Styrene-based Shape Memory Polymer Research Articles

Effect of microstructural features on the thermal conducting behavior of carbon nanofiber–reinforced styrene-based shape memory polymer composites

This article presents a novel hierarchical micromechanics approach to carefully investigate the thermal conductivities of styrene-based shape memory polymer composites containing carbon nanofibers. The research is mainly focused on the simulation of carbon nanofiber/shape memory polymer interfacial thermal resistance and carbon nanofiber agglomeration as two critical microstructural features of carbon nanofiber–shape memory polymer composite materials. The computed results are compared with the available experimental measurements. It is found that both of those microstructural factors along with carbon nanofiber non-straight shape significantly affecting the thermal conducting behavior must be incorporated in the analysis to have a more realistic prediction. The thermal conductivity of carbon nanofiber–reinforced shape memory polymer composites reduces significantly due to the effects of carbon nanofiber/shape memory polymer interfacial resistance and carbon nanofiber agglomeration and waviness. It is suggested to uniformly disperse carbon nanofibers into the shape memory polymers and reduce interfacial resistance for improving the carbon nanofiber–styrene composite thermal properties. In addition, the present study reveals that the effective thermal conductivities of the shape memory polymer composites reinforced by aligned carbon nanofibers are greatly enhanced over those of the shape memory polymer composites containing randomly dispersed carbon nanofibers. The effects of percentage, waviness parameters, degree of agglomeration, material properties, length and diameter of carbon nanofibers as well as interfacial thermal resistance value on the thermal behavior of carbon nanofiber–reinforced styrene-based shape memory polymer composites are investigated.

Triple-shape memory effect in a styrene-based shape memory polymer: Characterization, theory and application

A segmented styrene-based shape memory polymer (SMP) comprising two types of SMP materials (S1-SMP and S2-SMP) was fabricated by using a two-step curing method to exhibit the triple shape memory effect (triple-SME). The material properties of S1-SMP and S2-SMP parts were explored using dynamic mechanical analysis, multi-frequency scan testing, thermal expansion measurements, static tensile testing and shape memory testing, respectively. Meanwhile, the triple-SME of segmented SMP was also characterized by shape memory testing with continue heating step. These experimentally determined material properties were incorporated into the theoretical model for the triple-SME based on a phase transition model and Generalized Maxwell model. Experimental verification was obtained by observing the triple-SME behavior under uniaxial tensile strain of 20%. Finally, the triple-SME behavior of SMP was assessed in two engineered implementations; a programmable self-deployed structure model and double bottle-shaped smart mandrel. Good agreement was demonstrated between experimental result and a finite-element model (FEM) simulation during the continue heating recovery step.

Shape retainability and reusability investigation of bottle-shaped SMP mandrel

Shape memory polymer (SMP) mandrel, a kind of mandrel for fabrication of composite structures, has attracted great attention due to the advantages of low cost, simple operation and easy demoulding. In this paper, a type of styrene-based SMP with good shape retainability and recoverability were synthesized and examined by uniaxial tensile test and dynamic mechanical analysis test. Then, a bottle-shaped smart mandrel with shape memory effect was prepared by inflation method. Short/long-time shape retainability and reusability were characterized. Finally, the SMP mandrel was used to form a bottle-shaped composite structure model by filament winding technology. The excellent demoulding property and good reusable ability of SMP mandrel provided potential applications in the composite part production.

Thermomechanical and electroactive behavior of a thermosetting styrene‐based carbon black shape‐memory composite

ABSTRACTA thermosetting styrene‐based shape memory polymer (SMP) filled with nanoscale (30 nm) carbon black are prepared to reinforce the thermomechanical performances and realize the high‐efficient electronic actuation at macro scale due to the carbon–carbon network morphology at nano/micro scale. The elastic modulus of this thermosetting SMP composite is significant strengthened and can maintain at 1–2.5 GPa at around the room temperature, which is suitable for used as a structural material. The electronic resistivity decreases sharply at a quite low percolation threshold range (2–5%), and maintains at a relatively low and stable level of electronic resistivity. Furthermore, the electronic resistivity also exhibits relative stability in terms of the resistivity–temperature–time relationship and the evolution of resistivity upon heating–cooling cycles. This shape memory styrene‐based composite is suitable to be used as an electroactive functional material in realistic engineering. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45978.

