Water Boundary Layer Research Articles

Control effect on the divergent and convergent riblets in particle-laden turbulent boundary layer

Particle image velocimetry was employed to investigate the impact of convergent–divergent riblets on turbulent boundary layers in both clear water and liquid–solid two-phase flow fields containing 155 μm polystyrene particles. The turbulence statistics such as turbulence intensity and Reynolds stress were investigated. The spatial topology of spanwise vortex head and the development and evolution process of hairpin vortices were explored from Euler and Lagrange perspectives, respectively. Additionally, the particle distribution, concentration, and dispersion within the turbulent boundary layer were statistically analyzed. The results indicated that the boundary layer thickness, friction resistance, integrated turbulence intensity, and Reynolds stress were significantly lower on divergent riblet walls compared to convergent riblet walls. Notably, divergent riblets with a yaw angle of 30° exhibited the best drag reduction effect in both single-phase and two-phase flow fields. The addition of particles resulted in an increase in boundary layer thickness but effectively reduced turbulent fluctuations in the logarithmic region, enhancing drag reduction. This extended the drag reduction range of divergent riblets to a yaw angle of 45°, increasing the maximum drag reduction rate to 26.18%. Through spatial multi-scale local average structure function and finite-time Lyapunov exponent field analysis, it was found that the 30° divergent riblet wall significantly inhibited the development of vortex structures and reduced momentum exchange within the boundary layer. Conversely, the 30° convergent riblet wall had the opposite effect, while the particle phase inhibited the development of all wall turbulent structures. Analysis of particle concentration variations within different regions of the turbulent boundary layer revealed that as the normal height of the boundary layer increased, particle concentration gradually increased, and particle dispersion decreased accordingly. The analysis further showed that particle dispersion was mainly influenced by flow structures, whereas concentration was significantly affected by turbulence intensity. These findings elucidate the effect of the flow field on the particle phase and provide insights into the interaction mechanism between the flow field and particles.

Breaking barriers in passive sampling: The potential of PTFE membranes in the monitoring of hydrophilic micropollutants

Passive samplers are key tools to sample hydrophilic micropollutants in water. Two main approaches address the influence of hydrodynamics: (1) determining site-specific sampling rate (RS) by characterizing kw, the mass transfer coefficient of the water-boundary layer (WBL), and (2) reducing WBL impact using a diffusive material to control the uptake. The first requires calibration data and the second has only been achieved using fragile diffusive material. This study assesses the transfer of hydrophilic contaminants through polytetrafluoroethylene (PTFE; 30 µm thick), a new membrane material with lower sorption than commonly used polyethersulfone (PES). Combined for the first time in a Chemcatcher-like configuration, we calibrated the modified samplers for 44 micropollutants to provide RS – kw relationships for in-situ RS determination (approach 1). Micropollutants accumulated over 2000 times more on the sorbent than on PTFE. PTFE-based RS (0.027 to 0.300 L day-1) were 2.5 higher than previously reported with PES. Membrane property measurements (porosity, tortuosity) indicated that accumulation is primarily controlled by the membrane. Extrapolation indicated that using thicker PTFE membranes (≥ 100 µm) would shift uptake control entirely to the membrane in river conditions (approach 2). This finding could enable RS prediction based on contaminants properties, thus representing a significant advancement in passive sampling.

Complexity of Arctic Ocean water isotope (δ18O, δ2H) spatial and temporal patterns revealed with machine learning

The stable isotope compositions of water (δ18O, δ2H, deuterium-excess) are important tracers that help illuminate the changing Arctic water cycle and how Arctic-sourced water can influence lower latitudes. We present simultaneous boundary layer water vapor and ocean water isotope data that were measured continuously in the western Arctic Ocean. Sea surface water isotopes varied between the shallower continental Chukchi Shelf and the deeper Chukchi Borderlands to the north. The Chukchi Borderlands surface waters were less saline than the offshore Chukchi Shelf, as the Borderlands are influenced by greater sea ice cover and contribution of sea ice melt to surface freshwater. This greater contribution of sea ice melt resulted in lower deuterium-excess (δ2H − 8*δ18O) in surface water values in the deeper Chukchi Borderlands than on the shallower Chukchi Shelf. Additionally, the sea ice melt contributions to freshwater were less prominent than river runoff, but freshwater from both sources decreased substantially below 70 m depth in the Chukchi Borderlands. Our observed water isotope values provided the foundation for producing water isotope maps (isoscapes) based on remote sensing and machine learning which incorporate parameters that can influence ocean circulation and thus water isotopes (e.g., salinity, sea surface temperature, water depth). These isoscapes suggest spatial complexity in the distribution of stable water isotopes in the Arctic, including sharp gradients in the distribution of the isotopes in seawater that were studied. These isoscapes can be improved in future iterations, for example, with the availability of more spatially continuous, remotely sensed oceanic variables or continuous ship-based measurements to use as additional predictors. As a result, the generation of these isoscapes could become a useful tool for understanding the past, present, and future Arctic water cycle in the context of the global hydrologic cycle.

