Method for preparing oriented liquid crystal elastomers

Abstract

A method for preparing an oriented nematic liquid crystal elastomer with a reduced authentic response threshold, comprising the step of applying pre-strain conditions to the liquid crystal elastomer.

Description

[Technical Field]

[0001] The present invention relates to a method for reducing the authentic response threshold of a liquid crystal elastomer. [Background technology]

[0002] Auxetic materials have a negative Poisson's ratio, which is described as the negative ratio of the proportional decrease in transverse measurements to the proportional increase in length in a sample of elastically stretched material. When stretched, auxetic materials become thicker in one or both directions perpendicular to the applied deformation.

[0003] Austhetic materials are of particular interest due to their desirable enhanced mechanical properties and potential meta-acoustic properties. Some authetic materials exist naturally, while others, including the first synthetic authetic materials, are carefully manipulated structures that exhibit their authetic behavior due to their bulk honeycomb-like structure. Such authetic materials are used in applications including sportswear due to their improved shock absorption and shear resistance performance.

[0004] As described in International Publication No. 2019077361A1, oriented nematic liquid crystal elastomers with authentic properties have recently been developed. Austhetic liquid crystal elastomers offer significant advantages over conventional synthetic authentic structures, including transparency, no effective lower limit on material / device size, improved strength (non-porous), and the availability of a wide variety of manufacturing methods. Austhetic liquid crystal elastomers can also be chemically modified, which also offers significant advantages over existing technologies. Molecular liquid crystal elastomers are softer materials and have a greater potential to conform to biological tissues, thus potentially providing improved performance in biomedical applications.

[0005] A limiting factor in the potential applications of molecular authentic liquid crystal elastomer materials is that a negative Poisson's ratio is observed only after a certain deformation threshold, which is referred to below as the authentic response threshold. [Overview of the Initiative] [Means for solving the problem]

[0006] The present invention provides a method according to the appended claims. Other features of the present invention will become apparent from the dependent claims and the following description.

[0007] According to one aspect of the present invention, a method is provided for preparing an oriented nematic liquid crystal elastomer with a reduced authentic response threshold, the method comprising the step of applying pre-strain conditions to the liquid crystal elastomer.

[0008] Applying pre-straining conditions to lower the authentic response threshold may expand the applicability of authentic liquid crystal elastomers. The authentic response threshold is dependent on the strain rate, and it has been confirmed that the authentic threshold decreases as the rate at which strain is applied decreases. (approximately 10 -5 s -1 It has been confirmed that when quasi-static strain (at a strain rate) is applied to a liquid crystal elastomer, the authentic response threshold approaches its formulation-dependent minimum. However, reaching the authentic response threshold by applying quasi-static strain can be very time-consuming; when a liquid crystal elastomer is strained at a quasi-static rate, it typically takes about 10 hours to reach the authentic response threshold. By applying pre-straining conditions to the liquid crystal elastomer, a liquid crystal elastomer with a reduced authentic response threshold at equilibrium may be produced without the need for straining at a quasi-static rate. This may significantly reduce the time required for the liquid crystal elastomer to enter the authentic regime.

[0009] Applying pre-straining conditions may include straining the liquid crystal elastomer. Straining the liquid crystal elastomer may include straining the liquid crystal elastomer to a predetermined strain. The predetermined strain may be at least 0.1, for example at least 0.15, for example at least 0.2, for example at least 0.25, for example at least 0.3, for example at least 0.35, for example at least 0.4, for example at least 0.45, for example at least 0.5, for example at least 0.55, for example at least 0.6, for example at least 0.65, for example at least 0.7, for example at least 0.75, for example at least 0.8, or even at least 0.82. The specified strain may be a maximum of 1.9, for example a maximum of 1.85, for example a maximum of 1.8, for example a maximum of 1.75, for example a maximum of 1.7, for example a maximum of 1.65, for example a maximum of 1.6, for example a maximum of 1.55, for example a maximum of 1.5, for example a maximum of 1.45, for example a maximum of 1.4, for example a maximum of 1.35, for example a maximum of 1.3, for example a maximum of 1.25, for example a maximum of 1.2, for example a maximum of 1.15, for example a maximum of 1.1, for example a maximum of 1.05, for example a maximum of 1, or even a maximum of 0.98.

