Contribution Of Surface Roughness Research Articles

Ligand-Assisted self-assembly of colloidal Ag2S nanoparticles

Over the last decade, great attention of researchers has been focused on nanoscale self-assembly due to increasingly technology-relevant applications. Pattern formation by colloidal droplet evaporation is one of the fascinating subjects to study. A deep understanding of physical and chemical processes of the deposited structure formation allows the development of bioprinting methods, nanoarchitectures for optics and electronics, methods for detecting the state of peptides, proteins, etc. In the present work, the effect of organic ligands (MPS, BSA, GSH, EDTA, TG) on Ag2S NP self-assembly during solution droplet evaporation was investigated. The synthesis conditions were optimized to minimize or neglect the contribution of surface roughness, substrate thermal conductivity, NP shape and size, type of solvent. Properties of a stabilizer, such as molecular length, reactivity, tendency to polycondensate or chelate, and their relative concentration affect the nanoparticle–nanoparticle interactions, which results in several types of pattern formation. The dominant forces in different regions of the evaporated droplet via ligand were discussed. The models of pattern formation were proposed. Thus, depending on the ligand, Ag2S NPs tend to form rings (MPS, BSA), concentric rings (BSA), net like structures (TG), and chains (MPS, TG). In addition, it was shown that replacing water with deuterium can significantly change self-organized architectures.

Contributions of surface roughness and oxygen-containing groups to the interfacial shear strength of carbon fiber/epoxy resin composites

Contributions of surface roughness and oxygen-containing groups to the interfacial shear strength of carbon fiber/epoxy resin composites

Contribution of surface roughness and oxygen-containing groups to the interfacial shear strength of carbon fiber/epoxy resin composites

The interfacial shear strength (IFSS) between carbon fibers (CFs) and the matrix is crucial to the performance of CF-reinforced polymer composites. To evaluate the contribution of mechanical interlocking and chemical anchoring at the interfaces of a polyacrylonitrile-based CF (TORAYCA T800SC-12000-10E)-reinforced epoxy resin (EP: bisphenol A type epoxy resin and tetrafunctional epoxy resin) composites, the surface roughness and content of oxygen-containing functional groups of the CFs were respectively altered by ammonia treatment and electrochemical oxidation. The results showed that ammonia treatment increased the surface roughness without much change to the surface elemental composition, while electrochemical oxidation increased the number of surface oxygen groups without changing the surface roughness. The IFSS of CF/EP composites was tested by the micro-droplet method. The relationships between IFSS, and surface roughness and oxygen content were obtained by linear fitting. The results showed that in the interfacial bonding of CF to epoxy resin, the contribution of chemical anchoring to the IFSS is larger than that of mechanical interlocking.

Morphology-Dependent Interaction of Silica Nanoparticles with Intestinal Cells: Connecting Shape to Barrier Function.

The intestinal compartment ensures nutrient absorption and barrier function against pathogens. Despite decades of research on the complexity of the gut, the adaptive potential to physical cues, such as those derived from interaction with particles of different shapes, remains less understood. Taking advantage of the technological versatility of silica nanoparticles, spherical, rod-shaped, and virus-like materials were synthesized. Morphology-dependent interactions were studied on differentiated Caco-2/HT29-MTX-E12 cells. Contributions of shape, aspect ratio, surface roughness, and size were evaluated considering the influence of the mucus layer and intracellular uptake pathways. Small particle size and surface roughness favored the highest penetration through the mucus but limited interaction with the cell monolayer and efficient internalization. Particles of a larger aspect ratio (rod-shaped) seemed to privilege paracellular permeation and increased cell-cell distances, albeit without hampering barrier integrity. Inhibition of clathrin-mediated endocytosis and chemical modulation of cell junctions effectively tuned these responses, confirming morphology-specific interactions elicited by bioinspired silica nanomaterials.