Insights Into the Flow Field and Performance of a Boundary Layer Pump

Abstract A flow field analysis of a realistic, integrated, multidisk boundary layer pump as is necessary for investigating the reasons for typically quoted low efficiencies in such pumps is described. The study focuses on the three-dimensional RANS solutions of a water boundary layer pump model created to replicate a design by Morris, 1973, which consists of 170 disks and a volute channel. A baseline study is performed to investigate the rotor-only performance after which a volute alone is separately simulated to identify the performance and losses in each as separate systems. Thereafter, an integrated model is characterized across mass flow rates and rotational speeds. The flow fields of all three models are discussed and the results of the integrated model are compared to the experimental data. The results from the model with the rotor only confirm the typically made claim that the efficiency of the rotor in a boundary layer pump possesses relatively high values which in this case is ∼87% at the design point, reinforcing results from previous studies that the rotor assembly is not the cause of inefficiency. The volute on its own indicated a hydraulic efficiency of around 97%. However, the integrated model yielded a rotor efficiency of around 74\% and an overall pump efficiency of 51% at the design point, clearly outlining the fact that the effect of the volute integrated with the rotor is the reason for both the rotor and pump efficiency degradation. The reason for this drop in efficiency is discussed in detail by highlighting the change in the flow topologies. The insights into the flow field and the identification of the reason for inefficiencies using a separated component analysis approach provide directions for avenues in which design improvements would need to be attempted.

Prediction of the wall pressure spectrum over a curved structure excited by a non-homogeneous turbulent boundary layer in water

In the present study, we introduce a volume approach based on the Poisson equation solved using a Green's function and a semi-analytical turbulence model in space domain. This model can be built from either a Reynolds-Averaged Navier-Stokes (RANS) simulation or an estimation of the boundary layer parameters. Predictions for the power spectral density of the wall pressure fluctuations are compared against measured data obtained for various flow conditions inside a cavitation tunnel. Two geometries are considered. First, we use a NACA 0012 hydrofoil of constant chord length to validate predictions for different flow velocities and angles of attack. Then, we consider a NACA 0009 hydrofoil with a spanwise varying chord length to investigate the contribution of three-dimensional effects.

Factors affecting diffusion of polar organic compounds in agarose hydrogel applied to control mass transfer in passive samplers.

Diffusive hydrogel-based passive sampler (HPS) based on diffusive gradients in thin films (DGT) is designed for monitoring polar organic contaminants in the aquatic environment. DGT technique controls the compound's overall uptake rate by adding a hydrogel layer of known thickness, which minimizes the importance of the resistive water boundary layer in the compound uptake process. In this work, we investigated several factors which may influence the diffusion of a range of aquatic contaminants in 1.5% agarose hydrogel. Diffusion in hydrogel was tested using the sheet stacking method. We demonstrated that a thin nylon netting incorporated into the diffusive hydrogel for mechanical strengthening does not significantly affect the diffusion of 11 perfluoroalkyl compounds. Further, we investigated the effect of pH in the range from 3 to 11 on the diffusion of a range of 39 aromatic amines (AAs)-36 aromatic, 2 aliphatic, and azobenzene in hydrogel. AAs were chosen as representatives of compounds with pH-dependent dissociation in water. Analysis of variance showed no significant difference in meandiffusion coefficient log D value at five pH values. The demonstration that the diffusion coefficient D and thus the sampling rate Rs are independent on pH simplifies the interpretation of data from field studies because we can neglect the influence of pH on the Rs. log D values (m2 s-1) of tested AAs ranged from to - 9.77 for 3,3'-dimethylbenzidine to - 9.19 for azobenzene. A negative correlation of log D with molar mass (log M) and molecular volume (log Vm) was observed (R = - 0.57 and - 0.56, respectively). The diffusion coefficient presents a critical parameter for the sampling rate estimation of HPS. Theoretical sampling rates Rs of AAs were calculated for a HPS using the average D values. TheoreticalRs values calculated for AAs at 22°C ranged from 29 mL day-1 for 3,3'-dimethylbenzidine to 106 mL day-1 for 2-aminopyridine. Our calculated values of Rs are in the same range as those already published for a range of low-molecular polar organic contaminants, which supports the possibility of deriving sampler performance parameters in the field from laboratory-derived diffusivity of analytes in hydrogel.

