Entering the Fourth Dimension - Manufacturing Responsive Liquid Crystal Elastomer Structures

Description:

The University of Texas at Dallas is seeking companies interested in commercializing an innovative method for fabricating Liquid Crystal Elastomer (LCE) structures that undergo reversible actuation in a wide variety of environments. This method uses direct-write additive manufacturing to locally-control the molecular orientation of LCEs, thereby programming a stimuli-responsive 3D product – also known as four-dimensional (4D) printing. By strategically controlling and varying the print path of the printer, the LCE can be created with unique layers that allow for anisotropic optical properties, elastic modulus, and stimulus response. The specialized cross-linked elastomers within the ink allows the printed structures to morph into different 3D structures when activated by certain stimuli, including heat or light. Consequently, the shape and molecular orientation of the printed object can be controlled for applications such as medical devices, thermal insulation, soft robots, and more. Compared to other 4D printing technologies, using the present technology enables the fabrication of structures with a combination of 3D features and programmable shape change that are impossible to produce with previous methods.

Figure 1: Thermally responsive liquid crystal elastomers (LCEs) are direct-write printed into 3D structures with a controlled molecular order. Molecular order is locally programmed by controlling the print path used to build the 3D object, and this order controls the stimulus response. Each aligned LCE filament undergoes 40% reversible contraction along the print direction on heating. By printing objects with controlled geometry and stimulus response, magnified shape transformations are realized (e.g. volumetric contractions or rapid, repetitive snap-through transitions).

Technical Summary:

Unlike many materials that undergo reversible shape change, LCEs neither require an external load nor an aqueous environment – making them ideal candidates for a wide range of applications. Rheological behavior of the LC oligomer ink is advantageous for direct-write printing; the ink behaves as a viscous liquid during the extrusion process and has a nematic phase (between 65C and 85C) wherein shear-thinning occurs at rates consistent with 3D printing. The properties of the ink ensure that the geometry of the LC filament is maintained through the photopolymerization step, with a material modulus that retains its structural integrity in the absence of direct support features.

The present 4D printing method enables the fabrication of aligned LCE structures with positive or negative Gaussian curvature – such combinations of alignment and geometry are impossible to create using previous methods. This allows for the creation of printed LCE structures that exhibit snap-through actuation capable of performing useful work.

Value Proposition:

The present technology enables 4D printing of LCEs that exhibit large, reversible shape changes by controlling the molecular orientation at every point throughout the manufacturing process.

Applications:

Aerospace – responsive structures
Soft Robotics
Morphing Medical Devices
Responsive Microstructures – Valves and pumps in microfluidic systems
Tunable Grating – Heat-dependent change of diffraction patterns

Key Benefits:

Rapid Deformation – Can undergo snap-through transitions in a matter of 16ms
Reversible Deformation – LCE structures actuate reversibly at the macroscale based on its programmed microstructures
Large Deformation – Reversible 40% contraction along the director is achieved upon heating from room temperature to 200C
Scalable – May be implemented for all applications from the microscale to macroscale
Programmable – Provides ability to control molecular orientation at every point, enabling structures impossible to fabricate by previous methods
Range of Operation – Unlike many materials that undergo reversible shape change, LCEs neither require an external load nor an aqueous environment, making them ideal candidates for many applications

Inventors:

Taylor H. Ware, Ph.D.

Cedric P. Ambulo

Jennifer M. Boothby

Julia J. Burroughs

M. Ravi Shankar, Ph.D.

Publication:

Ambulo, C P, Burroughs J J, Boothby J M, Kim H, Shankar M R, Ware T H*. “4D Printing of Liquid Crystal Elastomers.” ACS Applied Materials and Interfaces. (2017) DOI: 10.1021/acsami.7b11851.