Roughness surface of raspberry-shaped silica nanoparticles effect on shear thickening colloidal suspensions

Control over the surface roughness of silica nanoparticles can offer exciting opportunities to increase the rheological properties of the silica-based shear thickening fluids. Designing surface roughness as a significant tool indicates the possibility of connecting distinct rheological phenomena and surface chemical functionalized materials. We have experimentally synthesized two kinds of silica nanoparticles with different particle size and different functional groups at the end, which can be combined via chemical covalent coupling to generate raspberry-shaped silica nanoparticles. The dynamic viscosity of the shear thickening fluids was evaluated by rheological experiments. And the maximum impact force of puncture and drop hammer experiments were performed for composite shear thickening materials with different factors. The results showed that the essential contribution of silica nanoparticles surface roughness and covalent force illustrate that stress-activated frictional contacts can play a key role in this shear thickening phenomena. We tried to propose a damage mechanism of the shear thickening materials. The results indicate that the roughness, morphology and diameter of particles, the thickening effect of shear thickening fluids with higher volume fraction, the increase of both the number of layers and the impregnation content can significantly improve the mechanical properties of the materials.

Experimental investigation of cutting temperature and surface roughness for different cutting fluids during turning of Duplex stainless steel-2205 under minimum quantity lubrication technique

Duplex stainless steel (DSS)-2205 comes under hard to machine material owing to its inherent properties but more applications in severe working conditions hence, selection of turning process parameters and suitable cutting fluids of DSS-2205 is essential. In the present work, investigate the performance of Deionized water, neat cut oil, and emulsified fluid on cutting temperature and surface roughness during turning of duplex stainless steel-2205 under minimum quantity lubrication technique. Based on a face-centered composite design, 20 experiments were conducted with varying speed, feed, and depth of cut in three levels for three different fluids. Analysis of variance (ANOVA) is used to identify significant parameters that affect the response. Numerical optimization was carried out under Desirability Function Analysis (DFA) for cutting temperature during deionized water cutting fluid for surface roughness during emulsified cutting fluid. Depth of cut is the significant factor for cutting temperature contribution is 74.83% during Deionized water as a fluid, and feed is the significant factor for surface roughness contribution is 93.57% during emulsified fluid. The optimum cutting parameters were determined for speed (50m/min), feed (0.051mm/rev) and depth of cut (0.4mm). Experimental results revealed that Deionized water gives better results for reduced the cutting temperature and emulsified fluid for surface roughness reduction.

Exploring the roles of roughness, friction and adhesion in discontinuous shear thickening by means of thermo-responsive particles

Dense suspensions of colloidal or granular particles can display pronounced non-Newtonian behaviour, such as discontinuous shear thickening and shear jamming. The essential contribution of particle surface roughness and adhesive forces confirms that stress-activated frictional contacts can play a key role in these phenomena. Here, by employing a system of microparticles coated by responsive polymers, we report experimental evidence that the relative contributions of friction, adhesion, and surface roughness can be tuned in situ as a function of temperature. Modifying temperature during shear therefore allows contact conditions to be regulated, and discontinuous shear thickening to be switched on and off on demand. The macroscopic rheological response follows the dictates of independent single-particle characterization of adhesive and tribological properties, obtained by colloidal-probe atomic force microscopy. Our findings identify additional routes for the design of smart non-Newtonian fluids and open a way to more directly connect experiments to computational models of sheared suspensions.

Precision Deep Reactive Ion Etching of Monocrystalline 4H-SiCOI for Bulk Acoustic Wave Resonators with Ultra-Low Dissipation

Integrated mechanical resonators with high quality factors (Q) made in high acoustic velocity materials are essential for a wide range of applications, including chemical sensors, timing resonators, and high-performance inertial sensors for navigation in GPS-occluded environments. While silicon is the most popular substrate for the implementation of microelectromechanical systems (MEMS) resonators, SiC exhibits an exceptionally small intrinsic phononic dissipation due to its low Akhiezer damping limit. This paper reports on the latest developments of precision deep reactive ion etching (DRIE) of monocrystalline 4H SiC-on-Insulator (SiCOI) substrates with the aim to fully take advantage of the exquisite mechanical properties of crystalline SiC. To wit, capacitive Lamé mode micromechanical resonators exhibit ƒ·Q products beyond 1 × 1014 Hz independent of crystalline orientation. The contribution of surface roughness to dissipation and practical considerations to etch mirror-polished trenches in SiCOI substrates are discussed, paving the way towards micromechanical monocrystalline SiC resonators with Qs beyond 100 Million.

