Molecular dynamics simulations of diffusion and clustering along critical isotherms of medium-chain <i>n</i>-alkanes

Mutoru, J. Wambui; Smith, William R.; O’Hern, Corey S.; Firoozabadi, Ali Dehghan

doi:10.1063/1.4773282

Cited by 12 publications

(4 citation statements)

References 35 publications

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“…Typically, the agreement is better than 1% for all mixture compositions. The diffusion coefficients of pure components were also reported and compared with experimental and some simulation data of other force fields available in [73]. As seen from Table 4.3, the self diffusion coefficients of nC 5 and nC 10 obtained from this work were in very good agreement with the experimental data with an error of 8.1% and 3.42%, respectively.…”

Section: Validation Of the Force Field Modelsupporting

confidence: 64%

“…Note that the data extracted from Ref. [73] were interpolated to get values at the same temperature of 300.15 K and the statistical errors for experimental densities and self diffusion coefficients were estimated from the standard deviation from the mean using uncorrelated data [74]. The continuity of the three gradients indicates that the system behavior, despite strong thermal gradients (highest value of 1.79 × 10 1 0 K/m attained for x C 10 = 0.2), is still in the domain of linear response.…”

Section: Validation Of the Force Field Modelmentioning

confidence: 99%

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Enhanced Molecular Dynamics Approach for Thermal Transport Phenomena in Complex Systems

Antoun¹

2021

Preprint

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This thesis introduces an enhanced Molecular Dynamics (MD) approach, blended with fine-tuned Force Field (FF) models to reflect more realistic experimental conditions and achieve a precise representation of the atomic interactions in complex systems. Firstly, an enhanced MD algorithm consisting of an upgraded non-equilibrium integration scheme, namely eHEX, coupled with an augmented TraPPE-UA force field, was generated and put to use to predict Soret effect in a binary mixture: n-pentane/n-decane. The results were compared to other MD approaches and validated with respect to benchmarked experimental data. The suggested method showed a closer agreement with experimental data than the previous MD findings. The reinforced potential field (TraPPE-UA) was capable of reflecting the real molecular interactions between the hydrocarbons and reproduce the liquid mixture properties at different conditions. Moreover, the extended HEX method succeeded in conserving the system’s overall energy with minor fluctuations and attaining a stationary state, ensuring the precision of the integration scheme and the satisfaction of local equilibrium. Secondly, the performance of the previously proposed approach was further studied to test its performance on a ternary mixture of methane/n-butane/n-dodecane at five different compositions. Thermodiffusion separation ratio of each component was assessed at 333.15 K and 35 MPa, and compared to the experimental data as well as 3 other MD models from the literature. A good qualitative agreement between the experimental data and the MD model observed in this work was observed, displaying the least deviation when compared to the other MD approaches. The method was capable of adequately representing the physics behind the thermodiffusive separation and deepening the microscopic understanding of the segregation process in a ternary mixture undergoing large thermal gradients. Put differently, the approach elucidates the relative contribution of the cross-interactions found between the unlike species in the mixture and their corresponding composition. Next, an enhanced MD approach was also presented to predict the dynamics and thermophysical properties of suspended γ-alumina nanoparticles (NPs) in acidic aqueous solutions. The previous MD work have unveiled numerous impediments in terms of reproducing the thermal transport phenomena in nanofluids. A hybrid potential field, comprised of refined orce field models (ClayFF and SPC/E), was implemented to allow a precise integration of the nanoscale phenomena into the dynamics and structure of charged alumina NPs, thereby bridging the challenging gap between the solid-liquid interfacial chemistry and the overall thermodynamic properties. The original CLAYFF was augmented to properly account for the energy and momentum transfer between the water molecules and the positively charged NPs, while keeping the number of parameters small enough to allow modeling of a relatively large nanofluidic system.The results were in good agreement with the experimental data. An increase of the NPs volumetric concentration (φ) lead to the enhancement of thermal conductivity along with an increase of viscosity. The results demonstrate the crucial role played by the repulsive electrostatic forces yielding well-dispersed NP suspensions, specially at low φ. The post analysis of Mouromtseff number demonstrated that at lower φ, the system show a higher propensity for stability and enhancement for φ less than 2%, specially at high temperatures. On the contrary, for volumetric concentrations higher than 2%, the system thermal performance deteriorates which is expected due to the fact that the system exhibit a critical condition of aggregation and clogging. With all of the above findings in mind, the MD framework presented in this thesis represents an improved step towards a precise and computationally balanced MD modelling that bridges the relation between molecular signatures and macroscopic features, capable of overcoming the shortcomings present in mainly two emerging thermal applications: 1) Soret effect in hydrocarbon mixture and 2) thermal transport of alumina-water nanofluids.

