Micron Size Scale Research Articles

Multiscale characterizations of structural evolution in mesoporous CeO2.

In situ ultra-small-angle and wide-angle X-ray scattering enables simultaneous tracking of the structural parameters of mesoporous CeO2 from the atomic scale to the micron-size scale. This multiscale approach provides a path to better understand structure-property relationships in mesoporous polycrystalline materials under dynamic conditions such as high temperature cycling.

Characterization of microparticles derived from waste plastics and their bio-interaction with human lung A549 cells.

Microplastics (MPs) represent a worldwide emerging relevant concern toward human and environmental health due to their intentional or unintentional release. Human exposure to MPs by inhalation is predicted to be among the most hazardous. MPs include both engineered, or primary MPs, and secondary MPs, materials obtained by fragmentation from any plastic good. The major part of the environmental MPs is constituted by the second ones that are irregular in size, shape and composition. These features make the study of the biological impact of heterogenous MPs of extremely high relevance to better estimate the real toxicological hazards of these materials on human and environmental organisms. The smallest fractions of plastic granules, relying on the micron-sized scale, can be considered as the most abundant component of the environmental MPs, and for this reason, they are typically used to perform toxicity tests using in vitro systems representative of an inhalation exposure scenario. In the present work, MPs obtained from industrial treatment of waste plastics (wMPs < 50 μm) were investigated, and after the physico-chemical characterization, the cytotoxic, inflammatory and genotoxic responses, as well as the modality of wMPs interactions with alveolar lung cells, were determined. Obtained results indicated that, at high concentrations (100 μg/ml) and prolonged exposure time (48 h), wMPs affect biological responses by inducing inflammation and genotoxicity, as a result of the cell-wMP interactions, also including the uptake of the smaller particles.

Effect of micro-aeration on the mechanical behaviour of chocolates and implications for oral processing.

Aeration in foods has been widely utilised in the food industry to develop novel foods with enhanced sensorial characteristics. Specifically, aeration at the micron-sized scale has a significant impact on the microstructure where micro-bubbles interact with the other microstructural features in chocolates. This study aims to determine the effect of micro-aeration on the mechanical properties of chocolate products, which are directly correlated with textural attributes such as hardness and crumbliness. Uniaxial compression tests were performed to determine the mechanical properties such as Poisson's ratio, Young's modulus and macroscopic yield strength together with fracture tests to estimate the fracture toughness. In vivo mastication tests were also conducted to investigate the link between the fracture properties and fragmentation during the first two chewing cycles. The uniaxial stress-strain data were used to calibrate a viscoplastic constitutive law. The results showed that micro-aeration significantly affects mechanical properties such as Young's modulus, yield and fracture stresses, as well as fracture toughness. In addition, it enhances the brittle nature of the chocolate, as evidenced by lower fracture stress but also lower fracture toughness leading to higher fragmentation, in agreement with observations in the in vivo mastication tests. As evidenced by the XRT images and the stress-strain measurements micro-aeration hinders the re-arrangement of the microscopic features inside the chocolate during the material's deformation. The work provides a new insight of the role of bubbles on the bulk behaviour of complex multiphase materials, such as chocolates, and defines the mechanical properties which are important input parameters for the development of oral processing simulations.

Stochastically Realized Observables for Excitonic Molecular Aggregates.

We show that a stochastic approach enables calculations of the optical properties of large 2-dimensional and nanotubular excitonic molecular aggregates. Previous studies of such systems relied on numerically diagonalizing the dense and disordered Frenkel Hamiltonian, which scales approximately as for N dye molecules. Our approach scales much more efficiently as , enabling quick study of systems with a million of coupled molecules on the micrometer size scale. We calculate several important experimental observables, including the optical absorption spectrum and density of states, and develop a stochastic formalism for the participation ratio. Quantitative agreement with traditional matrix diagonalization methods is demonstrated for both small- and intermediate-size systems. The stochastic methodology enables the study of the effects of spatial-correlation in site energies on the optical signatures of large 2D aggregates. Our results demonstrate that stochastic methods present a path forward for screening structural parameters and validating experiments and theoretical predictions in large excitonic aggregates.

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research.

