An investigation on multilayer shape memory polymers under finite bending through nonlinear thermo-visco-hyperelasticity

This study presents a semi-analytical solution to describe the behavior of shape memory polymers(SMPs) based on the nonlinear thermo-visco-hyperelasticity which originates from the concepts of internal state variables and rational thermodynamics.This method is developed for the finite bending of multilayers in a dual-shape memory effect(SME) cycle.The layer number and layering order are investigated for two different SMPs and a hyperelastic material.In addition to the semi-analytical solution,the finite element simulation is performed to verify the predicted results,where the outcomes demonstrate the excellent accuracy of the proposed solution for predicting the behavior of the multilayer SMPs.Since this method has a much lower computational cost than the finite element method(FEM),it can be used as an effective tool to analyze the SMP behavior under different conditions,including different materials,different geometries,different layer numbers,and different layer arrangements.

Shape Memory Polymer Composite Booms with Applications in Reel-Type Solar Arrays

Solar arrays are the primary energy source for spacecraft.Although traditional rigid solar arrays improve power supply,the quality increases proportionally.Hence,it is difficult to satisfy the requirements of high-power and low-cost space applications.In this study,a shape-memory polymer composite(SMPC)boom was designed,fabricated,and characterized for flexible reel-type solar arrays.The SMPC boom was fabricated from a smart material,a shape-memory polymer composite,whose mechanical properties were tested.Additionally,a mathematical model of the bending stiffness of the SMPC boom was developed,and the bending and buckling behaviors of the boom were further analyzed using the ABAQUS software.An SMPC boom was fabricated to demonstrate its shape memory characteristics,and the driving force of the booms with varying geometric parameters was investigated.We also designed and manufactured a reel-type solar array based on an SMPC boom and verified its self-deployment capability.The results indicated that the SMPC boom can be used as a deployable unit to roll out flexible solar arrays.

Switchable dry adhesive based on shape memory polymer with hemispherical indenters for transfer printing

Transfer printing based on switchable adhesive is essential for developing unconventional systems,including flexible electronics,stretchable electronics,and micro light-emitting diode(LED)displays.Here we report a design of switchable dry adhesive based on shape memory polymer(SMP)with hemispherical indenters,which offers a continuously tunable and reversible adhesion through the combination of the preloading effect and the thermal actuation of SMP.Experimental and numerical studies reveal the fundamental aspects of design,fabrication,and operation of the switchable dry adhesive.Demonstrations of this adhesive concept in transfer printing of flat objects(e.g.,silicon wafers),three-dimensional(3D)objects(e.g.,stainless steel balls),and rough objects(e.g.,frosted glasses)in two-dimensional(2D)or 3D layouts illustrate its unusual manipulation capabilities in heterogeneous material integration applications.

Switchable shape memory polymer bio-inspired adhesive and its application for unmanned aerial vehicle landing

Controlled and switchable adhesion is commonly observed in biological systems.In recent years,many scholars have focused on making switchable bio-inspired adhesives.However,making a bio-inspired adhesive with high adhesion performance and excellent dynamic switching properties is still a challenge.A Shape Memory Polymer Bio-inspired Adhesive(SMPBA)was successfully developed,well realizing high adhesion(about 337 kPa),relatively low preload(about90 kPa),high adhesion-to-preload ratio(about 3.74),high switching ratio(about 6.74),and easy detachment,which are attributed to the controlled modulus and contact area by regulating temperature and the Shape Memory Effect(SME).Furthermore,SMPBA exhibits adhesion strength of80–337 kPa on various surfaces(silicon,iron,and aluminum)with different roughness(Ra=0.021–10.280)because of the conformal contact,reflecting outstanding surface adaptability.The finite element analysis verifies the bending ability under different temperatures,while the adhesion model analyzes the influence of preload on contact area and adhesion.Furthermore,an Unmanned Aerial Vehicle(UAV)landing device with SMPBA was designed and manufactured to achieve UAV landing on and detaching from various surfaces.This study provides a novel switchable bio-inspired adhesive and UAV landing method.

