Diffusion Of Nanoparticles Research Articles

Theory and Simulation of Attractive Nanoparticle Transport in Polymer Melts

We theoretically study the diffusion of a single attractive nanoparticle (NP) in unentangled and entangled polymer melts based on combining microscopic “core–shell” and “vehicle” mechanisms in a dynamic bond percolation theory framework. A physical picture is constructed which addresses the role of chain length (N), degree of entanglement, nanoparticle size, and NP–polymer attraction strength. The nanoparticle diffusion constant is predicted to initially decrease with N due to the dominance of the core–shell mechanism, then to cross over to the vehicle diffusion regime with a weaker N dependence, and eventually plateau at large enough N. This behavior corresponds to decoupling of NP diffusivity from the macroscopic melt viscosity, which is reminiscent of repulsive NPs in entangled melts, but here it occurs for a distinct physical reason. Specifically, it reflects a crossover to a transport mechanism whereby nanoparticles adsorb on polymer chains and diffuse using them as “vehicles” over a characteristic d...

High-yield synthesis of bundles of double- and triple-walled carbon nanotubes on aluminum flakes

High-quality double- and triple-walled carbon nanotubes have been synthesized using Fe−Co catalysts supported on aluminum flake powder. The diameters and lengths of the obtained nanotubes are in the ranges of 3–8 nm and 150–300 μm, respectively, and the specific surface area were quoted as 600 m2/g. The yield of the nanotubes synthesis relative to the initial weight of the catalyst is in the order of 1200%, with 70% of the resulting material consisting of thin carbon nanotubes with less than 6 nm of outer diameter and carbon purity of greater than 90%. Our results indicate that the use of aluminum as catalyst support have a profound effect in the formation of the metal nanoparticles. In addition to boost the reduction the catalyst precursors, the high chemical reactivity of metallic aluminum drives the thermal formation of an oxide layer on the Al surface that suppresses the diffusion and aggregation of catalyst nanoparticles. As a result, a simple impregnation method can be adopted to produce catalyst nanoparticles with narrow size distribution that are suitable for the growth of few wall carbon nanotubes at high yield and large scale.

DNA nanoparticles are safe and nontoxic in non-human primate eyes.

IntroductionDNA nanoparticles (NPs) comprising polylysine conjugated to polyethylene glycol efficiently target murine photoreceptors and the retinal pigment epithelium (RPE) and lead to long-term phenotypic improvement in models of retinal degeneration. Advancing this technology requires testing in a large animal model, particularly with regard to safety. So, herein we evaluate NPs in non-human primates (baboon).Methods and resultsNPs with plasmids carrying GFP and a ubiquitous, RPE-specific, or photoreceptor-specific promoter were delivered by either subretinal or intravitreal injection. We detected GFP message and protein in the retina/RPE from eyes dosed with NPs carrying ubiquitously expressed and RPE-specific vectors, and GFP message in eyes injected with NPs carrying photoreceptor-specific vectors. Importantly, we observed NP DNA in the retina/RPE following intravitreal injection, indicating the inner limiting membrane does not prevent NP diffusion into the outer retina. We did not observe any adverse events in any baboon, and there were no NP-associated changes in retinal function. Furthermore, no systemic or local inflammatory reaction to the vectors/injections was observed, and no NP DNA was found outside the eye.ConclusionTaken together with the well-established rodent safety and efficacy data, these findings suggest that DNA NPs may be a safe and potentially clinically viable nonviral ocular therapy platform for retinal diseases.

Formation of microstructures on Ni film surface by nanosecond laser irradiation

The formation of microstructures on a Ni film surface by nanosecond laser irradiation was investigated. The microstructures were formed by the interaction between the laser-induced plume and the film surface. The laser process was conducted in air and under slight vacuum pressure. The microstructures were formed around the laser-irradiated area and transitioned from a layer to flocculating structures upon repeated laser irradiation. The conifer-like structure was formed by scanning the laser. In addition, it was not formed under low pressure as a result of which the confinement effect of the plume was weak. Surface and cross-sectional observation suggested that the diffusion of nanoparticles on the film surface shaped the topography of the microstructure.

Microscopic investigation of" topically applied nanoparticles for molecular imaging of fresh tissue surfaces.

