Abstract
Photomechanical nanocomposites embedded with light-absorbing nanoparticles show promising applications in photoresponsive actuations. Near infrared (nIR)-responsive nanocomposites based photomechanical soft actuators can offer lightweight functional and underexploited entry into soft robotics, active optics, drug delivery, etc. A novel graphene-based photomechanical soft actuators, constituted by Polydimethylsiloxane (PDMS)/graphene-nanoplatelets (GNPs) layer (PDMS/GNPs) and pristine PDMS layer, have been constructed. Due to the mismatch of coefficient of thermal expansion of two layers induced by dispersion of GNPs, controllable and reversible bendings response to nIR light irradiation are observed. Interestingly, two different bending behaviors are observed when the nIR light comes from different sides, i.e., a gradual single-step photomechanical bending towards PDMS/GNPs layer when irradiation from PDMS side, while a dual-step bending (finally bending to the PDMS/GNPs side but with an strong and fast backlash at the time of light is on/off) when irradiation from PDMS/GNPs side. The two distinctive photomechanical bending behaviors are investigated in terms of heat transfer and thermal expansion, which reveals that the distinctive bending behaviors can be attributed to the differences in temperature gradients along the thickness when irradiation from different sides. In addition, the versatile photomechanical bending properties will provide alternative way for drug-delivery, soft robotics and microswitches, etc.
Highlights
In the past decade, responsive polymers that can offer external stimuli induced controllable actuations are of fundamental interest[1]
It is observed that the thickness of the bilayer is 130 μm in total, in which the PDMS/graphene nanoplatelets (GNPs) composited layer is 80 μm, and the pristine PDMS is 50 μm
When the soft actuators are illuminated form the side of PDMS thin layer, it would experience a single-step bending towards PDMS/GNPs side
Summary
Responsive polymers that can offer external stimuli induced controllable actuations are of fundamental interest[1]. Most mechanical response was constrained by the exerted pre-strains when actuations, which limited the various applications of these GNPs-based photomechanical soft actuators While impressive of these achievements in photomechanical graphene nanocomposites, it is necessary to develop fabricated nanocomposites exploiting the photothermal ability of graphene and accomplishing fast response and widely photomechanical actuations. Inspired by a bilayer phenomenon that two sheet-like components with different mechanical properties coupled together will attain a shape to facilitate an equilibrium between its constituent elements[29], a soft actuator is constituted by a bilayer structure It is composed of Polydimethylsiloxane (PDMS)/graphene-nanoplatelets (GNPs) composited layer (PDMS/GNPs) and pristine PDMS layer. Given the brilliant photothermal effect of graphene, and the thermal-expansion mismatch between PDMS and PDMS/GNPs thin layer due to the dispersion of GNPs, controllable and reversible bending response to nIR light irradiation was observed. It reveals that the two distinctive bending behaviors can be attributed to the heat transfer process and the transient temperature gradient along the thickness at the time of irradiation on/off when irradiation from different sides
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