Rigid Segments Research Articles

Facile In-situ Polymerization of Thermotropic Liquid Crystalline Polymers as Thermally Conductive Matrix Materials

Although thermally conductive composites that can efficiently dissipate the heat generated from electronic devices are in high demand, most neat polymers used as matrix materials are problematic because they have poor thermal conductivities. The low thermal conductivity of polymeric materials is caused by structural defects; therefore, it can be improved by increasing the orientational regularity of the polymer chains. Here, main-chain liquid crystalline polymers (LCPs) were designed and synthesized to investigate the effects of liquid crystallinity-induced structural regularity on the thermal conductivity of the polymers. In addition, an in-situ polymerization method was devised for commercial applicability, and the thermal conductivity of the obtained polymer was compared to that of a conventionally polymerized polymer having the same structure. The designed polymers exhibited thermotropic liquid crystalline characteristics, and the polymer with longer spacers between the rigid segments showed relatively higher thermal conductivity exceeding 0.5 W·m-1· K-1 after sample preparation by injection molding. In addition, X-ray diffraction analysis revealed that the differences in the thermal conductivity, depending on the molding temperature during specimen preparation, were caused by variations in chain orientation within the same polymer. Based on the obtained results, it was concluded that LCPs are strong candidate matrix materials for thermally conductive composites; the suggested in-situ polymerization method could be applied practically to the polymerization of polyester-type LCPs.

Effects of Regular Networks Composed of Rigid and Flexible Segments on the Shape Memory Performance of Epoxies

A series of regular rigid–flexible cross-linking epoxy networks were prepared from dithiol allyl glycidyl ethers (DTAGEs) and 4,4′-diaminodiphenylmethane (DDM). In these networks, the chemical structure of DTAGEs was tidily flexible and that of DDM was simply rigid, which ensured the flexible segments were more distinguishable from the rigid units. The effects of regularity and rigid–flexible character of the networks on shape memory properties, especially shape recovery speed, were investigated in detail. It was found that the shape recovery speed was reversely proportional to the flexibility of the regular cross-linking networks. Compared with flexibility, regularity had a greater impact on the recovery speed. In addition, regularity had a significant influence on the recovery speed of the rigid units while it had little influence on that of the flexible segments. The well-designed regular rigid–flexible cross-linking networks exhibited excellent shape memory performance with high shape memory fixity (≥...

Preparation and characterization of titanium-segmented polyurethane composites for bone tissue engineering.

Segmented polyurethanes were prepared with polycaprolactone diol as soft segment and 4,4-methylene-bis cyclohexyl diisocyanate and l-glutamine as the rigid segment. These polyurethanes were filled with 1 wt.% to 5 wt.% titanium particles (Ti), physicochemically characterized and their biocompatibility assessed using human dental pulp stem cells and mice osteoblasts. Physicochemical characterization showed that composites retained the properties of the semicrystalline polyurethane as they exhibited a glass transition temperature (Tg) between -35°C and -45°C, melting temperature (Tm) at 52°C and crystallinity close to 40% as determined by differential scanning calorimetry. In agreement with this, X-ray diffraction showed reflections at 21.3° and 23.6° for polycaprolactone diol and reflections at 35.1°, 38.4°, and 40.2° for Ti particles suggesting that these particles are not acting as nucleating sites. The addition of up to 5 wt.% of Ti reduced both, tensile strength and maximum strain from 1.9 MPa to 1.2 MPa, and from 670% to 172% for pristine and filled polyurethane, respectively. Although there were differences between composites at low strain rates, no significant differences in mechanical behavior were observed at higher strain rate where a tensile stress of 8.5 MPa and strain of 223% were observed for 5 wt.% composites. The addition to titanium particles had a beneficial effect on both human dental pulp stem cells and osteoblasts viability, as it increased with the amount of titanium in composites up to 10 days of incubation.

