Soft Nanocomposites Research Articles

Soft magnetic nanocomposites based on adaptive matrix of wormlike surfactant micelles

The paper describes a new type of soft magnetic nanocomposite (SMN) based on a transient network of wormlike surfactant micelles with embedded oppositely charged submicron particles of magnetite acting as cross-linking agents. We study the change of the rheological properties of the SMNs with different contents of particles in response to magnetic field. We show that even at low field strengths the system acquires solid-like behavior, which can be attributed to the aggregation of particles into chain-like/column structures. A solid-like behavior appears at a rather small volume fraction of particles (0.002–0.04) indicating weak restrictions imposed by the matrix to the reorganization of particles under magnetic field, which can be due to the self-assembled structure of the micellar network. In the oscillatory rheological measurements, SMNs show a linear viscoelastic response in an unusually wide region of values of strain, magnetic field strength and content of particles, which is caused by the viscoelastic contribution of the micellar network. Upon gradual increase of magnetic field strength H, the dynamic moduli G′ and G′′ demonstrate slow growth followed by a sharp rise with a scaling law H3.0 and reach a plateau at 0.15 T. The highest values of the storage modulus G′ in SMNs are close to those in magnetorheological fluids with liquid Newtonian carrier, where particles move freely and the G′ value is defined by the interactions of magnetized particles and chain-like/columns structures. SMNs have a yield stress, which grows with the increase of magnetic field strength and finally levels off just at the same magnetic field strength at which the G′ and G′′ values reach a plateau indicating the saturation of the particles magnetization. The concentration dependencies of the elastic modulus and yield stress suggest the transition from chain-like to columnar structures of the particles. The new SMNs possessing the features of both magnetic fluids and magnetic gels have promising potential in a wide range of applications requiring responsiveness to magnetic field.

Magnetic Alloy‐MWNT Heterostructure as Efficient Electromagnetic Wave Suppressors in Soft Nanocomposites

AbstractFeNi (iron‐nickel) alloy particles were coated with MWNTs (Multiwalled carbon nanotubes) using simple ball milling technique at various alloy to MWNT ratios. These hybrid heterostructure were then dispersed in PVDF/TPU (Polyvinylidene fluoride/ Thermoplastic polyurethane) blends to develop flexible composite materials that can shield electromagnetic (EM) radiations. These alloy particles coated with MWNT localise mostly in the TPU phase of the binary blends. The shielding effectiveness (SE) measurements obtained from the scattering parameters reveal that for a particular ratio of FeNi/MWNT (3:1), the SE was the highest (‐35.7 dB) among the different composites studied here and manifested in improved microwave absorption in the blends. The absorption driven shielding is due to various polarization in the shield, thereby increasing the dielectric loss. It was observed that these MWNT wrapped magnetic alloy particles shielded the incoming EM radiations more effectively as compared to only MWNTs or only alloy particles. The soft nanocomposites designed here absorb up to 95 % of the incoming EM radiations. The lowest skin depth and highest specific EMI (Electromagnetic interference) shielding attained was 1.4 mm and −20.5 dB cm2 g−1 respectively for composites containing FeNi/MWNT‐ 3:1. The attenuation constant derived from different parameters of these blends were also analysed in order to develop a multi‐layered structure, having absorption‐multiple reflection‐absorption pathways. This was used to assess the effect of different layers and their sequence in the multi‐layered structure on final EM wave attenuation. Interestingly, multi‐layered architecture with a similar thickness showed three‐fold increase in the total shielding as compared to their bulk counterpart.

Graphene Derivatives Doped with Nickel Ferrite Nanoparticles as Excellent Microwave Absorbers in Soft Nanocomposites