Revealing the Surface Effect on Gas Transport and Mechanical Properties in Nonporous Polymeric Membranes in Terms of Surface Free Energy.

The contribution of surface roughness of nonporous polymeric membranes to their gas separation and mechanical properties was studied in terms of surface free energy. The membranes samples were prepared based on glassy polymers with different chain rigidity, namely polysulfone (PSU), cellulose triacetate (CTA), and poly(vinyl alcohol) (PVA). The results were obtained by atomic force and scanning electron microscopy (AFM and SEM) with individual gas permeation, wettability, and mechanical testing. The specific surface free energy (as well as its polar and dispersive components) for the polymers was calculated by the Owens-Wendt method. It was proven that the surface roughness of the polymer membranes affects both energy components; however, the degree of this influence depends on the chemical nature of the corresponding polymer. Moreover, it was assumed that the dispersive energy component is inversely correlated with any gases' total permeability. In contrast, the polar one is inversely correlated with the permeability by gases with the ability for site-specific interactions. The gas separation results confirmed this assumption. It was also shown that the mechanical properties of the polymer membranes are also influenced by the surface energy, namely, its dispersive component.

Surface-roughness-boosted critical heat flux enhancement during quenching boiling on wicking surfaces

Wicking surfaces have been widely proven to enhance critical heat flux (CHF) by improving liquid replenishment when approaching the dry-out area during vapor bubble evolution within the nucleate boiling regime. However, different than the vapor column growth mechanism for CHF of regular boiling by heating up a surface, during rapid-cooling-induced quenching boiling processes, CHF occurs upon collapse of vapor film within the transition boiling regime, resulting in a difference in the effect of surface properties on CHF. In this work, we show experimentally that the surface wickability is unable to fully elucidate the enhancement of quenching CHF on wicking surfaces with superhydrophilicity, and that the surface roughness could facilitate collapse of vapor film, thus leading to an extra boost of quenching CHF over the contribution of surface wickability. We propose an improved CHF correlation based on the introduction of a roughness-weighted wicking number, which accounts for the extra contribution of surface roughness in breaking the vapor film barrier and promoting the occurrence of wicking phenomena.

Whitecap Observations by Microwave Radiometers: With Discussion on Surface Roughness and Foam Contributions

Ocean surface whitecaps manifest surface wave breaking. Most of the whitecap data reported in the literature are based on optical observations through photographic or video recording. The air in whitecaps modifies the dielectric properties of microwave emissions and scattering. Therefore, whitecap information is intrinsic to microwave signals. This paper discusses a method to retrieve the ocean surface whitecap coverage from microwave radiometer signals.

Silica-Based Nanoparticles for Biomedical Applications: From Nanocarriers to Biomodulators.

