Computational assessment of hexadecane freezing by equilibrium atomistic molecular dynamics simulations

Iliev, Stoyan; Tsibranska, Sonya; Ivanova, Anela; Denkov, Nikolai

doi:10.1016/j.jcis.2023.01.126

Cited by 10 publications

(4 citation statements)

References 71 publications

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“…These droplets were stabilized by surfactants with hydrophobic tails that were similar in length to or longer than the alkane chain. In contrast, no such phases were detected for bulk C 16 in our experiments, whereas earlier studies indicated the formation of transient rotator phase in bulk hexadecane in approximately 10% of the cooling experiments. , The orthorhombic rotator phase structure observed experimentally in hexadecane emulsion droplets, stabilized by appropriate long-chain surfactants, has been reproduced recently by molecular dynamics simulations. , …”

Section: Introductioncontrasting

confidence: 52%

“…9,21 The orthorhombic rotator phase structure observed experimentally in hexadecane emulsion droplets, stabilized by appropriate long-chain surfactants, has been reproduced recently by molecular dynamics simulations. 22,23 Alkane mixing is also known to enhance the stability of the rotator phases. This effect is usually explained with a reduction in the interlayer coupling interaction, combined with an increase in the lamellar surface roughness and void volume.…”

Section: Introductionmentioning

confidence: 99%

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Structure of Rotator Phases Formed in C₁₃–C₂₁ Alkanes and Their Mixtures: In Bulk and in Emulsion Drops

Cholakova,

Pantov,

Tcholakova

et al. 2023

Crystal Growth & Design

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Crystallization of alkane mixtures has been studied extensively for decades. However, the majority of the available data consider the behavior of alkanes with chain length of 21 C atoms or more. Furthermore, important information about the changes of the unit cell structure with the temperature is practically absent. In this work, the phase behavior of several pure alkanes C n H 2n+2 , with n ranging between 13 and 21, and their binary, ternary, or multicomponent equimolar mixtures are investigated by X-ray scattering techniques. Both bulk alkanes and oil-in-water emulsions of the same alkanes were studied. The obtained results show the formation of mixed rotator phases for all systems with chain length difference between the neighboring alkanes of Δn ≤ 3. Partial demixing is observed when Δn = 4, yet the main fraction of the alkane molecules arranges in a mixed rotator phase in these samples. This demixing is suppressed if an alkane with an intermediate chain length is added to the mixture. Interestingly, a steep temperature dependence of the interlamellar spacing in mixed rotator phases was observed upon cooling to temperatures down to 10 °C below the melting temperature of the mixture. The volumetric coefficient of thermal expansion of the rotator phases of mixed alkanes (α V ≈ 2 × 10 −3 °C−1 ) is around 10 times bigger compared to that of the rotator phases of pure alkanes. The experiments performed with emulsion drops containing the same alkane mixture while stabilized by different surfactants showed that the surfactant template also affects the final lattice spacing which is observed at low temperatures. In contrast, no such dependence was observed for drops stabilized by the same surfactant while having different initial diameters; in this case, only the initial temperature of the crystallization onset was affected.

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Section: Introductioncontrasting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Structure of Rotator Phases Formed in C₁₃–C₂₁ Alkanes and Their Mixtures: In Bulk and in Emulsion Drops

Cholakova,

Pantov,

Tcholakova

et al. 2023

Crystal Growth & Design

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“…Recently, the Williams force field has been optimized to accurately reproduce melting points and transport properties in addition to crystal-rotator phase transitions. 27 Iliev et al 34 utilized long simulation times of up to 500 ns to study nucleation and crystallization of C 16 from the liquid, both in bulk and at the water/C 16 interface with surfactant, using the CHARMM36 force field. This resulted in systems containing many small crystallites, with the tilt angle of the molecules (relative to the crystallite plane) varying considerably between them.…”

Section: ■ Introductionmentioning

confidence: 99%

Structure of the Hexadecane Rotator Phase: Combination of X-ray Spectra and Molecular Dynamics Simulation

