Film Shape Memory Research Articles

Thermo-Activated Shape Memory Films Based on Chitosan Reinforced With Silk Fibroin, Obtained by an Environmentally Friendly Process Using a Deep Eutectic Solvent

Thermo-Activated Shape Memory Films Based on Chitosan Reinforced With Silk Fibroin, Obtained by an Environmentally Friendly Process Using a Deep Eutectic Solvent

Multiferroic Microstructure Created from Invariant Line Constraint

AbstractFerroic materials enable a multitude of emerging applications, and optimum functional properties are achieved when ferromagnetic and ferroelectric properties are coupled to a first‐order ferroelastic transition. In bulk materials, this first‐order transition involves an invariant habit plane, connecting coexisting phases: austenite and martensite. Theory predicts that this plane should converge to a line in thin films, but experimental evidence is missing. Here, the martensitic and magnetic microstructure of a freestanding epitaxial magnetic shape memory film is analyzed. It is shown that the martensite microstructure is determined by an invariant line constraint using lattice parameters of both phases as the only input. This line constraint explains most of the observable features, which differ fundamentally from bulk and constrained films. Furthermore, this finite‐size effect creates a remarkable checkerboard magnetic domain pattern through multiferroic coupling. The findings highlight the decisive role of finite‐size effects in multiferroics.

Electric-driven shape memory deformation control and verification of composite films based on PVA/WPU/SCFs

Based on the research of Polyvinyl alcohol (PVA)/Waterborne Polyurethane (WPU)/Short Carbon Fibers (SCFs) novel electrochemically shape memory composites, this study delved into an exploration of factors influencing the shape memory deformation of shape memory film samples when subjected to voltage stimulation. These main affecting factors encompassed sample thickness, activation voltage, and wire layout. Subsequently, based on the above conclusions, the viscoelastic constitutive model of PVA/WPU/SCFs composite was established based on Maxwell model and the deformation deflection of the composite film was predicted by shape memory recovery, and the electrothermal coupling simulation analysis and shape memory recovery and deformation simulation verification were carried out. Finally, based on the shape memory recovery performance of the composite film, a new reciprocating moving deformation structure was conceptualized, characterized by distinct cycles of motion, each analyzed individually.

Deposition and nanoindentation study of a novel TiNi/Ag bi-layer shape memory film

Compositions, surface morphologies and mechanical properties of a novel designed TiNi/Ag bi-layer film grown by DC magnetron sputtering at various processes have been investigated. Ar pressure and sputtering power had significant effects on quality and composition of TiNi/Ag bi-layer films. The TiNi/Ag bi-layer film processed by sputtering under high Ar pressure (0.36 Pa) was porous, while better density films can only be obtained at low pressure (0.12 Pa). The composition of TiNi/Ag bi-layer films can be adjusted by sputtering power. The load-displacement curves show the multiple “pop-ins”along nanoindentation loading, as indentation depth does not exceed the pure Ag film thickness (∼340 nm). At the maximum loading of 140 mN, martensitic transformation induced by nanoindentation in TiNi/Ag bi-layer films was not found, and depth recovery ratio was 39%. Moreover, based on the load displacement curve analysis, the hardness and elastic modulus values of TiNi/Ag bi-layer films were 4 ± 0.2 Gpa and 79 ± 2 Gpa, respectively. Comparing with martensitic phase of single-layer TiNi thin films at room temperature, the coexistence of parent phase and martensitic phase of TiNi/Ag bi-layer films were mainly due to strong confinement effect of Ag layer deposition on TiNi thin film. The residual stress calculated by using conventional sin2ψ method was around −0.458 GPa. The present study provided an important theoretical basis for the preparation of TiNi/Ag bi-layer film with higher quality and performance.

