Reconstruction of drive assembly and magnetic particles multicomponent super

Particle assemble into higher order structure portion originated mesoscopic matter. Super-particles is such a class of colloids, colloidal super-scale structure must be assembled in a precise control of the local interaction. Traditionally colloidal self-assembly is driven by non-specific interactions, such as van der Waals and electrostatic forces. An effective method of long-range interactions between the colloidal particles orientation is induced by the application of an external electromagnetic field. However, the external field drive assembly can not provide control over the internal local alignment of the particles. Species lack limit colloids assembled configuration control super-dimensional chain structure is a two-dimensional isotropic crystal and other global cluster. Therefore, the use of remote-field drive assembly interacting with discrete particles of ultra-clear structure remains a challenge. 磁场驱动的多组分超粒子的组装和重构 Recently, Bhuvnesh Louisiana State University professor Bharti team on \”Science Advances\” describes the dynamic assembly of discrete particles of an anisotropic ultra-discrete \”nuclear\” and non-magnetic \”satellite\” composed of particles . Analysis by vapor deposition controlling local surface iron polystyrene manufactured nuclear magnetic layer, and a magnetic field induced by the interaction between particles is programmed. By connecting the control member, the composition and distribution, the authors show three-dimensional assembly of multicomponent super-particles, the super-particles may be dynamically reconfigurable in response to the external field variation. Adjustable having a predetermined symmetry, the body assembly provides a platform colloidal substances, it may be designed with a functional material microstructure physical and chemical characteristics may be preprogrammed. On the nucleus and polystyrene particles into satellite superparamagnetic Fe3O4 nano-particles in the aqueous ferrofluid suspensions configuration, and exposed to a uniform magnetic field of satellite particles are attached to the core to form a discrete anisotropic ultra particle assembly. To assemble the ferromagnetic layers provides a strong directivity, most satellite particles are deposited on the iron layer. Assembled structure is transient and disappear when the external magnetic field off. Due to their negative surface charge, all particles in the suspension will initially mutually exclusive. Upon application of an external magnetic field, the assembly will follow multistep growth mechanism. Proportional to the number of particles and the growth rate over the satellite particles, the particle concentration of the satellite also determines the maximum size of the super-particles may be achieved. Exposure to a magnetic field (2500 A m-1) after about 35 minutes, the clusters reaches near equilibrium state.

Figure 1 SuperParticle assembly and test equipment. (A) SEM and (B) a fluorescence micrograph Janus particles. (C) on a microscope stage for the Helmholtz coil assembly. Schematic and corresponding bright-field image (D) model of the assembled system. (E to I) to four satellites multistep particle aggregation over the nucleation and growth of particles. (J to N) assembled ferrofluid kinetics of fluorescence micrographs.

solution over the particles will experience the competition between the magnetic attraction and repulsion: assembling a multi-pole due to the interaction, and can lead to long-range repulsion magnetic separation, and limits the close packing of the crystalline phase form. Self-avoidance between the super-particles are repelled by the A-A induced dipole. This self-limiting behavior causes the magnetic particles orderly arranged in a hexagonal array of super. Depending on the electric field intensity, and the size of the iron layer ferrofluid concentration factors, clusters occur in a variety of configurations. In some cases, the particles not only gather the satellite on the metal layer, and will collect on the non-magnetic core hemisphere, the composition having the same composition and different configurations of colloidal isomers. The total proportion of the core particles and the satellite will lead to increased particle capture characteristics Janus space to increase the number of non-magnetic particles, favors the formation of large clusters.

Figure 2. Effect of colloidal particles cluster and satellite / core ratio of the number. (A) a two-dimensional hexagonal array of super-particles. (B) colloidal clusters classification: top to bottom, the particles increase in number of satellites; left to right, a non-magnetic particles on the satellite scaled hemisphere. (C) increases as the number of core particles satellite / ratio, the frequency of the assembly is reduced smaller clusters, favors the formation of ultra-large particles.

magnetic energy is represented by a magnetic field applied to the plane of the satellite particle orientation angle θ of a function. Surprisingly, the magnetic energy in the θ = 109 ° is displayed at local minima. The presence of such minimum value due to the attraction between the satellite particles and the layer reaches the delicate balance iron, together with the results of non-magnetic repulsion between the hemisphere and the satellite particle. During assembly, the proximity Janus particles from non-magnetic particles may be hemispherical side satellite strong repulsion pole 90 ° and 180 ° of the equator weak repulsion. At the same time, it will be to attract metal layer cross-Janus particles. Local minimum orientation angle depends on the balance between the magnetic interactions. Low enthalpy of formation of clusters with a thermodynamic advantage. Thus, for a given cluster size, X isomers than Y, in which the non-magneticA particle adhered on the hemisphere, Y isomer Z isomer is more advantageous than the thermodynamically.

Fig 3. Janus magnetic particles. (A) particles to the satellite positioning Janus particles. (B) applying a fixed lower case 2500 A m-1, the relationship between θ and FIG dipole magnetic field strength calculated H =. Minimum value found in the total energy at θ = 0 °, θ = 109 ° at the local minimum value found. Around the magnetic flux density (C) calculated using COMSOL Janus particle distribution.

For the iron layer J cluster size has a great influence of the magnetic energy distribution. Submerged in the ferrofluid layer in the non-ferrous particles exhibit a single global minimum at the pole (90 °), the introduction of the iron so that the new layer is moved to the global minimum equatorial iron layer (0 °). For Janus particles, from the location of this local minimum of 93 ° J = 0.1 J = 0.5 moves the 109 °. The increased J = 0 J = 0.5, in the position of the satellite particles from the local minima becomes δ = 0.05μm δ = 1.1μm (the distance between the center of the core particle [delta] Satellite polar axis). A ferromagnetic core having a highly asymmetric quadrupole polarization, satellite attract core particles at the equator near the poles and repel them. Iron layer increases means strengthening the two kinds of interactions. If J is reduced, the strength of the interaction will also reduce nuclear and nearly isotropic case.

Effects 磁场驱动的多组分超粒子的组装和重构
Figure 4. size J of the iron layer. (A) for different sizes of the iron layer, the relationship between the calculated and θ of the dipole magnetic energy. (B) from the measured and calculated values ​​of δ with increasing J increases. (C) from the upper to the lower, AB Y image obtained by increasing the size of the super-particles of the iron layer having a different structure.

colloidal interactions tuning techniques constitute a set of functions in the future application development tools. In this context, this study connects the two super-particle research trends in the field of engineering: simple, scalable way to obtain the repeatability of the cost, and highly precise structure assembled through multiple complex stages.