Properties Of Soft Materials Research Articles

Highly luminescent soft aggregates and films assembled by amphiphilic polyoxometalate complex in a polymerizable aprotic ionic liquid

Hybrid co-assembly from lanthanide-containing polyoxometalates (POMs) and surfactants could efficiently optimize the formed aggregate luminescent properties and structural diversity. Meanwhile, compared to conventional solvents, aprotic ionic liquids (ILs) are not only excellent assembly media but also ideal solvents for luminescent lanthanide compounds. Therefore, in this work, the luminescent amphiphilic POM complex, namely surfactant-encapsulated POM hybrid (SEP) was initially prepared mainly through electrostatic interaction from polyanionic lanthanide-containing POM, Na9(EuW10O36)·32H2O (EuW10) and cationic surfactant, 1-octadecyl-3-methylimidazolium bromide ([C18mim]Br, OB). Then, highly luminescent lamellar micro-fiber aggregates were assembled by SEP in a polymerizable imidazolium-IL solvent, i.e. 1-vinyl-3-butyl imidazolium terafluoroborate ([Vbim]BF4). After morphology and structure characterizations for soft aggregates in detail, a lamellar aggregation arrangement mechanism was proposed. Further through in situ photopolymerization for such aggregate matrices, the flexible and organized films with enhanced luminescent properties were obtained. Our work indicates that the rational design of polymerizable organized aggregate matrices in ILs could greatly improve the photophysical properties of such luminescent soft materials and also expand their practical applications.

Investigation of variety of valence metal ions combinated novel Co‐rich high entropy oxides and its magnetic properties and microstructure

In this work, a series of five spinel-structured oxides were synthesized using a straightforward and effective solid-state methodology. Departing from the conventional design concept, we opted for the substitution of Fe3 + with five metal cations, all possessing trivalent average valence states and equivalent proportions. X-ray diffraction, scanning electron microscope, energy spectrum analyzer, vibrating sample magnetometer were used to detect the phase, micro-structure, element distribution, magnetism of the samples, respectively. The test results show that samples have the spinel structure (Fd3(_)m), and the element composition and distribution are the same as expected. The test results of magnetic properties reveal that these five samples exhibit the properties of soft magnetic materials. The maximum adjustment range of saturation magnetization (Ms) is increased from 23.5 emu/g to 34.8 emu/g by adjusting the elemental composition. Besides, the maximum adjustment range of coercivity (Hc) is increased from 11 Oe to 60 Oe. Furthermore, these materials exhibit a low remanent magnetization ratio, indicating that high-entropy oxides with spinel structures are highly sensitive to changes in an applied magnetic field. The high-entropy oxide is a new material with great prospect. It creates new possibilities for the design of magnetic materials.

Small and large deformation rheology on pizza cheese as an example of application to study anisotropic properties of food soft materials

Various rheological techniques were applied to study pizza cheese, as a model anisotropic material. Small Amplitude Oscillatory Shear (SAOS) was combined with Large Amplitude Oscillatory Shear (LAOS) rheology, and the data compared to large deformation tests and confocal microscopy. Pizza cheese was analyzed at various stages of processing: before/during mixing, freshly stretched and after 1 and 2 weeks of storage. Directional sampling and testing were of critical importance for data interpretation. LAOS data were evaluated using a recently developed software that, with visual interactive analysis, including layover plots and similarity maps, allowed to provide a rheological fingerprint of the cheese's process and storage-induced structural changes. This work demonstrated that by using complementary rheological and microstructural techniques it is possible to improve our understanding of the anisotropy at different length scales, and to distinguish the differences in the networks among samples after various processing stages.