Performance comparison of three passive samplers for monitoring of polar organic contaminants in treated municipal wastewater

Over the past decades, several types of passive samplers have been developed and used to monitor polar organic compounds in aquatic environments. These samplers use different sorbents and barriers to control the uptake into the sampler, but their performance comparison is usually not well investigated. This study aimed to directly compare the performance of three samplers, i.e., the Polar Organic Chemical Integrative Sampler (POCIS), the Hydrogel-based Passive Sampler (HPS, an upscaled version of o-DGT), and the Speedisk, on a diverse suite of pharmaceuticals, per- and polyfluoroalkylated substances (PFAS), and pesticides and their metabolites. The samplers were deployed side-by-side in the treated effluent of a municipal wastewater treatment plant for different exposure times. All samplers accumulated a comparable number of compounds, and integrative uptake was observed for most compounds detected up to 28 days for POCIS, up to 14 days for HPS, and up to 42 days for Speedisk. In the integrative uptake phase, consistent surface-specific uptake was observed with a significant correlation between samplers (r ≥ 0.76) despite differences in sampler construction, diffusion barrier, and sorbent material used. The low sampling rates compared to the literature and the low estimated overall mass transfer coefficient suggests that the water boundary layer was the main barrier controlling the uptake for all samplers. Although all devices provided comparable performance, Speedisk overcomes POCIS and HPS in several criteria, including time-integrative sampling over a long period and physical durability.

Технология использования чернового концентрата в качестве минералов-носителей

Технология использования чернового концентрата в качестве минералов-носителей

Bio-geophysical feedback to climate caused by the conversion of Amazon Forest to soybean plantations

Over the past two decades, soybean cultivation has become one of the principal replacements for forests in the Brazilian Amazon. Previous studies showed that the conversion of forests into large-scale soybean farms has different effects on local and regional climate than other forms of land use, e.g., conversion to pasture. The bio-geophysical feedbacks that lead to changes in temperature and rainfall caused by the expansion of commodity crops is not fully understood, and this has implications for both modelling potential future climatic change and understanding its impact. Here we performed model simulations to characterize the feedback to climate caused by the replacement of Amazonian forests with soybean and pastures. Our results show that: when compared to deforestation caused by pastures, the conversion of forests into soybean plantations results in more pronounced changes in the atmospheric boundary layer. Because they are characterized by a period of the year with bare soil, soybean fields transmit more long-wave radiation to the atmosphere than pastures, leading to an increase in boundary layer average temperature by 2.4 K. Although soybean plantations tend to strengthen convective lifting, the decrease in boundary layer water vapor content plays a decisive role in reducing rainfall. Finally, we demonstrate that the climatic impacts associated with the replacement of forests by soybean is likely to be magnified with agricultural expansion along new frontiers in the northern and western regions of the Amazon basin due to a more pronounced reduction in water vapor content.

Comparative Analysis of the Effect of Native and Polymeric β-Cyclodextrins on the Solubility and Membrane Permeability of Baricitinib

A study is performed of the effect native and polymeric β-cyclodextrins have on the solubility and membrane permeability of baricitinib, a new generation immunomodulator. It is found that native and polymeric β-cyclodextrins exhibit the same solubilizing effect in relation to baricitinib, while their effect on the membrane permeability of the drug differs. The increased solubility of baricitinib is due to the formation of inclusion complexes that have the same stability but are enthalpy-entropy stabilized in native β-cyclodextrin and enthalpy stabilized in polymeric β-cyclodextrin. The effect cyclodextrins on baricitinib’s coefficients of permeability of through a model membrane is discussed in terms of complexation, changes in the viscosity of the medium, and the state of the water boundary layer near the membrane’s surface.

