Dodecane Droplets Research Articles

Effect of air preheating temperature on the dynamic behaviour of a swirled spray flame

The effects of the air inlet temperature on the dynamic behaviour of a spray flame are reported for different air flow rates. Dodecane droplets are generated through a pressurised nozzle and introduced in the combustion chamber fed with air via two co-rotating swirlers. The flow rate of dodecane is kept constant (1.24gs-1) while the air flow rate is changed from 28gs-1 to 35gs-1 and its temperature from 70°C to 220°C. Microphones are used to record the different dynamics observed while a camera and a Phase Doppler Anemometry system allow to monitor the flame and the fuel spray.For low flow rates (between 28gs-1 and 32gs-1, leading to an overall equivalence ratio ranging between 0.6 and 0.7), the pressure fluctuations start by increasing with an increase of the temperature until, for a given temperature, the pressure fluctuations suddenly drop. This threshold temperature depends on the air flow rate. When displaying the pressure fluctuation level as a function of the bulk velocity (taking both air flow rate and temperature into account), the curves collapse into a similar shape. The instability frequency monotonically increases with the bulk velocity. For high flow rates (between 32gs-1 and 35gs-1, leading to overall equivalence ratio ranging between 0.5 and 0.6), a hysteresis phenomenon is found. Pressure fluctuations are relatively high for constantly decreasing temperature conditions and have almost similar levels as those obtained for lower flow rates. When constantly increasing the temperature, the levels are much lower, showing a bi-stable behaviour for the pressure fluctuations at a given operating point. A simple analysis based on the acoustic energy balance equation allows to qualitatively retrieve the behaviour of the pressure fluctuations amplitude and frequency for the low flow rate cases.

Effect of Na+ on the collision of the dodecane droplet and kinetic energy transfer

Using a high-speed motion acquisition system, the dodecane droplet size and the interface energy of the dodecane-solution interface during the collision between the dodecane droplet and the dodecane layer at different Na+ concentrations were studied. The collision process is divided into three stages: Contact stage, Stretch stage and Attenuation amplitude stage. The size of the dodecane droplet gradually decreases as the Na+ concentration increases, and the stretching time does too. The kinetic energy of the dodecane droplet, the surface energy of the dodecane-solution interface, and the net force of the dodecane droplet all decrease with an increase in Na+ concentration, but the dodecane droplet rate of energy dissipation increases. The effect of Na+ concentration on dodecane-solution interfacial tension is the main reason for the collision difference. The Na+ added to the solution forms a hydration shell around it, weakening the interaction between water molecules at the dodecane-solution interface and within the solution, leading to reduced interfacial tension. The advancement of mineral flotation technology may benefit greatly from these findings.

STABILIZATION OF PICKERING EMULSIONS WITH HETEROAGGREGATES OF DETONATION NANODIAMONDS AND SIO2 NANOPARTICLES

The stabilization of Pickering emulsions with mixtures of similarly and oppositely charged detonation nanodiamonds and silica nanoparticles has been studied. Dynamic light scattering has been employed to study the influence of pH and the mass ratio of the particles on the sizes and ζ-potentials of aggregates. The formation of heteroaggregates from mixtures of similarly charged nanoparticles and the efficient stabilization of dodecane droplets have been shown and theoretically substantiated. Submicron droplets of Pickering emulsion stabilized with the mixtures of oppositely charged silica nanoparticles and detonation nanodiamondshave been obtained.

Molecular dynamics of interfacial crystallization of dodecane on hydroxylated silica surface impacted by H2O and CO2.

