3D Anisotropic Polyethylene as Light‐Responsive Grippers and Surfing Divers

Abstract

Untethered soft actuators are usually based on 3D engineered special polymers such as liquid crystal networks or hydrogels that require complex fabrication methods. Here, an easy‐to‐process, anisotropic composite soft actuator based on a simple photothermal dye‐doped polyethylene film is presented. The 3D anisotropic polymer films are prepared by solution‐casting and subsequent thermal solid‐stretching. The resulting soft actuators exhibit large and controllable bending in response to light (UV and/or near‐infrared (NIR)) and are able to act as grippers picking up cargo. Additionally, the films are capable of realizing “diving” and “surfing” locomotion in and over a liquid via the photothermal induced Marangoni effect, yielding a NIR light‐fueled transporter able to pick up cargo. The results open up new possibilities of using commodity polymers in a broad range of applications including untethered soft actuators and robotic devices.

NIR–vis–UV Light‐Responsive High Stress‐Generating Polymer Actuators with a Reduced Creep Rate

“…To prepare the NIR–vis–UV responsive actuators, PE composite (PE‐BZT‐GN‐QR) films were fabricated via solution‐casting and subsequent solid‐state film drawing following our protocol reported earlier (Figure S1, Supporting Information). [ 36 ] In the composite films, three light‐responsive additives were used: (2‐(2 H ‐benzotriazol‐2‐yl)‐4, 6‐ditertpentylphenol, BZT) to absorb UV light and improve the visible light transmission of ultradrawn films ( Figure a); [ 28 ] graphene as a NIR–vis–UV light‐absorbing additive to improve the thermal conductivity of the actuator; [ 37 ] and a dye to absorb NIR (650–850 nm), visible (400–480 nm), and UV (<400 nm) light simultaneously (Figure 1c; Figure S2, Supporting Information). [ 38 ] In addition, BZT is beneficial in dispersing both the GN and NIR dye.…”

“…[ 38 ] In addition, BZT is beneficial in dispersing both the GN and NIR dye. [ 36 ] Photographs taken from the PE composite films demonstrate optical transmission is retained after adding BZT and graphene (Figure 1a; Figure S2, Supporting Information). It should be noted that ultradrawn PE films exhibit anisotropic coefficients of thermal expansion (CTE) (Figure 1b), with a large, draw ratio‐dependent negative CTE parallel to the drawing direction.…”

“…The resulting stress-generating actuators are fast (<0.8 s) and can be repeatedly and reversibly driven with NIR, blue, and UV lights. The maximum specific actuation stress (35)(36)(37)(38)(39)(40)) was achieved at a draw ratio of 70. The stable photoinduced stress with reduced stress relaxation was obtained due to the reduced chain slip in the plastic region of ultradrawn composite films.…”

“…Recently, we reported on stretched 3D anisotropic UHMWPE composite actuators containing graphene, BZT, and NIR dye additives. [ 36 ] Film strips cut parallel to the stretching direction showed no obvious bending while the films cut perpendicular to the stretching direction bent. [ 36 ] In this work, we report on stress‐generation along the stretching direction of these oriented UHMWPE composite films.…”

“…[ 36 ] Film strips cut parallel to the stretching direction showed no obvious bending while the films cut perpendicular to the stretching direction bent. [ 36 ] In this work, we report on stress‐generation along the stretching direction of these oriented UHMWPE composite films. The ultradrawn films have a high visible (vis) light transmission (≈80% at 550 nm) and a fast ( t 0.9 < 0.8 s), reversible stress change (10–35 MPa) at different illumination wavelengths, including NIR (780 nm), blue (455 nm), and UV (365 nm) lights.…”