Mixtures containing ferroelectric nematic phases and methods of forming and using same - Patents.com

Abstract

A material is disclosed that includes a ferroelectric nematic phase. The material can include a mixture including a first molecule and a second molecule. At least one of the first molecule fluid and the second molecule fluid exhibits a ferroelectric nematic phase. The first molecule and the second molecule are miscible. The first molecule can induce a polar orientational order in the second molecule.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 240,666, entitled "Preparation and Characterization of Mixtures Displaying the Ferroelectric Nematic Liquid Crystal Phase," filed September 3, 2021, and also claims the benefit of U.S. Provisional Patent Application No. 63 / 278,039, entitled "Mixture Including Ferroelectric Nematic Phase and Methods of Forming and Using Same," filed November 10, 2021, the contents of each of which are hereby incorporated by reference herein to the extent the contents thereof are not inconsistent with this disclosure. Federally Sponsored Research This invention was made with Government support under Grant Nos. DMR2005270, DNR1710711, and DMR1420736 awarded by the National Science Foundation. The Government has certain rights in this invention.

[0002] The present disclosure relates generally to materials that include a ferroelectric nematic phase. More specifically, the present disclosure relates to materials that include mixtures that include a ferroelectric nematic phase, methods of forming the materials, and devices that include the materials. [Background technology]

[0003] Ferroelectricity in liquids was predicted in the 1910s by P. Debye and M. Born. They applied the Langevin-Weiss model of ferromagnetism to the orientational ordering of molecular electric dipoles. Recently, interest in nematic ferroelectricity has been gaining attention. Nematic ferroelectricity offers opportunities for novel liquid crystal science and technology due to its unique combination of macroscopic polar ordering and fluidity. The ferroelectric nematic (NF) phase of RM734 exhibits rapid electro-optical response at high temperatures in its NF range, but exhibits a strongly increasing viscosity upon crystallization and slow cooling. On the other hand, the room temperature NF phase obtained upon quenching is glassy. Therefore, improved materials exhibiting nematic ferroelectricity are widely desired.

[0004] Any discussion of problems and solutions described in this section is included in this disclosure solely for the purpose of providing a context for the disclosure, and should not be construed as an admission that any or all of the discussion was known at the time the invention was made. Summary of the Invention [Means for solving the problem]

[0005] This Summary is provided to introduce a selection of concepts, is not necessarily intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0006] The embodiments of the present disclosure relate to a material comprising a ferroelectric nematic phase. The material may comprise a mixture comprising a first molecule and a second molecule, where at least one of the first molecule fluid and the second molecule fluid exhibits a ferroelectric nematic phase, the first molecule and the second molecule are miscible, and the first molecule induces a polar orientational order in the second molecule. According to examples of these embodiments, the first molecule and the second molecule are chemically dissimilar. In this regard, chemical dissimilarity can be defined by a molecular similarity coefficient S (vector representation of chemical structure) calculated from a fingerprint based on the topology of the molecules. A pair of distinct molecules with S less than 0.33 is highly dissimilar, and a pair with S greater than 0.8 is highly similar. A widely used measure of chemical similarity is the Dice similarity coefficient calculated from the extended connectivity (Morgan) fingerprint [D. Rogers and M. Hahn, J. Chem. Inf. and Model. 50, pp. 742-754 (2010)]. Based on this measure of similarity, RM734 and DIO are highly dissimilar (S=0.29), while all previously reported binary mixtures of rod-like molecules exhibiting ferroelectric nematic phases consist of highly similar (S>0.85) first and second molecules. According to examples, the chemical dissimilarity may be S less than 0.75, 0.5, 0.33, or 0.3. According to further examples, at least one of the first and second molecules includes a halogen. According to further examples, at least one of the first and second molecules does not include a halogen. In some examples, at least one of the first and second molecules may include multiple halogen atoms. According to further examples of the present disclosure, each of the first molecules comprises a first backbone, a first terminal functional group of the first molecule, and a second terminal functional group of the first molecule, and each of the second molecules comprises a second backbone, a first terminal functional group of the second molecule, and a second terminal functional group of the second molecule. In some examples, the first backbone (e.g., its chemical structure) and the second backbone are different. Additionally or alternatively, the first terminal functional group of the first molecule is different from the first terminal functional group of the second molecule, and / or the second terminal functional group of the first molecule is different from the second terminal functional group of the second molecule.The one or more end groups may include halogen (e.g., fluorine), alkyl groups, or alkoxy groups. The backbone may include three or four ring structures, at least one linker group, and optionally side chains on one or more of the ring structures. Exemplary ring structures include, for example, phenyl rings, cyclohexane rings, dioxane rings, thiophene rings, monoxane rings, pyridine rings, pyrimidine rings, or any other heterocyclic groups. The first and second molecules may exhibit similar charge distributions, for example, as defined by a similarity coefficient S, which is a measure of the similarity of shape and electrostatic potential. [A. Kumar and K.Y. J. Zhang, Frontiers in Chemistry 6, 315 (2018)]. A pair of distinguishable molecules with S less than 0.33 is highly dissimilar, and a pair with S greater than 0.8 is highly similar. In this case, similarity may be S=0.5, 0.7, or 0.8, or more. The material may include one or more additional molecules that are miscible in the mixture. By way of further example, the nonlinear optical material may include any of the materials described herein.

[0007] According to a further embodiment of the present disclosure, a method for forming a material having a tunable ferroelectric nematic phase is provided. An exemplary method includes mixing a first molecule and a second molecule to form a mixture having a ferroelectric nematic phase, the first molecule inducing a polar orientational order in the second molecule. The first, second and any further optional molecules may be as described above.

[0008] As a specific example, the first molecule comprises RM734 and the second molecule comprises DIO. Devices, including electronic, electro-optical, and non-linear devices, may include one or more (eg, two) electrodes and the materials / mixtures described herein.

[0009] A more complete understanding of the embodiments of the present disclosure can be derived by reference to the detailed description and claims when considered in conjunction with the following illustrative drawings. [Brief description of the drawings]

[0010] [Figure 1] RM734 and DIO, representative members of a family of nitro- and fluoro-based molecules that exhibit novel polar nematic phases. Ferroelectric nematics (NF) have been observed independently in both materials and in close homologs within each family. DIO further exhibits the mesophase SmZA, which has recently been shown to be antiferroelectric smectic. [Diagram 2] FIG. 1 shows a synthetic scheme for DIO according to an embodiment of the present disclosure. [Diagram 3] Figure 1 shows the phase diagram of a binary mixture of RM734 and DIO. The phase transition temperatures were determined using polarized light microscopy, DSC, and polarization current measurements. The continuous miscibility among the Iso, N, and NF phases indicates that they are identical in RM734 and DIO. The transition is first order, and the average entropy change across the phase diagram is ▼-ΔS~(0.16±0.01)R;

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[0011] The description of exemplary embodiments provided below is merely exemplary and is intended for purposes of explanation only. The following description is not intended to limit the scope of the disclosure or the claims. Moreover, reference to multiple embodiments having described features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the described features.

[0012] In this disclosure, any two variables may constitute a workable variable range, and any range indicated may or may not include the endpoints. Furthermore, any value of an indicated variable (whether or not they are indicated as "about") may mean an exact or approximate value, including equivalents, and may mean an average, median, representative value, majority, value ±10% (e.g., volume, atomic, or mass %), etc. Furthermore, in this disclosure, the terms "comprise", "consist of", and "having" may, in some embodiments, independently mean "typically or extensively include", "comprise", "consist essentially of", or "consist of". In this disclosure, any defined meaning does not necessarily exclude the ordinary and customary meaning.

