Alkane Chain Length Research Articles

Effect of gas type on properties of anionic surfactant foam system

The foam drainage technique is considered to be a promising measure for solving the problem of liquid accumulation in natural gas wells and gathering pipelines. However, differences in gases can greatly affect the performance of surfactant foam, thus limiting the application of this technology. To elucidate the mechanism of natural gas components influencing foam properties, the interfacial properties of hydrocarbon gas-surfactant-water system were analyzed thermodynamically and kinetically by combining molecular dynamics simulations and foaming experiments. The results show that with the increasing alkane chain length, the foaming volume and half-life of the foam are gradually rising, while the gas–liquid interfacial tension is decreasing, which is consistent with the results of molecular dynamics simulations. Compared with air, hydrocarbon gases are more beneficial for foam generation and stabilization. The interfacial adsorption of alkane molecules and the interaction between alkanes and surfactants are the main factors affecting the interfacial tension and film stability of different systems.

Effect of oil structure on adsorption behavior of emulsifier at the oil-polyol interface and the emulsion features

The aim of this study was to investigate the effect of oil structure on the dynamic adsorption behavior of emulsifier at the oil-polyol interface and the corresponding emulsion feature. Glycerol was used as the representative polyol, and the emulsifier was Polyglyceryl-2 Dipolyhydroxystearate (PGPH). Three kinds of alkanes and three kinds of ester oils were chosen for investigation. Firstly, the properties of each oil were studied by measuring surface tension (σ), interfacial tension with glycerol (γ0), and affinity between oils and PGPH. The results indicated that there was little difference in the fundamental characteristics of oils, with the exception of GTCC. Due to its triglyceride structure, GTCC exhibited similar polarity to glycerol, resulting in low interfacial tension and a strong affinity with PGPH. Secondly, the interfacial critical micelle concentration (CMCIFT), saturation adsorption amount (Γ∞), Langmuir constant (κ) and minimum molecular area (Amin) of PGPH were obtained by measuring the dynamic interfacial tension of PGPH adsorption at different oil-glycerol interfaces. The experimental results indicate that for alkanes, the longer the alkane chain length and the more the number of branch chains, the higher the emulsifier Γ∞ at the interface, leading to improved emulsion stability. In ester oils, the greater the affinity between the oil and glycerol, resulting in the lower the initial interfacial tension, a smaller Γ∞ and consequently smaller emulsion particle size. However, this also led to poor emulsion stability. Finally, Pearson correlation analysis was conducted between oil properties, adsorption parameters and emulsion size and stability. The results indicated that for alkanes, there was a negative correlation between particle size and emulsion stability with surface tension and Γ∞. In ester oils, there was a strong positive correlation between particle size and interfacial tension as well as κ. Additionally, the creaming of emulsions showed a strong negative correlation with interfacial tension and Γ∞.

Quantum chemical modeling of alkane 2D monolayer formation on graphene

The paper presents a quantum chemical approach for assessment of the thermodynamic parameters of association for alkanes CnH2n+2 (n = 6–14) and polyaromatic hydrocarbons (PAH) of the coronene series as model structures of the graphene surface within the framework of semiempirical methods. The enthalpy, entropy and Gibbs energy of formation and binding for alkanes with PAH were calculated using the PM3 and PM6-DH2 methods. It is shown that an adequate description of the interactions in the regarded complexes requires the use of PM6-DH2 method, since it contains corrections for dispersion interactions and hydrogen bonds. The parallel orientation of the alkane molecule relative to the coronene plane is proved to be more energetically preferable than perpendicular one, which is consistent with experimental data.Intermolecular C–H/π interactions are revealed to be crucial in the 2D film formation of alkanes on graphene/graphite. While interactions between alkane molecules make a destabilizing contribution due to the implementation of energetically unfavorable types of intermolecular CH/HC interactions. This stipulates a threshold chain length of alkanes capable of film formation on the graphene/graphite surface at standard temperature: 14 and 19 carbon atoms for parallel and perpendicular oriented alkanes, respectively. The obtained threshold values of the alkane chain length, as well as the geometric parameters of their orientation in 2D monolayers on the graphene/graphite surface are consistent with available experimental data.

Short- and medium-chain chlorinated paraffins in surface sediment from Lake Ontario.

