Diffusion Of Nanoparticles Research Articles

Vehicular and Core–Shell Nanoparticle Diffusion in Attractive Entangled Polymer Melts

Vehicular and Core–Shell Nanoparticle Diffusion in Attractive Entangled Polymer Melts

Natural convection of water-based nanofluids in three-dimensional enclosures

The single-phase approach, in which nanofluids are treated as pure fluids assuming that the solid and liquid phases are in local thermal and hydrodynamic equilibrium, has been used with good results to simulate forced convection flows. Conversely, its extension to natural convection has revealed to be more problematic, as the obtained numerical results are substantially different from the experimental data, mainly due to the effects of the slip motion occurring between the suspended nanoparticles and the base liquid, whose consequent nonuniform distribution of the solid phase concentration can significantly affect both heat and momentum transfer. In the present article, a two-phase model based on a double-diffusive approach is proposed to study the natural convection flows of water-based metal oxide nanofluids inside cylindrical and rectangular enclosures heated and cooled at their opposite sides with the scope to reproduce a number of experimental data-sets available in the literature. Given the assumption of local thermal equilibrium between nanoparticles and host liquid, and considering the Brownian and thermophoretic diffusion as responsible for causing significant relative velocity between the solid and liquid phases, the governing equations are solved by a control-volume numerical method implemented using the open-source platform OpenFOAM (Open Field Operation and Manipulation). It has been found that the nanoparticle diffusion gives the major contribution to the decrease of the heat transfer rate red usually observed experimentally in natural convection flows of nanofluids inside differentially-heated enclosures. This means that a two-phase model, in conjunction with proper correlations for the evaluation of the nanofluid effective physical properties, must be necessarily enforced to obtain reliable results for many engineering applications.

Numerical simulation study of nanoparticle diffusion in gray matter

PurposeNanomedicine-based approaches have shown great potential in the treatment of central nervous system diseases. However, the fate of nanoparticles (NPs) within the brain parenchyma has not received much attention. The complexity of the microstructure of the brain and the invisibility of NPs make it difficult to study NP transport within the grey matter. Moreover, regulation of NP delivery is not fully understood. Methods2D interstitial system (ISS) models reflecting actual extracellular space (ECS) were constructed. A particle tracing model was used to simulate the diffusion of the NPs. The effect of NP size on NP diffusion was studied using numerical simulations. The diffusion of charged NPs was explored by comparing experimental and numerical simulation data, and the effect of cell membrane potential on the diffusion of charged NPs was further studied. ResultsThe model was verified using previously published experimental data. Small NPs could diffuse efficiently into the ISS. The diffusion of charged NPs was hindered in the ISS. Changes in cell membrane potential had little effect on NP diffusion. ConclusionThis study constructed 2D brain ISS models that reflected the actual ECS and simulated the diffusion of NPs within it. The study found that uncharged small NPs could effectively diffuse within the ISS and that the cell membrane potential had a limited effect on the diffusion of charged NPs. The model and findings of this study can aid the design of nanomedicines and nanocarriers for the diagnosis and treatment of brain diseases.

Determination of Translational and Rotational Diffusivities of Anisotropic Nanoparticles by Heterodyne Polarized and Depolarized Dynamic Light Scattering

Determination of Translational and Rotational Diffusivities of Anisotropic Nanoparticles by Heterodyne Polarized and Depolarized Dynamic Light Scattering

Modeling of spatiotemporal dynamics of ligand-coated particle flow in targeted drug delivery processes