AbstractHerein, we report the development of soft polymeric composites containing multiwall carbon nanotubes (MWNTs, 1–3 wt%) and graphene derivatives doped with nickel ferrite nanoparticles (rGO@NF, 10 wt%) as lightweight microwave absorbers. The soft nanocomposites were designed using melt‐mixed blends of varying compositions of PC (polycarbonate) and SAN (poly styrene acrylonitrile) by compartmentalized functional nanoparticles in one of the components of the blend (here PC). Maximum attenuation of the incoming electromagnetic (EM) radiation mainly through absorption was achieved. The hetero‐dielectric media at microscopic length scale in the PC component provided large interfaces which facilitated multiple scattering thereby attenuating the incoming EM radiation. This strategy of positioning the functional nanoparticles in one of the components in the blends resulted in significantly enhanced shielding effectiveness (SE), at any given concentration of MWNTs, in contrast to PC based composites. This enhancement in SE was realized in the special morphology of the bicomponent PC/SAN=60/40 wt% blends where both the components are continuous. The enhanced SE in co‐continuous blends is due to combined effect of enhanced electrical conductivity (more precisely due to interconnected network of the nanoparticles) and the presence of a hetero‐dielectric media generating large scattering interfaces. For instance, the PC/SAN (60/40 wt%) co‐continuous blend containing 3 wt% MWNTs and 10 wt% rGO@NF manifested in a total shielding effectiveness (SET) of −32.3 dB (i. e. more than 99.9 % attenuation of incoming EM radiation) mainly through absorption.

Heterogeneity Assisted Damping Enhancement of Low and High Frequency Mechanical Waves in a Soft Polymer Nanocomposite

Low-amplitude dynamic and morphological heterogeneities of a biphasic copolymeric matrix were amplified by soft nanoparticle loading and thermally induced phase separation (TIPS). The evolution of system concentration fluctuation size (ξ) was quantified as a function of quench depth in its closed-loop like phase diagram. The system characterization was then complemented by extracting its bimodal heterogeneity index as normalized interface length over area (L/A) from phase imaging analysis of atomic force microscopy (AFM). Both criteria were amplified by annealing temperature rise, resulting in damping enhancement under low and high frequency mechanical waves, shown by dynamic mechanical thermal analysis (DMTA) and ultrasound spectroscopy, respectively. At the highest annealing temperature, 160 °C, the morphogenesis led to simultaneous increase of effective damping temperature range (ΔTeff) and maximum tan δ to 190 °C and 2, respectively. Finally, damping efficacy (Deff, i.e., ΔTeff[tan δ]max) and the ultr...

Soft nanocomposites of gelatin and poly(3-hydroxybutyrate) nanoparticles for dual drug release

We developed a nanocomposite gel composed of gelatin and poly(3-hydroxybutyrate) polymeric nanoparticles (PNP) to be used as an injectable gel for the contemporaneous, dual sustained release of bioactive molecules. The hydrogel matrix was formed by a very simple process, using either the physical gelation of gelatin or the natural enzyme transglutaminase to covalently cross-link the gelatin chains in the presence of embedded PNP. Oscillatory rheological measurements showed that the addition of the PNP induced an increase in the storage modulus compared to pure gelatin gels, for both physical and chemical gels. Micrographs from scanning electron microscopy revealed that the presence of PNP disrupted the native structure of the gelatin chains in the hydrogel matrix. Dual drug encapsulation was achieved with curcumin (CM) in the PNP and naproxen sodium(NS) in the gelatin matrix. In vitro release studies showed that the hydrogel matrix acts both as a physical and chemical barrier, delaying the diffusion of the drugs. An initial burst release was observed in the first hours of the measurement, and around 90% was released on the third day for naproxen sodium. In free PNP, 82% of curcumin was relased after four days, while when PNP were embedded in the gelatin matrix only 40% was released over the same time period. Overall, these simple, sustainable soft nanocomposites show potential as an injectable co-sustained drug release system.

Phase Distribution and Magnetic Properties of Mechanically Alloyed Hard/Soft Ferrite Nanocomposites

Improvement in the magnetic properties of hard/ soft ferrite nanocomposites was studied by varying the composition of the soft phase in SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposites. The SrFe12O19/Ni0.5Zn0.5Fe2O4 nanocomposites were prepared using the mechanical alloying method. The samples were prepared by varying the amount of the soft phase from 10 to 50 wt% while the amount of the hard phase remained 100 wt% in the ferrite nanocomposites. X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), and a transmission electron microscope (TEM) were used to characterize the samples. From the result, it was found that the nanocomposite magnet with 10 wt% of soft phase content had the highest remanence ratio, Mr/ Ms, which was 0.61, while the values of the coercivity, Hc, and magnetization, Ms, measured were 4482.4 G and 9.71 emu/g, respectively, and the average particle size of the ferrite nanocomposites was < 50 nm for all the samples. It was also shown that Hc decreased as the weight percent of the soft ferrite increased, which resulted from the dipolar interaction that occurred in the ferrite nanocomposites, showing the effect of phase distribution on the magnetic properties.