Theoretical Analysis of the Buckling Behaviors of Inhomogeneous Shape Memory Polymer Composite Laminates Considering Prestrains

The mismatch in thermal expansion coefficients between the fiber-rich and resin-rich regions of a shape memory polymer composite(SMPC)laminate,along with the residual strain during SMPC fabrication,results in buckling deformation of the inhomogeneous laminate.This paper presents a macroscopic model for buckling of an inhomogeneous SMPC laminate under initial biaxial prestrains.Both linear and nonlinear buckling analyses are carried out using the energy method.The influences of prestrain biaxiality,temperature,and ply angle on the buckling wavelength,critical buckling prestrain,and buckling amplitude are calculated.The results demonstrate that the critical buckling wavelength of the SMPC laminate is independent of the prestrain,while the amplitude is almost independent of temperature.In addition,the optimal fiber stacking configuration with the maximum critical buckling prestrains of inhomogeneous SMPC laminates is determined by a genetic algorithm.

Adjustable volume and loading release of shape memory polymer microcapsules

Research on microcapsules has been conducted in recent years given trends in miniaturization and novel functionalization.In this work,we designed and prepared a series of unique shape memory polyurethane(SMPU)microcapsules with stimuli-responsive func-tions.The microcapsule has a core-shell structure in which the surface morphology can be adjusted,and it has a certain loadbearing capacity.In addition,the SMPU microcapsule has a stimuliresponsive function for shape memory and solvent response.The temperature of its shape recovery is approximately body tempera-ture,and it can swell to rupture under the stimulation of organic solvents.Thus,the SMPU microcapsule has potential applications in biomedical fields,such as drug release.

Smart Multiple Wetting Control on ZnO Coated Shape Memory Polymer Arrays

Recently,surfaces with intelligent wetting controllability have aroused increased attention.Endowing the surface with stimuli-responsive surface chemistry and tunable surface microstructure can achieve a surface with smart wetting performances.However,almost all existing surfaces only focused on single surface chemistry or micromorphology,thus to achieve smart multiple wetting regulation is still difficult.Herein,we report a ZnO coated shape memory polymer(SMP)surface,and the surface chemistry and micromorphology can be synergistically regulated.ZnO can provide adjustable surface chemistry under UV irradiation,and SMP can offer tunable micromorphology due to its shape memory effect(SME).Based on the combined effect between the above two features,surface wetting performance can be smartly regulated among multiple states.Moreover,due to the excellent controllability of the surface,the application in directional droplet transportation was also demonstrated.This paper offers a new surface with tunability in both surface chemistry and micromorphology,and given the excellent wetting controllability,the surface is believed to be applied in a lot of fields,such as droplet manipulation,fluidic devices and selective catalysis.

A thermoviscoelastic finite deformation constitutive model based on dual relaxation mechanisms for amorphous shape memory polymers

This paper proposes a new thermoviscoelastic finite deformation model incorporating dual relaxation mechanisms to predict the complete thermo-mechanical response of amorphous shape memory polymers.The model is underpinned by the detailed microscopic molecular mechanism and effectively reflects the current understanding of the glass transition phenomenon.Novel evolution rules are obtained from the model to characterize the viscous flow,and a new theory named an internal stress model is introduced and combined with the dual relaxation mechanisms to capture the stress recovery.The rationality of the constitutive model is verified as the theoretical results agree well with the experimental data.Moreover,the constitutive model is further simplified to facilitate engineering applications,and it can roughly capture the characteristics of shape memory polymers.

World’s first spaceflight on-orbit demonstration of a flexible solar array system based on shape memory polymer composites

With a 10%reversible compressive strain in more than 10 deformation cycles,the shape memory polymer composites(SMPCs)could be used for deployable structure and releasing mechanism.In this paper,without traditional electro-explosive devices or motors/controllers,the deployable SMPC flexible solar array system(SMPC-FSAS)is studied,developed,ground-based tested,and finally on-orbit validated.The epoxy-based SMPC is used for the rolling-out variable-stiffness beams as a structural frame as well as an actuator for the flexible blanket solar array.The releasing mechanism is primarily made of the cyanate-based SMPC,which has a high locking stiffness to withstand 50 g gravitational acceleration and a large unlocking displacement of 10 mm.The systematical mechanical and thermal qualification tests of the SMPC-FSAS flight hardware were performed,including sinusoidal sweeping vibration,shocking,acceleration,thermal equilibrium,thermal vacuum cycling,and thermal cycling test.The locking function of the SMPC releasing mechanisms was in normal when launching aboard the SJ20 Geostationary Satellite on 27 Dec.,2019.The SMPC-FSAS flight hardware successfully unlocked and deployed on 5 Jan.,2020 on geostationary orbit.The triggering signal of limit switches returned to ground at the 139 s upon heating,which indicated the successful unlocking function of SMPC releasing mechanisms.A pair of epoxy-based SMPC rolled variable-stiffness tubes,which clapped the flexible blanket solar array,slowly deployed and finally approached an approximate 100%shape recovery ratio within 60 s upon heating.The study and on-orbit successful validation of the SMPC-FSAS flight hardware could accelerate the related study and associated productions to be used for the next-generation releasing mechanisms as well as space deployable structures,such as new releasing mechanisms with low-shocking,testability and reusability,and ultra-large space deployable solar arrays.

