Triple Shape Research Articles

Triple Shape Memory Polymers: Constitutive Modeling and Numerical Simulation

Recently, triple shape memory polymers (TSMPs) have been discovered; these materials can be programmed to switch between three distinct shapes. Previously, we introduced a model to describe the mechanical behavior of TSMPs; however, the earlier study was limited in scope to simple cases of uniaxial deformation. In this work, we build upon our prior work, and develop robust numerical methods and constitutive equations to model complex mechanical behavior of TSMPs in inhomogeneous deformations and loading conditions using a framework based on the theory of multiple natural configurations. The model has been calibrated to uniaxial experiments. In addition, the model has been implemented as a user material subroutine (UMAT) in the finite element package abaqus. To demonstrate the applicability of the developed constitutive model, we have numerically simulated two cases of three-dimensional bodies undergoing triple-shape cycles; triple-shape recovery response of a complex TSMP geometry and the triple-shape recovery response of a stent when it is inserted in an artery modeled as a compliant elastomeric tube.

Dual responsive shape memory polymer/clay nanocomposites

In this study, a novel dual-responsive shape-memory polymer/clay nanocomposite is successfully prepared using in situ polymerization approach with the presence of exfoliated clay platelets. With the adjustable glass transition temperature, the nanocomposites have been used to construct triple shape memory devices via two-step polymerization methods. The physical crosslinking network formed by strong hydrogen interactions between polymer chains and clay platelets contribute to a significant enhancement in the mechanical properties of the resultant nanocomposites, which ensured that they can lift the load of 200 times its own weight upon exposure to infrared light (IR). Incorporation of clays into polymer matrix effectively improved the hydrophilic performance of materials, thus the water-induced shape recovery process of the nanocomposites can be finished within 6 s with excellent recovery ratio. Therefore, the preparation of dual responsive shape memory polymer/clay nanocomposites pave a new way to design and fabricate high mechanical shape memory materials with dual triggering mechanism.

Triple-shape memory effects of bismaleimide based thermosetting polymer networks prepared via heterogeneous crosslinking structures

A series of bismaleimide based triple shape memory polymers with heterogeneous crosslinking structures were synthesized, and their shape memory behaviours are characterized.

Photoinduced triple shape memory polyurethane enabled by doping with azobenzene and GO

A polymer-dispersed azobenzene and GO nanocomposite film was fabricated with shape memory polyurethane as a matrix.

A multi-responsive hydrogel with a triple shape memory effect based on reversible switches.

A novel multi-responsive shape memory hydrogel is described. The hydrogel shows multi-responsive shape memory performance and a programmable triple shape memory effect based on dual multi-responsive reversible switches, which will inspire the design and fabrication of novel shape memory systems.

Stretchable supramolecular hydrogels with triple shape memory effect.

Shape memory polymers based on reversible supramolecular interactions have invoked growing research interest, but still suffer from limitations such as poor mechanical strength and finite shape memory performance. Here, we present a novel mechanical stretchable supramolecular hydrogel with a triple shape memory effect at the macro/micro scale. The introduction of a double network concept into supramolecular shape memory hydrogels endows them with excellent mechanical properties. The design of two non-interfering supramolecular interaction systems of both dynamic phenylboronic (PBA)-diol ester bonds and the chelation of alginate with Ca2+ endues the hydrogel with outstanding triple shape memory functionalities.

New low-energy0+state and shape coexistence inNi70

In recent models, the neutron-rich Ni isotopes around $N=40$ are predicted to exhibit multiple low-energy excited ${0}^{+}$ states attributed to neutron and proton excitations across both the $N=40$ and $Z=28$ shell gaps. In $^{68}\mathrm{Ni}$, the three observed ${0}^{+}$ states have been interpreted in terms of triple shape coexistence between spherical, oblate, and prolate deformed shapes. In the present work a new $({0}_{2}^{+})$ state at an energy of 1567 keV has been discovered in $^{70}\mathrm{Ni}$ by using $\ensuremath{\beta}$-delayed, $\ensuremath{\gamma}$-ray spectroscopy following the decay of $^{70}\mathrm{Co}$. The precipitous drop in the energy of the prolate-deformed ${0}^{+}$ level between $^{68}\mathrm{Ni}$ and $^{70}\mathrm{Ni}$ with the addition of two neutrons compares favorably with results of Monte Carlo shell-model calculations carried out in the large $fp{g}_{9/2}{d}_{5/2}$ model space, which predict a ${0}_{2}^{+}$ state at 1525 keV in $^{70}\mathrm{Ni}$. The result extends the shape-coexistence picture in the region to $^{70}\mathrm{Ni}$ and confirms the importance of the role of the tensor component of the monopole interaction in describing the structure of neutron-rich nuclei.

