Development of Paper Actuators Based on Carbon-Nanotube-Composite Paper

We propose a unique soft actuator—a paper actuator—based on carbon-nanotube-composite paper (CNT-composite paper), which is a composite of carbon nanotubes (CNTs) and paper. CNT-composite paper has highly efficient properties because of the contained CNTs, such as high electrical conductivity and semiconducting properties. We are considering using CNT-composite paper for various devices. In this study, we successfully developed a paper actuator. We determined the structure of the paper actuator by referencing that of bucky-gel actuators. The actuator operates using the force generated by the movement of ions. In addition to making the paper actuator, we also attempted to improve its performance, using pressure as an index and an electronic scale to measure the pressure. We investigated the optimal dispersant for use in paper actuators, expecting the residual dispersant on the CNT-composite paper to affect the performance differently depending on the type of dispersant. Referring to research on bucky-gel actuators, we also found that the addition of carbon powder to the electrode layers is effective in improving the pressure for paper actuators. We believe that the paper actuator could be used in various situations due to its ease of processing.     

Flow control with plasma-based actuator in different velocity regimes: Momentum and heat transfer effects

In this study, control of the airflow by the direct current (DC) electrical discharge with bare electrodes has been investigated in different velocity regimes. The discharge characteristics of the plasma model are obtained numerically. An induced electrohydrodynamic (EHD) force on neutral flow was characterized based on momentum transfer from charged particles. The change in the incident flow parameters was studied by applying Navier–Stokes (N-S) equations, considering source terms arising from a weakly ionized plasma. The effect of the discharge on the low- and high-speed flow was simulated in this study. It was concluded that the changes of the velocity profile, airflow pressure, and oblique shock wave could be attributed to the EHD force from a nonthermal plasma to the incoming airflow. It was seen that the incident airflow is accelerated also by the induced EHD force. Our results show that the most important mechanism in the plasma-based flow control is the momentum transfer from the electrical discharge to the incident flow and that the gas heating has no significant role.     

Synthesis and characterization of an azobenzene‐ and acrylamide‐based photoresponsive copolymer and gel

This article reports the synthesis and characterization of a new type of copolymer consisting of acrylamide and trans‐4‐methacroyloxyazobenzene and their gel. Free‐radical polymerization initiated with 2,2′‐azobisisobutyronitrile was used to conduct the synthesis although N,N′‐methylene bisacrylamide was used as a crosslinking agent for the gel synthesis. Despite the insolubility of the different monomers in a single solvent, a certain ratio of water/tetrahydrofuran (THF) enabled the propagating species to stay in the solution and thus to facilitate chain growth. The solubility, Fourier transform infrared spectra, and solid‐state ¹³C NMR investigations revealed that two monomers in the copolymer were chemically bonded. The compositions of the incorporated acrylamide and azobenzene in the copolymer and the gel were determined by NMR spectroscopy. Because the potential actuating behavior of such materials was due to the volume change involved in reversible solvent uptake, the sorption and evaporation of the gel were also investigated and showed that the gel could absorb about 460% water, which corresponded to a polymer content of the weight gel of 18% and was compatible with thermogravimetric analysis of a saturated gel that revealed about 83 wt % of a swollen gel was lost within 12 h. Finally, photoinduced trans–cis isomerization kinetics of the copolymer was investigated in a 30:70 mixture of water and THF against irradiation time. A photostationary state was reached within 5.5 min with a corresponding conversion of 70% of the trans isomer to the cis form. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2886–2896, 2004     

溶剂型智能驱动材料的研究进展

智能驱动材料可对光、电、温度、溶剂、湿度等外界刺激做出可控的力学响应,并将这些能量转化为机械能而被广泛关注.溶剂型驱动材料是基于简单的湿度或溶剂气氛变化将化学能转换成机械能,并在机械发电、微型器件制备等方面具有重要的潜在应用.本文综述了溶剂型智能驱动材料的驱动类型、驱动原理,性能及其相关应用进展,并对溶剂型智能驱动材料在未来人工智能方面的应用前景进行了展望.     

Experimental and computational study of the flow induced by a plasma actuator

A complementary experimental and computational study of the flow field evoked by a plasma actuator mounted on a flat plate was in focus of the present work. The main objective of the experimental investigation was the determination of the vector force imparted by the plasma actuator to the fluid flow. The force distribution was presently extracted from the Navier–Stokes equations directly by feeding them with the velocity field measured by a PIV technique. Assuming a steady-in-mean, two-dimensional flow with zero-pressure gradient, the imbalance between the convective term and the momentum equation’s right-hand-side terms reveals the desired resulting force. This force-distribution database was used afterwards as the source term in the momentum equation. Furthermore, an empirical model formulation for the volume-force determination parameterized by the underlying PIV-based model is derived. The model is tested within the RANS framework in order to predict a wall jet-like flow induced by a plasma actuator. The Reynolds equations are closed by a near-wall second-moment closure model based on the homogeneous dissipation rate of the kinetic energy of turbulence. The computationally obtained velocity field is analysed along with the experimental data focussing on the wall jet flow region in proximity of the plasma actuator. For comparison purposes, different existing phenomenological models were applied to evaluate the new model’s accuracy. The comparative analysis of all applied models demonstrates the strength of the new empirical model, particularly within the plasma domain. In addition, the presently formulated empirical model was applied to the flow in a three-dimensional diffuser whose inflow was modulated by a pair of streamwise vortices generated by the present plasma actuator. The direct comparison with existing experimental data of Grundmann et al. (2011) demonstrated that the specific decrease of the diffuser pressure corresponding to the continuous forcing was predicted correctly.     