The Balanced Insulating Performance and Mechanical Property of PP by Introducing PP-g-PS Graft Copolymer and SEBS Elastomer

The PP/PP-g-PS/SEBS blends are prepared by melt extrusion in order to improve both insulating properties and toughness of PP. SEBS is used to reduce the rigidity of PP, while the insulating properties are improved by adding PP-g-PS without decreasing mechanical properties. The microstructure of PP blends is carefully investigated by SEM, DMA, XRD, and DSC. It is interesting to find that a core–shell dispersion phase formed in the blend with the adding of PP-g-PS, and the size of core is decreased while the thickness of shell is increased with further increasing volume of PP-g-PS. Due to this special structure, the nucleation ability of SEBS is decreased. Meanwhile, the rigid segments and compatibilization effect of PP-g-PS not only increased the glass transition temperature of both PP and SEBS, but also enhanced their adhesion. Therefore, the electrical properties were increased without decreasing the mechanical properties of the blends. Consequently, an insulation material with excellent mechanical prope...

Parametric study of an enhanced passive absorber used for tremor suppression

Passive absorbers are designed to be attached to upper limb systems to reduce tremor of patients suffering from Parkinson's disease. Several works were done previously to show the effectiveness of the low cost passive controllers, which can reduce the undesired vibrations without power requirements. An improved type of such controllers is suggested in this paper. The mechanical absorber is a two-degree-of-freedom (DOF) system, which is formed by an elastic absorber connected in series to a viscous damper one, naming the system the Series Elastic Viscous Damper (SEVD). It was able to cause a high reduction in the amplitude of the tremor and operate over a wide frequency range. The lumped parameters of each absorber within the SEVD absorber are chosen to satisfy the tuning conditions. The device is tested numerically on the forearm of a biodynamic upper limb structure to check its capability in reducing the tremor at the limb's proximal joints. The limb was modeled as rigid segments with a three DOF flexion-extension angular motion in the horizontal plane. This study seeks to analyze the effect of the SEVD damping coefficient, total mass, and mass distribution on the reduction of the displacement amplitude at the joints, with stiffness chosen to satisfy the tuning condition for the undesired frequency of tremor. It was found that very low damping coefficients are not suitable to provide reduction at all joints simultaneously; high absorber's total mass can slightly increase the performance and equally, distributed dual masses can be a good selection.

Soft Gripper using Variable Stiffness Mechanism and Its Application

Soft robots have advantages such as low weight and compact size compared to rigid robots. Variable stiffness is one of the key methods of improving the performance of a soft robot. The soft gripper grasps objects of various shapes or sizes based on the variable stiffness. In a previous study, we validated the variable stiffness mechanism where flexible and rigid segments were connected alternately in series. This paper presents a soft variable stiffness gripper that can be used to control the stiffness by pulling tendons. The soft gripper has three variable stiffness structures acting as fingers and the stiffness can be controlled using two motors by winding tendons. To understand the tendency of the stiffness variation and determine the design parameters, a compliant mechanism was developed using a pseudo-rigid-body model (PRBM). The experimental results show that the difference between the lowest and highest stiffness values of the fabricated variable stiffness gripper was 5.6 times the original. Similarly, the difference in the gripping weight was 19 times. Using the experimental results, the variable stiffness gripper can be designed and manufactured based on the required stiffness and used to grip various types of objects.

Amyloid structure of high-order assembly of Leucine-rich amelogenin revealed by solid-state NMR

High-order assemblies of amelogenin, the major protein in enamel protein matrix, are believed to act as the template for enamel mineral formation. The Leucine-rich amelogenin (LRAP) is a natural splice-variant of amelogenin, a functional protein in vivo, containing conserved domains of amelogenin. In this work, we showed LRAP aggregates hierarchically into assemblies with various sizes including scattered beads, beads-on-a-string and gel-like precipitations in the presence of both calcium and phosphate ions. Solid-state NMR combined with X-ray diffraction and microscopic techniques, was applied to give a picture of LRAP self-assemblies at the atomic level. Our results, for the first time, confirmed LRAP assemblies with different sizes all contained a consistent rigid segment with β-sheet secondary structure (residues 12–27) and the β-sheet segment would further assemble into amyloid-like structures.

