Interparticle Distance Increases Research Articles

Effect of electrostatic interactions on structure and mechanical properties of ice templated colloid-polymer composites

When an aqueous dispersion of negatively charged colloids, cationic polymer and crosslinker is frozen and the polymer is allowed to crosslink in the frozen state, we obtain a self-standing macroporous composite foam. This material is soft, despite the high concentration of colloids and yet is remarkably elastic to large compressive strains. In these macroporous composites, the pore walls comprise colloidal particles held within a crosslinked polymer network. Here, we investigate the effect of varying colloid- polymer interactions in pre-fabricated macroporous composites on their microstructure and mechanical properties. During preparation of the composite, cationic polymer adsorbs on the negatively charged colloids. We tune the surface charge of particles embedded in a macroscopic monolith by immersing the composites in water maintained at different pH. In this way, we tune polymer-particle interactions in the composite. We observe a sudden increase in interparticle distance and swelling of composite when pH is decreased below the particle’s isoelectric point. Correspondingly, we observe reduction in Young’s and shear moduli, compression strength and macroscopic energy dissipation. We did not observe any pH dependent changes in pure polymer sponges (prepared by ice templating and crosslinking a polymer solution that does not contain colloidal particles). Therefore, the pH dependent structural and mechanical property changes arise from the composite structure rather than purely from the crosslinked polymer. We believe that the reduction in mechanical stiffness when the polymer–particle interaction becomes repulsive is because of the reduction in interfacial contacts between particle and polymer. Therefore, the mechanical stiffness of ice templated composite is strongly influenced by interactions between the polymer and particle surface.

2D melting of confined colloids with a mixture of square and triangular order

We implement Brownian dynamics to investigate the melting processes of colloidal particles confined isotropically and interacting via a potential which can be tailored in a repulsive–attractive–respulsive fashion as the interparticle distance increases. The stable configurations of such a system is composed of a large diversity of structures, which includes quasicrystalline, triangular, square, and mixed orderings, as well as the presence of fringes and holes, which are located, respectively, at the border and interior of the clusters. Our simulations demonstrate that during the melting process particles are able to swing between different micro phases. This intermediary stage, present in a finite range of temperature, precedes the melting in all cases investigated and is different from the hexatic phase of the KTNHY framework. We also test the fringes stability and find it to be higher than the one found in compact clusters. Finally, we show that, at the high temperature regime, the system loses its angular ordering while still preserves its radial interparticle confinement, which, ultimately, causes the proliferation of small subclusters.

Quantum particle interacting with a metallic particle: Spectra from quantum Langevin theory

The effect of a nearby metallic particle on the quantum optical properties of a quantum particle in the four-level double Raman configuration is studied using the quantum Langevin approach. We obtain analytical expressions for the correlated quantum fields of Stokes and anti-Stokes photons emitted from the system and perform analysis on how the interparticle distance, the direction of observation or detection, the strengths of controllable laser fields, the presence of surface plasmon resonance, and the number density of the quantum particle affect the quantum spectra of the Stokes and anti-Stokes fields. We explore the physics behind the quantum-particle\char21{}metallic-nanoparticle interaction within the dipole approximation, that is, when the interparticle distance is much larger than the sizes of the particles. Our results show the dependence of the spectra on the interparticle distance in the form of oscillatory behavior with damping as the interparticle distance increases. At weaker laser fields the enhancement of quantum fields which manifests itself in the form of a Fano dip in the central peak of the spectra becomes significant. Also, the quantum-particle\char21{}metallic-nanoparticle coupling, which is affected by the size of the metallic nanoparticle and the number density of the quantum particle, changes the angular dependence of the spectra by breaking the angular rotational symmetry. In the presence of surface plasmon resonance the oscillatory dependence of the spectra on the interparticle distance and angles of observation becomes even stronger due to the plasmonic enhancement effect.

