Liquid crystal elastomer adhesives with gradient-pattern orientation and articles including the same

Abstract

Provided are articles including a substrate and a cured composition of a curable composition comprising 50 to 81 weight percent of a liquid crystal monomer, 1 to 24 weight percent of a chain extender, 6 to 26 weight percent of a crosslinker, and 0 to 1.5 weight percent of an initiator, wherein the curable composition is adjacent to the substrate, wherein the curable composition is in the form of a continuous or discontinuous layer, and wherein the cured composition comprises a mesogen orientation gradient. Also provided are methods of making mesogen orientation gradients and articles including the same.

Description

[0001] PA103325W002

[0002] LIQUID CRYSTAL ELASTOMER ADHESIVES WITH GRADIENT-PATTERN ORIENTATION AND ARTICLES INCLUDING THE SAME

[0003] BACKGROUND

[0004] 5 Adhesives are used in a variety of marking, holding, protecting, sealing, and masking applications. One type of adhesive, a pressure-sensitive adhesive, is particularly preferred for many applications. Pressure-sensitive adhesives (“PSAs”) are well known to persons of ordinary skill in the relevant arts to possess certain properties at room temperature (e.g., 23 °C), including: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength. Materials that have been found to function well as pressure-sensitive adhesives are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear strength. Characteristics of PSAs are described, for example, in the Encyclopedia of Polymer Science and Engineering, Vol. 13, Wiley -Interscience Publishers (New York, 1988) and the Encyclopedia of Polymer Science and 5 Technology, Vol. 1, Interscience Publishers (New York, 1964).

[0005] SUMMARY

[0006] The present disclosure provides articles including a pressure-sensitive adhesive derived from a liquid crystal elastomer (“LCE”) using thiol-ene chemistry, wherein the cured composition comprises a0 mesogen orientation gradient.

[0007] In one aspect, provided herein are articles including a substrate and a cured composition of a curable composition, the curable composition comprising 50 to 81 weight percent of a liquid crystal monomer, 1 to 24 weight percent of a chain extender, 6 to 26 weight percent of a crosslinker, and 0 to 1.5 weight percent of an initiator, wherein the weight percent values are based on a total weight of the curable5 composition, wherein the curable composition is adjacent to the substrate, wherein the curable composition is in the form of a continuous or discontinuous layer, and wherein the cured composition comprises a mesogen orientation gradient.

[0008] In another aspect, provided herein are methods of making a mesogen orientation gradient.

[0009] As used herein, the term “mesogen orientation gradient” refers to a gradual change in orientation of the LCE mesogens that emerges over a measurable distance, that can be expressed as a change in angle per unit length (e.g., A7mm), and is contrasted with a sudden change in orientation of the LCE mesogens at the interface between two discretely oriented monodomains.

[0010] As used herein, the term “% blur " refers to the fractional length of the image over which the original image is blurred, expressed as the % of the dimensions of the full image. For example, a 46%5 blur over the length of a 30 mm long image creates a gradient across 13.8 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. l is a graph showing the effect of mesogen orientation on peel strength.

[0012] FIG. lb shows an LCE having a parallel mesogen orientation peeled from a substrate.

[0013] FIG. 1c shows an LCE having a perpendicular mesogen orientation peeled from a substrate.

[0014] FIG. 2 shows blur filter settings applied to the greyscale image inputs to the Spatial Light Modulator (SLM) for some gradient patterns in Example 7.

[0015] FIG. 3a is a graph showing peel data for 0%, 32%, and 46% mesogen orientation gradient samples.

[0016] FIG. 3b shows the greyscale images generated to be uploaded for the SLM to provide the 0%, 32%, and 46% mesogen orientation gradient samples (top) and a plot of the average slope corresponding to the graph in FIG. 3a (bottom).

[0017] DETAILED DESCRIPTION

[0018] Reference will now be made to various embodiments of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

[0019] The terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that section.

[0020] In many applications involving bonding interactions between an adhesive and a substrate it may be beneficial to control the strength of the adhesive-substrate bond. This can involve, for example, some form of "debond- or bond-on-demand" functionality that enables the adhesive to adhere with appropriate strength to the substrate while also allowing for ease of separation under certain conditions. In some adhesive-substrate constructions an external stimulus (e.g., heat, electricity, light) may be required to change the adhesion strength. However, in some applications the ability to apply an external stimulus is limited. To address at least these issues, the present disclosure provides articles including a pressuresensitive adhesive (“PSA”) derived from a liquid crystal elastomer (“LCE”). LCEs are known to those of ordinary skill in the relevant arts and are described, for example, by Herbert et al., “Synthesis and Alignment of Liquid Crystalline Elastomers,” Nature Reviews Materials, Nature Research, January 1, 2022, pp 23-38.