Controlling Molecular Conformation for Highly Efficient and Stable Deep-Blue Copolymer Light-Emitting Diodes.

We report a novel approach to achievedeep-blue, high-efficiency, and long-lived solution-processed polymer light-emitting diodes (PLEDs) via a simple molecular level conformation change of an emissive conjugated polymer.We introduce rigid β-phase segments into a 95% fluorene-5% arylamine copolymer emissive layer. The arylamine moieties at low density act as efficient exciton formation sites in PLEDs, whereas the conformational change alters the nature of the dominant luminescence from a broad, charge transfer like emission to a significantly blue-shifted and highly vibronically structured excitonic emission. As a consequence, we observe a significant improvement in the Commission International de L'Eclairage ( x, y) coordinates from (0.149, 0.175) to (0.145, 0.123) while maintaining high efficiency and improved stability. We achieve a peak luminous efficiency, η = 3.60 cd/A, and a luminous power efficiency, ηw = 2.44 lm/W, values that represent state-of-the-art performance for single copolymer deep-blue PLEDs. These values are 5-fold better than for otherwise-equivalent, β-phase poly(9,9-dioctylfluorene) PLEDs (0.70 cd/A and 0.38 lm/W). This report represents the first demonstration of the use of molecular conformation as a simple but effective method to control the optoelectronic properties of a fluorene copolymer; previous examples have been confined to homopolymers.

Direct Position‐Based Solver for Stiff Rods

AbstractIn this paper, we present a novel direct solver for the efficient simulation of stiff, inextensible elastic rods within the position‐based dynamics (PBD) framework. It is based on the XPBD algorithm, which extends PBD to simulate elastic objects with physically meaningful material parameters. XPBD approximates an implicit Euler integration and solves the system of non‐linear equations using a non‐linear Gauss–Seidel solver. However, this solver requires many iterations to converge for complex models and if convergence is not reached, the material becomes too soft. In contrast, we use Newton iterations in combination with our direct solver to solve the non‐linear equations which significantly improves convergence by solving all constraints of an acyclic structure (tree), simultaneously. Our solver only requires a few Newton iterations to achieve high stiffness and inextensibility. We model inextensible rods and trees using rigid segments connected by constraints. Bending and twisting constraints are derived from the well‐established Cosserat model. The high performance of our solver is demonstrated in highly realistic simulations of rods consisting of multiple 10 000 segments. In summary, our method allows the efficient simulation of stiff rods in the PBD framework with a speedup of two orders of magnitude compared to the original XPBD approach.

Solvent effect on FRET spectroscopic ruler.

A discrepancy has emerged in recent years between single-molecule Förster resonance energy transfer (smFRET) measurements and small angle X-ray scattering (SAXS) or small angle neutron scattering experiments in the study of unfolded or intrinsically disordered proteins in denaturing solutions. Despite significant advances that have been made in identifying various factors which may have contributed to the manifestation of the so-called smFRET-SAXS discrepancy, no consensus has been reached so far on its original source or eventual resolution. In this study, we investigate this problem from the perspective of the solvent effect on FRET spectroscopic ruler (SEFSR), a generic term we use to describe various solvent-dependent factors affecting the accuracy of the FRET experimental method that is known as a "spectroscopic ruler." Some factors belonging to SEFSR, such as direct dye-solvent interaction and labeling configuration, seem to have not received due attention regarding their significance in contributing to the discrepancy. We identify SEFSR by measuring a rigid segment of a double-stranded DNA in various solutions using the smFRET method and evaluate its relative importance in smFRET experiments by measuring segments of a single-stranded DNA and polyethylene glycol (PEG) in solutions. We find that SEFSR can produce non-negligible FRET-inferred interdye distance changes in various solutions, with an intensity following the Hofmeister series in ionic solutions and dependent on labeling configurations. SEFSR is found to be significant in GuHCl and urea solutions, which can fully cover the apparent expansion signal of dye-labeled PEG. Our findings suggest that SEFSR may have played an important role in contributing to the smFRET-SAXS discrepancy.