Oligomer-grafted graphene in a soft nanocomposite augments mechanical properties and biological activity

The present work aims to develop strong yet tough composites of polycaprolactone (PCL) reinforced with 5wt% graphene oxide (GO) covalently modified with PCL chains by “graft-from” approach. Oligomers were grafted by in situ polymerization from GO and amine-functionalized GO (AGO) yielding GO-g-PCL and AGO-g-PCL, respectively. The elastic modulus of PCL increased by 48% with the addition of unmodified GO. With GO-g-PCL and AGO-g-PCL, the modulus was increased by 76% and 71%, respectively. Similarly, the yield strength increased by 21%, 50% and 14% for GO, GO-g-PCL and AGO-g-PCL, respectively. Whereas GO significantly compromised the elongation to break of PCL (970%) to 93%, GO-g-PCL and AGO-g-PCL based composites exhibited remarkably higher ductility of 560% and 367%, respectively. These observations may be attributed to the grafted oligomers affording enhanced interfacial interactions at the soft-hard interface. Cell studies in vitro revealed that composites containing oligomer grafted GO significantly enhanced the proliferation and osteogenesis of human mesenchymal stem cells compared to neat PCL. Thus, the grafting of polymeric chains on the filler is a promising strategy for engineering graphene composites with enhanced modulus and strength that exhibit excellent ductility and toughness in combination with enhanced biological activity for bone tissue regeneration.

A novel multifunctional soft robotic transducer made with poly (ethylene-co-methacrylic acid) ionomer metal nanocomposite

Reported is realization of a novel ionic electro-active biomimetic soft robotic polymer metal nanocomposite known as poly (ethylene-co-methacrylic acid) metal composite (called EMAMC in this paper) capable of functioning as soft robotic biomimetic actuators, energy harvesters and sensors. By soft robotic it is meant that these materials are easily deformable soft plastics like an elephant trunk. Further reported is the manufacturing methodology of the novel multi-functional electroactive polymer metal nanocomposite EMAMC. The electro-less chemical plating is performed by a chemical REDOX operation on poly (ethylene-co-methacrylic acid) or (PEMAA) ionomer with a metal. PEMAA is a commercially available ionomer commercially known as Surlyn® by DuPont and used for manufacturing golf balls. Surlyn® is a copolymer of ethylene and methacrylic acid groups and is partially neutralized with Na+ ions. To increase the ion exchange capability of Surlyn® the polymer is subjected to a chemical hydrolysis in potassium and sodium hydroxides (KOH, NaOH) and dimethyl sulfoxide (DMSO). This procedure is followed by a chemical REDOX procedure in which PEMAA is first oxidized in a metallic salt solution followed and then reduced in a lithium and sodium borohydride solutions to deposit metallic nanoparticles near boundaries and on the surfaces of hydrolyzed Surlyn®. This REDOX operation creates highly conductive electrodes on and near boundary surfaces. It is then observed that application of a low voltage across the EMAMC causes it to deform softly (actuation mode) with a significant force density and soft bending and deforming the EMAMC will generate electricity (energy harvesting and sensing modes). The preliminary results of actuation and sensing of the EMAMC are reported in this paper.

Soft magnetic nanocomposite microgels by in-situ crosslinking of poly acrylic acid onto superparamagnetic magnetite nanoparticles and their applications for the removal of Pb(II) ion

FeCl3·6H2O and FeCl2·4H2O is used to produce a water-based nanometer Fe3O4 magnetic fluid, which is in-situ modified in liquid paraffin with silane in the form of water-in-oil emulsion. The emulsion of the resulting multi-functionalized Fe3O4 magnetite nanoparticles is then used as the only crosslinker and in-situ grafted with acrylic acid to produce beaklike soft magnetic nanocomposites microgels. This “one-pot” process has a number of advantages over the traditional methods: it is a simpler process; it avoids aggregation of nanometer Fe3O4; and it shows a much improved mechanical strength credited to the covalent crosslinking between the rigid Fe3O4 skeleton and the soft PAA blocks. The obtained microgels have showed selective adsorption to Pb(II), and the adsorbed Pb(II) can be easily desorbed, suggesting good reusability. Also, the microgels exhibit certain magnetic properties, therefore providing a convenient approach for stirring or separation by applying external magnetic field.

