Composite materials

Abstract

A composite material comprising multiple particles scattered within an elastomer, wherein the elastomer is an authetic-oriented nematic liquid crystal elastomer. Another composite material comprising a first outer layer, a second outer layer, and an intermediate layer between the first and second outer layers, wherein the intermediate layer comprises an authetic-oriented nematic liquid crystal elastomer.

Description

Technical Field

[0001] The present invention relates to a composite material including a nematic liquid crystal elastomer.

Background Art

[0002] The composite material may be layered and include a plurality of layers. Other types of composite materials may be particulate composites in which particles of a first material are provided in a second material. Composite materials are used in a wide range of industries such as aerospace and aircraft structures, automotive structures, and microelectromechanical systems.

[0003] Debonding can be a significant problem in composite material systems. The layers of a layered composite material may become separated, and the particles may become separated from the surrounding material in a particulate composite. Such separation can result from a plurality of factors including free-edge effects, structural discontinuities, and local disturbances due to shock, moisture, and temperature variations. The thermomechanical reliability of microelectronic packaging is a major concern in the electronics industry. Interlayer delamination is also a significant problem faced by the glass industry.

[0004] Some composite material systems may expel a self-healing material when debonding occurs, and this self-healing material may act to prevent debonding. Fiber composite material systems may utilize Z-pin bridging in which through-thickness reinforcements are provided. However, such methods of addressing debonding may only be effective for some composite material systems.

Summary of the Invention

Means for Solving the Problems

[0005] According to the present invention, an apparatus and method as set forth in the appended claims are provided. Other features of the present invention will become apparent from the dependent claims and the following description.

[0006] According to a first embodiment, a composite material comprising an auxetic-aligned liquid crystal elastomer is provided.

[0007] The composite material may be a granular composite material and may contain multiple particles scattered within the elastomer. The composite material may be a layered composite material and the elastomer may form an intermediate layer between the first outer layer and the second outer layer.

[0008] As described in International Publication No. 2019077361A1, oriented nematic liquid crystal elastomers with authentic properties have recently been developed. Austhentic 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 stretched sample of the material. When stretched, authentic materials become thicker in one or both directions perpendicular to the applied deformation.

[0009] Surprisingly, composites containing authetic-oriented nematic liquid crystal elastomers have been found to provide resistance to delamination. In composites where particles are scattered within the elastomer, resistance to delamination between the elastomer and particles has been found to be improved. The delamination resistance properties of such composites may be useful in applications such as body armor or semiconductor packaging. In composites where the liquid crystal elastomer is an intermediate layer between a first outer layer and a second outer layer, interlayer delamination can be reduced. Such composites may be used in applications such as automotive glazing and photovoltaic device encapsulants, and the authetic-oriented nematic liquid crystal elastomer intermediate layer may replace current intermediate layer materials such as polyvinyl butyral layers.

[0010] The particle composite material may be a film. This film may have a thickness of 100 μm or less. In other examples, the film may have a thickness greater than 100 μm.

[0011] The particles may be of any shape. Preferably, the particles may be spherical. In other examples, the particles may be elongated, such as rod-shaped.

[0012] The particle size may be smaller than the film thickness. Spherical particles may have a diameter of 100 μm or less. Preferably, spherical particles may have a diameter of 10 μm. In other examples, particles may have a diameter greater than 100 μm.

[0013] The liquid crystal elastomer may be a monodomain liquid crystal elastomer. In this specification, "monodomain" means that the orientation vectors of the elastomer are aligned macroscopically within the sample. Monodomain orientation across a sample can be determined, for example, by polarized light microscopy, in which monodomain orientation is characterized by uniform birefringence when the macroscopic sample is observed between orthogonal nicols (orthogonal polarizers).

[0014] The liquid crystal elastomer may be oriented in the direction of the longitudinal axis of the film.

[0015] In the above-described layered composite material, the authentic liquid crystal elastomer may be oriented in a predetermined direction. This predetermined direction may be substantially parallel to the outer layer, or perpendicular to the outer layer. In another example, the predetermined direction may be at an oblique angle to the outer layer. The layered composite material may include an orientation layer between at least one of the first outer layer and the second outer layer, and this orientation layer is configured to promote the orientation of the liquid crystal elastomer in the predetermined direction. In the layered composite material, at least one of the outer layers may be glass.