[0010] The specified strain may be 0.1 to 1.9, for example 0.15 to 1.9, for example 0.2 to 1.9, for example 0.25 to 1.9, for example 0.3 to 1.9, for example 0.35 to 1.9, for example 0.4 to 1.9, for example 0.45 to 1.9, for example 0.5 to 1.9, for example 0.55 to 1.9, for example 0.6 to 1.9, for example 0.65 to 1.9, for example 0.7 to 1.9, for example 0.75 to 1.9, for example 0.8 to 1.9, or even 0.82 to 1.9. The specified strain may be 0.1 to 1.85, for example 0.15 to 1.85, for example 0.2 to 1.85, for example 0.25 to 1.85, for example 0.3 to 1.85, for example 0.35 to 1.85, for example 0.4 to 1.85, for example 0.45 to 1.85, for example 0.5 to 1.85, for example 0.55 to 1.85, for example 0.6 to 1.85, for example 0.65 to 1.85, for example 0.7 to 1.85, for example 0.75 to 1.85, for example 0.8 to 1.85, or even 0.82 to 1.85. The specified strain may be 0.1 to 1.8, for example 0.15 to 1.8, for example 0.2 to 1.8, for example 0.25 to 1.8, for example 0.3 to 1.8, for example 0.35 to 1.8, for example 0.4 to 1.8, for example 0.45 to 1.8, for example 0.5 to 1.8, for example 0.55 to 1.8, for example 0.6 to 1.8, for example 0.65 to 1.8, for example 0.7 to 1.8, for example 0.75 to 1.8, for example 0.8 to 1.8, or even 0.82 to 1.8. The specified strain may be 0.1 to 1.75, for example 0.15 to 1.75, for example 0.2 to 1.75, for example 0.25 to 1.75, for example 0.3 to 1.75, for example 0.35 to 1.75, for example 0.4 to 1.75, for example 0.45 to 1.75, for example 0.5 to 1.75, for example 0.55 to 1.75, for example 0.6 to 1.75, for example 0.65 to 1.75, for example 0.7 to 1.75, for example 0.75 to 1.75, for example 0.8 to 1.75, or even 0.82 to 1.75.The specified strain may be 0.1 to 1.7, for example 0.15 to 1.7, for example 0.2 to 1.7, for example 0.25 to 1.7, for example 0.3 to 1.7, for example 0.35 to 1.7, for example 0.4 to 1.7, for example 0.45 to 1.7, for example 0.5 to 1.7, for example 0.55 to 1.7, for example 0.6 to 1.7, for example 0.65 to 1.7, for example 0.7 to 1.7, for example 0.75 to 1.7, for example 0.8 to 1.7, or even 0.82 to 1.7. The specified strain may be 0.1 to 1.65, for example 0.15 to 1.65, for example 0.2 to 1.65, for example 0.25 to 1.65, for example 0.3 to 1.65, for example 0.35 to 1.65, for example 0.4 to 1.65, for example 0.45 to 1.65, for example 0.5 to 1.65, for example 0.55 to 1.65, for example 0.6 to 1.65, for example 0.65 to 1.65, for example 0.7 to 1.65, for example 0.75 to 1.65, for example 0.8 to 1.65, or even 0.82 to 1.65. The specified strain may be 0.1 to 1.6, for example 0.15 to 1.6, for example 0.2 to 1.6, for example 0.25 to 1.6, for example 0.3 to 1.6, for example 0.35 to 1.6, for example 0.4 to 1.6, for example 0.45 to 1.6, for example 0.5 to 1.6, for example 0.55 to 1.6, for example 0.6 to 1.6, for example 0.65 to 1.6, for example 0.7 to 1.6, for example 0.75 to 1.6, for example 0.8 to 1.6, or even 0.82 to 1.6. The specified strain may be 0.1 to 1.55, for example 0.15 to 1.55, for example 0.2 to 1.55, for example 0.25 to 1.55, for example 0.3 to 1.55, for example 0.35 to 1.55, for example 0.4 to 1.55, for example 0.45 to 1.55, for example 0.5 to 1.55, for example 0.55 to 1.55, for example 0.6 to 1.55, for example 0.65 to 1.55, for example 0.7 to 1.55, for example 0.75 to 1.55, for example 0.8 to 1.55, or even 0.82 to 1.55.The specified strain may be 0.1 to 1.5, for example 0.15 to 1.5, for example 0.2 to 1.5, for example 0.25 to 1.5, for example 0.3 to 1.5, for example 0.35 to 1.5, for example 0.4 to 1.5, for example 0.45 to 1.5, for example 0.5 to 1.5, for example 0.55 to 1.5, for example 0.6 to 1.5, for example 0.65 to 1.5, for example 0.7 to 1.5, for example 0.75 to 1.5, for example 0.8 to 1.5, or even 0.82 to 1.5. The specified strain may be 0.1 to 1.45, for example 0.15 to 1.45, for example 0.2 to 1.45, for example 0.25 to 1.45, for example 0.3 to 1.45, for example 0.35 to 1.45, for example 0.4 to 1.45, for example 0.45 to 1.45, for example 0.5 to 1.45, for example 0.55 to 1.45, for example 0.6 to 1.45, for example 0.65 to 1.45, for example 0.7 to 1.45, for example 0.75 to 1.45, for example 0.8 to 1.45, or even 0.82 