Temporary shape development in shape memory nanocomposites using magnetic force

Direct mechanical force is used to create a temporary shape in shape memory polymers. This can become difficult in situations where the sample is not directly accessible such as interior in the body. In these cases it is not possible to use a direct mechanical force to deform the sample into temporary shape; therefore other alternative routes should be proposed. The magnetic force is a good candidate for inducing remote deformation. The ability of magnetic field to cause deformation in soft matters has already been revealed. To prove the hypothesis of using magnetic force to create temporary shape, magnetic field active shape memory polymeric nanocomposites were manufactured by incorporation of NdFeB ferromagnetic micro particles in a nanocomposite based on crosslinked low density polyethylene loaded with 2 wt.% of organoclay. The results indicate that as the NdFeB content increases, the reversible temporary deformation induced in the samples by the magnetic force increases. The effect of NdFeB concentration on the shape recovery progress and the possibility of heat induction in NdFeB filled samples through the application of an alternating magnetic field were also examined.     

Nonlinear deformation of a ferrofluid droplet in a uniform magnetic field

This paper reports experimental and numerical results of the deformation of a ferrofluid droplet on a superhydrophobic surface under the effect of a uniform magnetic field. A water-based ferrofluid droplet surrounded by immiscible mineral oil was stretched by a magnetic field parallel to the substrate surface. The results show that an increasing flux density increases the droplet width and decreases the droplet height. A numerical model was established to study the equilibrium shape of the ferrofluid droplet. The governing equations for physical fields, including the magnetic field, are solved by the finite volume method. The interface between the two immiscible liquids was tracked by the level-set method. Nonlinear magnetization was implemented in the model. Comparison between experimental and numerical results shows that the numerical model can predict well the nonlinear deformation of a ferrofluid droplet in a uniform magnetic field.     

Deformation of magnetosensitive emulsion microdroplets in magnetic and electric fields

A magnetosensitive emulsion comprising an ensemble of nonmagnetic oil droplets suspended in a kerosene-based magnetic fluid is studied. It is found that the droplets of such an emulsion are deformed in both magnetic and electric fields. The character of microdroplet deformation in the electric field depends on the field frequency: at low frequencies, the droplets are flattened; at high frequencies, the droplets are stretched along the force lines of the field. It is established that the deformation caused by the electric field can be compensated for by the imposition of an additional magnetic field, and the conditions of this compensation are determined. It is revealed that, under the action of a magnetic field directed normal to a thin layer of the emulsion, the droplets “split” into branched structures. The action of a similarly directed alternating electric field leads to the transformation of the droplets into tori followed by their rupture. It is concluded that the structure of the emulsion can be efficiently controlled using the combined action of magnetic and electric fields. Original Russian Text ? Yu.I. Dikanskii, O.A. Nechaeva, A.R. Zakinyan, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68, No. 2, pp. 161–165.     

Dynamical behavior of magnetic polarizable microsphere using whispering gallery mode

In this article, analytical and experimental studies are carried out to investigate the dynamical behavior of polymer microspheres that are doped with magnetic polarizable microparticles. The effect of a static and harmonic inductive magnetic field on the elastic deformation of the microsphere is investigated. The elastic deformation that is induced by the magnetic forces (magnetostrictive effect) acting on the microsphere is measured using an optical technique that is based on the whispering gallery mode (WGM) of the microsphere. The WGMs experience a shift when the morphology of the resonator is perturbed by the elastic deformation. Therefore, the elastic deformation of the microsphere is measured by monitoring the shift of the optical resonances. For these studies, the microsphere has a radius of ∼600 µm and is fabricated by mixing polyvinyl chloride (PVC) with magnetic polarizable microparticles. The microsphere is further coated with a thin layer of pure PVC that serves as a wave‐guide for the optical modes. Experiments are carried out to validate the analysis. Measurements are taken up to a frequency of 200 Hz, showing that the microspheres can be used as magnetic field sensors or as element for the fabrication of smart structures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 598–603     

A model of spin crossover in manganese(III) compounds: effects of intra- and intercenter interactions

A microscopic approach to the problem of cooperative spin crossover in the [MnL2]NO3 crystal, which contains Mn(III) ions as structural units, is elaborated on, and the main mechanisms governing this effect are revealed. The proposed model also takes into account the splitting of the low-spin 3T1 (t(2)(4)) and high-spin 5E (t(2)(3)e) terms by the low-symmetry crystal field. The low-spin → high-spin transition has been considered as a cooperative phenomenon driven by interaction of the electronic shells of the Mn(III) ions with the all-around full-symmetric deformation that is extended over the crystal lattice via the acoustic phonon field. The model well explains the observed thermal dependencies of the magnetic susceptibility and the effective magnetic moment.     