[0013] In 2017, two groups independently reported novel nematic phases of polar molecules, namely, an antiferroelectric splay nematic in molecule RM734 and a “ferroelectric-like” phase in molecule DIO. Ferroelectricity was subsequently demonstrated in RM734 and DIO. The serendipity of this development is remarkable, since RM734 and DIO are members of distinct molecular families with distinctly different molecular structures, as is evident from Figure 1. Novel polar nematics were independently observed in close homologs and mixtures within these families. Meanwhile, DIO and RM734 have similar molecular shapes and sizes, and both molecules have a longitudinal molecular dipole moment of about 11 Debye, a similarity that may be advantageous for their miscibility in the NF phase.

[0014] These observations motivated us to pursue studies of the interactions between these distinguishable molecular species with respect to nematic ferroelectricity. Here we present an experimental examination of the phase and electro-optical behavior of binary DIO / RM734 mixtures. Although similarities in the optical texture, calorimetry, and second harmonic generation of RM734 and DIO have been recently reported, the question of whether the ferroelectric nematics identified in RM734 and DIO are the same phase can only be definitively answered by examining binary miscibility. The phenomenology of mixing these materials in their ferroelectric nematic phase was unknown, but because they are chemically distinct, it is unlikely that these molecules would be highly miscible in their crystalline phase, promising an opportunity to suppress crystallization and achieve ferroelectric mixtures at room temperature. In conjunction with this work, we have examined the M2 phase, originally reported in DIO but not structurally characterized. Synchrotron-based microbeam small-angle X-ray scattering (SAXS) and electro-optic polarizing microscopy have demonstrated that M2 is a density-modulated antiferroelectric LC with lamellar, nematic directors parallel to the layer planes, and is characterized as a smectic Z (SmZ) LC in our previously reported work. A ) is named after the phase.

[0015] Nematic ferroelectricity offers opportunities for novel liquid crystal science and technology due to its unique combination of macroscopic polar ordering and fluidity. For example, the ferroelectric nematic (N F ) phase is N F It shows a rapid electro-optic response at high temperatures in the range, but exhibits a strong increase in viscosity upon crystallization and slow cooling. F The phase is glassy. In the application development of liquid crystal technology, the exploration of mixtures is an approach to address such challenges as preventing crystallization, expanding the phase range, and tuning the liquid crystal properties. The study of mixtures is also key to advancing liquid crystal science, providing methods to test structural models of phases by continuously varying the composition, to discover phases in mixtures not exhibited by any of their components, and to discover new phases. result Phase Diagram- RM734 and DIO were synthesized using the scheme shown in Figure 1. The phase diagram for various weight percentages (wt%) of DIO in the mixture determined upon slow cooling from the isotropic (Iso) phase using polarized light microscopy (PLM), differential scanning calorimetry (DSC), polarization measurements, and SAXS experiments is shown in Figure 3. Distinct phase fronts passing through the cell at each transition were observed under the microscope, allowing for precise determination of the transition temperatures. The observed transition temperatures of the pure components are in good agreement with published values. Upon cooling of the mixture, three different liquid crystal phases were observed, namely paraelectric nematic (N), antiferroelectric smectic Z (SmZ ... A ), and ferroelectric nematic (N F ) was observed. Using the standard simplified material terminology for disordered phases beyond ferroelectrics or antiferroelectrics, the N phase is referred to as the "paraelectric phase". At the lowest temperatures, a crystalline phase was observed, but its properties and composition were not investigated. The Iso, N, and N phases F The phases appear in a continuous manner throughout the phase diagram, indicating that the two components are completely miscible in these phases at all concentrations. According to the miscibility laws, this observation answers the question posed above, and the Iso, N, and N phases in RM734 are F The phase is the same as that in DIO. A The phase range of N decreases with decreasing DIO concentration and disappears below c ≒ 50 wt%. F The phase boundary to α slopes linearly with c, suggesting ideal mixing behavior at this transition, as discussed in detail below.

[0016] Notable phase characteristics can be summarized as follows: · Isotropic Phase (Iso) - The Iso phase exhibits extinction of transmitted light between crossed polarizers and analyzer and exhibits no detectable response to applied electric fields up to 100 V / mm. · Paraelectric nematic phase (N) - As expected, the N phase has planar alignment with a uniform, in-plane director field n(r) parallel to the buffing direction. Excellent extinction is achieved when the cell is oriented with the director parallel to the polarizer or analyzer (Figure 5(A), Figure 9(B)). A Freederickss transition driven by a 200 Hz square wave electric field is observed in the N phase (Figure 9(C)), where the in-plane electric field induces a twisting deformation of the director [RMS threshold voltage

[0017]

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[0018] , an electric field perpendicular to the cell plate causes splay bending deformation [RMS threshold voltage

[0019]

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[0020] where D is the in-plane electrode gap, K T and K. S are the Frank elastic constants for twist and untwist, and Δε is the low-frequency dielectric anisotropy. The temperature dependence of the threshold voltage in RM734 and DIO is shown in Figure 10. RM734 and DIO exhibit a typical Freedericks-like threshold orientation response to an applied electric field. Both RM734 and DIO exhibit a rough increase in Δε upon cooling. However, the Freedericks threshold is lower in RM734, with a strong pretransition growth of Δε and K S Due to the decrease in F This phenomenon does not occur in the N phase of DIO because N approaches the antiferroelectric phase. The splay threshold voltage observed in RM734 is the K S and Δε values ​​were used to calculate

[0021]

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[0022] Theoretical twist / spread threshold ratio

[0023]

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[0024] By comparing the measured values, the elastic constant ratio K T / K S It is possible to estimate the

[0025]

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[0026] The NN in RM734 is obtained. F Except for the vicinity of the transition, K S The pre-transition drop in K S >K T In DIO, K S ≒10K T It is. Lamellar antiferroelectric LC with in-plane nematic director (SmZ A )-Recently, using non-resonant SAXS on magnetically aligned capillaries and PLM electro-optics in aligned cells, we have determined that the previously reported but unstructured M2 phase of DIO is a layered (density modulated) antiferroelectric LC, which we classify as a smectic Z A (SmZ AThey named this material SmZ, which contains 9-nm-thick polar layers with alternating polarization and a periodic array of nematic directors parallel to the layer planes. Within the cell, these layers fill the three-dimensional space in a distinct smectic-like arrangement, with the layers either parallel or perpendicular to the plates. Upon cooling from the N-phase in a cell with a buffed polyimide surface, the layers grow perpendicular to the plates, suppressing the in-plane twisting Freedericks response to electric fields applied in the plane of the cell, but sustaining the splay-bend-Freedericks transition for electric fields applied perpendicular to the plates. These features lead to the discovery of SmZ. A N phase and N F It becomes easy to distinguish between the two phases. Ferroelectric nematic phase (N F )- SmZ in pure DIO A The N obtained by cooling the homogeneous domain of the phase F The evolution of the phase texture is shown in the PLM images in Figure 4 (A-D), which show the N phase obtained upon cooling homogeneous domains of N phase in the c = 40 wt% DIO mixture. F The evolution of the texture of the phases is shown in Figure 5, both in the absence of an electric field. In addition to undergoing characteristic optical changes, the N F The transition from a few tenths of a volt in the N phase to the N F The new cell is characterized by an increase in the threshold for the splay-bend-Fredericks transition to over 100 V in the splay-bend phase. This is a result of the large electrostatic energy cost of rotating the ferroelectric polarization P in an initially planar cell to give it a component perpendicular to the cell plates. At the same time, the threshold field for the twist induced by the in-plane electric field is reduced by a factor of almost 1000 due to the progression of the ferroelectric coupling of P and E, as shown by N F All director states exhibit extreme electro-optical response at very weak in-plane applied electric fields (in the range of 0.1 to 1 V / mm). F At the transition to N, a surface characterized by local orientation fluctuations passes through the cell (Figure 4B), followed by N F The smooth, planar texture of the N F The N phase (and SmZ phase) with n parallel to the buffing axis several degrees into the phase AThe cell retains a uniform director field (U state) of 100 nm (phase). However, upon further cooling, a structural transition occurs where distinct transition lines (π-twist disclination lines formed at one surface) pass laterally through the cell, mediating the formation of left-handed and right-handed (LH and RH) π-twist domains. These are not quenched and are themselves separated by another distinct line defect (2π-twist line at the mid-plane of the cell) as seen in Figure 4(A), Figure 5(C). Although these twist states appear optically identical between crossed polarizers and analyzer, their equivalence is lost when the polarizers are uncrossed and the LH and RH domains exhibit distinct colors / shades that are exchanged when the polarizers are otherwise uncrossed (Figure 4(BD)). This behavior was first observed in ANTIPOLAR cells of pure RM734, showing the spontaneous conversion of a uniform nematic director / polarization state to a π-twist state by the passage of a π-twist line. This observation is important and unequivocal confirmatory evidence for nematic ferroelectricity. F The spontaneous uniformity to π-twist transition in phase antiparallel buffed cells is a uniquely ferroelectric nematic phenomenon, requiring not only macroscopic polar ordering of the bulk LC, but also polar coupling to a macroscopically polar surface. The LH and RH π-twist states support half a turn of a left- or right-handed director helix, respectively, and are separated by a topological 2π-twist line. The two twist states have opposite net polarizations perpendicular to the buffing axis, and can thereby be switched between them using reversal of an electric field applied in this direction, as shown in Figure 4(EG). Such π-twist states were observed in all blends and pure DIO, exhibiting qualitatively similar behavior to that observed in pure RM734, thereby allowing us to characterize the N F It is concluded that the phase diagram is continuous. Similarities in the textures of RM734 and DIO are observed in random planar cells.