to 1.45. The specified strain may be 0.1 to 1.4, for example 0.15 to 1.4, for example 0.2 to 1.4, for example 0.25 to 1.4, for example 0.3 to 1.4, for example 0.35 to 1.4, for example 0.4 to 1.4, for example 0.45 to 1.4, for example 0.5 to 1.4, for example 0.55 to 1.4, for example 0.6 to 1.4, for example 0.65 to 1.4, for example 0.7 to 1.4, for example 0.75 to 1.4, for example 0.8 to 1.4, or even 0.82 to 1.4. The specified strain may be 0.1 to 1.35, for example 0.15 to 1.35, for example 0.2 to 1.35, for example 0.25 to 1.35, for example 0.3 to 1.35, for example 0.35 to 1.35, for example 0.4 to 1.35, for example 0.45 to 1.35, for example 0.5 to 1.35, for example 0.55 to 1.35, for example 0.6 to 1.35, for example 0.65 to 1.35, for example 0.7 to 1.35, for example 0.75 to 1.35, for example 0.8 to 1.35, or even 0.82 to 1.35.The specified strain may be 0.1 to 1.3, for example 0.15 to 1.3, for example 0.2 to 1.3, for example 0.25 to 1.3, for example 0.3 to 1.3, for example 0.35 to 1.3, for example 0.4 to 1.3, for example 0.45 to 1.3, for example 0.5 to 1.3, for example 0.55 to 1.3, for example 0.6 to 1.3, for example 0.65 to 1.3, for example 0.7 to 1.3, for example 0.75 to 1.3, for example 0.8 to 1.3, or even 0.82 to 1.3. The specified strain may be 0.1 to 1.25, for example 0.15 to 1.25, for example 0.2 to 1.25, for example 0.25 to 1.25, for example 0.3 to 1.25, for example 0.35 to 1.25, for example 0.4 to 1.25, for example 0.45 to 1.25, for example 0.5 to 1.25, for example 0.55 to 1.25, for example 0.6 to 1.25, for example 0.65 to 1.25, for example 0.7 to 1.25, for example 0.75 to 1.25, for example 0.8 to 1.25, or even 0.82 to 1.25. The specified strain may be 0.1 to 1.2, for example 0.15 to 1.2, for example 0.2 to 1.2, for example 0.25 to 1.2, for example 0.3 to 1.2, for example 0.35 to 1.2, for example 0.4 to 1.2, for example 0.45 to 1.2, for example 0.5 to 1.2, for example 0.55 to 1.2, for example 0.6 to 1.2, for example 0.65 to 1.2, for example 0.7 to 1.2, for example 0.75 to 1.2, for example 0.8 to 1.2, or even 0.82 to 1.2. The specified strain may be 0.1 to 1.15, for example 0.15 to 1.15, for example 0.2 to 1.15, for example 0.25 to 1.15, for example 0.3 to 1.15, for example 0.35 to 1.15, for example 0.4 to 1.15, for example 0.45 to 1.15, for example 0.5 to 1.15, for example 0.55 to 1.15, for example 0.6 to 1.15, for example 0.65 to 1.15, for example 0.7 to 1.15, for example 0.75 to 1.15, for example 0.8 to 1.15, or even 0.82 to 1.15.The predetermined strain may be 0.1 to 1.1, for example 0.15 to 1.1, for example 0.2 to 1.1, for example 0.25 to 1.1, for example 0.3 to 1.1, for example 0.35 to 1.1, for example 0.4 to 1.1, for example 0.45 to 1.1, for example 0.5 to 1.1, for example 0.55 to 1.1, for example 0.6 to 1.1, for example 0.65 to 1.1, for example 0.7 to 1.1, for example 0.75 to 1.1, for example 0.8 to 1.1, or even 0.82 to 1.1. The predetermined strain may be 0.1 to 1.05, for example 0.15 to 1.05, for example 0.2 to 1.05, for example 0.25 to 1.05, for example 0.3 to 1.05, for example 0.35 to 1.05, for example 0.4 to 1.05, for example 0.45 to 1.05, for example 0.5 to 1.05, for example 0.55 to 1.05, for example 0.6 to 1.05, for example 0.65 to 1.05, for example 0.7 to 1.05, for example 0.75 to 1.05, for example 0.8 to 1.05, or even 0.82 to 1.05. The predetermined strain may be 0.1 to 1, for example 0.15 to 1, for example 0.2 to 1, for example 0.25 to 1, for example 0.3 to 1, for example 0.35 to 1, for example 0.4 to 1, for example 0.45 to 1, for example 0.5 to 1, for example 0.55 to 1, for example 0.6 to 1, for example 0.65 to 1, for example 0.7 to 1, for example 0.75 to 1, for example 0.8 to 1, or even 0.82 to 1. The predetermined strain may be 0.1 to 0.98, for example 0.15 to 0.98, for example 0.2 to 0.98, for example 0.25 to 0.98, for example 0.3 to 0.98, for example 0.35 to 0.98, for example 0.4 to 0.98, for example 0.45 to 0.98, for example 0.5 to 0.98, for example 0.55 to 0.98, for example 0.6 to 0.98, for example 0.65 to 0.98, for example 0.7 to 0.98, for example 0.75 to 0.98, for example 0.8 to 0.98, or even 0.82 to 0.98.

