Properties Of Soft Materials Research Articles

New quaterphenyls laterally substituted by methyl group and their influence on the self-assembling behaviour of ferroelectric bicomponent mixtures

ABSTRACT Design of new functional binary mixtures possessing the self-assembling behaviour remains a highlighted task in order to tune the resulting properties of soft materials according to specific application demands. Three new chiral compounds with a quaterphenyl core substituted by the methyl group in different positions and having different linkage groups between the chiral chain and the rigid core were synthesised and used as smart dopants to the basic compound possessing a highly tilted orthoconic ferroelectric smectic phase. The main aim is to establish the effect of the miscibility on the basic parameters of the resulting binary mixtures, specifically on the mesomorphic behaviour, values of the spontaneous polarisation, tilt angle, helical pitch length and dielectric behaviour. As the quaterphenyl dopants differ between each other in the linkage group placed between the chiral chain and the rigid core, these compounds influence physical parameters of the resultant mixtures in a different way. A small amount of quaterphenyl dopants does not considerably decrease the tilt angle, but in the case of the -O- atom presence, it results in a visible decrease of the spontaneous polarisation and increase of the helical pitch length. However, in the case of the -COO- group presence, it increases spontaneous polarisation and decreases the helical pitch (<200 nm).

Optical tweezer measurements of asymptotic nonlinearities in complex fluids.

This article presents micro-medium-amplitude oscillatory shear (μMAOS), a method to measure the frequency-dependent micromechanical properties of soft materials in the asymptotically nonlinear regime using optical tweezers. We have developed a theoretical framework to extract these nonlinear mechanical properties of the material from experimental measurements and also proposed a physical interpretation of the third-order nonlinearities measured in single-tone oscillatory tests. We validate the method using a well-characterized surfactant solution of wormlike micelles, and subsequently employ this technique to demonstrate that the cytoplasm of a living cell undergoes strain softening and shear thinning when locally subjected to weakly nonlinear oscillatory deformations.

Hierarchical geometric designs for Fe-based amorphous materials with tunable soft magnetic properties

Tailoring the soft magnetic properties of magnetic materials is highly desired from both academic and technological standpoints. In this study, we propose an alternative approach to manipulate the magnetic susceptibility and related properties of soft magnetic materials by geometric designs. For example, porous honeycomb structures of Fe92.9C3.5Si3.6 amorphous ribbons are fabricated with control over the wall width, which ranges from 60 to 130 μm. The magnetic field dependence of the magnetization shows that the magnetic susceptibility strongly depends on the wall width of porous honeycomb structures, i.e., the smaller the width, the higher the susceptibility. In addition, the susceptibilities of porous honeycomb structures are larger than that of their continuous counterpart. The geometrical dependence of the magnetic susceptibility is confirmed by phase field modeling. The simulation results suggest that a high density of domain walls can be accommodated in a porous honeycomb structure with a small wall width. Thus, the transitions of domain configurations under the magnetic field can be tailored, which brings about a geometrical dependence of the magnetic susceptibility. The present work opens a broad avenue for the geometric design of magnetic properties.

Untethered Origami Worm Robot with Diverse Multi-Leg Attachments and Responsive Motions under Magnetic Actuation

Nowadays, origami folding in combination with actuation mechanisms can offer deployable structure design, yield compliance, and have several properties of soft material. An easy complex folding pattern can yield an array of functionalities in actuated hinges or active spring elements. This paper presents various cylinder origami robot designs that can be untethered magnetically actuated. The different designs are analyzed and compared to achieve the following three types of motion: Peristaltic, rolling, and turning in different environments, namely, board, sandpaper, and sand. The proposed origami robot is able translate 53 mm in peristaltic motion within 20 s and is able to roll one complete cycle in 1 s and can turn ≈180∘ in 1.5 s. The robot also demonstrated a peristaltic locomotion at a speed of ≈2.5 mm s−1, ≈1.9 mm s−1, and ≈1.3 mm s−1 in board, sandpaper, and sand respectively; rolling motion at a speed of 1 cycle s−1, ≈0.66 cycles s−1, and ≈0.33 cycles s−1 in board, sandpaper, and sand respectively; and turning motion of ≈180∘, ≈83∘, and ≈58∘ in board, sandpaper, and sand respectively. The evaluation of the robotic motion and actuation is discussed in detail in this paper.

Lightweight, Thermally Conductive Liquid Metal Elastomer Composite with Independently Controllable Thermal Conductivity and Density.