Towards Shape-Changing Devices: Physical Interface Control with an Active Contour Model

This paper proposes a novel tangible interface system to enhance the immersive experience in virtual reality environments. The proposed system allows representing physical properties of the tool, such as the deflection of the elastic rods, which users handle in a virtual and physical environment. This system is composed of two parts; one is an articulated interface to visually represent the physical behavior and the other is a computational algorithm that can compute a set of 6-DOF positions of the links. The proposed computational algorithm extends an active contour model, which is used primarily in computer vision and image processing, incorporating a spring and damping constraint energy functional. An elastic rod is modeled as a series of rigid line segments with a symmetric relationship between neighboring segments, and its shape is modeled to be influenced by energies that are induced by a user, and the external deformation of the spline. The symmetric and sparse properties of the proposed model enable an efficient energy minimization process, and the modification of a number of the line segments. Based on this configuration, we construct an energy generation method based on the positional displacement of the base element to generate the deflection behavior of the contour according to the user’s motion in the space. Therefore, the physical device can simulate a variety of deformable objects by modulating energy parameters during the energy minimization process. Experimental results demonstrate the feasibility of emulating various behaviors of deformable splines, and applying to virtual reality system without interfering with the motion-to-photon latency. We also discuss the method’s limitations and explore its potential.

Flutter instability of freely hanging articulated pipes conveying fluid

We experimentally investigate the stability of freely hanging articulated pipes made of rigid segments connected by flexible joints and with their displacements constrained in a vertical plane. When the velocity of the fluid conveyed by the pipe is increased, flutter-type instability occurs above a critical value. The critical velocity and the characteristics of the flutter modes (frequency, amplitude, and shape) are determined as a function of the number n of segments into the pipe which is varied from 2 to 5. Experimental results are compared to predictions from linear stability analysis extending previous studies by taking into account damping due to the dissipation in the joints. Qualitative agreement is found and the limits of the analysis are discussed.

Hencky Bar-Net Model for Vibration of Rectangular Plates with Mixed Boundary Conditions and Point Supports

This paper is concerned with the development of the Hencky bar-net model (HBM) for free vibration analyses of rectangular plates with mixed boundary conditions and point supports. The HBM is a two-dimensional discrete net system composed of rigid segments connected by frictionless hinges and rotational springs. In the model, bending is accommodated by rotational springs at each joint while the twisting by a diagonal spring system in each grid cell. The total mass of the plate is distributed as lumped mass at each joint and the continuous boundary stiffness of plate is simulated by springs located at the edge joints. Owing to the discrete property of HBM, it is able to readily handle any boundary conditions of plates including mixed boundary conditions and point supports. The HBM is herein used to solve some vibration problems of rectangular plates with mixed boundary conditions and point supports to demonstrate its accuracy and convenience for plate analyses.

Design of a one-dimensional flexible structure for desired load-bearing capability and axial displacement

ABSTRACTA flexible spine is capable of bearing both transverse and axial external loads. At the same time, it is observed in animals that the spine deforms substantially during their motion and this allows the body to move efficiently and achieve high speeds. This paper deals with the modeling and design of one-dimensional flexible objects for a desired load-carrying capability and axial deflection. The flexible one-dimensional object is modeled as a serial chain of rigid segments connected by one-degree-of-freedom rotary joints with torsional springs and dampers at the joints. For a desired transverse and axial loading, optimization techniques are used to obtain the values of orientation of the rigid segments, the joint stiffness and damping, which gives the desired axial displacement and the shape. It is shown that changing the orientation or the shape of the one-dimensional structure has more effect than changing the stiffness at the joints. Various types of loading and axial deflections are considered and the optimization procedure is illustrated through numerical examples. The response of such a flexible structure to a transient periodic loading is also obtained.