[0011] The predetermined strain may be 0.2 to 1.8, for example 0.3 to 1.7, for example 0.35 to 1.66, or even 0.82 to 1.66.

[0012] Applying the pre-strain condition may include allowing the liquid crystal to relieve stress. Allowing the liquid crystal to relieve stress may include allowing it to relieve stress while being maintained in a strained state. The appropriate time for stress relaxation may depend on the composition of the liquid crystal elastomer and the temperature relative to the glass transition temperature T g of the liquid crystal elastomer. For example, the liquid crystal elastomer may be allowed to relax for about 30 to 120 minutes at a temperature about 8 °C higher than the T g of the liquid crystal elastomer. At temperatures raised until exceeding T g , the time during which the liquid crystal elastomer is exposed to stress relaxation may be shortened.

[0013] The liquid crystal elastomer may be a film. In some examples, the film may preferably have a large x / y aspect ratio greater than 4 in order to avoid a non-uniform strain profile. In other examples, the aspect ratio may be greater than or less than 4.

[0014] By allowing the liquid crystal elastomer film to relieve stress, the liquid crystal elastomer film may be equilibrated. Thereafter, the liquid crystal elastomer film may have a reduced cholesteric response threshold. In some examples, the liquid crystal elastomer film may be at the cholesteric response threshold in an equilibrium state such that when additional strain is applied to the liquid crystal elastomer film, the liquid crystal elastomer film exhibits cholesteric behavior. In other examples, the liquid crystal elastomer film may have a cholesteric response threshold above zero when in an equilibrium state, but is reduced compared to the cholesteric response threshold of the film before the pre-strain condition is applied, so that as a result, only a reduced amount of deformation is required for the liquid crystal elastomer film to exhibit cholesteric behavior.

[0015] Straining the liquid crystal elastomer may include at least one of mechanically straining the liquid crystal elastomer, swelling or deswelling the liquid crystal elastomer with a solvent, or heating or cooling the liquid crystal elastomer.

[0016] Mechanically straining the liquid crystal elastomer may include applying strain in a direction perpendicular to the director of the liquid crystal elastomer. The strain rate may not be quasi-static. The applied strain rate may be determined based on the temperature of the liquid crystal elastomer with respect to T g and may be continuous up to a predetermined strain. Mechanically straining the liquid crystal elastomer may include straining the liquid crystal elastomer at a rate of 0.05 / min or more. The liquid crystal elastomer may be strained at least 0.1 / min, such as at least 0.15 / min, such as at least 0.2 / min, such as at least 0.25 / min, such as at least 0.3 / min, such as at least 0.35 / min, such as at least 0.4 / min, such as at least 0.45 / min, such as at least 0.5 / min, such as at least 0.55 / min, such as at least 0.6 / min, such as at least 0.65 / min, such as at least 0.7 / min, such as at least 0.75 / min, such as at least 0.8 / min, such as at least 0.85 / min, such as at least 0.9 / min, such as at least 0.95 / min, and even at least 1 / min. Preferably, the liquid crystal elastomer is strained at a rate of 0.01 / sec or more.

[0017] The predetermined strain may be the strain at which the liquid crystal elastomer reaches the cholesteric response threshold when strained at a quasi-static rate.

[0018] The method may include a step of determining the predetermined strain. The step of determining the predetermined strain may include determining the cholesteric response thresholds when the liquid crystal elastomer is strained at each of a plurality of different rates, and determining the cholesteric response threshold for straining the liquid crystal elastomer at a quasi-static rate by extrapolating from the determined cholesteric response thresholds. The plurality of different rates are 10 -4 s -1 、10 -3 s -1 、10 -2 s -1 、and 10-1 s -1 That's fine.

