Showing papers by "Yanju Liu published in 2008"

Significantly reducing electrical resistivity by forming conductive Ni chains in a polyurethane shape-memory polymer/carbon-black composite

Abstract: We demonstrate an approach to significantly reduce the electrical resistivity in a polyurethane shape-memory polymer (SMP) filled with randomly distributed carbon black (CB). With an additional small amount of randomly distributed Ni microparticles (0.5vol%) in the SMP/CB composite, its electrical resistivity is only reduced slightly. However, if these Ni particles are aligned into chains (by applying a low magnetic field on the SMP/CB/Ni solution before curing), the drop of the electrical resistivity is significant. This approach, although demonstrated in a SMP, is applicable to other conductive polymers.

Synergic effect of carbon black and short carbon fiber on shape memory polymer actuation by electricity

Abstract: This paper presents a study on the effect of carbon black (CB) and short carbon fibers (SCFs) on shape memory polymer (SMP) actuation by applying electric current. The coexistence of CB and SCF electrically conductive networks, supporting each other, resulting in significant improvement of electrical properties, was supported by optical microscopy, while the roles of particulate and fibrous fillers were distinguished by scanning electron microscopy. In sequence, the volume resistivity curves of one filler systems and two fillers systems were figured out and compared. Moreover, experimental results substantiated that the actuation voltage of two-filler SMP composites’ shape recovery was prominently lower in comparison with that of one-filler systems at the same filler content. Additional, the response of glass transition temperature (Tg) and thermomechanical properties to filler content and two fillers’ synergic effect were characterized and illuminated experimentally.

Comment on “Method to analyze electromechanical stability of dielectric elastomers”[Appl. Phys. Lett. 91, 061921 (2007)]

Abstract: We would like to thank Zhao and Suo [Appl. Phys. Lett. 91, 061921 (2007)] for their insights and help on “Method to analyze electromechanical stability of dielectric elastomers;” Suo provided the theory of stability of dielectric elastomers. In this Comment, the nonlinear electromechanical theory for deformable dielectrics described in Suo’s paper is applied to analyze the stability of dielectric elastomers. Different from that given in Suo’s paper, in the current work, elastic strain energy functional with two material constants is used for the stability analysis. Dielectric materials with different values of k are analyzed, and the results seem to support Suo’s theory. These results can be applied in the design of dielectric elastomer actuator and in larger application spectrum.

Comment on “Water-driven programmable polyurethane shape memory polymer: Demonstration and mechanism” [Appl. Phys. Lett. 86, 114105 (2005)]

Abstract: We would like to thank Huang et al. for their insightful and helpful research on “Water-driven programable polyurethane shape memory polymer: Demonstration and mechanism.” We agree that hydrogen bonding is identified as the reason behind these features of polyurethane shape memory polymer SMP : water-driven actuation and recovery in sequence i.e., programable . We also want to provide further clarification about the mechanism. In addition to the waterdriven actuation of polyurethane SMP, this comment is focused on rules, which may be used to trigger other types of SMP by their interactive solution. There are two points essentially made by Huang et al. which we address here. 1 Hydrogen bonding is identified as the reason behind water-driven programable polyurethane SMP. 2 The absorbed water is quantitatively separated into two parts, namely, the free water and bound water. At the beginning, we address the point which Behl and Lendlein analyzed in their review: “indirect actuation of the shape-memory effect has been realized to low transition temperature by diffusion of low molecular weight molecules into the polymer, which works as a plasticizer.” On the basis of solution theory of polymer physics, the glass transition temperature of polymers decreases when a liquid, such as an organic solvent or water, is mixed with them. Liquids added to polymers to make them softer and more flexible at ambient temperature are known as plasticizers. When polymer is immersed in solution, the solution molecule has plasticizing effect on the polymer first, followed by chemical or physical interaction, resulting in transition temperature, being reduced to the ambient temperature. However, the plasticizing effect plays the more important role on transition temperature than the chemical or physical interaction. At the same time, we also want to point out the mechanism of hydrogen bonding, which is identified as the reason for water-driven polyurethane SMP in the research of Huang et al., increases the flexibility of macromolecular chains virtually. That is to say, the hydrogen bonding just has an indirect effect on the transition temperature. In fact, only the flexibility can be used to account for transition temperature decreasing, as shown in Fig. 1. Sometimes, it can be increased by chemical interaction or physical swelling effect. It had been demonstrated that the swelling effect can be used to drive styrene-based SMP in toluene solvent. Finally, we would like to address solution theory, free volume theory, and Fujita’s diffusion theory to qualitatively separate of the effects of free water and bound water on the polyurethane SMP. The amount of free water is determined by free volume which generally is chosen as a constant of 2.5%. In the research of Huang et al., the amount of free water is appropriate to 3% from Fig. 5 a . The different amounts of water and moisture in polymer in Fig. 5 can be explained by Fick’s law of diffusion: one belongs to liquid diffusion process; the other belongs to gaseous diffusion process. Thus, the role of bound water playing is determined by diffusion law. In summary, polyurethane SMP in response to water or, to the extension, SMP in response to solution namely, solvent or mixture , is due to the plasticizing effect of the solution molecule, on polymeric materials which then increases the flexibility of macromolecule chains. These two effects reduce the transition temperature of materials until shape recovery occurs. Our study is made in context and refers to the many reported theories explaining the mechanism of waterdriven polyurethane SMP and enlarging its extension. We conclude that the research of Huang et al. makes tremendous process in the actuation of SMP. Many extension results and achievements are based on their conclusion.