The morphology of dodecane in a nanopore at temperatures typical in exploited or depleted oil reservoirs is investigated using molecular dynamics simulation. The dodecane morphology is found to be determined by interactions between interfacial crystallization and surface wetting of the simplified oil, while "evaporation" only plays a minor role. The morphology changes from an isolated, solidified dodecane droplet to a film with orderly lamellae structures remaining within, and finally to a film containing randomly distributed dodecane molecules, as the system temperature increases. In a nanoslit under the impact of water, since water wins against oil in surface wetting on the silica surface due to electrostatic interaction induced hydrogen bonding between water and the silanol group of silica, the spreading of dodecane molecules over the silica surface is impeded by this water confinement mechanism. Meanwhile, interfacial crystallization is enhanced, leading to always an isolated dodecane "droplet," with crystallization weakening as the temperature increases. Since dodecane is immiscible to water, there is no mechanism for dodecane to escape the silica surface, and the competition of surface wetting between water and oil determines the morphology of the crystallized dodecane droplet. For the CO2-dodecane system in a nanoslit, CO2 is an efficient solvent for dodecane at all temperatures. Therefore, interfacial crystallization rapidly disappears. The competition of surface adsorption between CO2 and dodecane is secondary for all cases. The dissolution mechanism is a clear clue for the fact that CO2 is more effective than water flooding in oil recovery for a depleted oil reservoir.

Direct numerical simulation of spray and dispersion of liquid fuel droplets

A review of the existing phenomenological models was carried out, which gives a deep understanding of the features and characteristics of the formation of spray and dispersion of a liquid jet. These models give insight into the mechanisms of primary and secondary atomization of a liquid jet by tracing the behavior of a single fuel droplet placed in a stationary gaseous medium. The paper uses the direct numerical simulation method to present the computer simulation results of the atomization, dispersion, and evaporation of octane and dodecane droplets. To describe the interfacial interactions and track the particle's shape and position in the dispersed phase, the volume of fluid (VOF) method was used, which belongs to the class of Eulerian methods and is a non-autonomous algorithm. According to the results of computational experiments on the study of the processes of spraying, dispersion, and evaporation of octane and dodecane, the optimal combustion mode was established. Obtained results in this work have scientific and practical applications in constructing the fundamental theory of combustion and designing the injection systems structure with optimal parameters.

Directional Self-Transportation of Droplets on Superwetting Wedge-Shaped Surface in Air and Underliquid Environments.

The directional self-transportation of droplets has aroused great attention in microfluidic systems. However, most reported surfaces are mainly designed for driving water droplets to move in air, displaying low adaptability in complex environments. This work presents a wedge-shaped surface with multiple superwettability, i.e., superhydrophilicity/superoleophilicity and underwater superoleophobicity/underoil superhydrophobicity, fabricated by electrodeposition of a metal-organic framework on a copper sheet. This surface exhibited excellent performance for driving droplet self-transportation, regardless of the droplet type (water or oil) and environmental media (air or underliquids). In air, the wedge-shaped surface with wedge angle of 9.2° could move droplets of water and dodecane up to 24.5 mm and 17.9 mm, respectively. The movement of water droplet under dodecane, however, dropped from 24.5 mm to 22.1 mm, while the dodecane droplet underwater increased from 17.9 mm to 20.3 mm in moving displacement, indicating the underliquid environment is in favor of manipulation of oil droplets. Furthermore, the droplet convergence, transportation, and separation were achieved on the well-designed multiple wedge tracks in air with a total movement distance up to 60.0 mm. The test of micro-oil droplets collecting under water demonstrated that a sponge with two wedges has 2.1 times the oil droplet collection capacity over that of the sponge only, providing a new strategy for efficient treatment of the micro-oil droplets contaminated water.

Slippery and Sticky Superoleophobicities on Hierarchical Aluminum Surfaces Fabricated by Electrochemical Etching and Anodizing Methods

Slippery and sticky superoleophobic aluminum surfaces were fabricated by electrochemical etching and anodizing methods. Collective structures of sub-micrometer-scale cubic-shaped aluminum were formed by electrochemical etching of high-purity aluminum in HCl. The etched specimens were then anodized in H4P2O7 to form anodic alumina nanofibers (AANFs) on the cubic aluminum surface, resulting in a hierarchical aluminum-alumina structure. As the water/oil-repellent self-assembled monolayers were formed on their surfaces, the superoleophobicity of dodecane was more than 150° in the advancing contact angle exhibited on the anodizing surfaces. Conversely, the receding contact angle changed drastically with anodizing time because of the different nanomorphology of AANFs; short anodizing caused slippery superoleophobicity with high contact angle values, whereas long anodizing resulted in sticky superoleophobicity with 0°. We demonstrated the slipping behavior of dodecane droplets on superoleophobic aluminum surfaces with completely opposite sliding properties. The corrosion resistant property of the superoleophobic aluminum surface was also investigated by the measurements of potentiodynamic curve in a 3.5 wt% sodium chloride solution.