[0027] N F Phase transition - This transition is clearly distinct at the two ends of the phase diagram. In the RM734 rich mixture, the NN FAs the transition is approached, a random pattern of fluctuating polar domains is observed, as previously reported for pure RM734 and shown in Figure 5(B). These domains extend along the director orientation n as a manifestation of electrostatic suppression of the longitudinal fluctuations of the polarization P. N F The details of the coarsening of these domains upon cooling to 0.05 depend on the surface conditions, but in rubbed polyimide cells a few microns thick, the domains typically grow to a size of a few microns, erasing the texture defects and forming large uniform monodomains followed by a twisted state. In thicker cells or more weakly aligned cells, the coarsening of the domains occurs in RM734 and N to N F As seen in the DIO homologue with a direct transition to , the length scale of the coarsening domains is observed to increase continuously upon cooling to millimeter scales, with irregular macroscopic patterns of inverted polarization extending along the director. In a typical test cell, the uniform N F The domains are separated by purely poled or splay-bend walls. This behavior is consistent with the ferroelectric uniform and twisted state observed in DIO, as well as the N F Phase N in RM734 and DIO F This suggests that it is the same as the phase.

[0028] N of any preparation of RM734, DIO, or their mixture F The RM734 family of N-type nanotubes, whether in standard thin cells, capillaries, or thicker (10-50 μm) cells, aligned in a planar or random plane rather than in a phase, F It is noted that periodic birefringent (splay nematic) stripes spaced about 9 μm apart of the type previously reported in the phase were not observed.

[0029] At the DIO end of the phase diagram, the transition sequence upon cooling is first N-SmZ A , followed by SmZ A -N F These transitions are weakly first order and the phase changes to NN FThe SmZ transition occurs without the dramatic polarization fluctuations seen in the SmZ transition. A This is believed to be due to the antiferroelectric ordering of the SmZ phase. A Over most of the phase, the in-plane reorientation of the director field is strongly suppressed, whereas the N F At lower temperatures, approaching the phase transition, ferroelectric fluctuations appear and there is an increased sensitivity to electric field induced reorientation, as will be discussed in a later publication.

[0030] Ferroelectric Polarization - A typical set of measurements of the polarization current i(t) in response to an applied electric field in the plane of a 50 Hz, 104 V / mm square wave at various temperatures versus time is plotted in Figure 6(A), in this case for a DIO mixture with c = 90 wt%, with additional data included in Figure 11. This weak applied electric field is N F It is large enough to reverse the polarization in the Iso phase, N phase, and SmZ A In the N-phase, the current consists only of a signal that peaks immediately after the reversal of the sign of the applied voltage and then decays exponentially. This signal corresponds to the linear response of the RC circuit and the series resistance of the cell, N F The increase in ε in the N phase as ε approaches T causes the initial upward curvature of the measured P. F Upon the transition to , a much larger current signal appears at a longer time due to the spontaneous polarization reversal in the sample. This current peak is integrated with respect to time to obtain the net charge flow Q = ∫i(t)dt and the corresponding charge density Q / 2A shown in Figure 6(B) and Figure 11, where A is the cross-sectional area of ​​the liquid crystal sample in a plane perpendicular to the applied electric field midway between the two electrodes.

[0031] Initial qualitative observations showed that the width in time of the current peaks increased dramatically with decreasing T (Figure 11), motivating the choice of square wave driving to minimize the width in time of the current response. Thus, at high temperatures, polarization reversal is completed during the available 10 ms integration time between applied field reversals. In this regime, the quantity Q / 2A is proportional to the N of the bulk by P(c,T)=Q(c,T) / 2A, as shown by the solid square symbols in Figure 6(B). F In this temperature range, the dependence of P(T) on temperature is quite similar for all mixtures, and N F As the transition to the N (or SmZ) phase is approached, the polarization increases in an S-shape, and the initial upward curvature corresponds to the N (or SmZ) phase observed in both RM734 and DIO. A ) phase.

[0032] However, as shown in Fig. 6(A) and Fig. 6(C), the full width at half maximum of the current peak accompanying the polarization reversal, τ R increases rapidly upon cooling. sat Below this threshold, polarization reversal cannot be completed within the available 10 ms time window even with square wave drive, and the measured Q(c,T) / 2A values ​​decrease with decreasing T. sat (solid circles in FIG. 6(B)). Pilot experiments with longer integration times confirm these data by showing that P decreases with decreasing T, as observed in RM734 and confirmed in atomistic simulations of RM734. sat (c) does not reflect the true polarization, which increases by several percent. In the following analysis of the time-reversal dynamics, T sat The polarization at temperatures below P is simply sat (c). Under this assumption, we use time-reversal dynamics to obtain T sat Measurements of the orientational viscosity at temperatures T below can be obtained.

[0033] The saturation values ​​of polarization were similar for all mixtures, as seen in Figure 6(B). sat ≒6μC / cm 2and P sat (c) decreases slightly from the RM734-rich end to the DIO-rich end, as seen in Figure 6(D).

[0034] At low temperatures, polarization measurements were taken at approximately 30 min intervals to allow time for possible crystallization. The inset in Figure 6(A) shows the current response after field reversal for the c=90% DIO mixture at the lowest temperature. In this mixture, crystallization occurred between the T=26.5°C and T=25.5°C scans, eliciting a rapid drop in the integrated current as is evident from the plot. Crystallization was observed in the N F Crystallization is generally observed upon cooling of mixtures at both ends of the phase diagram near c≈0% and c≈100% (gray crystalline regions in Figure 3), since the phase becomes thermodynamically favored at higher temperatures where it still has a relatively low viscosity. Interestingly, crystallization is largely suppressed in the c=90% DIO mixture while a square-wave poling field is applied, whereas the sample crystallizes within about 1 h at T=25°C in the absence of a field. The poling time was measured as a function of temperature for all mixtures, and the results are shown in Figure 6(C).

