Bulk Characteristics Research Articles

Highly antifouling polymer-nanoparticle-nanoparticle/polymer hybrid membranes

We introduce highly antifouling Polymer-Nanoparticle-Nanoparticle/Polymer (PNNP) hybrid membranes as multi-functional materials for versatile purification of wastewater. Nitrogen-rich polyethylenimine (PEI)-functionalized halloysite nanotube (HNT-SiO2-PEI) nanoparticles were developed and embedded in polyvinyl chloride (PVC) membranes for protein and dye filtration. Bulk and surface characteristics of the resulting HNT-SiO2-PEI nanocomposites were determined using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Moreover, microstructure and physicochemical properties of HNT-SiO2-PEI/PVC membranes were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and attenuated total reflectance (ATR)-FTIR. Results of these analyses indicated that the overall porosity and mean pore size of nanocomposite membranes were enhanced, but the surface roughness was reduced. Additionally, surface hydrophilicity and flexibility of the original PVC membranes were significantly improved by incorporating HNT-SiO2-PEI nanoparticles. Based on pure water permeability and bovine serum albumin (BSA)/dye rejection tests, the highest nanoparticle-embedded membrane performance was observed at 2 weight percent (wt%) of HNT-SiO2-PEI. The nanocomposite incorporation in the PVC membranes further improved its antifouling performance and flux recovery ratio (96.8%). Notably, dye separation performance increased up to 99.97%. Overall, hydrophobic PVC membranes were successfully modified by incorporating HNT-SiO2-PEI nanomaterial and better-quality wastewater treatment performance was obtained.

Fine-tuning of bulk and interfacial characteristics of two-antennary oligoglycines in aqueous solutions

The structure of the two-antennary oligoglycines molecules presumes a complex interplay of their bola-amphiphilic nature and the possibility for the onset of Polyglycine II structural motifs in aqueous solutions. These tendencies lead to the appearance of various supramolecular self-assemblies (tectomers). The complex fluid formulations which contain them exhibit high potential for the application of easy fine-tuning procedures. In the present study the possibility for smart regulation of the properties of aqueous solutions of C8H16(-CH2-NH-Gly5)2 (T2-C8-Gly5) is investigated through the variations of pH and changes of the initial incubation time of the systems. A combined investigation protocol, including Dynamic Light Scattering, Profile Analysis Tensiometry, and microscopic Thin-Liquid-Film techniques is developed. The key results are: (i) the size distribution is bimodal in acidic conditions (pH ≤ 6.0) and becomes visibly mono-modal for pH ≥ 7.1; (ii) upon increase of the solution pH the dimensions of the tectomers is shifted towards larger structural entities. These tendencies are enhanced with the raise of the initial incubation time of the aqueous systems. The study permits to draw essential conclusions about the possible coupling mechanism of bulk and interfacial phenomena, and gives key grounds for further fine-tuning of the tectomer-formation phenomena. The obtained results add important new knowledge about the nature of these new materials in view of possible applications in the development of e.g. drug nanocarriers, for extraction of various impurities from water media, etc.

Experimental investigation of wave attenuation and bulk drag coefficient in mangrove forest with complex root morphology

Mangrove forests play a crucial role in coastal protection. Numerous experimental studies have been performed to examine the interaction between wave flows and mangrove forests, while the mangrove forests are commonly modeled as cylinder arrays, and the effect of the complex root system on wave attenuation is still unclear. A series of physical experiments were conducted to study the hydrodynamic characteristics induced by a 10-m-long mangrove forest model, which was built to reproduce a mature Rhizophora forest. Wave-attenuation analysis was performed to highlight the importance of considering the wave damping produced by mangrove roots under different water depths. In addition, the wave-attenuation coefficient β increases linearly with an increase in the relative wave height and wave steepness to varying degrees. In addition, the bulk drag coefficient (CD), a key parameter for quantifying the mean vegetation resistance, was obtained based on the classical model proposed by Dalrymple et al. (1984). The influences of several dimensionless hydrodynamic parameters on the CD are discussed in detail. The results show that the Ursell number and Keulegan–Carpenter number (KCd) have stronger correlations with CD for vegetation models without roots. The KCLe number calculated using effective characteristic length Le is suitable for describing the CD of the mangrove model for given water depth. Then, a new parameter, KCrv, was defined using the average pore velocity and vegetation-related hydraulic radius by considering the bulk characteristics of the wave and vegetation. Finally, a generic empirical formula was proposed for the CD to reveal the drag coefficient characteristics of vegetation with a relatively high correlation.

