Motion Of Nanoparticles Research Articles

Trapping plasmonic nanoparticles with MHz electric fields

Dielectrophoresis drives the motion of nanoparticles through the interaction of their induced dipoles with a non-uniform electric field. We experimentally observe rf dielectrophoresis on 100 nm diameter gold nanoparticles in a solution and show that for MHz frequencies, the nanoparticles can reversibly aggregate at electrode gaps. A frequency resonance is observed at which reversible trapping of gold nanoparticle “clouds” occurs in the gap center, producing almost a 1000-fold increase in density. Through accounting for gold cores surrounded by a conducting double layer ion shell, a simple model accounts for this reversibility. This suggests that substantial control over nanoparticle separation is possible, enabling the formation of equilibrium nanoarchitectures in specific locations.

Optical force spectroscopy for measurement of nonlinear optical coefficient of single nanoparticles through optical manipulation.

Compared with manipulation of microparticles with optical tweezers and control of atomic motion with atom cooling, the manipulation of nanoscale objects is challenging because light exerts a significantly weaker force on nanoparticles than on microparticles. The complex interaction of nanoparticles with the environmental solvent media adds to this challenge. In recent years, optical manipulation using electronic resonance effects has garnered interest because it has enabled researchers to enhance the force as well as sort nanoparticles by their quantum mechanical properties. Especially, a precise observation of the motion of nanoparticles irradiated by resonant light enables the precise measurement of the material parameters of single nanoparticles. Conventional spectroscopic methods of measurement are based on indirect processes involving energy dissipation, such as thermal dissipation and light scattering. This study proposes a theoretical method to measure the nonlinear optical constant based on the optical force. The nonlinear susceptibility of single nanoparticles can be directly measured by evaluating the transportation distance of particles through pure momentum exchange. We extrapolate an experimentally verified method of measuring the linear absorption coefficient of single nanoparticles by the optical force to determine the nonlinear absorption coefficient. To this end, we simulate the third-order nonlinear susceptibility of the target particles with the kinetic analysis of nanoparticles at the solid-liquid interface incorporating the Brownian motion. The results show that optical manipulation can be used as nonlinear optical spectroscopy utilizing direct exchange of momentum. To the best of our knowledge, this is currently the only way to measure the nonlinear coefficient of individual single nanoparticles.

Numerical investigation and optimization of natural convection and entropy generation of alumina/H2O nanofluid in a rectangular cavity in the presence of a magnetic field with artificial neural networks

The SIMPLE algorithm and the volume control technique are used to investigate the natural convection of alumina/H2O nanofluids (NFs) flow in a cavity. The cavity consists of two hot triangular blades on the bottom wall. The two sidewalls are insulated and the upper wall is at a low-temperature. The cavity can have different angles. Brownian nanoparticle motion is also considered to model their thermal conductivity and viscosity. Finally, the values ​​of Nusselt number (Nu), Bejan number (Be) entropy generation rate (Sgen) are estimated by changing the cavity angle (γ), the Hartmann number (Ha), and the Rayleigh number (Ra). It is found that an increment in the Ra enhances the amount of Nu and Sgen, but the amount of Be is reduced. An enhancement in the Ha does not effect on Sgen and Nu at low values of Ra, while for high amounts of Ra, Sgen and Nu are reduced. The maximum value of Sgen and Nu and the minimum amount of Be, which are 10.36, 5.21, and 0.34, respectively, occur when γ = 30°. Also, the minim values of Nu and Sgen occur for strong free convection in the horizontal and vertical cavity, respectively.

High-resolution STEM observation of the dynamics of Pt nanoparticles in a liquid

The dynamics of Pt nanoparticles (NPs) in water are observed by high-resolution scanning transmission electron microscopy with a home-made static sandwich-type liquid cell (LC). Carbon is coated on both sides of the membrane windows of the LC to make them conductive. The slow motion of Pt NPs in thin water droplets enables us to acquire high-resolution scanning transmission electron microscopy images. Using a dose rate of 3 × 105 e nm−2s, some Pt NPs with a diameter of less than 2 nm disappear into the water, some move around, and others repeatedly attach to and detach from each other. The density of Pt NPs larger than 2 nm remains unchanged with further observation. However, by increasing the dose rate to 5.3 × 105 e nm−2s, the Pt NPs gather at the beam illumination area, and then form aggregates with chain network structures. It is also determined that the NPs attach to each other at their {111} surfaces.