[0035] T sat For T less than 100 nm, the measured Q(T) data shows that complete polarization does not occur, but sat P(c,T)=P for T less than sat (c) An upper estimate of the fraction of reoriented polarization within a 10 ms integration window, f(T)=(Q(T) / 2A) / P sat (c). The sharp drop in measured charge density at the lowest temperature coincides with a sharp increase in switching time due to the rapid rise in effective orientational viscosity with approach to the glassy state. There is no evidence of crystallization in the intermediate range of concentrations. This is prevented by the high viscosity and depression of the freezing point at low T; cooling instead leads to a glassy state. Crystallization is suppressed by rapid cooling at all DIO concentrations, allowing any mixture to be quenched to a room temperature glass.

[0036] Dynamics of Polarization Reorientation: Measurement of Orientational Viscosity - NF The characteristic time for the electric-field-driven reorientation in the phase is τ = η / PE, i.e., the intrinsic response time for an induced 90° rotation starting from a state of high torque when P is perpendicular to E, where η is the orientational viscosity, which is N F The driving voltages used in these measurements are RM734 with a time interval of τ R ≈10τ = 10η / PE. Under conditions of rapid electric field reversal, the polarization reversal takes this long because P typically aligns antiparallel to E in a very low torque orientation throughout most of the cell volume immediately after the electric field is switched. Therefore, to get an estimate of η(c,T), we use η(c,T) = 0.1[P(c,T)τ R (c,T)]E can also be used. The results are plotted in Figure 6(C). The measurements were performed at a fixed electric field amplitude, so τ R The data is T sat P(T)=P for T less than sat As N F It directly indicates the viscosity over the entire temperature range (τ R P / P sat (is proportional to η) R (T)P(T) / P sat Plot as.

[0037] The measured viscosities of all mixtures were N F At the maximum temperature in the phase, η ≒ 0.05 Pa s, and the maximum time that can be measured during cooling (where τ R The viscosity of each mixture exhibits an approximately Arrhenius-type dependence on temperature (Figure 6(C)), suggesting a barrier-limited dissipation process. The experimental data generally exhibit an upward curvature that indicates a tendency to cross the Arrhenius line at the lowest temperatures, which can be attributed to approaching the transition to the glassy state. The measured polarization P sat The onset temperature Tg(c), which is considered to be the temperature at which the temperature drops to 80% (f(T) = 0.8), happens to be τ R≒5 msec, which is shown as a hollow triangle in Fig. 3. This transition temperature varies almost linearly with concentration, T NF It is parallel to the transition temperature.

[0038] Room temperature ternary mixture - its N F The low temperature dynamics of the c=90 wt% DIO mixture, whose phase persists up to room temperature, was further explored by blending it into a third component, W1027 (shown in Figure 2), to produce a (70 wt% DIO) / (15 wt% RM734) / (15 wt% W1027) mixture. Samples of this mixture were stored in N2O, which is fluid at room temperature and stable against crystallization for several hours. F The temperature dependence of the viscosity of this mixture is plotted as the open circles in Figure 6(C).

[0039] The polarization versus temperature of the ternary DIO / RM734 / W1027 mixture described in the text is plotted in Figure 7(A), and the magnified viscosity of this mixture is plotted in Figure 7(B). Experimental evidence of polar ordering of dipolar chromophores in ferroelectric nematic hosts - multicomponent chromophores containing nonlinear optical (NLO) chromophores, as shown in Figure 8. N The measurement of the ferroelectric polarization density P in the F mixture revealed that the host N F Compelling evidence is provided that the mixture induces a high degree of polar orientational ordering of the chromophore molecules. The structure of a typical NLO chromophore molecule, shown diagrammatically in Figure 8(A), consists of an electron donor, a pi-conjugated bridge, and an electron acceptor. Such "push-pull" type molecules have a large electric dipole moment (about 10 D) and a large first hyperpolarizability. Polarization measurements were performed using two N F A mixture, i.e., N, which consists of dipolar molecules similar to RM734 but does not contain NLO chromophores. F The host mixture PM146 and the NLO chromophore molecules obtained by adding 25 wt. % of the NLO chromophore molecules to the host mixture PM146. FAs shown in Figure 8(B), the polarization of PM158 is observed to be comparable to that of the host mixture PM146 over a wide temperature range. This is consistent with the lack of polar alignment, as it leads to a significant decrease in P with increasing chromophore concentration. F This is convincing evidence for the polar alignment of the dipolar chromophore molecules by the host. Complementary UV-Vis dichroism measurements on PM158 also show that the chromophore molecules are aligned in a nematic order parameter of S ≈ 0.7 with N F Indicates that the host is strongly aligned.

[0040] Phase behavior - In the case of DIO / RM734, a binary mixture is observed that exhibits a first-order transition between two phases spanning the phase diagram over all DIO concentrations c. Such a mixture is considered "ideal" if, in the calculation of the phase boundary temperature T(c), the entropy of mixing is the only specifically mixing-related thermodynamic contribution to be considered, in addition to the linear weighting of the changes in the enthalpy (ΔH) and entropy (ΔS) of the transition of the individual components based on their mole fractions. This means that "extra" contributions to the difference in the Gibbs potential ΔG between the two phases may be neglected. For example, if there were any attractions, repulsions, disordering, or ordering in the pairing of AB molecules that differed from the simple averaging of these effects in the pairing of AA and BB, such contributions would appear in the A / B mixture. Under ideal phase behavior conditions, N F The central temperature T of the phase coexistence range for the phase transition NF (c) The Schroeder-van Laer (SvL) equation:

[0041]

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[0042] where x = mole fraction, T DIO =343K and T RM734 =405K is pure DIO and RM734 N F Transition temperature to ΔS DIO =0.07R, ΔSRM734 =0.06R, ΔH DIO = 0.2 kJ / mol, and ΔH RM734 = 0.2 kJ / mol per mole of the pure component. This theoretical SvL phase boundary is generally curved in the x,T plane, but T DIO <T(x)<T RM734 Under ideal mixing conditions, ΔS(x) will be linearly interpolated between these limits. DIO = ΔS RM734 Then, we can see that the condition for the RM734 / DIO mixture is obtained. ΔS(x) is a constant and is eliminated from the equation, T(x) is a linear function of x, and the phase boundary is T across the phase diagram at x. DIO and T RM734 A straight line is formed between the two, and the difference in molecular weight is small (MW RM734 =423, M.W. DIO = 510), forming an almost linear relationship at c. DSC measurements of ΔS(x) at intermediate concentrations gave 〈ΔS(x)〉 = 0.056 ± 0.02R, which is the same as the ΔS value already presented in this paragraph. DIO and ΔS RM734 is approximately the same as the value.

[0043] At the RM734 end of the phase diagram, NN F The transition is direct and first order, while at the DIO end the phase sequence is two first order transitions N-SmZ A -N F However, the linear variation of T(x) with respect to x is N F The transition from N phase to SmZ A This is maintained regardless of the phase. T(x) is NN F The linearity of T(x) is governed by the intercept of the Gibbs free energy surface governing the transition (which is linearly interpolated between the free energy surfaces of the pure components). A This suggests that the thermodynamic effects of the transition are smaller. This is probably due to the extremely small N-SmZ A Transition enthalpy (ΔH NZ =0.003 kJ / mol), and the paranematic N phase and the antiferroelectric SmZA This is consistent with the P=0 nature of the N phase. F The net polarization of all phases is N at the phase boundaries marked by the round dots in Figure 3. F It proceeds through the final transition to a small ΔH NZ , T for c NF (c) Linearity of the dependence of N F The similarity across the phase diagram of the transition entropy for the final transition to is consistent with the P(T,c) curves having similar saturation values.