Burrows,

Lin,

Cholakova

et al. 2023

J. Phys. Chem. B

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Rotator phases are rotationally disordered plastic crystals, some of which can form upon freezing of alkane at alkane–water interfaces. Existing X-ray diffraction studies show only partial unit cell information for rotator phases of some alkanes. This includes the rotator phase of n-hexadecane, which is a transient metastable phase in pure alkane systems, but shows remarkable stability at interfaces when mediated by a surfactant. Here, we combine synchrotron X-ray diffraction data and molecular dynamics (MD) simulations, reporting clear evidence of the face-centered orthorhombic RI rotator phase from spectra for two hexadecane emulsions, one stabilized by Brij C10 and another by Tween 40 surfactants. MD simulations of pure hexadecane use the recently developed Williams 7B force field, which is capable of reproducing crystal-to-rotator phase transitions, and it also predicts the crystal structure of the RI phase. Full unit cell information is obtained by combining unit cell dimensions from synchrotron data and molecular orientations from MD simulations. A unit cell model of the RI phase is produced in the crystallographic information file (CIF) format, with each molecule represented by a superposition of four rotational positions, each with 25% occupancy. Powder diffraction spectra computed using this model are in good agreement with the experimental spectra.

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“…Several structural and chemical dependencies of the freezing point from all materials included in a PCS, such as surfactant, nucleation agent, and PCM, itself can be investigated. [14,[29][30][31] This enables the search for highly efficient nucleation starters for subsequent experimental verification. [32] For immersed heat exchanger systems, the PCM is filled in a storage tank.…”

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confidence: 99%

Thermal Storage: From Low‐to‐High‐Temperature Systems

et al. 2023

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Different technologies of cold and heat storages are developed at Fraunhofer ISE. Herein, an overview of ongoing research for sensible and latent thermal energy storages is provided. Phase change emulsions are developed supported by molecular dynamic simulations. A narrow temperature range of the phase change is crucial for the applicability. By the simulations, a nucleation additive is identified that reduces supercooling by up to 9 K. The long‐term stability of phase change material is investigated by degradation experiments. Thermal cycling and ageing of materials at elevated temperature are applied. The change of melting enthalpy and characteristic temperatures are evaluated. Among erythritol, adipic acid, and myristic acid, the smallest degradation is observed for the latter. For sensible storage, the reduction of thermal oil by low‐cost filler materials and their compatibility is investigated at elevated temperature. It can be concluded that the materials are compatible up to 320 °C. At the component level, different macroencapsulations and immersed heat exchangers are tested for phase change materials. The investigated configurations achieve similar values of thermal power during (dis‐)charge. Compared to water as storage medium, the capacity increases by a factor of 2.2 and 4.1 for the macroencapsulation and the immersed heat exchanger, respectively.

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Computational assessment of hexadecane freezing by equilibrium atomistic molecular dynamics simulations

Cited by 10 publications

References 71 publications

Structure of Rotator Phases Formed in C₁₃–C₂₁ Alkanes and Their Mixtures: In Bulk and in Emulsion Drops

Structure of Rotator Phases Formed in C₁₃–C₂₁ Alkanes and Their Mixtures: In Bulk and in Emulsion Drops

Structure of the Hexadecane Rotator Phase: Combination of X-ray Spectra and Molecular Dynamics Simulation

Thermal Storage: From Low‐to‐High‐Temperature Systems

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Computational assessment of hexadecane freezing by equilibrium atomistic molecular dynamics simulations

Cited by 10 publications

References 71 publications

Structure of Rotator Phases Formed in C13–C21 Alkanes and Their Mixtures: In Bulk and in Emulsion Drops

Structure of Rotator Phases Formed in C13–C21 Alkanes and Their Mixtures: In Bulk and in Emulsion Drops

Structure of the Hexadecane Rotator Phase: Combination of X-ray Spectra and Molecular Dynamics Simulation

Thermal Storage: From Low‐to‐High‐Temperature Systems

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Structure of Rotator Phases Formed in C₁₃–C₂₁ Alkanes and Their Mixtures: In Bulk and in Emulsion Drops

Structure of Rotator Phases Formed in C₁₃–C₂₁ Alkanes and Their Mixtures: In Bulk and in Emulsion Drops