A Magnetic Bio-Inspired Soft Carrier as a Temperature-Controlled Gastrointestinal Drug Delivery System

Currently, gastrointestinal bleeding in the colon wall and the small bowel is diagnosed and treated with endoscopes. However, the locations of this condition are often problematic to treat using traditional flexible and tethered tools. New studies commonly consider untethered devices for solving this problem. However, there still exists a gap in the extant literature, and more research is needed to diagnose and deliver drugs in the lower gastrointestinal tract using soft robotic carriers. This paper discusses the development of an untethered, magnetically-responsive bio-inspired soft carrier. A molding process is utilized to produce prototypes from Diisopropylidene-1,6-diphenyl-1,6-hexanediol-based Polymer with Ethylene Glycol Dimethacrylate (DiAPLEX) MP-3510 - a shape memory polymer with a low transition temperature to enable the fabrication of these carriers. The soft carrier design is validated through simulation results of deformation caused by magnetic elements embedded in the carrier in response to an external field. The thermal responsiveness of the fabricated prototype carriers is assessed ex vivo and in a phantom. The results indicate a feasible design capable of administering drugs to a target inside a phantom of a large intestine. The soft carrier introduces a method for the controlled release of drugs by utilizing the rubbery modulus of the polymer and increasing the recovery force through magnetic actuation.     

Vinyl Polymerization. 436. Effect of Magnetic Field on Uncatalyzed Polymerization

The radical polymerization of vinyl monomers initiated with several kinds of hydrophilic macromolecule was carried out in a magnetic field. The magnetic field promoted the polymerization; the conversion of monomers and the molecular weight of the polymers obtained increased with increasing field strength in the range of 0–0.1 T. The dependence of the composition and tacticity of the mother polymer on the magnitude of the magnetic field was studied. Using graft or block copolymers, which consisted of hard and soft segments, the effect of a magnetic field was further investigated. The degree of hardness and tightness of the hydrophobic areas (reaction areas) formed by the mother polymer in the aqueous solution was found to affect the magnetic field effect on the uncatalyzed polymerization. The overall activation energy obtained in the magnetic field was almost equal to that obtained without a magnetic field.     

Scattering from Ferrogels

Summary: This paper introduces a simple mean‐field theory for gels with magnetic properties. The main emphasis in this paper is the discussion of the scattering properties. Therefore, a simple model is introduced, such that the chains carry magnetic moments along their main axis. Naturally these magnetic moments interact sensitively to theory orientation with each other. Thus a distinguished interplay between chain and dipole orientation induces strong coupling between the macroscopic deformation and magnetic properties. These effects can be experimentally demonstrated with scattering methods. Here some mean‐field expressions for the structure factors are predicted and discussed in some detail.

The configurations adopted by polymers possessing a magnetic moment and undergoing dipole‐dipole interactions.     

Hysteretic behavior of diamagnetic molecular assembly: Magnetic field-induced deformation of tubular self-assemblies composed of amphiphilic molecules

Real-time observation of a morphologies of a multi-component tubular giant vesicle (tGV), which is a self-assembly composed of plural amphiphiles with different packing parameters, was carried out under application of a magnetic field. A tGV, one of the terminals of which was fixed to a bottom of a cell, exhibited the bending deformation under a magnetic field along the perpendicular direction of the long axis. Moreover, the hysteretic behavior in this deformation was observed associated with the increase and decrease of the magnetic fields repeatedly, regardless of the presence or absence of a paramagnetic species. To understand the hysteretic behavior, the molecular cooperative effect, which stabilizes the bending deformation by replacing of the plural kinds of amphiphiles with different packing parameters within a membrane, must be taken into consideration.     

On-chip magnetic bead microarray using hydrodynamic focusing in a passive magnetic separator

Implementing DNA and protein microarrays into lab-on-a-chip systems can be problematic since these are sensitive to heat and strong chemicals. Here, we describe the functionalization of a microchannel with two types of magnetic beads using hydrodynamic focusing combined with a passive magnetic separator with arrays of soft magnetic elements. The soft magnetic elements placed on both sides of the channel are magnetized by a relatively weak applied external magnetic field (21 mT) and provide magnetic field gradients attracting magnetic beads. Flows with two differently functionalized magnetic beads and a separating barrier flow are introduced simultaneously at the two channel sides and the centre of the microfluidic channel, respectively. On-chip experiments with fluorescence labeled beads demonstrate that the two types of beads are captured at each of the channel sidewalls. On-chip hybridization experiments show that the microfluidic systems can be functionalized with two sets of beads carrying different probes that selectively recognize a single base pair mismatch in target DNA. By switching the places of the two types of beads it is shown that the microsystem can be cleaned and functionalized repeatedly with different beads with no cross-talk between experiments.     

