Penetrable Particles Research Articles

CREEPING FLOW OF COUPLE STRESS FLUID OVER A SPHERICAL FIELD ON A SATURATED BIPOROUS MEDIUM

This problem emphasizes the dynamic interaction between a biporous medium and a couple stress fluid of laminar flow. The flow around a permeable field engulfed in a couple stress fluid is examined. When examining the motion of an oil droplet in a porous collector that is surrounded by an aqueous medium (oil-in-water emulsion) and is subject to an external pressure drop, this formulation of the problem is typical. A similar issue arises when lymph enters the tissues of humans or animals: the inside permeable spherical field saturated with viscous fluid and outside region saturated with couple stress fluid. The Brinkman equations are utilized to characterize the couple stress fluid flow in a saturated biporous medium. The couple stress tensor and velocity fields are expressed using Gegenbauer polynomials and Macdonald functions. For the axially symmetric motion, both pressure distribution and the stream function solution are explicitly solved. The method of variable separation is used to investigate an analytical resoluteness for the flow field. The drag force on a saturated biporous medium and the drag coefficient <i>D<sub>N</sub></i> are calculated, and the impacts of the permeability κ, the ratio of viscosity (γ<sup>2</sup> = μ<sub>1</sub> /μ<sub>2</sub>), the couple stress viscosity ratio (τ = η'/η), and the parameter of couple stress (λ = √μ/η). The appropriate dependencies are graphically delineated and reviewed, including the permeability κ, couple stress parameter λ, viscosity ratio γ<sup>2</sup>, and couple stress viscosities (η, η'). According to the findings, increasing permeability gradually raises the drag coefficient, which is used to describe a spherical field’s surface with a high level resistance of flow. Limits statements are used to illustrate specific cases that are well-known. The current study is significant primarily in the course through a layer formed by penetrable particles and has very important and compelling applications in both nature and innovation, with a variety of potential outcomes.

Motion through a viscous liquid sphere enclosed by a solid core embedded into a Brinkman medium

AbstractThe flow around a solid spherical particle encased in a Newtonian liquid sphere and immersed in a couple stress fluid medium is studied. The problem is expressed by using the Brinkman and Stokes equations, which describe both the flow outside and inside the liquid sphere, respectively. The Gegenbauer polynomials and modified Bessel function are used to express the stream function solution for the internal and external regions. An analytical determination for the flow field in terms of stream function is examined by wielding the method of separation of variables. The drag force on a solid spherical particle placed in a permeable region is calculated. On the drag coefficient, the effects of the permeability κ, the viscosity ratio γ2, and the couple stress parameter λ are investigated. Corresponding dependencies (such as the permeability parameter, couple stress parameter, viscosity ratio, and separation parameter) are graphically represented and discussed. The findings shows when the separation parameter is increased the drag coefficient gradually increases, it refers to a sphere surface with a high level of flow resistance. Passages to the limits are used to describe known specific cases. The present study is essentially significant in the course through a layer developed by penetrable particles and has very important and persuasive applications both in nature and innovation, with various potential outcomes. Thus, the discoveries of this article are comprehensively pertinent to the investigation of the flow of permeable liquids past spherical permeable rocks, aloxite materials, sand beds, earthen soil, petrol supply rocks, and so forth. The present application will support in planning a productive bearing framework.

Soft Poly(N-vinylcaprolactam) Based Aqueous Particles.

Soft nanoparticles are an important class of material with potential to be used as carriers of active compounds. Swollen, penetrable particles can act as a host for the active ingredients and provide stability, stimuli-responsiveness and recyclability for the guest. Thermoresponsive colloidal gel particles are especially attractive for such applications due to the extremely soft structure, size and responsiveness. Poly(N-vinylcaprolactam) (PNVCL) is a much studied, popular thermoresponsive polymer. The polymer has low toxicity and the phase transition temperature is close to body temperature. During the phase transition, the polymer becomes less soluble, the particle expels a large part of water and the particle collapses to a more compact form. The diffusion of material in and from the particles is largely affected by this transition. As the solubility of the polymer changes, so do the interactions with the loaded compound. This feature article focuses on the synthetic methods, properties and applications of soft PNVCL particles.

