基金Project supported by the National Natural Science Foundation of China(No.12332011)。
文摘The photo-induced buckling of axially periodic glassy nematic films with alternating stripped director domains is explored by the F¨oppl-von K′arm′an plate theory along with a modified kinetics approach.The effects of domain widths on the critical light intensity as well as the buckling morphology are examined numerically.It is found that in most cases the buckled film forms regularly aligned dimples and protrusions,but shows large scale bending perpendicular to the periodic axis if the widths of the stripes are nearly the same.In addition,change in light intensity is shown to alter the wavenumber of the buckling pattern.These results are expected helpful to the design of shape-shifting structures with glassy nematic films.
基金This work was supported by the National Key Projects for Fundamental Research, "Macromolecular Condensed State" of Ministry of Science and Technology of China.
文摘The kinetics of I→N transition of a side chain nematic polymethacrylate has been studied by small angle depolarized light scattering intensity measurements using a charge coupled device linear image sensor. The polymer shows transition of a liquid crystalline polymer is a spinodal type of phase transition mediated by orientation fluctuation.
基金Supported by the Hebei Province Natural Science Foundation of China under Grant No.198002.
文摘Nematic liquid crystal system of interacting biaxial particles via dispersion forces is studied.The molecular orienting potential form in a magnetic field is given for the first time.Weakly ordered isotropic phase is treated in the two-particle cluster approximation.Taking account of the molecular biaxiality,it is found that the ratio of the lowest supercooling temperature T^(*)to the nematic-isotropic phase transition temperature TC approaches the observed value,and the validity of the mean field theory is clarified.
基金Supported by’94 Outstanding Young Scientist Foundation of NSFC
文摘The disadvantages of Normally White Twisted Nematic Liquid Crystal Display (NW-TN-LCD) were discussed. The reason that the negative birefringent polyimide thin filmswere used to compensate NW-TN-LCD to decrease off-axis leakage, improve contrast ratiosand enlarge viewing angles was explained in this paper. A certain polyimide thin film wastaken as an example to show compensation effect on NW-TN-LCD.
基金The work was supported by the Foundation of State Education Committee of China
文摘Semi-rigid liquid crystal polymer is a class of liquid crystal polymers different from long rigidrod liquid crystal polymer to which the well-known Onsager and Flory theories are applied. Inthis paper, three statistical models for the semi-rigid nematic polymer were addressed. They arethe elastically jointed rod model, worm-like chain model, and non--homogeneous chain model.The nematic-isotropic transition temperature was examined. The pseudo-second transition tem-perature is expressed analytically. Comparisons with the experiments were made and the agree-ments were found.
文摘A schlieren texture with six dark brushes emanating from a point and a closed inversion wall have been observed under polarizing optical microscope in nematic state of a thermotropic aromatic copolyester, which have not been reported so far in the field of liquid crystalline polymers (LCPs).
文摘Basea on the new model and concept of mtramolecular orientational order parameter, a molecular field theory was built up for main chain liquid crystalline polymer (MC-LCPs) with flexible spacers. The theory takes account of orientational correlation among all mesogens in a polymer chain and the relationship between the intramolecular orientation and spatial orientation of the mesogens. The free energy, temperature and entropy of the nematic-isotropic transition were determined with the theory and compared with experiments in current work. It was found that many unique transition properties of the MC-LCPs comprising flexible spacer are correctly predicted by the theory and the agreement of the theory with the experiments is impressive.
文摘The experimental investigation on the conformation of a thermotropic main-chain nematic polymer by small-angle X-ray scattering (SAXS) has been carried out. The average radius of gyration of the polymer has been determined in nematic and isotropic state respectively. The experiment shows that the boundary between domains is not sharp but diffuse, and the diffuse-boundary thickness of the polymer as a function of temperature has been given.
文摘The banded texture in films prepared from nematic poly （1,4-benzamide） （PBA）/H<sub>2</sub>SO<sub>4</sub> solution by shearing and without shearing has been studied by using microscopy techniques. The kinetic parameters of banded texture formation γ<sub>c</sub> and τ<sub>b</sub> were measured for nematic solution of PBA by using parallel-plate shearing apparatus. The banded texture was also observed in randomly packed domains for nematic solution of PBA on standing without shearing. The properties of banded texture show no difference between the two samples with or without shearing.
基金supported by the National Key Research and Development Program of China (Grant No. 2018YFB0703701)the National Natural Science Foundation of China (Grant No. 61475042)。
文摘A 90°mixed-mode twisted nematic liquid-crystal-on-silicon(90°-MTN LCoS) with protrusion located between the adjacent pixels is proposed to reduce the effect of fringing field. The influence of the protrusion with different widths from0.5 μm to 0.9 μm and different heights from 0.3 μm to 0.7 μm is investigated. The results demonstrate that the invalid pixel region width can be reduced by 31.5% via using the protrusion with the suitable width and height compared with no protrusion case, which provides a higher display quality, such as the higher reflectance and contrast ratio.
基金the National Science Foundation(No.20674005)the Flat-Panel Display Special Project of China 863 Plan(No.2008AA03A318)Projects of Chinese National Science and Technology Tackling Key Problems(No.2007BAE31B02)
文摘A novel series of chiral dopants synthesized from(S)-1,2-propanediol and mesogenic carboxylic acids were characterized by FT-IR,~1H NMR,elemental analysis and their helical twisting properties were investigated by doping the chiral dopants into a nematic liquid crystal host(SLC-1717).The results show that,the helical pitch of N~*-LC mixture exhibited a terminal alkyl chain length dependence and the molecular twisting power β also exhibited a temperature dependence(increasing β with increasing temperature...