Previous studies have shown that functionalized nanoparticles (NPs) topically applied on fresh tissues are able to rapidly target cell-surface protein biomarkers of cancer. Furthermore, studies have shown that a paired-agent approach, in which an untargeted NP is co-administered with a panel of targeted NPs, controls for the nonspecific behavior of the NPs, enabling quantitative imaging of biomarker expression. However, given the complexities in nonspecific accumulation, diffusion, and chemical binding of targeted NPs in tissues, studies are needed to better understand these processes at the microscopic scale. Here, fresh tissues were stained with a paired-agent approach, frozen, and sectioned to image the depth-dependent accumulation of targeted and untargeted NPs. The ratio of targeted-to-untargeted NP concentrations-a parameter used to distinguish between tumor and benign tissues-was found to diminish with increasing NP diffusion depths due to nonspecific accumulation and poor washout. It was then hypothesized and experimentally demonstrated that larger NPs would exhibit less diffusion below tissue surfaces, enabling higher targeted-to-untargeted NP ratios. In summary, these methods and investigations have enabled the design of NP agents with improved sensitivity and contrast for rapid molecular imaging of fresh tissues.

High-Performance Quantum Dot Thin-Film Transistors with Environmentally Benign Surface Functionalization and Robust Defect Passivation.

The recent development of high-performance colloidal quantum dot (QD) thin-film transistors (TFTs) has been achieved with removal of surface ligand, defect passivation, and facile electronic doping. Here, we report on high-performance solution-processed CdSe QD-TFTs with an optimized surface functionalization and robust defect passivation via hydrazine-free metal chalcogenide (MCC) ligands. The underlying mechanism of the ligand effects on CdSe QDs has been studied with hydrazine-free ex situ reaction derived MCC ligands, such as Sn2S64-, Sn2Se64-, and In2Se42-, to allow benign solution-process available. Furthermore, the defect passivation and remote n-type doping effects have been investigated by incorporating indium nanoparticles over the QD layer. Strong electronic coupling and solid defect passivation of QDs could be achieved by introducing electronically active MCC capping and thermal diffusion of the indium nanoparticles, respectively. It is also noteworthy that the diffused indium nanoparticles facilitate charge injection not only inter-QDs but also between source/drain electrodes and the QD semiconductors, significantly reducing contact resistance. With benign organic solvents, the Sn2S64-, Sn2Se64-, and In2Se42- ligand based QD-TFTs exhibited field-effect mobilities exceeding 4.8, 12.0, and 44.2 cm2/(V s), respectively. The results reported here imply that the incorporation of MCC ligands and appropriate dopants provide a general route to high-performance, extremely stable solution-processed QD-based electronic devices with marginal toxicity, offering compatibility with standard complementary metal oxide semiconductor processing and large-scale on-chip device applications.

Nanoscale Heterogeneities Drive Enhanced Binding and Anomalous Diffusion of Nanoparticles in Model Biomembranes.

Interaction of functional nanoparticles with cells and model biomembranes has been widely studied to evaluate the effectiveness of the particles as potential drug delivery vehicles and bioimaging labels as well as in understanding nanoparticle cytotoxicity effects. Charged nanoparticles, in particular, with tunable surface charge have been found to be effective in targeting cellular membranes as well as the subcellular matrix. However, a microscopic understanding of the underlying physical principles that govern nanoparticle binding, uptake, or diffusion on cells is lacking. Here, we report the first experimental studies of nanoparticle diffusion on model biomembranes and correlate this to the existence of nanoscale dynamics and structural heterogeneities using super-resolution stimulated emission depletion (STED) microscopy. Using confocal and STED microscopy coupled with fluorescence correlation spectroscopy (FCS), we provide novel insight on why these nanoparticles show enhanced binding on two-component lipid bilayers as compared to single-component membranes and how binding and diffusion is correlated to subdiffraction nanoscale dynamics and structure. The enhanced binding is also dictated, in part, by the presence of structural and dynamic heterogeneity, as revealed by STED-FCS studies, which could potentially be used to understand enhanced nanoparticle binding in raft-like domains in cell membranes. In addition, we also observe a clear correlation between the enhanced nanoparticle diffusion on membranes and the extent of membrane penetration by the nanoparticles. Our results not only have a significant impact on our understanding of nanoparticle binding and uptake as well as diffusion in cell and biomembranes, but have very strong implications for uptake mechanisms and diffusion of other biomolecules, like proteins on cell membranes and their connections to functional membrane nanoscale platform.

