Non-uniform Deposition Research Articles

Some fluid mechanical aspects of artistic painting

Painting is a fluid mechanical process. The action of covering a solid surface with a layer of a viscous fluid is one of the most common human activities; virtually all man-made surfaces are painted to provide protection against the environment or simply for decoration. This process, in an industrial context, has been vastly studied and it is well understood. In case of artistic painting the purpose is different. Painters learn how to manipulate the non-uniform deposition of paint onto a surface, through lengthy empirical testing of the action and modifying the physical properties of the fluids, to create textures and patterns of aesthetic value. In this paper, an analysis of some notable painting techniques is presented from the point of view of fluid mechanics. In particular, we discuss the so-called `accidental painting' technique, originally devised by David A. Siqueiros, which is the result of a Rayleigh-Taylor instability. An analysis of several techniques used by Jackson Pollock is also presented, showing how he learned to carefully control the motion of viscous filaments to create his famous abstract compositions. We also briefly discuss how pattern and textures are produced in decalcomania and watercolor painting. These investigations indicate that it is possible to establish concrete scientific discussions among modern fluid mechanics, art, art history and conservation.

A bench-scale flow loop study on hydrate deposition under multiphase flow conditions

Gas hydrates are crystalline compounds containing water and small guest molecules. Hydrates, if not properly managed, can cause capital losses and raise safety concerns. In recent years, hydrate control strategies have changed from complete prevention to proper management. Hydrate management requires satisfactory understanding in all hydrate challenges, including agglomeration, deposition, and bedding. The importance of deposition motivates the investigation of its mechanisms. This work aims to provide further insights into hydrate deposition under multiphase flow conditions using a bench-scale single-pass flow loop. The flow loop was equipped with a horizontal test section, transparent windows, temperature sensors, and differential pressure transducers. The experiments were performed with a methane/ethane gas mixture at constant 38.7 bara. The mutual effects between the flow pattern and the deposit growth were observed. Most experiments in this study started with stratified flow. Non-uniform hydrate deposition was observed with relatively slow growth of the top deposit exposed to the gas phase and relatively fast growth of the bottom deposit with direct contact to the liquid phase. The hydrate buildup gradually changed the flow pattern from stratified flow to stratified wavy flow and eventually to slug/bubble flow. The deposit growth and the flow pattern change were reflected on the pressure drop measurement across the test section. The wall temperature showed a big effect on the growth rate and the steady-state thickness. The hydrate slurry presence and the water cut did not noticeably affect the steady-state deposit thickness, while the MEG addition seemed to reduce the thickness.

Factors That Control the Formation of Dendrites and Other Morphologies on Lithium Metal Anodes

Author(s): Frenck, L; Sethi, GK; Maslyn, JA; Balsara, NP | Abstract: Lithium metal is a promising anode material for next-generation rechargeable batteries, but non-uniform electrodeposition of lithium is a significant barrier. These non-uniform deposits are often referred to as lithium “dendrites,” although their morphologies can vary. We have surveyed the literature on lithium electrodeposition through three classes of electrolytes: liquids, polymers and inorganic solids. We find that the non-uniform deposits can be grouped into six classes: whiskers, moss, dendrites, globules, trees, and cracks. These deposits were obtained in a variety of cell geometries using both unidirectional deposition and cell cycling. The main result of the study is a figure where the morphology of electrodeposited lithium is plotted as a function of two variables: shear modulus of the electrolyte and current density normalized by the limiting current density. We show that specific morphologies are confined to contiguous regions on this two-dimensional plot.

Linking heterogeneous distribution of radiocaesium in soils and pond sediments in the Fukushima Daiichi exclusion zone to mobility and potential bioavailability

During the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011 significant amounts of radiocaesium were released into the atmosphere from the reactor units 1, 2 and 3. This caused a non-uniform deposition, in composition and direction, of 134Cs and 137Cs in the near field (<30 km) from the reactors. In this work, we elucidate the influence of speciation, including radioactive particles, on mobility and potential bioavailability of radiocaesium in soils and sediments from sites located in different directions and distances from the FDNPP. Samples collected in September 2016 were characterized and subjected to sequential chemical extractions and simulated gastrointestinal fluid leaching, and the 137Cs and 134Cs activities were determined in bulk, grain-size and extracted fractions. The results show that radiocaesium was mainly irreversibly bound and in an inert form. Combined, the two forms contained >90% of the activity present in soils and ~84% in sediments. Digital autoradiography revealed that the inert fraction was predominantly associated with heterogeneities, an indication of radioactive particles. The frequency of heterogeneities was correlated with 137Cs activity concentrations, and both were in agreement with the ambient equivalent air doses measured in situ during sampling. Moreover, in situ gamma spectrometry measurements were used in the InSiCal software tool to derive 134Cs and 137Cs surface contamination. Soil activity concentrations and contamination density estimations, decay-corrected to the day of the FDNPP accident, resulted in 134Cs/137Cs ratios that match the reported release and deposition plumes from the reactor units. Overall, these results demonstrate the persistence of the particle contamination in the Fukushima near field and highlight the importance of including radioactive particles in environmental impact assessments.