Silica-based nanoparticles (SNPs) are a classic type of material employed in biomedical applications because of their excellent biocompatibility and tailorable physiochemical properties. Typically, SNPs are designed as nanocarriers for therapeutics delivery, which can address a number of intrinsic drawbacks of therapeutics, including limited bioavailability, short circulation lifetime, and unfavorable biodistribution. To improve the delivery efficiency and spatiotemporal precision, tremendous efforts have been devoted to engineering the physiochemical properties of SNPs, including particle size, morphology, and mesostructure, as well as conjugating targeting ligands and/or "gatekeepers" to endow improved cell selectivity and on demand release profiles. Despite significant progress, the biologically inert nature of the bare silica framework has largely restricted the functionalities of SNPs, rendering conventional SNPs mainly as nanocarriers for targeted delivery and controlled release. To meet the requirements of next generation nanomedicines with improved efficacy and precision, new insights on the relationship between the physiochemical properties of SNPs and their biological behavior are highly valuable. Meanwhile, a conceptual shift from a simple spatiotemporal control mechanism to a more sophisticated biochemistry and signaling pathway modulation would be of great importance.In this Account, an overview of our recent contribution to the field is presented, wherein SNPs with rationally designed nanostructures and nanochemistry are applied as nanocarriers (defined as "nanomaterials being used as a transport module for another substance" according to Wikipedia) and/or biomodulators (defined as "any material that modifies a biological response" according to Wiktionary). This Account encompasses two main sections. In the first section, we focus on the conventional nanocarriers concept with new insights on the design principles of the nanostructures. We present examples to demonstrate the engineering of pore geometry, surface topology, and asymmetry of nanoparticles to achieve enhanced drug, gene, and protein delivery efficiency. The contribution of surface roughness of SNPs on improving the cellular uptake efficiency, adhesion property, and DNA transfection capacity is particularly highlighted. In the second section, we discuss novel SNPs designed as biomodulators to regulate intracellular microenvironment and cell signaling, such as the oxidative stress and glutathione levels for improving the anticancer efficacy of therapeutics and mRNA transfection in specific cell lines. The interplay between the nanoparticles, biological system, and drugs is discussed. We further discuss how to engineer the composition of SNPs to modulate metal hemostasis to realize inherent anticancer activity. Two typical examples, including modulating copper signaling for tumor vasculature targeted therapy and controlling iron signaling for macrophage polarization based immunotherapy, are presented to highlight the unique advantages of SNPs as nanosized therapeutics in comparison to molecular drugs. Moreover, utilizing these two examples, we showcase the possibility of designing SNPs with intrinsic pharmaceutical activity to indirectly control tumor growth without inducing significant cytotoxicity, thus alleviating the biosafety concerns of nanomedicines. At the end of this Account, we discuss our personal perspectives on the promises, opportunities, and issues in engineered SNPs as nanocarriers as well as their transition toward biomodulators. With a major focus on the latter scenario, the current status and possible future directions are outlined.

A three-variables cokriging method to estimate bare-surface soil moisture using multi-temporal, VV-polarization synthetic-aperture radar data

A cokriging model using three variables is developed to estimate bare-surface soil moisture content based on multi-temporal synthetic-aperture radar (SAR) data. This model utilizes cross-semivariogram function to take into account spatially varied correlation among multiple variables. Here, five sentinel-1 SAR scenes were acquired on different dates using the interferometric wide-swath (IW) mode and a mean incidence angle of 39.02° to build the backscatter temporal-ratio in VV polarization. This algorithm is generally based on the assumption of contributions of soil moisture and surface roughness to the backscattering coefficient under the given radar configurations. In this study, soil moisture is the target variable, and the surface roughness and backscatter temporal-ratio in VV polarization are the auxiliary variables. A cross-semivariogram relationship is formulated among those three spatial variables; then ordinary cokriging is used, based on that cross-semivariogram formula, to estimate the spatial distribution of bare soil moisture content. The root mean square error (RMSE) of soil-moisture retrieval ranges from 2.62 to 2.66 vol%. The new empirical model described in this paper will provide new insights into the study of soil environments.

(Invited) Nano-Precision Deep Reactive Ion Etching of Monocrystalline 4H-SiCOI for Bulk Acoustic Wave Resonators with Ultra-Low Dissipation

Integrated mechanical resonators with high quality factors (Q) made in high acoustic velocity materials are essential for a wide range of applications, including chemical sensors, timing resonators, and high-performance inertial sensors for navigation in GPS-occluded environments. While silicon is the most popular substrate for implementation of microelectromechanical systems (MEMS) resonators, SiC exhibits an exceptionally small intrinsic phononic dissipation due to high Akhiezer limits. This paper reports the latest results on nano-precision deep reactive ion etching (DRIE) of monocrystalline 4H SiC-on-Insulator (SiCOI) substrates to explore dissipation limits of bulk acoustic wave (BAW) SiC resonators. We report for the first time on capacitive Lamé mode resonators with ƒ·Q products beyond 1×1014 Hz. The contribution of surface roughness to dissipation and practical considerations to etch mirror-polished trenches in SiCOI substrates are discussed, paving the way towards micromechanical SiC resonators with Qs beyond 100 M.