[0044] Quadruple but non-polar N phase to quadrupole with polarity N F The currently proposed model for the phase change to the α phase is that it is either a first-order Landau-Degennes mean-field transition or an Ising-like orientational transition of molecular dipoles with a binary choice of orientation (along +n or -n), made first-order by long-range dipole-dipole interactions. In either case, the polarization P(T) is the main order parameter of the transition. Figure 6(B) shows that the growth of P(T) is similar for different concentrations, and Figure 6(D) shows that the growth of P(T) is similar for different concentrations, and Figure 6(C) shows that the growth of P(T) is similar for different concentrations, and Figure 6(D ...C) shows that the growth of P(T) is similar for different concentrations, and Figure 6( sat (c) has a weak linear dependence on c. For ideal mixtures, this observation constrains the dependence of parameters on c in the theory of such transitions. For example, in Ising-like systems, T DIO is T RM734 , giving a local ferroelectric interaction between pairs of dipoles (i,j = DIO,DIO; i = DIO,j = RM734; i,j = RM734,RM734) with an Ising interaction energy J proportional to T(x). ij (x) is T NF (x) must be linearly interpolated. This is J DR =(J DD +J RR ) / 2, in which condition ΔG has no "excess" internal energy. For the nearest-neighbor Ising model (which undergoes a second-order phase transition in 3D), the entropy is a universal function of T / J, and there is also no "excess" entropy contribution to ΔG.

[0045] However, N F The transition to is found to be first-order, mean-field-like, and to exhibit highly anisotropic orientational correlations in the N phase, a feature that can be understood by models that include the effect of long-range dipole-dipole interactions on the fluctuations in the N phase. Although important behaviors of Ising systems with long-range interactions have been extensively studied in the context of certain magnetic materials with short-range ferroelectric exchange forces, long-range dipole interactions are also important. Renormalization group analysis shows that the long-range interactions, as observed in RM734, make the magnetic correlations dipole-anisotropic near the transition in the high-temperature phase and extend these along the n and z axes by strongly suppressing the longitudinal charge-density fluctuations δPz / δz. Specifically, starting from the free energy equation Eq. (1) and adding the dipole-dipole interaction terms, we obtain the P z The structure factor for the Ornstein-Zernicke polarization fluctuations of is χ(q)=1 / [τ(T)(1+ξ(T) 2 q 2 )+(2π / ε)(q z / q) 2 ] as P z (q)P z (q) * 〉=k B Tχ(q), where the correlation length ξ(T) 2 =b / τ(T), τ(T) is (TT NF ) / T NF where b is a constant and q=q z +q y The dipole-dipole (third) term is expressed as ξ(τ) along x and y, but ξ(τ) along z. 2 As can be qualitatively observed from the image sequences of the textures as they pass through the phase transition, and from their optical Fourier transforms, for finite q z Because of this anisotropy, the correlation volume in this model is isotropic in 3D, V ≒ ξ(τ) 3 rather V ≒ ξ(τ) 4, which reduces the upper dimensionality of the transition to three and makes the transition mean-field like with a logarithmic correction rather than being fluctuation-dominated by 3D Ising universality. The dipole-dipole term is P 2 and thus the nearly equal dipole moments and nearly equal J of DIO and RM734 tend to make this behavior similar across the phase diagram. DIO =T RM734 Assume that, therefore, J DD =J RR If we assume that the "ideal" mixed averaging condition J DR =(J DD +J RR ) / 2 is J DR =J DD =J RR The molecule is reduced to N F The pairwise interaction energies that stabilize the phases behave similarly.

[0046] Viscosity - The measured viscosity is the effective barrier height E η To determine the η(T)=Aexp[E η / k B As can be seen from the uniformity of the gradient, E η is essentially independent of c, and E η is 7800 K across the phase diagram. In contrast, the coefficient A varies substantially with c, a behavior that can be quantified by measuring viscosity versus concentration at a single temperature, e.g., 80 °C. The plot in Figure 6(D) shows the additivity of the logarithm of η(T) for the DIO / RM734 mixture, ln[η(80 °C)] = (x)ln[η DIO (80℃)]+(1-x)ln[η RM734(80 °C)]. A fundamental understanding of this behavior can be obtained by using the combined Cohen-Turnbull free volume / Eyring velocity theory model proposed by Macedo and Litovitz. This model is based on Maxwell's intuitive illustration or its modern implementation, in which the viscosity η = G / ν, i.e. the ratio of the typical elastic modulus G for local shear deformation to the average per-molecule rate ν of randomly occurring local structural deconfinement / relaxation events. The rate ν is given by ν = ν T p=ν T p E p V where ν T is the frequency of testing, and p is the probability of success, i.e., the probability that sufficient energy E is available. E =exp(-E η / E) and the probability that sufficient free volume V is available p V =exp(-V / V f ) and V f is the mean free volume per particle. These probabilities relate the viscosity to temperature and density, respectively, by the generalized relationship η(T)=G / (ν T p E p V )=(G / ν T )exp(cV o / V f +E η / k B T), where V o is the close-packed volume per particle, and the available energy is, on average, k B T. Applying this to the DIO / RM734 mixture, G and ν T is the same for the two components and is independent of temperature since the Kelvin range is fairly narrow, and the difference in viscosity of the components is V f In general, for binary mixtures, ν = ν T p=ν T (p DIO ) x (p RM734 ) 1-x =νT[(p E ) DIO x (pV ) DIO x (p E ) RM734 1-x (p V ) RM734 1-x ]. This formula can be seen from the similar slope of the approximation of lnη(T) for 1 / T in Figure 6(C) η is the same for the two components, i.e. (E η ) DIO =(E η ) RM734 This can be simplified by noting that (p E ) DIO =(p E ) RM734 =p E =exp(-E η / k B Therefore, the viscosity of the mixture is η(x,T) = (G / ν T )[p E x p E 1-x (p V ) DIO x (p V ) DIO 1-x ] -1 = η DIO (T) x η RM734 (T) 1-x which predicts the logarithmic additivity of viscosity, a behavior evident from the experimental data plotted in Figure 6(D). In relation to the above model, (E η ) DIO =(E η ) RM734 Assuming that the effective free volume in a mixture is V0 / V f This implies that it can be obtained from a linear combination of

[0047] Enantiotropic N F Phase and SmZ A Phase - All single component N phases reported to date FThe materials are monotropic, including RM734 and DIO, and N F The phase was only observed upon cooling, and N F This implies that the N state is thermodynamically metastable compared to the crystalline state. F When held at a fixed temperature in the N state, such single-component materials eventually crystallize on time scales ranging from seconds to days. F For practical applications of materials, enantiotropic behavior (i.e., thermodynamically stable N F Multicomponent blending is a well-established route to achieve enantiotropic behavior in liquid crystals, and indeed enantiotropic N F The behavior of has been previously described by Mandle and coworkers for mixtures of RM734 homologues. To study the enantiotropic behavior in mixtures of RM734 and DIO, samples were filled with the isotropic phase in 8 μm thick cells, cooled to room temperature, and left to stand for 2 months. Of all the mixtures that exhibited a glassy state, only the 90% DIO sample showed some recrystallization in parts of the cell after this period. The cells were slowly heated without an applied electric field, and the phase behavior was observed by polarized light microscopy. During subsequent heating cycles, spontaneous polarization was measured as a function of temperature using an in-plane electric field. Based on these observations, N F The phase was determined to be enantiotropic over the composition range of 10% to 80% DIO in RM734 / DIO mixtures (Figure 12, Table 1). For example, at 10% DIO, i.e., the broadest enantiotropic N F At temperatures in the range of F The SmZ phase is observed over a wide range of compositions in heating experiments. A Also, SmZ A is enantiotropic, in contrast to pure DIO, which is monotropic.