Engineering the Magnetic Dipolar Interactions in 3D Binary Supracrystals Via Mesoscale Alloying

Inspired by metallic alloys in atomic solids, two distinct metallic nanoparticles are used, considered as “artificial metal atoms,” to engineer ordered binary nanoparticle alloys at the mesoscale, called binary supracrystals. Here, ferromagnetic 7.2 nm Co nanoparticles are used as large “A” site particles, while either ferromagnetic 4.6 nm Co or nonmagnetic 4.0 nm Ag nanoparticles are used as small “B” site particles to fabricate long‐range ordered binary supracrystals with a stoichiometry of AB2 and AB13. The interparticle distances between 7.2 nm Co nanoparticles within the Co/Ag binary supracrystals can be tuned by a control of crystal structure from AB2 (CoAg2) to AB13 (CoAg13). A decrease of magnetic coupling between Co nanoparticles is observed as the Co–Co interparticle distance increases. Furthermore, by alloying 7.2 and 4.6 nm Co nanoparticles to form AB2 (CoCo2) binary supracrystals, a collective magnetic behavior of these two particle types, due to the dipolar interaction, is evidenced by observing a single peak in the zero‐field‐cooled magnetization curve. Compared with the CoAg2 binary supracrystals, a spin orientation effect in sublattice that reduces the dipolar interactions in the supracrystals is uncovered in CoCo2 binary supracrystals.

Structural orderings of anisotropically confined colloids interacting via a quasi-square-well potential.

We implement Brownian dynamics to investigate the static properties of colloidal particles confined anisotropically and interacting via a potential which can be tailored in a repulsive-attractive-respulsive fashion as the interparticle distance increases. A diverse number of structural phases are self-assembled, which were classified according to two aspects, that is, their macroscopic and microscopic patterns. Concerning the microscopic phases we found the quasicrystalline, triangular, square, and mixed orderings, where this latter is a combination of square and triangular cells in a 3×2 proportion, i.e., the so-called (3(3),4(2)) Archimedian lattice. On the macroscopic level the system could self-organize in a compact or perforated single cluster surrounded or not by fringes. All the structural phases are summarized in detailed phases diagrams, which clearly show that the different phases are extended as the confinement potential becomes more anisotropic.

Increase in interparticle distance of colloidal dipolar chain in nematic liquid crystal by trapping it on splay-bend wall

We demonstrate an increase in the interparticle distance of a colloidal dipolar chain in a nematic liquid crystal (NLC). Applying an in-plane electric field perpendicular to the rubbing direction induces a splay-bend wall defect in the middle of the electrode gap, which traps a dipolar chain. Above the Freedericksz threshold electric field, the interparticle distance increases with increasing applied electric field, owing to the reorientation of the NLC molecules. The maximum increase is 32% of the particle diameter.

Alignment of particles in a confined shear flow of a viscoelastic fluid

The alignment of particles in a confined shear flow of a viscoelastic fluid is quantitatively analyzed using an extended finite element method (XFEM) with a temporary arbitrary Lagrangian–Eulerian (ALE) scheme. The no-slip boundary condition on the particle surface is realized by using a newly proposed weak boundary condition, which is equivalent to adding a positive definite stabilizing term in the momentum balance. Once particles form a string-like structure, the final state is independent of the initial particle positions and the histories to reach the steady-state. For a certain fluid rheology, the maximum obtainable length of a string of particles is limited. As the Weissenberg number increases, particles can form longer strings. Moderate wall confinement promotes the alignment of particles, however, too strong confinement hinders the alignment by enhancing repulsive interaction between particles. The steady-state angular velocities of particles are compared with respect to the length of strings. If particles can form sufficiently long strings, the steady-state angular velocities of the two end-particles do not change significantly, and those of the non end-particles increase, as the string length increases. In a given string, the angular velocity of the two end-particles is faster than those of the particles in between. We have also presented the steady-state interparticle distance between two neighboring particles in a string. As the string length increases, the interparticle distance increases.

