Diffusion Of Small Particles Research Articles

Molecular dynamics supported thermal-moisture aging effects on properties of silicone rubber

Silicone rubber materials are widely used as protective coatings in multiple fields. In this work, accelerated artificial aging tests of silicone rubber under different thermal and hygrothermal conditions were performed to better understand how temperature and humidity affected aging behavior and mechanism. It was noticed that due to the presence of oxygen molecules, the main chain of silicone rubber broke and produced free radicals, while water molecules brought hydrolysis reactions and produced silicone hydroxyl structures. Furthermore, computer aided molecular simulation was carried out to better understand the diffusion of small particles in silicone rubber materials, as well as to study how they affect the chain structure, providing support for the mechanism of aging. Finally, two lifespan prediction models were proposed respectively to determine the usage life of silicone rubber under certain temperature and humidity conditions, which provides guidance value for the use of silicone rubber.

Does an Extraoral Suction Device Reduce Aerosol Generation and Prevent Droplet Exposure to the Examiner during Esophagogastroduodenoscopy?

Esophagogastroduodenoscopy (EGD) is an aerosol-generating procedure. A major challenge in the COVID-19 era is how to prevent the spread of aerosols and droplets in endoscopic units. We evaluated the effectiveness of an extraoral suction device in preventing indoor aerosol diffusion and droplet exposure for examiners. The study involved 61 patients who underwent EGD at our institution from 1 February to 31 March 2022. To determine whether aerosol spread increases before or after EGD examination with an extraoral suction device located in front of the patient's mouth, aerosols of 0.3, 0.5, 1, 3, 5, and 10 μm were measured with a handheld particle counter. The degree of contamination of the plastic gowns on the examiners was assessed using the rapid adenosine triphosphate test. The extraoral suction device significantly reduced the diffusion of large particles (3, 5, and 10 μm) after finishing the EGD examination. However, the diffusion of small particles (0.3 and 0.5 μm) was significantly increased. This extraoral suction device was effective in reducing large particle diffusion during EGD examination but was limited for minimizing small particle diffusion or droplet exposure to the examiner.

Diffusion Coefficient of a Brownian Particle in Equilibrium and Nonequilibrium: Einstein Model and Beyond.

The diffusion of small particles is omnipresent in many processes occurring in nature. As such, it is widely studied and exerted in almost all branches of sciences. It constitutes such a broad and often rather complex subject of exploration that we opt here to narrow our survey to the case of the diffusion coefficient for a Brownian particle that can be modeled in the framework of Langevin dynamics. Our main focus centers on the temperature dependence of the diffusion coefficient for several fundamental models of diverse physical systems. Starting out with diffusion in equilibrium for which the Einstein theory holds, we consider a number of physical situations outside of free Brownian motion and end by surveying nonequilibrium diffusion for a time-periodically driven Brownian particle dwelling randomly in a periodic potential. For this latter situation the diffusion coefficient exhibits an intriguingly non-monotonic dependence on temperature.

The structure of cellulose nanofibril networks at low concentrations and their stabilizing action on colloidal particles

The structure and dynamics of networks formed by rod-shaped particles can be indirectly investigated by measuring the diffusion of spherical tracer particles. This method was used to characterize cellulose nanofibril (CNF) networks in both dispersed and arrested states, the results of which were compared with coarse-grained Brownian dynamics simulations. At a CNF concentration of 0.2 wt% a transition was observed where, below this concentration tracer diffusion is governed by the increasing macroscopic viscosity of the dispersion. Above 0.2 wt%, the diffusion of small particles (20–40 nm) remains viscosity controlled, while particles (100–500 nm) become trapped in the CNF network. Sedimentation of silica microparticles (1–5 μm) in CNF dispersions was also determined, showing that sedimentation of larger particles is significantly affected by the presence of CNF. At concentrations of 0.2 wt%, the sedimentation velocity of 5 μm particles was reduced by 99 % compared to pure water.

