Mesoscale Approaches Research Articles

Modeling the effect of material heterogeneity on the thermo-mechanical behavior of concrete using mesoscale and stochastic field approaches

The adverse impact of high temperatures on concrete is a well-recognized issue that can lead to significant mechanical deterioration and structural integrity loss. Factors such as aggregate type, cement composition, temperature, duration of exposure, and moisture content can substantially influence the fire resistance of concrete. To simulate and better understand the effects arising from the heterogeneity of concrete in a fire situation, a mesoscale approach is proposed, using the Mesh Fragmentation Technique (MFT) to assess the complex thermo-mechanical behavior of concrete. The MFT introduces high aspect ratio interface elements to model crack propagation and interfacial transition zones by means of an appropriated tensile damage constitutive law. In this extended framework, a fully-coupled thermo-mechanical model is proposed. The modeling approach includes considerations of both macroscopic and mesoscopic scales, in which the coarse aggregate, mortar matrix and interfacial transition zones are represented. Besides, a stochastic distribution is assumed for the material properties to account for the lower scale heterogeneity. The main novelty proposed in this study consists in the synergy of mesoscale and stochastic approaches that are herein combined to model the effect of heterogeneity on the concurrent macro-mesoscale thermo-mechanical behavior of concrete. To validate the numerical model’s capabilities in capturing thermally induced cracks, benchmark cases and a simulation of a bending beam exposed to elevated temperatures are presented. The results demonstrate the potential of the proposed approach in predicting the behavior of concrete subjected to thermal loading and the role played by heterogeneity in the thermally induced cracking.

An early indicator index of tornadic storms for Euro-Mediterranean region

Tornadoes are the most violent and destructive of all the severe weather phenomena that localized convective storms produce. There is a requirement in operational meteorology increasing nowadays that an indicator index which allows to reduce the uncertainty of severe convective storms and tornadoes in the scope of climate change adaptation strategies. The main intention is not to replace or substitute mesoscale modeling approaches, or composite indexes, but to warn operationally to draw attention to the Eastern Mediterranean and Türkiye in particular a few days in advance. The development of some indicators using atmospheric variables can undertake a crucial role by enabling such numerical models to be run only at certain time intervals, thus enduring lower computational costs. In this study, Eastern Mediterranean oscillation index (EMEDOi) has been developed in order to be able to detect the presence of ULLs (upper-level low) and frontogenesis approach is employed for selected tornadic storm events in Türkiye. EMEDOi has 7 different its variations (members) which these members have been developed to detect differences depending on the entry directions of cyclones and storms influencing Türkiye from the west of the country. In line with the GDAS data analysis, values of geopotential height are derived for the requirement of EMEDOi in a limited area. A few of the results from the study are as in the following: 86% of the trained tornado events revealed that the EMEDO-Oper index was in negative phase at the time a tornado was reported, regardless of whether the events featured a supercell mesoscale convective storm or a frontal movement. The hourly period until the local minimum is obtained can be described and characterized as the process by which the EMEDO-Oper index value decreases continuously. The time required to reach the local minimum varies based on the tornado occurrence. Based on the tornadic storm scenario in the test cluster in 2022 and the train cluster, this timeframe is predicted to be roughly 33.2 h on average. In western Türkiye, there is a 79% chance of a tornado occurring between six and forty-two hours after the EMEDO-Oper index reaches its local minimum. In particular, the projected chance for this period is 63% between 12 and 30 h after the local minimum is obtained. Besides, the majority of the tornado incidents with EMEDO-Oper values below − 0.75 were evaluated. After an EMEDO-Oper index value falls below that threshold, it is likely to forecast the risk period of a tornado in Türkiye with a probability of 79% and the local minimum point must be identified.