A mini review： Shape memory polymers for biomedica applications

Shape memory polymers （SMPs） are smart materials that can change their shape in a pre-defined manner under a stimulus. The shape memory functionality has gained considerable interest for biomedical applications, which require materials that are biocompatible and sometimes biodegradable. There is a need for SMPs that are prepared from renewable sources to be used as substitutes for conventional SMPs. In this paper, advances in SMPs based on synthetic monomers and bio-compounds are discussed. Materials designed for biomedical applica- tions are highlighted.

Recent Progress in Shape Memory Polymers for Biomedical Applications

Shape memory polymers （SMPs） as one type of the most important smart materials have attracted increasing attention due to their promising application in the field of biomedicine, textiles, aerospace et al. Following a brief intoduction of the conception and classification of SMPs, this review is focused on the progress of shape memory polymers for biomedical applications. The progress includes the early researches based on thermo-induced SMPs, the improvement of the stimulus, the development of shape recovery ways and the expansion of the applications in biomedical field. In addition, future perspectives of SMPs in the field of biomedicine are also discussed.

Shape Memory Polymer Fibers:Materials,Structures,and Applications

Shape memory polymer(SMP)is a kind of material that can sense and respond to the changes of the external environment,and its behavior is similar to the intelligent refection of life.Electrospinning,as a versatile and feasible technique,has been used to prepare shape memory polymer fbers(SMPFs)and expand their structures.SMPFs show some advanced features and functions in many felds.In this review,we give a comprehensive overview of SMPFs,including materials,fabrication methods,structures,multifunction,and applications.Firstly,the mechanism and characteristics of SMP are introduced.We then discuss the electrospinning method to form various microstructures,like non-woven fbers,core/shell fbers,hollow fbers and oriented fbers.Afterward,the multiple functions of SMPFs are discussed,such as multi-shape memory efect,reversible shape memory efect and remote actuation of composites.We also focus on some typical applications of SMPFs,including biomedical scafolds,drug carriers,self-healing,smart textiles and sensors,as well as energy harvesting devices.At the end,the challenges and future development directions of SMPFs are proposed.

A Shape-Memory Deployable Subsystem with a Large Folding Ratio in China’s Tianwen-1 Mars Exploration Mission

Once China’s Tianwen-1 Mars probe arrived in a Mars orbit after a seven-month flight in the deep cold space environment,it would be urgently necessary to monitor its state and the surrounding environment.To address this issue,we developed a flexible deployable subsystem based on shape memory polymer composites(SMPC-FDS)with a large folding ratio,which incorporates a camera and two temperature telemetry points for monitoring the local state of the Mars orbiter and the deep space environment.Here,we report on the development,testing,and successful application of the SMPC-FDS.Before reaching its Mars remote-sensing orbit,the SMPC-FDS is designed to be in a folded state with high stiffness;after reaching orbit,it is in a deployed state with a large envelope.The transition from the folded state to the deployed state is achieved by electrically heating the shape memory polymer composites(SMPCs);during this process,the camera on the SMPC-FDS can capture the local state of the orbiter from multiple angles.Moreover,temperature telemetry points on the SMPC-FDS provide feedback on the environment temperature and the temperature change of the SMPCs during the energization process.By simulating a Mars on-orbit space environment,the engineering reliability of the SMPC-FDS was comprehensively verified in terms of the material properties,structural dynamic performance,and thermal vacuum deployment feasibility.Since the launch of Tianwen-1 on 23 July 2020,scientific data on the temperature environment around Tianwen-1 has been successfully acquired from the telemetry points on the SMPCFDS,and the local state of the orbiter has been photographed in orbit,showing the national flag of China fixed on the orbiter.