Nanoparticles tethered with vasculature-binding epitopes have been used to deliver the drug into injured or diseased tissues via the bloodstream. However, the extent that blood flow dynamics affects nanoparticle retention at the target site after adhesion needs to be better understood. This knowledge gap potentially underlies significantly different therapeutic efficacies between animal models and humans. An experimentally validated mathematical model that accurately simulates the effects of blood flow on nanoparticle adhesion and retention, thus circumventing the limitations of conventional trial-and-error-based drug design in animal models, is lacking. This paper addresses this technical bottleneck and presents an integrated mathematical method that derives heavily from a unique combination of a mechanics-based dispersion model for nanoparticle transport and diffusion in the boundary layers, an asperity model to account for surface roughness of endothelium, and an experimentally calibrated stochastic nanoparticle-cell adhesion model to describe nanoparticle adhesion and subsequent retention at the target site under external flow. PLGA-b-HA nanoparticles tethered with VHSPNKK peptides that specifically bind to vascular cell adhesion molecules on the inflamed vascular wall were investigated. The computational model revealed that larger particles perform better in adhesion and retention at the endothelium for the particle sizes suitable for drug delivery applications and within physiologically relevant shear rates. The computational model corresponded closely to the in vitro experiments which demonstrates the impact that model-based simulations can have on optimizing nanocarriers in vascular microenvironments, thereby substantially reducing in vivo experimentation as well as the development costs.

Largely enhanced Piezoelectric-Fenton capability in rationally designed PVDF/Fe2O3 flexible porous film

The burgeoning piezocatalysts have attracted huge attentions due to their ability to convert natural mechanical energy to degrade water pollutants. However, traditional powder-based piezocatalysts still face an inevitable bottleneck of the secondary pollution because of the diffusion of nanoparticles during the piezocatalysis process. In this work, novel porous polymer-based composite films combining Fenton fillers (α-Fe2O3) and ferroelectric polymer (polyvinylidene fluoride, PVDF) are prepared by rationally designed solution-casted method with a sacrificial “hard template” of table salt. The as-prepared porous PVDF/Fe2O3 film exhibits superior decomposition efficiency of organic pollutants under ultrasonication. Particularly, the easily recyclable porous film with optimized composition and spatial structure offers an ultrahigh rate constant of 0.0498 min−1, which means it can degrade 94.8% rhodamine B (RhB) in 60 min, exceeding that of most reported polymer-based piezocatalysts. Additionally, it has a comprehensive decomposition effect on dyes, antibiotics and natural water with a good cycle performance. The outstanding degradation performance is attributed to the massive hydroxyl radical generated from the enhanced Piezoelectric-Fenton effect, which is ascribed to the synergistic effect of improved piezoelectricity in PVDF, enhanced hydrophilicity and optimized spatial structures in the porous composite films.

Brownian Diffusion of Nanoparticles in a Liquid and a “Laser Mill”

Brownian Diffusion of Nanoparticles in a Liquid and a “Laser Mill”

Tumor penetrating Janus prodrug nanoassemblies for enhanced synergistic chemotherapy and photodynamic therapy of colon cancer

Intelligent nanodrug delivery systems that respond to tumor microenvironment have been extensively utilized in cancer therapy research. However, the passive diffusion of prodrug nanoparticles is hindered due to the absence of capillaries and dense extracellular matrix in the tumor microenvironment, resulting in low efficiency of anti-tumor drug delivery. In this study, we developed a metal matrix proteinase 2 (MMP2) and glutathione (GSH) responsive Janus prodrug nanoassemblies targeted towards tumors. The Janus prodrug nanoassemblies consist of targeted micelles and prodrug nanoaggregates linked by click chemistry. The size of the nanoassemblies can be reduced within the tumor microenvironment of high concentrations of MMP2. Active targeting and size shrinkage synergistically enhance cell uptake efficiency and tumor penetration capacity of nanoassemblies. The release of camptothecin (CPT) occurs in a GSH-dependent manner, while under irradiation with 660-nm red light, the photosensitizer introduced in the prodrug generates reactive oxygen species (ROS) to induce tumor cell death. Fluorescence imaging results demonstrate enhanced tumor targeting capabilities of Janus prodrug assemblies. As a theranostic agent for tumors, Janus prodrug assemblies achieve desirable synergistic chemotherapy and photodynamic therapy for colon cancer treatment. This work would provide a novel strategy for cancer diagnosis and treatment.