Sphenopterid diversity in the Kungurian of Tregiovo (Trento, NE-Italy)

The lower Permian fossiliferous deposit of Tregiovo, in the upper Val di Non (Trento Province, N-Italy), is known from the beginning of last century, since it has yielded invertebrate and vertebrate footprints, palynomorphs, conchostracans, and especially plant remains. In recent years, a new section in the Tregiovo Formation, called “Le Fraine”, located along the Lauregno provincial road, has been discovered. Two fossiliferous layers in this new section, one in the lower and one in the upper part of the section, yielded different plant assemblages. The radiometric dating of the volcanic formations under- and overlying the Tregiovo Formation, indicates a middle Kungurian age for the fossil-bearing sequence. More than 1000 specimens, impressions and compressions but without cuticles, have been found. The two plant assemblages are rich and diverse, and both are dominated by conifers (e.g., Feysia, Hermitia, Dolomitia) that range from 60 to 80% of the total assemblage, but also sphenophytes (Annularia), taeniopterids (Taeniopteris) and ginkgophytes (Sphenobaiera) occur. Most remarkable of these two assemblages is the high diversity of sphenopterids that are sometimes preserved as complete fronds. At least five different species can be attributed to the genus Sphenopteris, i.e. Sphenopteris kukukiana, Sphenopteris suessii, Sphenopteris. sp. cf. S. geinitzii, Sphenopteris sp. and a morphotype that represents a new species, Sphenopteris valentinii. The leaves of most Sphenopteris species look pretty stiff and have strongly dissected pinnules with very narrow, linear rigid segments, apparently being an adaptation to arid conditions. The Tregiovo flora is of great importance, not only because of its richness and diversity, especially with regard to sphenopterids, but also because it is one of the very few well-dated Kungurian floras from Euramerica.

Epoxidized Lignin Derivatives as Bio-based Cross-linkers Used in the Preparation of Epoxy Resins

Lignin, which is the most abundant aromatic polymer in nature, was used as a green substitute for the toxic bisphenol A. In particular, the ability of epoxidized lignin to simultaneously serve as a cross-linker and rigid segment was investigated. The epoxidized lignin was preferably reacted with a monofunctional amine, which acted as a chain extender, to evaluate its performance as a cross-linker, and in the presence of poly(ethylene glycol) diglycidyl ether as a soft segment to adjust the resin properties. Different poly(ethylene glycol) diglycidyl ether/lignin stoichiometric ratios were tested, whereas the amine/epoxy equivalent ratio was fixed at 1:2. Some of the remarkable resin samples were subjected to differential scanning calorimetry analysis and compared with blank samples that did not include lignin in the composition. Moreover, the evolution over time of the molecular weight distribution of the selected compositions was analyzed by gel permeation chromatography until the solubility in tetrahydrofuran was appreciable.

The Role of the Midfoot in Drop Landings.

The midfoot is instrumental to foot function; however, quantifying its roles in human movement has been difficult. A forceful dynamic activity like landing may help elucidate the midfoot's contribution to foot energetics and function. The main purpose of this study was to measure midtarsal joint kinematics and kinetics during a barefoot single-leg landing task. A secondary aim of this study was to explore the relationship between static foot posture and dynamic midfoot function. In a cross-sectional study design, 48 females (age = 20.4 ± 1.8 yr, body mass index = 21.6 ± 1.7 kg·m) performed drop landings from a height of 0.4 m onto split force platforms. Subjects hung from wooden rings and landed on their dominant leg. Midtarsal joint kinematic and kinetic data were recorded using a 14-camera optical motion capture system in conjunction with two in-ground force platforms and a custom kinetic three-segment foot model. Foot structure was measuring using the arch height index (AHI) and the static midtarsal joint angle from motion capture. Kinematic data revealed an average sagittal plane midtarsal joint range of motion of 27° through the landing phase. Kinetic data showed that between 7% and 22% of the total lower extremity joint, work during the landing was performed by the midtarsal joint. Both standing AHI and static midtarsal joint angle (static MA) were correlated with sagittal plane midtarsal joint range of motion (standing AHI: r = -0.320, P = 0.026; static MA: r = 0.483, P < 0.001) and with midtarsal joint work (standing AHI: r = 0.332, P = 0.021; static MA: r = -0.323, P = 0.025). The midfoot contributes substantially to landing mechanics during a barefoot single-leg landing task. Static foot posture measures have limited value in predicting midfoot kinematics and kinetics during sportlike landings.