Concentrations of short- and medium-chain chlorinated paraffins (SCCPs and MCCPs) were analyzed and investigated in surficial sediment collected in 2018 from ten different nearshore sites in Lake Ontario and the St. Lawrence River influenced by inputs from varying urban and historical land uses. Sites were grouped into two categories of tributary and lake according to their location. Results show that tributary sites had higher concentrations of total chlorinated paraffin (CP) than lake sites. Humber Bay, a lake site, had the highest total CP concentration (55,000ng/gTOC) followed by Humber River, a tributary site (50,000ng/gTOC). The lowest concentrations were found in eastern Lake Ontario and Lake St. Francis in the St. Lawrence River (540ng/gTOC). Higher concentrations of chlorinated paraffins (CPs) were found where runoff and wastewater inputs from urban areas, current industrial activities, and population were the greatest. Levels of MCCPs were higher than SCCPs at all sites but one, Lake St. Francis. Among the SCCPs, C13 and among the MCCPs C14 were the dominant chain length alkanes, with C14 being the highest among both groups. The SCCPs and MCCPs profiles suggest that they can be used to distinguish between sites impacted by local sources vs. sites impacted by short-/long-range transport of these chemicals.

Rheological Behaviors and Fractional Viscoelastic Modeling of Glucopone (APG)/Water/Hydrocarbons Solutions

The aims of this work are to study the rheological behaviors of a microemulsion of Glucopone–water–hydrocarbon systems and to use a fractional model to describe several experimental results of these systems. Four different types of hydrocarbons were considered. The frequency dependent storage, G′, and loss modulus, G″, were investigated below the critical strain. The critical strain was found to decrease as the alkane chain lengths increased, while the opposite behavior was observed for zero shear viscosity, η0. Most of the microemulsions exhibited stable elastic fluid behavior (G′ > G″) below 10 rad s−1 angular frequency. For all systems, elastic modulus values were found to be greater than loss modulus in the frequency range studied, indicating more elastic behaviors. Shear-thinning behaviors were observed, and the complex viscosity decreased with an increase in hydrocarbon chain lengths. The effects of hydrocarbon types on the rheological behaviors were more profound in the dodecane systems which showed maximum values of G′ and η0. The Friedrich–Braun model was introduced and was used to describe several experimental results on Alkyl polyglocoside solutions. Fractional rheology successfully described the viscoelastic phenomena in Glucopone surfactant solutions and the comparisons between the experimental results and the theoretical predictions were found to be satisfactory.

Investigation of Alkane-Assisted dodecylamine on flotation desilication of magnesite Tailings: Molecular dynamics simulations and model optimization

Investigating the reverse flotation desilication process of magnesite tailings (MT) holds substantial merit in the context of magnesium metal recovery from solid waste. However, scant attention has been devoted to exploring the influence of the carbon chain length of diverse alkanes on the reverse flocfloatation desilication of MT. This research systematically delved into the selective adsorption behavior exhibited by dodecylamine (DDA) and its compound collectors on the surfaces of quartz and magnesite. As the carbon chain length of alkanes increases, the efficacy of reverse flotation desilication of MT diminishes. Under optimized conditions, the concentration of MgO in the concentrate registers a 0.93% increment, accompanied by a 2.05% reduction in SiO2 content. The optimal MgO grade attains 42.68%. The augmenting carbon chain length of alkanes leads to a decline in the dispersibility of the compound collector and a reduction in the diffusion coefficient of the monolayer film at the alkane/water interface. The compound collector, comprising n-heptane and DDA, manifests a noteworthy synergistic promotion effect on the flotation desilication of MT. This effect reduces the multilayer adsorption of DDA, promotes more hydrogen bonding formation, and favors DDA adsorption on the quartz surface over magnesite. Consequently, issues related to froth entrapment and poor selectivity are alleviated. Longer alkane chains in the compound collectors result in a stronger van der Waals force effect between the carbon chains. This effect causes DDDA to slide more easily on the quartz surface, which is not conducive to enhancing the hydrophobicity of the surface. Furthermore, alkane-induced hydrophobic flocculation increases the floccules size of quartz, enhancing the likelihood of bubble-particle adhesion. This investigation elucidates the molecular-level mechanism underlying alkane hydrophobic flocculation with varying chain lengths, contributing a theoretical foundation and technical support for the large-scale MT management and the sustainable production of magnesium metal.