Diffusion of rod-like nanoparticles in non-adhesive and adhesive porous polymeric gels

It is known that rod-like nanoparticles (NPs) can achieve higher diffusivity than their spherical counterparts in biological porous media such as mucus and tumor interstitial matrix, but the underlying mechanisms still remain elusive. Here, we present a joint experimental and theoretical study to show that the aspect ratio (AR) of NPs and their adhesive interactions with the host medium play key roles in such anomalous diffusion behaviors of nanorods. In an adhesive polymer solution/gel (e.g., mucus), hopping diffusion enables nanorods to achieve higher diffusivity than spherical NPs with diameters equal to the minor axis of the rods, and there exists an optimal AR that leads to maximum diffusivity. In contrast, the diffusivity of nanorods decreases monotonically with increasing AR in a non-adhesive polymer solution/gel (e.g., hydroxyethyl cellulose, HEC). Our theoretical model, which captures all the experimental observations, generalizes the so-called obstruction-scaling model by incorporating the effects of the NPs/matrix interaction via the mean first passage time (MFPT) theory. This work reveals the physical origin of the anomalous diffusion behaviors of rod-like NPs in biological gels and may provide guidelines for a range of applications that involve NPs diffusion in complex porous media.

Gamma radiation-assisted diffusion of Au nanoparticles in nanocavities of polycarbonate: nano-structural and surface properties

The in situ gamma ray-assisted diffusion of gold nanoparticles in a polycarbonate film modified the nano-structural and surface properties to enable control of functional use with decreases in the free volume nano-hole size and in the fractional free volume measured using positron annihilation lifetime spectroscopic techniques. Coincidenace Doppler broadened spectra showed the identifiable spreading of the gold broadened region of the intensity ratio relative to the pristine polycarbonate film. These results were further corroborated by x-ray photoelectron spectroscopy and Transmission electron microscopy which showed the diffused gold nanoparticles had an average size of about 8 nm, and also showed the bonding of gold nanoparticles with the oxygen functional groups of polycarbonate film.

A general strategy for printing colloidal nanomaterials into one-dimensional micro/nanolines.

Though patterned one-dimensional (1D) micro/nanoline arrays are of great importance in the field of integrated circuits and optoelectronics, the fabrication of high-precision micro/nanolines with excellent optical and electrical performance remains a great challenge. Herein, a general strategy for printing 1D micro/nanolines is proposed by manipulating the self-assembly of functional nanoparticles as a multilayer or monolayer stack with a single-nanoparticle width. This method is universal for dispersible nanoparticles, and the silver nanoparticle was selected as a model nanoparticle due to its good conductivity, dispersibility and narrow-size distribution. The results indicate that the morphologies of printed micro/nanolines can be precisely regulated by the substrate wettability and the suspension concentration. Specifically, 1D nanoparticle-assembled architectures are printed as a monolayer stack on the substrate with a low contact angle (below 45°), while a multilayer stack is formed on the substrate with a high contact angle (above 50°) or a high concentration (more than 0.12%). The controllability of micro/nanoline morphologies can be interpreted through the influence of the three phase contact line slipping motion and the nanoparticle diffusion on diverse substrates at different concentrations. Alteration of the printing template structures enables the intervals of 1D micro/nanolines to span from 16 μm to 48 μm. These results provide an efficient methodology for fabricating micro/nano-circuits or optics and strengthening the understanding of the self-assembling process.

Diffusion tensor optical coherence tomography

In situ measurements of diffusive particle transport provide insight into tissue architecture, drug delivery, and cellular function. Analogous to diffusion-tensor magnetic resonance imaging (DT-MRI), where the anisotropic diffusion of water molecules is mapped on the millimeter scale to elucidate the fibrous structure of tissue, here we propose diffusion-tensor optical coherence tomography (DT-OCT) for measuring directional diffusivity and flow of optically scattering particles within tissue. Because DT-OCT is sensitive to the sub-resolution motion of Brownian particles as they are constrained by tissue macromolecules, it has the potential to quantify nanoporous anisotropic tissue structure at micrometer resolution as relevant to extracellular matrices, neurons, and capillaries. Here we derive the principles of DT-OCT, relating the detected optical signal from a minimum of six probe beams with the six unique diffusion tensor and three flow vector components. The optimal geometry of the probe beams is determined given a finite numerical aperture, and a high-speed hardware implementation is proposed. Finally, Monte Carlo simulations are employed to assess the ability of the proposed DT-OCT system to quantify anisotropic diffusion of nanoparticles in a collagen matrix, an extracellular constituent that is known to become highly aligned during tumor development.