文摘The dielectric properties of the nematic mesophase, p-methoxy benzylidene p-decyl aniline(MBDA), measured in planar geometry with a function of frequency and temperature are investigated in detail. The complex dielectric permittivity(ε' and ε'') is also studied at a bias voltage of 10 V for planar aligned sample cell of nematic mesophase. The dielectric permittivity with bias voltage attains a higher(> 2 times) value than that without bias voltage at a temperature of 56℃,which is due to the fact that the linking group of nematic molecules is internally interacted with an applied bias voltage.This is supported by observing an enhanced dielectric permittivity of nematic liquid crystal(LC) in the presence of bias voltage, which can be fully explained as the increasing of the corresponding dipole moment. The dielectric relaxation behaviors of nematic LC are also demonstrated for planar aligned sample cell. The remarkable results are observed that the relaxation frequency shifts into low frequency region with the increase of the bias voltage applied to the planar aligned sample cells. The dielectric relaxation spectra are fitted by Cole–Cole nonlinear curve fitting for nematic mesophase in order to determine the dielectric strength.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11888101,91421107,and 11574004)the National Key Research and Development Program of China(Grant Nos.2016YFA0301003 and 2018YFA0305602).
文摘Nematic phase intertwines closely with high-Tc superconductivity in iron-based superconductors.Its mechanism,which is closely related to the pairing mechanism of superconductivity,still remains controversial.Comprehensive characterization of the electronic state reconstruction in the nematic phase is thus crucial.However,most experiments focus only on the reconstruction of band dispersions.Another important characteristic of electronic state,the spectral weight,has not been studied in details so far.Here,we studied the spectral weight transfer in the nematic phase of FeSe0.9S0.1 using angle-resolved photoemission spectroscopy and in-situ detwinning technique.There are two elliptical electron pockets overlapping with each other orthogonally at the Brillouin zone corner.We found that,upon cooling,one electron pocket loses spectral weight and fades away,while the other electron pocket gains spectral weight and becomes pronounced.Our results show that the symmetry breaking of the electronic state is manifested by not only the anisotropic band dispersion but also the band-selective modulation of the spectral weight.Our observation completes our understanding of the nematic electronic state,and put strong constraints on the theoretical models.It further provides crucial clues to understand the gap anisotropy and orbital-selective pairing in iron-selenide superconductors.
基金supported by the Natural Science Key Foundation of Universities of Fujian Province(JZ160406)Natural Science Foundation of Fujian Province(2015J01582)
文摘In this paper,we consider the short time classical solution to a simplified hydrodynamic flow modeling incompressible,nematic liquid crystal materials in R^3. We establish a criterion for possible breakdown of such solutions at a finite time. More precisely,if(u,d)is smooth up to time T provided that ∫_0~T||▽×u(t,·)||_(BMO)(R^3)+||▽d(t,·)||_(L^4(R^3))~8dt<∞.
基金Project supported by the National Key R&D Program of China(Grant Nos.2017YFA0303000 and 2016YFA0300201)the National Natural Science Foundation of China(Grant No.11888101)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000).
文摘The driving mechanism of nematicity and its twist with superconductivity in iron-based superconductors are still under debate.Recently,a dominant B1g-type strain effect on superconductivity is observed in underdoped iron-pnictides superconductors Ba(Fe_(1-x)Co_(x))_(2)As_(2),suggesting a strong interplay between nematicity and superconductivity.Since the long-range spin order is absent in FeSe superconductor,whether a similar strain effect could be also observed or not is an interesting question.Here,by utilizing a flexible film as substrate,we successfully achieve a wide-range-strain tuning of FeSe thin flake,in which both the tensile and compressive strain could reach up to~0.7%,and systematically study the strain effect on both superconducting and nematic transition(T_(c)and Ts)in the FeSe thin flake.Our results reveal a predominant A1g-type strain effect on T_(c).Meanwhile,Ts exhibits a monotonic anti-correlation with T_(c)and the maximum T_(c)reaches to 12 K when Ts is strongly suppressed under the maximum compressive strain.Finally,in comparison with the results in the underdoped Ba(Fe_(1-x)Co_(x))_(2)As_(2),the absence of B1g-type strain effect in FeSe further supports the role of stripe-type spin fluctuations on superconductivity.In addition,our work also supports that the orbital degree of freedom plays a key role to drive the nematic transition in FeSe.
文摘A theoretical treatment of photo-refractive effect and experimental verifications of the associated nonlinear-optical processes in the nematic phase of liquid crystals are presented. The effect is attributed to the dc space charge fields induced by the photo-charges which may come from the photoionization impurities. The phenomenon is analyzed and a theoretical modeI of photorefractivity in nematic liquid crystals is developed. New experimental results are found to be in good agreement with the theory.
文摘The elastic pair potential model of liquid crystal molecules was described. On the basis of Poniewiersky-stecki statistical theory of the elastic constants of nematic liquid crystals, the effects of non-ideal rigid repulsion between molecules on the elastic constants of nematics were studied.
基金Supported by the National Natural Science Foundation of China (No.9020301)
文摘Director field in a bipolar configured nematic droplet is analyzed numerically. Results of the calculation are expressed as the tilted angle of the director in the droplet, which balance between torque by elastic energy and the torque by external electrical field. The tilted angle is expressed as the function depending on latitude angle and relative radius r / R in the spherical droplet. The result shows that the maximum difference of the tilted angle happens at 0.87 R, where the tilted angle varies 12°C before applying external field (0 V/μm.) and after applying electrical field (0.62 V/μm). If nematic droplet would be applied as a micro lens, its focus would vary because the refractive index changes due to the change of tilted angle. According to the calculation, maximum modification of refractive index is 0.036, if E7 would be adapted as the nematic phase in the droplet.