Resistive switching and impedance properties of soft nanocomposites based on Ag nanoparticles

Polymeric nanocomposites (NCs) containing Ag nanoparticles (NPs) feature interesting properties arising from the interaction between a confined metallic system, its surface and a viscoelastic matrix whose electronic properties range between a dielectric and an ionic conductor. They are currently exploited in a number of applications as electronic materials, among the others the most promising being high-K extrinsic dielectrics and resistive switching devices (RSDs). A large diffusivity through the polymeric network permits the displacement of Ag ions to sustain reversible electrochemical states that store information in impedance states. We present a detailed study showing how the interaction between polymeric matrix and dispersed NPs, thanks to its huge specific surface, influences the resistive switching and electrical impedance in view of an application as soft neuromorphic devices, going beyond the simple superposition of effects due to the pure matrix and the filler alone.

Soft Nanocomposite Based Multi-point, Multi-directional Strain Mapping Sensor Using Anisotropic Electrical Impedance Tomography

The practical utilization of soft nanocomposites as a strain mapping sensor in tactile sensors and artificial skins requires robustness for various contact conditions as well as low-cost fabrication process for large three dimensional surfaces. In this work, we propose a multi-point and multi-directional strain mapping sensor based on multiwall carbon nanotube (MWCNT)-silicone elastomer nanocomposites and anisotropic electrical impedance tomography (aEIT). Based on the anisotropic resistivity of the sensor, aEIT technique can reconstruct anisotropic resistivity distributions using electrodes around the sensor boundary. This strain mapping sensor successfully estimated stretch displacements (error of 0.54 ± 0.53 mm), surface normal forces (error of 0.61 ± 0.62 N), and multi-point contact locations (error of 1.88 ± 0.95 mm in 30 mm × 30 mm area for a planar shaped sensor and error of 4.80 ± 3.05 mm in 40 mm × 110 mm area for a three dimensional contoured sensor). In addition, the direction of lateral stretch was also identified by reconstructing anisotropic distributions of electrical resistivity. Finally, a soft human-machine interface device was demonstrated as a practical application of the developed sensor.

Analytical, numerical, and experimental studies of viscoelastic effects on the performance of soft piezoelectric nanocomposites.

Piezoelectric composite (p-NC) made of a polymeric matrix and piezoelectric nanoparticles with conductive additives is an attractive material for many applications. As the matrix of p-NC is made of viscoelastic materials, both elastic and viscous characteristics of the matrix are expected to contribute to the piezoelectric response of p-NC. However, there is limited understanding of how viscoelasticity influences the piezoelectric performance of p-NC. Here we combined analytical and numerical analyses with experimental studies to investigate effects of viscoelasticity on piezoelectric performance of p-NC. The viscoelastic properties of synthesized p-NCs were controlled by changing the ratio between monomer and cross-linker of the polymer matrix. We found good agreement between our analytical models and experimental results for both quasi-static and dynamic loadings. It is found that, under quasi-static loading conditions, the piezoelectric coefficients (d33) of the specimen with the lowest Young's modulus (∼0.45 MPa at 5% strain) were ∼120 pC N-1, while the one with the highest Young's modulus (∼1.3 MPa at 5% strain) were ∼62 pC N-1. The results suggest that softer matrices enhance the energy harvesting performance because they can result in larger deformation for a given load. Moreover, from our theoretical analysis and experiments under dynamic loading conditions, we found the viscous modulus of a matrix is also important for piezoelectric performance. For instance, at 40 Hz and 50 Hz the storage moduli of the softest specimen were ∼0.625 MPa and ∼0.485 MPa, while the loss moduli were ∼0.108 MPa and ∼0.151 MPa, respectively. As piezocomposites with less viscous loss can transfer mechanical energy to piezoelectric particles more efficiently, the dynamic piezoelectric coefficient (d'33) measured at 40 Hz (∼53 pC N-1) was larger than that at 50 Hz (∼47 pC N-1) though it has a larger storage modulus. As an application of our findings, we fabricated 3D piezo-shells with different viscoelastic properties and compared the charging time. The results showed a good agreement with the predicted trend that the composition with the smallest elastic and viscous moduli showed the fastest charging rate. Our findings can open new opportunities for optimizing the performance of polymer-based multifunctional materials by harnessing viscoelasticity.