Environmental-friendly, flexible silk fibroin-based film as dual-responsive shape memory material

Bio-based shape memory materials have attracted wide attention due to their biocompatibility, degradability and safety. However, designing and manufacturing wearable bio-based shape memory films with excellent flexibility and toughness is still a challenge. In this work, silk fibroin substrate with a β-sheet structure was combined with a tri-block shape memory copolymer to prepare a transparent composited shape memory film. The silk fibroin-based film showed a dual-responsive shape memory function, which can respond to both temperature and water stimuli. This film has a sensitive water-responsive shape memory, which starts deforming after exposure to water for 3 s and fully recovers in 30 s. In addition, the composite film shows highly stretchable (>300 %) and could maintain its high tensile properties after 5 cycles of regeneration. The films also exhibited rapid degradation ability. This study provides new insights for the design of dual-responsive shape memory materials by combining biocompatible matrix and multi-block SMP to simultaneously enhance the mechanical properties, which can be used for intelligent packaging, medical supplies, soft actuators and wearable devices.

Preparation and evaluation of luteolin-loaded PLA-based shape memory gastroretentive drug delivery systems

Luteolin, a natural flavonoid, is gaining growing attention for its potential in the treatment of gastric cancer. However, its clinical application is limited by factors such as poor aqueous solubility. This study aimed to develop a novel gastroretentive drug delivery system (GRDDS) to both enhance the oral bioavailability of luteolin and prolong its release and in vivo circulation time. Out of 10 luteolin-loaded PLA-based shape memory films prepared in this study, the LPC-PLA/PEG(7/3) formulation incorporated with PEG, HPMC, and NaHCO3 exhibited optimal properties in terms of drug release and inhibitory activity against SGC-7901 cells. Moreover, small-animal imaging revealed that LPC-PLA/PEG(7/3) exhibited a prolonged gastric retention time of approximately 8 h. Furthermore, the pharmacokinetic studies indicated a 354 % increase in the oral bioavailability of LPC-PLA/PEG(7/3) in rats compared to luteolin. In sum, a novel GRDDS was developed to enhance the relative bioavailability of luteolin, offering a potential strategy for practical oral administration.

Two-Pronged Approach: Synergistic Tuning of the Surface and Carbon Core to Achieve Yellow Emission in Lignin-Based Carbon Dots.

In this study, yellow emissive lignin-based carbon dots (Y-CDs) were successfully prepared through a synergistic approach to adjust its surface and carbon core states. The lignin was initially effectively oxidized and carboxymethylated to impart abundant -COOH onto the precursor, which eventually adjusts the surface state of the CDs. Subsequently, α-naphthol was employed during the solvothermal treatment of lignin with the aim of elevating the sp2 domain content in the CDs and, thus, adjusting its carbon core state. The obtained Y-CDs possessed abundant carboxyl groups and nanoscale spherical shape with an average diameter of 5.21 nm. Meanwhile, the energy gap of Y-CDs was 2.46 eV and the optimal emission wavelength was 561 nm under the excitation wavelength of 410 nm. Synergistic adjusting carbon core and surface of the Y-CDs would alter the surface charge distribution and promote the delocalization of π electrons, and thus lead to a red shifting with the emission wavelength of 154 nm. Furthermore, a shape memory film with excellent recovery performance and fluorescent properties was designed by embedding the Y-CDs into polyvinyl alcohol (PVA) polymer. The incorporation of Y-CDs could impart the film with considerable high-value applications in the fields of intelligent sensing, biomedicine, and tissue engineering.

Design and multilevel structuring of shape memory polymers for pleochroism control

AbstractBrands and products counterfeiting, and falsification are global problems for the development and distribution of high‐tech industrial and food products, which affect world economies. One way to solve these problems is to develop original packaging with protection elements and labeling against counterfeiting, which excludes the possibility of replication and forgery by printing or other methods. The most reliable way to protect packaging from counterfeiting is the use of new materials with unique optical properties and constantly updated technologies for packaging manufacturing and labeling. This paper proposes a new multi‐level technology for the design, manufacture and hidden labeling of polymer packaging made from several layers of transparent polymer films. The design and marking of the multilayer films are combined with perforation, thermal treatment and heat sealing of the package. The reliability of the proposed markings is based on the characterization of optical pleochroism effects in transparent multilayer polymer materials with shape memory. The thermomechanical and optical properties of films made of bulk thermoplastics (polypropylene, polystyrene, polyvinyl chloride and polyethylene) were characterized in polarized light. The modification and combination of these films provide a high color difference and sufficient contrast of hidden markings, allowing to identify genuine products by bar codes formed from shape memory films in sealing seams of flexible polymer packaging.