[0016] In particle composites, the bulk liquid crystal elastomer may have a monodomain orientation, and the liquid crystal elastomer may have different orientations in the vicinity of the particles. Nematic liquid crystal elastomer molecules may be aligned parallel or perpendicular to the surface of the particles. The orientation of liquid crystal molecules around the particles may depend on the particle material.

[0017] The particulate composite material may include an oriented surface provided on the surface of the particles, and the oriented surface is configured to promote the orientation of the liquid crystal elastomer in a direction parallel or perpendicular to the surface of the particles. The particles may be pretreated to select a perpendicular or parallel orientation. For example, a solution may be applied to the particles to promote alignment.

[0018] Although some 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 present invention as defined in the appended claims.

Brief Description of the Drawings

[0019] To better understand the present invention and to show how embodiments of the present invention may be implemented, reference will now be made, by way of example only, to the accompanying schematic drawings.

[0020] [Figure 1] FIG. 1 shows a first example of a composite material.

[0021] [Figure 2] FIG. 2 shows a second example of a composite material.

[0022] [Figure 3A] FIGS. 3A and 3B show graphs depicting the Freedericksz threshold of an aligned nematic liquid crystal elastomer. [Figure 3B] FIGS. 3A and 3B show graphs depicting the Freedericksz threshold of an aligned nematic liquid crystal elastomer.

[0023] [Figure 4A] FIGS. 4A - E show images of an aligned nematic liquid crystal elastomer in which particles are embedded. [Figure 4B] FIGS. 4A - E show images of an aligned nematic liquid crystal elastomer in which particles are embedded. [Figure 4C]Figures 4A-E show images of oriented nematic liquid crystal elastomers with embedded particles. [Figure 4D] Figures 4A-E show images of oriented nematic liquid crystal elastomers with embedded particles. [Figure 4E] Figures 4A-E show images of oriented nematic liquid crystal elastomers with embedded particles.

[0024] [Figure 5A] Figures 5A-5F show images of isotropic elastomers with embedded particles. [Figure 5B] Figures 5A-5F show images of isotropic elastomers with embedded particles. [Figure 5C] Figures 5A-5F show images of isotropic elastomers with embedded particles. [Figure 5D] Figures 5A-5F show images of isotropic elastomers with embedded particles. [Figure 5E] Figures 5A-5F show images of isotropic elastomers with embedded particles. [Figure 5F] Figures 5A-5F show images of isotropic elastomers with embedded particles. [Modes for carrying out the invention]

[0025] As shown in Figure 1, the exemplary composite material 10 includes a first outer layer 12, a second outer layer 14, and an intermediate layer 16 between the first outer layer 10 and the second outer layer 12. The intermediate layer 16 is formed of an authetic-oriented nematic liquid crystal elastomer, for example, a liquid crystal elastomer described later in Example 1.

[0026] The nematic liquid crystal elastomer is oriented in the Y direction, parallel to the outer layer. When strain is applied in the X direction, the liquid crystal elastomer undergoes a mechanical Fredericks transition (MFT), in which the orientation direction effectively rotates in the Z direction.

[0027] The mechanical Fredericks transition is defined as a deformation mode of aligned elastomers, where the in-plane orientation vector of the elastomer film appears to rotate abruptly at critical strain and reorient in a direction parallel to the stress axis at critical elongation. Materials exhibiting this property have been described by Mitchell et al. (Mitchell, GR, Davis, FJ, and Guo, W., Phys. Rev. Lett., 1993, 71(18), 2947) and Roberts et al. (Roberts, PMS, Mitchell, GR, and Davis, FJ, J. Phys. II). The MFT was first described by France, 1997, 7, 1337 and by Roberts, PMS, Mitchell, GR, Davis, FJ, and Pople, JA, Mol.Cryst.Liq.Cryst., 1997, 299, 181. The MFT is often described by analogy to the well-known electric field (or magnetic field) Fredericks transition (EFT) that occurs in low molar mass nematic display devices. In the EFT, the orientation vectors reorient abruptly beyond a clear critical field (or voltage) and gradually align with respect to the electric field as the field amplitude increases. The EFT threshold is theoretically discontinuous, but it is known to soften when an ideal LC monodomain with orientation precisely parallel or perpendicular to the substrate is not actually achieved. Nevertheless, the threshold is sharp and distinct. The apparent sharp rotation of the orientation vectors observed in the MFT is due to an alternative deformation mode called semi-soft elasticity. This differs from the orientation vector rotation response of oriented elastomers that deform via elasticity (SSE). In the case of semi-soft elasticity, the orientation vector rotates relatively gradually, rotating over a plateau-like region of the tensile load curve on the deformation plane.