Constitutive modeling of the mechanics associated with triple shape memory polymers

Shape memory polymers (SMPs) are smart materials that alter their shape in response to external stimuli. Dual-shape SMPs are widely recognized and are characterized by two shapes involved in a typical shape memory cycle. Recently, triple-shape memory polymers (TSMPs) have been introduced that have the ability to remember three shapes. Thermo-sensitive TSMPs can perform two sequential shape changes in response to heat, which were programed previously in a triple-shape creation process (TSCP). TSMPs are technologically significant as their development of has led to emergence of many complex potential applications that cannot be achieved by dual-shape polymers (Zhao et al., 2013). Crystallizable TSMPs are a class of thermo-sensitive TSMPs, where the shape creation is due to formation of crystalline phases. Different TSCPs have been reported which enable to control the triple shape capability of these materials. In this work the mechanical behavior of TSMPs has been modeled using a framework that has been developed recently for studying crystallization in polymers (Rao, 2003; Rao and Rajagopal, 2001, 2002, 2004). The framework has been used successfully to model SMPs (Barot and Rao, 2006; Barot et al., 2008), light activated SMPs (Sodhi and Rao, 2010) and is based upon the theory of multiple natural configurations. The model has been used to simulate a uni-axial deformation cycle for different types of TSCPs and the results have been compared with experimental data.

Lignin-Based Triple Shape Memory Polymers.

Lignin-based triple shape memory polymers comprised of both permanent covalent cross-links and physical cross-links have been synthesized. A mixing phase with poly(ester-amine) and poly(ester-amide) network having two distinct glass transitions was hot mixed with more structurally homogenized methanol soluble lignin fraction by one-pot, two-step method. Triple shape properties arise from the combined effect of the glass transition of polyester copolymers and lignin and the dissociation of self-complementary hydrogen bonding and cross-link density. The percentage of recovery in each stage was investigated and it was proved that the first recovery is related with lignin-poly(ester-amine) rich network and the second recovery stage is related with lignin-poly(ester-amide) rich network. The thermal and mechanical properties of the lignin-copolymer networks were also investigated using differential scanning calorimetry and dynamic mechanical analysis.

Isothermal programming of triple shape memory

Here we present a new strategy for enabling triple shape memory (TSM), in which different shapes may be programmed at one constant fixation temperature during isothermal crystallization of a poly(octylene adipate) elastomer. Unlike traditional TSM programming techniques that utilize separate thermal transitions to encode each distinct shape, here we report that multiple shapes may be encoded independently at different time stages of the same isothermal crystallization process, and then recovered sequentially at different temperatures upon heating. As such, the new method extends TSM capabilities to conventional semicrystalline elastomers that exhibit a single and narrow thermal transition. Unexpectedly, shape fixation does not depend on crystallinity acquired prior to sample deformation, which suggests that different shapes are secured by an individual crystalline scaffold with minor contribution of the pre-existing crystals. To that end, the isothermal protocol for TSM programming was utilized to demonstrate a “one-way reversible” shape memory transformation controlled by fixation time.

A facile approach to fabricate a UV/heat dual-responsive triple shape memory polymer

In the present work, a facile approach was employed to fabricate a UV/heat dual-responsive triple shape memory polymer (SMP) by simply mixing Zn(Mebip)2(NTf2)2, a metallosupramolecular unit formed by coordinating 2,6-bis(N-methyl-benzimidazolyl)-pyridine (Mebip) ligands to zinc di[bis(trifluoromethylsulfonyl)-imide] (Zn(NTf2)2), into one part of epoxy resin.

Elaborate fabrication of well-defined side-chain liquid crystalline polyurethane networks with triple-shape memory capacity

A series of side-chain liquid crystalline polyurethane networks (SCLCPU-Ns) with well-defined architecture are prepared via an elaborate strategy. The SCLCPU-Ns display dual thermal transition temperatures (Tg and Tcl), which can be utilized as Ttrans to trigger the triple shape memory effect.

Dually actuated triple shape memory polymers of cross-linked polycyclooctene-carbon nanotube/polyethylene nanocomposites.