Using a thin actuator as secondary source for hybrid passive/active absorption in an impedance tube

This paper describes the practical implementation of a piezoelectric actuator as secondary source for hybrid passive/active broadband sound absorption in a standing-wave tube. This actuator consists of a thin circular aluminium plate driven by a piezoelectric patch and glued to a flexible rubber support. The resulting device has been mounted in a thin metallic ring that fits perfectly to the tube diameter. Passive absorption is afforded by either a porous layer or a microperforated panel, backed by an air gap. Active absorption is accomplished by releasing the sound pressure at a microphone behind the material, using either a loudspeaker or the actuator as secondary source. Results of broadband sound absorption reveal the feasibility of the piezoactuator. Compared to the loudspeaker, this actuator allows to greatly reduce the whole thickness of the hybrid absorber.     

Preparation of liquid crystalline polymer networks containing a cinnamyl group in the main chain with tunable thermal actuation behavior

A series of liquid crystalline copolyesters (LCPs) with different concentrations of a photocrosslinking moiety have been synthesized by random polycondensation with 4,4′‐bis(6‐hydroxyhexyloxy)biphenyl, 2‐phenylsuccinic acid, and 4‐(6‐hydroxyhexyloxy)cinnamic acid (6HCA). Multifunctional monodomain liquid crystal networks (LCNs) with considerable and tunable actuation behavior are obtained by postphotocrosslinking. The influence of the photocrosslinking moiety on the phase transition behavior of the LCP and actuation behavior of the LCN has been investigated. The results suggest that incorporating 6HCA suppresses the smectic phase of the LCP and decreases the nematic‐isotropic phase transition temperature. Moreover, the starting actuation temperature of the LCN decreases from 55 to 40 °C as the 6HCA reached 50%. In addition, the actuation force and storage modulus of the LCN actuators are enhanced by incorporating a high concentration of 6HCA. A 1.64 MPa contractile force can be achieved, and it can lift burdens 1300 times heavier than its weight when 50% 6HCA is incorporated into the LCP. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 904–911     

Polymeric piezoelectric cantilever and tubular actuators

Electroactive polymers (EAPs) have attracted a great deal of attention in the last decade due to their unique properties that are applicable to many advanced applications. The present work aims to study the materials–property relationship of this class of materials, and thus facilitate the implementation of EAPs in more applications. The present work investigated the feasibility of adapting cantilever and tubular configurations to the polymeric piezoelectric actuators. The polarization and displacement of samples (fabricated from Poly(Vinyldene fluoride‐trifluroethylene) [P(VDF‐TrFE)] thin film) were measured under both dynamic and static driving conditions. The polarization loops for all the samples exhibit little hysteresis under weak field and the polarization changes linearly with voltage for most samples. The frequency‐dependent polarization behavior is consistent with the previous reported work. The displacements for both cantilever and tubular samples are also noted to be in agreement with the theoretical prediction. Significant displacement (1079 µm) was achieved for samples, even under weak field (60 MV/m). In summary, the results have suggested that the relationship between geometric variables and the performance is also applicable to polymeric materials. Thus, the constitutive relationship can also be applied as a guideline for designing and optimizing the polymeric actuators beyond P(VDF‐TrFE) copolymer materials. Copyright © 2009 John Wiley & Sons, Ltd.     

Simulation of an electrohydrodynamic DC actuator

A semiempirical model of the electrohydrodynamic actuator operating on the basis of a dc corona discharge is proposed. The model is based on calculations of an electric field and a unipolar ion jet generated by a linear ion source on the surface of a dielectric plate and propagating along the plate in the laminar boundary layer. The ion source intensity and the potential difference on the actuator electrodes are determined experimentally. Estimates of the velocity induced by the electrohydrodynamic action in the flat-plate laminar boundary layer are obtained on the basis of the model. A comparison of the calculation results with the available experimental data confirms the adequacy of the model proposed. The effect of the adsorption properties of the dielectric surface on the distributions of the volume and surface electric discharge in the boundary layer is investigated within the framework of this model.     

Effect of chitosan and ions on actuation behavior of cellulose–chitosan laminated films as electro-active paper actuators

Cellulose-chitosan laminated films were made for Electro-Active Paper (EAPap) actuators and the effect of chitosan and different types of free ions namely, Cl⁻, NO₃⁻ and CF₃COO⁻ were investigated on the actuation behavior. The fabrication process of the films was explained and the actuation performance was tested in terms of bending displacement of the actuators. It was observed that, chitosan content and type of free ions influence the tip displacement of the actuators. Cl⁻ was found the best free ion among others, and detail observations are explained. By laminating chitosan layer on the cellulose films, the humidity sensitiveness of cellulose EAPap actuators was reduced.