Lightweight and elastically deformable soft materials that are thermally conductive are critical for emerging applications in wearable computing, soft robotics, and thermoregulatory garments. To overcome the fundamental heat transport limitations in soft materials, room temperature liquid metal (LM) has been dispersed in elastomer that results in soft and deformable materials with unprecedented thermal conductivity. However, the high density of LMs (>6 g cm-3 ) and the typically high loading (⩾85 wt%) required to achieve the desired properties contribute to the high density of these elastomer composites, which can be problematic for large-area, weight-sensitive applications. Here, the relationship between the properties of the LM filler and elastomer composite is systematically studied. Experiments reveal that a multiphase LM inclusion with a low-density phase can achieve independent control of the density and thermal conductivity of the elastomer composite. Quantitative design maps of composite density and thermal conductivity are constructed to rationally guide the selection of filler properties and material composition. This new multiphase material architecture provides a method to fine-tune material composition to independently control material and functional properties of soft materials for large-area and weight-sensitiveapplications.

Quantitative spectral electromechanical characterization of soft piezoelectric nanocomposites

We present a modular system for the quantitative characterization of the piezoelectric coefficient of piezoelectric polymers and soft polymeric nanocomposites in the compression mode. Our approach is based on an apparatus providing spectral information on the electro-mechanical response in aselected range of frequencies of compressive loads (10–1200 Hz), with high sensitivity (down to 0.5 pC/N) and automated data acquisition modalities, enabling repeatability and reproducibility of the electro-mechanical characterization in the low-force regime (0.1 N 1.5 N). The system is modular and can be developed to cover the 2 mHz-1.2 kHz frequency range in charge mode and the 2 μHz-1200 Hz in voltage mode. We calibrated and validated the apparatus functionality using a commercial PVDF piezoelectric polymer. The suitability of the system for the quantitative measurements of the piezoelectricity of soft polymeric nanocomposites was then assessed by performing measurements of a novel piezoelectric nanocomposite material. This consisted of a polydimethylsiloxane (PDMS) matrix with embedded BaTiO3 nanoparticles, engineered with functional surface coatings to favor their homogeneous dispersion into the polymer. The proposed system demonstrated to be an effective solution for the systematic characterization of the electro-mechanical conversion properties of soft piezoelectric materials in view of soft robotics and energy harvesting applications.

Multiscale Microrheology Using Fluctuating Filaments as Stealth Probes.

The mechanical properties of soft materials can be probed on small length scales by microrheology. A common approach tracks fluctuations of micrometer-sized beads embedded in the medium to be characterized. This approach yields results that depend on probe size when the medium has structure on comparable length scales. Here, we introduce filament-based microrheology using high-aspect-ratio semiflexible filaments as probes. Such quasi-1D probes are much less invasive than beads due to their small cross sections. Moreover, by imaging transverse bending modes, we simultaneously determine the micromechanical response of the medium on multiple length scales corresponding to the mode wavelengths. We use semiflexible single-walled carbon nanotubes as probes that can be accurately and rapidly imaged based on their stable near-IR fluorescence. We find that the viscoelastic properties of sucrose, polyethylene oxide, and hyaluronic acid solutions measured in this way are in good agreement with those measured by conventional micro- and macrorheology.

Inverse Dynamics Model-Based Shape Control of Soft Continuum Finger Robot Using Parametric Curve

Soft continuum robots are more and more used in various applications due to the multiple advantages offered by the properties of hyper-elastic soft materials, such as resilience, flexibility, etc. Despite all these essential properties that make the soft robots good candidates for some real-life needs (form enclosure grasping, obstacle-free navigation, etc.), controlling their shape remains challenging because of their hyper-redundancies. This letter investigates an inverse dynamics model-based shape control of soft continuum robots in the presence and absence of external efforts. To that end, modeling based on Pythagorean Hodograph (PH) curves with prescribed lengths is combined with Euler-Bernoulli modeling to reconstruct the robot shapes and then calculate the actuator inputs in the case of external efforts. Thus, a relationship between the actuator inputs and the PH control points is obtained. With the above strategy, the actuator inputs can be computed accordingly, and therefore, real-time shape control of the soft robots for various tasks becomes possible. The results of the proposed approach are validated both numerically and experimentally using two classes of soft continuum robots - a Fluidic Elastomeric Actuator (FEA), describing a 2D soft finger robot, with a single and multiple phalanges, and a 3D continuum manipulator, namely the Compact Bionic Handling Assistant (CBHA).