A New Approach for Measuring Viscoelastic Properties of Soft Materials Using the Dynamic Response of a Spherical Object Placed at the Sample Interface

BackgroundThere are several techniques to characterize the mechanical properties of soft materials, such as the indentation method and the method based on the application of a spherical object placed inside the sample. The indentation systems usually yield the elastic properties of materials and their mathematical models do not consider the inertia of the sample involved in motion and radiation damping, while placing an object inside the sample is not practical and this procedure can alter the mechanical properties of the sample for the method based on the application of a bubble/sphere placed inside the sample.ObjectiveA new approach for the identification of the viscoelastic properties of soft materials using the dynamic response of a spherical object placed at the sample interface was proposed.MethodsThe spherical object placed at the sample interface was pressed using an electromagnet and the dynamic response of the spherical object was tracked using a high-speed camera, while the dynamic response of the spherical object placed at the sample interface was estimated using a comprehensive analytical model. The effects of the shear modulus, viscosity, Poisson’s ratio and density of the soft sample, the radius and density of the spherical object and the damping due to radiation were considered in this mathematical model. The shear modulus and viscosity of the soft sample were determined by matching the experimentally identified and theoretically estimated responses of the spherical object.ResultsThe shear moduli and viscosities of the three phantoms with the gelatin mass ratios of 0.20, 0.25 and 0.29 were measured to be 3450, 4300 and 4950 Pa and 12.5, 14.0 and 15.0 Pa⋅s, respectively. The shear modulus and viscosity of the phantom increases as the gelatin mass ratio increases. The frequency of oscillations of the hemisphere placed at the phantom interface increases as the gelatin mass ratio increases due to stiffness increase.ConclusionsAfter matching the experimental and theoretical steady-state displacements and amplitudes of oscillations of the hemisphere at the sample interface, the comparison of the experimentally identified and theoretically predicted frequency of oscillations further confirmed the identified material properties of the samples. The approach presented here is expected to provide valuable information on material properties in biomedical and industrial applications.

Adaptive discrete mapping of dynamic nanomechanical property of soft materials on atomic force microscope

In this paper, an adaptive discrete nanomechanical mapping (A-DNM) technique is proposed for mapping time-varying nanomechanical properties of soft samples using atomic force microscope (AFM). Mapping time-varying nanomechanical properties is needed to investigate samples such as live cells undergoing dynamic evolutions. However, the existing methods based on continuous scanning are either too slow to capture time-elapsing variations of the sample over the entire sampled area, or only capable of mapping a small sample area. Contrarily, we propose to extend a discrete nanomechanical mapping scheme where only a set of chosen discrete locations (points of interests, POIs) are measured, thereby, dramatically increasing the number of measurements acquired at these POIs during the dynamic evolution of the sample occurring in minutes or faster. Specifically, through the proposed A-DNM approach, two challenges are addressed: First, the effect of time-varying sample topography during the nanomechanical evolution is accounted for by updating the estimation of the sample height at each POI during the mapping and compensating for it in the cantilever transition and engagement process. Secondly, an adaptive planning of the mapping sequence is proposed to adjust the distribution of the measurements between the POIs to accomodate the sample dynamic evolution. A POI-dynamics index is introduced to estimate the relative speeds of the nanomechanical evolutions at the POIs based on the measured data, and then online assign more measurements to those POIs of faster nanomechanical evolutions. The proposed approach is demonstrated through an experiment of mapping nanomechanical evolution of a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) polymer undergoing crystallization process.

Measurement and analysis of magnetic properties under SVPWM excitation for soft magnetic composites (SMCs) and silicon steel

This study developed a system for measuring the magnetic properties of soft magnetic materials under space vector pulse width modulation (SVPWM) excitation, enabling testing at different modulation indexes, frequencies, and carrier frequencies. Two types of soft magnetic materials were tested, and the effects of SVPWM waveform parameters on material loss were analyzed. The results show that the loss of SMCs is higher than that of silicon steel when the max magnetic flux density is close to 1.5 T. In contrast, at the modulation frequencies are 100 Hz and 200 Hz, the loss of SMCs is lower than that of silicon steel. The reliability of the testing system was validated through magnetic characterization of the two materials, providing a reference for their application and preparation.

In-situ shearing process observation system forsoft materials via transmission electron microscopy.

We developed an in-situ shear test system suitable for transmission electron microscopy (TEM) observations, which enabled us to examine the shear deformation behaviours inside soft materials at nanoscale resolutions. This study was conducted on a nanoparticle-filled rubber to investigate its nanoscale deformation behaviour under a large shear strain. First, the shear deformation process of a large area in the specimen was accurately examined and proven to exhibit an almost perfect simple shear. At the nanoscale, voids grew along the maximum principal strain during shear deformation. In addition, the nanoscale regions with rubber and silica aggregates exhibited deformation behaviours similar to the global shear deformation of the specimen. Although the silica aggregates exhibited displacement along the shearing directions, rotational motions were also observed owing to the torque generated by the local shear stress. This in-situ shear deformation system for TEM enabled us to understand the nanoscale origins of the mechanical properties of soft materials, particularly polymer composites. Graphical Abstract.