Structural Design of a Large-Scale 3D-Printed High-Altitude Propeller: Methodology and Experimental Validation

This paper presents an original approach to the structural design and analysis of a 3D-printed thermoplastic-core propeller blade for high-altitude UAVs. A macroscale linear isotropic numerical model for the behavior of 3D-printed parts (in Tough PLA, as well as ABS) is fed with values from tensile and bending testing on standard specimens (ISO 527-2/1A and ASTM D5023) before validation by experiments on a representative scaled substitute blade and blade root. The influence of printing parameters, such as material, layer thickness, and raster orientation, is also addressed, as well as variability between prints. To conclude on the validity of the present methodology for complex shapes, a validation of the numerical results with experiments was performed on a scaled 3D-printed twisted blade. The presented macroscale approach to 3D-printed materials was able to predict tensile and bending deformation with good accuracy compared to previously published micro- or meso-scale approaches since it is built from systematic tensile and bending testing on standard specimens to representative blade assemblies. It provides a reliable digital twin for the early design stages of 3D-printed propeller blades. As a proof-of-concept, the validated methodology was then used to design and numerically analyze a large-scale blade using steady one-way Fluid-Structure Interaction in take-off and cruise conditions. The computed stress levels in the blade structure were within safe margins, thereby proving the feasibility of the 3D printing of full-scale propeller blades for high-altitude platforms.

A novel unsupervised method for assessing mesoscale river habitat structure and suitability from 2D hydraulic models in gravel‐bed rivers

AbstractApplication of mesoscale habitat models in gravel‐bed rivers is increasingly common for a variety of purposes, from ecological flow design, impact assessment and conservation programmes. Integration with 2D hydraulic modelling offers the potential for broader applicability of mesoscale habitat models, extending applications to larger streams and nonwadable flow conditions, when on‐the‐ground and in‐stream surveys are challenging or even prohibitive. In this work, a novel fully unsupervised procedure that allows the segmentation of the river channel area at a given flow condition at a scale that is consistent with the mesoscale is presented. Further, it defines an objective methodology to choose segmentation parameters and thus an optimal segmentation, based on intrinsic spatial properties of the resulting regions. Segmentation parameters are objectively selected by minimising a Global Score, which is based on three metrics representing intrasegment homogeneity, intersegment heterogeneity and an optimal range of segment numbers based on an empirically defined mesoscale. Applications of the model are tested on two reaches of the multithread Mareta and meandering Aurino Rivers in South Tyrol (NE, Italy). Model outcomes are compared with ground mesohabitat surveys, and habitat suitability is then assessed for three fish species (marble trout, grayling and European bullhead). A high level of agreement is found when comparing model‐ and survey‐based habitat suitability estimates, with an overall value of . The proposed approach shows potential for application of the mesohabitat concept for large gravel‐bed rivers and nonwadable flow conditions. By allowing habitat estimates at flow ranges that could not be surveyed in‐stream, the approach facilitates applicability of mesoscale habitat models to nonwadable conditions and large streams. The workflow is river‐independent and fully unsupervised, as it does not require calibration or subjective choices of segmentation parameters.Significance statementQuantifying suitable habitat for riverine fauna is increasingly used for ecological flows assessment, with the use of mesoscale habitat modelling approaches becoming more common in the past few decades. Existing mesoscale habitat modelling approaches often rely on field surveys, which, however, become prohibitive at nonwadable flow conditions and in large streams. Here we develop and test against field data a fully unsupervised approach able to extract mesohabitats and their hydraulic characteristics from the outputs of 2D hydraulic models. Compared with existing approaches, our approach allows an automated segmentation of the wetted reach into mesoscale units through the implementation of an unsupervised optimality step in which optimal segmentation parameters are defined, and a final mesohabitat mosaic is selected. The methodology makes it easier to expand the applicability of mesoscale habitat modelling to a broader range of river sizes and conditions.

Comprehensive unified model and simulation approach for microstructure evolution

The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials. There have been considerable efforts to model and simulate microstructure evolution using a wide spectrum of models and simulation approaches. This paper initially reviews the atomistic and mesoscale simulation approaches for microstructure evolution, emphasizing their advantages and disadvantages. Atomistic approaches, such as molecular dynamics, are restricted by the scale of the studied system because they are computationally expensive. Continuum mesoscale simulation approaches, such as phase field, cellular automata, and Monte Carlo, have inconsistent phenomenological equations, each of which only describes one aspect of microstructure evolution. To provide comprehensive insight into microstructure evolution, a unified model that is capable of equally evaluating the nucleation and growth processes is required. In this paper, a physics-based model is proposed that incorporates statistical mechanics, the energy conservation law, and the force equilibrium concept to include all aspects of microstructure evolution. A compatible simulation approach is also described to simulate microstructure evolution during thermomechanical treatments. Furthermore, the microstructure evolution of AISI 304 austenitic steel during isothermal heat treatment and fusion welding is simulated and discussed. The use of fundamental physical rules instead of phenomenological equations, together with the real spatial and temporal scales of the proposed model, facilitates the comparison of the simulation results with experimental results. To examine the accuracy of the proposed simulation approach, the isothermal heat treatment simulation results are compared with experimental data over a broad region of temperatures and time periods.