This article aims to provide an overview of broad range of applications of synchrotron scattering methods in the investigation of nanoscale materials. These scattering techniques allow the elucidation of the structure and dynamics of nanomaterials from sub-nm to micron size scales and down to sub-millisecond time ranges both in bulk and at interfaces. A major advantage of scattering methods is that they provide the ensemble averaged information under in situ and operando conditions. As a result, they are complementary to various imaging techniques which reveal more local information. Scattering methods are particularly suitable for probing buried structures that are difficult to image. Although, many qualitative features can be directly extracted from scattering data, derivation of detailed structural and dynamical information requires quantitative modeling. The fourth-generation synchrotron sources open new possibilities for investigating these complex systems by exploiting the enhanced brightness and coherence properties of X-rays.

Broad studies of graphene and low-density polyethylene composites

Graphene (Gr) distribution in low-density polyethylene (LDPE) considerably increased thermal stability, thermal conductivity, mechanical properties, and flexural properties of LDPE/Gr composites. Addition of Grs to LDPE postponed the time for making the polymer brittle. High specific surface area and superior properties of Gr improved thermal stability, conductivity, storage modulus, and mechanical properties of composites. The electrical conductivity of LDPE/Grs composites upgraded owing to the thermal stability of Grs in LDPE matrix. In terms of rheology, the addition of Grs augmented viscosity of the LDPE matrix. Addition of Grs to LDPE nucleates crystallization by reducing the activation energy along with rising crystallization onset temperature. Adding Gr facilitated decreasing aggregation, expanded crystallinity, improved the local lattice order of LDPE/Grs, and advanced Grs contact with LDPE. Thus, on a macroscopic scale, Gr constrains mobility of polymer chains, causing a growth in stiffness and strength of the composite. The distribution of Grs in LDPE at micron size scale was verified by atomic force microscopy and other microscopic testers. With further Grs inclusions to LDPE, the activation energy reduced, Grs proceeded as nucleating agents throughout the crystallization of composites, and increased the enhancement of relative crystallinity of LDPE/Gr compounds. The percolation phenomenon of LDPE/Gr composite occurred about 0.5 wt% of Gr loading. Due to further addition of Gr to LDPE, the impermeability of oxygen through the conduit raised somehow the LDPE/Gr sample with 0.5 wt% Gr content, generated a sharp improvement, and dropped fuel permeation with about 37% in comparison with pure LDPE.

Energy efficiency and performance of bubble generating systems

The energy efficiency of bubble generating systems of gas-liquid contacting reactors is reviewed and analyzed quantitatively. The key metrics that emerge from a new theoretical analysis are: i) gas fraction of the output dispersion (εgen), ii) interfacial area density of the output dispersion (agen), iii) the energy necessary to create interfacial area (ξ), and iv) cost and maintenance. These metrics are then used to create a literature review of the performance of existing technologies for bubble generation. thus producing a conceptual framework for process intensification and future designs for bubble generating systems. A novel micro-ejector device is then studied within this framework, and is found to have desirable performance, hypothetically because it limits fluid shear to be located on at the gas injection site, on micron size scales. A physical model of the gas entrainment and bubble creation mechanisms in the micro-ejector is described and validated with empirical data.

Microfluidic production of degradable thermoresponsive poly(N-isopropylacrylamide)-based microgels.

Highly monodisperse and hydrolytically degradable thermoresponsive microgels on the tens-to-hundreds of micron size scale have been fabricated based on simultaneous on-chip mixing and emulsification of aldehyde and hydrazide-functionalized poly(N-isopropylacrylamide) precursor polymers. The microfluidic chip can run for extended periods without upstream gelation and can produce monodisperse (<10% particle size variability) microgels on the size range of ∼30-90 μm, with size tunable according to the flow rate of the oil continuous phase. Fluorescence analysis indicates a uniform distribution of each reactive pre-polymer inside the microgels while micromechanical testing suggests that smaller microfluidic-produced microgels exhibit significantly higher compressive moduli compared to bulk hydrogels of the same composition, an effect we attribute to improved mixing (and thus crosslinking) of the precursor polymer solutions within the microfluidic device. The microgels retain the reversible volume phase transition behavior of conventional microgels but can be hydrolytically degraded back into their oligomeric precursor polymer fragments, offering potential for microgel clearance following use in vivo.

Preparation and In-vitro Evaluation of Rifampin-loaded Mesoporous Silica Nanoaggregates by an Experimental Design.