Enhanced cycling performance of cylindrical lithium-ion battery with high areal capacity electrodes via non-uniform load

Increasing the areal capacity of electrodes in lithium-ion batteries (LIBs) is one of the effective ways to increase energy density due to increased volume fraction of active materials. However, the disassembly of cylindrical lithium iron phosphate (LFP) cell with high areal capacity electrodes at full charge state shows that the negative electrode exhibits a gradient color from golden to silvery white, which indicates a non-uniform lithium deposition, is attributed to the unreasonable capacity matching between positive and negative electrodes after winding process. Inductively coupled plasma-optical emission spectrometry (ICP-OES) tests show that more irreversible lithium content is gradually distributed on negative electrode after cycling test. Herein, inspired by this phenomenon, asymmetric electrodes produced by the non-uniform loading process were successfully designed to avoid non-uniform lithium deposition, which increase the capacity retention of cylindrical cell with high areal capacity electrodes from 75.8 to 91.7% at 1 C rate after 500 cycles.

Lithiophilic 3D Porous CuZn Current Collector for Stable Lithium Metal Batteries

Lithium (Li) dendrites formed from nonuniform Li deposition limit potential uses of Li metal as an anode material. Here, we report a lithiophilic 3D porous CuZn current collector that mitigates den...

Laser-Induced Deposition of Carbon Nanotubes in Fiber Optic Tips of MMI Devices.

The integration of carbon nanotubes (CNTs) into optical fibers allows the application of their unique properties in robust and versatile devices. Here, we present a laser-induced technique to obtain the deposition of CNTs onto the fiber optics tips of multimode interference (MMI) devices. An MMI device is constructed by splicing a section of no-core fiber (NCF) to a single-mode fiber (SMF). The tip of the MMI device is immersed into a liquid solution of CNTs and laser light is launched into the MMI device. CNTs solutions using water and methanol as solvents were tested. In addition, the use of a polymer dispersant polyvinylpyrrolidone (PVP) in the CNTs solutions was also studied. We found that the laser-induced deposition of CNTs performed in water-based solutions generates non-uniform deposits. On the other hand, the laser-induced deposition performed with methanol solutions generates uniform deposits over the fiber tip when no PVP is used and deposition at the center of the fiber when PVP is present in the CNTs solution. The results show the crucial role of the solvent on the spatial features of the laser-induced deposition process. Finally, we register and study the reflection spectra of the as-fabricated CNTs deposited MMI devices.

Enabling rapid charging lithium metal-based rechargeable batteries through suppression of dendrite growth and ion depletion in the electrolyte via surface acoustic wave-driven mixing

Lithium metal is an attractive material for use as anodes in batteries due to its high energy density. However, it is unstable during recharging, with non-uniform Li deposition that leads to porosity, dendrites, rechargeable lithium metal batteries (LMB) have been unrealistic for fifty years with serious safety problems. Over this time, research on chemistry modifications have produced modest improvements, but none that have justified considering LMB over lithium-ion batteries in rechargeable applications. Nonuniform Li deposition during charging occurs due to a Li ion depletion layer adjacent to the anode, especially at high charge rates. By including a small surface acoustic wave device (SAW) into the LMB that produces intense acoustic waves in the electrolyte, rapid submicron boundary layer mixing flow may be generated during charging. This flow largely eliminates the Li ion depletion layer, and because the SAW device is small, solid state, and requires only 10 mW h/cm2 during battery charging, there is a realistic possibility of incorporating this technology into current batteries under consideration for an electric vehicle, consumer device, and medical applications. The elimination of the ion depletion layer furthermore allows high-rate charging, as we will demonstrate in our electrochemistry and morphological results. The underlying physics will be explained using a closed-form model formed from intermediate asymptotics, and will show the crucial impact of the Peclet number in avoiding the ion depletion layer.