Microphase separation idea to toughen CO2-based waterborne polyurethane

CO2 based waterborne polyurethane (CO2-WPU), especially high CO2 content one, suffered from the poor flexibility at low temperature due to high content of rigid carbonate segment. Here a microphase separation idea was proposed by introducing poly(butyl acrylate) (PBA) as soft phase to toughen CO2-WPU via an organic solvent free route, i.e., the polymerizable butyl acrylate acted as a pseudo-solvent during CO2-WPU prepolymer synthesis, it then experienced radical polymerization after formation of CO2-WPU, and finally forming a material with multi-phase structure. Benefiting from the separation of soft PBA phase and hard CO2-WPU phase in micro-size, a 368% increase in elongation at break (εb) and nearly 65 times increase in toughness at -10 °C was observed when PBA loading increased from blank to 65 wt%. As a comparison, the tensile strength (σm) and εb of the PBA/CO2-WPU blending film at room temperature was only 4.4 MPa and 383% when PBA loading was 50 wt%, while the PBA/CO2-WPU multi-phase film showed σm of 18.8 MPa and εb of 489%, respectively. The toughening effect was attributed to the more uniform micro-phase separation structure caused by molecular level inter-migration between PBA and CO2-WPU during preparation process.

Bioinspired, Spine-Like, Flexible, Rechargeable Lithium-Ion Batteries with High Energy Density.

The rapid development of flexible and wearable electronics proposes the persistent requirements of high-performance flexible batteries. Much progress has been achieved recently, but how to obtain remarkable flexibility and high energy density simultaneously remains a great challenge. Here, a facile and scalable approach to fabricate spine-like flexible lithium-ion batteries is reported. A thick, rigid segment to store energy through winding the electrodes corresponds to the vertebra of animals, while a thin, unwound, and flexible part acts as marrow to interconnect all vertebra-like stacks together, providing excellent flexibility for the whole battery. As the volume of the rigid electrode part is significantly larger than the flexible interconnection, the energy density of such a flexible battery can be over 85% of that in conventional packing. A nonoptimized flexible cell with an energy density of 242 Wh L-1 is demonstrated with packaging considered, which is 86.1% of a standard prismatic cell using the same components. The cell also successfully survives a harsh dynamic mechanical load test due to this rational bioinspired design. Mechanical simulation results uncover the underlying mechanism: the maximum strain in the reported design (≈0.08%) is markedly smaller than traditional stacked cells (≈1.1%). This new approach offers great promise for applications in flexible devices.

Sequential limit analysis of pipe–soil interaction during large-amplitude cyclic lateral displacements

A newly developed sequential limit analysis (SLA) technique is used to perform large-displacement numerical simulations relevant to thermally induced lateral buckling of untrenched subsea pipelines. A rigid plane-strain pipe segment, partially embedded in undrained clay, is subjected to cyclic lateral displacements with amplitudes of up to eight pipe diameters. A constant vertical dead load is applied to the pipe during each lateral sweep, but in some analyses this load is varied from one sweep to the next. The SLA method directly models the evolution of the soil surface profile, including active and dormant berms, and incorporates strain softening behaviour caused by soil remoulding. Comparisons of the numerical results with published centrifuge model test data, for a range of loading cases, are provided in terms of the pipe invert trajectory and lateral soil resistance. There is good overall agreement between the numerical and experimental results, demonstrating the suitability of SLA for solving such problems. Detailed aspects of the cyclic loading behaviour are discussed with reference to soil failure mechanisms and bearing capacity failure envelopes for combined vertical and horizontal loading. Finally, two brief parametric studies are used to explore the effects of the initial pipe embedment and vertical loading history on the subsequent lateral loading behaviour.