Thermal-induced surface plasmon band shift of gold nanoparticle monolayer: morphologyand refractive index sensitivity

In this paper, thermal-induced behaviors of a gold nanoparticle monolayer onglass slides are investigated. First, through horizontal lifting, gold nanoparticlemonolayers are transferred from a water/hexane interface to glass slides. Thenthermal treatment is carried out in air, after which an apparent color changeof the obtained samples is noticed, depending on the annealing temperature,reflecting a shift of the surface plasmon band (SPB). Depending on the trend ofSPB shift, the overall thermal process is divided into three stages. In the firststage, SPB shows a redshift trend with concomitant band broadening. Furtherincrease of the annealing temperature in the second stage results in an increase ofinterparticle distance. Thus an apparent decrease in absorbance takes place withSPB shift to shorter wavelengths. In the third stage, the SPB redshifts again.Bulk refractive index sensitivity (RIS) measurements are taken by immersing theobtained samples in solutions of various refractive indices and a linear dependence ofRISλ andRISext on refractive index is concluded. In particular, the influences of parameters such as particlesizes, location of SPB, substrate effect and morphology effect on RIS are discussed indetail. The corresponding performance of each sample as a localized surface plasmonresonance-based sensor is evaluated by a figure of merit (FOM) represented asFOMλ andFOMext. It is found that the optimum annealing temperature is500 °C. In terms of nanoparticle sizes, samples with a 35 nm gold nanoparticle monolayer performbetter than those with 15 nm. The current strategy is simple and facile to achieve finecontrol of the SPB, in which large-size precision instruments or complex chemosynthesis areunnecessary. Therefore, this method has not only significance for theory but also usefulnessin practical applications.

Mechanically tunable surface plasmon resonance based on gold nanoparticles and elastic membrane polydimethylsiloxane composite

Surface plasmon in nanoscaled materials has recently attracted a great deal of attention due to its possibility in a wide range of application. From a practical standpoint, it is desirable for the devices having a tunability of surface plasmon frequency. To achieve this goal, in this study, a composite consisting of two-dimensional gold nanoparticles array embedded in elastic polydimethylsiloxane (PDMS) membrane has been synthesized. Because the elastic PDMS membrane has a high malleability, with an external stress, it is very easy to regulate the interparticle distance in the gold nanoparticle array. The change in the distance between each nanoparticle will alter the surface plasmon interaction, and hence surface plasmon frequency can be manipulated. It is found that when the interparticle distance increases, the enhanced surface plasma mutual coupling will cause the blueshift of surface plasmon resonance frequency. The observed result satisfies the forecast based on electromagnetic theory.

Gravitational dynamics of an infinite shuffled lattice: Particle coarse-graining, nonlinear clustering, and the continuum limit

We study the evolution under their self-gravity of particles evolving from infinite "shuffled lattice" initial conditions. We focus here specifically on the comparison between the evolution of such a system and that of "daughter" coarse-grained particle distributions. These are sparser (i.e., lower density) particle distributions, defined by a simple coarse-graining procedure, which share the same large-scale mass fluctuations. We consider both the case that such coarse-grainings are performed (i) on the initial conditions, and (ii) at a finite time with a specific additional prescription. In numerical simulations we observe that, to a first approximation, these coarse-grainings represent well the evolution of the two-point correlation properties over a significant range of scales. We note, in particular, that the form of the two-point correlation function in the original system, when it is evolving in the asymptotic "self-similar" regime, may be reproduced well in a daughter coarse-grained system in which the dynamics are still dominated by two-body (nearest neighbor) interactions. This provides a simple physical description of the origin of the form of part of the asymptotic nonlinear correlation function. Using analytical results on the early time evolution of these systems, however, we show that small observed differences between the evolved system and its coarse-grainings at the initial time will in fact diverge as the ratio of the coarse-graining scale to the original interparticle distance increases. The second coarse-graining studied, performed at a finite time in a specified manner, circumvents this problem. It also makes it more physically transparent why gravitational dynamics from these initial conditions tends toward a self-similar evolution. We finally discuss the precise definition of a limit in which a continuum (specifically Vlasov-type) description of the observed linear and nonlinear evolution should be applicable. This requires the introduction of an additional intrinsic length scale (e.g., a physical smoothing in the force at small scales), which is kept fixed as the particle density diverges. In this limit the different coarse-grainings are equivalent and leave the evolution of the "mother" system invariant.