[0021] LCEs are lightly crosslinked polymer networks that contain mesogen (i.e., liquid crystal) phases that can be oriented into monodomains via processing, such as, for example, by exposure to polarized light or by applying some order or orientation to the substrate on which they are applied, such as, for example, by rubbing a surface to form aligned micro grooves that the mesogens align to. The alignment of the mesogen phases into one or more monodomains can impart anisotropic mechanical properties to the LCE and by introducing these alignment effects to the LCE PSA, the adhesive may have a peel force that depends on the direction in which it is peeled. For example, in an unaligned case, the tacky LCE PSA has some baseline strength of adhesion, which can be controlled by conventional means (e.g., crosslinking density, modulus, glass transition temperature). However, if the LCE is oriented during and / or prior to use through processing, the strength of the adhesion to a substrate can be changed, for example as illustrated by the graph in FIG. la, to be weaker than the baseline in the parallel mesogen direction (FIG. lb) and stronger than the baseline in the perpendicular mesogen direction (FIG. 1c).

[0022] Use of LCE PSAs in bonded articles allows for sophisticated bond design, such as, for example, articles where the bonding strength increases in a first direction, while allowing for easy removal when debonding along a second direction. Directional peel force is an advantageous property for enabling on- demand disbondment of an adhesive, where its holding power it optimized along its principal usage direction but the user could remove it with minimal force by peeling it along some other direction. Applications that could benefit from such a property could include adhesives used for temporary bonding, such as those used in pick-and-place manufacturing; static applications like supporting wall-mounted brackets where the usage direction is fixed, but release and repositioning can be achieved quickly by removing it along an alternative direction; and adhesives for access panels where ease of removal aids in repair of a device. These characteristics can be further exploited by changing mesogen orientation, for example, by exposure of the bonded article to heat or light, thereby allowing the adhesive strength to be tuned throughout the life of the article. Articles including patterned LCE PSAs, where the mesogen orientation can be locally tuned to provide complex bonding profiles, are also contemplated.

[0023] Liquid crystal elastomer (LCE) adhesives have demonstrated the ability to exhibit directional- dependence on their mechanical properties, such as tensile modulus and peel force. This can be controlled by alignment of the LCE mesogen structures by various methods, including, for example, mechanically scratched or rubbed surfaces and / or photoalignment by linearly polarized light, the methods of which are known to those of ordinary skill in the relevant arts. In this case, the source of orientation is known as the “director,” which imparts its orientation onto the liquid crystal material, which can then be cured to maintain the orientation after the director is removed. Typically, for LCE-based adhesives, peeling in a direction parallel to the mesogen orientation results in a low peel force, while peeling orthogonal to the mesogen orientation results in a high peel force. This orientation can be patterned by allowing different areas of the director to take on different alignment. Such an invention was disclosed in PCT / US2024 / 037819, “Liquid Crystal Elastomer Adhesives and Articles Including the Same” in which only discrete patterns, with regions called “monodomains, were employed. Within a monodomain all mesogens have the same orientation. This work opens the possibility for blending / blurring of these monodomains that was not previously disclosed. The previous disclosure explored the use of discrete patterns with a series of monodomains.

[0024] However, this excludes many possible patterns that utilize a gradient in orientation as opposed to discrete patterns with sharp edges. For certain applications, a gradient in mesogen orientation may have a number of desirable features, including, for example, a gradual transition in optical properties (such as, for example, polarization) instead of sharp lines which may be unsightly to a customer, a means to eliminate or “blunt” a potential stress concentration at sharp comers or edges of a discrete pattern (by gradually transitioning to the new orientation via a gradient pattern), and in making an adhesive with strength fully along the spectrum between the high and low adhesion limits of the LCE (as opposed to on / off functionality of standard patterns). Such a gradient in orientation could have value in directing crack propagation to a certain side of a removable adhesive (like a bandage), or could be designed to target improved anti-lifting behavior of an adhesive at the comers of a display, graphic or signage attachment, or any bond area more generally (where most unintentional removal or damage would initiate) while still allowing for removal of the adhesive starting from a different portion of the adhesive and allowing that to transition to a state that allows easy removal from said comers when needed. Orientation gradients may also pave the way for novel LCE adhesive actuators, which move based on changing their orientation in response to an external stimulus like heat or light.

