This paper reports large light-induced reversible and elastic responses of graphene nanoplatelet (GNP) polymer composites. Homogeneous mixtures of GNP/polydimethylsiloxane (PDMS) composites (0.1‐5 wt%) were prepared and their infrared (IR) mechanical responses studied with increasing pre-strains. Using IR illumination, a photomechanically induced change in stress of four orders of magnitude as compared to pristine PDMS polymer was measured. The actuation responses of the graphene polymer composites depended on the applied pre-strains. At low levels of pre-strain (3‐9%) the actuators showed reversible expansion while at high levels (15‐40%) the actuators exhibited reversible contraction. The GNP/PDMS composites exhibited higher actuation stresses compared to other forms of nanostructured carbon/PDMS composites, including carbon nanotubes (CNTs), for the same fabrication method. An extraordinary optical-to-mechanical energy conversion factor ( M) of 7‐9 MPa W 1 for GNP-based polymer composite actuators is reported. (Some figures may appear in colour only in the online journal)

https://iopscience.iop.org/article/10.1088/0957-4484/23/4/045501/pdf

Graphene-nanoplatelet-based photomechanical actuators

The addition of nanomaterials to polymers can result not only in significant material property improvements, but also assist in creating entirely new composite functionalities. By dispersing graphene nanoplatelets (GNPs) within a polydimethylsiloxane matrix, we show that efficient light absorption by GNPs and subsequent energy transduction to the polymeric chains can be used to controllably produce significant amounts of motion through entropic elasticity of the pre-strained composite. Using dual actuators, a two-axis sub-micron resolution stage was developed, and allowed for two-axis photo-thermal positioning (~100 μm per axis) with 120 nm resolution (feedback sensor limitation), and ~5 μm/s actuation speeds. A PID control loop automatically stabilizes the stage against thermal drift, as well as random thermal-induced position fluctuations (up to the bandwidth of the feedback and position sensor). Maximum actuator efficiency values of ~0.03% were measured, approximately 1000 times greater than recently reported for light-driven polymer systems.

/pdf/graphene-elastomer-composite-based-photo-thermal-1h3hk9c9qg.pdf

Graphene/elastomer composite-based photo-thermal nanopositioners.

New molybdenum disulfide (MoS2)-based polymer composites and their reversible mechanical responses to light are presented, suggesting MoS2 as an excellent candidate for energy conversion. Homogeneous mixtures of MoS2/polydimethylsiloxane (PDMS) nanocomposites (0.1–5 wt.%) were prepared and their near infrared (NIR) mechanical responses studied with increasing pre-strains. NIR triggering resulted in an extraordinary change in stress levels of the actuators by ~490 times. Actuation responses of MoS2 polymer composites depended on applied pre-strains. At lower levels of pre-strains (3–9%) the actuators showed reversible expansion while at high levels (15–50%), the actuators exhibited reversible contraction. An optomechanical conversion (η)∼0.5-3 MPa W �1 was calculated. The ratio of maximum stress due to photo-actuation (σmax) at 50% strain to the minimum stress due to photo-actuation (σmin )a t 3% strain was found to be ∼315-322% for MoS2 actuators (for 0.1 to 5 wt.% additive), greater than single layer graphene (∼188%) and multi-wall nanotube (∼172%) photo-mechanical actuators. Unlike other photomechanical actuators, the MoS2 actuators exhibited strong light–matter interactions and an unambiguous increase in amplitude of photomechanical response with increasing strains. A power law dependence of σmax/σmin on strains with a scaling exponent of β= 0.87–1.32 was observed, suggesting that the origin of photomechanical response is intertwined dynamically with the molecular mechanisms at play in MoS2 actuators.

https://iopscience.iop.org/article/10.1088/0957-4484/26/26/261001/pdf

MoS2 actuators: reversible mechanical responses of MoS2-polymer nanocomposites to photons.

This paper reports dimensional dependence of the mechanical response in carbon nanostructure composites to near-infrared (NIR) light. Using polydimethylsiloxane, a common silicone elastomer, composites were fabricated with one-dimensional multi-wall carbon nanotubes (MWNTs), two-dimensional single-layer graphene, two-and-a-half-dimensional graphene nanoplatelets and three-dimensional highly ordered pyrolytic graphite. An evaporative mixing technique was utilized to achieve homogeneous dispersions of carbon in the polymer composites, and their photomechanical responses to NIR illumination were studied. For a given carbon concentration, both steady-state photomechanical stress response and energy conversion efficiency were found to be directly related to the dimensional state of the carbon nanostructure additive. A maximum observed stress change of 60 kPa and 5 10 3 % efficiency were obtained with just 1 wt% MWNT loading. Actuation and relaxation kinetic responses were found to be related not to dimensionality, but to the percolation threshold of the carbon nanostructure additive in the polymer. Establishing a connective network of the carbon nanostructure additive allowed for energy transduction responsible for the photomechanical effect to activate carbon beyond the NIR illumination point, resulting in enhanced actuation. For samples greater than percolation threshold, photoconductivity of the nanocomposite structure as a function of applied pre-strain was measured. Photoconductive response was found to be inversely proportional to applied pre-strain, demonstrating mechanical coupling. Mechanical response dependence to the carbon nanostructure dimensional state could have significance in developing new types of carbon-based mixed-dimensional composites for sensor and actuator systems. (Some figures may appear in colour only in the online journal)

http://eri.louisville.edu/papers_pres/Panchapakesan_Nanotechnology_2012.pdf

Dimensional dependence of photomechanical response in carbon nanostructure composites: a case for carbon-based mixed-dimensional systems.

Photostrictive materials, exhibiting light-induced strain, are of interest for the future generation of wireless remote control photo-actuators. Photostrictive actuators are expected to be used as the driving component in optically controlled flexible structures. In this paper, the photonic control of flexible spherical shells using discrete photostrictive actuators is investigated. This paper presents a coupled opto-piezothermoelastic shell theory that incorporates photovoltaic, pyroelectric and piezoelectric effects, and has the capability to predict the response of a spherical shell driven by the photostrictive actuators. In this study, the effects of actuator location as well as membrane and bending components on the control action have been analyzed. The results obtained indicate that the control forces are mode and location dependent. Analysis also shows that the membrane control action is much more significant than the bending control action.

http://iopscience.iop.org/article/10.1088/0964-1726/16/5/025/pdf

Photostrictive actuators for photonic control of shallow spherical shells

Photostrictive materials, exhibiting light-induced strains, are of interest for future generation wireless remote control photo-actuators, micro-actuators, and micro-sensors applications. (Pb, La)(Zr, Ti) O3 (PLZT) ceramics doped with WO3 exhibit large photostriction under uniform illumination of near-ultraviolet light. Using a bimorph configuration, a photo-driven relay and a micro walking device have been demonstrated. However, for the fabrication of these devices, higher response speed must be achieved. The present paper reviews a new theoretical model for photovoltaic effect first, then enhanced performance through sample thickness and surface characteristics, finally its potential future applications.

P. Poosanaas

Papers

Photostrictive actuators - New perspective

Photostrictive actuators - New perspective - New p