Light Activated Shape Memory Polymers Research Articles

4D printing of light activated shape memory polymers with organic dyes

An ink based on azodyes is presented, allowing fabrication of light activatable 4D shape memory geometries with spatiotemporal response control.

Remote actuation of light activated shape memory polymers via D-shaped optical fibres

Shape memory polymers (SMPs) and their composites (SMPCs) can hold a programmed temporary shape and recover to their original shape once exposed to a particular external stimulus. The stimulus light has the advantage of being both an excitation energy source and a control signal carrier for remote actuation of SMP materials. Here we present the capability of D-shaped optical fibres to send near infrared (NIR) light into a light activated shape memory polymer composite (LASMPC) which generates the adequate photothermal effect necessary for the shape recovery process of relatively large samples. A D-shaped optical fibre enables dispersion of light through the polished area around the fibre than the dispersion of light through the tip of the fibre. Embedment of a D-shaped optical fibre in a LASMPC creates a single unit smart actuator, which can be remotely activated by light. Remotely controllable smart actuators can be located at any difficult to reach positions and controlled safely with light energy. It would be a breakthrough technology for biomedical, aerospace and many other engineering applications.

Computer modelling of origami-like structures made of light activated shape memory polymers

The so-called smart structures are frequently inspired by the art of origami, and they are in many cases considered to be manufactured of smart materials such as shape memory materials. We propose a mathematical model for such origami-like structures made of light activated shape memory polymers, and we develop a reference code for computer simulations of such structures. The proposed mathematical model is based on an existing macroscopic phenomenological model by (Sodhi & Rao 2010, Int. J. Eng. Sci. 48, 1576), which has been developed in order to describe full three-dimensional deformation of light activated shape memory polymers. This model is suitably modified for the reduced representation of origami-like structures which is based on the bar-and-hinge approach. The numerical solution of the corresponding governing equations is implemented using a transparent modification of a state-of-the-art code for numerical simulation of purely elastic origami-like structures developed by (Liu & Paulino 2017, Proc. R. Soc. A: Math. Phys. Eng. Sci. 473, 20170348).

Modeling deformation induced anisotropy of light-activated shape memory polymers

Light-activated shape memory polymers (LASMPs) are a new generation of active materials that undergo phase transformations upon light irradiation at different wavelength and intensities. This type of material shows much promise in its use in adaptive and shape reconfiguration structures for applications in biomedical and aerospace engineering. LASMPs exhibit nonlinear viscoelastic behavior due to the rearrangements in the macromolecular networks of the polymers when they are mechanically deformed. The deformed configuration can have a different symmetry group than the original undeformed configuration. In this study we assume that the body has multiple natural configurations in order to incorporate the microstructural changes in the viscoelastic polymers due to mechanical loading and light irradiation. We also account for the directional preference of the new network that is formed due to stretching the polymers. In this paper, the constitutive models developed for elastic and viscoelastic LASMPs in our previous work (Yuan and Zhi, 2017; Zhi and Yuan, 2017) are modified to include the changes in the symmetry group of the new network due to mechanically stretching the polymer. The models are implemented within ABAQUS finite element (FE) through the use of user-material subroutines (UMAT).

Vibration Control of Hemispherical Shells with Light-Activated Shape Memory Polymers

Light-activated shape memory polymer (LaSMP) is a novel actuator with dynamic Young’s modulus and strain when exposed to ultraviolet lights, which can be used in noncontact vibration control. This study focuses on the vibration control effect of LaSMP patches on hemispherical shells with free boundaries. An LaSMP strain variation model is presented with experimental verifications. Based on the strain model, the control forces of LaSMP patches on hemispherical shells are introduced. The FEM method is used to obtain natural frequencies of the free hemispherical shell by solid modeling in ANSYS and proved by comparing numerical results with analytical and experimental results. Using the modal expansion method, the LaSMP vibration control of hemispheres is investigated, and independent modal responses are presented and evaluated. The results indicate that LaSMP patch can control vibrations of hemispherical shells by reducing vibration amplitudes. And the control effect is better for low modal vibration, as the LaSMP-induced strain is relatively smaller. By establishing the relationship between LaSMP actuator forces and modal amplitude reduction, this study offers an analytical tool and procedure for future LaSMP application to vibration controls of flexible structures.