The goal of this research is preparation, optimization and in-vitro evaluation of rifampin-loaded silica nanoparticles in order to use in the pulmonary drug delivery. Nanoparticles are exhaled because of their small size. Preparation of nanoaggregates in a micron-size scale and re-dispersion of them after deposition in the lung is an approach to overcome this problem. We used this approach in our research. Rifampin was selected as a model lipophilic molecule since it was a well-documented and much used anti tuberculosis drug. A half factorial design was used to identify significant parameters of the spray drying process. The results showed that feed concentration, feed pH and the interaction between feed flow rate and gas atomizer flow rate had statistically significant effects on the particle size of nanoaggregates. The Box-Behnken design was employed to optimize the spray drying process. Finally, a quadratic equation which explains the relation between independent variables and aerodynamic diameter of nanoaggregates was obtained. Rifampin-loaded silica nanoaggregates underwent different in-vitro tests including: SEM, Aerosol performance and drug release. The in-vitro drug release was investigated with buffer phosphate (pH=7.4). Regarding the drug release study, a triphasic pattern of release was observed. The rifampin-loaded silica nanoaggregates were capable of releasing 90% drug content after 24 h in combination patterns of release. The prepared rifampin-loaded nanoaggregates seem to have a potential to be used in a pulmonary drug delivery.

Surface plasmon resonance and photoluminescence studies of Au and Ag micro-flowers

The surface plasmon resonance (SPR) and photoluminescence characteristics of gold and silver micro-flowers were compared to those of gold and silver nanoparticles. The micro-flower structures were grown under electron beam deposition using an alumina template. Both types of metallic micro-flowers showed systematic arrangements; they formed islands of flowers about 20 µm across, each one comprised of spikes ranging from 1 to 5 µm in length. A red shift in the SPR and enhancement intensity was observed for both micro-flowers and nanoparticles; the incremental increase was more than 50%. These results, which showed that gold and silver micro-flowers agglomerate at a micron size scale, are useful for the design of easier and more cost effective methods for large area fabrication, especially for particular plasmonic applications.

A stochastic crystal plasticity framework for deformation of micro-scale polycrystalline materials

In this paper we investigate the stochastic behavior in the mechanical response of polycrystalline materials consisting of few grains to hundreds of grains at micron size scales. We study the transition from stochastic (at small scale) to deterministic (at large scale) deformation behavior in polycrystalline samples using both simulation and nanoindentation experiments. Specifically, we develop a stochastic crystal plasticity model combining a Monte Carlo method with a polycrystal continuum dislocation dynamics model in a self-consistent viscoplasticity framework. Using this framework, we numerically calculate the mechanical properties of the polycrystal and gather randomized sampling data of the flow stress. The numerical results are compared to nanoindentation experimental data from three samples with ultra-fine grain structures manufactured via the severe plastic deformation method. The controlling mechanisms of the observed stochastic yield behavior of polycrystals are then discussed using simulations and experimental results. Our results suggest that it is the combination of stochastic plasticity at small scales (where the strength may vary from grain to grain) coupled with the effects of microstructural features such as grain size distribution and crystallite orientations that govern the uncertainty in the mechanical response of the polycrystalline materials. The extent of the uncertainty is correlated to the “effective cell size” in the sampling procedure of the simulations and experiments. The simulations and experimental results demonstrate similar quantitative behavior in terms of coefficient of variation within the same effective cell size.

Chemical disorder effect on orthorhombic-rhombohedral structural transition in La0.7Ca0.3MnO3

High temperature X-ray powder diffraction technique was employed to study the orthorhombic to rhombohedral (O-R) structural transition (ST) in single crystal and ceramics of La0.7Ca0.3MnO3. The data obtained evidence that such ST in both samples occurs in the vicinity of temperature T ∼ 700 K and demonstrates O and R phases coexistence within the T-intervals of about 20 K in crystal and ∼60 K in ceramics. This first order transition is hysteretic on heating and cooling procedures and it is shifted on ΔT ∼ 10 K to higher temperatures in crystal as compared to the ceramics of the same composition. We have described these features in the terms of the difference between “technologically driven” chemical disorder characteristic for considered samples. Thus, it seems that spatial (up to the micron size scale) fluctuations of the Ca-dopant content in crystal and “mesoscopic scale disorder” within grain boundary regions in ceramics are responsible for both: above noted difference of ST parameters and reported earlier difference in magnetic ordering of these samples.