Spectral analysis of the photoconductivity for characterization of CdTe И CdZnTe detectors

The results of the application of optical methods are considered: spectral analysis of photoconductivity in the range 400–1800 nm and field measurements of stationar photoconductivity to study the bulk and surface characteristics of CdTe and CdZnTe gamma-ray detectors. The studies of the photoresponse of the samples were carried out in different irradiation modes: modulated at a frequency of 25 Hz and a constant light flux. The measurements were carried out at room temperature on domestic and foreign materials of detector quality. Using the spectral photoconductivity method, the parameters of deep levels, which affect the detector properties, have been estimated in the studied materials. Based on the calculations of the field dependences of the photoconductivity, the volume and surface parameters of the capture and recombination of non-equilibrium carriers in the investigated detectors were determined. The results of calculating the transport characteristics of charge transfer by electrons μτe in detectors are compared with similar parameters measured using the traditional method of irradiating the detector with alpha particles. To measure the band gap in CdTe and CdZnTe at room temperature the method was modified for calculating ΔEg. The possibility of monitoring the Zn content in CdZnTe detectors using the spectral photoconductivity method is shown.

Formation of Zn-rich ZnO films with improved bulk and surface characteristics by approach of magnetron sputtering technique

In this work Zn-rich ZnO films were formed by unconventional magnetron sputtering approach where oxygen flow cyclically varied between two different values during deposition process. Specifically, ZnO films were deposited using radio frequency power source with Zn target, while argon flow was set to keep total deposition pressure at constant and oxygen flow cyclically varied between stoichiometric ZnO and intermediate Zn/ZnO formation regimes. Such modification of physical vapor deposition method allowed to form complex structure ZnO films with altered bulk and surface characteristics. X-ray diffraction analysis of deposited films revealed highly expressed wurtzite structure with existence of small fraction of metallic Zn phase. In comparison to regular ZnO film surface morphology analysis of complex structure Zn-rich ZnO films showed significant increment of grain size and more than three times larger surface roughness. The reduction of optical transmittance as well as band gap value were observed by analysing optical properties of deposited films. Urbach energy analysis revealed that deposited Zn-rich ZnO films had higher level of disorder, dopants or defects comparing to the regular ZnO. Such combination of deposited films properties leads to the significant improvement of photocatalysis efficiency measured by the bleaching of methylene blue solution.

Surface and Bulk Oxygen Kinetics of BaCo0.4Fe0.4Zr0.2-XYXO3-δ Triple Conducting Electrode Materials.

Triple ionic-electronic conductors have received much attention as electrode materials. In this work, the bulk characteristics of oxygen diffusion and surface exchange were determined for the triple-conducting BaCo0.4Fe0.4Zr0.2−XYXO3−δ suite of samples. Y substitution increased the overall size of the lattice due to dopant ionic radius and the concomitant formation of oxygen vacancies. Oxygen permeation measurements exhibited a three-fold decrease in oxygen permeation flux with increasing Y substitution. The DC total conductivity exhibited a similar decrease with increasing Y substitution. These relatively small changes are coupled with an order of magnitude increase in surface exchange rates from Zr-doped to Y-doped samples as observed by conductivity relaxation experiments. The results indicate that Y-doping inhibits bulk O2− conduction while improving the oxygen reduction surface reaction, suggesting better electrode performance for proton-conducting systems with greater Y substitution.