A piezoelectric energy harvester with light-activated shape memory polymers

In this research, a host thin-plate laminated with LASMP and piezoelectric patch was presented to investigate its natural frequencies and further developed into a hybrid energy harvester to study its energy harvesting responses. The dynamic stiffness and noncontact mechanism which are special to LASMP are employed to adjust the natural frequencies of the hybrid energy harvester so as to achieve broadband resonance energy harvesting responses. Furthermore, effect of piezoelectric patch thickness on power output is discussed in detail. Numerical discussions indicate that the power output of the self-tuned energy harvester increases 40% for each mode.

Frequency Control of Thin Plates with Light-Activated Shape-Memory Polymers

Light-activated shape-memory polymer (LaSMP) is a novel shape-memory material whose Young’s modulus can be manipulated with high-energy light irradiations. This study focuses on the frequency control of LaSMP-laminated simply supported thin plate by light-induced actuations. The governing equation of thin plate covered by LaSMP patch with arbitrary distribution is derived. The controlled frequency is solved numerically based on the Rayleigh–Ritz method and degenerates to an analytical solution of the fully laminated plate. The finite element method (FEM) is used to validate numerically solved analytical solutions, and FEM results are compared favorably with those solutions. Based on the numerical results of thin plate with partly covered LaSMP, the influences of LaSMP size and location on frequency control are investigated. The data suggest that the effect of frequency control is best when LaSMP is placed at the peak amplitude of the mode shapes with larger covering area. This study indicates that LaSMP can be a potential smart material for controlling frequency of thin plates by noncontact light actuations.

Responses of rings with light-activated shape memory polymers regulated by neural network and phase shift

Light-activated shape memory polymer is able to hold the temporary shape and to change the permanent shape upon exposures of ultraviolet lights with specific wavelengths. The study aims to provide a non-contact and temperature-independent technique to suppress the vibration of rings using light-activated shape memory polymer. Forced responses of flexible rings laminated with light-activated shape memory polymer patches are evaluated. Dynamic equations of light-activated shape memory polymer–laminated rings are established first. With the modal expansion method, the modal force of light-activated shape memory polymer actuators is derived and then the modal responses (with or without control) are evaluated. A generic kth order and its simplified light-activated shape memory polymer constitutive equations are established based on the chemical kinetics. Light-activated shape memory polymer shows the dynamic stiffness when exposed to ultraviolet lights, and this feature is reflected in its constitutive equations influenced by light intensity, material constant, thickness, and so on. With these derivations, the relationship of light intensity and modal force is established and it exhibits a hysteresis phenomenon. The procedure of identifying the hysteresis model using the neural network is described. Then, the phase shift and neural network control techniques are, respectively, applied to enhance the control effects. The neural network vibration control (with a maximal reduction in 98.1%) is very effective to improve light-activated shape memory polymer’s actuation capability.

Quasi-linear viscoelastic modeling of light-activated shape memory polymers

In this article, we model the mechanical behavior of light-activated shape memory polymers with a view toward determining the effect of the viscoelasticity of the polymers with regard to their shape memory response. This study is a companion to our earlier investigation of both isotropic and anisotropic elastic light-activated shape memory polymers. The constitutive model is based on a multi-network approach consisting of two microstructural networks, the original network and the second network that is formed due to light irradiation. A single integral model is adopted to incorporate the viscoelastic response in the original and second networks. We study the response of viscoelastic light-activated shape memory polymers subject to uniaxial and biaxial tension. Parametric studies are carried out to obtain a better understanding of the effect of quantities such as relaxation time and the ratio of the relaxation modulus to the instantaneous modulus. A combination of the classical trapezoidal integration method, recursive scheme, and root-finding methods is adopted to solve the governing equations. Finally, the model is used to describe the stress relaxation behavior of light-activated shape memory polymer reported in the literature.