In this work, electrically and thermally actuated triple shape memory polymers (SMPs) of chemically cross-linked polycyclooctene (PCO)-multiwalled carbon nanotube (MWCNT)/polyethylene (PE) nanocomposites with co-continuous structure and selective distribution of fillers in PCO phase are prepared. We systematically studied not only the microstructure including morphology and fillers' selective distribution in one phase of the PCO/PE blends, but also the macroscopic properties including thermal, mechanical, and electrical properties. The co-continuous window of the immiscible PCO/PE blends is found to be the volume fraction of PCO (vPCO) of ca. 40-70 vol %. The selective distribution of fillers in one phase of co-continuous blends is obtained by a masterbatch technique. The prepared triple SMP materials show pronounced triple shape memory effects (SMEs) on the dynamic mechanical thermal analysis (DMTA) and the visual observation by both thermal and electric actuations. Such polyolefin samples with well-defined microstructure, electrical actuation, and triple SMEs might have potential applications as, for example, multiple autochoke elements for engines, self-adjusting orthodontic wires, and ophthalmic devices.

Preparation and characterization of triple shape memory composite foams.

Foams prepared from shape memory polymers (SMPs) offer the potential for low density materials that can be triggered to deploy with a large volume change, unlike their solid counterparts that do so at near-constant volume. While examples of shape memory foams have been reported in the past, they have been limited to dual SMPs: those polymers featuring one switching transition between an arbitrarily programmed shape and a single permanent shape established by constituent crosslinks. Meanwhile, advances by SMP researchers have led to several approaches toward triple- or multi-shape polymers that feature more than one switching phase and thus a multitude of temporary shapes allowing for a complex sequence of shape deployments. Here, we report the design, preparation, and characterization of a triple shape memory polymeric foam that is open cell in nature and features a two phase, crosslinked SMP with a glass transition temperature of one phase at a temperature lower than a melting transition of the second phase. The soft materials were observed to feature high fidelity, repeatable triple shape behavior, characterized in compression and demonstrated for complex deployment by fixing a combination of foam compression and bending. We further explored the wettability of the foams, revealing composition-dependent behavior favorable for future work in biomedical investigations.

Triple Shape Memory Materials Incorporating Two Distinct Polymer Networks Formed by Selective Thiol–Michael Addition Reactions

We present a composite material composed of dual polymer networks uniquely formed from a single reaction type and catalyst but involving monomers with dramatically different reactivities. This powerful new approach to creating polymer networks produces two narrow glass transition, homogeneous networks sequentially from a single reaction but with all monomers present and uniformly mixed prior to any polymerization. These materials exhibit a triple shape memory effect based on the dual polymer networks, which were both formed using the thiol–Michael addition reaction. Two multifunctional thiol monomers (i.e., mercaptoacetate (MA) and mercaptopropionate (MP)) and two multifunctional vinyls (i.e., vinyl sulfone (V) and acrylate (A)) were polymerized in situ using a nucleophilic initiator. The MA-V polymer network (Tg = 55 °C) was generated first associated with the higher functional group reactivities followed by the formation of the MP-A network (Tg = 10 °C) which was confirmed by FT-IR, SEM, DMA, and a sepa...

Experimental and computational study of triple line shape and evolution on heterogeneous surfaces

Wetting of smooth, chemically heterogeneous surfaces was studied experimentally and computationally during the advancing and receding processes. The motion of the triple line is known to play an important role in determining the macroscopic contact angle due to its ability to be pinned at various defect locations on real surfaces. This effect is known to cause contact angle hysteresis. The shape of the triple line during these pinning/de-pinning events on various chemically heterogeneous surfaces was captured using an experimental and a computational technique. The experimental study employed a Modified Wilhelmy Plate Technique. The novelty in the current experimental setup lies in its ability to capture the microscopic triple line shape and its evolution in addition to measuring the local contact angles, which were both studied. The triple line shape was observed to be very sensitive to minor imperfections of the substrate. In addition, Surface Evolver was used to study the triple line shape computationally. Evolver was used to solve the complete three-dimensional problem by minimization of the total energy taking into consideration, both gravity and contact angle hysteresis. The studies showed that the temporal evolution of the triple line was significantly different during the advancing and receding processes based on the nature of the chemical heterogeneity. The results from the current work could be used in the design and fabrication of chemically heterogeneous surfaces for desired wetting applications.