A macro-mechanical constitutive model for shape memory polymer

It is of theoretical and engineering interest to establish a macro-mechanical constitutive model of the shape memory polymer (SMP), which includes the mechanical constitutive equation and the material parameter function, from the viewpoint of practical application. In this paper, a new three-dimensional macro-mechanical constitutive equation, which describes the mechanical behaviors associated with the shape memory effect of SMP, is developed based on solid mechanics and the viscoelasticity theorem. According to the results of the DMA test, a new material parameter function is established to express the relationship of the material parameters and temperature during the glass transition of SMP. The new macro-mechanical constitutive equation and material parameter function are used to numerically simulate the process producing the shape memory effect of SMP, which includes deforming at high temperature, stress freezing, unloading at low temperature and shape recovery. They are also used to investigate and analyze the influences of loading rate and temperature change rate on the thermo-mechanical behaviors of SMP. The numerical results and the comparisons with Zhou’s material parameter function and Tobushi’s mechanical constitutive equation illustrate that the proposed three-dimensional macro-mechanical constitutive model can effectively predict the thermo-mechanical behaviors of SMP under the state of complex stress.

A hygro-thermo-mechanical constitutive model for shape memory polymers filled with nano-carbon powder

The nano-carbon powders are often used as fillers to endow the shape memory polymers(SMPs)with electroconductivity.It has been found that the shape memory effects(SMEs)of SMPs filled with nano-carbon powder can be triggered both by temperature and by water.To reveal the driving mechanism of SMEs,a constitutive model for describing the thermally activated and moisture activated SMEs of these shape memory polymer composite(SMPCs)is developed here.Because both of the SMEs share the same driving mechanism,the variable moisture is incorporated into the framework of a thermo-mechanical modeling approach to disclose the effect of moisture on the thermoviscoelastic properties.The SMPCs are regarded as isotropic materials and the effect of carbon powder on the mechanical properties of the matrix is also considered in the paper.Because the complete recovery may not be reached even they are exposed to the stimulus environment long enough,the blocking mechanism is also considered here.This is the mainly new contribution compared to the early work.Using the method of parameter determination presented here,the effectiveness of the proposed hygro-thermo-mechanical constitutive model is confirmed by comparing the model results with the test data of uniaxial deformation from the literature.

Constitutive model for epoxy shape memory polymer with regulable phase transition temperature

The epoxy shape memory polymer(SMP)with adjustable phase transition temperature is a kind of high-performance shape mem-ory polymer,which can change its phase transition temperature and improve its mechanical properties through the process of photo curing.An epoxy SMP constitutive model combining phase transition and viscoelasticity is established by discretizing the epoxy SMP into several glass phase units and rubbery phase units in this paper.The model includes the viscoelastic constitutive equa-tions of glass phase units and rubber phase units,the parameter expression during shape memory process,and material parameter equation during photocuring process.And the stress relaxation behavior of epoxy SMP at different temperatures and the change of material parameters during the photo-curing process are simu-lated numerically,and the simulation results perform consistency with the experimental data.The model can not only relate shape memory effect and phase transformation in physics but also better characterize the viscoelastic properties of SMP and predict the shape memory response of SMP.

Preliminary design and analysis of a cubic deployable support structure based on shape memory polymer composite

The deployable structures based on shape memory polymer com-posites(SMPCs)have been developed for its unique properties,such as high reliability,low-cost,lightweight,and self-deployment without complex mechanical devices compared with traditional deployable structures.In order to increase the inflatable structure system’s robustness and light the weight of it,a cubic deployable support structure based on SMPC is designed and analyzed pre-liminarily.The cubic deployable support structure based on SMPC consists of four dependent spatial cages,each spatial cage is composed of 12 three-longeron SMPC truss booms and end con-nections.The shape recovery of arc-shaped deployable laminates drive the three-longeron SMPC truss booms to unfold,thus realize the expansion of the deployable support structure.The concept and operation of the cubic deployable support structure are described in detail.A series of experiments are performed on the three-longeron deployable laminates unit and the simplified cubic deployable support structure to investigate the shape recovery behavior in the deployment process.Results indicate that the cubic deployable support structure has a high deployment-tgo-stowage volume ratio and can achieve self-deployment,package,and deploy without complex mechanical devices.