[0028] As shown in Figure 2, another exemplary composite material 20 includes a film formed of an authetic-oriented nematic liquid crystal elastomer 22 and a plurality of particles 24 scattered therein. In the composite material 20, the bulk of the liquid crystal elastomer is oriented in the Y direction, and in the vicinity of the particles 24, the liquid crystal elastomer is positioned around the particles. When strain is applied in the X direction, the liquid crystal elastomer undergoes MFT, and its orientation direction rotates in the Z direction. [Examples]

[0029] An authentic-oriented nematic liquid crystal elastomer 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)

[0030] The elastomers were prepared using the following starting monomer mixture. [Table 1]

[0031] Silica microspheres (1 wt%) with a diameter of 10 μm and no surface treatment were immersed in a liquid crystal monomer mixture. In other examples, particles of other materials and diameters may be immersed in the liquid crystal monomer mixture.

[0032] A liquid crystal elastomer film was prepared by polymerizing a monomer mixture inside a mold for thin films with a thickness of approximately 100 μm, a width of approximately 15 mm, and a length of approximately 60 mm. The first film according to the present invention was cured at room temperature in a planar orientation in the nematic phase, with the mold surface coated with a thin layer of PVA orientation and the rubbing direction being antiparallel. In other examples, other orientation layers, such as polyimide, may be used. A second film as a comparative example was cured at 50°C in the isotropic phase without an orientation layer. A third film as a comparative example was cured at room temperature in a planar orientation in the nematic phase in the absence of microsphere particles. Each of the first, second, and third films was polymerized for 2 hours. After polymerization, the films were removed from the mold and held overnight in a methanol / DCM solvent mixture to wash away 6OCB.

[0033] Figures 3A and 3B show that authentic behavior is present in the first film. A strain in the x-direction was applied, and the strains in the x and y directions were measured by particle tracking as the elastomer was deformed in the x-direction. The selected particles were close to the center of the elastomer. The strain in the z-direction (authentic response) is calculated based on the measured strains in the x and y directions using Equation 1, assuming that the volume of the liquid crystal elastomer remains constant.

[0034]

number

[0035] 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.

[0036] ν xz =-dε z,真 / dε x,真 (Formula 2)

[0037] ε 真 =ln(ε 工学 +1) (Formula 3)

[0038] Figure 3A shows the instantaneous Poisson's ratio as a function of strain, and Figure 3B shows the strain in the z direction as a function of the strain in the x direction. Figure 3A shows that as the x strain (axis 30) increases, the Poisson's ratio (axis 32) decreases and becomes negative, thereby exhibiting authentic behavior. Figure 3A shows that for the first film (labeled 34 in Figure 3A), the Poisson's ratio becomes negative at a lower strain than for the third film without particles (labeled 36 in Figure 3A). Figure 3B shows the authentic threshold at which the z strain (axis 38) increases with increasing x strain (axis 40). Figure 3B shows that the first film with particles (labeled 42 in Figure 3B) has an authentic threshold at a reduced x strain compared to the third film without particles (labeled 44 in Figure 3B).

[0039] The peel resistance of the first film is shown in Figures 4A–4E. The images in Figures 4A–4E were taken while the first film was distorted when placed between orthogonal polarizers with a 50x objective lens. The film was distorted in 0.2 mm step sizes and allowed to relax for 120 seconds before the next distortion step. The distortion was applied along the axis indicated by arrow X in Figures 4A–4E. In each of Figures 4A–4E, the image labeled (i) shows the appearance of the first film through orthogonal polarizers, and the image labeled (ii) shows the appearance of the first film through orthogonal polarizers with a waveplate. The positions of the orthogonal polarizers are indicated by label 52.