A Comparison of Models for Transport Resistance in Fuel-Cell Catalyst Layers

The vexing rise in resistance to oxygen transport that accompanies reductions in the amount of catalyst in polymer-electrolyte fuel cells is theoretically investigated. Expressions for transport resistance stemming from common models for oxygen transport in electrodes are developed and compared to published experiments. Particular emphasis is placed upon how predicted transport resistances vary with platinum loading, mass fraction of platinum in supported catalysts, ionomer to carbon ratio, and overpotential. Most frequently applied models do not match all empirically observed trends. Models that include nanoparticle diffusion or adsorption demonstrate qualitatively correct behavior and provide quantitatively reasonable predictions for transport resistance.

'Nano on micro' hierarchical porous all carbon structures: an insight into interfacial interactions with bacteria.

Micron long carbon nanofibers (CNFs) were grown on porous carbon beads to give an active surface for rapid immobilization of guest molecules. The fabrication of nanostructures using a catalytic route involving chemical vapour deposition on a porous substrate was accomplished by the controlled synthesis of iron nanoclusters on the surface of porous carbon beads. The challenge of catalyst nanoparticle diffusion into the porous substrate was addressed by using iron coordinated ligand complexes and optimizing the loading percentage of metal salts onto beads. The effect of using tethered bottom up surface processed CNFs on the porous beads' morphologies was established using structural characterization. The protruding architecture of CNFs on the porous carbon surface was subjected to bacterial colonisation in order to determine the efficiency of cell conjugation onto hairy structures, particularly at a low concentration. The interfaces of immobilized bacteria on the textured surface were studied by varying the pH and external physical stimuli to check the biofilm formation. The strategy of fabricating all carbon porous beads, which had topologically controlled 'nano on micro' geometries, to give fast immobilization of guest molecules could be useful in the future for developing an active disinfectant surface.

Comparison of nanoparticle diffusion using fluorescence correlation spectroscopy and differential dynamic microscopy within concentrated polymer solutions

We studied the diffusion of nanoparticles (NPs) within aqueous entangled solutions of polyethylene oxide (PEO) by using two different optical techniques. Fluorescence correlation spectroscopy, a method widely used to investigate nanoparticle dynamics in polymer solution, was used to measure the long-time diffusion coefficient (D) of 25 nm radius particles within high molecular weight, Mw = 600 kg/mol PEO in water solutions. Differential dynamic microscopy (DDM) was used to determine the wave-vector dependent dynamics of NPs within the same polymer solutions. Our results showed good agreement between the two methods, including demonstration of normal diffusion and almost identical diffusion coefficients obtained by both techniques. The research extends the scope of DDM to study the dynamics and rheological properties of soft matter at a nanoscale. The measured diffusion coefficients followed a scaling theory, which can be explained by the coupling between polymer dynamics and NP motion.

Control of viscous fingering by nanoparticles.

A substantial viscosity increase by the addition of a low dose of nanoparticles to the base fluids can well influence the dynamics of viscous fingering. There is a lack of detailed theoretical studies that address the effect of the presence of nanoparticles on unstable miscible displacements. In this study, the impact of nonreactive nanoparticle presence on the stability and subsequent mixing of an originally unstable binary system is examined using linear stability analysis (LSA) and pseudospectral-based direct numerical simulations (DNS). We have parametrized the role of both nondepositing and depositing nanoparticles on the stability of miscible displacements using the developed static and dynamic parametric analyses. Our results show that nanoparticles have the potential to weaken the instabilities of an originally unstable system. Our LSA and DNS results also reveal that nondepositing nanoparticles can be used to fully stabilize an originally unstable front while depositing particles may act as temporary stabilizers whose influence diminishes in the course of time. In addition, we explain the existing inconsistencies concerning the effect of the nanoparticle diffusion coefficient on the dynamics of the system. This study provides a basis for further research on the application of nanoparticles for control of viscosity-driven instabilities.

MMP-2-Sensitive HA End-Conjugated Poly(amidoamine) Dendrimers via Click Reaction To Enhance Drug Penetration into Solid Tumor.