Mikto-Arm Stars as Soft-Patchy Particles: From Building Blocks to Mesoscopic Structures.

We present an atomistic molecular dynamics study of self-assembled mikto-arm stars, which resemble patchy-like particles. By increasing the number of stars in the system, we propose a systematic way of examining the mutual orientation of these fully penetrable patchy-like objects. The individual stars maintain their patchy-like morphology when creating a mesoscopic (macromolecular) self-assembled object of more than three stars. The self-assembly of mikto-arm stars does not lead to a deformation of the stars, and their shape remains spherical. We identified characteristic sub-units in the self-assembled structure, differing by the mutual orientation of the nearest neighbor stars. The current work aims to elucidate the possible arrangements of the realistic, fully penetrable patchy particles in polymer matrix and to serve as a model system for further studies of nanostructured materials or all-polymer nanocomposites using the mikto-arm stars as building blocks.

Thermodynamic collapse in a lattice-gas model for a two-component system of penetrable particles.

We study a lattice-gas model of penetrable particles on a square-lattice substrate with same-site and nearest-neighbor interactions. Penetrability implies that the number of particles occupying a single lattice site is unlimited and the model itself is intended as a simple representation of penetrable particles encountered in realistic soft-matter systems. Our specific focus is on a binary mixture, where particles of the same species repel and those of the opposite species attract each other. As a consequence of penetrability and the unlimited occupation of each site, the system exhibits thermodynamic collapse, which in simulations is manifested by an emergence of extremely dense clusters scattered throughout the system with energy of a cluster E∝-n^{2}, where n is the number of particles in a cluster. After transforming a particle system into a spin system, in the large density limit the Hamiltonian recovers a simple harmonic form, resulting in the discrete Gaussian model used in the past to model the roughening transition of interfaces. For finite densities, due to the presence of a nonharmonic term, the system is approximated using a variational Gaussian model.

Enhanced Capture of Particulate Matter by Molecularly Charged Electrospun Nanofibers

We introduce molecularly charged electrospun nanofibers obtained by soft chemical treatment for the capture of particulate matter (PM). These PMs, along with certain volatile organic compounds (VOCs), pose a severe threat not only to human health but also to the environment. As the concentrations of these PMs have been steadily increasing in the Southeast Asian countries, a dire need for protection against these particles is warranted. Filtering out the polluted air using various filtration media, such as face masks and nasal filters, has been the standard method for minimizing exposure to PM. Here, we demonstrate the removal of PM and VOCs by utilizing electrospun nanofibers of polystyrene (PS) and polyacrylonitrile (PAN) with molecular charges imparted on them via chemical treatment. The chemically treated fibers were successful in capturing even particles measuring 300 nm, which are considered to be the most penetrable particles. We report a filtration efficiency of ∼93% for removing such particles, which is ∼3 ± 1.5% enhancement when compared to the untreated fibers. The fibers have been subjected to extreme haze conditions (∼1413 μg m–³) of PM₂.₅ for a duration of 1 h, and the filtration efficiency was measured to be ∼99.01%. These fibers also possess the capability to capture model VOCs such as aniline, toluene, tetrahydrofuran, and chloroform. When PAN, PS, and their chemically treated counterparts were tested for their antibacterial activity, these filter mats had bactericidal effect on Escherichia coli, Bacillus subtilis, and Enterococcus faecalis. A nasal plug hosting these filter mats has been designed, which can offer personal protection from PM. Enhanced removal of residual particles is extremely important, and this difficult task is made possible with our approach. The efficiency of our approach is due to the charged nature of PM, especially of the smaller size regime.

Laser-triggered polymeric lipoproteins for precision tumor penetrating theranostics