Multifunctional electro-thermal superhydrophobic shape memory film with in situ reversible wettability and anti-icing/deicing properties

Shape memory polymer (SMP) surfaces can achieve wettability transition by controlling microstructure have attracted great attention. However, attempts at achieving in situ reversible switching capability remain largely challenging. This paper aims to elaborate on the preparation of a shape memory superhydrophobic surface with switchable wettability and electrothermal performance. The surface microstructure array is regulated by the shape memory effect based on the electrothermal response, and the reversible switching of the wetting state is realized under the action of voltage and external force. Different microstructural morphologies exhibit different solid-liquid contact states, as well as large/small contact angles and low/high adhesion. In addition, the rapid thermal response, excellent thermal conductivity, and satisfactory durability provide the possibility for anti-icing/deicing. The structure can prevent droplet aggregation, greatly delay the nucleation of droplet crystallization, and remove ice by Joule heat. In short, this work successfully realized the in-situ control of surface wettability which also provided a significant application potential in droplet manipulation, droplet writing, anti-icing/deicing, and other fields.

Bio-based castor oil and lignin sulphonate: aqueous dispersions and shape-memory films

Aqueous polyurethane dispersions based on castor oil and lignin sulphonate (LS) were successfully synthesized in homogenous solution with nanoscale PU-lignin particle sizes as small as 35 nm. The particles size was found to be LS independent, while the dispersion viscosity increases dramatically with increasing the LS content. The increase in viscosity with increasing LS content was explained based on the chemical structure of LS. The LS is a water-soluble material and chemically reacted with diisocyanate to become a part of the dispersion particle (i.e., the nanoparticles is in fact a mixture or copolymer of castor oil-based polyurethane and lignin dispersed in water). The affinity of the PU-LS nanoparticle towards water could be increased with increasing the content of LS. Therefore, the PU-LS nanoparticle can adsorb thick water layer with increasing the LS content. According to this suggestion, the free water in the dispersion would significantly decrease and consequently the dispersion viscosity increases considerably. The cross-link density was also increase with increasing the LS content of the thin films obtained from dispersion cast. The PU-LS thin films obtained from dispersion cast showed an excellent shape-memory effect and the shape recovery was found to be strongly LS dependent. Furthermore, the supper critical CO2 solution was used successfully to create three-dimensional porous structure of PU-LS with cell size depends on LS content. The temporary folded shape of PU-LS with 5 wt.% LS changed to its permanent shape (plane stripe) within just 17 s once the sample was immersed in a water bath at the programing temperature.

Programming of micro/nano‐scale information on low switching temperature shape memory film

AbstractShape memory polymer films have been of great interests in storing functional information because of their optical and mechanical variability. High molecular weight polyvinyl acetate (PVAc) is an ideal shape memory material to program micro‐ and nano‐scale patterns on the surface of highly transparent films. By blending PVAc with polyethylene glycol (PEG) plasticizer, lower switching temperatures could be achieved. We develop a shape memory PVAc/PEG blend film system featuring a unique design by taking advantage of multiple switching temperatures. The effect of the PEG composition was studied relative to different surface patterns, switching temperatures and efficiency of information retrieval by utilizing differential scanning calorimetry and UV/Vis analysis. The results indicate that higher contents of PEG enhanced the recovery efficiency of both the micro‐scale and nano‐scale patterns and the corresponding optical properties. Furthermore, a dual switching shape memory film was developed enabling multiple switching temperatures that can lead to versatile applications.