Phase specific dispersion of functional nanoparticles in soft nanocomposites resulting in enhanced electromagnetic screening ability dominated by absorption.

The effect of phase specific localisation of MWNTs (multiwalled carbon nanotubes) and magnetic FeNi (iron-nickel) alloy particles on bulk electrical conductivity and electromagnetic (EM) wave attenuation was investigated in biphasic co-continuous blends of PVDF/SMA (polyvinylidene fluoride/styrene maleic anhydride). It is envisaged that packing different functional nanoparticles in a given phase of a co-continuous blend can impede the charge transport phenomenon and the overall dispersion state. Therefore, phase specific localisation can facilitate the tuning of the functional properties in biphasic blends. This strategy was adopted here wherein conducting MWNTs and magnetic FeNi particles were surface tailored to position them in different phases during processing. As the functional particles prefer the PVDF phase by virtue of thermodynamics, by harnessing amine functional moieties on the surface, their localisation can be tuned to position them in the SMA phase (due to amine-anhydride coupling). This was achieved by sequential mixing during processing. For the best combination, SET was observed to be -23 dB when MWNTs were localised in the SMA phase and magnetic particles in the PVDF phase of the blend with an impressive 92% absorption of the incident EM radiation.

The Effects of a High Magnetic Field on the Annealing of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb₄ Bulk Metallic Glass.

In contrast with amorphous alloys, nanocrystalline soft magnetic materials show improved thermal stability and higher soft magnetic properties. The nanocrystalline soft magnetic composites are usually fabricated by partially crystallizing from parent amorphous alloys. This paper reports our experimental observation on the sequence of crystallization in metallic glass under a high magnetic field (HMF). An application of a HMF to bulk metallic glass (BMG) of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 prioritizes the precipitation of α-(Fe,Co) phase separated from the subsequent precipitation of borides, (Fe,Co)23B6, upon isothermal annealing at a glass transition temperature. Furthermore, it was observed that, through the annealing treatment under a HMF, a soft magnetic nanocomposite, in which only α-(Fe,Co) phase uniformly distributes in amorphous matrix, was achieved for boron-bearing BMG. The promotion of the α-Fe or (Fe,Co) phase and the prevention of the boride phases during the isothermal annealing process help to produce high-quality soft magnetic nanocomposite materials. The mechanism by which a HMF influences the crystallization sequence was interpreted via certain changes in Gibbs free energies for two ferromagnetic phases. This finding evidences that the annealing treatment under a HMF is suitable for enhancing the soft magnetic properties of high B content (Fe,Co)-based bulk amorphous and nanocrystalline materials.

Multiblob coarse-graining for mixtures of long polymers and soft colloids.

Soft nanocomposites represent both a theoretical and an experimental challenge due to the high number of the microscopic constituents that strongly influence the behaviour of the systems. An effective theoretical description of such systems invokes a reduction of the degrees of freedom to be analysed, hence requiring the introduction of an efficient, quantitative, coarse-grained description. We here report on a novel coarse graining approach based on a set of transferable potentials that quantitatively reproduces properties of mixtures of linear and star-shaped homopolymeric nanocomposites. By renormalizing groups of monomers into a single effective potential between a f-functional star polymer and an homopolymer of length N0, and through a scaling argument, it will be shown how a substantial reduction of the to degrees of freedom allows for a full quantitative description of the system. Our methodology is tested upon full monomer simulations for systems of different molecular weight, proving its full predictive potential.

SiO2@MFe2O4 core-shell nanostructures: Efficient photocatalysts with excellent dispersion properties

In the present investigation core-shell structures of silica coated soft ferrite MFe2O4 nanocomposites have been successfully prepared through stobber’s method and have been structurally diagnosed by various techniques. Powder XRD diffraction pattern revealed the cubic crystal structure of the metal ferrite nanoparticles. HRTEM was used to visualize the coating of silica on the surface of MFe2O4 ferrite nanoparticles. Coating of silica on the soft ferrite nanoparticles lowered the band gap values in comparison to the corresponding pristine ferrite nanoparticles. VSM studies were carried out and ferrite nanoparticles retained their magnetic behavior with little reduction in the saturation and coercivity values on coating with the silica layer. Present protocol provides very efficient core shell structural nanocatalysts for the photocatalytic degradation of toxic organic pollutants with very good dispersion properties.