Study on the Effect of Alkane Chain Length on the Extraction of Ethyl Acrylate from Aqueous Solution and Correlation of Thermodynamic Model

Study on the Effect of Alkane Chain Length on the Extraction of Ethyl Acrylate from Aqueous Solution and Correlation of Thermodynamic Model

Effect of line tension on domain formation of fluorinated compounds at alkane/water interface

Condensed domain formation of fluorinated compounds (alcohol and ester) in adsorbed films at alkane/water interfaces was investigated by interfacial tensiometry, X-ray reflectometry, and BAM observation. The results obtained are explained by the effects of contact energy and dipole-dipole interaction, which are competitive contributions to the line tension acting at the domain boundary. Estimation of the two contributions indicated that the former is more dominant than the latter for the domain formation. In the adsorbed films of fluorinated alcohol, F8H2OH, at alkane/water interfaces, the domain formation was suppressed with increasing alkane chain length due to an increase in contact energy. The mixing of hybrid alcohol with fluorocarbon and hydrocarbon chains of the same carbon number, F6H6OH, in adsorbed film reduces contact energy. This stabilizes the dispersion of many domains with small size. On the other hand, when F8H2OH molecules are mixed with a cationic surfactant, C12TAB, in the adsorbed film, an attractive dipole-ion interaction between the hydrophilic groups relaxes the repulsive dipole-dipole interaction between F8H2OH molecules, resulting in the formation of domains with smooth boundary and large size. Furthermore, fluorinated ester, FC12Me molecules form flower shaped domains with intricate boundary mainly due to a larger dipole moment of FC12Me than F8H2OH.

Regulation of Nontraditional Intrinsic Luminescence (NTIL) in Hyperbranched Polysiloxanes by Adjusting Alkane Chain Lengths: Mechanism, Film Fabrication, and Chemical Sensing.

Biocompatible polymers with nontraditional intrinsic luminescence (NTIL) possess the advantages of environmental friendliness and facile structural regulation. To regulate the emission wavelength of polymers with NTIL, the alkane chain lengths of hyperbranched polysiloxane (HBPSi) are adjusted. Optical investigation shows that the emission wavelength of HBPSi is closely related to the alkane chain lengths; namely, short alkane chains will generate relatively long-wavelength emission. Electronic communication among functional groups is responsible for the emission. In a concentrated solution, HBPSi molecules aggregate together due to the strong hydrogen bond and amphiphilicity, and the functional groups in the aggregate are so close that their electron clouds are overlapped and generate spatial electronic delocalizations. HBPSi with shorter alkane chains will generate larger electronic delocalizations and emit longer-wavelength emissions. Moreover, these polymers show excellent applications in the fabrication of fluorescent films and chemical sensing. This work could provide a strategy for regulating the emission wavelengths of unconventional fluorescent polymers.

Giant room-temperature electrical switching effects in water-in-oil emulsions

Thermally-triggered electrical switching materials are of urgent demand for developing novel temperature sensors, overheat protection circuits, thermal controllers, battery management systems against overheating, etc. Here, we report a water-in-oil emulsion system with giant electrical switching ratios at room temperature prepared by a simple and efficient method. The temperature-sensitive phase transition process of alkanes as the oil phase causes the formation and collapse of conductive paths in the emulsion, resulting in electrical switching ratios of up to 6 orders of magnitude. The emulsions have good thermal cycle stability, and the switching ratio remains essentially unchanged after 100 cycles. The switching temperature can be easily adjusted by using alkanes of various chain lengths. In addition, the similar electrical switching effect is observed in four emulsions containing different neutral salts, ensuring the tunability and versatility of the system. The electrical switching emulsions offer a promising avenue to developing future high-performance, energy-saving, and low-cost electrical switching systems.