Investigation of the film-forming flooding mechanism of molecular deposition in tight oil reservoirs

Most of the oil fields in China have entered the stage of high-water-content development, which has become the primary means to improve the recovery rate of high-water-content oil fields by changing the injection agent. MDFFA membrane oil drive technology is a new type of tertiary oil recovery technology that uses an aqueous solution as the transfer medium; however, it is rarely applied in the field of tight oil reservoirs in China. In this study, molecular film-wall microgravity and water-wall microgravity were compared for tight reservoirs in the Shengli oilfield. It was concluded that the MDFFA dominates in competitive adsorption, breaks through and removes the hydrated layer, and finally adsorbs firmly on the pore wall to form a nanoscale ultrathin film. The application conditions of the MDFFA were also explored, and its wetting angle was tested. Further, the variation law of MDFFA adsorption was studied, and the mechanism of MDFFA drag reduction was explained in terms of reducing the boundary layer effect and water injection friction resistance. The natural cores procured from the Shengli tight oil field were analyzed for MDFFA membrane drive cores, and a reasonable injection concentration was selected. Through a series of mechanistic and experimental studies, we provided theoretical and technical references for the development of increased tight oil production.

The diurnal variation of wet bulb temperatures and exceedance of physiological thresholds relevant to human health in South Asia

Extreme heat is increasingly being acknowledged as a serious hazard to human health, through a combination of physiological responses to heat, expressed as dry and wet bulb temperatures, and personal factors. Here we present an analysis of the diurnal variability of dry and wet bulb temperatures using station data in South Asia during both regular and heatwave days. We find that diurnal cycles differ, with the daily maximum wet bulb temperature occurring several hours after the daily maximum dry bulb temperature. Using radiosonde profiles, we show that the timing and amplitude of the diurnal variability of wet bulb temperature can be explained by changes in boundary layer depths and water content. Physiological thresholds for uncompensable heat stress were exceeded even in the evenings, many hours after dry bulb temperature peaks. Cumulative exceedances occurred in 105 instances, corresponding to at least 300 hours of exposure to uncompensable heat stress in South Asia between 1995 and 2020. We conclude that physiologically relevant thresholds provide a more robust way to estimate health impacts, and that wet bulb temperature alone is insufficient as an indicator of hazardous heat.

Numerical study of the natural transition of water boundary layers over heated/cooled flat plates

The natural transition of water boundary layers on heated/cooled flat plates is investigated using numerical methods. The influences of wall temperature, oncoming flow velocity, and onco ming flow temperature on the transition are studied. Laminar basic flows are obtained by solving the Blasius equations, while water temperature is taken into consideration. Linear stability analyses of the basic flows are performed, and the transition positions are predicted using the eN method. The spectra of wall pressure fluctuations in the laminar region are also predicted. The results show that the heated wall produces a fuller velocity profile and a thinner boundary layer for the laminar flow and that a cooled wall causes the opposite effects. Consequently, the heated wall delays transition, while the cooled wall advances transition. As wall temperature increases, the effect of transition delay becomes stronger until the maximal delay effect occurs at an optimal wall temperature. Wall temperatures higher than the optimal value weaken the transition delay effect. This phenomenon of the heated wall is called transition reversal. A heated wall suppresses the wall pressure fluctuation, and a cooled wall has the opposite effect. The oncoming flow velocity has little influence on the non-dimensional transition position, while the oncoming flow temperature has a strong influence on it. At the same wall temperature, a higher oncoming flow temperature leads to a thicker boundary layer, stronger instability, and an earlier transition. A lower oncoming flow temperature leads to stronger sensitivity of the transition to the wall temperature.

Nanoclusters and sol–gel transition in water solutions of rigid-chain polymers

We describe a mechanism of pre-transition process near the sol-gel transition temperature in the sol-phase of water solutions of rigid-chain polymers. During this process the water boundary layer is disordered, and voids are formed in it. The variation of density of the hydroxypropyl methylcellulose with temperature is measured experimentally for temperatures between 25 and 80 °C. The experiment supports the proposed mechanism.

Influence of Electrodes Configuration on Hydraulic Characteristics of Constructed Wetland–Microbial Fuel Cell Systems Using Graphite Rods and Plates as Electrodes