[0025] A solution is to apply a “blur” to the photopatteming approach to director orientation. In photopatteming, linearly polarized light is digitally tuned to create domains of differing orientation, but when the pattern is designed to include a continuous change in direction, the result is a gradual switch between the adjacent orientations. The blur could be tuned to cause a gradient over a variable distance. As a hypothetical example, blurring could result in changing from 0° orientation to 90° orientation over the span of 18 mm, or over the span of 9 mm, etc., which could be equivalently expressed as a “slope” of orientation equal to 10° / mm or 5° / mm, respectively.

[0026] For example, the planar patterns disclosed thus far have employed simple binary orientations of orthogonal and parallel configurations. LCE patterning offers the flexibility to incorporate gradient patterns into the material, enabling intermediate peel strengths. These gradients provide an alternative means to adjust peel strength beyond pattern resolution. Gradient patterns were examined to assess the transition regime's slope from low (parallel) to high (orthogonal) peel force and vice versa. Three gradient samples were tested, ranging from parallel to orthogonal peel regimes: a control sample with no gradient (0%), and two gradient samples with increasing gradient blurring (32% and 46%). Raw peel data was recorded during peeling, with FIG. 3a displaying an example mn for each sample (solid lines). The right axis illustrates the greyscale pixel value, with dotted lines depicting corresponding greyscale values of the uploaded images, shown in FIG. 3b, to the Spatial Light Modulator (SLM) as the sample peeled simultaneously. The plot presents the SLM greyscale image for the three samples, alongside the average and standard deviations of the peel slopes in the transition regime. As anticipated, the 0% gradient sample exhibited the steepest transition from parallel to orthogonal regime. Conversely, the other two gradient samples demonstrated approximately six times lesser slope, with the 46% gradient showing the lowest slope. This data underscores the potential for gradient designs between maximal high and low peel regimes, a distinct advantage of LCE PSAs over classical PSAs, which are typically limited to binary patterning.

[0027] In one aspect, provided are articles comprising a substrate and a cured composition of a curable composition, the curable composition including 50 to 81 weight percent of a liquid crystal monomer, 1 to 24 weight percent of a chain extender, 6 to 26 weight percent of a crosslinker, and 0 to 1.5 weight percent of an initiator, wherein the weight percent values are based on a total weight of the curable composition, wherein the curable composition is adjacent to the substrate, wherein the curable composition is in the form of a continuous or discontinuous layer, and wherein the cured composition comprises a mesogen orientation gradient. In some embodiments, the cured composition comprises a pressure-sensitive adhesive. In some embodiments, the cured composition is a pressure-sensitive adhesive, the substrate is a backing, and the article is an adhesive tape. In some embodiments, the substrate comprises a tape backing. In some embodiments, wherein the liquid crystal monomer is represented by the structure

[0028] In some embodiments, the chain extender is represented by the structure

[0029] In some embodiments, the crosslinker is represented by the structure

[0030] In some embodiments, the initiator comprises a photoinitiator. In some embodiments, the article further comprises a primer layer between the substrate and the curable composition. In some embodiments, the primer layer comprises a polyamide resin. In some embodiments, the cured composition comprises a plurality of mesogen orientation gradients. In some embodiments, the ratio of Average Peel Strength Orthogonal to Nematic Director of LCE: Average Peel Strength Parallel to Nematic Director of LCE is 1.1:1 to 100:1; optionally 1.1:1 to 75:1; optionally 1.1:1 to 50:1; optionally 1.1:1 to 40:1; optionally 1.1:1 to 30:1; 1.1:1 to 25:1; optionally 1.1:1 to 20:1; optionally 1.1:1 to 15:1; optionally 1.1:1 to 10:1; optionally 1.2:1 to 100:1, optionally 1.3:1 to 100:1, optionally 1.4:1 to 100:1, optionally 1.4:1 to 9:1 as determined by the Peel Test.

[0031] In another aspect, provided are methods of making mesogen orientation gradients.