Engineered Latex Particles Using Core–Shell Emulsion Polymerization: From a Strawberry-like Surface Pattern to a Shape-Memory Film

Engineered Latex Particles Using Core–Shell Emulsion Polymerization: From a Strawberry-like Surface Pattern to a Shape-Memory Film

Multifunctional Shape Memory Films for a Flexible Electrical Sensor

AbstractShape memory polymers exhibit great potential for applications in aeronautics, astronautics, biomedicine, intelligent robots, and electronics. Based on traditional fabrication methods, as‐prepared shape memory micro‐/nanodevices are brittle with poor deformability. For instance, these devices shatter or crack when they are bent, which greatly limit their practical applications. In particular, there has been little use of shape memory films for high performance sensing devices in electrical circuits. Here, a novel polyvinyl alcohol (PVA) film is fabricated from a mixture of graphene nanosheets (GNs), sisal cellulose microcrystals (CNC), polyamine‐functionalized perylene bisimide derivative (APBI), and PVA through a simple electrospinning technique. These novel PVA films exhibit excellent thermal, mechanical, and shape memory properties. Moreover, after spin‐coating with Ag nanowires, the PVA films show excellent conductivity and flexibility in shape memory recovery cycles, and are used as a flexible sensing device in the circuit.

Preparation and characterisation of PCL shape-memory films via photo-crosslinking

ABSTRACT A facile and ecologically friendly method to prepare shape-memory Poly(ϵ-caprolactone) (PCL) films via Ultraviolet (UV) irradiation is described in this work. Benzophenone (BP), as a photoinitiator, was melt-blended with PCL particles directly and then melt-pressed into films. Afterward, a series of shape-memory films were obtained by UV (at around λ=365 nm) irradiation crosslinking. A sequence study and comparison on the properties changes caused by the effect of irradiation temperature was carried out and it turns out that the gel fraction, shape-memory properties and tensile properties of the PCL films, which were photo-crosslinked at 55°C, were significantly higher than that at 25°C. The effect of photoinitiator contents and irradiation time on gel fraction, shape memory properties and tensile properties was also studied. It is considered that UV irradiation is an efficient method to prepare PCL shape-memory films.

Biotemplated Fabrication of a Multifunctional Superwettable Shape Memory Film for Wearable Sensing Electronics and Smart Liquid Droplet Manipulation.

Wearable superwettable surfaces with dynamic tunable wettability and self-healability are promising for advanced wearable electronics, whereas have been rarely reported. Herein, a flexible superhydrophobic shape memory film (SSMF) with switchable surface wettability and high strain sensitivity has been conveniently fabricated. The surface topography of the SSMF can be finely adjusted by a reversible stretching (bending)/recovery way, which makes it feasible to control the surface-switchable adhesive superhydrophobicity by simple body movements, demonstrating great advantages in selective droplet manipulation and smart control of droplet movement. Moreover, benefitting from the hierarchical micro/nanostructures and outstanding sensing performance, the flexible SSMFs with good adaptivity and durability can serve as smart wearable sensors attached to human skin to achieve full-range and real-time detection of human motions and intelligent control of Internet of Things. More interestingly, the unique dynamic dewetting property enables the sensors to work in a humid environment or rainy days. Overall, this work successfully integrates dynamic tunable superwettability into design of intelligent wearable electronics with multifunctions. The obtained SSMF-based wearable surface with dynamic dewetting properties reveals great potential in versatile application fields such as liquid-repellent electronics, wearable droplet manipulators, and all-weather intelligent actuators.

Rapid water-responsive shape memory films for smart resistive bending sensors

Development of multi-functional water-sensitive shape memory material is crucial for applications in smart textiles, artificial intelligence, and biomedical areas. However, it remains a great challenge to achieve good biocompatibility, rapid water response, and robust mechanical strength in one single material. In this respect, we report a green approach to produce a series of multi-functional water-sensitive memory films (named MCP films) from sisal cellulose microcrystals (MSF-g-COOH), peach gum polysaccharide (PGP), citric acid (CA), and graphene nanosheets (GN). After crosslinking with CA, MCP films exhibit excellent water-induced shape memory and rapid pH stimulus response. More importantly, MCP films can effectively amplify different external motion stimuli by converting them into independent electrical signals to achieve accurate and continuous perception of bending. A high-performance resistive bending sensor was further fabricated from the MCP films to mimic natural human skin. The resistive bending sensor exhibited excellent water-responsive shape memory, self-adhesion, and bending sensitivity, which can be used in electronic skin, human-machine interactions, intelligent wearable devices, personalized health monitoring and other applications. Our work successfully demonstrates the application of the water-sensitive shape memory films in electronic skin and health-monitoring components, and fills the gap between material design and high-performance devices.