A finite element method for light activated shape‐memory polymers

SummaryShape‐memory polymers (SMPs) belong to a class of smart materials that have shown promise for a wide range of applications. They are characterized by their ability to maintain a temporary deformed shape and return to an original parent permanent shape. In this paper, we consider the coupled photomechanical behavior of light activated shape‐memory polymers (LASMPs), focusing on the numerical aspects for finite element simulations at the engineering scale. The photomechanical continuum framework is summarized, and some specific constitutive equations for LASMPs are described. Numerical implementation of the multiphysics governing partial differential equations takes the form of a user defined element subroutine within the commercial software package ABAQUS. We verify our two‐dimensional and three‐dimensional finite element procedure for multiple analytically tractable cases. To show the robustness of the numerical implementation, simulations are performed under various geometries and complex photomechanical loading. Copyright © 2016 John Wiley & Sons, Ltd.

Modeling the response of light-activated shape memory polymers

The aim of this paper is to model the macroscopic response of light-activated shape memory polymers (LASMPs) subject to mechanical loadings and exposure to light at certain wavelengths and frequencies. When exposed to external stimuli of mechanical, thermal, photochemical and other origins, polymers undergo microstructural changes, e.g., scission, cross-linking, crystallization, etc. These microstructural changes affect the macroscopic performance of the polymers. In this study, in order to incorporate the effect of microstructural changes on the macroscopic response of light-activated shape memory polymers, we formulate constitutive models based on the notion that the natural configuration of the body under consideration evolves during its response. The theoretical framework appeals to a multinetwork approach consisting of two microstructural networks, which are the original network and the new network formed owing to a light activation. An important distinction between the approach considered here and the usual multinetwork approaches is that there is no conversion of one network to another; instead, what we have is the formation of a second network owing to the linking of photosensitive particles that get linked due to light irradiation. Furthermore, two different constitutive models are considered. The first model assumes the two networks are isotropic. The second model takes into account the directional preference of the second network that is formed. Both these models build on the work of Sodhi and Rao, which is based on the framework developed by Rajagopal and Srinivasa. Several classical boundary value problems involving homogeneous and inhomogeneous deformations are studied. We also investigate two nonlinear constitutive relations and different loading modes. The results highlight the differences in the responses when isotropic and anisotropic models are considered.

Frequency Control of Beams and Cylindrical Shells With Light-Activated Shape Memory Polymers

Light activated shape memory polymer (LaSMP) is a novel smart material. It realizes the shape memory function under the exposure of laser lights with two different wavelengths. During the exposure process, the stiffness of LaSMPs also changes. With this noncontact actuation feature, this study presents a new technique to manipulate frequencies of beams and cylindrical shells. Fundamental LaSMP mechanism and its stiffness manipulation are presented first. The LaSMP/elastic coupled dynamic equations of cylindrical shells coupled with LaSMPs are established first and then simplified to the governing equation of beams. In case studies, the natural frequency of a cantilever beam laminated with LaSMP patches is studied. Furthermore, the length of LaSMP patches is varied to broaden its frequency variation range. Results show that the maximum frequency change ratio reaches to about 24.5% on beams. A simply supported cylindrical shell laminated with LaSMPs on both the inner and outer surfaces is also analyzed and its frequency varies about 6% for the lowest (1,4) mode. Thus, adopting LaSMPs to manipulate the structural frequencies is a new noncontact actuation technique in vibration controls.

Inhomogeneous deformations of Light Activated Shape Memory Polymers

Shape memory polymers (SMP’s) belong to a large family of shape memory materials, which are defined by their capacity to store a deformed (temporary) shape and recover an original (parent) shape. SMP’s have the ability to change size and shape when activated through a suitable trigger. This trigger, which can be heating the polymer or exposing it to light of a specific frequency, is responsible for the new temporary shape. Return to the original shape can be achieved by a suitable reverse trigger.Light Activated Shape Memory Polymers (LASMP) are recently developed smart materials which are synthesized with special photosensitive molecules. These molecules when exposed to Ultraviolet (UV) light at specific wavelengths, form covalent crosslinks that are responsible for providing LASMP with their temporary shape. Light activation removes temperature constraints faced by thermoresponsive SMP for medical applications and also brings the added advantage of remote activation. Thus LASMP find use in a variety of applications ranging from MEMS devices to widespread usage for biomedical devices such as intravenous needles and stents. Furthermore, the aerospace industry has found use for these materials for applications ranging from easily deployable space structures to morphing wing aircraft.The authors have introduced a constitutive model to model the mechanics of these LASMP (Sodhi & Rao, 2010). The modeling is done using a framework based on the theory of multiple natural configurations. A few homogenous and inhomogeneous examples were solved in Sodhi and Rao (2010), but with tacit understanding that the intensity of light and hence the extent of reaction is homogenous throughout the polymer sample. In this paper we use the developed model to solve a series of inhomogeneous deformation boundary value problems of interest with inhomogeneous exposure to light.