[0048] [Table 1]

[0049] Consideration The commonalities observed in the phase behavior of different molecular species with widely differing molecular structures for the isotropic-nematic liquid crystal transition have stimulated and supported the idea that the essential elements of nematic liquid crystal structure and ordering can be modeled on the basis of some relevant molecular features. Thus, nematics are found to be dielectric and nonpolar in the absence of an electric field, separated from the isotropic phase by a first-order phase transition with a transition enthalpy of about 1 kJ / mol, optically uniaxial, and to have a birefringence that increases slowly with decreasing temperature or increasing concentration. Anisotropic configuration and / or van der Waals forces, employed to describe the intermolecular interactions in simple mean-field or second virial statistical mechanical models, have been shown to be the molecular features required to obtain a fundamental explanation of nematic ordering.

[0050] The results herein suggest that a similar distillation is possible for ferroelectric nematic phases, and show that the effect of family origin on the interactions of molecularly distinguishable species that result in ferroelectric nematic phases can be explained by the simplest averaging procedure to obtain ΔH(T,x) and ΔS(T,x). This means that when, for example, the concentration of any component is low, the isolated molecule interacts with a sea of ​​families of other molecules in a manner similar to how it interacts with its own kind.

[0051] What are the general molecular features required for nematic ferroelectricity? Currently, there are about 60 molecules in two families known to induce nematic ferroelectricity, over 40 molecules synthesized from the two families have been reported, and Mandle et al. have reported 25 variants in the RM734 family. Figure 3 and Table 1 summarize the observed phase behavior of the Li compounds as pure materials, which fall into three categories: enantiotropic N F Nine molecules that exhibit a monotropic N phase, which has been difficult to study due to rapid crystallization F 12 molecules that exhibit phases, and N FThis impressive exploration of the effects of various substitutions reveals that within these families, N F It shows a general tendency to form phases.

[0052] The similar molecular-rod shape and size (approximately three ring lengths) and similarly large molecular dipole moments (approximately 11 Debye) within the family suggest that these are N F While it is believed that this combination may be necessary, (i) N for longitudinally polar LCs that exhibit only reentrant nematic / smectic paraelectric or antiferroelectric phases. F Based on previous extensive literature and (ii) the replacement of -NO2 with -CN in otherwise identical molecules, despite their comparable dipole moments, F This is clearly not sufficient, based on the observation that the phase disappears. This latter result may explain the importance of the details of the observed tendency for electrostatic head-to-tail self-assembly.

[0053] In the RM734 family, bulky side chains such as MeO at the ortho position make the molecule more pear-shaped, which allows the formation of novel N X We hypothesize that this is necessary to stabilize the antiferroelectric periodic array of splay stripes, i.e., the N F We show that the phase texture is largely not macroscopically modulated or is locally extended on any observable length scale. F Some of the more recent additions to the molecular palette that exhibit phases have side chains in the middle or at the other end of the molecule, or lack side chains altogether (eg, many members of the DIO family and the RM734 family).

[0054] The near-ideal mixing behavior of the chemically dissimilar compounds DIO and RM734, while seemingly surprising, suggests a major role for electrostatic interactions and electrostatic intermolecular associations in the thermodynamics of mixing in binary mixtures of these materials. Despite their distinct functional groups and patterns of chemical substitution, DIO and RM734 have similar dipole moments (~11D) and charge distributions characterized by alternation of charge sign along the length of the molecule, a feature that correlates strongly with typical pair association motifs (e.g., head-to-tail "chaining" and side-chain-to-side "docking") observed in atomistic simulations of RM734 and related compounds. F The role of longitudinal charge density modulation in phase stabilization has also been addressed in recent theoretical studies. We hypothesize that the nearly ideal miscibility of RM734 and DIO originates from their similar molecular shapes, charge distributions, and electrostatic interactions, a hypothesis that can be demonstrated by the mixing behavior of analogs of RM734 and DIO with modified intramolecular charge distributions.

[0055] N F The material is a highly unusual polar solvent that quite commonly induces polar orientational order in dipolar solute molecules, a phenomenon we term "solvent poling". The degree of induced polar order can be quite large, as evidenced by the ferroelectric polarization measurements reported here in binary mixtures of RM734 and DIO. The measurements are consistent with the results of the ferroelectric polarization measurements of RM734 N F We show that the host confers nearly perfect order to the DIO solute molecules in the limit of low DIO concentrations (DIO N F (This is also true for low concentrations of RM734 solute molecules in the host.) This solvent poling phenomenon is not simply a F Large (approximately 10 9 The effect of solvent poling can be due to the orientation of the solute electric dipoles in a local electric field (V / m), but more generally depends on the details of the intramolecular charge distribution and molecular geometry. Solvent poling is a facile route to create novel functional materials with optimized material properties. For example, materials with large second-order nonlinear optical susceptibility have been found in N FHigh beta chromophore molecules can be designed by solvent poling in the host.

[0056] The organic mesogens RM734 and DIO are members of distinct molecular families characterized by distinct molecular structures. These families are known to exhibit ferroelectric nematic liquid crystal (LC) phases. Here we present experimental phase diagrams and electro-optical studies of binary mixtures of RM734 and DIO. Both materials exhibit paraelectric nematic (N) and ferroelectric nematic (N F ) phases were observed, each of which exhibited complete miscibility across the phase diagram, indicating that the paraelectric and ferroelectric properties are the same phases in RM734 as DIO. Remarkably, these molecules form ideal mixtures with respect to both the mixture's paraelectric-ferroelectric nematic phase behavior and the ferroelectric polarization density, which are the key order parameters of the transition. The ideal mixture is also manifested in the occurrence of orientational viscosity and glassy dynamics at low temperatures. This behavior is partially attributed to the similarity of their overall molecular shapes and net longitudinal dipole moments (~11 Debye), as well as their common tendency toward head-to-tail molecular association. In contrast, the marked difference in molecular structure results in low solubility in the crystalline phase, enhancing the stability of the ferroelectric nematic phase in the mixture at low temperatures and enabling electro-optical effects at room temperature. In mixtures containing excess DIO, an intermediate phase emerges from the N phase via an extremely weak first-order transition in the narrow temperature range between the paraelectric and ferroelectric nematics. material and method Synthesis of DIO - DIO (2,3',4',5'-tetrafluoro-[1,1'-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl)benzoate, Figure 2, compound 3) is a rod-like molecule about 20 Å long and 5 Å in diameter, with a longitudinal electric dipole moment of about 11 Debye. The compound synthesized melts at T = 173.6 °C and is found to have an isotropic (I) phase and two additional nematic-like phases. The transition temperatures on cooling are I-173.6 °C-N-84.5 °C-M2-68.8 °C-N F It was -34℃-X.

[0057] Our synthetic scheme based on the general synthesis reactions is shown in Figure 2. Key intermediate 1 was purchased from Manchester Organics Ltd., UK and intermediate 2 from Sigma-Aldrich Inc., USA. Reactions were carried out in oven-dried glassware under a dry argon atmosphere. Purification was carried out by flash chromatography using silica gel (40-63 microns) purchased from Zeochem AG. Analytical thin layer chromatography (TLC) was performed using silica gel 60 F from Millipore Sigma, Darmstadt. 254 on TLC plates. Compounds were visualized using short-wave ultraviolet (UV). Nuclear magnetic resonance (NMR) spectra were obtained using a Bruker Avance-III 300 spectrometer. NMR chemical shifts were referenced to deuterated chloroform ( 1 H 7.24 ppm, 13 77.16 ppm for C).

[0058] To a suspension of compound 1 (3.44 g, 12 mmol) and intermediate 2 (2.91 g, 12 mmol) in CH2Cl2 (125 mL) was added DCC (4.95 g, 24 mmol) and a trace amount of DMAP.