Currently, the limited penetration of nanoparticles remains a major challenge for antitumor nanomedicine to penetrate into the tumor tissues. Herein, we propose a size-shrinkable drug delivery system based on a polysaccharide-modified dendrimer with tumor microenvironment responsiveness for the first time to our knowledge, which was formed by conjugating the terminal glucose of hyaluronic acid (HA) to the superficial amidogen of poly(amidoamine) (PAMAM), using a matrix metalloproteinase-2 (MMP-2)-cleavable peptide (PLGLAG) via click reaction. These nanoparticles had an initial size of ∼200 nm, but once deposited in the presence of MMP-2, they experienced a dramatic and fast size change and dissociated into their dendrimer building blocks (∼10 nm in diameter) because of cleavage of PLGLAG. This rapid size-shrinking characteristic not only promoted nanoparticle extravasation and accumulation in tumors benefited from the enhanced permeability and retention effect but also achieved faster nanoparticle diffusion and penetration. We have further conducted comparative studies of MMP-2-sensitive macromolecules (HA-pep-PAMAM) and MMP-2-insensitive macromolecules (HA-PAMAM) synthesized with a similar particle size, surface charge, and chemical composition and evaluated in both monolayer cells and multicellular spheroids. The results confirmed that the enzyme-responsive size shrink is an implementable strategy to enhance drug penetration and to improve therapeutic efficacy. Meanwhile, macromolecule-based nanoparticles with size-variable characteristics not only promote drug penetration, but they can also be used as gene delivery systems, suggesting great potential as nano-delivery systems.

A novel multiscale silver paste for die bonding on bare copper by low-temperature pressure-free sintering in air

Nanosilver sintering is expected to overcome the limitation of relatively high production cost and become widely available for the die bonding of power electronics. A potential application of nanosilver sintering is bare copper bonding, where replacing substrates with auxiliary silver or other plating that can damage bonding would be advantageous. Here, we introduce a novel multiscale silver paste containing both nanoparticles (20–100nm) and microparticles (1–5μm) for the bonding of high-power chips on a bare copper substrate by pressure-free sintering in air. The energy potential difference generated in the surface force field was critical in the formation of sintering necks between the nano and microparticles, which, together with other microparticles, formed the high-density sintered structure. Despite the development of a copper oxide film, the interfacial bonding was comparable to or higher than the sintering force due to the high surface energy of porous sintered structure and easy diffusion of nanoparticles occurred. A processing temperature of 265°C was considered optimal for bare copper joint (shear strength: 53MPa, transient thermal impedance: 0.132°C/W) considering the trade-off between achieving excellent mechanical and thermal properties while minimizing oxidation.

Peristaltically assisted nanofluid transport in an asymmetric channel

This paper aims to study the diffusion-thermo analysis on the peristaltic flowing pseudoplastic nanofluid in an asymmetric channel. Mathematical formulation is based on basic laws and governing equations of pseudoplastic nanofluid under long wavelength approach. Solution is developed numerically with a focus towards the effects of thermophoretic diffusion and Brownian motion of nano particle. Diverse parameters approaching the problem are studied on velocity, stream function, concentration, pressure drop and temperature. Moreover, comparison between pseudoplastic and viscous nanofluid is also given in the present study.

Coloration and structure behavior after silver and copper nanoparticles formation in soda lime glass

AbstractIn this work, an ion exchange non‐conventional process commonly called ancient painting process without using molten salts is used as a method for glass coloring. In this process of coloration, a mixture of metallic particles with kaolin and arabic adhesive is applied on the soda lime glass surface. Afterwards, the painted glass is submitted to the heat treatment to obtain the color. A comparative study is carried out in order to investigate the diffusion of metallic nanoparticles (silver and copper) in soda lime glasses depending on several parameters as the concentration and composition of stain spread on glass, and the heat treatment temperature. Characterization of the composition and structure of the painted glasses is performed by UV‐visible spectroscopy. In addition, nanoindentation and scanning electron microscopy (SEM) with energy dispersive X‐ray analysis (EDS) techniques are used to determine the penetration of metallic nanoparticles into glass. The obtained result shows that the coloration of painted glass differs and depends on the concentration and the kind of the mixture of the paw. Moreover, it was found that the effect of the heat treatment temperature is primordial on the formation and diffusion of metallic nanoparticles.

IMPROVING THE PHOTORESPONSE OF POROUS SILICON FOR SOLAR CELL APPLICATIONS BY EMBEDDING OF CdTe NANOPARTICLES

The present work is concerned with the preparation of thin films of nanocrystalline porous silicon (PSi) by the method of electrochemical etching. CdTe nanoparticles (NPs) have been prepared by utilizing the pulsed laser ablation in liquid. The measurements of tunneling microscopy, X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and atomic force microscopy (AFE) were carried out and revealed that the PSi was nanostructured and the produced CdTe NPs were ball shaped, having good disposability. The diffusion of CdTe NPs on the properties of PSi solar cell assures that there was an improvement upon their properties. The relationship between [Formula: see text] and the reverse bias voltage was observed to be linear. Values of the built-in potential were observed to be dependent on the laser fluence, current density and the etching time.