Heterostructured C@Fe3O4@FeSiCr composite absorbing material derived from MIL-88(Fe)@FeSiCr

The C@Fe3O4@FeSiCr composites with carbon-covered heterostructures were obtained by constructing C and Fe3O4 derived from carbonized MIL-88(Fe)@FeSiCr to form heterogeneous interfaces with FeSiCr. The electromagnetic parameters of the composites were regulated by adjusting the compound amount of MIL-88(Fe). The impedance matching performance was optimized, and this further improved the microwave absorbing performance. At a MIL-88(Fe) compound amount of 30 wt%, the composite achieves a minimum reflection loss (RLmin) of –68.07 dB at 4.83 GHz with an absorbing coating thickness of 3.33 mm. In the field of microwave absorbing materials, these results provide valuable guidelines for constructing heterogeneous interface coatings and optimizing the impedance matching properties of soft magnetic alloys materials.

Ultra-durable and high-output triboelectric nanogenerator based on coupling of soft-soft contact and volume effect

Output performance and durability are two key issues for the practical application of triboelectric nanogenerators (TENGs). Although the soft contact structure design is a preferred strategy currently for improving the working life of TENGs, it is difficult to achieve a high output performance. Exploring physical and chemical properties of soft contact materials is a reliable way to achieve ultra-durable and high-output TENGs. Herein, an advanced structure for soft-soft contact is designed by combining ultra-soft PU foam and a spring steel sheet. The soft-soft contact triboelectric nanogenerator (SS-TENG) maintains 100 % of the initial output after 1000,000 operation cycles. More importantly, the high leakage characteristics of PU foam enable the triboelectric charge to migrate up and down inside the dielectric material, significantly improving the output performance of the SS-TENG (charge density and peak power are 144 μC/m−2 and 178 mW, respectively). This study provided an effective approach for promoting the output and durability of TENGs. Meanwhile, this work offers a reliable solution for the development of self-powered sensor networks for smart agriculture.

Caloric effects in liquid crystal-based soft materials

With the increased environmental awareness, the search for environmentally friendlier heat-management techniques has been the topic of many scientific studies. The caloric materials with large caloric effects, such as the electrocaloric (EC) and elastocaloric (eC) effects, have increased interest due to their potential to realize new solid-state refrigeration devices. Recently, caloric properties of soft materials, such as liquid crystals (LCs) and LC elastomers (LCEs), are getting more in the focus of caloric materials investigations, stimulated by large caloric effects observed in these materials. Here, an overview of recent direct measurements of large caloric effects in smectic LC 14CB and main-chain LCEs is given. Specifically, high-resolution thermometric measurements revealed a large EC response in 14CB LC exceeding 8 K. Such a large effect was obtained at a relatively moderate electric field of 30 kV cm−1 compared to solid EC materials. We demonstrate that such a small field can induce the isotropic to smectic A phase transition in 14CB, releasing or absorbing relatively large latent heat that enhances the EC response. Furthermore, it is demonstrated that in main-chain LCEs, the character of the nematic to isotropic transition can be tuned from the supercritical towards the first-order regime by decreasing the crosslinkers’ density. Such tuning results in a sharper phase transition and latent heat that enhance the eC response, exceeding 2 K and with the eC responsivity of 24 K MPa−1, about three orders of magnitude larger than the average eC responsivity found in the best shape memory alloys. Significant caloric effects in soft LC-based materials, observed at much smaller fields than in solid caloric materials, demonstrate their ability to play an important role as new cooling elements, thermal diodes, and caloric-active regeneration material in new heat-management devices.