The impact of the movement of the gyrotactic microorganisms on the heat and mass transfer characteristics of Casson nanofluid

This article focuses on analyzing the impact of the movement of gyrotactic microorganisms on the heat and mass transfer characteristics of Casson nanofluid flowing between divergent. Further, the analysis is performed through simulation to have a better understanding of the impact. Since the microorganisms are self-propelled, they move on their own in the nanofluid due to the concentration gradient and stabilize the nanoparticle suspension. This movement of microorganisms constitutes the formation of bioconvection. Further, the random motion of nanoparticles gives rise to two major slip mechanisms termed thermophoresis and Brownian motion. The mathematical model comprising these effects is designed using partial differential equations that are converted to ordinary differential equations with the help of suitable similarity transformation. The resulting system of equations is then solved using the differential transformation method and the outcomes are interpreted through graphs. It is indicated that the nanoparticle concentration and the motile density profiles increase with the increase in Schmidt number and also, the concentration profile is found to be increasing for higher Brownian motion parameter and lower thermophoretic parameter. The simulations performed through the finite element method portrayed that the heat flow in the diverging channel is occurring along the isothermal planes.

Effects of the presence and absence of nanoparticles in the hold-up and hydrodynamic velocities in the pulsed disc and doughnut column by using central composite design method

The pulsed disc and doughnut column (PDDC) presents a valuable and profoundly satisfying solution for recovering and purifying components from mixtures when a separation challenge involves purifying a liquid or recovering components from mixtures. Furthermore, because of their improved mass transfer and efficiency, the application of nanofluids within liquid-liquid extraction systems has lately received with increased interest. In the behavior of silica nanoparticles (0, 0.025, and 0.05 wt percent), the hydrodynamic velocities and dispersed phase hold-up between the aqueous and organic phases were measured. The central composite design (CCD) was adopted to assess the impacts of three running parameters on slip velocity (Vs) and dispersed phase hold-up (φ) at five levels. The findings revealed that higher intensity and higher aqueous phase velocity led to the decrement of slip velocity, and increment of hold-up. The higher number of droplets into column leads to the larger values for Vs, and φ. The correlation coefficients (R2) equals to 0.9627, and 0.9838 were obtained for hold-up and slip velocity with the predicted quadratic model with the presence of 0.025% nanoparticles. The presence of nanoparticles increased the dispersed phase hold-up and a decrease in slip velocity, which was connected to a reduction of interfacial tension with nanofluids, Brownian motion of nanoparticles, and a negative impact on droplet stability due to increased internal mixing inside droplets. A CCD proposes new and simple experimental relationships as the slip velocity and dispersed phase hold-up.

Motion of nanoparticles near rising and dissolving microbubbles

This paper presents a computational study of the motion of inertia-less particles in the vicinity of freely rising bubbles of carbon dioxide that dissolve into the suspension. The purpose is to assess the extent of particle motion due to diffusiophoresis that is caused by ion concentration gradients, in this case protons and bicarbonate ions. Calculations are reported for spherical bubbles with diameters from 10 to 100μm. Particle trajectories are computed for bubbles with slip and no slip surfaces, which (respectively) represent the extremes of a high purity system and a contaminated system in which surfactants fully immobilise the surface. The extent of particle motion towards or away from the bubbles (depending on the sign of the diffusiophoretic mobility) is quantified. Particle motion due to removal of dissolved carbon dioxide from a suspension into air bubbles is also considered. In the cases where particles are attracted to the bubbles, some particle trajectories reach the surface of the bubble. The results suggest that this mechanism could therefore be exploited to extend the use of flotation to separate smaller particles.

Unsteady periodic natural convection in a triangular enclosure heated sinusoidally from the bottom using CNT-water nanofluid

This research examines the natural convection phenomena in a triangular enclosure, assumed as a mechanical chamber. Water-based CNT-nanofluid was used as the fluid. The nature of the flow is unsteady, and a sinusoidal heat source is situated at the bottom of the triangle. The inclined two walls of the triangle are assumed as cold temperature. Based on the finite element method, dimensionless nonlinear governing equations were obtained employing the Galerkin weighted residual method. Brownian motion of nanoparticles was considered to determine the thermal conductivity and dynamic viscosity. Rayleigh number (Ra), oscillation period τp, and dimensionless time τ are assumed as primary controlling factors, and nanofluid concentration is considered as constant φ = 0.04. The result indicates that the heat transfer rate displays varied patterns varying the Rayleigh number, and it rises as the oscillation period increases. The fluid temperature and flow fields exhibit periodic behavior due to the sinusoidal heat source. The findings of this work can be utilized to build an effective cooling or heating system for the mechanical chamber, ensuring that temperature distributions are effective and consistent.