Constructed wetland–microbial fuel cell coupling systems (CW–MFCs) have received significant academic interest in the last decade mainly due to the promotion of MFCs in relation to pollutants’ degradation in CWs. Firstly, we investigated the effect of hydraulic retention time (HRT) and electrode configuration on the flow field characteristics of CW–MFCs using graphite rods and plates as electrodes, as well as the optimization of electrode configuration using computational fluid dynamics (CFD) numerical simulation. The results showed that: (1) the apparent HRT was the most influential and decisive factor, with a contribution of over 90% for the average HRT of CW–MFCs; (2) anode spacing was the most influential factor for the hydraulic performance of CW–MFCs, with contributions of over 50% for water flow divergence and hydraulic efficiency (λ) and over 45% for effective volume ratio (e); (3) anode size was significant for e and λ, with a contribution of over 20%; (4) cathode position and cathode size had no statistically significant effect on the hydraulic performance of CW–MFCs. It was mainly through the blocking of water flows, flows around, compressing water flow channels and boundary layer separation that the MFC electrodes influenced the hydraulic characteristics of the flow field in CW–MFCs. Optimizing the flow field by optimizing the electrode configuration helped to facilitate electricity generation and pollutants’ removal in CW–MFCs. This study offers a scientific reference for improving the hydraulic performance of CW–MFCs, and it also provides a new research perspective for improving the wastewater treatment and electricity production performance of CW–MFCs.

Mass transfer characteristics of chiral pharmaceuticals on membrane used for polar organic chemical integrative sampler

Passive sampling technology has good application prospects for monitoring trace pollutants in aquatic environments. Further research on the sampling mechanism of this technology is essential to improve the measurement accuracy and extend the application scope of this approach. In this study, adsorption and permeation experiments were performed to investigate the sorption and mass transfer properties of five chiral pharmaceuticals at the enantiomeric level on polyethersulfone (PES) and polytetrafluoroethylene (PTFE) membranes used in a polar organic chemical integrative sampler. Batch adsorption experiments showed that the PES membrane had an adsorption phenomenon for most selected pollutants and an insignificant sorption behavior was observed for all selected pharmaceuticals on the PTFE membrane except for R(S)-fluoxetine. The diffusion coefficients of selected pharmaceuticals onto the PTFE membrane were approximately one order of magnitude higher than those onto the PES membrane. The permeation experiment indicated that under different hydraulic conditions, the change of the relative pollutant concentration through the PTFE membrane for the composite pollutant system was more obvious than that for the single pollutant system, and mass transfer hysteresis exists for both contaminant systems through PES membranes. Using the first-order equation or 3-component model to estimate the overall mass transfer coefficients, the results showed that the overall mass transfer coefficient values of pollutants in the composite pollutant system onto both membranes were higher than those in the single pollutant system. This parameter was mainly influenced by the synergistic effects of the multi-analyte interaction and diminished water boundary layers during the mass transfer process.

Ethylene vinyl acetate copolymer is an efficient and alternative passive sampler of hydrophobic organic contaminants. A comparison with silicone rubber

There is a growing demand for assessing the concentrations of Hydrophobic Organic Contaminants (HOCs) in aquatic environments, including Persistent Organic Pollutants (POPs). The hydrophobicity of POPs challenges their quantification in waters due to the sub-trace concentrations, especially when using conventional spot sampling. The results from the conventional samples are only a “snapshot” of the concentrations (if detected) at the specific sampling moment. Contrary, passive sampling provides average concentration levels over weeks or months from the quantification of accumulated pollutants during the deployment period. The present work compared ethylene vinyl acetate (EVA) and silicon rubber (SR) as monophasic passive samplers to measure dissolved concentrations of HOCs. Four classes of POPs were studied: (i) polychlorinated dibenzo-p-dioxins (PCDDs), (ii) polychlorinated dibenzofurans (PCDFs), (iii) polychlorinated biphenyls (PCBs), including the dioxin-like congeners, and (iv) the polybrominated diphenyl ethers (PBDEs). The polymer-water partition coefficients (Kpw), determined by the cosolvent and crossed calibrations, were, on average, one logarithmic unit larger in EVA than in the SR. The diffusion coefficients (Dp) estimated by the “film-stacking” method were, on average, two orders of magnitude smaller in the EVA than in the SR. For both polymers, the theoretical model of mass transfer resistance confirmed that the water boundary layer controlled the absorption, thus allowing the use of Performance Reference Compounds (PRCs) to estimate the in-situ sampling rates.Larger Kpw's in EVA may be an advantage because they imply longer time scales to reach equilibrium, higher absorption capacities and hence a higher absorbed contaminant mass, especially for compounds that reach equilibrium relatively faster (log Kow < 5). In addition, the longer times to attain equilibrium for EVA maintain this sampler longer in the linear phase of absorption, and the time-weighted average concentration may only be assessed in this phase when the compounds have not yet reached equilibrium.