A finite deformation thermomechanical constitutive model for triple shape polymeric composites based on dual thermal transitions

Shape memory polymers (SMPs) have gained strong research interests recently due to their mechanical action that exploits their capability to fix temporary shapes and recover their permanent shape in response to an environmental stimulus such as heat, electricity, irradiation, moisture or magnetic field, among others. Along with interests in conventional “dual-shape” SMPs that can recover from one temporary shape to the permanent shape, multi-shape SMPs that can fix more than one temporary shapes and recover sequentially from one temporary shape to another and eventually to the permanent shape, have started to attract increasing attention. Two approaches have been used to achieve multi-shape shape memory effects (m-SMEs). The first approach uses polymers with a wide thermal transition temperature whilst the second method employs multiple thermal transition temperatures, most notably, uses two distinct thermal transition temperatures to obtain triple-shape memory effects (t-SMEs). Recently, one of the authors’ group reported a triple-shape polymeric composite (TSPC), which is composed of an amorphous SMP matrix (epoxy), providing the system the rubber-glass transition to fix one temporary shape, and an interpenetrating crystallizable fiber network (PCL) providing the system the melt-crystal transition to fix the other temporary shape. A one-dimensional (1D) material model developed by the authors revealed the underlying shape memory mechanism of shape memory behaviors due to dual thermal transitions. In this paper, a three-dimension (3D) finite deformation thermomechanical constitutive model is presented to enable the simulations of t-SME under more complicated deformation conditions. Simple experiments, such as uniaxial tensions, thermal expansions and stress relaxation tests were carried out to identify parameters used in the model. Using an implemented user material subroutine (UMAT), the constitutive model successfully reproduced different types of shape memory behaviors exhibited in experiments designed for shape memory behaviors. Stress distribution analyses were performed to analyze the stress distribution during those different shape memory behaviors. The model was also able to simulate complicated applications, such as a twisted sheet and a folded stick, to demonstrate t-SME.

Triple Frequency Fractal Patch Structure Antenna for C Band Applications

In this study, a triple frequency fractal triangular shape microstrip patch antenna is presented for C band applications. The proposed antenna comprises of two triangular shape patches with two triangular slots and excited by a 50 Ω microstrip transmission line. The antenna excites three separate resonant modes where lower resonant mode of the antenna has an impedance bandwidth (VSWR<2) of 50 MHz (5.64-5.69 GHz), middle resonant modes impedance bandwidth 140 MHz (6.47-6.61 GHz) and the upper resonant mode impedance bandwidth of 140 MHz (7.59-7.73 GHz). It has achieved stable radiation pattern in the operating frequency band. The proposed fractal triangular patch antenna is presented and discussed in details.

Properties of triple shape memory composites prepared via polymerization-induced phase separation

Research in the field of shape memory polymers has recently witnessed the introduction of increasing complexity of material response, including such phenomena as triple/multishape behavior, temperature memory, and reversible actuation. Ordinarily, such complexity in physical behaviour is achieved through comparable complexity in material composition and synthesis. Seeking to achieve a triple shape behaviour with a simple route to materials synthesis, we introduce here a method that utilizes polymerization induced phase separation (PIPS) to yield the requisite combination of microstructure and composition. Thus, two blends incorporating epoxy and poly(ε-caprolactone) were developed using commercially available reactants, one featuring a semicrystalline epoxy and the other featuring an amorphous epoxy. We show that both blends exhibited distinct transition temperatures and three modulus-temperature plateaus needed for triple shape behaviour. Despite these similarities, their physical character at room temperature is vastly different: the semicrystalline epoxy material is elastomeric and the amorphous epoxy material is highly stiff. Characterization of the triple shape behaviour revealed an ability of both systems to fix two separate deformations independently, one by PCL crystallization and a second one by epoxy crystallization or vitrification, and recover both programmed shapes separately upon heating. Given the simplicity of fabrication, we envision application as multi-shape coatings, adhesives, and films.

Triple Shape Memory Effects of Cross-Linked Polyethylene/Polypropylene Blends with Cocontinuous Architecture

In this paper, the triple shape memory effects (SMEs) observed in chemically cross-linked polyethylene (PE)/polypropylene (PP) blends with cocontinuous architecture are systematically investigated. The cocontinuous window of typical immiscible PE/PP blends is the volume fraction of PE (v(PE)) of ca. 30-70 vol %. This architecture can be stabilized by chemical cross-linking. Different initiators, 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexane (DHBP), dicumylperoxide (DCP) coupled with divinylbenzene (DVB) (DCP-DVB), and their mixture (DHBP/DCP-DVB), are used for the cross-linking. According to the differential scanning calorimetry (DSC) measurements and gel fraction calculations, DHBP produces the best cross-linking and DCP-DVB the worst, and the mixture, DHBP/DCP-DVB, is in between. The chemical cross-linking causes lower melting temperature (Tm) and smaller melting enthalpy (ΔHm). The prepared triple shape memory polymers (SMPs) by cocontinuous immiscible PE/PP blends with v(PE) of 50 vol % show pronounced triple SMEs in the dynamic mechanical thermal analysis (DMTA) and visual observation. This new strategy of chemically cross-linked immiscible blends with cocontinuous architecture can be used to design and prepare new SMPs with triple SMEs.