Insight into the motion of water conveying three kinds of nanoparticles shapes on a horizontal surface: Significance of thermo-migration and Brownian motion

Thermo-migration and erratic/random motion of tiny particles are some of the attributes of these objects in liquid medium that can affect the performance and transportation of nanofluids. With major emphasis on the fluctuation of friction, heat, and mass transfer rates across the domain, little is known about the dynamics of water colloidally mixed with three distinct types of nano-sized particles. The suitable models, as well as the dimensional governing equation, were non-dimensionalized and parameterized using appropriate similarity variables for analyzing the colloidal mixture of platelet, cylindrical, and spherical nanoparticles. The validity, reliability of the numerical integration and the newly acquired findings were extensively investigated. The results for boundary layer flow show that increasing the density of spherical nanoparticles causes (a) a reduction in the friction between the layers of water-based ternary-hybrid nanofluid and the wall (b) an increment in the friction from the wall till the free stream. Accumulation of species that form water-based ternary-hybrid nanofluid decline due to higher erratic motion and thermo-migration of different nanoparticles. But there is an enhancement in the mass transfer rate near the wall due to erratic motion and thermo-migration of different nanoparticles. The Nusselt number proportionate to heat transfer rate decreases with increased thermo-migration of nanoparticles. With increasing Brownian motion of three distinct nanoparticles, the heat transfer and temperature distribution diminish across the fluid flow but mass transfer is magnified.

Heat transfer enhancement of Fe 3 O 4 ‐water nanofluid by the thermo‐magnetic convection and thermophorestic effect

The promotion of the heat transfer by ferro-nanofluid under a magnetic field has caught more extensive attention in the field of nuclear industry and energy engineering. Firstly, a modified model based on the Buongiorno model was proposed to investigate the heat transfer considering the Kelvin force in the presence of an inhomogeneous magnetic field to elevate the heat transfer performance of nanofluid using thermomagnetic convection. Secondly, the influence of Kelvin force, thermophoresis, and Brownian motion of nanoparticles on the heat transfer at a moderate Reynolds number was investigated. The numerical results indicate that the chaotic convection induced by the Kelvin force and the thermophoretic effect are much important factors. Thirdly, the numerical results demonstrate that the NSN and NSN/SNS arrangements of magnets should be the preferential selection. Besides, the more powerful magnetic field and greater volume fraction of nanoparticle can produce better heat transfer performance. Finally, the discussions on the underneath mechanisms for heat transfer augment are conducted, and it can be concluded the thermomagnetic convection induced the combination of the magnetic effect and thermophoretic effect may be the key mechanism.

Thermal Evolution of C-Fe-Bi Nanocomposite System: From Nanoparticle Formation to Heterogeneous Graphitization Stage.

Carbon xerogel nanocomposites with integrated Bi and Fe particles (C–Bi–Fe) represent an interesting model of carbon nanostructures decorated with multifunctional nanoparticles (NPs) with applicability for electrochemical sensors and catalysts. The present study addresses the fundamental aspects of the catalyzed growth of nano-graphites in C–Bi–Fe systems, relevant in charge transport and thermo-chemical processes. The thermal evolution of a C–Bi–Fe xerogel is investigated using different pyrolysis treatments. At lower temperatures (~750°C), hybrid bismuth iron oxide (BFO) NPs are frequently observed, while graphitization manifests under more specific conditions such as higher temperatures (~1,050°C) and reduction yields. An in situ heating TEM experiment reveals graphitization activity between 800 and 900°C. NP motion is directly correlated with textural changes of the carbon support due to the catalyzed growth of graphitic nanoshells and nanofibers as confirmed by HR-TEM and electron tomography (ET) for the graphitized sample. An exponential growth model for the catalyst dynamics enables the approximation of activation energies as 0.68 and 0.29–0.34 eV during reduction and graphitization stages. The results suggest some similarities with the tip growth mechanism, while oxygen interference and the limited catalyst–feed gas interactions are considered as the main constraints to enhanced growth.

Real-Time Observation and Analysis of Magnetomechanical Actuation of Magnetic Nanoparticles in Cells.

The origin of cell death in the magnetomechanical actuation of cells induced by magnetic nanoparticle motion under low-frequency magnetic fields is still elusive. Here, a miniaturized electromagnet fitted under a confocal microscope is used to observe in real time cells specifically targeted by superparamagnetic nanoparticles and exposed to a low-frequency rotating magnetic field. Our analysis reveals that the lysosome membrane is permeabilized in only a few minutes after the start of magnetic field application, concomitant with lysosome movements toward the nucleus. Those events are associated with disorganization of the tubulin microtubule network and a change in cell morphology. This miniaturized electromagnet will allow a deeper insight into the physical, molecular, and biological process occurring during the magnetomechanical actuation of magnetic nanoparticles.