Influence of Si content on the microstructure and mechanical properties of silicon stainless steel

The influence of Si addition on the microstructure and mechanical behavior of cast silicon stainless steel alloys was investigated. It was recognized that after incorporation of Si in the range of ∼ 2–6 wt%, microstructure changes significantly. It transforms from single-phase austenitic to duplex microstructure containing ferrite and austenite. In addition, TiC precipitates with angular and spherical morphology were observed in all the sample conditions. Uniaxial tensile tests suggested that the incorporation of Si improved the strength and ductility as long as the microstructure remains primarily austenitic. However, at much higher silicon content (∼6 wt%), microstructure transformed to duplex structure, followed by the drastic reduction in ductility and toughness. Overall, the alloy with ∼4 wt% Si exhibited comparatively better strength, ductility as well as toughness. The mechanical properties of the individual phases, characterized using nanoindentation, indicated that the hardness and modulus of the austenite phase improved significantly after Si incorporation up to ∼6 wt%. Concomitantly correlation between the mechanical properties and crystallographic orientation of grains was also established by performing post-nanoindentation EBSD analysis. The results indicated that the average hardness and modulus of each phase are significantly related to the crystallographic orientation of grains, i.e., it is highly anisotropic. Finally, the nanomechanical properties of the individual phases were utilized to predict and compare the bulk mechanical properties using the ECM model. A reliable quantitative comparison between nanomechanical and bulk mechanical properties of alloys with single-phase microstructure was obtained, whereas a more refined ECMs are required for envisaging the bulk characteristics of the materials with duplex microstructure.

Precipitation Properties of Supercell Hook Echoes

Recent studies have suggested that thermodynamic properties of supercell rear-flank downdrafts (RFDs) can affect whether or not tornadogenesis occurs. The thermodynamic characteristics of RFDs are determined in part by microphysical processes such as evaporation of raindrops and melting of hailstones. Whereas in situ measurements of hook-echo particle size distributions (PSDs) are exceedingly rare, polarimetric radars can be used to determine the bulk characteristics of these PSDs remotely. A preliminary analysis of polarimetric radar data from a small sample of supercell hook echoes reveals unusual drop size distributions compared to typical rainfall in Oklahoma, as well as spatially inhomogeneous structures. The inner edge of the hook echo is often characterized by low or moderate reflectivity factor at horizontal polarization (ZH), with very high differential reflectivity factor (ZDR), indicating a sparse population of very large drops. The southern and/or western (back) portion of the hook is characterized by moderate to high ZH and rather low ZDR, indicating a surplus of small drops and/or a lack of larger drops. Hypotheses explaining the unusual drop size distributions are presented. Additionally, the time evolution of these characteristics is explored using data collected with a special rapid scanning strategy.

Enhanced Longitudinal Heat Transfer in Oscillatory Channel Flow—A Theoretical Perspective

Abstract Enhanced longitudinal heat transfer in viscous, laminar, single-phase, oscillatory channel flow is investigated in this paper. Kurzweg (ASME J. Heat Transfer-Trans. ASME. 107, 1985) analyzed this case theoretically and derived a correlation for a nondimensionalized effective thermal conductivity in terms of Prandtl and Womersley numbers. The present investigation contributes analysis of limiting cases and physical interpretation to the results of Kurzweg. A simplified model with isothermal walls is proposed, applicable if working fluid and channel wall material exhibit sufficiently large differences in thermal inertia. Examined over a wide range of Womersley numbers, this model reveals six distinct regimes characterized by the Prandtl number of the fluid. The respective thickness of hydrodynamic and thermal boundary layers relative to the channel width is relevant in this context. Maximum effective thermal conductivity is attained when the thermal boundary layer expands over the full channel width. The influence of Womersley number is discussed and explained in terms of the interplay of hydrodynamic and thermal flow characteristics. These patterns reveal either quasi-steady parabolic or oscillating bulk characteristics. The importance of the thermal boundary layer thickness motivates the introduction of a new nondimensional group, making it easier to classify the various regimes of enhanced longitudinal heat transfer.