Dielectric Loss Tangent Extraction Using Modal Measurements and 2-D Cross-Sectional Analysis for Multilayer PCBs

Frequency-dependent electrical properties of dielectric materials are one of the most important factors for high-speed signal integrity design. To accurately characterize material's dielectric loss tangent (tanδ) after multilayer printed circuit board fabrication a novel method was proposed recently to extract tanδ using coupled striplines' measured S-parameters and cross-section geometry. By relating modal attenuation factors to the ratio between the differential and common mode per-unit-length resistances, the surface roughness contribution is eliminated and the contributions of dielectric and conductor loss are separated. Here, we specifically decided to avoid using any physical dielectric model in the extraction algorithm in order to eliminate a need for any a priori information about dielectric behavior. Further analysis and improvement of the tanδ extraction approach is presented in this article. To evaluate the accuracy of the extraction, the impact of errors due to de-embedding, vector network analyzer measurement, and two-dimensional solver's calculation are taken into account by a statistical error model. A confidence interval of extracted tanδ is provided. To describe the frequency dependence of tanδ, a two-term Djordjevic model is proposed to fit the extracted tanδ curve, which guarantees causality and gives better agreement with measured insertion loss compared to the traditional Djordjevic model.

Pore-Scale Modeling of Fluid-Fluid Interfacial Area in Variably Saturated Porous Media Containing Microscale Surface Roughness.

A pore-scale model is developed to simulate fluid-fluid interfacial area in variably saturated porous media, with a specific focus on incorporating the effects of solid-surface roughness. The model is designed to quantify total (film and meniscus) fluid-fluid interfacial area (Anw ) over the full range of wetting-phase fluid saturation (Sw ) based on the inherent properties of the porous medium. The model employs a triangular pore space bundle of cylindrical capillaries (BCC) framework, modified with three surface roughness-related parameters. The first parameter (surface roughness factor) represents the overall magnitude of surface roughness, whereas the other two parameters (interface growth factor and critical adsorptive film thickness) reflect the micro-scale structure of surface roughness. A series of sensitivity analyses was conducted for the controlling variables, and the efficacy of the model was tested using air-water interfacial area data measured for three natural porous media. The model produced good simulations of the measured Anw data over the full range of saturation. The results demonstrate that total interfacial areas for natural media are typically much larger than those for ideal media comprising smooth surfaces due to the substantial contribution of surface roughness to wetting-film interfacial area. The degree to which fluid-fluid interfacial area is influenced by roughness is a function of fluid-retention characteristics and the nature of the rough surfaces. The full impact of roughness may be masked to some degree due to the formation of thick wetting films, which is explicitly quantified by the model. Application of the model provides insight into the importance of the interplay between pore-scale distribution and configuration of wetting fluid and the surface properties of solids.

Quantum Engineering of Atomically Smooth Single-Crystalline Silver Films

There is a demand for ultra low-loss metal films with high-quality single crystals and perfect surface for nanophotonics and quantum information processing. Many researches are devoted to alternative materials, but silver is by far theoretically the most preferred low-loss material at optical and near-IR frequencies. Usually, epitaxial growth is used to deposit single-crystalline silver films, but they still suffer from unpredictable losses and well-known dewetting effect that strongly limits films quality. Here we report the two-step approach for e-beam evaporation of atomically smooth single-crystalline metal films. The proposed method is based on the thermodynamic control of film growth kinetics at atomic level, which allows depositing state-of-art metal films and overcoming the film-surface dewetting. Here we use it to deposit 35–100 nm thick single-crystalline silver films with the sub-100pm surface roughness and theoretically limited optical losses, considering an ideal material for ultrahigh-Q nanophotonic devices. Utilizing these films we experimentally estimate the contribution of grain boundaries, material purity, surface roughness and crystallinity to optical properties of metal films. We demonstrate our «SCULL» two-step approach for single-crystalline growth of silver, gold and aluminum films which open fundamentally new possibilities in nanophotonics, biotechnology and superconductive quantum technologies. We believe it could be readily adopted for the synthesis of other extremely low-loss single-crystalline metal films.