An improved Chemcatcher-based method for the integrative passive sampling of 44 hydrophilic micropollutants in surface water – Part A: Calibration under four controlled hydrodynamic conditions

When monitoring water quality with hydrophilic integrative passive sampling devices, it is crucial to use accurate sampling rates (RS) that account for exposure conditions such as hydrodynamics. This study aims at calibrating Chemcatcher-like passive samplers – styrene-divinylbenzene reverse phase sulfonate (SDB-RPS) extraction disk covered by a polyethersulfone (PES) membrane – at four water flow velocities (5 to 40 cm s−1) in a channel system. First, the four hydrodynamic conditions were characterized by measuring the mass transfer coefficients of the water boundary layer (kw) at the surface of the samplers using the alabaster dissolution method. Then, fifty-six samplers were deployed in the channels and exposed for 7 different intervals varying from 1 to 21 days. Thus, RS were determined at four different kw for 44 hydrophilic compounds, ranging from 0.015 to 0.115 L day−1. Relationships were established between kw and RS using models for mixed rate control by the membrane and the water boundary layer. The estimated parameters of those relationships are suitable for the determination of accurate RS when kw is measured in situ, for example by co-deploying silicone disks spiked with performance and reference compounds (PRC) as implemented in Part B.

Using of large eddy simulation model for a spatially developing turbulent natural convection boundary layer in water along a side-heated vertical wall with high Rayleigh number ([formula omitted

To further understand the turbulent natural convection in the residual heat removal process of a nuclear reactor in accidental condition, a spatially developing natural convection boundary layer along a side-heated vertical plane in water is simulated with Large Eddy Simulation (LES) strategy. The maximum modified Rayleigh number (Ra*=Ra×Nu) reaches 8×1014 with the uniform heat flux input (≈10000W/m2). In particular, the buoyancy driven flow is simulated by an incompressible flow solver with Boussinesq approximation. The Wall Adaptive Local Eddy (WALE) model is selected as the sub-grid scale model for the LES simulation. After comparing with available measurements, it is found that reasonable agreement has been achieved in wall temperature distribution along the heated wall, heat transfer rate as well as mean temperature, mean velocity and turbulent statistics in the boundary layer. The detailed vortex structure and velocity spectra in the boundary layer corresponding to different regime are clearly demonstrated. It is shown that the transition process in the boundary layer can be accurately presented with the refined mesh (x+≈0.1) in the near wall region. To be more specific, the appeared ordered vortex street in the transition stage and the estimated critical Rayleigh number for turbulence inception correspond well to previous experimental observations. The significant effect of early transformation of two-dimensional (2D) linear Tollmien–Schlichting waves on the heat transfer is also proved. It is expected that current study can enhance the understanding of turbulent boundary layer at high heat flux and high Rayleigh number.

Understanding plasticiser leaching from polystyrene microplastics.

Plastic pollution in our oceans is of growing concern particularly due to the presence of toxic additives, such as plasticisers. Therefore, this work aims to develop a comprehensive understanding of the leaching properties of plasticisers from microplastics. This work investigates the leaching of phthalate acid ester (dioctyl terephthalate (DEHT) and diethylhexyl phthalate (DEHP)) and diphenol (bisphenol A (BPA) and bisphenol S (BPS)) plasticisers from polystyrene (PS) microplastics (mean diameter = 136 μm to 1.4 mm) under controlled aqueous conditions (temperature, agitation, pH and salinity). The leaching behaviours of plasticised polymers were quantified using gel permeation chromatography, high performance liquid chromatography and thermal gravimetric analysis, and the particle's plasticisation characterised using differential scanning calorimetry. Leaching rates of phthalate acid ester and diphenol plasticisers were modelled using a diffusion and boundary layer model, whereby these behaviours varied depending on their plasticisation efficiency of PS, the size of the microplastic particle and the surrounding abiotic conditions. Leaching behaviours of DEHT and DEHP were strongly influenced by the microplastic-surface water boundary layer properties, thus wave action (i.e., water agitation) increased the leaching rate of these plasticiser up to 66 % over 21-days, whereas BPA and BPS plasticisers displayed temperature- and size-dependent leaching and were limited by molecular diffusion throughout the bulk polymer (i.e., the microplastic). This information will improve predictions of plasticiser concentration (both that remain in the plastic and released into the surrounding water) at specific time points during the lifetime of a plastic, ultimately ensuring greater accuracy in the assessment of toxicity responses and environmental water quality.