Physical Experiment and Modeling of the Transport and Deposition of Polydisperse Particles in Stormwater: Effects of a Depth-Dependent Initial Filter Coefficient

The artificial recharge of stormwater is an effective approach for replenishing aquifer and reduce urban waterlogging, but prone to clogging by suspended particles (SP) that are highly heterogeneously sized. In this paper, the transport and deposition of SP in a sand column were investigated under a constant flow condition, for five stormwater concentrations. A depth-dependent initial filter coefficient is incorporated into the conventional filtration model. This modified model considers the heterogeneity of the particle population by lumping the capture of heterogeneous SP into a capture probability. The good agreement between the results of the modified model and the experimental results of measured outlet concentration and average specific deposit validated the modified model. The experiment data and the simulation results both indicate that the highly hyper-exponential retention profiles are caused by non-uniform deposition of heterogeneous SP; and, the conventional model was found to homogenize the spatial distribution of SP retention and overestimate retention of the porous medium. Local and overall permeability reductions were assessed by an empirical relationship and the Kozeny-Carman model, respectively. It is shown that consideration of polydisperse suspended particles is of primary importance. This study highlights the effects of polydisperse particles on SP deposition in a saturated porous medium.

Cadmium toxicity and its relationship with disturbances in the cytoskeleton, cell cycle and chromosome stability.

This study aimed to investigate the mode of action of cadmium (Cd) toxicity at cell level, especially at early stages of plant exposure. Tomato seedlings were cultivated in growth media containing from 0.1 to 70 µM CdCl2 for 24 h. Mitotic index, chromosome abnormality, DNA integrity and organization of tubulin-based structures were assessed in root cells. As higher the Cd concentration in the growth media, higher was the DNA damage intensity and the occurrence of chromosomal abnormalities that included chromosome lost, bridges, stickiness, C-metaphase and polyploidy. The profile of chromosomal aberrations also varied with elevated Cd concentration, being observed increases in the frequency of chromosome stickiness. The mitotic index was reduced at the lowest Cd concentration, but such reduction was statistically similar to that detected at the highest concentration, suggesting that mitotic depression is a rapid outcome and, at same time, a Cd-induced effect that is limited at the first 24 h of direct root exposure to this metal. Under exposure to 20 µM CdCl2, heterogenous distribution of the spindle fibers, formation of two spindle complexes in both of the cell poles, absence of centrosome center, polarization of the spindle fibers during cell division, and non-uniform tubulin deposition in microtubule and phragmoplast were noticed. The results indicate that the tubulin-dependent components of cytoskeleton are Cd targets, and the sensitivity of tubulin-based structures to Cd exposure depends on cell cycle phase. Moreover, DNA damage intensity and chromosomal abnormality profile can be employed as markers of Cd toxicity level.

Role of Substrate Surface Morphology on the Performance of Graphene Inks for Flexible Electronics.

Two-dimensional (2D) materials, such as graphene, are seen as potential candidates for fabricating electronic devices and circuits on flexible substrates. Inks or dispersions of 2D materials can be deposited on flexible substrates by large-scale coating techniques, such as inkjet printing and spray coating. One of the main issues in coating processes is nonuniform deposition of inks, which may lead to large variations of properties across the substrates. Here, we investigate the role of surface morphology on the performance of graphene ink deposited on different paper substrates with specific top coatings. Substrates with good wetting properties result in reproducible thin films and electrical properties with low sheet resistance. The correct choice of surface morphology enables high-performance films without postdeposition annealing or treatment. Scanning terahertz time-domain spectroscopy (THz-TDS) is introduced to evaluate both the uniformity and the local conductivity of graphene inks on paper. A paper-based strain gauge is demonstrated and a variable resistor acts as an on–off switch for operating an LED. Customized surfaces can thus help in unleashing the full potential of ink-based 2D materials.

Characterization of multi-element impurity deposited on EAST divertor tile using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been applied for the depth-resolved identification of impurity deposited on EAST divertor tile. LIBS spectra show the presence of impurity elements (W, Mo, Li, Na, Ca, Cr) and tile material (C, Si, Ti) in the layer deposited on the graphite tile surface. The analysis of impurity deposition was performed in different positions on tile surface. The results indicate that the interaction of high heat plasma with plasma facing components (PFCs) leads to erosion of Mo from first wall and W from upper divertor. Depth profiling measurements show decay of impurity signals with successive laser shots and non-uniform impurity deposition in the different positions on tile surface. The impurity deposition was also measured at the different depths in the tile. The measurements show a non-uniform deposition at various depths in the deposition layer. Surface morphology and composition of tile were verified by SEM and EDX techniques. The study indicates that LIBS has potential to monitor the erosion and deposition of PFCs in fusion devices. The results obtained from LIBS technique are important for long pulse of H-mode plasma operation in EAST.