Ultrasound enhanced diffusion in hydrogels: An experimental and non-equilibrium molecular dynamics study.

Focused ultrasound has experimentally been found to enhance the diffusion of nanoparticles; our aim with this work is to study this effect closer using both experiments and non-equilibrium molecular dynamics. Measurements from single particle tracking of 40nm polystyrene nanoparticles in an agarose hydrogel with and without focused ultrasound are presented and compared with a previous experimental study using 100nm polystyrene nanoparticles. In both cases, we observed an increase in the mean square displacement during focused ultrasound treatment. We developed a coarse-grained non-equilibrium molecular dynamics model with an implicit solvent to investigate the increase in the mean square displacement and its frequency and amplitude dependencies. This model consists of polymer fibers and two sizes of nanoparticles, and the effect of the focused ultrasound was modeled as an external oscillating force field. A comparison between the simulation and experimental results shows similar mean square displacement trends, suggesting that the particle velocity is a significant contributor to the observed ultrasound-enhanced mean square displacement. The resulting diffusion coefficients from the model are compared to the diffusion equation for a two-time continuous time random walk. The model is found to have the same frequency dependency. At lower particle velocity amplitude values, the model has a quadratic relation with the particle velocity amplitude as described by the two-time continuous time random walk derived diffusion equation, but at higher amplitudes, the model deviates, and its diffusion coefficient reaches the non-hindered diffusion coefficient. This observation suggests that at higher ultrasound intensities in hydrogels, the non-hindered diffusion coefficient can be used.

Label-Free Light Scattering Imaging with Purified Brownian Motion Differentiates Small Extracellular Vesicles in Cell Microenvironments.

Small extracellular vesicles (sEVs) are heterogeneous biological nanoparticles (NPs) with wide biomedicine applications. Tracking individual nanoscale sEVs can reveal information that conventional microscopic methods may lack, especially in cellular microenvironments. This usually requires biolabeling to identify single sEVs. Here, we developed a light scattering imaging method based on dark-field technology for label-free nanoparticle diffusion analysis (NDA). Compared with nanoparticle tracking analysis (NTA), our method was shown to determine the diffusion probabilities of a single NP. It was demonstrated that accurate size determination of NPs of 41 and 120 nm in diameter is achieved by purified Brownian motion (pBM), without or within the cell microenvironments. Our pBM method was also shown to obtain a consistent size estimation of the normal and cancerous plasma-derived sEVs without and within cell microenvironments, while cancerous plasma-derived sEVs are statistically smaller than normal ones. Moreover, we showed that the velocity and diffusion coefficient are key parameters for determining the diffusion types of the NPs and sEVs in a cancerous cell microenvironment. Our light scattering-based NDA and pBM methods can be used for size determination of NPs, even in cell microenvironments, and also provide a tool that may be used to analyze sEVs for many biomedical applications.

Transmission Electron Microscopy and Dynamic Light Scattering-Fundamental Perspective

Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) are fundamental tools in nanotechnology and materials science, providing information about the structural and dynamic properties of nanomaterials and colloidal systems. This review provides a thorough examination of TEM and DLS, beginning with a discussion of their fundamental principles. It discusses the interaction of electron beams in TEM and the dynamics of scattered light in DLS, followed by an examination of instrumentation and experimental setups, including recent advances for increased resolution and sensitivity. The article then discusses the numerous applications of TEM and DLS in nanomaterial characterization. It includes analyses of nanoparticle size, shape, morphology, and distribution, as well as research into colloidal system dynamics such as nanoparticle aggregation, diffusion, and stability. The review concludes with a forward-looking perspective on emerging trends and future directions in nanomaterial characterization. It emphasizes the potential of TEM and DLS to overcome current challenges and advance our understanding of nanoscale phenomena. Overall, this comprehensive review provides researchers and practitioners with a solid understanding of the TEM and DLS principles, methodologies, and applications, as well as valuable fundamental insights.

