Nanocellulose-based soft actuators and their applications

Nanocellulose has aroused growing attention in the design and fabrication of multifarious soft actuators thanks to its abundant source, appropriate mechanical properties, and sustainability. In this mini-review, an up-to-date account of recent progresses in nanocellulose-based actuators with homogeneous and heterogeneous structures is provided. The fundamental design concepts and synthesis strategies for nanocellulose-based soft actuators with a wide array of micro-architecture are described. Moreover, their actuation mechanisms, structure–function relationships, and emerging applications in the fields of soft robotics, biomedical science and bioelectronics are highlighted. Finally, a brief conclusion, the current challenges, and future perspectives in the development of nanocellulose-based actuators is presented. This mini-review provides new insights into the fundamental research and the technological application of advanced nanocellulose-based soft actuators.     

八极杆碰撞/反应池(ORS)-电感耦合等离子体质谱(ICP-MS)法测定复杂矿物中的稀土元素

对未知复杂矿物样品采用扫描电子显微镜-能谱法解析样品,确定基本成分后选择合适的样品前处理方法。实验中采用过氧化钠熔融法熔解样品,用水浸出,硝酸酸化后制备待测样品溶液。以Rh为内标,用八极杆碰撞/反应池(ORS)-电感耦合等离子体质谱(ICP-MS)法测定了复杂样品中的稀土元素。多次测定同一混合标准溶液结果的相对标准偏差(RSD,n=11)小于4%,加标回收率为90%~110%。方法适用于未知复杂矿物中稀土元素的测定。     

Negative thermal expansion of poly(vinylidene fluoride) and polyethylene tie molecules: A molecular dynamics study

The mechanism of thermal actuation for poly(vinylidene fluoride) (PVDF) and polyethylene (PE) tie molecules has been investigated using molecular dynamics simulations. Tie molecules are found in semicrystalline polymers and are polymer chains that link two (or more) crystalline lamellae, allowing for the transfer of force between these regions. A novel simulation technique has been developed to enable measurement of changes in the tie molecule length upon heating. We investigate the dependence of the percentage actuation observed upon heating, on the external applied force that stretches the tie molecules, the temperature range used for heating as well as the length and the number of tie molecules. Two molecular level mechanisms for actuation are identified. An entropically driven mechanism occurs at low applied forces and is applicable to all flexible polymers. A second mechanism due to conformational changes is observed for PVDF but not for PE at intermediate applied forces. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2223–2232     

Liquid crystal elastomer actuators: Synthesis,alignment, and applications

Liquid crystal elastomers (LCEs) are a unique class of materials which combine rubber elasticity with the orientational order of liquid crystals. This combination can lead to materials with unique properties such as thermal actuation, anisotropic swelling, and soft elasticity. As such, LCEs are a promising class of materials for applications requiring stimulus response. These unique features and the recent developments of the LCE chemistry and processing will be discussed in this review. First, we emphasize several different synthetic pathways in conjunction with the alignment techniques utilized to obtain monodomain LCEs. We then identify the synthesis and alignment techniques used to synthesis LCE‐based composites. Finally, we discuss how these materials are used as actuators and sensors. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 395–411     

Extraordinarily large swelling energy of iodine‐treated poly(vinyl alcohol) demonstrated by jump of a film

Organic material characteristics of volume change and stress generation have attracted the attention of many researchers aiming to develop chemomechanical systems such as artificial muscles and polymer engines having the advantages of high energy density and silent operation. Although polymer gels offer a relatively large actuator stroke, their mechanical properties are relatively poor and the working temperature is relatively low, often limited by the evaporation of liquid if contained. We have developed an iodine‐treated poly(vinyl alcohol) having extraordinarily large vapor‐induced deswelling stress reaching 59 MPa, which is one to two orders of magnitude greater than those of ordinary polymer gels. Furthermore, this material has extremely large volumetric and gravimetric energy densities reaching 1.3 × 10⁶ J m^?3 and 9.6 × 10² J kg^?1, respectively, and an elastic modulus of a few GPa and is heat‐resistant to at least 200 °C. The high performance of this material can be demonstrated by a jump of a film. © 2014 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1357–1365     