Simultaneous energy storage and recovery in triplex-tube heat exchanger using multiple phase change materials with nanoparticles

This study investigates the thermal response of triplex-tube heat exchanger (TTHX) systems and their simultaneous storage and recovery qualities using novel designs with multiple-phase change materials (PCMs). Specifically, the effects of nanoparticles and different PCM design configurations are studied. A numerical model that includes the Brownian motion of nanoparticles, and the convection motion of liquid PCM, is developed and first validated, with results showing close correspondence and outcome to those obtained from physical experiments. Results from this study demonstrate that the lower region of the horizontal TTHX shows weak natural convection that can be effectively improved when multiple PCMs are applied, resulting in a significantly improved uniform convection in both the lower and upper regions of the TTHX. Stored latent energy is analyzed for different cases, and results show that using two or more PCMs can significantly increase the stored latent energy by at least 40%, after 1 h This study also shows that the thermal response of a TTHX may be dramatically improved when 5% of aluminium oxide (Al₂O₃)nanoparticles are added to the PCMs. The design with 3 PCMs and with the integration of nanoparticles demonstrates the fastest thermal responses for the fully melted and fully solidified initial conditions. Additionally, the time-averaged values of heat storage and recovery enhancement ratios are found to be 68.95%, and 50.33%, respectively. Depending on the initial temperature of the system, applying multiple PCMs with nanoparticles can accelerate the energy storage and recovery times by up 2.25 and 5.57 times compared to the baseline case (1 PCM without nanoparticles), highlighting the benefits of improving performances of TTHX using multiple PCMs with nanoparticles.

In Situ Liquid Phase TEM of Nanoparticle Formation and Diffusion in a Phase-Separated Medium.

Colloidal nanoparticles are synthesized in a complex reaction mixture that has an inhomogeneous chemical environment induced by local phase separation of the medium. Nanoparticle syntheses based on micelles, emulsions, flow of different fluids, injection of ionic precursors in organic solvents, and mixing the metal organic phase of precursors with an aqueous phase of reducing agents are well established. However, the formation mechanism of nanoparticles in the phase-separated medium is not well understood because of the complexity originating from the presence of phase boundaries as well as nonuniform chemical species, concentrations, and viscosity in different phases. Herein, we investigate the formation mechanism and diffusion of silver nanoparticles in a phase-separated medium by using liquid phase transmission electron microscopy and many-body dissipative particle dynamics simulations. A quantitative analysis of the individual growth trajectories reveals that a large portion of silver nanoparticles nucleate and grow rapidly at the phase boundaries, where metal ion precursors and reducing agents from the two separated phases react to form monomers. The results suggest that the motion of the silver nanoparticles at the interfaces is highly affected by the interaction with polymers and exhibits superdiffusive dynamics because of the polymer relaxation.

Thermophysical properties of Kerosene oil-based CNT nanofluid on unsteady mixed convection with MHD and radiative heat flux

Oil-based nanofluids are used to strengthen the stability of nanofluids as well as their thermophysical properties when they are exposed to high temperatures. The time-dependent thermophysical characteristics of multiwalet carbon nanotubes for kerosine oil-based nanofluid are numerically explored in this study. Considering a constant magnetic field, the radiative domain is examined in a lid-driven squared shape cavity with a semicircular heater on the middle part of the bottom wall. The Galerkin residual technique based on finite elements is used to obtain nonlinear dimensionless governing equations. Thermal conductivity along with dynamic viscosity models integrate Brownian motion of nanoparticles. The Reynolds number, the Hartmann number, the Radiation Parameter and the Richardson number are assumed to be constant to account for the fluctuation in solid volume fraction (ϕ = 0% to 10%). The results demonstrated that particle concentration improves the nanofluid’s thermophysical properties from 1 to 9 times than the 0% concentration and the heat transfer rate from 1 to 3 times. In addition, dimensionless time enhances all except the heat transfer rate and drag force of the sliding lid. It is worth noting that the considered parameter exhibits consistent behavior after a while.