Thermal-mechanical behavior of styrene-based shape memory polymer tubes

Styrene-based shape memory polymer (SMP) tubes were fabricated and their basic mechanical properties in different deformation states were investigated. The tensile, compression, bending and twisting shape memory properties of the tubes were analyzed and discussed, and the results indicated that SMP tubes exhibit good shape fixity ratio and shape recovery ratio. In addition, the shape recovery behavior was investigated at different heating rates. These experimental results will provide guidance for future applications of SMP tube structures.

Controlled wettability based on reversible micro-cracking on a shape memory polymer surface.

Wettability modification on a polymer surface is of immense importance for flexible electronics and biomedical applications. Herein, controlled wettability of a styrene-based shape memory polymer has been realized by introducing micro-cracks on the polymer surface for the first time. The cracks were purposely prepared by thin metal film constrained deformation on the polymer. After the removal of the metallic film, wettability was dramatically enhanced by showing a remarkable reduction in the contact angle with water droplets from 85° to 25°. Subsequent systematic characterization techniques like XPS and SEM revealed that such observation could be attributed to the increased density of hydrophilic groups and the roughened surface. In addition, by controlling the temperature for annealing the treated polymer, the surface could be switched reversely to water-repellent. Therefore, this paper offers a smart tactic to manipulate the surface wettability of a shape memory polymer freely. The features of the controlled wettability surface such as high tenability, high stability and easy fabrication are promising for microfluidic switching and molecule/cell capture-release.

Design and analysis of smart release devices based on shape memory polymer composites

Pyrotechnic release devices of spacecraft produce high-shock and contamination, which are hazardous. Mechanical release devices can overcome these disadvantages, but they tend to be complex and costly. In this paper, new kinds of release devices (smart release devices) with the advantages of no pyrotechnic, light weight, and simple structure are proposed, which are made of carbon fiber reinforced styrene-based shape memory polymer composite. The key element of the devices is the shape memory polymer composite cylinder (thin-walled tube). First, the smart release devices are designed based on three different deformation ways of the cylinder. Second, the deformation models are analyzed to verify the feasibility of the smart release devices. Then the smart release devices are made according to the design, they agree well with the simulations obtained from ABAQUS. Finally, the tensile experiments were conducted to get the structural strength of the devices. Different forms of the deformation were tested and compared, obtained the release time of the devices.

Selectively actuated multi-shape memory effect of a polymer multicomposite

The multicomposite styrene-based shape memory polymer can be selectively actuated by applying selective stimuli due to the selective heating properties of Fe3O4(30 kHz alternating magnetic field) and CNT (13.56 MHz radiofrequency field) nanofillers. Therefore, the multicomposite possesses a well-controlled multiple temporary shape recovery capability.

Mechanical and shape recovery properties of shape memory polymer composite embedded with cup-stacked carbon nanotubes

This study investigated the mechanical and shape recovery properties of a styrene-based shape memory polymer composite reinforced by cup-stacked carbon nanotubes. Due to their unique morphology, cup-stacked carbon nanotubes could be well dispersed in the polymer matrix and offer remarkable benefits in the load transfer between the reinforcement fillers and shape memory polymer. Under the same amount of fillers, shape memory polymer composites embedded with cup-stacked carbon nanotubes exhibit superior mechanical properties in comparison with those embedded with multiwalled carbon nanotubes and carbon nanofibers. The elastic modulus, tensile strength, and flexural strength of the 2 wt% cup-stacked carbon nanotube–reinforced shape memory polymer composite increased by 61%, 66%, and 84%, respectively. It was also found that the glass transition temperature of shape memory polymer composite decreased from 61.9°C to 52.8°C by introducing 2 wt% cup-stacked carbon nanotubes, indicating that the shape recovery process could be triggered more easily by external stimulus due to the role of reinforcement fillers. Finally, under the external resistance load, the developed shape memory polymer composite was successfully driven to recover their shapes under thermal stimulus. The cup-stacked carbon nanotubes were proved to be a promising candidate for the polymer reinforcement.