Electrospun Liquid-Infused Membranes for Emulsified Oil/Water Separation.

From an environmental perspective, microfiltration membranes are attractive for the separation of emulsified oils from contaminated water. However, fouling of the membrane is a major drawback of the technology. "Liquid-infused membranes" (LIMs) have the potential to eliminate membrane fouling. Here, we demonstrate the practical application of LIMs for the separation of oil from a stable oil-in-water emulsion and characterize their resistance to fouling. The base membrane is an electrospun nonwoven fibrous layer of the fluorinated copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP). The surface energy of the PVDF-co-HFP fibers was lowered by the covalent attachment of a fluorinated silane (PFOCTS), and then, the membrane was infused with a perfluoropolyether. The membrane was then challenged with model emulsions of dodecane in water in a cross-flow configuration. This PFOCTS-modified LIM showed better infused liquid stability, permeation selectivity, higher permeate flux than the unmodified LIM, and better anti-fouling properties than the bare membrane without infused liquid. We also examine the mechanism for transport of the dispersed oil phase through the liquid-infused membrane. We find a linear relationship between the dodecane flux and dodecane concentration in the feed and a higher dodecane flux through the PFOCTS-modified membrane than the unmodified one, which suggests that the capture of dodecane droplets from the feed plays an important role in determining the overall rate of permeation. Other factors such as lower viscosity of the infused liquid, larger pore size, and higher operating pressure also improved the permeate flux through the LIMs. Overall, this work provides some guidelines on the design of composite membranes comprising infused liquids and the choice of operating conditions for the filtration process.

Insights into the dynamics of wake flame in a freely falling droplet

The combustion of a freely falling dodecane droplet has been studied experimentally in a droptower-like facility under ambient conditions. A unique ignition mechanism is used by igniting the droplet in pendant mode and releasing it to fall freely. This unveils a different type of droplet wake flame behavior which is explored in this study. Initially, the droplet flame transitions from fully enveloped to a wake flame configuration due to forward extinction. The wake flame has similar characteristics as a laminar lifted triple-flame. As the droplet accelerates, the flame stand-off increases continuously. The change in wake flame topology and intensity occurs in two different regimes corresponding to different droplet diameters. A new non-dimensional parameter has been derived to account for the local balance between buoyancy and momentum diffusion that alters the fuel availability. To explain the flame topological evolutions and transitions for different droplet diameters and Reynolds numbers, a theoretical formulation has been proposed based on the momentum diffusion from surrounding due to relative motion. Further, at very high Reynolds number, flame stretching or shedding regime occurs, causing momentary spikes in flame intensity due to the interaction with asymmetric vortex shedding induced by the Bernard–Von Karman instability. Interestingly, the flame shedding height follows the buoyant flickering scaling, even for the momentum-dominant droplet wake flame. Additionally, the circulation build-up mechanisms are shown to be responsible for the flame shedding events for droplet wake flame at high Reynolds number.

Coarse-Grain molecular model development and dynamics simulations study of dodecane droplet spreading at the coal-water interface

The mesoscopic scale is usually used to realize the dynamics calculation on a larger spatial scale and time scale. However, there have been few dynamic simulation calculations attempted on the mesoscopic scale for coal flotation systems. In this study, based on the Martini force field, the Coarse-Grain (CG) models of coal, dodecane, and water were established, and the dynamics simulations were performed to study the collector droplet spreading at the coal-water interface. The CG dynamics simulations results showed that the interaction between dodecane and coal was a spontaneous process, and dodecane existed as a collector at the coal-water interface. The radial distribution function of dodecane around coal and water indicated that dodecane was more likely to be distributed around the coal, and as far away as possible from the water. The CG dynamics simulations also revealed the specific spreading stages of the dodecane droplet. The dodecane drop first moved in the form of droplets to the coal-water interface in the aqueous phase. Then at the coal-water interface, the circular droplet broke its shape and spread rapidly on the coal surface through the dodecane CG molecules. Finally, the dodecane CG molecules penetrated deeper into the coal surface layer and formed a dynamic and stable oil film. This provided a good attempt and reference for studying the spreading of collector droplets on the coal-water interface.