Numerical investigation of spudcan-footprint interaction in non-uniform clays

The re-installation of jack-up rigs near an existing footprint left by the previous installation can be problematic due to the development of horizontal and moment loads on the spudcan footing and hence on the rigs. This paper reports large deformation finite element results of spudcan-footprint interaction in non-uniform clay deposits. The performance of the numerical model was verified by simulations of existing centrifuge tests. A detailed parametric study was carried out varying influential factors including the initial spudcan penetration depth to form the footprint, spudcan diameters, soil sensitivity, undrained shear strength profile and the offset distance between spudcan and footprint centres. The effects of these factors on the development of the vertical, horizontal and moment loads are quantified, and the peak magnitudes of the induced horizontal and moment loads at different offset distances are then compared. It is found through the numerical analyses that the critical offset distance, which maximises the peak horizontal and moment loads on the spudcan, ranges between 0.5 and 0.75 times the diameter of the spudcan used for the formation of the footprint. By contrast, an offset distance of 1.5–2.0 times the diameter of the larger spudcan of those used for initial penetration and re-installation is able to result in a minimal influence of the footprint on the re-installation.

Reshaping the size distribution of aerosol elemental carbon by removal of coarse mode carbonates

To investigate the size distribution of organic carbon (OC) and elemental carbon (EC), an impactor sampler was conventionally employed to collect size-resolved aerosols. The impactor sampling technique may be subject to nonuniform deposits of particles on the sampling substrates, thus affecting the optical correction of the pyrolyzed fraction and leading to errors in the partitioning of OC and EC during determination. Based on one-year observations, these optical correction errors were evaluated by comparison between the first four stages of the impactor (PM2.1) and PM2.5 samples collected at the bypass line of tapered element oscillating microbalance (TEOM). The PM2.5 to PM2.1 ratio of OC is close to 1, indicating that the optical correction errors in size-resolved OC can be ignored. In contrast, the PM2.5 to PM2.1 ratio of EC is much higher than 1, suggesting that the size-resolved EC data should be corrected (with a factor of 1.6 in this study). In addition, the size distribution of EC (ECoriginal) exhibited an obvious peak in the coarse mode. We argued that carbonate carbon (CC) might account for this coarse peak and hence biased the size distribution of EC. We then employed a calcium equivalent method to estimate CC, allowing the EC data can be corrected. As a result, CC contributed less than 7% of ECoriginal in the fine mode but accounted for 20%–88% of ECoriginal in the coarse mode. Thus, ignoring the CC may overestimate the coarse model EC and hence misinterpret the EC size distribution, with significant implications in characterization of EC and its dry deposition and climate effects.

Operational strategy to stabilize lithium metal anodes by applied thermal gradient

External thermal gradients have a profound impact on lithium metal battery plating and stripping stability, potentially providing a path to safe, rechargeable, lithium metal batteries. The direction of the thermal gradient for the first Li plating determines whether the cell is stable and capable of high-rate, high-capacity plating/stripping or is instead unstable and vulnerable to internal shorting. Symmetric lithium metal batteries with a negative thermal gradient (0 °C negative electrode, 40 °C positive electrode) reproduce conditions known to result in high-aspect ratio plating deposits and high surface non-uniformity for the first Li plating. Non-uniform deposition increases unfavorable side reactions between freshly plated Li and the electrolyte that increases interfacial resistance, reduces ionic conductivity due to electrolyte consumption, and forms a mass transport-limiting layer of electrochemically inactive lithium at the electrode surface—similar to observations for isothermal 0 °C and 20°C control cases. Alternatively, a positive thermal gradient (40 °C negative electrode, 0 °C positive electrode) forms a uniform initial electrodeposit that predisposes the cell to stable, long-term cycling. A positive thermal gradient reduces detrimental electrode-electrolyte reactions, reduces electrochemically inactive lithium formation, and maintains a low tortuosity diffusion pathway for higher effective ionic conductivity and lower interfacial resistances. A positive thermal gradient reduces cell voltage hysteresis by up to 39% compared to isothermal 20 °C control at a broad range of current densities and capacities (up to 5.0 mA cm−2 and 10 mAh cm−2), dramatically enhancing high-rate cycling and demonstrating promise for a positive thermal gradient as an operational strategy to enable faster charging for batteries with lithium metal anodes.