The modulation of canine mesenchymal stem cells by nano-topographic cues

Mesenchymal stem cells (MSCs) represent a promising cellular therapeutic for the treatment of a variety of disorders. On transplantation, MSCs interact with diverse extracellular matrices (ECMs) that vary dramatically in topographic feature type, size and surface order. In order to investigate the impact of these topographic cues, surfaces were fabricated with either isotropically ordered holes or anisotropically ordered ridges and grooves. To simulate the biologically relevant nano through micron size scale, a series of topographically patterned substrates possessing features of differing pitch (pitch=feature width+groove width) were created. Results document that the surface order and size of substratum topographic features dramatically modulate fundamental MSC behaviors. Topographically patterned (ridge+groove) surfaces were found to significantly impact MSC alignment, elongation, and aspect ratio. Novel findings also demonstrate that submicron surfaces patterned with holes resulted in increased MSC alignment to adjacent cells as well as increased migration rates. Overall, this study demonstrates that the presentation of substratum topographic cues dramatically influence MSC behaviors in a size and shape dependent manner. The response of MSCs to substratum topographic cues was similar to other cell types that have been studied previously with regards to cell shape on ridge and groove surfaces but differed with respect to proliferation and migration. This is the first study to compare the impact of anisotropically ordered ridge and groove topographic cues to isotropically order holed topographic cues on fundamental MSC behaviors across a range of biologically relevant size scales.

A method to determine site-specific, anisotropic fracture toughness in biological materials

Many biological materials are hierarchically structured, with highly anisotropic structures and properties on several length scales. To characterize the mechanical properties of such materials, detailed testing methods are required that allow precise and site-specific measurements on several length scales. We propose a fracture toughness measurement technique based on notched focused ion beam prepared cantilevers of lower and medium micron size scales. Using this approach, site-specific fracture toughness values in dental enamel were determined. The usefulness and challenges of the method are discussed.

Improved bio‐implant using ultrafast laser induced self‐assembled nanotexture in titanium

The most successful metal implant materials currently have relatively smooth surfaces on the micron size scale, with most failures occurring after only 10 years. To move beyond this limiting time scale, texturing methods have been developed to modify the metal surface to enhance integration of the implant directly with surrounding bone. A flexible single-step ultrafast-laser texturing process has been developed that results in a surface texture that exhibits micron scale peaks and troughs with superimposed submicron and nano-scale features. The textured titanium samples remain completely hydrophilic with no measurable contact angle even after several weeks in normal atmosphere. An increase in mesenchymal stem cell number is observed over that on an untreated control titanium surface. Extensive formation of cellular bridges by stromal cells between pillars shows the favorable response of differentiated cells to the surface and the promotion of their attachment. Expression of the alkaline phosphatase and osteocalcin genes in human bone marrow cells were seen to increase on the textured surface. The development of this single-step method for creating micron, submicron, and nano-scale surface texture directly on metals makes a significant contribution to the goal of improving the integration and life span of joint replacement implants.

PID feedback control of monochromator thermal stabilization

The desire for increasingly smaller X-ray beams for macromolecular crystallography experiments also stimulates the need for improvements in beam stability. There are numerous sources of instability, which influence beam quality on the micron-size scale. Typically, the most problematic source is thermal drift within the double crystal monochromators . In addition to using liquid nitrogen to indirectly cool both the first and second crystals, GM/CA-CAT previously used a combination of flowing water at constant temperature and copper braiding to stabilize the mechanics, mounts, and the Compton scatter shielding. However, the copper braids inefficiently stabilized the temperature of components that were distant from the water lines. Additionally, vibrations in the water lines propagated throughout the vibrationally dampened monochromator, thereby introducing both positional and intensity instabilities in the transmitted X-ray beam. To address these problems, heating pads were placed directly onto the temperature-sensitive components, with output controlled by a PID-feedback loop. As a result, there is negligible temperature change in the first crystal radiation shielding over the entire range of operational heat loads. Additionally, the angular drift in the second crystal induced by temperature changes in other components is dramatically decreased.