Droplet evaporation and phase transition modes in supercritical environment by molecular dynamic simulation

The phase change process of a single hydrocarbon droplet in a supercritical environment has different features compared with subcritical evaporation. In this study, droplets surrounded by supercritical nitrogen are investigated by molecular dynamic simulation. Dodecane droplets are considered in order to reproduce the phase change process of actual fuel, and the radius ranges from 10 nm to 25 nm under various subcritical, transcritical, and supercritical conditions. The emphasis is to describe the entire phase change process and distinguish its different stages. Under supercritical conditions, traditional D2-law theory is invalid and the radius of droplets increases dramatically accompanied by huge fluctuation after a special time. Based on analysis toward fluid properties crossing this time point, the phases classification for supercritical mixture is provided and three phase change stages are distinguished in order, which can be divided by the onset time of supercritical transition, the disappearance of surface tension, and one-phase diffusion, respectively. Additionally, gas/liquid-like features have been observed in the supercritical binary dodecane–nitrogen coexisting system and the defined pseudo-boiling mole fraction (Xpb) is introduced to clarify such deviation in properties of supercritical mixture. At last, by judging whether supercritical transition and undroplet phenomenon will happen, three phase transition modes are summarized for droplets under supercritical conditions.

Autoignition Dynamics of N-dodecane Droplets under Normal Gravity

ABSTRACT Experimental observations of two-stage autoignition dynamics of fiber-supported normal dodecane droplets in air under normal gravity are presented for a range of pressures and temperatures. High-speed shadowgraph imaging of the autoignition process reveals cool-flame and hot-flame front-formation and propagation dynamics. During two-stage ignition, a cool-flame kernel is first formed below the droplet; it then propagates toward the droplet along the fuel-vapor plume, and subsequently a hot-flame kernel is established behind the cool-flame front which rapidly expands, engulfing the droplet and establishing the classical diffusion flame. Results for the cool-flame and hot-flame kernel locations and their propagation speeds are presented for a range of ambient pressures, varying between normal atmospheric pressure and super-critical pressures and temperatures.

The effect of polyglycol-type frothers on the interfacial characteristics of oily collector dispersion

Frothers are used in mineral flotation to form small bubbles and a froth layer. As surfactants, frothers may also disperse oily collectors and promote their adsorption on mineral surfaces. Following the previous work showing that aliphatic alcohol frothers inhibited the dispersion of dodecane in de-ionised water, but promoted the dispersion in NaCl solution, this study examined the effect of polyglycol-type frothers, including Dowfroth 250 (DF250) and Dowfroth 400 (DF400), on the dispersion of dodecane in de-ionised water and NaCl solution. Dispersion tests, interfacial tension measurements, zeta potential measurements and viscosity measurements show that DF400 and DF250 were able to enhance dodecane dispersion in both de-ionised water and NaCl solution by promoting the formation and stabilisation of dodecane droplets. DF250 dispersed dodecane more than DF400 mainly through producing more stabilised dodecane droplets driven by stronger electrostatic and steric repulsion. Although NaCl inhibited dodecane dispersion in water, synergy occurred between NaCl and DF400/DF250 to facilitate dodecane dispersion.

The effect of aliphatic alcohol frothers on the dispersion of oily collector

There has been perception that flotation frothers, a type of surfactants, can disperse oily collectors in water, promoting oil attachment on mineral particles. In this study, the effect of aliphatic alcohol frothers (including MIBC, 1-hexanol and diacetone) on the dispersion of dodecane in de-ionised water and NaCl solution was studied. It turned out that these frothers actually inhibited the dispersion of dodecane in de-ionised water, but promoted the dispersion in NaCl solution. The underpinning mechanism was then investigated to decouple the effect of these frothers on the subprocesses of dodecane dispersion, emulsion formation controlled by the interfacial tension between oil and water, and emulsion stabilisation controlled by zeta potential and rheology of oil droplets. It was found that these frothers could decrease the interfacial tension of dodecane/water interface to facilitate the formation of dodecane droplets in water, but they were unable to form stable protective coatings around dodecane droplets in de-ionised water, resulting in the coalescence of dodecane droplets. In NaCl solution, the presence of Na+ can improve the strength of protective coatings formed by frother molecules around dodecane droplets and therefore the stability of dodecane emulsion.