Concurrent determination of two opposite phase transitions in a soft polymer nanocomposite by rheology and their theoretical evaluations

The polymerization-induced biphasic nature of an emulsion 30/70wt.% methyl methacrylate (MMA)/butyl acrylate (BA) copolymer was deeply scrutinized with different techniques as the MMA-rich/BA-rich copolymers blend. Its experimentally found upper critical solution temperature (UCST) was then confirmed by the Sanchez-Lacombe lattice fluid (SLLF) and compressible regular solution (CRS) models. Characterization of soft polymer nanocomposites (SPNs) from the aforementioned system as the matrix and different fractions of mono-size poly(styrene-co-acrylonitrile) soft nanoparticles made of 70wt.% styrene (SAN70) with dynamic mechanical thermal analysis (DMTA), atomic force microscopy (AFM), and rheometry approved their multi-phase character. Homogenization temperatures of the matrix components along with the phase separations of MMA-rich/SAN70 copolymers were concurrently determined by applying Ajji and Choplin’s mean field theory on rheological measurements as a closed loop-like phase diagram. Granular state assumption regarding the soft nanoparticles by imposing geometrical constraints on their interactions based on the generalized SLLF model led to acceptable predictions about the observed lower critical solution temperature (LCST) phase behavior.

Synthesis and magnetic properties of core-shell structured Finemet/Ni[sbnd]Zn ferrite soft nanocomposites by co-precipitation

Finemet/NiZn ferrite core-shell particles and toroid core have been synthesized by co-precipitation method combined with following compact pressure and high temperature sintering process. The toroid core were produced from these particles by mold compacting with a compact pressure of 1400 Mpa at room temperature, then sintered at 600 °C for 1 h. The SEM results indicated that a layer of ferrite was uniformly coated on the surface of Finemet particles, with the increase of ferrites thickness, the permeability, saturation magnetization and magnetic loss of toroid core decrease, and the toroid core with 5 wt% ferrites shows excellent soft magnetic properties. It exhibits a high permeability of 56, high saturation magnetization of 127.1 emu/g and lower core loss of about 1.51 w/kg at 100 kHz and 50 mT.

Development of novel exchange spring magnet by employing nanocomposites of CoFe2O4 and CoFe2

CoFe2O4CoFe2 hard–soft nanocomposites were prepared via reduction of the cobalt ferrite CoFe2O4 in hydrogen atmosphere at different temperature. The structure and the room temperature magnetization of the samples were characterized by X-ray diffraction, field emission scanning electron microscope (FESEM) and vibrating sample magnetometer (VSM). It was found that the saturation magnetization of the nanocomposite powders increases by reduction temperature while their coercivity decreases. The highest Mr/Ms ratio of 0.52 was obtained for sample reduced at 550°C. Single smooth hysteresis loops of nanocomposites show that these nanocomposites behave as the single-phase materials. This result indicates the presence of exchange coupling between two different hard and soft phases.

Role of in situ generated silica for rubber science and technology

AbstractFilled rubbers have a long history in rubber technology. Filler morphology in the rubber matrix significantly influences the performance of filled rubber products. Therefore, we have to achieve a certain morphology of filler in the rubbery matrix in order to enjoy good reinforcement. However, it has not been sufficiently known what kind of morphology is necessary for the reinforcement, because preparations of adequate models for the characterization of filler morphology have been difficult. The in situ silica filling of the rubber matrix can be modeled for the preparations. In this paper, the characteristic features of in situ silica generated in diene rubbers are reviewed, citing recent reports. Two important models are presented. One is a homogeneous silica filling in situ, producing soft rubber nanocomposites. The other is the formation of an in situ silica filler network, creating stiff rubber nanocomposites. The controlled in situ silica filling is useful to evaluate the reinforcement effect of filler in a rubber matrix. © 2016 Society of Chemical Industry