Dr. Bryan Beckingham Profile

Dr. Bryan Beckingham

at Auburn Univ

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Proceedings Article | 9 May 2024 Presentation + Paper

Self-folding behavior of bilayer films actuated by liquid crystal elastomers

Yi-Hung Lin, Braden Starver, Bryan Beckingham, Russell Mailen

Proceedings Volume 12947, 129470C (2024) https://doi.org/10.1117/12.3014639

KEYWORDS: Liquid crystals, Ultraviolet radiation, Film thickness, Polymers, Thermal deformation, Deformation, Glasses, Shape memory polymers, Photopolymerization

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Liquid crystal elastomers (LCEs) films enable thermally responsive shape change. Mesogenic segments in the elastomeric network can be aligned into crystalline domains via mechanical deformation of the film. If subjected to a second-stage UV cure in the deformed shape, the crystalline domains are retained upon release of the external load. This induces a temporary shape in the LCE. Subsequent heating of the LCE above the nematic-to-isotropic temperature disorders the liquid crystals, and strain energy stored in the elastomer causes the LCE to return to the undeformed. In a reversible manner, the LCE returns to the temporary shape when cooled. In this work, we use thermally responsive LCE films applied to passive thin films, such as mylar and Kapton. The passive film enhances the mechanical strength and stiffness of the film but prevents alignment of the LCE crystalline domains through stretching. Instead, these bilayer films are restricted to folding deformations, wherein the LCE layer is used to induce thermally responsive shape change. We study the effects of layer thickness ratios on the reversibly self-folding bilayer films. The LCE films are synthesized directly on the passive film layer using a two-stage thiol-acrylate Michael addition and photopolymerization (TAMAP) reaction in which the first stage is a thermal cure, and the second stage is a UV cure. We demonstrate the reversible shape change between flat and folded states, and quantify the shape change in terms of the shape fixity and recovered flatness ratios. Potential applications for this system are actuators for deployable structures and soft robotics.

Proceedings Article | 18 April 2023 Presentation

Self-folding of liquid crystal elastomer composite films (Conference Presentation)

Greg McCallum, Yi-Hung Lin, Bryan Beckingham, Russell Mailen

Proceedings Volume PC12484, PC1248407 (2023) https://doi.org/10.1117/12.2658534

KEYWORDS: Liquid crystals, Composites, Photopolymerization, Thin films, Temperature metrology, Robotics, Optical alignment, Multifunctional materials, Crystals, Actuators

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In this work, we seek to fabricate self-folding liquid crystal elastomer (LCE) composite films. Liquid crystal elastomers (LCEs) are a class of smart, multifunctional materials that can be imparted with enhanced, anisotropic mechanical properties through the alignment of crystalline domains. Crystalline order decreases with increasing temperature, and long-range order is lost above the nematic to isotropic transition temperature, TNI. This enables programmable, reversible actuation in response to temperature changes. The envisioned composite films comprise domains of active, monodomain LCEs to drive reversible self-folding, which are adhered to passive, thin films that serve as a framework to guide the self-folding response. LCEs will be synthesized using a two-stage thiol-acrylate Michael addition and photopolymerization (TAMAP) reaction. The first-stage consists of a room temperature cure to form polydomain films, and a second-stage photopolymerization of the mechanically deformed LCE film forms aligned liquid crystal monodomains. Composite films will be molded to a folded state prior to the second stage cure such that heating above TNI produces a reversible unfolding response. We characterize the self-folding behavior of these materials using a series of single-fold and multiple, intersecting fold geometries. We envision application of these composite films as actuators in soft robotics and morphing surfaces.

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