Microstructure, mechanical and soft magnetic properties of in-situ TiC reinforced Fe27.5Ni27.5Co45-based medium entropy composites

The insufficient mechanical properties of conventional soft magnetic materials (SMMs) hinder their widespread applications, and unfortunately, traditional strengthening mechanisms could dramatically deteriorate their soft magnetic properties without adjusting the alloy composition. Here, we developed TiC/Fe27.5Ni27.5Co45 medium-entropy composites (MECs) possessing multi-scale microstructure consisting of ultrafine and micron-sized grains by introducing in-situ formed TiC nano particles during the spark plasma sintering (SPS) process. Compared with the precipitate-free Fe27.5Ni27.5Co45 medium-entropy alloy, TiC/Fe27.5Ni27.5Co45 MEC with ∼ 8.7 vol% TiC (noted as Ti5-MEC) demonstrated a significant improvement in compressive yield strength (from 459 MPa to 1114 MPa), attributing to the grain-boundary strengthening and dispersive precipitation strengthening, as well as hetero-deformation induced (HDI) strengthening. Meanwhile, the Ti5-MEC exhibits a high saturation magnetization (Ms) of 153.1 emu/g and a low coercivity (Hc) of ∼ 8.2 Oe, indicating excellent soft magnetic properties, primarily due to the multi-scale microstructure. Our work has demonstrated that engineering multi-scale microstructures in MECs is an effective strategy to achieve desirable combinations of soft magnetic and mechanical properties.

Photocontrollable Elongation Actuation of Liquid Crystal Elastomer Films with Well-Defined Crease Structures.

Although liquid crystal elastomers (LCEs) have demonstrated various applications in artificial muscles and soft robotics, their inherent flexibility and orientation-dependent forces limit their functions. For instance, LCEs can sustain a high actuation force when they contract but cannot elongate to drive loads with large displacements. In this study, it is demonstrated that photocontrollable elongation actuation with a large strain can be achieved in polydomain LCEs by programming the crease structures in a well-defined order to couple the actuation forces. Efficient photoactuation without overheating-induced damage to the materials is favored, based on the well-designed photosensitive molecular switch crosslinker via the synergy of photochemical and photothermal effects. The LCE actuator can jack up heavy loads, elongate freely, and contract back to manipulate distant objects. Theoretical analysis based on a finite element simulation of the deformation energy during the actuation process reveals a trade-off between the abilities of jacking-up and withstanding load. More importantly, this study simplifies the design of a single material with functions inherent only in other soft robotic devices based on the assembly of multiplemodules, thus providing a design strategy for surpassing instinctive properties of conventional soft materials to expand the functions of soft robotics.

Effect of Ionic Liquids on Mechanical, Physical, and Antifungal Properties and Biocompatibility of a Soft Denture Lining Material.

This study aims to evaluate the effect of ionic liquids and their structure on the mechanical (tensile bond strength (TBS) and Shore A hardness), mass change, and antifungal properties of soft denture lining material. Butyl pyridinium chloride (BPCL) and octyl pyridinium chloride (OPCL) were synthesized, characterized, and mixed in concentrations ranging from 0.65-10% w/w with a soft denture liner (Molloplast-B) and were divided into seven groups (C, BPCL1-3, and OPCL1-3). The TBS of bar-shaped specimens was calculated on a Universal Testing Machine. For Shore A hardness, disc-shaped specimens were analyzed using a durometer. The mass change (%) of specimens was calculated by the weight loss method. The antifungal potential of ionic liquids and test specimens was measured using agar well and disc diffusion methods (p ≤ 0.05). The alamarBlue assay was performed to assess the biocompatibility of the samples. The mean TBS values of Molloplast-B samples were significantly lower (p ≤ 0.05) for all groups except for OPCL1. Compared with the control, the mean shore A hardness values were significantly higher (p ≤ 0.05) for samples in groups BPCL 2 and 3. After 6 weeks, the OPCL samples showed a significantly lower (p ≤ 0.05) mass change as compared to the control. Agar well diffusion methods demonstrated a maximum zone of inhibition for 2.5% OPCL (20.5 ± 0.05 mm) after 24 h. Disc diffusion methods showed no zones of inhibition. The biocompatibility of the ionic liquid-modified sample was comparable to that of the control. The addition of ionic liquids in Molloplast-B improved the liner's surface texture, increased its hardness, and decreased its % mass change and tensile strength. Ionic liquids exhibited potent antifungal activity.