Computational study of nanoparticle-induced endothelial leakiness

Nanomaterial-induced endothelial leakiness (NanoEL) is an interfacial phenomenon that the nanomaterials induce the micrometer sized gaps between the endothelial cells. It has been suggested that the disruption of homophilic interaction of vascular endothelial (VE)-cadherin through the physical interaction with nanomaterials causes the NanoEL. However, the molecular details of the cadherin destabilization by nanomaterials have not been elucidated yet. To understand the molecular mechanism of the cadherin dissociation affected by nanomaterials, we performed in silico investigation of the NanoEL phenomenon elicited by gold nanoparticles (AuNPs) by combining the steered discrete molecular dynamics (sDMD) simulations and mesoscale modeling approaches.

A two-level macroscale continuum description with embedded discontinuities for nonlinear analysis of brick/block masonry

A great proportion of the existing architectural heritage, including historical and monumental constructions, is made of brick/block masonry. This material shows a strong anisotropic behaviour resulting from the specific arrangement of units and mortar joints, which renders the accurate simulation of the masonry response a complex task. In general, mesoscale modelling approaches provide realistic predictions due to the explicit representation of the masonry bond characteristics. However, these detailed models are very computationally demanding and mostly unsuitable for practical assessment of large structures. Macroscale models are more efficient, but they require complex calibration procedures to evaluate model material parameters. This paper presents an advanced continuum macroscale model based on a two-scale nonlinear description for masonry material which requires only simple calibration at structural scale. A continuum strain field is considered at the macroscale level, while a 3D distribution of embedded internal layers allows for the anisotropic mesoscale features at the local level. A damage-plasticity constitutive model is employed to mechanically characterise each internal layer using different material properties along the two main directions on the plane of the masonry panel and along its thickness. The accuracy of the proposed macroscale model is assessed considering the response of structural walls previously tested under in-plane and out-of-plane loading and modelled using the more refined mesoscale strategy. The results achieved confirm the significant potential and the ability of the proposed macroscale description for brick/block masonry to provide accurate and efficient response predictions under different monotonic and cyclic loading conditions.

Sheltering megalithic Temples in Malta – evaluating the process through data collection and modelling

Since their excavation, a number of the sites listed as part of “The Megalithic Temples of Malta” inscription on the UNESCO World Heritage list have been afflicted by material and structural problems, including collapses. Therefore, three of these sites, the Ħaġar Qim, Mnajdra and Tarxien Temples, were protected by open-sided shelters, to address some of the principal causes of deterioration (e.g. direct rainfall, surface weathering, thermal stress). Environmental monitoring, condition assessments and biological surveys of the three sites took place before and after sheltering and are still in progress. To understand how the shelters are affecting these structures, a research programme has started aimed at analysing, through Computational Fluid Dynamics (CFD), the environmental data collected over a period of more than ten years. The aim of using CFD on the Temples is to provide detailed information on how different environmental conditions can affect the sites. For the CFD, macro and meso scale approaches will be used. The macroscale model represents the regional environment, including the all-terrain features around the Temples. Mesoscale modelling represents the Temple structures in a more detailed way. The final goal is to find confident correlations between CFD, and representative areas selected within the Temples showing particular deterioration patterns. All this information will be integrated with the results of in situ analyses to identify the causes of material deterioration and possibly mitigate against them.

Experimental and numerical study on stiffness and damage of glass/epoxy biaxial weft-knitted reinforced composites

This paper deals with investigating the tensile characteristics of biaxial weft-knitted reinforced composites in terms of stiffness, strength and failure mechanism. The biaxial weft-knitted fabric was produced on an electronic flat knitting machine by E-glass yarns and then was impregnated with epoxy resin. Using an accurate geometrical model, the composite unit cell was designed in Abaqus software’s environment. Tensile tests were simulated in different directions on the created unit cell and the stiffness was calculated. By applying the proper failure theories, the composite strength was predicted and then critical regions of the unit cell were determined. In the next step, a micromechanical approach was also applied to estimate the same tensile features. Failure theories were also applied to predict the strength and most susceptible areas for failure phenomenon in the composite unit cell. The tensile properties of the produced composites were measured and compared with outputs of the finite element and micromechanical approaches. The results showed that the meso-scale finite element analysis approach can well predict the composite strength. In contrast, the meso-scale analytical equation model was not able to predict it acceptably because this model ignores the strain concentration. Both meso-scale finite element analysis and meso-scale analytical equation approaches predicted the similar locations for the composite failure in wale and course directions.