Natural particles ranging from various cell membranes to nascent proteins are highly optimized for their specific functions in vivo and possess features that are desired in drug delivery carriers. However, the current endeavor in research on bioparticles is still seeking the appropriate strategy to shield multiple agents and circumvent biological hurdles. These issues have propelled the advancement of lipid-polymer hybrid nanocarriers, which could be employed as drug reservoirs and strive to meet these expectations. We thereby proposed functionalized biopeptide-lipid hybrid particles, which were applied to encapsulating a PLGA polymeric core together with indocyanine green (ICG) and packaged by a lipoprotein-inspired structural shell. To initiate precision tumor-penetrating performance, tLyP-1-fused apolipoprotein A-I-mimicking peptides (D4F) were exploited to impart tumor-homing and tumor-penetrating biological functions. The sub-100 nm drug vehicle possessed a long circulation time with uniform mono-dispersity but was stable enough to navigate freely, penetrate deeply into tumors and deliver its cargoes to the targeted sites. Moreover, ICG-encapsulated penetrable polymeric lipoprotein particles (PPL/ICG) could realize real-time fluorescence/photoacoustic imaging for monitoring in vivo dynamic distribution. Upon near-infrared (NIR) laser irradiation, PPL/ICG demonstrated a highly efficient phototherapeutic effect to eradicate orthotopic xenografted tumors, resulting in an 88.77% decrease from the initial tumor volume and inhibited tumor metastasis with good biosafety. Therefore, the described bio-strategy opens new avenues for creating polymeric lipoproteins with varied hybrid functionalities, which may be applied to provide a basis and inspiration for improved nanoparticle-based precision theranostic nanoplatforms.

Soft-particle lattice gas in one dimension: One- and two-component cases

The object of the present article is a 1d lattice-gas system comprised of soft-particles, wherein particles interact only if they occupy the same or a neighboring site, as a simple representation of penetrable particles of soft condensed matter. To represent different scenarios, two different realizations of the lattice model are considered, a one-component and a two-component system, where in the two-component case particles of the same species repel and those of opposite species attract each other. The systems are analyzed entirely within the transfer matrix framework. Special attention is paid to the criterion devised in Ref. [Phys. Rev. E 63, 031206 (2001)], which serves to separate two classes of behavior encountered in a one-component penetrable particle systems. In addition to confirm the existence of a similar criterion for the one-component lattice-gas model, we find that the same criterion can be applied to the two-component system to provide conditions for thermodynamic catastrophe.

Morphological Modification of Carbon Nanoparticles after Interacting with Methotrexate as a Potential Anticancer Agent.

Production of highly penetrable and targetable drug delivery particles is mainly focused by current therapy and such focus is achieved in our present study. The carbon nanoparticle (CNP) prepared from purely natural source was modified from spherical shape to cylindrical floral like structure after treatment with the anticancer drug methotrexate (CM). The physiochemical properties of the CNP and CM was characterized using FT-IR/Raman Spectrometer, XRD, SEM, AFM, particle size analyzer and its biological evaluation using haemolysis and MTT assay. The shift in FT-IR peaks at 1592, 1120cm-1 and peaks of raman spectra observed at 1303, 1300cm-1 represents ordered carbon nanotubes. The morphological change from spherical to cylindrical floral like structure was observed using SEM and AFM and its particle size distribution analysis shows an average diameter of 269nm for CM. XRD peak at 2θ = 23.86° (002) indicates the presence of large amount of amorphous material that corresponds to multi-walled carbon nanotubes. Haemocompatibility studies proved the safety level usage as 100μg/ml and MTT assay shows viability rate of 85-98% with mouse embryonic fibroblast (NIH/3T3) and 30-45% with pancreatic carcinoma (MIA PaCa-2) and gastric cancer cell lines (SNU- 484) respectively.These results are also supported by phase contrast microscope images observed after staining with calcein AM and EthD-1. The morphologically modified CNPs has shown good anticancer, biocompatibility and haemocompatibility property which is an important criterion to be satisfied by a biomedical product.

Flow induced crystallisation of penetrable particles

For a system of Brownian particles interacting via a soft exponential potential we investigate the interaction between equilibrium crystallisation and spatially varying shear flow. For thermodynamic state points within the liquid part of the phase diagram, but close to the crystallisation phase boundary, we observe that imposing a Poiseuille flow can induce nonequilibrium crystalline ordering in regions of low shear gradient. The physical mechanism responsible for this phenomenon is shear-induced particle migration, which causes particles to drift preferentially towards the center of the flow channel, thus increasing the local density in the channel center. The method employed is classical dynamical density functional theory.

Dynamical density functional theory analysis of the laning instability in sheared soft matter.