Deciphering non-Gaussianity of diffusion based on the evolution of diffusivity

Non-Gaussian diffusion of nanoparticles in complex media disrupts Einstein's picture of Brownian motion, and non-Gaussianity is thought to be closely related to diffusing diffusivity generated by spatiotemporal heterogeneities. However, the correlation between non-Gaussianity and the dynamics of heterogeneous environments in anomalous diffusion remains uncertain. Inspired by a recent study by Alexandre [], we demonstrate that non-Gaussianity can be deciphered through the spatiotemporal evolution of heterogeneity-dependent diffusivity distribution. Using diffusion experiments in a linear temperature field and Brownian dynamics simulations, we found that short-time non-Gaussianity can be predicted based on the boundary ratio of the diffusivity distribution; the long-time non-Gaussianity either approaches an asymptotic value of −2 or scales with 1/t, depending on the dominance of particle migration. The temporal variation of non-Gaussianity is determined by an effective Péclet number, which represents a competition between the varying rate of diffusivity and the diffusivity of diffusivity and reveals whether the tail distribution expands or contracts. The tail is more Gaussian than exponential over long times, with exceptions significantly dependent on the diffusivity distribution. Our findings provide a versatile framework for understanding non-Gaussian diffusion in probability space, and shed light on establishing a diffusion spectrum in cells and characterizing nanomedicine transport in biological microenvironment using non-Gaussian statistics. Published by the American Physical Society 2024

Synthesis and dynamics of PtSi nanoparticles on a carbon nanofilm by in-situ TEM Joule heating

In-situ transmission electron microscopy has evolved to be a unique technique to study process dynamics down to the atomic scale. Here, we show that in-situ Joule heating of carbon nanofilms facilitates the investigation of the nucleation, annealing, diffusion and evaporation of PtSi nanoparticles in a controlled way. The nanoparticles form from Pt-based hydrocarbon molecules and silicon oxide present on the amorphous carbon nanofilm. The in-situ transmission electron microscopy approach permits shedding light on the interaction between the nanoparticles and the carbon support, crucial information when aiming for stable catalytic applications. The method is versatile, allows reaching very high temperatures and could be applied to study many different combinations of bimetallic and even multimetallic high-entropy alloy nanoparticles.

Triple diffusive free magneto-convection of electro-conductive nanofluid from a vertical stretching sheet

In the present investigation, an analysis is carried out to study the MHD triple diffusive free thermo-solutal convection boundary layer flow of an electro-conductive nanofluid flow over a vertical stretching sheet. This problem is relevant to magnetic nanomaterials fabrication operations in which multiple species in addition to nanoparticles are present. In addition to the nanoparticle diffusion, two different salts (species) having different properties are considered. A variable magnetic field is applied transverse to the vertical sheet. It is assumed that the surface is in contact with the hot magnetic nanofluid at a temperature which provides a variable heat transfer coefficient. Buongiorno’s model is employed for the nanofluid. It is also assumed that the Oberbeck-Boussinesq approximation is valid and the mixture of nanofluid and salts is homogenous and is in local thermal equilibrium. In addition, the thermal energy equation features cross-diffusion (Soret and Dufour) terms for both components of salts having different concentration. Appropriate similarity transformations are deployed to render the model non-dimensional. The emerging transformed dimensionless non-linear non-dimensional ordinary differential boundary value problem is solved with the robust bvp4c method in MATLAB. Validation with previous studies has been included for special cases of the general model. The simulations show that the addition of nanoparticles and salts, strongly modifies Temperature and nanoparticle and salt 1 and 2 concentrations. With stronger magnetic field the velocity is suppressed as is momentum boundary layer thickness whereas temperatures are boosted.