Superhydrophobic shape memory film with switchable adhesion to both water and solid

• The membrane can regulate the adhesion to both solid and water droplets. • Both microstructure and surface energy were crucial for special adhesion. • The membrane can be used to in-situ capture/release both solid and liquid. Recently, inspired by gecko’s smart adhesion, many intelligent adhesive surfaces have been reported. However, all of these are focused on single adhesion to liquid or solid, to obtain a surface with switchable adhesion to both water and solid is still a challenge. Herein, by coating a layer of polyurethane (PU) with micropillar structures onto a shape memory polymer (SMP) substrate to imitate the skin and muscle of the gecko’s foot, respectively, we report a new shape memory film that can repeatedly display curved/unfolded shapes with the help of the excellent shape memory property. Research results indicate that besides the variation of the contact area, a proper surface energy is also crucial for the special adhesion. Furthermore, based on the smart adhesive performance, in-situ capture/release of both solid and liquid were demonstrated by using the film. This research proposes a film with tunable adhesion to both solid and liquid, which provides a fresh idea for designing novel adhesive film, and meanwhile broadens the application of the adhesive materials.

Design of recyclable, fast-responsive and high temperature shape memory semi-aromatic polyamide

Development of high temperature shape memory polymers with fast response time and recyclable performance is highly desired. In this study, a new semi-aromatic tri-amine (TRIA) containing thioether unit is prepared through the reaction of trifluoro-monomer and p-mercaptoaniline (p-MA). It is conducted to polymerize with 4,4′-thiodibenzoyl chloride (TDC) and different ratios of diamine (both of them contained flexible thioether group) to supply a series of slightly crosslinking semi-aromatic polyamide. It is found that the resultant polymers had excellent thermal properties (Tg, 237.9–245.8 °C, Td, 430.9–436.5 °C) and mechanical properties (tensile strength, 74–100 MPa). Because of the introduction of the large amount of flexible thioether group, the resultant polyamides can be dissolved in some aprotic solvents, and can be processed with solution method to fabricate a series of fast-responsive shape memory film (SMF) with a responsive time of 6–8 s, recovery rate of 98–99.5% after 20 cycles. What's more, the oxidized film can even lift a weight equal to about 2–3 times (vertical direction) and 5–8 times (horizontal direction) of its own weight. Interestingly, unlike other shape memory polymers, these SMF after multiple processes (after bending-recovery cycle at high temperature) can still be processed repeatedly with a solution route, which supplies a novel and recyclable candidate for excellent performance SMP. It is expected to be used in solar cell wingspan actuator to light the satellite weight.

Electrospinning preparation of perylene-bisimide-functionalized graphene/polylactic acid shape-memory films with excellent mechanical and thermal properties

Electrospinning preparation of perylene-bisimide-functionalized graphene/polylactic acid composite films with shape-memory properties.

Hot Embossing of Micro-Pyramids into Thermoset Thiol-Ene Film.

This paper presents the first attempt to texturize a fully crosslinked thermoset shape memory polymer using a hot embossing technique. UV-cured thiol-ene films were successfully embossed with anisotropically-etched Si (100) stamps at a temperature of 100 °C, which is about 50 °C above the glass transition temperature of the polymer. The low storage modulus of the polymer in a rubbery state allowed us to permanently emboss random micro-pyramidal patterns onto the surface of the film with high fidelity by applying 30 MPa pressure for 1 h. Atomic force microscopy (AFM) investigation showed perfect replication of the stamp micropattern with typical height of the largest inverted pyramids close to 0.7 µm and lateral dimensions in the range of 1–2 µm. Changes in surface roughness parameters of the embossed thiol-ene films after annealing them at 100 °C for 1 h or storing for 2 months in air at standard room conditions were negligible. The achieved results open new perspectives for the simple and inexpensive hot embossing technique to be applied for the micropatterning of prepolymerized thermoset shape memory films as an alternative to micropatterning using UV casting.