Implementation of the EU ecological flow policy in Italy with a focus on Sardinia

River ecosystems are characterised by a naturally high level of hydrodynamic perturbations which create aquatic-terrestrial habitats indispensable for many species, as well as for the human beings' welfare. Environmental degradation and habitat loss caused by increasing anthropogenic pressures and global change affect freshwater aquatic ecosystems worldwide and have caused changes in water flow regimes and channels morphologies. These, in turn, decreased the natural flow capacity and reduced habitat availability, thus causing severe degradation of rivers' ecological integrity. The ecological flow (e-flow) is commonly intended as the quantity, timing, duration, frequency and quality of water flows required to sustain freshwater, estuarine and near‐shore ecosystems and the human livelihoods and well‐being. Maintaining the e-flow represents a potential tool for restoring and managing river ecosystems, to preserve the autochthonous living communities, along with environmental services and cultural/societal values. In the last decade, methods for the determination of the e-flow in European rivers moved from a simply hydrological approach towards establishing a linkage between the hydrological regime and the good ecological status (GES) of the water bodies, as identified by the European Water Framework Directive (WFD; 2000/60/EC). Each Member State is required to implement and integrate into the River Basin Management Plans (RBMP) a methodology for the determination of the e-flow, ensuring that rivers can achieve and maintain the GES. The competent river basin authorities have thus to ascertain whether national methodologies to can be applied to different river typologies and basin environment characteristics. In this context, we narratively review the e-flow assessments in the heterogeneous Italian territory, in particular on a water scant region such as Sardinia, by analysing laws, guidelines and focusing on study cases conducted with micro and meso-scale hydraulic-habitat approaches. In the sight of a more ecological-based application of national e-flow policy, we suggest that meso-habitat methods provide a valuable tool to overcome several limitations of current e-flow implementation in the Italian territory. However, to face future challenges, such as climate change adaptation, we stress the need for further experimental studies to update water management plans with greater attention for nature conservation.

Predicting the overall response of an orthogonal 3D woven composite using simulated and tomography-derived geometry

Effects of two meso-scale geometry generation approaches on predicting effective elastic properties and thermal conductivity of an orthogonal 3D woven composite are studied in this paper. The two approaches used are fabric mechanics simulation (DFMA software, Kansas State University) and direct processing of X-ray microtomography (µCT) data. Two models are created in DFMA using two different sets of cross-sectional areas as input: nominal (based on the initial weave pattern) and adjusted (informed by volume fraction measurements obtained from microscopy data). In addition, one conformal mesh and three voxel mesh models are created from µCT data. Experimental measurements of transverse Young’s moduli are used to evaluate the accuracy of the predicted results.In each case, a unit cell with in-plane periodic boundary conditions is modeled, which has not been previously done in the case of µCT-based models. The effect of high frequency oscillations in local material orientations imparted by a wavy centerline (artifact of µCT image processing) on the elastic and thermal conductivity properties is studied. The differences in volume fractions and shapes of bundles of fibers (tows) between µCT-based and DFMA-based models are also investigated to determine sensitivity of effective thermo-mechanical properties to each of these factors.

A Multiresolution Mesoscale Approach for Microscale Hydrodynamics

AbstractA new class of multiscale scheme is presented for micro‐hydrodynamic problems based on a dual representation of the fluid observables. The hybrid model is first tested against the classical flow between two parallel plates and then applied to a plug flow within a micrometer‐sized striction and a shear flow within a microcavity. Both cases demonstrate the capability of the multiscale approach to reproduce the correct macroscopic hydrodynamics also in the presence of refined grids (one and two levels), while retaining the correct thermal fluctuations, embedded in the multiparticle collision method. This provides the first step toward a novel class of fully mesoscale hybrid approaches able to capture the physics of fluids at the micro‐ and nanoscales whenever a continuum representation of the fluid falls short of providing the complete physical information, due to a lack of resolution and thermal fluctuations.