[0059] The reaction mixture was stirred at room temperature for 4 days, then filtered, washed with water and brine, dried over MgSO4, filtered and concentrated under reduced pressure. The resulting product was purified by flash chromatography (silica gel, petroleum ether / 10% ethyl acetate). The crude product was crystallized by dissolving in 75 mL of boiling petroleum ether / 20% ethyl acetate solvent mixture, followed by cooling to -20°C for 1 h, to give 2.98 g (49%) of white needle-like crystals of compound 3. 1H NMR (300 MHz, chloroform-d) δ 7.64 - 7.35 (m, 1H), 7.24 - 6.87 (m, 6H), 5.40 (s, 1H), 4.42 - 4.14 (m, 2H), 3.54 (ddd, J = 11.6, 10.3, 1.5 Hz, 2H), 2.14 (tddd, J = 11.4, 9.2, 6.9, 4.6 Hz, 1H), 1.48 - 1.23 (m, 2H), 1.23 - 1.01 (m, 2H), 0.94 (t, J = 7.3 Hz, 3H). 13 C NMR (75 MHz, chloroform-d) δ 162.50, 162.43, 160.85, 159.08, 159.00, 157.52, 150.87, 150.72, 145.60, 145.47, 130.51, 130.46, 117.99, 117.94, 113.22, 113.17, 113.02, 112.93, 112.88, 110.65, 110.30, 110.26, 110.00, 109.95, 98.65, 98.62, 98.59, 72.41, 33.72, 30.05, 19.35, 14.01. Synthesis of W1027 - W1027 (4'-nitro-[1,1'-biphenyl]-4-yl 2,4-dimethoxybenzoate, compound 6) has a relatively broad nematic phase and is chemically similar to RM734, with the difference that the ester group near the nitro end of the molecule is replaced with a carbon-carbon linkage to form a biphenyl structure. The compound synthesized melts at T = 188 °C and was found to have isotropic (Iso) and N phases. The transition on cooling was Iso-154 °C-N-116 °C-X.

[0060] W1027 was synthesized according to the scheme depicted in Figure 2 and described below. Starting materials and reagents were purchased from regular suppliers and used without further purification. Intermediates 4 and 5 were purchased from Sigma-Aldrich Inc., USA. 2,4-Dimethoxybenzoyl chloride (4) (1.41 g, 7.1 mmol) and 4-hydroxy-4'-nitrobiphenyl (1.52 g, 7.1 mmol) were dissolved in tetrahydrofuran (50 mL), followed by dropwise addition of triethylamine (0.862 g, 8.5 mmol, 1.2 mL). The reaction mixture was stirred at room temperature overnight, extracted with chloroform, washed with water, sodium bicarbonate, and brine, and then dried over MgSO4. The mixture was then filtered and concentrated under reduced pressure. The crude product was crystallized twice from 150 mL of boiling acetonitrile to give W1027 as long pale yellow needles (2.11 g, 78%). 1 H NMR (300 MHz, chloroform-d) δ 8.34 - 8.24 (m, 2H), 8.17 - 8.03 (m, 1H), 7.78 - 7.70 (m, 2H), 7.70 - 7.60 (m, 2H), 7.39 - 7.29 (m, 2H), 6.63 - 6.51 (m, 2H), 3.92 (d, J = 10.4 Hz, 6H). 13 C NMR (75 MHz, chloroform-d) δ 165.29, 163.60, 162.47, 151.99, 147.16, 147.03, 136.14, 134.68, 128.50, 127.85, 124.26, 122.91, 110.97, 105.03, 99.16, 56.17, 55.73. HRMS-EI(m / z)C 21 H 17 NO6[MH] +1 Calculated value 380.1134; observed value 380.1147; difference +3.4 ppm.

[0061] The mixtures - RM734 and DIO, respectively, were synthesized using the scheme shown in Figure 2. Samples of the two materials were weighed separately, melted in the isotropic phase, and thoroughly mixed by stirring at 200 °C. To establish the appearance of spontaneous ferroelectric polarization, determine its magnitude, and measure the electro-optical response, the mixtures were studied using standard liquid crystal phase analysis techniques, including polarized light microscopy (PLM), differential scanning calorimetry (DSC), and small- and wide-angle X-ray scattering (SAXS and WAXS), as well as combined polarization measurements / electro-optical techniques. DSC studies on RM734, DIO, and their mixtures were carried out using a Mettler Toledo STARe system calorimeter. N-SmZ A The entropy change in the transition was too small to be observed.

[0062] Electro-optics - For electro-optical characterization, the mixtures were loosely packed into planar aligned in-plane switching test cells with uniform thickness d ranging from 3.5 μm to 8 μm obtained from Instec, Inc. In-plane indium-tin oxide (ITO) electrodes on one glass plate were spaced 1 mm apart. The alignment layer was buffed unidirectionally in a direction antiparallel to the two plates and approximately parallel to the edges of the electrodes. Such surfaces were characterized by the presence of N phase and N A This produces quadrupole alignment of the director along the buffing direction in the N F This results in polar alignment on each plate in the phase. F This results in an ANTIPOLAR cell with a director / polarization field in the plane of the cell in the N phase, but with a π-twist between the plates. The splay-bend-Fredericks transition in the N phase was studied using a conventional ITO sandwich cell with d=4.6 μm. Electro-optical measurements were performed using a Zeiss polarizing microscope, an EZ Digital FG-8002 function generator, and a Tektronix TDS 2014B oscilloscope. Temperature control was maintained using an Instec HCS402 hot stage.

[0063] Polarization measurements - The ferroelectric polarization density P was measured by measuring the current passing through the cell while applying an in-plane electric field that induces polarization reversal. p A square wave voltage of 100 V was applied to the 1 mm wide electrode gap of the sample cell. The polarization current i(t) was obtained by monitoring the voltage across a 55 kΩ resistor connected in series with the cell. The results for different temperatures are shown in Figure 6(A). It was observed that the polarization reversal was symmetric, with + / - and - / + reversals giving rise to essentially identical current signals. The isotropic, nematic, and smectic Z phases were A In the T phase, following a sign reversal of the applied voltage, the observed current has a small initial bump and then decays exponentially. This signal corresponds to the linear response of the RC circuit of the cell and the external resistor, and at T F The increase in ε in the N phase as it approaches causes an initial upward curvature in the measured P. F When the polarized phase is entered, an additional, much larger current peak appears at a longer time due to the field-induced polarization reversal, as shown in Figure 11. The switched net polarization current Q = ∫i(t)dt and the corresponding charge density Q / 2A (where A is the cross-sectional area of ​​the liquid crystal sample in the plane perpendicular to the applied electric field midway between the two electrodes) are shown in Figures 6(B) and 9. Q is obtained by integrating this current peak, N F The polarization density is generally given by P=Q / 2A, where A is the cross-sectional area of ​​the liquid crystal sample in a plane perpendicular to the electric field lines midway between the two electrodes.

[0064] The data acquisition system can sample the current with a period of 10 ms after the reversal. This finite data acquisition interval limits the temperature range where Q = 2AP because the current peak extends to longer times at low temperatures, as shown in Figure 11. At lower temperatures, Q is less than 2AP and decreases with T as the current peak lengthens (Figure 6). Polarization can also be measured using a triangle wave, where smaller voltages are applied near the + / - reversals, thus resulting in a smaller spurious contribution of dielectric polarization (T) near the phase transition. NFFor larger T, an upward curvature is induced. However, in the case of a triangular wave, the current peak is longer than in the case of a square wave, and the viscosity increases with decreasing T, so this case is more problematic than described for the square wave.