Penetration of topically applied polymeric nanoparticles across the epidermis of thick skin from rat

The barrier function of the epidermis poses a significant challenge to nanoparticle-mediated topical delivery. A key factor in this barrier function is the thickness of the stratum corneum (SC) layer within the epidermis, which varies across different anatomical sites. The epidermis from the palms and soles, for instance, have thicker SC compared to those from other areas. Previous studies have attempted to bypass the SC layer for nanoparticle penetration by using physical disruption; however, these studies have mostly focused on non-thick skin. In this study, we investigate the role of SC-disrupting mechano-physical strategies (tape-stripping and microneedle abrasion) on thick and thin skin, in allowing transdermal penetration of topically applied nanoparticles using an ex-vivo skin model from rat. Our findings show that tape-stripping reduced the overall thickness of SC in thick skin by 87%, from 67.4 ± 17.3 μm to 8.2 ± 8.5 μm, whereas it reduced thin skin SC by only 38%, from 9.9 ± 0.6 μm to 6.2 ± 3.2 μm. Compared to non-thick skin, SC disruption in thick skin resulted in higher nanoparticle diffusion. Tape-stripping effectively reduces SC thickness of thick skin and can be potentially utilized for enhanced penetration of topically applied nanoparticles in skin conditions that affect thick skin.

Imaging Diffusion and Stability of Single-Chain Polymeric Nanoparticles in a Multi-Gel Tumor-on-a-Chip Microfluidic Device.

The performance of single-chain polymeric nanoparticles (SCPNs) in biomedical applications highly depends on their conformational stability in cellular environments. Until now, such stability studies are limited to 2D cell culture models, which do not recapitulate the 3D tumor microenvironment well. Here, a microfluidic tumor-on-a-chip model is introduced that recreates the tumor milieu and allows in-depth insights into the diffusion, cellular uptake, and stability of SCPNs. The chip contains Matrigel/collagen-hyaluronic acid as extracellular matrix (ECM) modelsand is seeded with cancer cell MCF7 spheroids. With this 3D platform, it is assessed how the polymer's microstructure affects the SCPN's behavior when crossing the ECM, and evaluates SCPN internalization in 3D cancer cells. A library of SCPNs varying in microstructure is prepared. All SCPNs show efficient ECM penetration but their cellular uptake/stability behavior depends on the microstructure. Glucose-based nanoparticles display the highest spheroid uptake, followed by charged nanoparticles. Charged nanoparticles possess an open conformation while nanoparticles stabilized by internal hydrogen bonding retain a folded structure inside the tumor spheroids. The 3D microfluidic tumor-on-a-chip platform is an efficient tool to elucidate the interplay between polymer microstructure and SCPN's stability, a key factor for the rational design of nanoparticles for targeted biological applications.

Flow and irreversible mechanism of pure and hybridized non-Newtonian nanofluids through elastic surfaces with melting effects

Abstract The significance of nanofluid research in nanotechnology, pharmaceutical, drug delivery, food preparation, and chemotherapy employing single- and two-phase nanofluid models has drawn the attention of researchers. The Tiwari–Das model does not capture the diffusion and random movement of nanoparticles (NPs) when they are injected into complex functional fluids. In order to fix the peculiar behavior of NPs, more complex models like the Buongiorno model are coupled with the single-phase model. To examine the heat-mass transfer attributes of nanofluids, a single- and two-phase mixture model is coupled for the first time. The effect of hybrid NPs on the hemodynamic properties of the blood flow through a stretched surface with interface slip in the neighborhood of the stagnation point is examined. Due to their significance in medicinal uses and nominal toxicity, blood is loaded with zinc–iron ( ZnO − F e 2 O 3 ) {\rm{ZnO}}\left-{\rm{F}}{{\rm{e}}}_{2}{{\rm{O}}}_{3}) NPs. However, blood is speculated to have the hematocrit viscosity of the Powell–Eyring fluid. The single-phase model predicts an improvement in heat transport due to an increased volumetric friction of NPs, while the two-phase models provide closer estimates of heat-mass transfer due to Brownian and thermophoretic phenomena. Entropy evaluation predicts the details of irreversibility. The mathematical structures are effectively solved with a Runge–Kutta fourth-order algorithm along with a shooting mechanism. The Eyring–Powell parameters decrease the drag coefficient and mass/thermal transport rate. A higher estimation of the slip, material, and magnetic parameters decreases the flow behavior. The Bejan number increases with the diffusion parameter and decreases as the magnetic and Brinkman numbers increase. The effect of iron oxide ( F e 2 O 3 ) \left({\rm{F}}{{\rm{e}}}_{2}{{\rm{O}}}_{3}) is observed to be dominant.