[0019] According to another aspect of the present invention, a method is provided for preparing an oriented nematic liquid crystal elastomer with a reduced authentic response threshold, the method comprising the steps of applying strain to the liquid crystal elastomer in a series of steps and enabling the liquid crystal to relax between steps.

[0020] It has been found that applying strain step by step (gradually) and allowing the elastomer to relax between steps has the effect of lowering the authentic response threshold. By preparing liquid crystal elastomers, a reduction in the authentic threshold may be achieved without the need to strain the liquid crystal elastomer at a quasi-static rate. This may shorten the time required for the liquid crystal elastomer to enter the authentic state, thereby expanding the applicability of authentic liquid crystal elastomers.

[0021] The amount of distortion added at each step is T g The temperature of the liquid crystal elastomer may be determined based on the temperature of the liquid crystal elastomer. The liquid crystal elastomer may be strained by at least 0.02, e.g., at least 0.025, e.g., at least 0.03, e.g., at least 0.035, e.g., at least 0.04, e.g., at least 0.045, and even at least 0.05 in each step. The liquid crystal elastomer may be strained by a maximum of 0.1, e.g., a maximum of 0.095, e.g., a maximum of 0.09, e.g., a maximum of 0.085, e.g., a maximum of 0.08, e.g., 0.075, e.g., a maximum of 0.07, e.g., a maximum of 0.065, and even at a maximum of 0.06.

[0022] The distortion added in each step may be 0.02 to 0.1, for example 0.025 to 0.1, for example 0.03 to 0.1, for example 0.035 to 0.1, for example 0.04 to 0.1, for example 0.045 to 0.1, or even 0.05 to 0.1. The distortion added in each step may also be 0.02 to 0.095, for example 0.025 to 0.095, for example 0.03 to 0.095, for example 0.035 to 0.095, for example 0.04 to 0.095, for example 0.045 to 0.095, or even 0.05 to 0.095. The distortion added in each step may be 0.02 to 0.09, for example 0.025 to 0.09, for example 0.03 to 0.09, for example 0.035 to 0.09, for example 0.04 to 0.09, for example 0.045 to 0.09, or even 0.05 to 0.09. The distortion added in each step may also be 0.02 to 0.085, for example 0.025 to 0.085, for example 0.03 to 0.085, for example 0.035 to 0.085, for example 0.04 to 0.085, for example 0.045 to 0.085, or even 0.05 to 0.085. The distortion added in each step may be 0.02 to 0.08, for example 0.025 to 0.08, for example 0.03 to 0.08, for example 0.035 to 0.08, for example 0.04 to 0.08, for example 0.045 to 0.08, or even 0.05 to 0.08. The distortion added in each step may be 0.02 to 0.075, for example 0.025 to 0.075, for example 0.03 to 0.075, for example 0.035 to 0.075, for example 0.04 to 0.075, for example 0.045 to 0.075, or even 0.05 to 0.075. The distortion added in each step may be 0.02 to 0.07, for example 0.025 to 0.07, for example 0.03 to 0.07, for example 0.035 to 0.07, for example 0.04 to 0.07, for example 0.045 to 0.07, or even 0.05 to 0.07. The distortion added in each step may be 0.02 to 0.065, for example 0.025 to 0.065, for example 0.03 to 0.065, for example 0.035 to 0.065, for example 0.04 to 0.065, for example 0.045 to 0.065, or even 0.05 to 0.065.The distortion added at each step may be 0.02 to 0.06, for example 0.025 to 0.06, for example 0.03 to 0.06, for example 0.035 to 0.06, for example 0.04 to 0.06, for example 0.045 to 0.06, or even 0.05 to 0.06.

[0023] The liquid crystal elastomer may be allowed to relax stress between each step. The appropriate time for stress relaxation depends on the formulation of the liquid crystal elastomer and the T of the liquid crystal elastomer. g It may also depend on the temperature. For example, liquid crystal elastomers may have a T g It may be possible to allow relaxation at a temperature approximately 8°C higher for 5 to 120 minutes. It has been found that increasing the stress relaxation time between strain steps can lower the authentic response threshold.

[0024] Liquid crystal elastomer is T g It may be possible to allow stress relaxation at temperatures exceeding T. g It was found that the authentic response threshold could be lowered by increasing the temperature beyond a certain point.