Experimental study of turbulent thermal diffusion of particles in inhomogeneous and anisotropic turbulence

We experimentally studied the turbulent thermal diffusion of small particles in inhomogeneous and anisotropic stably stratified turbulence produced by one oscillating grid in the air flow. The velocity fields have been measured using Particle Image Velocimetry (PIV). We have determined various turbulence characteristics: the mean and turbulent velocities, two-point correlation functions of the velocity field, and an integral scale of turbulence from the measured velocity fields. The temperature field has been measured with a temperature probe equipped with 12 E thermocouples. Spatial distributions of micrometer-sized particles have been determined by a PIV system using the effect of the Mie light scattering by particles in the flow. The experiments have demonstrated that particles are accumulated at the minimum of mean fluid temperature due to the phenomenon of turbulent thermal diffusion. Using measured spatial distributions of particles and temperature fields, we have determined the effective turbulent thermal diffusion coefficient of particles in inhomogeneous temperature-stratified turbulence. This experimental study has clearly detected the phenomenon of turbulent thermal diffusion in inhomogeneous turbulence.

Liquid-Liquid Phase-Separated Systems from Reversible Gel-Sol Transition of Protein Microgels.

Liquid-liquid phase-separated biomolecular systems are increasingly recognized as key components in the intracellular milieu where they provide spatial organization to the cytoplasm and the nucleoplasm. The widespread use of phase-separated systems by nature has given rise to the inspiration of engineering such functional systems in the laboratory. In particular, reversible gelation of liquid-liquid phase-separated systems could confer functional advantages to the generation of new soft materials. Such gelation processes of biomolecular condensates have been extensively studied due to their links with disease. However, the inverse process, the gel-sol transition, has been less explored. Here, a thermoresponsive gel-sol transition of an extracellular protein in microgel form is explored, resulting in an all-aqueous liquid-liquid phase-separated system with high homogeneity. During this gel-sol transition, elongated gelatin microgels are demonstrated to be converted to a spherical geometry due to interfacial tension becoming the dominant energetic contribution as elasticity diminishes. The phase-separated system isfurther explored with respect to the diffusion of small particles for drug-release scenarios. Together, this all-aqueous system opens up a route toward size-tunable and monodisperse synthetic biomolecular condensates and controlled liquid-liquid interfaces, offering possibilities for applications in bioengineering and biomedicine.

Prediction of particle deposition on the walls of a cubical cavity with differentially heated opposed walls using heat and mass transfer laminar mixed convection boundary layer models

In this paper we present a model to predict particle deposition velocities on the isothermal walls bounding a turbulent natural convection flow at moderate Rayleigh numbers. The model is based on the laminar mixed convection characteristics of the velocity and thermal boundary layers near the thermally active walls of the cavity. These characteristics are verified with Direct Numerical Simulations reported elsewhere. The model considers the gravity force, the thermophoretic effect and the Brownian diffusion of small particles. The predicted deposition velocities are compared successfully with those obtained with one of the most popular particle deposition models and with experimental measurements reported in the literature and carried out in a cavity with the same thermal boundary conditions as those considered in this study.

Effect of Extended Thermal Exposure and Alloying Elements on the Morphology of Eutectic Si in Al–Si Cast Alloys

The main objective of the present work is to explore the morphological changes in the eutectic silicon particles associated with the increase in the solution treatment time up to 400 h by quantifying the characteristics of the eutectic silicon particles at different durations of solution heat treatment. Thermal modification of silicon particles proved to be more effective in the Sr-modified alloys rather than their Sr-free counterparts. The evolution of silicon particles during extended solution treatments followed the same trends and sequences for non-modified and Sr-modified 354-type and 356 alloys, at different evolution rates. The coarsening of eutectic Si particles occurred through particle coalescence and Ostwald ripening mechanisms. While both mechanisms were active at the same time, however, they operated independently and additively. The pinholes observed in the silicon particles derive from the impression or imprint left behind from the diffusion of small particles into larger particles.