[0032] Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

[0033] EXAMPLES

[0034] Materials l,l’-(2-Methyl-l,4-phenylene) bis[4-[(6-mercaptohexyl)oxy]benzoate] (RM2SH) (CAS Registry Number 1803269-66-0) was obtained from AlphaMicron Incorporated, Kent, OH. Glyoxal bis(diallyl acetal) (GBDA) (CAS Registry Number 16646-44-9) and trimethylolpropane diallyl ether (TMPDAE) (CAS Registry Number 682-09-7) were obtained from the Sigma-Aldrich Company, St. Louis, MO. IRGACURE 369 photoinitiator was obtained from IGM Resins, Charlotte, NC. ELVAMIDE 8023R polyamide resin was obtained from the DuPont Corporation, Wilmington, DE.

[0035] Methods

[0036] Gel Fraction Determination

[0037] A dry sample of LCE film was weighed and then submerged in cyclopentane for a minimum of 72 hours. The film sample was then removed from the cyclopentane and dried by placing on a hot plate set at 75 °C for 5 hours. The dried sample was removed from the hot plate, cooled to room temperature, and then weighed. The weight of the sample after the cyclopentane submersion / drying process was compared to the original recorded weight of the sample to calculate the gel fraction, defined as the weight fraction of the remaining insoluble portion.

[0038] Polarized Optical Microscopy

[0039] Surface alignment of LCE films was imaged using a Nikon Eclipse Ci-POL polarized light microscope (Nikon Instruments, Melville, NY) in reflection mode at 20x magnification.

[0040] Wide Angle X-ray Scattering (WAXS) Analysis LCE film samples were imaged with a Xenocs Xeuss 3.0 SAXS / WAXS beamline (Xenocs, Inc., Holyoke, MA). Patterns were collected with vacuum in transmission geometry using a copper source with x-ray energy at 8 keV. Scan times were 60 seconds per sample.

[0041] Example 1. Preparation of Liquid Crystal Elastomer (LCE) Film

[0042] Rectangular glass slides (38 mm (x-axis) by 25 mm (y-axis)) were plasma cleaned for 10 minutes under vacuum using a Harrick PDC-32G (115 V) basic plasma cleaner (Harrick Plasma, Ithaca, NY). ELVAMIDE 8023R polyamide resin (6-10 drops, 0.125 weight percent in methanol) was spin-coated onto the plasma coated surface of one side of each glass slide (10 seconds at 1500 rpm, 500 rpm / second acceleration, followed by 50 seconds at 3500 rpm, 1200 rpm / second acceleration) using a Laurell WS- 650-23B Spin Coater (Laurell Technologies, Lansdale, PA). To create an alignment surface for mesogens, the resulting resin coated surface of each slide was rubbed a minimum of 10 times in a single, linear direction (i.e., y-axis direction of the glass slide) using a velvet cloth with hand pressure. The velvet cloth was wrapped around a round glass vial. A first glass slide was placed on a solid horizontal surface with the rubbed surface exposed. A second slide was placed on top of the first slide with 30 micron glass bead spacers used to create a gap separating the slides. The rubbed surface of the second slide faced the rubbed surface of the first slide and the slides were edge aligned so as to have the same direction of surface rubbing.

[0043] The monomers RM2SH (50 mg), GBDA (5.32 microliters), and TMPDAE (9.40 microliters) were combined with the IRGACURE 369 photoinitiator (0.64 mg) in a vial. The molar ratio of GBDA:TMPD AE was about 1:2. The mixture was melt-mixed at 110 °C with vortexing to form a homogeneous mixture. The glass plate assembly was placed on a hot plate set at 110 °C. The melted mixture was applied to the edge of the heated glass plate assembly using a pipette so that the gap volume between the slides was filled with the mixture by capillary action. The assembly was then placed on a hot plate set at 75 °C to reach the nematic liquid crystal state and the monomer mixture was photopolymerized at 75 °C with 10 minutes of exposure to 100 mW / cm2 of 365 nm light (Dymax BlueWave MX-25 curing system, Dymax Company, Torrington, CT). The glass slide assembly was then submerged in room temperature water overnight, followed by removal of the resulting LCE film from the assembly. The film was dabbed with a dry paper towel to remove residual water. The gel fraction of the LCE film was 90.1%. Polarized optical microscopy images of the LCE film showed birefringence. The wide angle x-ray scattering (WAXS) image of the LCE film showed prominent eyebrow features consistent with monodomain LCE alignment.