Direct numerical simulation of supersonic nanoparticles flow in free-molecule regime using the angular coefficient method

We employ molecular flow methods to numerically simulate the supersonic nanoparticles flow in free-molecule regime. To streamline the computational complexity, interaction forces between the gas and solid particles are disregarded. We first develop a discrete phase model (DPM) method that integrates the non-rigid body collision model, enabling an accurate simulation of nanoparticle diffusion under the influence of the drag force and Brownian motion force. The nanoparticles considered in this study have sizes below 10 nm, and the accuracy of the DPM method is verified by comparing its results with experimental data. Subsequently, we theoretically and numerically investigate the transmission probability and number density of N2 molecules flowing through two-dimensional (2D) channels and three-dimensional (3D) tubes by using the angular coefficient (AC) method and the direct simulation Monte Carlo (DSMC) method. The findings indicate that as the diameter of the nanoparticle (dp) decreases to 1 nm, the diffusion coefficient (D) and the root mean square displacement (x) of nanoparticles approach the N2 molecules. The microscopic velocity of most N2 molecules falls within the range of 62–1400 m/s, and the macroscopic velocity of N2 flow falls within the range of Ma = 1.28–1.35. In contrast to the DSMC method, the AC method exhibits enhanced accuracy even with a reduced number of grids and obviates the process for large-scale sampling. Additionally, the solution time required by the AC method is approximately 1/10 and 1/13–1/32 of the DSMC method in 3D cylindrical tubes and 2D channels, respectively. Moreover, the AC method demonstrates superior adaptability when dealing with complex geometries.

Proton-Assisted Assembly of Colloidal Nanoparticles into Wafer-Scale Monolayers in Seconds.

Underwater adhesion processes in nature promise controllable assembly of functional nanoparticles for industrial mass production; However, their artificial strategies have faced challenges to uniformly transfer nanoparticles into a monolayer, particularly those below 100nm in size, over large areas. Here a scalable "one-shot" self-limiting nanoparticle transfer technique is presented, enabling the efficient transport of nanoparticles from water in microscopic volumes to an entire 2-inch wafer in a remarkably short time of 10 seconds to reach near-maximal surface coverage (≈40%) in a 2D mono-layered fashion. Employing proton engineering in electrostatic assembly accelerates the diffusion of nanoparticles (over 50 µm2/s), resulting in a hundredfold faster coating speed than the previously reported results in the literature. This charge-sensitive process further enables "pick-and-place" nanoparticle patterning at the wafer scale, with large flexibility in surface materials, including flexible metal oxides and 3D-printed polymers. As a result, the fabrication of wafer-scale disordered plasmonic metasurfaces in seconds is successfully demonstrated. These metasurfaces exhibit consistent resonating colors across diverse material and geometrical platforms, showcasing their potential for applications in full-color painting and optical encryption devices.

Resonance effect of a radio frequency field on the rotational diffusion of magnetic nanoparticles

The work investigates the rotational-stochastic dynamics (rotational diffusion) of magnetic suspension nanoparticles, created by random collisions of nanoparticles with liquid molecules. The flow of root-mean-square fluctuations of rotational motion acquires the character of periodic motion at large times. The frequency of this motion is due to the cyclicity of the angular variables of the nanoparticles and is proportional to the Brownian relaxation rate. It is shown that with the help of a weak radio-frequency field resonant with this periodic motion, it is possible to increase the average rotation speed. It is also shown that by selecting the parameters of the resonant field, it is possible to achieve a stationary deviation of the magnetic moments of nanoparticles by the desired angle.