Poisson’s ratio measurement through engraving the grid pattern inside poly(dimethylsiloxane) by ultrafast laser

This work demonstrates an application of ultrafast laser processing to engrave a grid pattern for evaluating mechanical properties. No observable changes in the material properties caused by laser engraving were confirmed if the grid pattern is engraved with laser energy of 0.21 μJ/pulse and pulse repetition rate of 1 kHz. The shape changes of grid pattern directly reveal whether the deformation accompanied with stretching is uniaxial or not. By analyzing the optical images of the grid pattern, Poisson ratio, Young’s modulus, and shear modulus of poly(dimethylsiloxane) (PDMS) with a weight percent of curing agent of 9% were estimated to be 0.49989 ± 0.00111, 1.45 ± 0.01 MPa, and 0.725 MPa, respectively. The comparison of the current results with the literature values suggests that the proposed method is appropriate to provide quantitative mechanical properties of soft materials with high accuracy.

Improved Preisach Model for the Vector Hysteresis Property of Soft Magnetic Composite Materials Based on the Hybrid Technique of SA-NMS

The two-dimensional hysteresis property of the soft magnetic composite (SMC) material under circular rotational excitation was measured by the experimental platform. The first-order reversal curves and the corresponding scalar Everett functions can be numerically generated by the measured major hysteresis loops along the orthogonal easy axis and hard axis. Different from the classical model, an improved vector Preisach hysteresis model that considers the anisotropic property of the SMC materials under vector magnetic excitation was put forward by introducing two parameters w and z. The two parameters were used to identify the vector Everett functions and adjust the shape of hysteresis curves under different magnitudes of the magnetic flux density. Furthermore, an efficient hybrid algorithm that combines simulated annealing with Nelder-Mead simplex technique was proposed for the accurate extraction of optimal parameters. The simulated results based on the improved model agree well with the measured ones; thus, the effectiveness and accuracy of the proposed method were verified.

Large amplitude vibrations of imperfect porous-hyperelastic beams via a modified strain energy

In this paper, the porous-hyperelastic properties of soft materials are obtained experimentally and a general model for a combination of porosity (of functional type) and hyperelasticity using the Mooney-Rivlin strain energy density is obtained. Porous-hyperelastic samples are fabricated using thermoplastics with different porosities by varying the infill rate of 3D-printing. Following the available standards, the stress-strain behaviour for different samples are obtained and a general model for hyperelastic closed-cell porosity is presented. After obtaining model's characteristics from the experimental testings, a general beam formulation is presented for hyperelastic beams with functional porosity through the length. Both the axial and transverse motions are considered in the model of hyperelastic beams in the framework of the Mooney-Rivlin material model and Hamilton's principle. A geometrical imperfection of the beam is also considered in the formulation. The nonlinear forced vibrations of the imperfect porous-hyperelastic beam are studied by simultaneously solving the axial and transverse nonlinear coupled equations using a dynamic equilibrium technique. It is shown that having a uniform and functional porosity has a significant effect in changing the nonlinear frequency response of the system. Geometrical imperfection leads to a significant coupling between the axial and transverse coordinates when the porosity varies functionally through the length which shows the importance of considering both motions while analysing such structures. The results are useful for better understanding the effects of imperfections in studying the mechanics of soft structures and can be useful in designing soft robotics and artificial organs.

Silicone‐based polymer blends: Enhancing properties through compatibilization

AbstractPolymer blending is a cost‐effective way to control the properties of soft materials, but the propensity for blends to macrophase separate motivates the development of efficient compatibilization strategies. Across this broad area, compatibilization is particularly important for polysiloxanes, which exhibit strong repulsive interactions with most organic polymers. This review analyzes state‐of‐the‐art polysiloxane compatibilization strategies for silicone–organic polymer blends. Emphasis is placed on chemical innovation in the design of compatibilization agents that may expedite the commercialization of new silicone–organic materials. We anticipate that hybrid silicone blends will continue to play an important role in fundamental and applied materials science across industry and academia.

Effect of the Temperature on the Magnetic and Energetic Properties of Soft Magnetic Composite Materials

In recent years, innovative magnetic materials have been introduced in the field of electrical machines. In the ambit of soft magnetic materials, laminated steels guarantee good robustness and high magnetic performance but, in some high-frequency applications, can be replaced by Soft Magnetic Composite (SMC) materials. SMC materials allow us to reduce the eddy currents and to design innovative 3D magnetic circuits. In general, SMCs are characterized at room temperature, but as electrical machines operate at high temperature (around 100 °C), an investigation analysis of the temperature effect has been carried out on these materials; in particular, three SMC samples with different binder percentages and process parameters have been considered for magnetic and energetic characterization.

Toward a mechanically stable solid electrolyte interphase

Toward a mechanically stable solid electrolyte interphase

The thermodynamic properties of soft magnetic materials containing superparamagnetic nanoparticles frozen in the nodes of the regular cubic lattice

The thermodynamic properties of soft magnetic materials containing superparamagnetic nanoparticles frozen in the nodes of the regular cubic lattice

Meso/macro-scale ultra-soft materials' mechanical property evaluation device and testbed.

