Directional Adhesion of Monodomain Liquid Crystalline Elastomers

Pranda, Paula A.; Hedegaard, Aaron; Kim, Hyunki; Clapper, Jason; Nelson, Eric; Hines, Lindsey; Hayward, Ryan C.; White, Timothy J.

doi:10.1021/acsami.3c16760

Cited by 8 publications

(1 citation statement)

References 51 publications

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“…Overall, the present results are useful for the practical applications of LCEs as soft actuators and are expected to contribute to the development of soft mechanical devices in the future. Furthermore, the results provide useful information for LCE applications other than actuators, such as those with adhesive strength changes ,− in response to large internal stress changes owing to phase transitions.…”

Section: Discussionmentioning

confidence: 99%

Thermally Generated Isometric Stress Performances of Polydomain and Monodomain Nematic Elastomers

Ohzono,

Minamikawa,

Watanabe

2024

ACS Appl. Polym. Mater.

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Nematic liquid-crystalline elastomers (NLCEs) have potential applications as soft actuators because of their ability to undergo large deformations or generate stress by phase transitions. However, the mechanical properties of the materials required to design their actual applications remain limited. In this study, isometric stresses generated via temperature changes on polydomain (PD) and monodomain (MD) NLCEs composed of the same components were evaluated at different strains, and their performances were compared. The results confirmed that the generated stress increased with the applied uniaxial strain. This implicates that the slope in the stress−strain response curve, i.e., the differential coefficient with respect to strain, increases with temperature at fixed strain. In terms of the true stress and strain units, the increasing trend of the PD and MD liquid-crystal elastomers (LCEs) did not differ significantly, which can be ascribed to similar thermodynamic state of both LCEs with similar effective cross-link densities and degree of liquid crystalline order in their stretched state. In MD, the deformation during the phase transition is expected to be higher owing to the initial alignment; therefore, the generated stress is also higher, at first glance. However, this study revealed that the creation method (genesis) did not make a significant qualitative difference when using the stresses generated in the stretched state. On the other hand, in the case of PD and MD materials of exactly the same dimensions, the ranges of useable strain, stress and generated stress are apparently very different, and this variety is useful as application choices. In addition, the evaluation of strain dependence on generated stress and the data analysis method for true stress employed in this study may be beneficial for understanding and enhancing the performance of polymer actuators in general, beyond just NLCEs.

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Section: Discussionmentioning

confidence: 99%

Thermally Generated Isometric Stress Performances of Polydomain and Monodomain Nematic Elastomers

Ohzono,

Minamikawa,

Watanabe

2024

ACS Appl. Polym. Mater.

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Monodomain Liquid‐Crystal Elastomer Lattices for Broad Strain‐Rate Mechanical Damping

Bischoff,

Bawcutt,

Sorkin

et al. 2024

Adv Eng Mater

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Designing structures that effectively dissipate energy across a broad range of mechanical loading rates, including those from compression, shock, and vibration, poses a significant engineering challenge. In this study, liquid‐crystal elastomers (LCEs), which possess anisotropic properties due to the alignment of their polymer backbone, are explored. As a result, LCEs exhibit a soft elastic response under mechanical loading, making them ideal for energy dissipation. Advances in additive manufacturing (AM) enable simple fabrication of foamlike dissipative structures with complex lattice geometries. Herein, direct ink write 3D printing, an extrusion AM method, is used to fabricate aligned, monodomain LCE lattice structures for broad strain‐rate mechanical damping. In this work, it is shown that these structures can dissipate strain energy in quasi‐static environments, comparable to traditional elastomeric lattices, and provide improved damping under high strain‐rate drop testing due to LCE soft elasticity. Additionally, under dynamic mechanical vibration, monodomain LCE lattices enhance damping at structural natural frequencies and provide high‐frequency attenuation. In these findings, a promising method is presented for fabricating mechanical damping devices that effectively dissipate energy across a broad range of loading rates.

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Harnessing Extreme Internal Damping in Polyrotaxane‐Incorporated Liquid Crystal Elastomers for Pressure‐Sensitive Adhesives

Choi,

Guo,

Kim

et al. 2024

Adv Funct Materials

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Liquid crystal elastomers (LCEs) exhibit extraordinary energy dissipation due to their unique viscoelastic response, resulting from the rotation of mesogens under mechanical stress. While recent studies demonstrate the LCE‐based pressure‐sensitive adhesives (PSAs) by exploiting the enhanced damping, all previous studies have focused on LCEs with covalent crosslinks. Here, a new class of PSAs is developed by integrating movable polyrotaxane crosslinkers into an LCE matrix (PRx‐LCEs). Dynamic viscoelastic measurements reveal that PRx‐LCE exhibits a remarkably high energy dissipation, as indicated by a large tan δ. Interestingly, the secondary tan δ peak associated with LCE damping is more pronounced than the primary peak of the glass transition. The exceptional energy dissipation in PRx‐LCE results in superior adhesion strength (≈1864 N m−1), which is 3.5 times higher than conventional LCEs and 13 times higher than commercial PSAs in the peel test. Additionally, PRx‐LCEs demonstrate thermally reversible adhesion, enabling clean removal at elevated temperatures. Furthermore, the sliding effect in PRx‐LCE enhances both deformability and stress relaxation under load, resulting in deeper indentation, and superior adhesion during the probe tack test. The combination of LCE and slidable crosslinks provides robust and switchable adhesion, making them promising for applications in biomedical engineering, display, and semiconductor industries.

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Directional Adhesion of Monodomain Liquid Crystalline Elastomers

Cited by 8 publications

References 51 publications

Thermally Generated Isometric Stress Performances of Polydomain and Monodomain Nematic Elastomers

Thermally Generated Isometric Stress Performances of Polydomain and Monodomain Nematic Elastomers

Monodomain Liquid‐Crystal Elastomer Lattices for Broad Strain‐Rate Mechanical Damping

Harnessing Extreme Internal Damping in Polyrotaxane‐Incorporated Liquid Crystal Elastomers for Pressure‐Sensitive Adhesives

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