[0040] Figure 4A shows the appearance of the first film before distortion, Figure 4B shows the appearance of the first film with a distortion of 0.25, Figure 4C shows the appearance of the first film with a distortion of 0.5, Figure 4D shows the appearance of the first film with a distortion of 0.75, and Figure 4E shows the appearance of the first film with a distortion of 1. Figures 4A-4E do not show evidence of separation of the liquid crystal elastomer from the spherical particles. Changes in birefringence are indicated by striations in the images at high distortion (Figures 4D and 4E), which may be due to strain interactions between the MFT and particles.

[0041] Figures 5A–5G show comparative examples of the second film being distorted in the X direction when placed between orthogonal polarizers. The images in Figures 5A–5G were taken while the second film was distorted when placed between orthogonal polarizers with a 50x objective lens. The second film was distorted in 0.2 mm step sizes, allowing (allowing) relaxation for 120 seconds before the next distortion step. In each of Figures 5A–4G, the image labeled (i) shows the appearance of the second film through orthogonal polarizers, the image labeled (ii) shows the appearance of the second film through orthogonal polarizers with a waveplate, the image labeled (iii) shows the appearance of a single particle in the second film through orthogonal polarizers, and the image labeled (iv) shows the appearance of a single particle in the second film through orthogonal polarizers with a waveplate. The positions of the orthogonal polarizers are indicated by label 52.

[0042] Figure 5A shows the appearance of the second film before distortion, Figure 5B shows the appearance of the second film with a distortion of 0.13, Figure 5C shows the appearance of the second film with a distortion of 0.32, Figure 5D shows the appearance of the second film with a distortion of 0.5, Figure 5E shows the appearance of the second film with a distortion of 0.65, Figure 5F shows the appearance of the second film with a distortion of 0.84, and Figure 5G shows the appearance of the second film with a distortion of 0.97. Figures 5F and 5G show that separation of the liquid crystal elastomer from the spherical particles is present at higher distortions. This separation can be seen as black triangles to the left and right of the particles. In Figure 5F, some particles exhibit this defect, and in Figure 5G, almost all particles exhibit this defect. Local distortion between particles causes birefringence, but this is very small. In Figures 5A-5G, the black background in the image labeled (i) is due to the isotropy of the elastomer in these regions.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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 composite material comprising multiple particles scattered within an elastomer, wherein the elastomer is an authetic-oriented nematic liquid crystal elastomer.

2. The composite material according to claim 1, wherein the composite material is a film.

3. The composite material according to claim 1 or claim 2, wherein the particles are spherical.

4. The composite material according to claim 3, wherein the spherical particles have a diameter of 100 μm or less, preferably 10 μm.

5. The composite material according to claim 1 or claim 2, wherein the particles are elongated.

6. The composite material according to any one of claims 1 to 5, wherein the liquid crystal elastomer is a monodomain liquid crystal elastomer.

7. The composite material according to any one of claims 1 to 6, comprising an orientation surface provided on the surface of the particles, wherein the orientation surface is configured to promote the orientation of the liquid crystal elastomer in a direction parallel or perpendicular to the surface of the particles.

8. A composite material comprising a first outer layer, a second outer layer, and an intermediate layer between the first outer layer and the second outer layer, wherein the intermediate layer comprises an authetic-oriented nematic liquid crystal elastomer.

9. The composite material according to claim 8, wherein the liquid crystal elastomer is a monodomain liquid crystal elastomer having a predetermined orientation direction substantially parallel to the first outer layer and the second outer layer.

10. The composite material according to claim 9, further comprising an orientation layer between at least one of the first outer layer and the second outer layer, wherein the orientation layer is configured to promote the orientation of the liquid crystal elastomer in the predetermined direction.

11. The composite material according to any one of claims 8 to 10, wherein at least one of the first outer layer and the second outer layer is glass.

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