Using dynamical density functional theory (DDFT) methods we investigate the laning instability of a sheared colloidal suspension. The nonequilibrium ordering at the laning transition is driven by nonaffine particle motion arising from interparticle interactions. Starting from a DDFT which incorporates the nonaffine motion, we perform a linear stability analysis that enables identification of the regions of parameter space where lanes form. We illustrate our general approach by applying it to a simple one-component fluid of soft penetrable particles.

One-Dimensional Fluids with Positive Potentials

We study a class of one-dimensional classical fluids with penetrable particles interacting through positive, purely repulsive, pair-potentials. Starting from some lower bounds to the total potential energy, we draw results on the thermodynamic limit of the given model.

Probing the existence of phase transitions in one-dimensional fluids of penetrable particles.

Phase transitions in one-dimensional classical fluids are usually ruled out by using van Hove's theorem. A way to circumvent the conclusions of the theorem is to consider an interparticle potential that is everywhere bounded. Such is the case of, e.g., the generalized exponential model of index 4 (GEM-4 potential), which in three dimensions gives a reasonable description of the effective repulsion between flexible dendrimers in a solution. An extensive Monte Carlo simulation of the one-dimensional GEM-4 model [S. Prestipino, Phys. Rev. E 90, 042306 (2014)] has recently provided evidence of an infinite sequence of low-temperature cluster phases, however, also suggesting that upon pushing the simulation forward what seemed a true transition may eventually prove to be only a sharp crossover. We hereby investigate this problem theoretically by use of three different and increasingly sophisticated approaches (i.e., a mean-field theory, the transfer matrix of a lattice model of clusters, and the exact treatment of a system of point clusters in the continuum) to conclude that the alleged transitions of the one-dimensional GEM-4 system are likely just crossovers.

Modeling Particle Penetrations Through Wall Assemblies Using Computational Fluid Dynamics

Outdoor particles can penetrate through wall assemblies and influence the indoor air quality (IAQ). In this study, a computational fluid dynamics (CFD) model was developed for predicting the particle penetration through wood-framed residential wall assemblies. The model included a simplified approach to account for the particle loss due to the fiberglass insulation material layer in the wall assemblies. Particles ranging from 0.001 to 10 μm in diameter were studied. Particle movement was modeled following an Eulerian approach, while particle deposition in the fiberglass insulation was accounted for by an additional sink term in the governing equation, derived from the classical filtration theory. The model was applied to a typical residential wall assembly, assuming crack heights of 1 mm in the vertical direction and 3 mm in the horizontal direction and a fiberglass insulation width of 0.14 m. The results showed that 0.05–1 μm particles were the most penetrable particles. The fiberglass insulation media r...

Structure of a tractable stochastic mimic of soft particles.

The structure and assembly of soft particles is difficult to characterize because their interpenetrability allows them to be packed at ever higher density albeit with an increasing penalty in energy and/or pressure. Alternatively, the use of impenetrable particles (such as hard spheres) as a reference model for soft particles can fail because the packing densities are limited by the impossibility of complete space filling. We recently introduced the stochastic penetration algorithm (SPA) so as to allow for the computationally efficient integration of hard sphere models while including overlaps seen in soft interactions [Craven et al., J. Chem. Phys., 2013, 138, 244901]. Moving beyond the initial one-dimensional case studied earlier, we now consider the spatial properties of systems of stochastically penetrable spheres in dimensions d≤ 3 through the use of molecular dynamics simulations and analytic methods. The stochastic potential allows spheres to either interpenetrate with a probability δ or collide elastically otherwise. For δ > 0 the particles interpenetrate (overlap), reducing the effective volume occupied by the particles in the system. We find that the occupied volume can be accurately predicted using analytic expressions derived from mean field arguments for the particle overlap probabilities with the exception of an observed clustering regime. This anomalous clustering behavior occurs at high densities and small δ. We find that this regime is coincident with that observed in deterministic penetrable models. The behavior of the stochastic penetrable particles also indicates that soft particles would be characterizable through a single reduced parameter that captures their overlap probability.