[0025] While several preferred embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims. [Brief explanation of the drawing]

[0026] To better understand the present invention and to illustrate how embodiments of the present invention may be carried out, the accompanying drawings are to be referenced hereby, merely as examples.

[0027] [Figure 1] Figure 1 shows an exemplary process for applying pre-strain conditions.

[0028] [Figure 2]Figure 2 shows an exemplary liquid crystal elastomer before mechanical deformation.

[0029] [Figure 3] Figure 3 shows an exemplary process for determining a given strain.

[0030] [Figure 4] Figure 4 shows an exemplary process that lowers the authentic response threshold.

[0031] [Figure 5A] Figure 5A is a graph of Poisson's ratio as the strain changes.

[0032] [Figure 5B] Figure 5B is a graph of true stress as true strain changes.

[0033] [Figure 6] Figure 6 is a graph showing the decrease in the true strain threshold due to the applied true pre-strain.

[0034] [Figure 7A] Figure 7A is a graph of z-strain as x-strain changes for different stress relaxation times between strain steps.

[0035] [Figure 7B] Figure 7B is a graph of Poisson's ratio as the strain changes for different relaxation times between strain steps.

[0036] [Figure 8A] Figure 8A is a graph of z-strain as x-strain changes at different temperatures.

[0037] [Figure 8B] Figure 8B is a graph of Poisson's ratio as the strain changes at different temperatures. [Modes for carrying out the invention]

[0038] According to an exemplary method, an oriented nematic liquid crystal elastomer with a reduced authentic response threshold is prepared by applying pre-straining conditions to the liquid crystal elastomer. An exemplary process 10 for applying pre-straining conditions is shown in Figure 1.

[0039] In step 12, the oriented nematic liquid crystal elastomer film is strained to a predetermined strain. This film is strained in a direction perpendicular to the orientation vector of the liquid crystal elastomer. The strain is applied mechanically by clamping (pressing down) the film at both ends in the longitudinal direction and straining the film in the longitudinal direction perpendicular to the orientation vector. Figure 2 shows the film 20 clamped at its x-direction (longitudinal direction) ends 22, 24, where arrow n indicates the direction of the liquid crystal orientation vector. In other examples, the strain may be applied by swelling or de-swelling the liquid crystal elastomer with a solvent, or by heating or cooling the liquid crystal elastomer.

[0040] In step 14, the distorted film is placed in a stress-relaxed state while the distorted state is maintained. The time the distorted film is placed in a stress-relaxed state is T g This may be determined based on the temperature of the film relative to the temperature.

[0041] For example, a predetermined strain is determined according to process 30 shown in Figure 3.

[0042] In step 32 of Figure 3, multiple auxetic response thresholds for the liquid crystal elastomer are determined when the liquid crystal elastomer film is strained at multiple different speeds. The first auxetic response threshold is determined when the liquid crystal elastomer film is strained at 10 -4 s -1 The second auxetic response threshold is determined when the liquid crystal elastomer film is distorted at a speed of 10 -3 s -1 The third auxetic response threshold is determined when the liquid crystal elastomer film is distorted at a speed of 10 -2 s -1The fourth auxetic response threshold is determined when the liquid crystal elastomer film is distorted at a speed of 10 -1 s -1 This is determined when the distortion is applied at a certain speed.

[0043] To determine multiple authentic response thresholds, local strains ε in the x and y directions are used. x and ε y Each of these strains is tracked. The directions of these strains are shown in Figure 2. Strain is added step by step, allowing the liquid crystal elastomer to relax between strain steps. The strain in the z direction (authentic response) is calculated based on the measured strains in the x and y directions using Equation 1, by assuming that the volume of the liquid crystal elastomer remains constant.

[0044]

number

[0045] Below the authentic response threshold, the strain in the z direction decreases as the applied strain in the x direction increases. Above the authentic response threshold, the strain in the z direction increases as the applied strain in the x direction increases. Therefore, the authentic response threshold can be determined based on the calculated strain in the z direction.

[0046] In step 34 of Figure 3, the authentic response threshold when the liquid crystal elastomer is deformed at a quasi-static rate is 10 from the determined authentic response threshold. -5 s -1 It is determined by extrapolating to the velocity. The determined authentic response threshold when the elastomer is strained at a quasi-static velocity is determined to be a given strain.

[0047] Figure 4 shows another exemplary method 40 for reducing the authentic response threshold of an oriented nematic liquid crystal elastomer. This method includes, in step 42, applying strain to the liquid crystal elastomer in each strain step. The liquid crystal elastomer is mechanically strained in a direction x perpendicular to the orientation vector of the liquid crystal elastomer, as shown in Figure 2.