The effects of sub/supercritical conditions on the spray interface characteristics of alkane fuel

ABSTRACT Alkane fuels are widely used in engines. The spray characteristics in supercritical environments are very different than in subcritical environments, and supercritical environments significantly impact the formation of the gas mixture in the engine. In this paper, the spray images of n-heptane and n-tetradecane in subcritical (500K-2MPa) and supercritical (700K-4MPa, 800K-6MPa) environments were obtained on the constant volume spray test platform. The effects of the supercritical environment and carbon chain length of alkane fuel on spray characteristic parameters were investigated. The results showed that the carbon chain length and ambient pressure are the main factors of penetration. The ambient pressure is the main factor of the spray cone angle and the spray non-liquid layer thickness. Compared with n-heptane, in the 500K-2MPa (subcritical) environment, the cone angle of n-tetradecane was reduced by 2°, the penetration was increased by 10 mm, and the spray non-liquid layer thickness was reduced by about 1 mm. In the 800K-6MPa (supercritical) environment, the cone angle of n-tetradecane was increased by 2°, the penetration was increased by 10 mm, and the spray non-liquid layer thickness was increased by about 1.2 mm. In addition, the calculation model of alkane fuel spray penetration in sub/supercritical environments was modified and achieved 95% prediction accuracy.

Structure and mechanism of the alkane-oxidizing enzyme AlkB

Alkanes are the most energy-rich form of carbon and are widely dispersed in the environment. Their transformation by microbes represents a key step in the global carbon cycle. Alkane monooxygenase (AlkB), a membrane-spanning metalloenzyme, converts straight chain alkanes to alcohols in the first step of the microbially-mediated degradation of alkanes, thereby playing a critical role in the global cycling of carbon and the bioremediation of oil. AlkB biodiversity is attributed to its ability to oxidize alkanes of various chain lengths, while individual AlkBs target a relatively narrow range. Mechanisms of substrate selectivity and catalytic activity remain elusive. Here we report the cryo-EM structure of AlkB, which provides a distinct architecture for membrane enzymes. Our structure and functional studies reveal an unexpected diiron center configuration and identify molecular determinants for substrate selectivity. These findings provide insight into the catalytic mechanism of AlkB and shed light on its function in alkane-degrading microorganisms.

Atomistic MD Simulations of n‐Alkanes in a Phospholipid Bilayer: CHARMM36 versus Slipids

AbstractLinear alkanes (n‐alkanes) are chemically the most simple linear hydrophobic molecules in nature. Studying the incorporation of n‐alkanes into lipid membranes is therefore a good starting point toward understanding the behavior of hydrophobic molecules in lipid membranes and to assess how accurately molecular dynamics models describe such systems. Here, the miscibility and structure of different n‐alkanes—n‐decane (C10), n‐eicosane (C20), and n‐triacontane (C30)—in dipalmitoylphosphatidylcholine membranes are investigated using two of the most used force fields for lipid membrane molecular dynamics simulations (CHARMM36 and Slipids). The n‐alkanes are miscible in the membrane up to a critical volume fraction, ϕc, that depends on the force field interaction parameters used. ϕc is dependent on alkane chain length only for the model with more disordered chains (Slipids). Below ϕc, a comparison with 2H nuclear magnetic resonance (NMR) spectra indicates that a more realistic structure of the longer alkane molecules (C20 and C30) is obtained using the Slipids force field. On the other hand, for the shorter alkane (C10), Slipids simulations underestimate molecular order and CHARMM36 simulations enable a precise prediction of its experimental spectrum. The predicted 2H NMR spectra are highly sensitive to 1–4 electrostatic interactions, and suggest that a reduction of the partial charges of the longer alkanes and acyl chains in CHARMM36 results in a better performance. The results presented indicate that lipid membranes with incorporated alkanes are highly valuable systems for the validation of force fields designed to perform lipid membrane simulations.

Unveiling the effect of molecular chain length on the thermal energy storage capacity and transition temperature of alkane-based phase change composites