Impact of Road Geometry on Vehicle Energy Consumption and CO2 Emissions: An Energy-Efficiency Rating Methodology

This study presents a methodology for classifying road traffic energy efficiency. The indicators defined discriminate the impact of the road vertical and horizontal alignments upon energy consumption, disclosing the improvement potential of the road as a function of the traffic origin–destination matrix. The methodologic approach is based on basic physical principals, thus guarantying its generality, as opposed to the usual empirical mesoscale approaches. A simplified algebraic procedure is also proposed, resorting to simplified driving cycles and a constant speed assumption (CSA), thus avoiding the intricacy of microscale/microsimulation models. The simplified methodology was validated against field data acquired on the Portuguese highway A25. A microscale vehicle specific power analysis combined with detailed fuel models is compared against CSA results. The findings demonstrate its adequacy for free-flow traffic conditions and the importance of classifying road traffic energy-efficiency. For the case studied, it was found that 49.5% of the round trip propulsive energy expended by a 37-ton truck on the A25, a modern road, was degraded as heat through braking. The difference found between the microscale analysis and CSA approach is 0.8%, despite the speed unevenness, varying between 32 and 96 km/h, with a standard deviation of 24% of the average speed.

Multiscale Modeling of a Notched Coupon Test for Triaxially Braided Composites

Braided composites have been widely used in aerospace and automotive structures due to their light weight and high strength. Unlike metal or laminated composite material, the complex braided structure brings a lot of challenges when conducting numerical simulation. In this paper, a finite element analysis based meso-mechanical modeling for the two dimensional triaxially braided composite was developed. This mesoscale modeling method is capable of considering the detailed braiding geometry and architecture as well as the mechanical behavior of fiber tows, matrix and the fiber tow interface. Furthermore, a multiscale model combined both macroscale and mesoscale approaches and it is realized within LS-DYNA environment through Interface_components and Interface_linking. This combined multiscale modeling approach enables the full advantage of both the macroscale and mesoscale approaches, which can describe the details of local deformation and the global overall response features of the entire structure with the minimum computational expense. The evaluation and verification of the mesoscale approach and combined multiscale modeling method is through a notched coupon tensile tests conducted by Kohlman in both axial and transverse direction. The multiscale modeling method captures the response feature accurately so it has the ability to analyze large scale structures.

First-principles study of surface properties of uranium silicides

Uranium silicides are currently under investigation as accident tolerant fuels for light water reactors because of its high uranium density and high thermal conductivity. Surface energy as an important material property is required for modeling of gas bubble behavior in nuclear fuels using mesoscale approaches, such as phase field and rate theory methods. However, there is no such information available for uranium silicides from either experiment or theory. To this end, we study the surface properties of two uranium silicide compounds U3Si2 and U3Si using first-principles calculations. Of the low-index facets of tetragonal U3Si2 and U3Si, we study a total of 13 surfaces up to a maximum Miller index of 3. From the calculated surface energies, the equilibrium single crystal shapes of U3Si2 and U3Si are obtained using Wulff construction. The dominant surface orientation, surface area weighted surface energy and surface anisotropy are predicted. The obtained surface properties of U3Si2 and U3Si can be used for an accurate description of the morphology of fission gas bubbles in uranium silicide fuels in the future.

An innovative micro-scale approach for vulnerability and flood risk assessment with the application to property-level protection adoptions

Economic damage assessment for flood risk estimation is established in many countries, but attentions have been focused on macro- or meso-scale approaches and less on micro-scale approaches. Whilst the macro- or meso-scale approaches of flood damage assessment are suitable for regional- or national-oriented studies, micro-scale approaches are more suitable for cost–benefit analysis of engineered protection measures. Furthermore, there remains lack of systematic and automated approaches to estimate economic flood damage for multiple flood scenarios for the purpose of flood risk assessment. Studies on flood risk have also been driven by the assumption of stationary characteristic of flood hazard, hence the stationary-oriented vulnerability assessment. This study proposes a novel approach to assess vulnerability and flood risk and accounts for adaptability of the approach to nonstationary conditions of flood hazard. The approach is innovative in which an automated concurrent estimation of economic flood damage for a range of flood events on the basis of a micro-scale flood risk assessment is made possible. It accounts for the heterogeneous distribution of residential buildings of a community exposed to flood hazard. The feasibility of the methodology was tested using real historical flow records and spatial information of Teddington, London. Vulnerability curves and residual risk associated with a number of alternative extents of property-level protection adoptions are estimated by the application of the proposed methodology. It is found that the methodology has the capacity to provide valuable information on vulnerability and flood risk that can be integrated in a practical decision-making process for a reliable cost–benefit analysis of flood risk reduction options.