[0065] Figure 13 shows a comparison of wide-angle X-ray scattering of RM734 and DIO. The samples have nematic directors that are magnetically aligned along z by a magnetic field of about 1 Tesla. The gamut of the color / grayscale is linear in intensity, with the lowest values ​​(black / darkest) corresponding to zero intensity. The scattering intensity line scan I(q z ) are shown in Figure 14. Overall, RM734 and DIO were A Apart from the appearance of a layering peak (seen in the SAXS images), they exhibit a remarkably similar characteristic WAXS scattering pattern that appears upon cooling to the N phase and does not change significantly upon cooling to lower temperature phases. The (AD)WAXS patterns are typically caused by the three-dimensional rod-like shape of the molecules and are approximately equal to (2π / molecule length approx. 0.25 Å), respectively. -1 ) and (2π / molecule width approx. 1.4 Å -1 ) arising from end-to-end and side-to-side pair correlations, respectively z Approximately 0.25Å -1 and q y Approximately 1.4 Å -1 In contrast to typical nematics, RM734 also exhibits the well-known diffuse scattering characteristic of nematics, q y <0.4 Å -1 and q z >0.25Å -1 For RM734, q exhibits a series of atypical scattering bands that were first reported in RM734 and its homologs. Interestingly, DIO shows a qualitatively very similar scattering pattern (A, B, D) but with a more distinct peak structure, likely the result of a larger variation in the excess electron density along the molecule associated with the fluorine. z Approximately 0.25Å -1 This characteristic is observed in typical nematics such as 5CB and all aromatic LCs. zIt is also noteworthy that the scattering is weaker compared to . This weak scattering is believed to be due to head-to-tail electrostatic adhesion in RM734, which makes the molecular correlations along z more polar and chain-like, resulting in smaller head-to-tail gaps between molecules. The resulting end-to-end correlations are then similar to those in ungapped main-chain LC polymers, resulting in q z Scattering along z is weaker than in monomeric nematics. In DIO, on the other hand, the trifluoro groups at the ends of the molecules give rise to large electron density peaks that periodically define chain correlations along z even in the absence of gaps, and q z Approximately 0.25Å -1 In B and C, q=0 (q<0.1Å) causes strong scattering. -1 The nearby signal comes from stray light.

[0066] Figure 14 shows the y =0.004Å -1 In q z Line scans of WAXS images of scattering from DIO and RM734 similar to those in Fig. 13 along I(q z (A)I(q z Comparison of RM734 at T = 160 °C, the temperature at which the peak structure of ) is strongest, and DIO at T = 85 °C reveals common features. These are the same as those reported previously. z Approximately 0.25Å -1 and q y Approximately 1.4 Å -1 Intensely broadened scattering features in and q already observed in the RM734 family z Pairs of similarly colored / shaded dots indicate similar peaks for the two compounds. zp ≒0.25 Å -1 The broadened peak (white dot) located at 2π / q zpThis corresponds to a short-range order with quasiperiodic spacing of p = 24 Å, comparable to the molecular length of DIO and RM734, and, in the case of RM734, the periodicity of molecular spacing along the director in the head-to-tail ensemble seen in the simulations. If such a head-to-tail ensemble is considered as a one-dimensional chain with fluctuations in the displacement along the chain, then the root-mean-square of the relative displacement of neighbouring molecules along the chain, √(δu 2 ) is q zp q for zp (0.04Å -1 ) can be estimated from the ratio of the half-width at half maximum of the scattering peak at √(δu 2 ) / p≒0.25 and √(δu 2 ) ≒ 5 Å. This is somewhat larger than the rms displacement found in atomistic computer simulations of about 400 RM734 molecules, suggesting that long-scale fluctuations may also contribute to the peak width. (B, C) Temperature dependence of WAXS in DIO and RM734. In the N phase of RM734, I(q z ) becomes dominated by increasing temperature, a striking behavior consistent with other results. In contrast, in DIO, I(q z ) is similar over much of the N range and below, with a distinct peak appearing at T = 85 °C (B) and broadening with increasing temperature only near the N-Iso transition before disappearing in the Iso phase. In the N phase, q z =[0.25, 0.50, 0.78, 1.25, 1.58Å -1 The arrangement of the DIO peak positions in the ratio q z / q zp = [1, 2.0, 3.1, 5.0, 7.8], which can be approximately exponentially expressed as a one-dimensional periodicity, q zp ≒0.25 Å -1 In the case of RM734, at T=100℃, q z / q zp Peak array q as = [1, 2.2, 3.1, 5.3, 7.0] z =[0.28, 0.60, 0.85, 1.46, 1.96Å -1A similar indexation of ] is possible, but there is a significant departure from harmonic behavior at T = 160 °C, as observed for other members of the RM734 family. In the iso phase, this structure is lost entirely.

[0067] The exemplary embodiments of the above disclosure are merely examples of embodiments of the present invention as defined by the appended claims and their legal equivalents, and therefore these embodiments do not limit the scope of the present invention. Any equivalent embodiments are intended to be within the scope of the present invention. Various modifications of the present disclosure, such as alternative useful combinations of the elements described in addition to the modifications shown and described herein, may become apparent to those skilled in the art from this specification. Such modifications and embodiments are also intended to be included within the scope of the appended claims.

Claims

1. A material comprising a ferroelectric nematic phase, a mixture comprising a first molecule and a second molecule; at least one of the first molecular fluid and the second molecular fluid exhibits a ferroelectric nematic phase; the first molecule and the second molecule are miscible; a first molecule induces polar orientational order in said second molecule; material.

2. The material of claim 1 , wherein the first molecule or the second molecule are chemically dissimilar.

3. The material of claim 1 , wherein at least one of the first molecule or the second molecule comprises a halogen.

4. 10. The material of claim 1, wherein at least one of the first molecule or the second molecule comprises a plurality of halogen atoms.

5. 2. The material of claim 1, wherein each of the first molecules comprises a first backbone, a first terminal functional group of the first molecule, and a second terminal functional group of the first molecule, and each of the second molecules comprises a second backbone, a first terminal functional group of the second molecule, and a second terminal functional group of the second molecule.

6. The material of claim 5 , wherein the first backbone and the second backbone are chemically distinct.

7. 6. The material of claim 5, wherein the first terminal functional group of the first molecule is different from the first terminal functional group of the second molecule.

8. 6. The material of claim 5, wherein the second terminal functional group of the first molecule is different from the second terminal functional group of the second molecule.

9. 6. The material of claim 5, wherein one or more of the first terminal functional group of the first molecule, the first terminal functional group of the second molecule, the second terminal functional group of the first molecule, and the second terminal functional group of the second molecule comprises a halogen.

10. 6. The material of claim 5, wherein one or more of the first terminal functional group of the first molecule, the first terminal functional group of the second molecule, the second terminal functional group of the first molecule, and the second terminal functional group of the second molecule comprises at least one of an alkyl group and an alkoxy group.

11. The material of claim 5, wherein at least one of the first skeleton or the second skeleton comprises three or four ring structures or at least one linker group.

12. 12. The material of claim 11, wherein the ring structure is selected from the group consisting of a phenyl ring, a cyclohexane ring, a dioxane ring, a thiophene ring, a monoxane ring, a pyridine ring, a pyrimidine ring, and any other heterocyclic group.

13. The material of claim 1 , wherein the first and second molecules exhibit similar charge distributions.

14. The material of claim 1 further comprising one or more additional molecules that are miscible in the mixture.

15. A nonlinear optical material comprising the material of claim 1.

16. 1. A method for forming a material having a tunable ferroelectric nematic phase, comprising: mixing the first molecule and the second molecule to form a mixture having a ferroelectric nematic phase; a first molecule induces polar orientational order in said second molecule; method.

17. 17. The method of claim 16, wherein the first molecule comprises RM734 and the second molecule comprises DIO.

18. 2. The material of claim 1, wherein the first molecule comprises RM734 and the second molecule comprises DIO.

19. A multi-component mixture comprising a ferroelectric nematic phase, the RM734 molecule, and DIO molecule A multi-component mixture comprising:

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