Long Liquid Crystal Elastomer Fibers with Large Reversible Actuation Strains for Smart Textiles and Artificial Muscles

Abstract

A method for fabricating long, soft, and reversibly actuatable liquid crystal elastomer (LCE) fibers by using direct ink write (DIW) printing was developed. Here, the LCE was produced based on a two-stage thermal-photo curing reaction between a difunctional acrylate monomer and thiol. The LCE ink, mixed with nanoclay to increase the viscosity, was extruded through a nozzle onto a rotating mandrel to obtain a long fiber. After printing, the fiber was first thermally cured on the mandrel, then mechanically stretched, and photocured to achieve liquid crystal chain alignment for stress-free reversible activation. Upon optimizing the ink viscosity and DIW printing parameters, long fibers (up to 1.5 m long from the laboratory) were obtained. The resulting fiber had a modulus of 2 MPa, 51% actuation strain, and a failure strain of well over 100%. The potential of these fibers for applications was demonstrated. The LCE fibers were knit, sewn, and woven to form a variety of smart textiles. The fiber was also used to mimic bicep muscles with both large activation force and activation strain. By incorporating further intelligent characteristics, such as conductivity and biosensing into a single fiber, the LCE fibers could be potentially used for smart clothing, soft robotics, and biomedical devices.

A highly stretchable strain sensor based on CNT/graphene/fullerene-SEBS

“…With the development of smart technology, exible electronic devices have been applied in various elds, including health monitoring, 1 human motion, 2 exible photoelectrics, 3 articial muscle design, 4 and intelligent weaving. 5 Due to better stretchability, 6,7 exibility, 8,9 skin adaptability and sensitivity of exible electronic devices, [10][11][12][13] much attention has been given to the potential applications of highly stretchable, linear, 14,15 and electrically conductive strain sensors.…”

Materials as Machines

“…The following year, Sharma and Lagerwall reported preparation of core–sheath LCE fibers through electrospinning that can undergo irreversible contraction due to the stiffness of the passive sheath polymer 559. More recently, Qi and co‐workers harnessed the thiol‐Michael reaction to extrude LCE fibers to emulate muscle fiber 560. By weaving fibers together, the force in an arm‐like actuator increases with fiber count.…”

A Hollow Polyethylene Fiber-Based Artificial Muscle

“…Compared with the complex transmission devices such as motors, gears and linkage rods, artificial muscle is mainly determined by the performance of the in-process material, and has the characteristics of small size, light-weight, and quiet operation [6][7][8][9][10][11]. Based on these special properties, the artificial muscle has a wide range of potential applications in industrial manipulators, artificial robots, artificial limbs et al Recently, special functional polymer materials and low-dimensional nanomaterials with various forms have been used to produce artificial muscles [3,[12][13][14][15]. Among them, the fiber-shape actuators, which are similar to human muscle fiber bundles, as well as high power-to mass ratio and fast temporal responsiveness [3,4], have attracted wide attention offered more possibilities for artificial muscles.…”

“…To date, novel materials with various attributes have been explored and investigated based on different driving mechanisms or stimulus sources to fabricate fiber-shaped actuators acting as artificial muscle. Even though significant progresses on artificial muscle, such as liquid crystal elastomer fibers [14], thermally set silk fibers [10], graphenebased composite fibers [16][17][18], electrospun microfiber yarns [19], coiled polymer (polyethylene or nylon) fibers [20][21][22][23], torsional or twisted carbon nanotube hybrid fibers [3,7,24], have been reported recently and provided people more understanding on this hot research topic. For the strict standards of artificial muscle applications, such as high sensitivity, environmental adaptability, control convenience, and large-scale preparation, these fiber-shaped actuators are still hard to meet the demanding.…”

“…For the strict standards of artificial muscle applications, such as high sensitivity, environmental adaptability, control convenience, and large-scale preparation, these fiber-shaped actuators are still hard to meet the demanding. For the liquid crystal elastomer fiber-based artificial muscle, although it could realize 51% reversible actuation responding to a temperature range from − 20 to 100 °C, its relatively low strength (< 2 MPa) has limited its practical applications [14]. The reported silk-based and graphene oxide-based fiber actuators, acting as a humidity sensitive actuator, are difficult to adapt to easy changing environments [10,16].…”