The role of topology in microstructure-property relations: a 2D DEM based study

We compare Rényi entropy-based mesoscale approaches for characterizing 2D polycrystalline network topology and geometry, based on the grain number of sides and grain areas, respectively. We study the effect of microstructure disorder on mechanical properties such as elastic and damage response by performing simulations of quasi-static uniaxial compression loading tests on an idealized material using grain-level micro-mechanical discrete element model. While not comprehensive enough to make general conclusions, this study allows us to make observations about the sensitivity of mechanical parameters such as Young's modulus, proportional limit, first yield stress, toughness and amount of microstructure damage to different entropy measures.

Local perspectives on the formalization of artisanal and small-scale mining in the Madre de Dios gold fields, Peru

A growing number of governments and donors are promoting the formalization of artisanal and small-scale mining (ASM). They believe that doing so puts them in a better position to govern the sector, and manage the social and environmental impacts of its activities. Mainstream formalization processes are based on the assumption that clear property rights enable the recipients of these rights to capitalize their possessions. Because of reciprocal obligations, the argument follows that formalized ASM actors then better embrace the social and environmental norms regulating their activity. This paper reflects critically on attempts made to formalize ASM in Madre de Dios in Peruvian Amazonia. We share local perceptions of ASM impacts, and broaden understanding of the relationship between mainstream formalization and more bottom-up processes for governing and managing ASM impacts. We forward mesoscale collaborative approaches to impact management. In Madre de Dios, this could involve the appointment of a regional mediator with a strong mandate, establishment of a mobile formalization office, and the implementation of a series of coordinated but independent impact management activities through an impact management plan. This approach would not involve a stepwise procedure in which the failure to achieve one goal would prevent the pursuit of others.

Multiscale simulations of protein-facilitated membrane remodeling.

Protein-facilitated shape and topology changes of cell membranes are crucial for many biological processes, such as cell division, protein trafficking, and cell signaling. However, the inherently multiscale nature of membrane remodeling presents a considerable challenge for understanding the mechanisms and physics that drive this process. To address this problem, a multiscale approach that makes use of a diverse set of computational and experimental techniques is required. The atomistic simulations provide high-resolution information on protein-membrane interactions. Experimental techniques, like electron microscopy, on the other hand, resolve high-order organization of proteins on the membrane. Coarse-grained (CG) and mesoscale computational techniques provide the intermediate link between the two scales and can give new insights into the underlying mechanisms. In this Review, we present the recent advances in multiscale computational approaches established in our group. We discuss various CG and mesoscale approaches in studying the protein-mediated large-scale membrane remodeling.

Bounce regime of droplet collisions: A molecular dynamics study

Droplet collisions have complex dynamics, which can lead to many different regimes of outcomes. The head-on collision and bounce back regime has been observed in previous experiments but numerical simulations using macro- or mesoscale approaches have difficulties reproducing the phenomena, because the interfacial regions are not well resolved. Previous molecular dynamics (MD) simulations have not reproduced the bounce regime either but have reported the coalescence and/or shattering regimes. To scrutinize the dynamics and mechanisms of binary collisions especially the interfacial regions, head-on collision processes of two identical nano-droplets with various impact velocities both in vacuum and in an ambient of nitrogen gas are investigated by MD simulations. With the right combination of the impact velocity and ambient pressure, the head-on collision and bounce back phenomenon is successfully reproduced. The bounce phenomena are mainly attributed to the “cushion effect” of the in-between nitrogen molecules and evaporated water molecules from the two nano-droplets. The analysis has verified and also extended the current gas film theory for the bounce regime through including the effects of evaporated water molecules (vapour). Some similarities and some dissimilarities between nanoscale and macro-/meso-/microscale droplet collisions have been observed. The study provides unprecedented insight into the interfacial regions between two colliding droplets.