New silicone dielectric elastomers with a high dielectric constant

Abstract: Dielectric elastomers (Des) are a type of EAPs with unique electrical properties and mechanical properties: high actuation strains and stresses, fast response times, high efficiency, stability, reliability and durability. The excellent figures of merit possessed by dielectric elastomers make them the most performing materials which can be applied in many domains: biomimetics, aerospace, mechanics, medicals, etc. In this paper, we present a kind of electroactive polymer composites based on silicone Dielectric elastomers with a high dielectric constant. Novel high DEs could be realized by means of a composite approach. By filling an ordinary elastomer (e.g. silicone) with a component of functional ceramic filler having a greater dielectric permittivity, it is possible to obtain a resulting composite showing the fruitful combination of the matrix's advantageous elasticity and the filler's high permittivity. Here we add the ferroelectric relaxor ceramics (mainly BaTiO3) which has high dielectric constant (>3000) to the conventional silicone Dielectric elastomers, to get the dielectric elastomer which can exhibit high elastic energy densities induced by an electric field of about 15 MV/m. Tests of the physical and chemical properties of the dielectric elastomers are conducted, which verify our supposes and offer the experimental data supporting further researches.

Comment on: Method to analyze electromechanical stability of dielectric elastomers

Abstract: We would like to thank Zhao and Suo [Appl. Phys. Lett. 91, 061921 (2007)] for their insights and help on “Method to analyze electromechanical stability of dielectric elastomers;” Suo provided the theory of stability of dielectric elastomers. In this Comment, the nonlinear electromechanical theory for deformable dielectrics described in Suo’s paper is applied to analyze the stability of dielectric elastomers. Different from that given in Suo’s paper, in the current work, elastic strain energy functional with two material constants is used for the stability analysis. Dielectric materials with different values of k are analyzed, and the results seem to support Suo’s theory. These results can be applied in the design of dielectric elastomer actuator and in larger application spectrum.

Inflated dielectric elastomer actuator for eyeball's movements: fabrication, analysis and experiments

Abstract: Bio-mimetic actuators are inspired to the human or animal organ and they are aimed at replicating actions exerted by the main organic muscles. We present here an inflated dielectric Electroactive Polymer actuator based on acrylic elastomer aiming at mimicing the ocular muscular of the human eye. Two sheets of polyacrylic elastomer coated with conductive carbon grease are sticked to a rotatable backbone, which function like an agonist-antagonist configuration. When stimulating the two elastomer sheets separately, the rotatable mid-arc of the actuator is capable of rotating from -50° to 50°. Experiments shows that the inflated actuator, compared with uninflated one, performs much bigger rotating angle and more strengthened. Connected with the actuator via an elastic tensive line, the eyeball rotates around the symmetrical axes. The realization of more accurate movements and emotional expressions of our native eye system is the next step of our research and still under studied. This inflated dielectric elastomer actuator shows as well great potential application in robofish and adaptive stucture.