Thermal energy storage systems based on phase-change materials (PCMs) have garnered significant attention, because they can overcome intermittency issues related to renewable energy sources. However, the energy storage capacity and phase-change temperature of phase-change composites largely depend on the PCM type and molecular weight, in addition to the supporting material type, and experimental studies on the thermal properties of PCMs with different molecular chain lengths are scarce. In this study, phase-change composites were prepared by the vacuum impregnation method using boron nitride (BN) as the support and n-alkanes of different chain lengths–dodecane (C12H26), and docosane (C22H46)–as the PCMs to study the effect of the alkane chain length on the thermal energy storage density and phase-change temperature. The BN@C22 composite exhibited greater latent heat storage capacity (125.11 kJ/kg) than the BN@C12 composite (70.84 kJ/kg), indicating the low confinement effect of the BN support on the long-chain n-alkane. In contrast, the BN functional groups and shorter-chain n-alkane had strong intermolecular interactions, which compromise the energy storage density for seepage resistance and shape stability. Both PCM composites exhibited good chemical compatibility between the two components, improved thermal durability, and insignificant leakage rate (up to 98.7% leakage resistance capability), while BN@C12 showed higher shape stability. The thermal performance of the as-prepared PCM composites, including their phase-transition temperature (range: −9.54 to + 43.53 °C), illustrates their potential for various thermal management applications, including indoor temperature-control systems. This study provides fundamental guidelines for tuning the working temperature range and improving the efficiency of thermal management systems.

Low-temperature oxidation of n-octane and n-decane in shock tubes: Differences in time histories of key intermediates

The impact of chain length on the time histories of key intermediate species that form upon first-stage ignition was studied experimentally in a shock tube using multi-color laser absorption diagnostics. CO, CH2O, OH, and composite time histories of heavier carbonyls were measured simultaneously during the low temperature oxidation of n-octane & n-decane in the temperature range of 720–860 K, and pressure range of 4.1–5.8 atm. The test mixtures were 0.64% & 0.6% fuel in oxygen, respectively. A two-color diagnostic was also developed and used in tandem with other diagnostics to quantify the evolution of temperature during oxidation. To our knowledge, this work reports the first measurement of CH2O, OH, and temperature during oxidation of C8 or heavier hydrocarbon fuels at low temperatures. The measured time histories were also compared against the predictions of two recent detailed kinetic models. Significant differences in the measured and predicted first-stage ignition delay times, absolute concentration of species post-ignition and the maximum rate of formation of species were observed. Our measurements will serve as targets for further refinement of these detailed kinetic models and in the development of rate rules for similar classes of fuels. The measurements also revealed significant differences in the relative reactivity of n-octane and n-decane. Taken together with previous speciation studies conducted in n-heptane, we observe a strong correlation between the species time histories, reactivity, and chain length of straight chain alkanes. This observation lends further support to the selection of CO and CH2O as target species for development of Low-Temperature Hybrid Chemistry (HyChem) models for real transportation and aviation fuels in future.

Understanding the miscibility of polyoxymethylene dimethyl ethers (OMEn) and diesel blend using molecular dynamics simulation

Polyoxymethylene dimethyl ethers (OMEn) as an alternative fuel have attracted considerable interest in recent years, owing to their much reduced environmental impact. Since OMEn is often blended with diesel, the miscibility and stability of OMEn/diesel mixtures are important for engine operation. In this study, molecular dynamics method was used to investigate the miscibility of OME1-6 and diesel blends. The results suggest that the miscibility of OMEn and diesel blends decreases with the increasing number of oxymethylene units. The aromatics and heteroatomic molecules help maintain the stability of OMEn/diesel blends. The intermolecular interactions between OME1-6 and diesel molecules were investigated, which revealed that the electrostatic interaction plays a significant role in the liquid–liquid equilibrium of OMEn/diesel blends. The molecules in diesel having strong electrostatic interaction with OMEn are prone to accumulate around OMEn. The electrostatic interaction between diesel and OMEn molecules depends on the molecular structure and electronegativity differences of atoms in diesel molecules. The analyses of MD results coupled to minimum-distance distribution functions show an accumulation of paraffins and naphthenes close to OMEn at ∼ 2.36 Å, and suggest a strong interaction of OMEn with diesel carbazole molecules via hydrogen bonds. The results also indicate that the chain length and structure of alkanes have little impact on the molecular distribution around OMEn.

ReaxFF Molecular Dynamics Simulations of Large Gold Nanocrystals.

A systematic study of gold nanocrystals is carried out using molecular dynamics simulations with reactive force fields. The nanocrystal size is varied between 2 and 10 nm with methane and butane thiolate as ligands. The reactive force fields allow investigation of the formation of staples. The simulations explain several experimental observations such as the number of staples per thiolate of about 40% and the occupation of the top adsorption sites on the facets. They also show that the frequency of staples is increased on the edges, which leads to a desorption of gold atoms from the nanocrystal edges. In contrast to previous nonreactive simulations, no difference between the distances of the ligands on the nanocrystal edges and facets is observed. Except for the 2 nm particles, the nanocrystal size and the alkane chain length of the ligands have only a small influence on the nanocrystal properties. The occupation of adsorption sites and staple frequencies are very slowly converging properties, taking more than ns.