UV light induced plasticization and light activated shape memory of spiropyran doped ethylene-vinyl acetate copolymers

Light activated shape memory polymers (LASMPs) are relatively new kinds of smart materials and have significant technological applications ranging from biomedical devices to aerospace technology. EVA films doped with spiropyran with contents ranging from 0.1% to 3% show efficient UV activated shape memory behaviors if the fixed shape deformation is limited within 80%. For EVA films containing 3% spiropyran, UV irradiation causes a decrease in EVA modulus of about 44%. FT-IR and solid (13)C NMR in association with UV-vis absorption analysis demonstrate that UV irradiation transforms spiropyran from the SP form to the MC form, meanwhile, it induces an increase in the molecular mobility in the amorphous phase of EVA. Thus, the spiropyran-doped EVA films act as LASMPs via a mechanism of light induced plasticization. Light activated spiropyran acts as a plasticizer to EVA.

Demonstration of a multiscale modeling technique: prediction of the stress–strain responseof light activated shape memory polymers

Presented is a multiscale modeling method applied to light activated shape memorypolymers (LASMPs). LASMPs are a new class of shape memory polymer (SMPs) beingdeveloped for adaptive structures applications where a thermal stimulus is undesirable.LASMP developmental emphasis is placed on optical manipulation of Young’s modulus. Amultiscale modeling approach is employed to anticipate the soft and hard statemoduli solely on the basis of a proposed molecular formulation. Employing such amodel shows promise for expediting down-selection of favorable formulations forsynthesis and testing, and subsequently accelerating LASMP development. Anempirical adaptation of the model is also presented which has applications insystem design once a formulation has been identified. The approach employsrotational isomeric state theory to build a molecular scale model of the polymerchain yielding a list of distances between the predicted crosslink locations, orr-values.The r-values are then fitted with Johnson probability density functions and used withBoltzmann statistical mechanics to predict stress as a function of the strain of thephantom polymer network. Empirical adaptation for design adds junction constrainttheory to the modeling process. Junction constraint theory includes the effects ofneighboring chain interactions. Empirical fitting results in numerically accurateYoung’s modulus predictions. The system is modular in nature and thus lends itselfwell to being adapted to other polymer systems and development applications.

Modeling the mechanics of light activated shape memory polymers

Shape memory polymers (SMP’s) are a relatively new kind of smart materials and have significant technological applications ranging from biomedical devices to aerospace technology. First generation SMP’s relied on changes in temperature to fix the temporary shape and have been studied quite extensively in the past. In the last few years a new generation of SMP’s have been synthesized in which the temporary shape is fixed by exposure to light at specific wavelengths (typically in the Ultraviolet, UV, range). Exposure to light at certain wavelengths causes photosensitive molecules, which are grafted on the polymer chains comprising the material, to form covalent bonds. These bonds act as crosslinks and are responsible for the temporary shape. On exposure to light at a different wavelength these bonds cleave and the material returns to its original shape. Our research focuses on modeling the mechanics associated with such light activated shape memory polymers (LASMP’s) undergoing complex deformations. The modeling is done using a framework based on the theory of multiple natural configurations taking into consideration the different aspects of modeling this material, which include developing a model for the original virgin network and for the other networks with different stress-free states, formed due to exposure to light. In addition to this, we also model the initiation and the formation of the light activated networks and the reverse transition resulting in the dissolution of these networks. Anisotropy in the mechanical response is also incorporated into the model. The model is then used to simulate results for specific boundary value problems, such as uni-axial extension and inflation of a cylinder.