Surfactant modulated interactions of hydrophobically modified ethoxylated urethane (HEUR) polymers with penetrable surfaces

HypothesisAdsorption of hydrophobically modified ethoxylated urethane polymers (HEURs) at the soft colloid interfaces of emulsion droplets will stabilise oil-in-water emulsions (a) via steric stabilisation induced by adsorption of the polymer at the droplet surfaces through the hydrophobic groups, and (b) via continuous phase viscosity enhancement through polymer self-association. Both of these mechanisms will be modulated by the presence of the surfactant, sodium dodecylsulfate (SDS). ExperimentsDodecane-in-water emulsions stabilised by three HEUR polymers with different structural composition were examined in the absence and presence of SDS by NMR spectroscopy and small-angle neutron scattering (SANS). The effect of adsorption of the polymer to the dodecane droplet surfaces, and the conformation of the self-associating polymer in the aqueous solution were quantified. FindingsAll emulsions were stable for days-weeks. Diffusion data showed the formation of oil droplets of hundreds of nm in size in the presence of all three HEURs, here denoted C6-L-(EO100-L)9-C6, C10-L-(EO200-L)4-C10, and C18-L-(EO200-L)7-C18, where EOx represents a block of ethylene oxide of x monomers, L denotes the linker group, and Cn the length of the hydrophobic end-group. No significant changes in droplet size across this series of polymers was observed. Collectively, the results point to adsorption of the polymer to the droplet surfaces, which results in a small decrease in the effective polymer solution concentration, thereby driving to significant changes in the structure and dynamics of the system. Evident in the SANS data in particular, is a subtle balance between the characteristic features reflecting polymer self-association, and those associated with polymer structures commensurate with a larger length-scale, dependent on the system composition. Surprisingly, the polymer and polymer/SDS complex in the presence of oil show slightly greater diffusive rates relative to the analogous systems in the absence of the oil.Finally, the partitioning of the three polymers in phase-separated samples was studied by 1H NMR, and it was shown that the C18-L-(EO200-L)7-C18 exhibited a greater partitioning in the oil phase compared with C6-L-(EO100-L)9-C6 and C10-L-(EO200-L)4-C10, an observation that may be understood in terms of the structural composition of the HEURs. The SDS showed a positive correlation between its partitioning in the two layers with the polymer partitioning, evidence of a strong interaction between the surfactant and the polymer, consistent with the behaviour observed in the oil-free system.

Unraveling Interaction Mechanisms between Molybdenite and a Dodecane Oil Droplet Using Atomic Force Microscopy

Molybdenite (MoS2) is a mineral that has drawn great interest because of its potential application in various fields. To facilitate the flotation of molybdenite, the mineral pulp is commonly treated with nonpolar oil additives to promote hydrophobicity and to form an oil bridge between ultrafine molybdenite particles for agglomeration. In this study, dodecane was chosen as a model oil to investigate the flotation mechanisms of molybdenite with nonpolar oil. The interaction forces between a micrometer-sized dodecane droplet and the molybdenite basal plane in various electrolyte solutions were directly measured by the atomic force microscope droplet probe technique. The effects of added salts, ionic strength, and solution pH on interaction forces were evaluated by considering van der Waals, electrical double-layer (EDL), and hydrophobic forces. The experimentally measured force curves were found to agree well with the Reynolds lubrication model and the augmented Young-Laplace equation. The results show that the competition between repulsive EDL forces and attractive hydrophobic forces was directly responsible for oil-molybdenite attachment behavior. High pH and low salinity (<24 mM NaCl) led to strong repulsive EDL forces, which stabilized the interaction and prevented the attachment of oil to molybdenite. Both low pH and high salinity facilitated the attachment of oil to molybdenite through the depression of EDL force, allowing attractive hydrophobic force to dominate. The hydrophobic attraction was quantified with an exponential decay length of 1.0 ± 0.1 nm. Furthermore, calcium ions decreased the magnitude of the surface potentials of both oil and molybdenite more than that seen with the same ionic strength of sodium ions, suggesting the suppressed EDL repulsion. This study provides quantitative information about the surface forces between oil and the molybdenite basal plane and an improved understanding of the fundamental interaction mechanisms governing molybdenite recovery by mineral flotation.