[0048] The method further includes, in step 44, allowing the liquid crystal to relax between steps.

[0049] Steps 42 and 44 are repeated with stress relaxation between consecutive steps. [Examples]

[0050] An authentic-oriented nematic liquid crystal elastomer film for use according to the present invention was synthesized as follows using the following materials. 2-ethylhexyl acrylate (EHA), 6-(4-cyano-biphenyl-4'-yloxy)hexyl acrylate (A6OCB), 1,4-Bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82), 4-Cyano-4'-hexyloxybiphenyl (6OCB), and Methyl benzoylformate (MBF)

[0051] The film was prepared using the following starting monomer mixture. [Table 1]

[0052] A liquid crystal elastomer film was prepared by polymerizing a monomer mixture inside a thin film mold with a thickness of approximately 100 μm, a width of approximately 15 mm, and a length of approximately 60 mm. In other examples, film molds of different thicknesses, widths, and lengths may be used. The film was cured at room temperature in a planar orientation with a nematic phase, while the surface of the mold was coated with a thin layer of PVA orientation, and the rubbing direction was antiparallel. The film was polymerized for 2 hours. After polymerization, the film was removed from the mold and held overnight in a methanol / DCM solvent mixture to wash away 6OCB.

[0053] The pre-strain condition was applied to the first film according to the method shown in Figure 1. The strain condition was set to approximately 0.01 s -1 The process was applied at a certain speed, and the film was equilibrated under strain for 0.5 to 1 hour. A second film, as a comparative example, was formed by the same method, but without pre-straining conditions.

[0054] Figure 5A shows a graph of the Poisson's ratio for the first film and the second film of the comparative example. Poisson's ratio ν xz The first factor is determined using Equation 2, and the true strain is determined based on the engineering strain using Equation 3.

[0055] ν xz =-dε z,真 / dε x,真 (Formula 2)

[0056] ε 真 =ln(ε 工学 +1) (Formula 3)

[0057] As shown in Figure 5A, the strain value at which Poisson's ratio becomes negative (authentic response threshold) is lower for the first film to which pre-straining conditions are applied (data point labeled 52) than for the second comparison film to which pre-straining conditions are not applied (data point labeled 54).

[0058] Figure 5B shows graphs of true stress as true strain increases for a first film to which pre-strain conditions are applied (data point labeled 56) and a second comparison film to which pre-strain conditions are not applied (data point labeled 58).

[0059] The graph in Figure 6 shows the strain for various predetermined strain values, calculated at approximately 0.01 s. -1 When applied at a certain rate and equilibrated under strain for 0.5 to 1 hour, the reduction in the authentic response threshold achieved by applying the method in Figure 1 to a liquid crystal elastomer film is shown. As shown in Figure 6, the reduction in the authentic response threshold can be achieved when pre-strain conditions are applied.

[0060] The method shown in Figure 4 was applied to multiple films, and the films were strained in 0.05 steps, and the films were equilibrated between strain steps over different durations at different temperatures. g The temperature was approximately 15°C. Local strains in the x and y directions were ε, respectively. x and ε y The z-direction strain (authentic response) was tracked and calculated using Equation 1, based on the measured strains in the x and y directions.

[0061] Figure 7A shows a graph of the strain in the z direction when the applied strain in the x direction increases step by step, and the stress relaxation times between strain steps are 5 minutes (data point 71), 10 minutes (data point 72), 60 minutes (data point 73), and 120 minutes (data point 74). The measurement was performed at T g The experiment was conducted using liquid crystal elastomer at a room temperature 8°C higher (23°C).

[0062] Figure 7B shows a graph of Poisson's ratio when the applied strain in the x-direction increases step by step, and the stress relaxation times between strain steps are 5 minutes (line 75), 10 minutes (line 76), 60 minutes (line 77), and 120 minutes (line 78). Poisson's ratio is calculated using Equation 2.

[0063] As shown in Figures 7A and 7B, the authentic response threshold (where the strain in the z-direction begins to increase in Figure 7A and Poisson's ratio becomes negative in Figure 7B) decreases as the stress relaxation period between strain steps increases.

[0064] Figure 8A shows that the liquid crystal elastomer is T g When the temperature is above 8°C (data point 81), and the liquid crystal elastomer is T g When heated to 15°C above (data point 82), and T g The graph shows the strain in the z direction when the material is heated to 20°C above (data point 83), with the applied strain in the x direction increasing step by step and the stress relaxation time between strain steps being 10 minutes.