Light‐ and Humidity‐Induced Motion of an Acidochromic Film

A smart acidochromic agarose‐based film with 1,4‐bis(para‐hydroxystyryl)benzene as the pH‐responsive fluorophore was prepared. This film can simultaneously harness the chemical potential of light and aerial humidity gradients to convert them into mechanical work. The strong reversible hygroscopicity of the agarose matrix induces swift locomotion by mechanical deformation owing to exchange of water with the surroundings. Driven by humidity, a 20 mg composite film coupled to a piezoelectric bending transducer sensor generates a peak output of approximately 80 mV, which corresponds to a power density of 25 μW kg^?1. Excitation with UV light triggers isomerization of the chromophore, which appears as reshaping by spiraling, bending, or twisting of the film. The material also responds to changes in the pH value by reversible protonation of the fluorophore with rapid changes in color and fluorescence. The threefold sensing capability of this smart material could be utilized for the fabrication of multiresponsive actuating dynamic elements in biomedicine and soft robotics.     

Structure and packing of aminoxyl and piperidinyl acrylamide monomers

The closely related title compounds, 4‐acrylamido‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl, C₁₂H₂₁N₂O₂, (I), and N‐(2,2,6,6‐tetramethylpiperidin‐4‐yl)acrylamide monohydrate, C₁₂H₂₂N₂O·H₂O, (II), are important monomers in the preparation of redox‐active polymers. They comprise an acrylamide group of the usual s‐cis configuration appended to a 2,2,6,6‐tetramethyl‐substituted piperidine‐1‐oxyl radical or a piperidinyl chair, respectively. The adjacent amide and piperidinyl H atoms are approximately trans across the C—N bond. The packing in (I) is dominated by N—H...O hydrogen bonds; these are supported by C—H...O contacts to form an R₂¹(6) ring repeat, a motif which has been observed in other acrylamide structures. In (II), hydrogen bonds are again key to the packing arrangements. In this case, the incorporated solvent water molecule acts as an acceptor through its O atom and as a donor through both H atoms, binding three adjacent piperidinylacrylamide molecules into layers. In both structures, weak C—H...O contacts involving the piperidinyl methyl H atoms and a proximal acrylamide carbonyl O atom extend the structure in the third dimension.     

Double-layered piezo-thermoelastic hollow cylinder under some coupled loadings

In the present paper, a long thick-walled piezo-thermoelastic hollow cylinder with double layers is studied. The effects of temperature on the performance of the cylinder are obtained. Based on the theory of elasticity, the exact solutions of the cylinder under some coupled loadings are found. In the present paper, differences of a piezoelectric parameter between the two layers is taken into account. For comparison, numerical results have been carried out for both double-layered and graded cylinders. At the end of the present paper some discussions are addressed.     

Regional eigenvalue-clustering robustness of linear output feedback systems with both time-varying structured and unstructured uncertainties as well as nonlinear actuators

This paper investigates the regional eigenvalue-clusteringrobustness of linear output feedback systems with both time-varyingstructured (elemental) and unstructured (norm-bounded) parameteruncertainties as well as nonlinear actuators. A sufficient conditionis proposed for ensuring that all the eigenvalues of outputfeedback systems with both time-varying structured and unstructuredparameter uncertainties as well as nonlinear actuators remaininside the specified region. No restriction is imposed on theshapes of the specified region. The proposed method is applicableto both the continuous-time case and the discrete-time case.When all the eigenvalues are just required to locate in thestable region, the proposed criterion will become the stabilityrobustness criterion. Two numerical examples are given to illustratethe application of the proposed sufficient condition.