Analyzing absorption and scattering spectra of micro-scale structures with spectroscopic optical coherence tomography

We demonstrate the feasibility of characterizing the absorption and scattering spectra of micron-scale structures in a turbid medium using a spectroscopic optical coherence tomography (SOCT) system with a bandwidth of 430-650 nm. SOCT measurements are taken from phantoms composed of fluorescent microspheres. The absorption and scattering spectra are recovered with proper selections of spatial window width in the post processing step. Furthermore, we present an analysis using numerical OCT simulation based on full-wave solutions of the Maxwell's Equation to elucidate the origination of the multiple peaks in the OCT image for a single microsphere. Finally, we demonstrate the possibility of identifying contrast agents concentrated in micron-sized scale in an SOCT image. Two different types of microspheres in gel phantom are discriminated based on their distinguished absorbent feature.

Analysis of viscous heating in a micro-rocket flow and performance

Micro-rockets for propulsion of small spacecrafts exhibit significant differences with regard to their macroscale counterparts, mainly caused by the role of the viscous dissipation and heat transfer processes in the micron-sized scale. The goal of this work is to simulate the transient operation of a micro-rocket to investigate the effects of viscous heating on the flow and performance for four configurations of the expanding gas and wafer material. The modelling follows a multiphysics approach that solves the fluid and solid regions fully coupled. A continuum-based description that incorporates the effects of gas rarefaction through the micro-nozzle, viscous dissipation and heat transfer at the solid-gas interface is presented. Non-equilibrium is addressed with the implementation of a 2nd-order slip-model for the velocity and temperature at the walls. The results stress that solid-fluid coupling exerts a strong influence on the flowfield and performance as well as the effect of the wafer during the first instants of the transient in micro-rockets made of low and high thermal conductivity materials.

Phenolic Resin/Octa(aminophenyl)-T8-Polyhedral Oligomeric Silsesquioxane (POSS) Hybrid Nanocomposites: Synthesis, Morphology, Thermal and Mechanical Properties

Octa(aminophenyl)-T8-polyhedral silsesquioxane, 1, can serve as a cross-linking agent for organic polymeric resins. Amino functional groups of 1 can form chemical bonds or hydrogen-bonds to appropriate matrix polymers or resins. Various resole phenolic resin/1 nanocomposites (0, 1, 3, 6, and 12 wt% 1) were prepared. Hydrogen bonding between phenolic hydroxyls and the amino groups of 1 in these nanocomposites were investigated by FT-IR. The aggregation morphologies of 1 within these samples were examined using SEM, TEM, and Wide Angle X-ray Diffraction (WAXD) studies. Small quasispherical nanometer-sized POSS particles which were further aggregated into clusters, like individual grapes in a bunch, formed into phase-separated domains as large as 400 nm in diameter as the loading of 1 increased. These particles exhibited a broad 2θ = 5.8° WAXD peak indicating the presence of some crystalline order within the nanoparticles of 1 making up the aggregates. This corresponds to an average crystalline plane lattice distance of 17.5 A. However, extraction of the finely powdered nanocomposites by refluxing THF failed to remove 1 indicating the vast majority of 1 must be chemically bound. Thus, the aggregates must have resin within their structure. The storage modulus (E') in both the glassy and rubbery regions, thermal stability, and glass transition temperature of the composites were improved by 1 wt% 1. However, at high loadings of 1, these properties gradually decreased. Surface extractions by THF removed only a portion of the 1 in the surface regions based on X-EDS analyses for Si, suggesting that a portion of 1 might chemically bond into the phenolic resin matrix during the cure. As the loading of 1 increased, the content of 1 at specific surface locations gradually tends to increase and confirmed excellent dispersion of 1 in the micron size-scale at all locations.

Size-affected single-slip behavior of pure nickel microcrystals

Spatial scales in crystal plasticity are understood to influence flow stresses and work-hardening rates. A direct assessment of the crystal-size dependence of the critical resolved shear stress has been made for single-slip oriented crystals of pure Ni having sample diameters that range from 40 to 1.0 μm. The sample dimensions directly limit the length scales available for plasticity, but without significant external or kinematical constraint. The results show strength increases of up to 15 times over pure Ni and size-affected hardening rates. Stresses are lower, but strengthening persists to larger sizes than for the prior work on face-centered cubic metal whiskers. The results emphasize that at the micron-size scale and below both external geometry and internal structure affect the micromechanisms of deformation and strength.