Magneto‐sensitive Elastomers in a Homogeneous Magnetic Field: A Regular Rectangular Lattice Model

A theory of mechanical behaviour of the magneto‐sensitive elastomers is developed in the framework of a linear elasticity approach. Using a regular rectangular lattice model, different spatial distributions of magnetic particles within a polymer matrix are considered: isotropic, chain‐like and plane‐like. It is shown that interaction between the magnetic particles results in the contraction of an elastomer along the homogeneous magnetic field. With increasing magnetic field the shear modulus, G, for the shear deformation perpendicular to the magnetic field increases for all spatial distributions of magnetic particles. At the same time, with increasing magnetic field the Young's modulus, E, for tensile deformation along the magnetic field decreases for both chain‐like and isotropic distributions of magnetic particles and increases for the plane‐like distribution of magnetic particles.

     

The leap-frog effect of ring currents in benzene

Symmetry arguments show that the ring-current model proposed by Pauling, Lonsdale, and London to explain the enhanced diamagnetism of benzene is flawed by an intrinsic drawback. The minimal basis set of six atomic 2p orbitals taken into account to develop such a model is inherently insufficient to predict a paramagnetic contribution to the perpendicular component of magnetic susceptibility in planar ring systems such as benzene. Analogous considerations can be made for the hypothetical H(6) cyclic molecule. A model allowing for extended basis sets is necessary to rationalize the magnetism of aromatics. According to high-quality coupled Hartree-Fock calculations, the trajectories of the current density vector field induced by a magnetic field perpendicular to the skeletal plane of benzene in the pi electrons are noticeably different from those typical of a Larmor diamagnetic circulation, in that (i) significant deformation of the orbits from circular to hexagonal symmetry occurs, which is responsible for a paramagnetic contribution of pi electrons to the out-of-plane component of susceptibility, and (ii) a sizable component of the pi current density vector parallel to the inducing field is predicted. This causes a waving motion of pi electrons; streamlines are characterized by a "leap-frog effect".     

Frequency variation of periodic distortion thresholds in a nematic liquid crystal

Investigations are reported on the electric field induced orientational transitions in the bend Freedericksz geometry under the action of a stabilizing magnetic field. When the magnetic field is strong enough, the deformation above electric threshold is periodic with the periodicity disappearing at a higher voltage. The alignment does not remain homeotropic below threshold and the sample exhibits pretransitional biaxiality. Every transition is discontinuous and accompanied by hysteresis. The expected form of scaling appears to hold for all the observed thresholds. The thresholds and the direction of the wave vector are frequency dependent, showing that the instability mechanism involves electrical conductivity.     

Magnetic characteristics of Fe4N epitaxial films grown by halide vapor phase deposition under atmospheric pressure

The thin films of Fe₄N, which were prepared by atmospheric pressure halide vapor phase deposition, were epitaxially grown on a MgO(100) substrate and have cubic structure with good crystallinity. The magnetic characteristics of Fe₄N epitaxial film show soft magnetic behavior under various temperatures and various external magnetic field directions. As the temperature is decreased, the saturation magnetization increases. Also, the magnetized behavior is observed when the magnetic field is applied parallel to the film plane. It was found that the magnetic moments of Fe₄N epitaxial film are facing parallel to the film plane.     

Magnetically-actuated artificial cilia for microfluidic propulsion

In this paper we quantitatively analyse the performance of magnetically-driven artificial cilia for lab-on-a-chip applications. The artificial cilia are fabricated using thin polymer films with embedded magnetic nano-particles and their deformation is studied under different external magnetic fields and flows. A coupled magneto-mechanical solid-fluid model that accurately captures the interaction between the magnetic field, cilia and fluid is used to simulate the cilia motion. The elastic and magnetic properties of the cilia are obtained by fitting the results of the computational model to the experimental data. The performance of the artificial cilia with a non-uniform cross-section is characterised using the numerical model for two channel configurations that are of practical importance: an open-loop and a closed-loop channel. We predict that the flow and pressure head generated by the artificial cilia can be as high as 18 microlitres per minute and 3 mm of water, respectively. We also study the effect of metachronal waves on the flow generated and show that the fluid propelled increases drastically compared to synchronously beating cilia, and is unidirectional. This increase is significant even when the phase difference between adjacent cilia is small. The obtained results provide guidelines for the optimal design of magnetically-driven artificial cilia for microfluidic propulsion.     