The Combined Effect of Cycling Strategy and Potential Electrolyte in Fast Charging/Discharging of Li-Metal Based Batteries

: Li-metal batteries with the configuration like Cu||LiFePO4 is a suitable tool to circumvent the dendritic Li growth, induced by non-uniform Li deposition during plating-stripping in direct using lithium anode, by forming good solid electrolyte interface (SEI) on the surface of in-situ deposited Li. However, the repeated SEI breaking induced by the uninterrupted volume change during Li plating and the formation of new SEI consumes the limited Li obtained only from the cathode and electrolyte and leads to a rapid capacity fading and low Coulombic Efficiency (CE). Here, we report that the combined effect between potential electrolytes and cyclic protocols could suppress the amount of Li and electrolyte consumed in the SEI formation process and prolongs cycle life of such an anode free battery (AFB) [Cu||LFP-type] at a high current density. In comparison to the carbonate based commercial 1MLiPF6, the synergy between the laboratory prepared ether based 3M LiFSI electrolyte and our new cycling protocol significantly enhanced the cyclic performance of AFB having the Cu||LiFePO4 Cu||Li half-cell at high current density. Eventually, Cu||Li half-cell manifested extraordinary cyclic performance and cycled up to 1000 cycles with the average CE of more than 99.9% at a high current density of 1.0 mA/cm2 using bare Cu without any modification. In addition, the Cu||LiFePO4 showed a remarkable cyclic performance at 0.2 mA/m2 attaining an average CE of up to 98.99% retaining more 40% of the initial discharge capacity after 100 cycles. More importantly, the Cu||LiFePO4 also cycled a higher rate up to 1.0 mA/cm2 with high CE and retaining a reasonable discharge capacity after 100 cycles. The fast cycling and stable performance these cells attributed to the formation robust, flexible and inorganic components rich conductive SEI on the surface of the in-situ deposited Li by the synergistic effect between our laboratory prepared electrolyte and the new cycling protocol. Keyword: anode free, synergy, cycling protocol, ether based electrolyte, Cu||LiFePO4, SEI

How do granular columns affect the seismic performance of non-uniform liquefiable sites and their overlying structures?

This paper presents results of a series of three dynamic centrifuge experiments to evaluate how granular columns affect the seismic performance of level and gently sloped sites that include a non-uniform liquefiable deposit and an overlying, 3-story structure. A slight variation in the thickness of the liquefiable layer is shown to produce unacceptable permanent lateral ground deformations, even in the absence of a surface slope or a structure. The presence of a gentle slope further amplified lateral displacements but did not influence settlements notably. Granular columns (with an area replacement ratio of 20%) were successful in reducing the extent and duration of large excess pore pressures, void redistribution, and shear strain localization in such layered deposits. Hence, they generally reduced settlements, rotations, and lateral displacements both near and away from structures, but not necessarily to acceptable design limits. Granular columns could increase the acceleration demand transferred to the foundation and superstructure by increasing soil stiffness and reducing damping. The impact of this mitigation on roof accelerations and beam/column bending strains was shown to depend on the intensity and frequency content of the input motion in relation to the modal frequencies of the structure. The presented experimental results highlight the importance of considering even slight variations in liquefiable layer thickness as well as soil-foundation-structure interaction when designing liquefaction mitigation strategies in the context of system performance.

Prediction of Tumor Control in 90Y Radioembolization by Logit Models with PET/CT-Based Dose Metrics.