Effect of Magnesium Treatment on Cleanliness, Microstructure, and Magnetic Properties of Fe–80Ni Permalloy

Cleanliness and microstructure significantly impact the magnetic properties of soft magnetic materials. This study investigates the impact of Mg treatment on the cleanliness, microstructure, and magnetic properties of Fe–80Ni alloy. The content of Mg ranges from 0% to 0.034%. The O and S contents can be reduced to 0.0006% and 0.0011%, respectively, when the content of Mg is 0.027%, and the number of inclusions is reduced. Simultaneously, the primary inclusions are modified to Mg‐containing inclusions. Based on electron backscattered diffraction results, Mg treatment can refine the deformed grain and enhance grain boundary energy after cold rolling. In addition, the grains exhibit enhanced growth after annealing with Mg treatment. Due to the improvement of cleanliness and microstructure, the magnetic properties of Fe–80Ni alloy are enhanced with Mg treatment. With Mg treatment, the coercivity of alloys is reduced, and maximum magnetic susceptibility (χmax) increases to 0.3247 with Mg treatment, while that is 0.1938 without Mg treatment.

Application of Hydrogels in the Device of Ophthalmic Iontophoresis: Theory, Developments and Perspectives.

The human eye is a consolidated organ with delicate structures and unique immune privileges. Ocular diseases are intractable due to the intrinsic biological barriers within the eyeball. Hydrogels are excellent drug-carrying substances with soft material and excellent properties. They have been extensively used to deliver drugs into ocular tissue via iontophoresis devices. Ophthalmic iontophoresis is an electrochemical technique using tiny electrical currents to deliver drugs into the eye non-invasively. The early infantile iontophoresis technique often required long applying time to achieve therapeutic dose in the posterior ocular segment. The potential limitations in the initial drug concentration and the maximum safe currents would also impede the efficiency and safety of iontophoresis. Moreover, the poor patient compliance always leads to mechanical damage to the cornea and sclera during application. Advantageously, the flexible drug-carrying hydrogel can be in direct contact with the eye during iontophoresis, thereby reducing mechanical damage to the ocular surface. Moreover, the water absorption and adjustable permeability of hydrogels can reduce the electrochemical (EC) reactions and enhance the efficiency of iontophoresis. In this review, we focus on recent developments of hydrogels iontophoresis in ophthalmologic practice. Refinements of the knowledge would provide an outlook for future application of hydrogels in treating ocular disease.

Concentration-dependent construction of raspberry-like SiO2 shell on spherical FeNi towards improved electromagnetic performance from kHz to GHz

Constructing resistive layer with novel structure holds great potential in upgrading electromagnetic properties of soft magnetic materials in a wide frequency range. In this work, FeNi@SiO2 composites with controllable core–shell structures, including 2D-type laminar shell and 3D-type raspberry-like shell, were fabricated by modified Stöber method. The structure of SiO2 shell depends highly on the concentration of tetraethyl orthosilicate (TEOS). In detail, a laminar shell can be formed at low TEOS concentration, owing to slow condensation. While at high TEOS concentration, heterogeneous growth on powder surface and homogeneous growth in solution of silica networks are significantly accelerated, resulting in the formation of the raspberry-like shell. Improved electromagnetic performance of FeNi@SiO2 cores at 2 MHz, including high resistivity, low eddy current loss, and low loss factor, should be ascribed to the unique raspberry-like shell structure. Meanwhile, raspberry-like shell also contributes to enhanced attenuation and acceptable impedance matching in GHz range. Consequently, a wide effective absorption bandwidth of 8.92 GHz can be achieved at a thin thickness of 1.85 mm. This work provides deep insights into the growth mechanism of different SiO2 shells and sheds new light on the design of high-performance soft magnetic composites working in different frequency bands.