Effect of Film Thickness on the Columnar Packing Structures of Discotic Supramolecules in Thin Films

The effects of film thickness on the columnar packing structure of discotic supramolecules in a thin supported film have been investigated by grazing‐incidence small‐angle X‐ray scattering technique using magnetically aligned cobalt octa(n‐decylthio)porphyrazine (CoS10) films on octadecyltrichlorosilane (OTS)‐functionalized substrates as model systems. Magnetically aligned CoS10 films with a range of film thicknesses (49–845 nm) form uniaxially oriented ‘edge‐on’ columnar superstructures with their columnar directors perpendicular to the applied magnetic field. However, the orientational ordering of the columnar packing in the plane perpendicular to the applied magnetic field is strongly dependent on the film thickness. While being damped by the elasticity of the side chains of CoS10, the strong interfacial interaction at the film‐substrate interface propagates up to 50–100 nm from the substrate, maintaining the orientation of columnar packing in the plane perpendicular to the applied magnetic field. When the distance from the film‐substrate interface becomes larger than about 100 nm, symmetric tilting of columnar layer orientation, which saturates at 11.5°, occurs due to longitudinal edge dislocations induced by accumulated elastic deformation.     

A bioinspired magnetic responsive cilia array surface for microspheres underwater directional transport

Bio-inspired surfaces are usually designed by imitating the surface properties of a particular biological species,or combing with the surface characteristics of multiple biological species to construct a cross-species surface.Herein,inspired by the structure and rhythmic swing of human pulmonary cilia,and the directional migration of pigeons by geomagnetic field,an integrated system of biomimetic hydrophobic magnetic cilia array surface with reversible deformation properties and excellent magnetic response performance for solid microspheres underwater transport is designed and constructed.Driven by an external magnetic field,the magnetic responsive cilia array surface can directionally and continuously transport microspheres underwater in periodic motion.This work will shed new light on the designing of micromanipulation systems for micro-objects transport,and promote the practical application of micro-operating systems in underwater transportation and drug delivery.     

Domain and segmental deformation behavior of thermoplastic elastomers using synchrotron SAXS and FTIR methods

Deformation behavior of the segmented block copolymers was studied with synchrotron small-angle X-ray scattering (SAXS) and Fourier transform infrared spectroscopy (FTIR) methods. Polyurethanes used in this work consist of 4,4′-methylene-bis(phenyl isocyanate) and butanediol as a hard segment, and poly(tetramethylene oxide) of various molecular weights as a soft segment. As expected, the deformation of the domain structure that is macroscopically isotropic before the drawing was anisotropic. Depending on the initial orientation of the hard domains, the deformation behavior was observed to be characteristically different. Whereas the hard domains oriented along the deformation direction underwent the extension of the domain separation distance at the low draw ratio, the perpendicular ones showed the shear compression. Further drawing was found to cause the breakup of the hard domains, followed by the formation of fibril structure oriented along the deformation direction. Based on SAXS and FTIR results, a model is proposed to explain the deformation behavior of the various domains and segments of the segmented block copolymers. By quantitatively analyzing the conformation of the soft segment during the deformation process, the model proposed has been consolidated. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3233–3245, 1999     

Photo-responsive liquid crystalline elastomer with reduced chemically modified graphene oxide

Photo-responsive liquid crystalline elastomer (LCE) with reduced chemically modified graphene oxide (RMGO) was fabricated and studied. Mesogenic groups modified graphene oxide (MGO) was prepared, reduced and characterised, then the obtained RMGO was mixed with an acrylate monomer containing a side-on mesogen, a crosslinker and a photoinitiator. After being oriented with magnetic field, well-defined LCE micropillar as photo-responsive actuators were fabricated from the mixture by the method combining soft lithography and photo-polymerisation/photo-crosslinking. The LCE micropillars showed reversible thermo-mechanical deformation during the nematic-to-isotropic transition temperature. Upon irradiating with red light (650 nm), photo-mechanical responses of the RMGO-containing LCE was demonstrated. This micron-sized LCE actuators can be used for remote photo-responsive devices.     

Magnetic field intensity effect on plane electric capacitor characteristics and viscoelasticity of magnetorheological elastomer

Magnetorheological (MR) elastomer was prepared using silicone rubber and soft magnetic carbonyl iron microspheres, and then examined as dielectric materials for manufacturing electric capacitors. As a specific element, capacity of the capacitors located in a magnetic field was found to be sensitive to both the MR suspension proportion to the silicone rubber and the intensity of the applied magnetic field. Viscoelastic characteristics of the MR elastomer, represented by storage modulus and creep behavior, were also studied.