Method to Analyze Chemo-Mechanical Behavior of Shape Memory Polymer in Response to Solvent

Thermo-responsive shape-memory polymer (SMP) has been experimentally demonstrated that shape recovery can be induced by plasticizing solvent. Subject to being immersed into solvent, deformed SMP recover from the temporary shape to original shape, leading to shape recovery induced by the molecular interaction. The actuation of styrene-based SMP has been carried out by electrostatic dipole-dipole interaction and physical swelling effect, respectively. The model can be used to predict the effect of prestress, strain, volume change and chemical potential on SMP actuation in the solvent. Finally, it is found that the simulation agrees well with experimental results. The authors show that the chemo-mechanical instability occurs when the Hessian of the free-energy function ceases to the positive definite. Their calculations show that the shape recovery behavior of SMP is driven by the entropy change markedly, agreeing with existing experimental observations.

Magnetically aligned carbon nanotube in nanopaper enabled shape-memory nanocomposite for high speed electrical actuation

A new shape-memory nanocomposite that exhibits rapid electrical actuation capabilities is fabricated by incorporating self-assembly multiwalled carbon nanotube (MWCNT) nanopaper and magnetic CNTs into a styrene-based shape-memory polymer (SMP). The MWCNT nanopaper was coated on the surface to give high electrical conductivity to SMP. Electromagnetic CNTs were blended with and, vertically aligned into the SMP resin upon a magnetic field, to facilitate the heat transfer from the nanopaper to the underlying SMP. This not only significantly enhances heat transfer but also gives high speed electrical actuation.

Conductive Shape Memory Polymer Composite Incorporated with Hybrid Fillers: Electrical, Mechanical, and Shape Memory Properties

In this article, separated carbon nanotubes (CNTs) aggregations were bridged by short carbon fibers in the conductive polymer composites, where a styrene-based shape memory polymer (SMP) was selected as the matrix resin. Due to the synergistic effect of hybrid fillers, the electrical resistivity of the SMP composites was significantly decreased in comparison with those with only CNTs embedded. Benefits offered by the hybrid fillers to the electrical, mechanical, and shape memory properties of the developed conductive SMP composites were experimentally demonstrated in detail. The additionally acquired shape memory capability could expand the application scope of traditional conductive polymer composites.

Qualitative separation of the physical swelling effect on the recovery behavior of shape memory polymer

The physical swelling effect-induced shape recovery is studied in a thermo-responsive styrene-based shape memory polymer (SMP). Fourier transform-infrared (FTIR) test reveals no apparent change in the characteristic polar bonds of C O and O–H after immersing the SMP into toluene solvent. Based on the rubber elastic and relaxation theory, the decrease in internal energy is identified as the driving force for the shape recovery. Subsequently, the rubber elastic theory is further applied to investigate the swelling-induced free/constraint shape recovery in this SMP, and the free-energy function is utilized to analyze the swelling-induced homogenous/inhomogeneous deformation. This study provides a framework to study both the swelling effect-induced shape recovery and complex shape memory behavior in solvent-responsive SMPs.

Sensing and actuating capabilities of a shape memory polymer composite integrated withhybrid filler

In this paper, hybrid fillers, including carbon black (CB) and chopped short carbon fibers(SCF), are integrated into a styrene-based shape memory polymer (SMP) with sensing andactuating capabilities. The hybrid filler is expected to transform insulating SMP intoconducting. Static mechanical properties of the SMP composites containing various fillerconcentrations of hybrid filler reinforcement are studied first, and it is theoreticallyand experimentally confirmed that the mechanical properties are significantlyimproved by a factor of filler content of SCF. The excellent electrical properties ofthis novel type of SMP composite are determined by a four-point-probe method.As a consequence, the sensing properties of SMP composite filled with 5 wt%CB and 2 wt% SCF are characterized by functions of temperature and strain.These two experimental results both aid the use of SMP composites as sensorsthat respond to changes in temperature or mechanical loads. On the other hand,the actuating capability of SMP composites is also validated and demonstrated.The dynamic mechanical analysis result reveals that the output strength of SMPcomposites is improved with an increase in filler content of SCF. The actuatingcapability of SMP composites is subsequently demonstrated in a series of photographs.

Study on the activation of styrene-based shape memory polymer by medium-infrared laser light

This paper demonstrates the feasibility of shape memory polymer (SMP) activation by medium-infrared laser light. Medium-infrared light is transmitted by an optical fiber embedded in the SMP matrix, and the shape recovery process and temperature distribution are recorded by an infrared camera. Light-induced SMP exhibits potential applications in biomedicines and flexible displays.