[0044] Comparative Example A. Poly do main LCE Polymer Film

[0045] The same procedure as reported in Example 1 was followed with the exception that the polyamide resin coated surfaces of the glass slides were not rubbed to create an alignment surface.

[0046] Example 2. Preparation of LCE Film with More GBDA Cross-Linker than in Example 1 The same procedure as described in Example 1 was followed with the exception that the monomer mixture contained RM2SH (50 mg), GBDA (7.45 microliters), and TMPDAE (5.64 microliters) were combined with the IRGACURE 369 photoinitiator (0.63 mg) in a vial. The molar ratio of GBDA:TMPDAE was about 1:1. The gel fraction of the LCE film was 91.9%. Polarized optical microscopy images of the LCE film showed birefringence. The wide angle x-ray scattering (WAXS) image of the LCE film showed prominent eyebrow features consistent with monodomain LCE alignment.

[0047] Comparative Example B. Poly do main LCE Polymer Film

[0048] The same procedure as reported in Example 2 was followed with the exception that the polyamide resin coated surfaces of the glass slides were not rubbed to create an alignment surface.

[0049] Example 3. Preparation of LCE Film with More GBDA Cross-Linker than in Example 2

[0050] The same procedure as described in Example 1 was followed with the exception that the monomer mixture contained RM2SH (50 mg), GBDA (9.58 microliters), and TMPDAE (1.88 microliters) were combined with the IRGACURE 369 photoinitiator (0.61 mg) in a vial. The molar ratio of GBDA:TMPDAE was about 4.5:1. The gel fraction of the LCE film was 87.1%. Polarized optical microscopy images of the LCE film showed birefringence. The wide angle x-ray scattering (WAXS) image of the LCE film showed prominent eyebrow features consistent with monodomain LCE alignment.

[0051] Comparative Example C. Poly do main LCE Polymer Film

[0052] The same procedure as reported in Example 3 was followed with the exception that the polyamide resin coated surfaces of the glass slides were not rubbed to create an alignment surface.

[0053] Example 4. Tensile Testing of Examples 1-3 and Corresponding Comparative Examples A-C

[0054] A DMA850 Dynamic Mechanical Analyzer (TA Instruments, New Castle, DE) was operated at room temperature for tensile testing of LCE film strips (cut to about 10 mm length and 2.5 mm width). For LCE films of Examples 1-3, sets of strips were cut in two different orientations. In the first set, strips were cut with the lengthwise direction of the strip parallel to the nematic director of the LCE film (i.e., cut in the direction of surface rubbing). In the second set, strips were cut with the lengthwise direction of the strip perpendicular to the nematic director of the LCE film (i.e., cut in the direction orthogonal to the direction of surface rubbing). The applied strain was 10% / minute. The Young’s modulus was taken in the linear regime in the stress-strain curve between 1-3% strain. Test strips were prepared from at least 3 different batches of each LCE film with at least 3 samples taken per batch. The average values determined for “stress at fracture” (MP), “strain at fracture” and “Young’s modulus” (with standard error of the mean (SE)) are presented in Tables 1-3.

[0055] Table 1.

[0056] N / A = Not Applicable

[0057] Table 2.

[0058] N / A = Not Applicable

[0059] Table 3.

[0060] N / A = Not Applicable

[0061] Example 5. Peel Test

[0062] Peel tests (180°) were performed using a TA.XTplus Texture Analyzer with a 500 g load cell (Stable Micro Systems, Surrey, England). ASTM Standard D3330 ‘Standard Test Method for Peel Adhesion of Pressure-Sensitive Tape’ was used as a guide for the procedure. Samples for peel testing were prepared by heat pressing an LCE film selected from Examples 1-3 and corresponding Comparative Examples A-C to the primed surface of a polyester terephthalate film (thickness of 51 microns) at 80 °C for 10 minutes. The resulting backed films were cut into strips (15 mm length by 2-4 mm width). For backed films prepared from LCE films of Examples 1-3, sets of strips were cut in two different orientations. In the first set, strips were cut with the lengthwise direction of the strip parallel to the nematic director of the LCE film (i.e., cut in the direction of surface rubbing). In the second set, strips were cut with the lengthwise direction of the strip perpendicular to the nematic director of the LCE film (i.e., cut in the direction orthogonal to the direction of surface rubbing).