Photo-responsive shape memory polymer composites enabled by doping with biomass-derived carbon nanomaterials

As photothermal conversion agents,carbon nanomaterials are widely applied in polymers for light-triggered shape memory behaviors on account of their excellent light absorption.However,they are usually derived from non-renewable fossil resources,which go against the demand for sustainable development.Biomass-derived carbon nanomaterials are expected as alternatives if they are designed with good dispersibility as well as splendid photothermal properties.Up to date,very few researches focused on this area.Herein,we report a novel light-triggered shape memory composite by incorporating renewable biomass-derived carbon nanomaterials into acrylate polymers without deep purification and processing.These functionalized carbon nanomaterials not only have stable dispersion in polymers as fillers,but also can endow the polymers with excellent and stable thermal and photothermal responsive properties in biological friendly environment.With the introduction of biomass-derived carbon nanomaterials,the mechanical properties of the composites are also further enhanced with the formation of hydrogen bonding between the carbon nanomaterials and the polymers.Notably,the doping of 1%carbon nanomaterials endows the polymer with sufficient hydrogen bonds that not only exhibit excellent thermal and photothermal responsive properties,but also with enough space for the motion of chains.These properties make such composite a promising and safe candidate for shape memory applications,which provide a new avenue in smart fabrics or intelligent soft robotics.

Sustainable shape memory polymers based on epoxidized natural rubber cured by zinc ferulate via oxa-Michael reaction

Although various shape memory polymers(SMPs)or diverse applications have been widely reported,the SMPs based on rubbers have been rarely realized due to the low triggering temperature of rubbers.In another aspect,the SMPs based on sustainable substances are highly desired for the growing shortage in fossil resources.In the present study,we accordingly developed the sustainable SMPs with tunable triggering temperature,based on natural rubber(NR)and ferulic acid(FA)as the raw materials.Specifically,the SMPs are based on a crosslinked network of epoxidized natural rubber(ENR)crosslinked by in situ formed zinc ferulate(ZDF)via oxa-Michael reaction.The excellent shape memory effect(SME)is found in these SMPs,as evidenced by the high fixity/recovery ratio and the tunable triggering temperature.With the incorpora-tion of natural halloysite nanotubes(HNTs),the stress and recovery rate of the SMPs are found to be tunable,which widens the application of this kind of SMPs.The combination of adoption of sustainable raw materials,and the excellent and tunable SME makes these SMPs potentially useful in many applications,such as various actuators and heat-shrinkable package materials.

Confined thin film wrinkling on shape memory polymer with hybrid surface morphologies

With appropriate stimuli,such as heat,humidity,or magnetic field,shape memory polymers(SMPs)can recover to their original shapes from temporary,programmed states.Using thermal responsive SMPs as substrates,we demonstrate a simple method to realize hybrid surface morphologies through confined thin film wrinkling in localized areas.The bilayer system was fabricated by depositing a layer of aluminum thin?lm on top of a SMP substrate programmed with a tensile strain.After the system was heated by a heating wire,hybrid wrinkling patterns were formed in a confined circular area around the heat source,with an inner spoke pattern and an outer ring pattern.Wrinkling patterns showed good symmetry,and the size of the wrinkling area can be tuned by controlling the heat input.This study o?ers a simple but effective approach to fabricate hybrid morphological features in micro-scale.With appropriate stimuli,such as heat,humidity,or magnetic field,shape memory polymers(SMPs)can recover to their original shapes from temporary,programmed states.Using thermal responsive SMPs as substrates,we demonstrate a simple method to realize hybrid surface morphologies through confined thin film wrinkling in localized areas.The bilayer system was fabricated by depositing a layer of aluminum thin?lm on top of a SMP substrate programmed with a tensile strain.After the system was heated by a heating wire,hybrid wrinkling patterns were formed in a confined circular area around the heat source,with an inner spoke pattern and an outer ring pattern.Wrinkling patterns showed good symmetry,and the size of the wrinkling area can be tuned by controlling the heat input.This study offers a simple but effective approach to fabricate hybrid morphological features in micro-scale.