Towards the prediction of feed intake capacity of modern broilers on bulky feeds

The use of alternative, often bulky ingredients is becoming widespread in poultry diets as the industry seeks to reduce its economic and environmental costs. Consequently, there is an increased need to accurately predict the performance of birds given such diets and identify their maximum capacity for bulk. We offered diets diluted with a range of bulky ingredients to male Ross 308 broilers to assess their capacity for bulk and identify a bulk characteristic responsible for limiting intake. Four hundred ninety-five day-old broilers allocated into 45 pens, were offered a common starter diet until day (d) 7, and 1 of 9 grower diets from d 8 to 29 (Period 1). Each of the grower diets was diluted with either 30 or 60% of oat hulls (OH), wheat bran (WB), or grass meal (GM), or a mixture of 2 bulky ingredients at an inclusion level of 30% each (OHWB, OHGM, WBGM). From d 29 to 43 (Period 2), all birds were offered the bulkiest diet (GM60). A number of bulk characteristics were measured on the diets. Feed intake was measured daily, and birds were dissected on d 29 and 43 for organ and carcass measurements. During d 8 to 14 diet water-holding capacity (WHC) was more consistent in predicting feed intake when scaled per unit of body weight than any other bulk characteristic. However, this was no longer the case during d 15 to 28. In Period 2, the response and adaptation to the bulkiest diet was determined by previous experience to bulk. Birds offered a bulkier diet during Period 1, were better able to adapt the size of their digestive organs and increase scaled feed intake, such that there were no differences between these birds and those offered the GM60; the converse was the case for birds on the least bulky diets. We conclude that WHC is able to predict maximum intake on bulky diets in unadapted birds. Adaptation to bulky diets can be very fast, so that their high bulk content no longer limits feed intake and performance.

Validation and Application of a Low-Cost Sorting Device for Fumonisin Reduction in Maize.

Fumonisin mycotoxins are a persistent challenge to human and livestock health in tropical and sub-tropical maize cropping systems, and more efficient methods are needed to reduce their presence in food systems. We constructed a novel, low-cost device for sorting grain, the “DropSort”, and tested its effectiveness on both plastic kernel models and fumonisin-contaminated maize. Sorting plastic kernels of known size and shape enabled us to optimize the sorting performance of the DropSort. The device sorted maize into three distinct fractions as measured by bulk density and 100-kernel weight. The level of fumonisin was lower in the heaviest fractions of maize compared to the unsorted samples. Based on correlations among fumonisin and bulk characteristics of each fraction, we found that light fraction 100-kernel weight could be an inexpensive proxy for unsorted fumonisin concentration. Single kernel analysis revealed significant relationships among kernel fumonisin content and physical characteristics that could prove useful for future sorting efforts. The availability of a low-cost device (materials~USD 300) that can be used to reduce fumonisin in maize could improve food safety in resource-limited contexts in which fumonisin contamination remains a pressing challenge.

3D enabled facile fabrication of substrates with human tongue characteristics for analysing the tribological behaviour of food emulsions

The mouth-feel or oral perception of a food may vary in different oral surfaces or tongue-palate environment depending on the physical characteristics of human tongue. Tribological measurements emulating the characteristics of tongue-palate environment will assist in the evaluation of oral perception of food materials. This study reports a 3D printing assisted approach for rapid fabrication of the soft elastomer substrates with different surface (roughness) and bulk characteristics (elastic modulus and thickness) for tribological measurements. The influence of substrates with various regularly patterned surfaces, elastic modulus, and thickness on the lubrication properties of four food emulsions (full-fat and skim milk, high-fat and low-fat yoghurt) has been investigated. It is observed that friction coefficient of food emulsions increases with a decrease in height or an increase in density of rectangular micro-scale pillars representing papillae on the surface of soft substrate. Interestingly, a decrease in the elastic modulus of the substrates causes an increase in the friction coefficient for the milk samples, whereas for yoghurt samples it causes a decrease. The variations in the thickness of the substrates have little effect on the friction coefficients of the food emulsions.

Engineered Polystyrene-Based Microplastics of High Environmental Relevance.