D–π–A–π–D Initiators Based on Benzophenone Conjugate Extension for Two-Photon Polymerization Additive Manufacturing

A two-photon polymerization initiator is a kind of nonlinear optical material. With the demand for more efficient initiators in two-photon polymerization additive manufacturing, there are more and more related studies. In this paper, four conjugate-extended two-photon polymerization initiators with different alkane chain lengths were designed and synthesized, and single-photon, two-photon, and photodegradation experiments were carried out. Additive manufacturing experiments illustrated that the designed molecules can be used as two-photon initiators, and the writing speed can achieve 100,000 μm/s at a laser power of 25 mW. Through theoretical calculation and experimental comparison of the properties of molecules with different conjugation degrees, it was proven that a certain degree of conjugation extension can improve the initiation ability of molecules; however, this improvement cannot be extended infinitely. Solubility tests of different acrylates showed that molecules with different alkane chain lengths have varying solubility. Changing the molecular alkane chain length may be favorable to adapt to different monomers.

Surface Chemistry Controls the Density of States in Metallic Nanoparticles.

Ligand-stabilized colloidal metallic nanoparticles are prized in science and technology for their electronic properties and tunable surface chemistry. However, little is known about the interplay between these two aspects of the particles. A particularly glaring absence concerns the density of electronic states, which is fundamental in explaining the electronic properties of solid-state materials. In part, this absence owes to the difficulty in the experimental determination of the parameter for colloidal systems. Herein, we demonstrate the density of electronic states for metallic colloidal particles can be determined from their magnetic susceptibility, measured using nuclear magnetic resonance spectroscopy. For this study, we use small alkanethiolate protected gold nanoparticles and demonstrate that changes in the surface chemistry, as subtle as changes in alkane chain length, can result inasmuch as a 3-fold change in the density of states at the Fermi level for these particles. This suggests that surface chemistry can be a powerful tool for controlling the electronic behavior of the materials to which they are attached, and suggests a paradigm that could be applied to other metallic systems, such as other metal nanoparticles, doped semiconductor systems, and even 2D metals. For all of these metallic systems, the Evans method can serve as a simple means to probe the density of states near the Fermi level.

Pinpointing Alkane Chain Length, Saturation, and Double Bond Regio- and Stereoisomers by Liquid Interfacial Plasmonic Enhanced Raman Spectroscopy.

The lipids with a rich diversity of isomers face a formidable challenge in comprehensive structural analysis. The commonly used mass spectrometry-based techniques usually require a considerable number of molecules with sophisticated chemical derivatization or ion mobility separation, but the co-existing of structurally similar isomers often makes the distinction impossible. Here, we develop an alternative powerful liquid/liquid interfacial surface-enhanced Raman spectroscopy (SERS) strategy at normal temperature and pressure without any sources of ionization or radiation. This strategy generates high-resolution fingerprints in molecular chain length, C═C position, saturation, and regio- and stereoisomers of both glycerides and fatty acids and requires only trace amounts of molecules down to 1 ppb to achieve discrimination and exhibits great potentials to push the identification capability to trace levels or even the single-molecule level. According to experimental data and theoretical simulations, these targets have the amphiphilic and emulsifying properties, exhibit ordered molecular orientation and adsorption patterns, promote the co-assembly with plasmonic nanoarrays at the immiscible liquid/liquid interface, and consequently amplify the detection sensitivity. As a contrast, the typical SERS based on solid/air interfacial plasmonic nanoarrays faces the intrinsic bottleneck of extremely weak intensity and indistinguishable spectral fingerprints of lipid molecules. The vibrational fingerprints exhibit a rich range of well-resolved absorption features that are clearly diagnostic for fine structural changes and pave a new way for straightforward measurement without laborsome sample purification, enrichment, or complex derivatization. Although challenging, its unprecedented resolving power expands the potentials of SERS, serving as an ultimate analytical method to provide insights into the detailed structural features of other lipids under facile conditions in the future.