[0063] Each strip had an overhang of the backing that was then taped onto a glass slide for attachment to a grip of the instrument. The exposed LCE surface was placed onto a piece of plasma-cleaned glass and maintained at 80 °C for one hour to ensure maximum conformality of the surface. The samples were then cooled to room temperature. Adherence pressure was standardized by rolling each sample 5 times with a weighted roller. The 180° peel tests were performed at room temperature at a velocity of 0.5 mm / second for 20 mm or until the entire sample strip was unpeeled. The peel force reading was normalized by the test sample width. Peel strength measurements were averaged across a plateau of force to record the steady-state peel force. For each peel test sample, the average peel strength (with standard error of the mean(SE)) was determined using LCE film prepared from at least three different batches and a minimum of 15 total strip measurements were conducted. The peel strength results (N / mm) are reported in Tables 4 and 5. Table 4. Peel Strength Measurements

[0064] N / A = Not Applicable

[0065] Table 5. Peel Strength Calculation

[0066] N / A = Not Applicable

[0067] Example 6. Preparation and Peel Testing of a Pressure Sensitive Adhesive with a Patterned LCE Surface Rectangular glass slides (38 mm (x-axis) by 25 mm (y-axis)) were plasma cleaned and coated with ELVAMIDE 8023R polyamide resin (0.125 weight percent in methanol) according to the method described in Example 1. The method of rubbing the resin coated surface was changed from Example 1 to create two sections (each section being 19 mm (x-axis) by 25 mm (y-axis)) with different (orthogonal) directions of rubbing. In the first section, the resin coated surface was rubbed a minimum of 10 times in the x-axis direction only using a velvet cloth with hand pressure. The velvet cloth was wrapped around a round glass vial. In the second section, the resin coated surface was rubbed a minimum of 10 times in the y-axis direction only using the velvet cloth. These sectioned glass slides were used to prepare a patterned LCE film according to the photopolymerization procedure described in Example 2.

[0068] The resulting LCE film was observed under cross polarizers and a prominent light scattering difference was evident for the two sections indicating that the nematic directors of the LCE film sections were aligned based on the direction of mbbing. The first LCE section (from rubbing the polyamide contact surface in the x-direction) was more opaque than the second LCE section (from rubbing the polyamide contact surface in the y-direction).

[0069] A backing was adhered to the LCE film according to the procedure described in Example 5. A sample strip (30 mm (x-axis direction) by 3.8 mm (y-axis direction) was cut from the backed film. The upper half of the strip (15 mm by 3.8 mm) was from the section of the slide in which the polyamide resin was rubbed in the x-axis direction and the lower half of the strip (15 mm by 3.8 mm) was from the section of the slide in which the polyamide resin was rubbed in the y-axis direction.

[0070] The peel test (180°) of the sample strip was conducted as described in Example 5 with the peel direction being parallel to the direction of rubbing used for aligning the upper LCE film section. The two sections of the patterned sample had significantly different peel strengths. The peel strength of the upper section was 0.09 N / mm. while the peel strength of the lower section was 0.49 N / mm (>5 times the peel strength of the upper section of the pattern).

[0071] Example 7. Preparation and Peel Testing of a Pressure Sensitive Adhesive Including a Mesogen Orientation Gradient

[0072] Optical patterning: A LC 2012 spatial light modulator (SLM) from HOLOEYE Photonics AG, Berlin, Germany was used along with HOLOEYE Pattern Generator software to create an imposed pattern on the photoalignment director surface. The collimated lenses and optical path were constructed with accessories available from ThorLabs, Inc., Newton, NJ. Greyscale images were created on MATLAB and subsequently uploaded to the software. The BY-coated glass cells were placed in the sample holder of the optical beam path and irradiated by a 10W HeNe optical diode laser system (RPMC Lasers Inc.) to pattern the cells.

[0073] For inducing gradient patterns, a % blur was applied to a discrete pattern to create a gradual change in polarization down a prespecified length of the greyscale image. FIG. 2 shows blur filter settings applied to the greyscale image inputs to the Spatial Light Modulator (SLM) for the 46% gradient patterns for Sample 6.

[0074] The SLM pixel ratio was 1024x768 pixels, which resulted in patterns that were 30mm x 22.5 mm.

[0075] The gradient % was applied to the length (in this case, the 30 mm distance).

[0076] Table 6: Mesogen Orientation Gradient Samples.