Diffusion and Brownian Motion: On the Possibility to Control Diffusion of Small Particles with Laser Radiation

Diffusion and Brownian Motion: On the Possibility to Control Diffusion of Small Particles with Laser Radiation

Diffusion of Nanoparticles in Polymer Systems

The state-of-the-art in research of the mobility of nanoparticles in polymer melts is presented. It is important to determine the mechanisms of diffusion processes in these systems and factors affecting the diffusion of nanoparticles of different sizes when developing methods for controlling the distribution of nanoparticles in polymer nanocomposites that play an increasingly important role in various industries. The modern theoretical concepts of the diffusion of small particles in solutions and polymer melts, as well as results of computer simulation and experimental studies, are discussed. It is shown that the key factor determining the nature of the motion of nanoparticles is the ratio of the particle size to the characteristic dimensions of the polymer, which explains the strong relationship between the mobility of nanoparticles and the local structure of polymer molecules.

Gravitational field flow fractionation: Enhancing the resolution power by using an acoustic force field

An acoustic field flow fractionation (FFF) device was developed to fractionate a micro-particle mixture on the basis of the particle diameter using an acoustic force field in a carrier liquid flow. In the acoustic FFF channel used in the device, ultrasound waves generated from piezoelectric transducers driven by a sinusoidal signal of 2.02 Mhz propagated into the carrier liquid flow and built up a quarter-wavelength ultrasound standing wave field across the channel height. It was experimentally demonstrated that the acoustic field with a pressure node plane at the bottom surface of the channel reduced the thickness of the particle diffusion layer in a stagnant liquid proportional to the applied voltage driving the piezoelectric transducer. In the size-dependent particle separation, the particle mixture flowing through the acoustic FFF channel experienced an acoustic radiation force in the gravitational direction. As a result, suppressing the diffusion of small particles, particles were transported along the bottom surface of the channel with the local velocity of the carrier liquid at the particle center. The developed acoustic FFF device successfully fractionated a fluorescent micro-particle mixture (1, 3, 5, and 10 μm diameter), whereas the 3 and 5 μm particles were not fractionated in the FFF device using only the gravitational force field due to the diffusion of 3 μm particles.

1D-Reactor Decentralized MDA for Uniform and Accurate Whole Genome Amplification.

Multiple displacement amplification (MDA), a most popular isothermal whole genome amplification (WGA) method, suffers the major hurdle of highly uneven amplification, thus, leading to many problems in approaching biological applications related to copy-number assessment. In addition to the optimization of reagents and conditions, complete physical separation of the entire reaction system into numerous tiny chambers or droplets using microfluidic devices, has been proven efficient to mitigate this amplifying bias in recent works. Here, we present another MDA advance, microchannel MDA (μcMDA), which decentralizes MDA reagents throughout a one-dimensional slender tube. Due to the double effect from soft partition of high molecular-weight DNA molecules and less-limited diffusion of small particles, μcMDA is shown to be significantly effective at improving the amplification uniformity, which enables us to accurately detect single nucleotide variants (SNVs) with higher efficiency and sensitivity. More importantly, this straightforward method requires neither customized instruments nor complicated operations, making it a ready-to-use technique in almost all biological laboratories.

Diffusion of small particles in polymer films.

The motion of small probe molecules in a two-dimensional system containing frozen polymer chains was studied by means of Monte Carlo simulations. The model macromolecules were coarse-grained and restricted to vertices of a triangular lattice. The cooperative motion algorithm was used to generate representative configurations of macromolecular systems of different polymer concentrations. The remaining unoccupied lattice sites of the system were filled with small molecules. The structure of the polymer film, especially near the percolation threshold, was determined. The dynamic lattice liquid algorithm was then employed for studies of the dynamics of small objects in the polymer matrix. The influence of chain length and polymer concentration on the mobility and the character of motion of small molecules were studied. Short- and long-time dynamic behaviors of solvent molecules were also described. Conditions of anomalous diffusions' appearance in such systems are discussed. The influence of the structure of the matrix of obstacles on the molecular transport was discussed.

Fickian yet non-Gaussian behaviour: A dominant role of the intermittent dynamics.