Microplastic (MP) pollution—an emerging environmental challenge of the 21st century—refers to accumulation of environmentally weathered polymer-based particles with potential environmental and health risks. Because of technical and practical challenges when using environmental MPs for risk assessment, most available data are generated using plastic models of limited environmental relevancy (i.e., with physicochemical characteristics inherently different from those of environmental MPs). In this study, we assess the effect of dominant weathering conditions—including thermal, photo-, and mechanical degradation—on surface and bulk characteristics of polystyrene (PS)-based single-use products. Further, we augment the environmental relevance of model-enabled risk assessment through the design of engineered MPs. A set of optimized laboratory-based weathering conditions demonstrated a synergetic effect on the PS-based plastic, which was fragmented into millions of 1–3 μm MP particles in under 16 h. The physicochemical properties of these engineered MPs were compared to those of their environmental counterpart and PS microbeads often used as MP models. The engineered MPs exhibit high environmental relevance with rough and oxidized surfaces and a heterogeneous fragmented morphology. Our results suggest that this top-down synthesis protocol combining major weathering mechanisms can fabricate improved, realistic, and reproducible PS-based plastic models with high levels of control over the particles’ properties. Through increased environmental relevancy, our plastic model bolsters the field of risk assessment, enabling more reliable estimations of risk associated with an emerging pollutant of global concern.

Development of a Multihole Atmospheric Plasma Jet for Growth Rate Enhancement of Broccoli Seeds

This work aims to develop a multihole atmospheric pressure plasma jet (APPJ) device to increase the plasma area and apply it to a continuous seed treatment system. Broccoli seed was used to study the effects of an atmospheric pressure plasma jet on seed germination and growth rate. An argon flow rate of 4.2 lpm, a plasma power of 412 W, and discharge frequency of 76 kHz were used for seed treatment. The contact angle decreased strongly with the increase in treatment time from 20 s to 80 s. The broccoli seed’s outer surface morphology seemed to have been slightly modified to a smoother surface by the plasma treatment during the treatment time of 80 s. However, the cross-sectional images resulted from Synchrotron radiation X-ray tomographic microscopy (SRXTM) confirmed no significant difference between seeds untreated and treated by plasma for 80 s. This result indicates that plasma does not affect the bulk characteristics of the seed but does provide delicate changes to the top thin layer on the seed surface. After seven days of cultivation, the seed treated by plasma for 30 s achieved the highest germination and yield.

Contrasting fates of terrestrial organic carbon pools in marginal sea sediments

Burial of terrestrial organic carbon (OCterr) in marginal sea sediments is a key component of the carbon cycle, exerting long-term influence on atmospheric CO2 and climate. Assessment of the burial efficiency of OCterr is of key importance, yet remains poorly constrained due to current gaps in our knowledge of mechanistic controls, including the influence of organic matter composition and age on the fate of OCterr in marine sediments. We measured bulk characteristics (δ13C and Δ14C of OC; mineral surface area, SA; grain size; n = 98 samples) and biomarker carbon isotopic compositions (fatty acid δ13C and Δ14C; n = 11) of a suite of surface sediment samples from the Bohai Sea and Yellow Sea (BS-YS). Combining with published results, bulk OC (n = 234) and biomarker (n = 19) carbon isotopic data are used to examine spatial variability in the sources and ages of OCterr in this shallow marginal sea system. Biomarker carbon isotopic values are used to constrain endmember values, and a dual carbon isotope mixing model was applied to all bulk samples to develop a spatially explicit assessment of contributions of different pools of OCterr. Although highly spatially variable, pre-aged OC (OCpre-aged) and fossil OC (OCfossil) when combined (i.e., “non-modern OC”) on average accounted for 51 ± 10% of the OC in BS-YS surface sediments. This was equivalent to the proportion of OCterr (ave., 51 ± 14%) estimated from a δ13COC binary mixing model, suggesting OCterr in the mixed layer of BS-YS sediments is predominantly composed of millennial-aged OC. The burial potential of pool-specific OCterr was then evaluated through comparison of corresponding mineral SA-normalized loadings of surface sediments with those of Yellow River suspended particulate matter. Both the regression slope and the arithmetic mean value approaches reveal high burial potential for all terrestrial OC pools delivered by Yellow River, which is attributed to the aged and refractory nature of OC exported from the Yellow River. However, differing relationships of pool-specific OCterr loadings between BS-YS and Yellow River sediments imply contrasting fates. In particular, we find that the burial potential of OCpre-aged is consistently greater than that of OCfossil. This surprising observation suggests either enhanced degradation of OCfossil during lateral transport (possibly as a consequence of different mineral associations and hydrodynamic sorting effects), or additional sources for OCpre-aged, such as from small rivers or aerosol deposition. Overall, OC age, mineralogical composition and hydrological settings contribute to the complex patterns of OC residing in northern China marginal sea surface sediments. This novel molecular-isotopic approach reveals significant spatial variability in proportions, contents and burial potential among terrestrial OC pools, and underlines the importance of considering organic matter age and composition in understanding and constraining the fate of OCterr in marine sedimentary environments.