[0077] LCE synthesis: LCEs were synthesized using a thiol-ene photopolymerization reaction involving 2- methyl-l,4-phenylene bis(4-(6-mercaptohexyloxy)benzoate (RM2SH, Daken), glyoxal bis(diallyl acetal) (GBDA, Sigma-Aldrich), and trimethylolpropane diallyl ether (TMPDAE, Sigma- Aldrich). The photopolymerization process, initiated by 1.5 wt %benzyl-2 -dimethylamino- l-(4-morpholinophenyl)- butanone-1 (Irgacure 369, IGM Resins), followed a 1:1 stoichiometric ratio of thiol to ene monomers. The RM2SH:GBDA:TMPDAE ratio was 1:0.7:0.3. The surface coating for the LCEs was a mixture of 0.3 wt% Brilliant Yellow (“BY”, Sigma-Aldrich) dye in dimethylformamide (photoalignment director). The LCE mixtures were homogenized through multiple heating and vortexing cycles before capillary filling at 111 °C between patterned BY glass slides with 30 pm glass bead spacers and cooled to 52 °C to achieve the nematic liquid crystal state. Photopolymerization was conducted at 52 °C with 10 minutes of exposure to 10 mW / cm2of 365 nm light. Post-polymerization, samples were immersed in deionized water and subsequently extracted using razor blades.

[0078] Peel testing: 180° peel testing of Samples 4-6 was conducted using a TA.XTplus Texture Analyzer equipped with a 50 kg load cell from Stable Micro Systems, following ASTM Standard D3330 guidelines. LCE samples, backed with a 50 pm thick PET layer (3M), were heat-pressed at 80 °C for 10 minutes. The samples were cut from the backing, with excess backing material for ease of handling. After adhering the backing to a glass slide, the LCE tape was affixed to a plasma-cleaned glass surface at 80 °C for a minimum of 4 hours to ensure optimal dwell time and surface conformality. Standardized pressure adherence was achieved using a weighted roller, rolling each sample five times. Peel strength values were averaged over a force plateau, derived from a minimum of three separate LCE samples with at least 10 peel measurements each.

[0079] Results for Gradient Patterned adhesives: The planar patterns explored thus far have employed simple binary orientations of orthogonal and parallel configurations. LCE patterning offers the flexibility to incorporate gradient patterns into the material, enabling intermediate peel strengths. These gradients provide an alternative means to adjust peel strength beyond pattern resolution. Gradient patterns were examined to assess the transition regime's slope from low (parallel) to high (orthogonal) peel force and vice versa. Three gradient samples were tested, ranging from parallel to orthogonal peel regimes: a control sample with no gradient (0%), and two gradient samples with increasing gradient blurring (32% and 46%). Raw peel data was recorded during peeling, with FIG. 3a displaying an example run for each sample (solid lines). Referring to FIG. 3a, the right axis illustrates the greyscale pixel value, with dotted lines depicting corresponding greyscale values of the uploaded images, to the SLM as the sample peeled simultaneously. FIG. 3b (top) presents the SLM greyscale image for the three samples, alongside the average and standard deviations of the peel slopes in the transition regime (bottom). As anticipated, Sample 4, the 0% gradient sample, exhibited the steepest transition from parallel to orthogonal regime. Surprisingly, the other two gradient samples, Samples 5 and 6, demonstrated approximately six times lesser slope, with the 46% gradient showing the lowest slope. This data underscores the potential for gradient designs between maximal high and low peel regimes, a distinct advantage of LCE PSAs over classical PSAs, which are typically limited to binary patterning. All cited references, patents, and patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims

What is claimed is:

1. An article comprising: a substrate; and a cured composition of a curable composition, the curable composition comprising: a) 50 to 81 weight percent of a liquid crystal monomer; b) 1 to 24 weight percent of a chain extender; c) 6 to 26 weight percent of a crosslinker; d) 0 to 1.5 weight percent of an initiator, wherein the weight percent values are based on a total weight of the curable composition, wherein the curable composition is adjacent to the substrate, wherein the curable composition is in the form of a continuous or discontinuous layer, and wherein the cured composition comprises a mesogen orientation gradient.

2. The article of claim 1, wherein the cured composition comprises a pressure-sensitive adhesive.

3. The article of claim 1 or claim 2, wherein the cured composition is a pressure-sensitive adhesive, the substrate is a backing, and the article is an adhesive tape.

