4.7 Article

Solvent Sorption-Induced Actuation of Composites Based on a Polymer of Intrinsic Microporosity

Journal

ACS APPLIED POLYMER MATERIALS
Volume 3, Issue 2, Pages 920-928

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsapm.0c01215

Keywords

actuator; polymer composite; polymer of intrinsic microporosity; drug delivery; micro-origami capsule

Funding

  1. UK Engineering and Physical Sciences Research Council (EPSRC) via SUPERGEN Grants [EP/K021109/1, EP/L018365/1]
  2. EPSRC [EP/K021109/1, EP/L018365/1] Funding Source: UKRI

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A new class of actuators based on polymer composites with intrinsic microporosity and activated carbon filler have been developed, showing repeatable three-dimensional actuation through solvent evaporation and wetting. The degree of curling and actuation can be controlled by adjusting the filler amount and evaporation rate, while actuation speed can be controlled by changing the solvent type. These actuators are insensitive to humidity and water, making them potentially useful in medical applications.
Materials that are capable of actuation in response to a variety of external stimuli are of significant interest for applications in sensors, soft robotics, and biomedical devices. Here, we present a class of actuators using composites based on a polymer of intrinsic microporosity (PIM). By adding an activated carbon (AX21) filler to a PIM, the composite exhibits repeatable actuation upon solvent evaporation and wetting and it is possible to achieve highly controlled three-dimensional actuation. Curled composite actuators are shown to open upon exposure to a solvent and close as a result of solvent evaporation. The degree of curling and actuation is controlled by adjusting the amount of filler and evaporation rate of the solvent casting process, while the actuation speed is controlled by adjusting the type of solvent. The range of forces and actuation speed produced by the composite is demonstrated using acetone, ethanol, and dimethyl sulfoxide as the solvent. The maximum contractile stress produced upon solvent desorption in the pure PIM polymer reached 12 MPa, with an ultimate force over 20 000 times the weight of a sample. This form of the composite actuator is insensitive to humidity and water, which makes it applicable in an aqueous environment, and can survive a wide range of temperatures. These characteristics make it a promising actuator for the diverse range of operating conditions in robotic and medical applications. The mechanism of actuation is discussed, which is based on the asymmetric distribution of the carbon filler particles that leads to a bilayer structure and the individual layers expand and contract differently in response to solvent wetting and evaporation, respectively. Finally, we demonstrate the application of the actuator as a potential drug delivery vehicle, with capacity for encapsulating two kinds of drugs and reduced drug leakage in comparison to existing technologies.

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