(Invited) Tuning Triblock Co-Polymer Silver Interactions on the Nanoscale to Enhance Transport in Electrodes for Electrochemical Devices Based on Anion Exchange Membranes

Anion exchange membranes (AEMs) have recently attracted interest for applications in fuel cells, electrolyzers, redox flow batteries, reverse electrodialysis, and water purification. In contrast to proton exchange membranes (PEMs), AEMs operate in base instead of acid and facilitate the transport of anionic species. In fuel cells and electrolyzers, this allows for more facile kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) respectively. Therefore, AEM-based devices provide the opportunity to utilize non-precious metal catalysts to achieve similar performance to Pt-based catalysts and a substantially reduced cost. The electrodes of these devices are comprised of a heterogeneous mixture of conductive carbon support, catalyst particles, and ionomer, which form a triple-phase boundary where the electrochemical reactions take place. The ionomer is an alkaline polymer electrolyte similar to the AEM which transports OH- and water to/from the catalyst surface and promotes reactant transport.The electrode layers in PEM-based fuel cells were developed empirically, and it was not until recently that research efforts were dedicated to investigating the heterogeneous microstructure and triple-phase boundary that form. Currently, the catalyst layer as it exists in an operating device is not well understood due to its complex nature; however, model interfaces between ionomers and catalyst particles have been used to provide valuable insight on ionomer-catalyst interfacial interactions. It is known from studies with Nafion® that restructuring of the polymer morphology can occur when it exists as an ionomer thin film at a catalyst interface. The behavior of the thin film ionomer changes compared to its bulk characteristics, which ultimately affects electrode kinetics by altering the nature of its microstructure, leading to shifts in morphology, water uptake properties, and ionic and water transport networks.Initial work was driven by the overarching hypothesis that the polymer-catalyst interfacial interactions could be modified by changing the ionomer chemistry. This was investigated by studying interactions between silver nanoparticles and anion exchange ionomers functionalized with two different quaternary ammonium cations, using our previously reported block copolymer backbone polychloromethylstyrene-b-polycyclooctene-b-polychloromethylstyrene (PCMS-b-PCOE-b-PCMS) functionalized with either trimethylammonium (TMA) or methylpiperidinium (MPRD) quaternary ammonium cations. Our early findings indicated there were interactions between silver nanoparticles and C=C groups in the polycyclooctene midblock of the polymer backbone. This motivated the development of a modified anion exchange polymer by hydrogenating the PCOE midblock in PCMS-b-PCOE-b-PCMS to synthesize a polyethylene (PE) midblock. Hydrogenation was achieved through a reaction with p-toluenesulfonyl hydrazide. The improved characteristics of the PE-based membrane have prompted studies investigating the comparison of saturated and unsaturated ionomers.A uniquely tunable polymer system was developed which has enabled further investigations of ionomer thin films on silver substrates. The thin film geometry allows for the use of grazing incidence small angle x-ray scattering (GISAXS) and atomic force microscopy (AFM) to study the interfacial morphology as a function of ionomer chemistry. Restructuring of the polymer morphology compared to its bulk properties has been confirmed, and our initial findings on the contribution of different cationic moieties will be discussed in the results of this report.

Bursting the bubble: A molecular understanding of surfactant-water interfaces.

Surfactant science has historically emphasized bulk, thermodynamic measurements to understand the microemulsion properties of greatest industrial significance, such as interfacial tensions, phase behavior, and thermal stability. Recently, interest in the molecular properties of surfactants has grown among the physical chemistry community. This has led to the application of cutting-edge spectroscopic methods and advanced simulations to understand the specific interactions that give rise to the previously studied bulk characteristics. In this Perspective, we catalog key findings that describe the surfactant-oil and surfactant-water interfaces in molecular detail. We emphasize the role of ultrafast spectroscopic methods, including two-dimensional infrared spectroscopy and sum-frequency-generation spectroscopy, in conjunction with molecular dynamics simulations, and the role these techniques have played in advancing our understanding of interfacial properties in surfactant microemulsions.