Time-Series Retrieval of Soil Moisture Using CYGNSS

Time-series retrievals of soil moisture obtained from the Cyclone Global Navigation Satellite System (CYGNSS) constellation are presented. The retrieval approach assumes that vegetation and roughness changes occur on timescales longer than those associated with soil moisture changes to allow soil moisture sensing in the presence of vegetation and surface roughness contributions as well as the varying incidence angles associated with spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R) systems. The approach is focused on incoherent scattering from land surfaces due to the expectation that coherent land surface returns arise primarily from inland water body contributions that are not directly representative of soil moisture. An approach for discarding coherent CYGNSS measurements is therefore developed and described. Because the approach requires the retrieval of $N$ temporal soil moisture samples at a given location but uses only $N-1$ ratios of CYGNSS measured quantities, ancillary information is incorporated in the retrieval through the use of maximum and minimum monthly soil moisture maps obtained from the Soil Moisture Active Passive (SMAP) mission. Retrieved soil moistures are presented for the 6-month period December 2017–May 2018 and are compared against values reported by the SMAP mission. The comparisons suggest that there exists the potential for using spaceborne GNSS-R systems for global soil moisture retrievals with an rms error on the order of 0.04 cm3/cm3 over varied terrain.

Analysis of the Radar Vegetation Index and Potential Improvements

The Radar Vegetation Index (RVI) is a well-established microwave metric of vegetation cover. The index utilizes measured linear scattering intensities from co- and cross-polarization and is normalized to ideally range from 0 to 1, increasing with vegetation cover. At long wavelengths (L-band) microwave scattering does not only contain information coming from vegetation scattering, but also from soil scattering (moisture & roughness) and therefore the standard formulation of RVI needs to be revised. Using global level SMAP L-band radar data, we illustrate that RVI runs up to 1.2, due to the pre-factor in the standard formulation not being adjusted to the scattering mechanisms at these low frequencies. Improvements on the RVI are subsequently proposed to obtain a normalized value range, to remove soil scattering influences as well as to mask out regions with dominant soil scattering at L-band (sparse or no vegetation cover). Two purely vegetation-based RVIs (called RVII and RVIII), are obtained by subtracting a forward modeled, attenuated soil scattering contribution from the measured backscattering intensities. Active and passive microwave information is used jointly to obtain the scattering contribution of the soil, using a physics-based multi-sensor approach; simulations from a particle model for polarimetric vegetation backscattering are utilized to calculate vegetation-based RVI-values without any soil scattering contribution. Results show that, due to the pre-factor in the standard formulation of RVI the index runs up to 1.2, atypical for an index normally ranging between zero and one. Correlation analysis between the improved radar vegetation indices (standard RVI and the indices with potential improvements RVII and RVIII) are used to evaluate the degree of independence of the indices from surface roughness and soil moisture contributions. The improved indices RVII and RVIII show reduced dependence on soil roughness and soil moisture. All RVI-indices examined indicate a coupled correlation to vegetation water content (plant moisture) as well as leaf area index (plant structure) and no single dependency, as often assumed. These results might improve the use of polarimetric radar signatures for mapping global vegetation.

Permafrost Soil Moisture Monitoring Using Multi-Temporal TerraSAR-X Data in Beiluhe of Northern Tibet, China

Global change has significant impact on permafrost region in the Tibet Plateau. Soil moisture (SM) of permafrost is one of the most important factors influencing the energy flux, ecosystem, and hydrologic process. The objectives of this paper are to retrieve the permafrost SM using time-series SAR images, without the need of auxiliary survey data, and reveal its variation patterns. After analyzing the characteristics of time-series radar backscattering coefficients of different landcover types, a two-component SM retrieval model is proposed. For the alpine meadow area, a linear retrieving model is proposed using the TerraSAR-X time-series images based on the assumption that the lowest backscattering coefficient is measured when the soil moisture is at its wilting point and the highest backscattering coefficient represents the water-saturated soil state. For the alpine desert area, the surface roughness contribution is eliminated using the dual SAR images acquired in the winter season with different incidence angles when retrieving soil moisture from the radar signal. Before the model implementation, landcover types are classified based on their backscattering features. 22 TerraSAR-X images are used to derive the soil moisture in Beiluhe, Northern Tibet with different incidence angles. The results obtained from the proposed method have been validated using in-situ soil moisture measurements, thus obtaining RMSE and Bias of 0.062 cm3/cm3 and 4.7%, respectively. The retrieved time-series SM maps of the study area point out the spatial and temporal SM variation patterns of various landcover types.