[0065] Figure 8B shows that the liquid crystal elastomer is T g When the temperature is above 8°C (line 84), and the liquid crystal elastomer is T g When heated to 15°C above (line 85), and T g The graph shows the Poisson's ratio when the material is heated to 20°C above (line 86), with the applied strain in the x-direction increasing step by step and the stress relaxation time between strain steps being 10 minutes. The Poisson's ratio is calculated using Equation 2.

[0066] As shown in Figures 8A and 8B, the authentic response threshold (where the strain in the z direction begins to increase in Figure 8A and the Poisson's ratio becomes negative in Figure 8B) decreases as the temperature of the liquid crystal elastomer increases during the strain step and stress relaxation.

[0067] Where used herein, unless otherwise explicitly stated, all numerical values, such as those representing values, ranges, quantities, or percentages, may be interpreted as if preceded by the word "approximately," even if the word "approximately" does not explicitly appear. Furthermore, numerical ranges indicated by endpoints include all integers and, where appropriate, fractions (fractions) contained within that range (for example, 1-5 may include 1, 2, 3, and 4 when referring to several elements, and may also include 1.5, 2, 2.75, and 3.80 when referring to measured values). Endpoint indications also include the endpoint values ​​themselves (for example, 1.0-5.0 includes both 1.0 and 5.0). Any numerical ranges listed herein are intended to include all subranges contained within them.

[0068] Attention is drawn to all papers and documents filed concurrently with or prior to this specification and made available to the public together with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0069] All of the features disclosed herein (including the appended claims, abstract and drawings), and / or all of the steps of any method or process so so disclosed, may be combined in any combination except in which at least some of such features and / or steps are mutually exclusive.

[0070] Each feature disclosed herein (including the attached claims, abstract, and drawings) may be replaced by an alternative feature serving the same, equivalent, or similar purpose unless expressly stated otherwise. Accordingly, unless expressly stated otherwise, each disclosed feature is merely an example of a general set of equivalent or similar features.

[0071] The present invention is not limited to the details of the embodiments described above. The present invention extends to any novel feature or any novel combination of any feature disclosed herein (including the appended claims, abstract and drawings), or to any novel step or any novel combination of any method or process as so disclosed herein.

Claims

1. A method for preparing an oriented nematic liquid crystal elastomer with a reduced authentic response threshold, comprising the step of applying pre-strain conditions to the liquid crystal elastomer.

2. The method according to claim 1, wherein the step of applying the pre-straining conditions includes straining the liquid crystal elastomer and enabling stress relaxation while the liquid crystal elastomer is maintained in a strained state.

3. The ability of the liquid crystal elastomer to undergo stress relaxation is determined by the glass transition temperature T of the liquid crystal elastomer. ｇ The method according to claim 2, comprising enabling the liquid crystal elastomer to relax under stress at a higher temperature.

4. The method according to claim 2 or 3, wherein the deformation of the liquid crystal elastomer includes at least one of mechanically deformation of the liquid crystal elastomer, swelling or deswelling of the liquid crystal elastomer with a solvent, and adjusting the temperature of the liquid crystal elastomer.

5. The method according to claim 4, wherein mechanically distorting the liquid crystal elastomer includes applying a strain in a direction perpendicular to the orientation vector of the liquid crystal elastomer.

6. The method according to any one of claims 2 to 5, wherein distorting the liquid crystal elastomer includes distorting the liquid crystal elastomer to a predetermined distortion.

7. The method according to claim 6, wherein the predetermined strain is the strain at which the liquid crystal elastomer reaches the authentic response threshold when it is strained at a quasi-static rate.

8. The method further includes a step of determining the predetermined strain, the step of determining the predetermined strain is Determining the auxetic response threshold when the liquid crystal elastomer is distorted at each of several different speeds, The authentic response threshold for deforming the liquid crystal elastomer at a quasi-static rate is determined by extrapolating from the determined authentic response threshold. The method according to claim 6 or claim 7, including the method described in claim 6 or claim 7.

9. The plurality of different speeds are 10 －４ s －１ 、10 －３ s －１ 、10 －２ s －１ 、and 10 －１ s －１ ; the method according to claim 10

10. A method for preparing an oriented nematic liquid crystal elastomer with a reduced authentic response threshold, comprising the steps of applying strain to the liquid crystal elastomer in a series of steps, and enabling the liquid crystal to relax between steps.

11. The method according to claim 10, wherein the distortion of the liquid crystal elastomer includes distorting the liquid crystal by 0.02 to 0.1 in each step.

12. The ability of the liquid crystal elastomer to relax stress is due to the T of the liquid crystal elastomer. ｇ The method according to claim 10 or claim 11, comprising enabling the liquid crystal to relax under stress at a higher temperature.

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