Solution-Responsive Shape-Memory Polymer Driven by Forming Hydrogen Bonding

Abstract: Recently, there is interest in triggering shape recovery of shape-memory polymers(SMPs) by novel non-external heating. In this paper, many hard works have been carried out to make SMP induced by solution. The main challenge in the development of such polymer systems is the conversion of solution-induced effects at the molecular level to macroscopic movement of working pieces. This paper presents a systematic study on the effects of solution on the glass transition temperature (Tg). The results reveal that the hydrogen bonding of shape memory polymer (SMP) was aroused by the absorbed solution that significantly reduces Tg of polymer. The mechanism behind it is solution firstly intenerates polymeric materials till the Tg of polymer lowered down to the temperature of ambient, then hydrogen bonding interaction improves the flexibility of polymeric macro-molecular chains. Thus, the shape memory effect (SME) can undergo solution-driven shape recovery. In addition, it provides a new approach that the SMP can be induced by applying non-energy stimulus. The Dynamic Mechanical Analyzer (DMA) results reveal that the modulus of polymer was softened gradually with immersion time increasing. The experimental result is approximate to the theory.

Analysis of the Novel Strain Responsive Actuators of Silicone Dielectric Elastomer

Abstract: The acrylic acid and silicone are common dielectric elastomer materials. These actuators have shown excellent activate properties including large strains up to 380% and high energy densities up to 3.4 J/g, high efficiency, high responsive speed , good reliability and durability, etc. When a voltage is applied on the compliant electrodes of the dielectric elastomers, the polymer shrinks along with the electric field and expands in the plain area which erects the orientation of the line. In this paper, we synthesize a novel silicone dielectric elastomer with high dielectric constant, large strain and high force output. Pre-strain and certain driving electric field are applied on the novel silicone film, respectively. The strain responsing to the Maxwell stress is measured. Using the large deformation theory of finite element method to simulate the deformable behavior of materials, the simulation results agree with the experiment. The coupling effect of the mechanics and electric fields applied on the electrode of the dielectric elastomers is inverstigated. The finite element simulation of large deformation theory can be used to describe the dielectric elastomers materials large deformation that induced by the static electric field.

Investigate of Electrical Conductivity of Shape-Memory Polymer Filled with Carbon Black

Abstract: A new system of thermoset styrene-based shape-memory polymer (SMP) filled with carbon black (CB) is investigated. To realize the electroactive stimuli of SMP, the electrical conductivity of SMP filled with various amounts of CB is characterized. The percolation threshold of electrically conductive SMP filled with CB is about 3% (volume fraction of CB), which is much lower than many other electrically conductive polymers. When applying a voltage of 30V, the shape recovery process of SMP/CB(10 vol%) can be realized in about 100s. In addition, the thermomechanical properties are also characterized by differential scanning calorimetery (DSC).

Conductive nanoparticles in electro activated shape memory polymer sensor and actuator

Abstract: There is a strong interest in the use of conductive shape memory polymer (SMP) for actuation by passing an electrical current. This paper presents a systematic study on the effect of multi-walled carbon nanotubes (MWCNTs) and carbon nanoparticles on the electro activate shape memory polymer (SMP). The first is the fabrication and characterization of styrene-based SMP filled with MWCNTs was investigated. Then the resistivity of 8 wt% MWNTs sample is 80 ohm•cm obtained by using four-point probe Van De Pawn method, and for 8.0×2.0×0.2 cm3 rectangle sheet, it can be triggered by passing an electrical current with a constant voltage of 200 V. The second is focused on the effect of conductive particulate and fibrous fillers on the electrical property of composite. The electrical conductivity of the composites achieves 8.73×10-2, 9.63×10-2 and 1.13×10-1 S/cm by DC measurement and 0.12, 1.05 and 3 S/cm by four-point probe Van De Pauw method. Their shape recovery can be activated by passing an electrical current of 25 V voltages. In this paper, the sensors using conducting SMP composites testified by the temperature-dependent resistance and strain-dependent resistance tests. At the same time, the shape self-recovery of SMPs and their composites when heated above transition temperature acts as actuator.