Profile estimation for Pt submicron wire on rough Si substrate from experimental data

An efficient forward scattering model is constructed for penetrable 2D submicron particles on rough substrates. The scattering and the particle-surface interaction are modeled using discrete sources with complex images. The substrate micro-roughness is described by a heuristic surface transfer function. The forward model is applied in the numerical estimation of the profile of a platinum (Pt) submicron wire on rough silicon (Si) substrate, based on experimental Bidirectional Reflectance Distribution Function (BRDF) data.

Ground State at High Density

Weak limits as the density tends to infinity of classical ground states of integrable pair potentials are shown to minimize the mean-field energy functional. By studying the latter we derive global properties of high-density ground state configurations in bounded domains and in infinite space. Our main result is a theorem stating that for interactions having a strictly positive Fourier transform the distribution of particles tends to be uniform as the density increases, while high-density ground states show some pattern if the Fourier transform is partially negative. The latter confirms the conclusion of earlier studies by Vlasov (in J. Phys. (USSR) IX:25–40, 1945), Kirzhnits and Nepomnyashchii (in Sov. Phys. JETP 32:1191–1197, 1971), and Likos et al. (in J. Chem. Phys. 126:224502, 2007). Other results include the proof that there is no Bravais lattice among high-density ground states of interactions whose Fourier transform has a negative part and the potential diverges or has a cusp at zero. We also show that in the ground state configurations of the penetrable sphere model particles are superimposed on the sites of a close-packed lattice.

Monte Carlo simulations of surfactant aggregation and adsorption on soft hydrophobic particles

Monte Carlo simulations with an explicit description of counterions are performed to investigate the adsorption of ionic surfactants at the interface between water and soft hydrophobic and penetrable particles. The surfactant molecules are represented at a coarse-grained level, their hydrophobic tails interact with each other through a Lennard-Jones potential, whereas their hydrophilic head and their counterions interact through a Coulombic potential. Two colloidal hydrophobic particles interact with the surfactant hydrophobic chains through a modified Lennard-Jones potential. By increasing the surfactant confinement between non-adsorbing colloidal particles, micellization is achieved and the micelle aggregation number is found to increase. Adsorption isotherms are determined for various interaction strengths between the surfactants and the particles. It is found that increasing this parameter increases the level of the adsorption plateau. The adsorbed surfactant molecules form conical aggregates which evolve into elongated structures by increasing the surfactant concentration and the strength of the interaction. The presence of micelles in solution is shown to be controlled by the level of adsorption and saturation of the hydrophobic particle surfaces. This study provides for the first time a comparison of surfactant micellization in solution and aggregate formation at one interface by considering hydrophobic and electrostatic interactions.

CG-FFT algorithm for three-dimensional inhomogeneous and biaxial metamaterials

We propose an accurate numerical method to compute the electromagnetic scattering from three-dimensional (3D) arbitrarily shaped objects composed of inhomogeneous and biaxial metamaterials, whose permittivity and permeability are both anisotropic. The basic theory for the numerical method is to set up the linear equations by the method of moments (MOM) with pulse basis functions and point matching. The resulting matrix equation is solved by the conjugate gradient (CG) method combined with the fast Fourier transform (FFT) to reduce the storage requirements and CPU time of the computer. The accuracy of the proposed CG-FFT method has been validated. We have applied the method to investigate scattering by penetrable particles with inhomogeneous and anisotropic permittivity and permeability, which will be important and helpful to analyse the scattering characteristics of metamaterials. Finally, a large 3D gradient-index lens has been investigated by using the proposed method, and the numerical result has a good match to the theoretical prediction.

Deposition of nanoparticles in filters composed of permeable porous fibers

The diffusion deposition of nanoparticles is studied from a flow at low Reynolds numbers in model filters composed of permeable circular porous fibers. The field of particle concentration is calculated and the capture coefficient is determined for a cell, as well as the isolated row of parallel fibers within a wide range of Peclet numbers (Pe) depending on the fiber permeability. It is shown that at Pe > 1, the diffusion capture coefficient η increases with permeability, while at Pe → ∞, it tends toward the limiting value, which is equal to the gas flow rate through the porous fiber. The capture coefficients calculated from a cell model and for a row of fibers are almost equal to each other. The diffusion deposition of aerosol particles in the highest penetration range is calculated with an allowance for their finite sizes and it is shown that the radii of most penetrable particles decrease with an increase in fiber permeability.