A Versatile Surface Modification Method via Vapor-phase Deposited Functional Polymer Films for Biomedical Device Applications.

For last two decades, the demand for precisely engineered three-dimensional structures has increased continuously for the developments of biomaterials. With the recent advances in micro- and nano-fabrication techniques, various devices with complex surface geometries have been devised and produced in the pharmaceutical and medical fields for various biomedical applications including drug delivery and biosensors. These advanced biomaterials have been designed to mimic the natural environments of tissues more closely and to enhance the performance for their corresponding biomedical applications. One of the important aspects in the rational design of biomaterials is how to configure the surface of the biomedical devices for better control of the chemical and physical properties of the bioactive surfaces without compromising their bulk characteristics. In this viewpoint, it of critical importance to secure a versatile method to modify the surface of various biomedical devices. Recently, a vapor phase method, termed initiated chemical vapor deposition (iCVD) has emerged as damage-free method highly beneficial for the conformal deposition of various functional polymer films onto many kinds of micro- and nano-structured surfaces without restrictions on the substrate material or geometry, which is not trivial to achieve by conventional solution-based surface functionalization methods. With proper structural design, the functional polymer thin film via iCVD can impart required functionality to the biomaterial surfaces while maintaining the fine structure thereon. We believe the iCVD technique can be not only a valuable approach towards fundamental cell-material studies, but also of great importance as a platform technology to extend to other prospective biomaterial designs and material interface modifications for biomedical applications.

On the three-dimensional features of a confined slug bubble in a flowing square capillary

The motion of long bubbles in tubular capillaries has typically been described by bulk characteristics. However, the dynamics of slug bubbles in square capillaries are more complex due to a corner flow and a thin film flow. The physics can be correctly explained by elucidating local 3D features of the two-phase flow field. To this aim, an experimental study based on particle tracking velocimetry (PTV) and a numerical simulation based on the volume-of-fluid method were conducted to investigate the dynamics of slug bubbles rising in a flowing square capillary with a cross-sectional area of 3 × 3 mm2. To precisely analyze the phases' interaction, interfacial flow data were mapped onto a radial-tangential coordinate system on central and diagonal planes. The simulated interface topology and velocity fields show a good agreement with the experimental PTV data on the central plane, with an absolute error of less than 1.2% for terminal bubble speed. Tangential speeds show their maxima occurring in the channel corners, where pressure is maximum. The thin liquid film flow that occurs where the bubble approaches the wall applies noticeable shear stress on the channel walls, where high and low-pressure regions are generated. Structures of vortices inside the bubble were identified using isosurfaces of the Q-criterion, and their cores were detected based on the parallel vector method. Results reveal a dominant vortex ring adjacent to the liquid film flow and two oblique vortex tubes close to the bubble's nose.

Fatigue strength assessment of additively manufactured metallic structures considering bulk and surface layer characteristics

This paper extends a previously published fatigue strength estimation methodology for additively manufactured metallic bulk material by additionally accounting for effects of as-built surface layers. Interaction of intrinsic defects and surface texture convergently initiates fatigue failure. Holistic consideration of influencing factors significantly contributes to scientific fatigue assessment of structures fabricated by Laser-Powder Bed Fusion (L-PBF). Surface texture is highly dependent on the building parameters and performed post treatments. Three dimensional, optical topography scans form the basis of determining representative areal surface texture parameters. Areal notch valley depth Sv, alongside notch radii ρ evaluation, enables usage of a modified Peterson’s approach. Effects of notch-like roughness features are quantified by a reduction factor ks, as analogously published for bulk material imperfections kb. Superimposition of ex- and intrinsic material characteristics is empirically assessed by an interaction exponent derived from experimental fatigue data. Macroscopic, tensile residual stresses acting as mean stresses are considered by Smith-Watson-Topper’s approach. Unifying presented influencing factors derives a comprehensive model, conceived to estimate fatigue strength of additively manufactured metallic structures. Regardless of post processing condition, sound applicability of developed design approach is substantiated by averaging −7.1%, comparing estimated fatigue strength to experimental results.