Infrared laser-activated shape memory polymer

Abstract: This paper is concerned about the drive of shape memory styrene copolymer through an infrared optical fiber carrying infrared laser. The infrared laser was chosen to drive the SMP through the optical fiber embedded into the SMP. The working frequency of infrared laser was installed in 3-4μm, the working band of optical fiber was 1-6μm. An optical fiber was embedded into the SMP for delivery of 3-4μm laser light for activation. The surface of the optical fiber was etched by the aqueous solution of sodium-hydroxide in order to increase transmission efficiency of the optical fiber. We synthesized thermoset SMP based on styrene copolymer, and measured Tg of SMP is the 53.7oC by the DMA. The thermally activated SMP is possible to initiate an originally shape by a touchless and highly selective infrared laser stimulus. The infrared laser-activated SMP could be recovered its original shape by less temperature than Tg, it was proved this driving method of SMP is more effective than conventional external heaters. Therefore infrared laser-activated method was advantageous for using in the low temperature condition. The increase in temperature of SMP which was embedded treated optical fiber indicated that the infrared laser irradiated into the SMP from here and heated the SMP. The optical fiber was treated by the aqueous solution of sodium-hydroxide, transmission efficiency of the optical fiber increased, and the total contact area between SMP and the optical fiber. The infrared laser stimulation of SMP was interest for actuator systems as well as medical applications.

Application of SMP composite in designing a morphing wing

Abstract: A new concept of a morphing wing based on shape memory polymer (SMP) and its reinforced composite is proposed in this paper. SMP used in this study is a thermoset styrene-based resin in contrast to normal thermoplastic SMP. In our design, the wing winded on the airframe can be deployed during heating, which provides main lift for a morphing aircraft to realize stable flight. Aerodynamic characteristics of the deployed morphing wing are calculated by using CFD software. The static deformation of the wing under the air loads is also analyzed by using the finite element method. The results show that the used SMP material can provide enough strength and stiffness for the application.

Study on shape recovery speed of SMP, SMP composite, and SMP foam

Abstract: Shape memory polymer (SMP) receives increasing attention along with its derivants - SMP composite and SMP foam in recent years. In this paper, after fabricating thermoset styrene-based SMP, SMP/carbon black (CB) composite and SMP foam, we studied their shape recovery speed in bending. Different from those reported in the literature, we propose a new approach, i.e., using infrared light, for actuating SMP materials for shape recovery. The results show that SMP, SMP/CB composite and SMP foam can recover to their original shape perfectly in a wide temperature range. Shape recovery speed of SMP composite is not uniform during the overall recovery process, and it is the same trend with SMP but not prominent with SMP foam. Repeatability of shape recovery speed for styrene-based SMP and SMP/CB composite are similarly stable and the former is the better, but it is so worse for SMP foam. Temperature-dependent of shape recovery speed test for styrene-based SMP and SMP/CB composite reveal that higher temperature increases their shape recovery speed.

Shape memory polymer composite and its application in deployable hinge for space structure

Abstract: This paper is concerned about the basic properties of deployment for shape memory polymer composite (SMPC) and its application in deployable hinge for space structure. Shape-memory polymers (SMP) are an emerging class of active polymers that have dual-shape capability. One of another advantage, compared with other traditional material hinge, the SMPC carpenter type hinge is that it will not produce a large shock when it spring into the deployed position. There are several kinds of shape memory polymer composite (fiber reinforced, powder reinforced, etc,). Styrene-based SMP, carbon fibre fabric reinforced SMPC was introduced in this work. In order to investigate the basic performances of SMPC hinge, the experimental methods are used as follows: dynamic mechanical analysis (DMA), three point bending test and the radio of shape recovery. In the end, the structure of the carpenter type hinge is introduced. The carpenter type hinge is one mechanism that has the advantage of high-reliability of the deployment; light weighted, and low cost. This SMPC carpenter type hinge performs good deployment performances during numerous thermomechanical cycles. So the potential applications for such materials as active medical devices are highlighted.