Mechanisms for thermal conduction in molten salt-based nanofluid

The addition of nanoparticles to molten salt can enhance its utility as a thermal energy storage material for concentrating solar power plants. The heat transfer property of solar salt loaded with Al2O3 nanoparticle is investigated by molecular dynamics simulations. The results show that the introduction of Al2O3 nanoparticles improves the thermal conductivity of solar salt, but its enhancement effect is not as significant as SiO2 nanoparticles. The increased thermal conductivity cannot be explained by the previously proposed hypothesis, such as the Brownian motion of nanoparticles, microconvection of base liquid, ordered layer of base liquid and coulombic potential energy. New insights into heat conduction performance of molten salt based nanofluid are given from the perspectives of material components and heat flux fluctuation modes. It is found that the nanofluid thermal conductivity is mainly contributed by the atom motions and interactions between atoms in Al2O3 nanoparticle, rather than in base fluid. The heat flux is concentrated in nanoparticle, which promotes the heat transfer. Furthermore, the collision involving the work done by the interatomic forces or the virial interaction dominates the heat conduction in nanofluid with lower mass fraction (< 6%), while the potential energy and collision both contribute to the nanofluid with higher mass fraction (> 6%). These new findings make a step forward in understanding the heat conduction mechanisms of molten salt based nanofluid.

Physical properties of the cytoplasm modulate the rates of microtubule polymerization and depolymerization.

The cytoplasm is a crowded, visco-elastic environment whose physical properties change according to physiological or developmental states. How the physical properties of the cytoplasm impact cellular functions invivo remains poorly understood. Here, we probe the effects of cytoplasmic concentration on microtubules by applying osmotic shifts to fission yeast, moss, and mammalian cells. We show that the rates of both microtubule polymerization and depolymerization scale linearly and inversely with cytoplasmic concentration; an increase in cytoplasmic concentration decreases the rates of microtubule polymerization and depolymerization proportionally, whereas a decrease in cytoplasmic concentration leads to the opposite. Numerous lines of evidence indicate that these effects are due to changes in cytoplasmic viscosity rather than cellular stress responses or macromolecular crowding per se. We reconstituted these effects on microtubules invitro by tuning viscosity. Our findings indicate that, even in normal conditions, the viscosity of the cytoplasm modulates the reactions that underlie microtubule dynamic behaviors.

Optical Levitation of Mie-Resonant Silicon Particles in the Field of Bloch Surface Electromagnetic Waves

Manipulating the motion of nanoparticles in liquid media using the near field of integrated optical elements is associated with enhanced viscous friction and an increased probability of adhesion. One of the ways to overcome these difficulties is the search for systems with a minimum of potential energy located at a distance from the structure surface. In this paper, we numerically study the forces acting on Mie-resonant silicon particles in water in the evanescent field of a Bloch surface wave and propose a method for localizing such particles at a controlled distance from the surface. For this purpose, we use surface waves at two optical frequencies, which provide different signs of interaction with the particle and different depths of field penetration into the medium. As an example, we consider a silicon sphere with a diameter of 130 nm in the field of laser radiation with wavelengths of 532 and 638 nm and a total power of 100 mW; taking into account the Brownian motion, we show that the proposed method provides stable particle localization at an equilibrium distance to the surface, adjustable in the range from 60 to 100 nm.

Machine learning-informed timescale dependent modes of nanoparticle diffusion through human mucus

Modes of diffusion and transport of nanomaterials through biological gels, like mucus, is of critical importance to many applied areas of research (e.g., drug delivery). However, it is often challenging to interpret the dynamics of nanoparticles within biological gel networks due to the complexity and inherent heterogeneity of their microstructure and biochemistry. In this study, we measured the diffusion of densely PEGylated, muco-inert nanoparticles (NP) in human airway mucus using multiple particle tracking and utilized machine learning to classify NP movement as either traditional Brownian motion (BM) or two different models of anomalous diffusion; fractional Brownian motion (FBM) and continuous time random walk (CTRW).

Squeezing Light via Levitated Cavity Optomechanics

Squeezing light is a critical resource in both fundamental physics and precision measurement. Squeezing light has been generated through optical-parametric amplification inside an optical resonator. However, preparing the squeezing light in an optomechanical system is still a challenge for the thermal noise inevitably coupled to the system. We consider an optically levitated nano-particle in a bichromatic cavity, in which two cavity modes could be excited by the scattering photons of the dual tweezers, respectively. Based on the coherent scattering mechanism, the ultra-strong coupling between the cavity field and the torsional motion of nano-particle could be achieved for the current experimental conditions. With the back-action of the optically levitated nano-particle, the broad single-mode squeezing light can be realized in the bad cavity regime. Even at room temperature, the single-mode light can be squeezed for more than 17 dB, which is far beyond the 3 dB limit. The two-mode squeezing light can also be generated, if the optical tweezers contain two frequencies, one is on the red sideband of the cavity mode, the other is on the blue sideband. The two-mode squeezing can be maximized near the boundary of the system stable regime and is sensitive to both the cavity decay rate and the power of the optical tweezers.