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Section: Validation Of the Force Field Modelsupporting

confidence: 64%

Section: Validation Of the Force Field Modelmentioning

confidence: 99%

Enhanced Molecular Dynamics Approach for Thermal Transport Phenomena in Complex Systems

Antoun¹

2021

Preprint

View full text Add to dashboard Cite

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“…On the other hand, the situation with respect to dynamics is relatively poor. Simulation studies, that helped achieving the objective for the static phenomena, gained momentum in the context of dynamic critical phenomena only recently [25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Such a status is despite the fact that adequate information on the equilibrium transport phenomena is very much essential for the understanding of even nonequilibrium phenomena like the kinetics of phase transitions [9,39].…”

Section: Introductionmentioning

confidence: 99%

Finite-size scaling study of dynamic critical phenomena in a vapor-liquid transition

Midya

Das

2017

The Journal of Chemical Physics

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Via a combination of molecular dynamics (MD) simulations and finite-size scaling (FSS) analysis, we study dynamic critical phenomena for the vapor-liquid transition in a three dimensional LennardJones system. The phase behavior of the model has been obtained via the Monte Carlo simulations. The transport properties, viz., the bulk viscosity and the thermal conductivity, are calculated via the Green-Kubo relations, by taking inputs from the MD simulations in the microcanonical ensemble. The critical singularities of these quantities are estimated via the FSS method. The results thus obtained are in nice agreement with the predictions of the dynamic renormalization group and mode-coupling theories.

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“…Liquid hydrocarbons interact primarily through dispersion and weak electrostatic forces. 42,[53][54][55] It is possible that these interactions are simply not strong enough to exert an observable influence on the energy levels of the unoccupied orbital states of the molecule that are probed in the X-ray experiment. However, the increased density in the liquid phase should result in inhomogeneous, collisional broadening that should be clearly evident in the liquid spectrum at the high resolution of the present X-ray experiments.…”

Section: Resultsmentioning

confidence: 99%

Electrokinetic detection for X-ray spectra of weakly interacting liquids: n-decane and n-nonane

Lam

Shih

Smith

et al. 2014

The Journal of Chemical Physics

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The introduction of liquid microjets into soft X-ray absorption spectroscopy enabled the windowless study of liquids by this powerful atom-selective high vacuum methodology. However, weakly interacting liquids produce large vapor backgrounds that strongly perturb the liquid signal. Consequently, solvents (e.g., hydrocarbons, ethers, ketones, etc.) and solutions of central importance in chemistry and biology have been inaccessible by this technology. Here we describe a new detection method, upstream detection, which greatly reduces the vapor phase contribution to the X-ray absorption signal while retaining important advantages of liquid microjet sample introduction (e.g., minimal radiation damage). The effectiveness of the upstream detection method is demonstrated in this first study of room temperature liquid hydrocarbons: n-nonane and n-decane. Good agreement with first principles’ calculations indicates that the eXcited electron and Core Hole theory adequately describes the subtle interactions in these liquids that perturb the electronic structure of the unoccupied states probed in core-level experiments.

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Molecular dynamics simulations of diffusion and clustering along critical isotherms of medium-chain n-alkanes

Cited by 12 publications

References 35 publications

Enhanced Molecular Dynamics Approach for Thermal Transport Phenomena in Complex Systems

Enhanced Molecular Dynamics Approach for Thermal Transport Phenomena in Complex Systems

Finite-size scaling study of dynamic critical phenomena in a vapor-liquid transition

Electrokinetic detection for X-ray spectra of weakly interacting liquids: n-decane and n-nonane

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