Influence of Radialization Dosage on Shape Memory Effect of Polystyrene Copolymer

Abstract: This paper is concerned about the synthesis of shape memory styrene copolymer and the investigation of the influence of radialization dosage on its shape memory effect. As one of novel actuators in smart materials, shape memory polymers (SMPs) have been investigated intensively. Styrene copolymer with proper cross-linking degree can exhibit shape memory effect (SME). In this paper, the influence of radialization on shape memory effect of styrene copolymer was investigated through altering the dosage of radialization. The radialization dosage of styrene copolymer was determined by changed radicalization time. The glass transition temperature (Tg) of styrene copolymerwas measured by Dynamic Mechanical Analysis (DMA). The shape memory performance of styrene copolymer with different radiated dosage was also evaluated. Results indicated that the shape memory polymer (SMP) was synthesized successfully. The Tg increased from 60°C to 65°C followed by increasing the radialization dosage. Moreover, the SMP experienced good SME and the largest reversible strain of the SMP reached as high as 150%. When heating above Tg+30°C (different copolymers performed different Tg), the shape recovery speed of the copolymers increased with increasing the radialization dosage. However, the recovery speed decreased with increasing the radialization dosage at the same temperature of 95°C.

Application of macro fibre composite in driving a tail of a biomimetic fish

Abstract: The Macro Fiber Composite (MFC) is an actuator that offers high performance and flexibility. The application of MFC in the field of driving biomimetic tail is discussed in the paper. Making full use of the d33 effect, a piece of aluminum lamina with certain thickness is sticked in order to make the structures divided by the PZT fibers in MFC dissymmetrical. When applying voltage on the MFC, the structure will have a certain bending angle which is utilized to offer swinging power for the tail. In this paper, the ideal driving effect has been got with the limited driving force via the study of material property, material thickness, shape and size of the metal piece connected to the MFC, method of connection, the shape of the under water part of the fish. A reasonable shape and swinging strategy for biomimetic fish is designed according to the observation to the movement of alive fish and the study of bionics. The results of the experiment indicate that the largest extend of the tail's swinging angle in the air is 4 degree. The available frequency for the fastest speed is 2.5Hz. Comparing with the traditional biomimetic fish, it has the advances of small cubage, little noise, simple structure, and could be controlled in speed and extent because there is no motor inside. And the limit ability of driving, the uncontrollable feature of floating and sinking, and the existence of the power wires need to be solved in the coming research.

Shape Memory Nanocomposite and Its Application

Abstract: This presentation cover s the fabrication ; characterization and potential application of electro activate shape memory polymer (SMP) containing multi -walled carbon nanotubes (MWCNTs) , hybrid fillers of carbon black (CB) and short carbon fiber (SCF) , and magnetic Ni power . The electrical conductivity of 8 wt% MWNTs composite is 1.25 ×10 -2 S/cm with dim ension of 8.0 cm × 2.0 cm × 0.2 cm rectangle sheet, it can be triggered by passing an electrical current with a constant voltage of 200 V. While, t he electrical conductivity of the composite , containing 5 wt% CB and 2 wt % SCF , reaches to 3 S/cm . Their shap e recovery can be induced by passing an electrical current of 25 V voltages . SMP filled with 10 vol % Ni, induced by 20 V. Then t emperature -dependent resistivity test is done to investigate the thermo -sensitive effects in conducting polymer composite , and it show s a classical negative temperature coefficient (NTC) effect ranged from 70 o C to 90 o C. Thus smart thermal sensor using conducting SMP composite can be realized through resistivity change.

Infrared Laser-Activated Shape Memory Actuators

Abstract: This paper is concerned about the drive of shape memory styrene copolymer through an infrared optical fiber carrying infrared laser. As one of novel actuators in smart materials, shape memory polymers (SMP) have been investigated widely. The infrared laser was chose to drive the SMP through the optical fiber embedded into the SMP. The working frequency of infrared laser was installed in 3-4µm, the working band of optical fiber was 1-6µm. An optical fiber was embedded into the SMP for delivery of 3 -4µm laser light for activation. The surface of the optical fiber was etched by the aqueous solution of sodium -hydroxide in order to increase trans mission efficiency of the optical fiber . The SMP based on styrene copolymer have been synthesized , the SMP was thermoset , and its Tg was the 53.7 o C. The thermally activated SMP is possible to initiate an originally shape by a touch less and highly selectiv e infrared laser stimulus. The optical fiber was treated by the aqueous solution of sodium -hydroxide, transmission efficiency of the optical fiber increased, and the total contact area between SMP and the optical fiber. The infrared laser stimulation of SM P is interest for sensor and actuator systems as well as medical applications.