We present a study of the dynamics of small solute particles in a solvent medium where the solute is much smaller in size, mimicking the diffusion of small particles in crowded environment. The solute exhibits Fickian diffusion arising from non-Gaussian Van Hove correlation function. Our study shows that there are at least two possible origins of this non-Gaussian behaviour: the decoupling of the solute-solvent dynamics and the intermittency in the solute motion, the latter playing a dominant role. In the former scenario when averaged over time long enough to explore different solvent environments, the dynamics recovers the Gaussian nature. In the case of intermittent dynamics the non-Gaussianity remains even after long averaging and the Gaussian behaviour is obtained at a much longer time. Our study further shows that only for an intermediate attractive solute-solvent interaction the dynamics of the solute is intermittent. The intermittency disappears for weaker or stronger attractions.

Mechanistic Model for Ash Deposit Formation in Biomass Suspension Firing. Part 2: Model Verification by Use of Full-Scale Tests

A model for deposit formation in suspension firing of biomass has been developed. The model describes deposit build-up by diffusion and subsequent condensation of vapors, thermoforesis of aerosols, convective diffusion of small particles, impaction of large particles and reaction. The model describes particle sticking or rebound by a combination of the description of (visco)elsatic particles impacting a solid surface and particle capture by a viscous surface. The model is used to predict deposit formation rates measured during tests conducted with probes in full-scale suspension-fired biomass boilers. The rates predicted by the model was reasonably able to follow the rates observed in the tests, although with some variation, primarily as overestimations of the deposit formation rates. It is considered that the captive properties of the deposit surface are overestimated. Further examination of some physical parameters related to the description of surface capture are suggested. Based on these examinations ...

Mechanistic Model for Ash Deposit Formation in Biomass Suspension Firing. Part 1: Model Verification by Use of Entrained Flow Reactor Experiments

Two models for deposit formation in suspension firing of biomass have been developed. Both models describe deposit buildup by diffusion and subsequent condensation of vapors, thermophoresis of aerosols, convective diffusion of small particles, impaction of large particles, and reaction. The models differ in the description of the sticking probability of impacted particles: model #1 employs a reference viscosity in the description of the sticking probability, while model #2 combines impaction of viscoelastic particles on a solid surface with particle capture by a viscous surface. Both models were used to describe the deposit formation rates and deposit chemistry observed in a series of entrained flow reactor (EFR) experiments using straw and wood as fuels. It was found that model #1 was not able to describe the observed influence of temperature on the deposit buildup rates, predicting a much stronger influence of this parameter. Model #2 was able to provide a reasonable description of the influence of temp...

Abstract A19: Patient-derived in vitro cancer model to study tumor-associated angiogenesis

Abstract Tumor-associated angiogenesis is the generation of new blood vessel networks that promote tumor growth and provide a pathway for tumor cells to spread to other organs. Even though recent research has revealed several key mechanisms in the association of angiogenesis to cancer, fundamental questions remain regarding the characteristics of tumor-associated angiogenesis and how it is different from the angiogenesis involved in normal physiological processes. It has been demonstrated that tumor blood vessels are phenotypically different from their normal counterparts, showing a defective endothelial monolayer and abnormal vessel hierarchy. However, it is still unknown how tumor-associated endothelial cells (TEnCs) compare functionally to normal endothelial cells (NEnCs) and how their differences subsequently impact cancer progression. Important functional differences may include differences in angiogenic activity that are inherent to these types of endothelial cells or that are dependent on their surrounding microenvironment. For our study the primary source of TEnCs is cell isolation from patient samples, which allows us to also isolated NEnCs and tumor and normal epithelial cells (TEpCs and NEpCs respectively) to have a direct comparison of tumor versus normal microenvironment. To further characterize differences of TEnCs and NEnCs, we used a biomimetic blood vessel microfluidic platform that allows the reconstruction of the blood vessel luminal structure in vitro. This platform provided a 3D microenvironment that allowed the discovery of previously unknown characteristics of TEnCs in monoculture. First, we found that TEnCs generate more angiogenic sprouts than cells from normal tissue. We also found that the architecture of the TEnC-generated blood vessels is significantly different from NEnC-generated blood vessels when stimulated with a VEGF gradient. In addition, TEnCs form an irregular and permeable endothelial wall, allowing diffusion of small particles out of the vessels, a previously described hallmark of tumor blood vessels. Finally, TEnC vessels have a different anti-angiogenic drug response compared to their normal counterpart and it varies between patient samples, where in some patients the anti-angiogenic drug stopped angiogenesis but in other patients the angiogenesis was enhanced or not affected. When TEpCs spheroids are added next to the biomimetic blood vessel to create a co-culture model, we found that angiogenesis is down-regulated in TEnCs vessels but up-regulated in NEnCs vessels. In addition, there is cell invasion from the TEpCs spheroids toward the vessel in the TEnCs/TEpCs co-culture model but not when co-cultured with NEnCs vessels. Here we show an in vitro organotypic model that can elucidate functional characteristics of TEnCs and NEnCs in co-culture with TEpCs and NEpCs, enabling a platform that can potentially be used for therapeutic drug screening and personalized medicine. Citation Format: Jose A. Jimenez-Torres, Kyung E. Sung, Moon He-Lee, Jason Abel, David J. Beebe. Patient-derived in vitro cancer model to study tumor-associated angiogenesis. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr A19.