Spiral‐Shape Fast‐Moving Soft Robots

AbstractSoft robots typically exhibit limited agility due to inherent properties of soft materials. The structural design of soft robots is one of the key elements to improve their mobility. Inspired by the Archimedean spiral geometry in nature, here, a fast‐moving spiral‐shaped soft robot made of a piezoelectric composite with an amorphous piezoelectric vinylidene fluoride film and a layer of copper tape is presented. The soft robot demonstrates a forward locomotion speed of 76 body length per second under the first‐order resonance frequency and a backward locomotion speed of 11.26 body length per second at the third‐order resonance frequency. Moreover, the multitasking capabilities of the soft robot in slope climbing, step jumping, load carrying, and steering are demonstrated. The soft robot can escape from a relatively confined space without external control and human intervention. An untethered robot with a battery and a flexible circuit (a payload of 1.665 g and a total weight of 1.815 g) can move at an absolute speed of 20 mm s−1 (1 body length per second). This study opens a new generic design paradigm for next‐generation fast‐moving soft robots that are applicable for multifunctionality at small scales.

Molecular Optomechanics Induced Hybrid Properties in Soft Materials Filled Plasmonic Nanocavities.

The optomechanical interaction between nanocavity plasmons and molecular vibrations can result in interfacial phenomena that can be tailored for sensing and photocatalytic applications. Here, we report for the first time that plasmon-vibration interaction can induce laser-plasmon detuning dependent plasmon resonance linewidth broadening, indicating energy transfer from the plasmon field to collective vibrational modes. The linewidth broadening accompanied by the large enhancement of the Raman scattering signal is observed as the laser-plasmon blue-detuning approaches the CH vibrational frequency of the molecular systems integrated in gold nanorod-on-mirror nanocavities. The experimental observations can be explained based on the molecular optomechanics theory that predicts dynamical backaction amplification of the vibrational modes and high sensitivity of Raman scattering when the plasmon resonance overlaps with the Raman emission frequency. The results presented here suggest that molecular optomechanics coupling may be manipulated for creating hybrid properties based on interactions between molecular oscillators and nanocavity electromagnetic optical modes.

Bridging the Gap in Ashby’s Map for Soft Material Properties for Tissue Engineering

Ashby's map's role in rationally selecting materials for optimal performance is well-established in traditional engineering applications. However, there is a major gap in Ashby's maps in selecting materials for tissue engineering, which are very soft with an elastic modulus of less than 100 kPa. To fill the gap, we create an elastic modulus database to effectively connect soft engineering materials with biological tissues such as the cardiac, kidney, liver, intestine, cartilage, and brain. This soft engineering material mechanical property database is created for widely applied agarose hydrogels based on big-data screening and experiments conducted using ultra-low-concentration (0.01-0.5 wt %) hydrogels. Based on that, an experimental and analysis protocol is established for evaluating the elastic modulus of ultra-soft engineering materials. Overall, we built a mechanical bridge connecting soft matter and tissue engineering by fine-tuning the agarose hydrogel concentration. Meanwhile, a soft matter scale (degree of softness) is established to enable the manufacturing of implantable bio-scaffolds for tissue engineering.

Prediction of Electronic Properties of Radical-Containing Polymers at Coarse-Grained Resolutions

The properties of soft electronic materials depend on the coupling of electronic and conformational degrees of freedom over a wide range of spatiotemporal scales. The description of such properties requires multiscale approaches capable of, at the same time, accessing electronic properties and sampling the conformational space of soft materials. This could in principle be realized by connecting the coarse-grained (CG) methodologies required for adequate conformational sampling to conformationally averaged electronic property distributions via backmapping to atomistic-resolution level models and repeated quantum-chemical calculations. Computational demands of such approaches, however, have hindered their application in high-throughput computer-aided soft materials discovery. Here, we present a method that, combining machine learning and CG techniques, can replace traditional backmapping-based approaches without sacrificing accuracy. We illustrate the method for an emerging class of soft electronic materials, namely, nonconjugated, radical-containing polymers, promising materials for all-organic energy storage. Supervised machine learning models are trained to learn the dependence of electronic properties on polymer conformation at CG resolutions. We then parametrize CG models that retain electronic structure information, simulate CG condensed phases, and predict the electronic properties of such phases solely from the CG degrees of freedom. We validate our method by comparing it against a full backmapping-based approach and find good agreement between both methods. This work demonstrates the potential of the proposed method to accelerate multiscale workflows and provides a framework for the development of CG models that retain electronic structure information.