4. The article of any one of claims 1 to 3, wherein the substrate comprises a tape backing.

5. The article of any one of claims 1 to 4, wherein the liquid crystal monomer is represented by the structure6. The article of any one of claims 1 to 5, wherein the chain extender is represented by the structure7. The article of any one of claims 1 to 6, wherein the crosslinker is represented by the structure8. The article of any one of claims 1 to 7, wherein the initiator comprises a photoinitiator.

9. The article of any one of claims 1 to 8, further comprising a primer layer between the substrate and the curable composition.

10. The article of claim 9, wherein the primer layer comprises a polyamide resin.

11. The article of any one of claims 1 to 10, wherein the cured composition comprises a plurality of mesogen orientation gradients.

12. The article of any one of claims 1 to 11, wherein the ratio of Average Peel Strength Orthogonal to Nematic Director of LCE: Average Peel Strength Parallel to Nematic Director of LCE is 1.1 : 1 to 100:1; optionally 1.1:1 to 75:1; optionally 1.1:1 to 50:1; optionally 1.1:1 to 40:1; optionally 1.1:1 to 30:1; 1.1:1 to 25:1; optionally 1.1:1 to 20:1; optionally 1.1:1 to 15:1; optionally 1.1:1 to 10:1; optionally 1.2:1 to 100:1, optionally 1.3:1 to 100:1, optionally 1.4:1 to 100:1, optionally 1.4:1 to 9:1 as determined by the Peel Test.

13. A method of making a mesogen orientation gradient, the method comprising: providing a substrate, wherein a surface of the substrate comprises a photoalignment director; exposing the photoalignment director to linearly polarized light to provide photoalignment to the photoalignment director; providing a curable composition, the curable composition comprising: a) 50 to 81 weight percent of a liquid crystal monomer; b) 1 to 24 weight percent of a chain extender; c) 6 to 26 weight percent of a crosslinker; d) 0 to 1.5 weight percent of an initiator, wherein the weight percent values are based on a total weight of the curable composition, wherein the curable composition is adjacent to the photoalignment director on the substrate, wherein the curable composition is in the form of a continuous or discontinuous layer, to provide a laminate structure; andexposing the laminate structure to actinic radiation to provide a cured composition, wherein the cured composition comprises a mesogen orientation gradient.

14. The method of claim 13, wherein the substrate is selected from the group consisting of a glass, a thermoplastic polymer tape backing, and combinations thereof.

15. The method of claim 13 or claim 14, wherein the photoalignment director comprises Brilliant Yellow.

16. The method of any one of claims 13 to 15, wherein wherein the cured composition comprises a pressure-sensitive adhesive.

17. The method of any one of claims 13 to 16, wherein the cured composition is a pressure-sensitive adhesive, the substrate is a backing, and the article is an adhesive tape.

18. The method of any one of claims 13 to 17, wherein the substrate comprises a tape backing.

19. The method of any one of claims 13 to 18, wherein the liquid crystal monomer is represented by the structure20. The method of any one of claims 13 to 19, wherein the chain extender is represented by the structure21. The method of any one of claims 13 to 20, wherein the crosslinker is represented by the structure22. The method of any one of claims 13 to 21, wherein the initiator comprises a photoinitiator.

23. The method of any one of claims 13 to 22, wherein laminate structure further comprising a primer layer.

24. The method of claim 23, wherein the primer layer comprises a polyamide resin.

25. The method of any one of claims 13 to 24, wherein the cured composition comprises a plurality of mesogen orientation gradients.

26. The method of any one of claims 13 to 25, wherein the ratio of Average Peel Strength Orthogonal to Nematic Director of LCE: Average Peel Strength Parallel to Nematic Director of LCE is 1.1:1 to 100:1; optionally 1.1:1 to 75:1; optionally 1.1:1 to 50:1; optionally 1.1:1 to 40:1; optionally 1.1:1 to 30:1; 1.1:1 to 25:1; optionally 1.1:1 to 20:1; optionally 1.1:1 to 15:1; optionally 1.1:1 to 10:1; optionally 1.2:1 to 100:1, optionally 1.3:1 to 100:1, optionally 1.4:1 to 100:1, optionally 1.4:1 to 9:1 as determined by the Peel Test.

27. The method of any one of claims 13 to 26, wherein the polarized light is provided by an optical diode laser system.

28. The method of any one of claims 13 to 27, wherein the actinic radiation comprises 300 nm to 400 nm light with intensity of 1 mW / cm2to 100 mW / cm2.

29. The method of any one of claims 13 to 28, wherein the polarized light has an imposed pattern.

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