Direct Measurement of Macromolecule-Coated Colloid-Mucus Interactions.

We report measurements of macromolecule-coated colloids interacting with mucus to understand colloidal particle diffusion near mucus-coated surfaces. Total internal reflection microscopy is used to measure colloids with adsorbed poly(ethylene glycol) (PEG), bovine serum albumin (BSA), and polyelectrolyte bilayers (PEB) interacting with mucus to obtain kT-scale energy landscapes and nanometer-scale diffusivity landscapes. Energy landscapes are quantified as a superposition of van der Waals, steric, and tethering potentials, and diffusivity landscapes are modeled by considering lubrication in the presence of permeable layers. PEG- and BSA-coated colloids have soft repulsion with mucus that could enable diffusion of small particles within mucus pores. PEB-coated colloids display attractive tethers to mucus that produce irreversible binding. Different interaction potentials for each particle coating confirm that the ζ-potential is not a successful predictor of particle-mucus interactions and diffusion. Diffusivity landscapes show thick mucus layers are permeable to the solvent and dominate particle-mucus hydrodynamic interactions relative to the thin, impermeable particle coatings. Our results show direct measurements and models to understand how particle coating properties (e.g., elasticity, porosity) control particle interactions and transport near mucus films to potentially aid the design of better particle-based therapeutics and diagnostics.

Diffusion of small particles in a solid polymeric medium

We analyze diffusion of small particles in a solid polymeric medium taking into account a short-range particle-polymer interaction. The system is modeled by a particle diffusion on a ternary lattice where the sites occupied by polymer segments are blocked, the ones forming the hull of the chains correspond to the places at which the interaction takes place, and the rest are voids, in which the diffusion is free. In the absence of interaction the diffusion coefficient shows only a weak dependence on the polymer chain length and its behavior strongly resembles the usual site percolation. In the presence of interactions the diffusion coefficient (and especially its temperature dependence) shows a nontrivial behavior depending on the sign of interaction and on whether the voids and the hulls of the chains percolate or not. The temperature dependence may be Arrhenius-like or strongly non-Arrhenius, depending on parameters. The analytical results obtained within the effective medium approximation are in qualitative agreement with those of Monte Carlo simulations.

Measurements of the near-wall hindered diffusion of colloidal particles in the presence of an electric field

Understanding near-wall diffusion of small particles and biomolecules is important in colloid science and many microfluidic devices. Our experimental measurements of the diffusion of 110–460 nm radii suspended particles in the presence of electric fields up to 3.1 kV/m using particle tracking are in agreement with theoretical predictions for diffusion hindered by the presence of a solid surface. The results suggest that the external electric field has little, if any, effect upon the hindered diffusion of colloidal particles, even when the electrophoretic force exceeds the Stokes drag.