Ultra-soft materials find applications in biomedical devices, sensors and actuators, robotics, and wearable electronics. The mechanical properties of soft materials are often determined using nanoindentation and atomic force microscope techniques, which provide localized properties at a small-scale length. There is a need to evaluate the meso/macro-scale properties of ultra-soft materials to develop integrated devices made of the same. Metallic probes in the existing macroscale equipment cannot be used as they can pierce through the soft materials and fail to capture the associated adhesion forces, resulting in inaccurate values. This study has developed a meso/macro-scale mechanical testing platform to characterize ultra-soft materials accurately. This probe can be adapted to any mechanical testing load frame with a small load cell to capture the adhesion forces during the approach and detachment segments of soft materials' indentation. The integrated camera with the probe enables overcoming the challenge of surface detection and capturing the pull-on and pull-off events. Indentation tests on soft materials with varying stiffness (e.g., high-fat yogurt, chicken breast, aloe Vera, toothpaste, gelatin, and a chocolate bar) were conducted using a 10mm stiff flat-end polymer probe. A variation of the Johnson-Kendall-Roberts technique was adopted to account for adhesion forces and compute stiffness. Our results suggest that the novel device and methodology can measure mechanical stiffness in the extensive range of 0.5kPa to a few MPa with high reproducibility at the macro-scale length. The validation was carried out using a commercially available nanoindenter for soft materials.

Design issues of Rotational Single Sheet Tester for Fe-Based Nanocrystalline Alloys at High Frequencies

Measuring the vector magnetic properties of nanocrystalline soft magnetic materials at high frequencies is of great significance to the optimal design and energy saving of the electrical equipment. In this paper, some key design issues are discussed for a rotational single sheet tester (RSST) to further studied the Two-Dimensional (2D) magnetic properties of nanocrystalline alloys in the kilohertz range. Firstly, the magnetization uniformity of the testing sample is analyzed and discussed considering the stray field. Secondly, the magnetizer

Automated Parameterization of Quantum Mechanically Derived Force Fields for Soft Materials and Complex Fluids: Development and Validation.

The reliability of molecular dynamics (MD) simulations in predicting macroscopic properties of complex fluids and soft materials, such as liquid crystals, colloidal suspensions, or polymers, relies on the accuracy of the adopted force field (FF). We present an automated protocol to derive specific and accurate FFs, fully based on ab initio quantum mechanical (QM) data. The integration of the Joyce and Picky procedures, recently proposed by our group to provide an accurate description of simple liquids, is here extended to larger molecules, capable of exhibiting more complex fluid phases. While the standard Joyce protocol is employed to parameterize the intramolecular FF term, a new automated procedure is here proposed to handle the computational cost of the QM calculations required for the parameterization of the intermolecular FF term. The latter is thus obtained by integrating the old Picky procedure with a fragmentation reconstruction method (FRM) that allows for a reliable, yet computationally feasible sampling of the intermolecular energy surface at the QM level. The whole FF parameterization protocol is tested on a benchmark liquid crystal, and the performances of the resulting quantum mechanically derived (QMD) FF were compared with those delivered by a general-purpose, transferable one, and by the third, "hybrid" FF, where only the bonded terms were refined against QM data. Lengthy atomistic MD simulations are carried out with each FF on extended 5CB systems in both isotropic and nematic phases, eventually validating the proposed protocol by comparing the resulting macroscopic properties with other computational models and with experiments. The QMD-FF yields the best performances, reproducing both phases in the correct range of temperatures and well describing their structure, dynamics, and thermodynamic properties, thus providing a clear protocol that may be explored to predict such properties on other complex fluids or soft materials.

Soft robotics: the route to true robotic organisms

Soft Robotics has come to the fore in the last decade as a new way of conceptualising, designing and fabricating robots. Soft materials empower robots with locomotion, manipulation, and adaptability capabilities beyond those possible with conventional rigid robots. Soft robots can also be made from biological, biocompatible and biodegradable materials. This offers the tantalising possibility of bridging the gap between robots and organisms. Here, we discuss the properties of soft materials and soft systems that make them so attractive for future robots. In doing so, we consider how future robots can behave like, and have abilities akin to, biological organisms. These include huge numbers, finite lifetime, homeostasis and minimal—and even positive—environmental impact. This paves the way for future robots, not as machines, but as robotic organisms.

Imperfection sensitivity of mechanical properties in soft network materials with horseshoe microstructures

Imperfection sensitivity of mechanical properties in soft network materials with horseshoe microstructures