Mechanical and Curing Properties of a Styrene-based Shape Memory Polymer

Presented is an experimental investigation into the characteristics of a particular styrene-based shape memory polymer, Veriflex®. Tensile, 3 point bend, and creep tests are conducted yielding the Young’s modulus, yield strength, flexural modulus, flexure strength, and creep modulus of the polymer both above and below the glass transition temperature. The results of the characterization may be used to populate a linear constitutive model appropriate for design. To populate the constitutive model parameters for viscosity, retardation time, and coefficient of thermal expansion are also developed. Initial experiments in this effort revealed the tendency for residual monomer to remain after curing. While the residual monomer ultimately evaporates from the sample, when present it acts as a plasticizer thereby increasing the glassy state compliance. Thus, also presented are strategies employed for eliminating residual monomer during sample preparation.

Study on Thermo-Mechanical Behaviors of Shape Memory Polymer

Dynamic mechanical analysis (DMA) tests are conducted on styrene-based shape memory polymer(SMP) to investigate its glass transition behaviors. The tensile tests at various temperatures are operated to detect the stress-strain relationship of styrene-based SMP. The material elastic moduli and yielding limits at 25oC, 30oC, 40oC, and 50oC are determined according to the results of tensile test. A new material parameter function is supposed to express the glass transition behavior of styrene-based SMP. The shape memory thermo-mechanical cycle of styrene-based SMP is numerically simulated by Tobushi’s constitutive equation coupled with the new material parameter function. Numerical results show the new material parameter function can express the thermo-mechanical properties of styrene-based SMP effectively.

Infrared light‐active shape memory polymer filled with nanocarbon particles

AbstractIn addition to the fabrication of thermoset styrene‐based shape memory polymer (SMP) and its nanocomposite filled with nanocarbon particles, this study presents the effect of nanocarbon particles on infrared light‐active shape recovery behaviors of this type of SMP material. The experimental results reveal that both pure SMP and SMP filled with nanocarbon particles can be actuated by infrared light in vacuum, while shape memory effect shown by the composite is stronger than that of in pure SMP. Shape memory effect is evaluated by shape recovery ability and shape recovery speed in detail. Moreover, factors which would influence the infrared light‐active shape memory effect in SMP with/without nanocarbon particles are explored by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and infrared absorption characteristic tests. The better shape memory effect of the nanocomposite attributes to its higher storage modulus and higher infrared absorption capability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Electroactive thermoset shape memory polymer nanocomposite filled with nanocarbonpowders

This paper concerns an electroactive thermoset styrene-based shape memory polymer (SMP)nanocomposite filled with nanosized (30 nm) carbon powders. With an increase of theincorporated nanocarbon powders of the SMP composite, its glass transition temperature (Tg) decreases and storage modulus increases. Due to the high micro-porosity andhomogeneous distributions of nanocarbon powders in the SMP matrix, the SMP compositeshows good electrical conductivity with a percolation of about 3.8%. This percolationthreshold is slightly lower than that of many other carbon-based conductive polymercomposites. Consequently, due to the relatively high electrical conductivity, asample filled with 10 vol% nanocarbon powders shows a good electroactive shaperecovery performance heating by a voltage of 30 V above a transition temperature of56–69 °C.

A GLASS TRANSITION MODEL FOR SHAPE MEMORY POLYMER AND ITS COMPOSITE

As novel smart materials, shape memory polymer (SMP) and its composite (SMPC) have the ability to regain its original shape after undergoing significant deformation upon heating or other external stimuli such as light, chemic condition and so on. Their special behaviors much depends on the glass transitions due to the increasing of material temperature. Dynamic Mechanical Analysis (DMA) tests are performed on the styrene-based SMP and its carbon fiber fabric reinforced SMPC to investigate their glass transition behaviors. Three glass transition critical temperatures of SMP or SMPC are defined and a method to determine their values from DMA tests is supposed. A glass transition model is developed to describe the glass transition behaviors of SMP or SMPC based on the results of DMA tests. Numerical calculations illustrate the method determining the glass transition critical temperature is reasonable and the model can well predict the glass transition behaviors of SMP or SMPC.