The aim of this work was to develop models for tumor control probability (TCP) in radioembolization with 90Y PET/CT-derived radiobiologic dose metrics. Methods: Patients with primary liver cancer or liver metastases who underwent radioembolization with glass microspheres were imaged with 90Y PET/CT for voxel-level dosimetry to determine lesion absorbed dose (AD) metrics, biological effective dose (BED) metrics, equivalent uniform dose, and equivalent uniform BED for 28 treatments (89 lesions). The lesion dose-shrinkage correlation was assessed on the basis of RECIST and, when available, modified RECIST (mRECIST) at first follow-up. For a subset with mRECIST, logit regression TCP models were fit via maximum likelihood to relate lesion-level binary response to the dose metrics. As an exploratory analysis, the nontumoral liver dose-toxicity relationship was also evaluated. Results: Lesion dose-shrinkage analysis showed that there were no significant differences between model parameters for primary and metastatic subgroups and that correlation coefficients were superior with mRECIST. Therefore, subsequent TCP analysis was performed for the combined group using mRECIST only. The overall lesion-level mRECIST response rate was 57%. The AD and BED metrics yielding 50% TCP were 292 and 441 Gy, respectively. All dose metrics considered for TCP modeling, including mean AD, were significantly associated with the probability of response, with high areas under the curve (0.87-0.90, P < 0.0001) and high sensitivity (>0.75) and specificity (>0.83) calculated using a threshold corresponding to 50% TCP. Because nonuniform AD deposition by microspheres cannot be determined by PET at a microscopic scale, radiosensitivity values extracted here by fitting models to clinical response data were substantially lower than reported for in vitro cell cultures or for external-beam radiotherapy clinical studies. There was no correlation between nontumoral liver AD and toxicity measures. Conclusion: Despite the heterogeneous patient cohort, logistic regression TCP models showed a strong association between various dose metrics and the probability of response. The performance of mean AD was comparable to that of radiobiologic dose metrics that involve more complex calculations. These results demonstrate the importance of considering TCP in treatment planning for radioembolization.

Properties of HPK UFSD after neutron irradiation up to 6e15 n/cm2

In this paper we report results from a neutron irradiation campaign of Ultra-Fast Silicon Detectors (UFSD) with fluences of 1e14, 3e14, 6e14, 1e15, 3e15, 6e15 n/cm2. The UFSD used in this study are circular 50 micro-meter thick Low-Gain Avalanche Detectors (LGAD), with a 1.0 mm diameter active area. They have been produced by Hamamatsu Photonics (HPK), Japan, with pre-radiation internal gain in the range 10-100 depending on the bias voltage. The sensors were tested pre-irradiation and post-irradiation with minimum ionizing particle (MIPs) from a 90Sr based \b{eta}-source. The leakage current, internal gain and the timing resolution were measured as a function of bias voltage at -20C and -30C. The timing resolution was extracted from the time difference with a second calibrated UFSD in coincidence, using the constant fraction method for both. The dependence of the gain upon the irradiation fluence is consistent with the concept of acceptor removal and the gain decreases from about 80 pre-irradiation to 7 after a fluence of 6e15 n/cm2. Consequently, the timing resolution was found to deteriorate from 20 ps to 50 ps. The results indicate that the most accurate time resolution is obtained at a value of the constant fraction discriminator (CFD) threshold used to determine the time of arrival varying with fluence, from 10% pre-radiation to 60% at the highest fluence. Key changes to the pulse shape induced by irradiation, i.e. (i) a reduce sensitivity of the pulse shape on the initial non-uniform charge deposition, (ii) the shortening of the rise time and (iii) the reduced pulse height, were compared with the WF2 simulation program and found to be in agreement.

Monte Carlo Simulations of Framework Defects in Layered Two-Dimensional Nanomaterial Desalination Membranes: Implications for Permeability and Selectivity.

Two-dimensional nanomaterial (2-D NM) frameworks, especially those comprising graphene oxide, have received extensive research interest for membrane-based separation processes and desalination. However, the impact of horizontal defects in 2-D NM frameworks, which stem from nonuniform deposition of 2-D NM flakes during layer build-up, has been almost entirely overlooked. In this work, we apply Monte Carlo simulations, under idealized conditions wherein the vertical interlayer spacing allows for water permeation while perfectly excluding salt, on both the formation of the laminate structure and molecular transport through the laminate. Our simulations show that 2-D NM frameworks are extremely tortuous (tortuosity ≈103), with water permeability decreasing from 20 to <1 L m-2 h-1 bar-1 as thickness increased from 8 to 167 nm. Additionally, we find that framework defects allow salt to percolate through the framework, hindering water-salt selectivity. 2-D NM frameworks with a packing density of 75%, representative of most 2-D NM membranes, are projected to achieve <92% NaCl rejection at a water permeability of <1 L m-2 h-1 bar-1, even with ideal interlayer spacing. A high packing density of 90%, which to our knowledge has yet to be achieved, could yield comparable performance to current desalination membranes. Maximizing packing density is therefore a critical technical challenge, in addition to the already daunting challenge of optimizing interlayer spacing, for the development of 2-D NM membranes.