Adhesion of Marinobacter hydrocarbonoclasticus to Surfactant-Decorated Dodecane Droplets.

We investigate the effect of interfacial properties on the adhesion of bacteria at oil/water interfaces using confocal microscopy. Surfactant-decorated dodecane droplets of diameter 20-60 μm are generated using a coflow microfluidic device, introduced into an aqueous saline suspension of Marinobacter hydrocarbonoclasticus bacteria, and imaged in 3-D over time. Using image analysis algorithms, we determine the number of bacteria adhering at oil/water interfaces over time in the presence of dioctyl sodium succinate (DOSS), a component of the dispersant used in oil-spill recovery. The adsorption of bacteria at the oil/water interface follows Langmuir first-order kinetics for all droplet sizes, with the greatest areal number density of bacteria adhered to the smallest droplets. We vary the surfactant type [DOSS, dicyclohexyl sodium sulfosuccinate, dibutyl sodium sulfosuccinate, cetyltrimethylammonium bromide, and Tween 20] and concentration and examine the effects on long-time adhesion of bacteria. For a fixed droplet size, the areal density of bacteria at the interface decreases with increasing surfactant concentration because of a reduction in oil/water interfacial tension that increases the free energy of adhesion of the bacterium.

Measurement of Instability of Thin Liquid Films by Synchronized Tri-wavelength Reflection Interferometry Microscope.

Film thickness measurement of unstable thin liquid films (TLFs) remains a challenge due to the difficulty in determining the order of fringes prior to the film rupture. In the present work, a synchronized tri-wavelength reflection interferometry microscope (STRIM) was developed and employed to determine the spatiotemporal thickness profiles of the TLFs between air bubbles and various hydrophobic surfaces in 10-2 M NaCl solutions. Both accuracy and precision of film thickness measurements were found to be better than 3 nm over the range of 0-1 μm. It was found that when the radii of air bubbles were in the range 0.71-0.88 mm, the critical rupture thicknesses of the wetting films formed on hydrophobic quartz surfaces having water contact angles of 95° scattered over a range of 57-335 nm with a medium rupture thickness of 122 nm. For smaller air bubbles with radii of 0.13-0.26 mm, the critical rupture thicknesses were much more narrowly distributed with a medium rupture thickness of 27 nm. The result obtained with the TLFs between two air bubbles, i.e., foam film, showed that the critical rupture thickness was increased from 25 to 40 nm, when the sizes of air bubbles were increased from 220 to 960 μm. Compared to rupture thickness of the foam film, the critical rupture thickness of the TLF between an air bubble and a dodecane droplet was smaller, indicating that the film rupture might be related to the hydrophobicity of interacting surfaces. In addition to attractive surface forces, both wave motions and gas molecules in TLF might be associated with the film rupture.

How boiling happens in nanofuel droplets

We report detailed analyses of evaporation and atomisation characteristics of nanofuel droplets in a contactless environment (acoustic levitation) under external radiative heating. Two base fuels, ethanol and n-dodecane with a significant difference in their respective vapour-pressures, are considered. Nanoparticles (NPs) of cerium oxides (CeO2) are utilised as nano-additives at a dilute particle loading rate (PLR) of 0%-0.5% by weight. Pure ethanol droplets vaporise at a faster rate than pure dodecane droplets and do not exhibit any secondary atomisation. However, pure dodecane droplets exhibit two modes of secondary breakup; Kelvin-Helmholtz instability induced stripping and catastrophic breakup beyond a certain threshold value of the initial droplet size. Nanofuel droplets of ethanol neither exhibit any significant change in the vaporisation rate nor exhibit secondary atomization. Contrarily, dodecane-based nanofuels show enhanced vaporisation due to heat absorption by nanoparticles and consequently different modes of secondary breakup. Interestingly, dodecane-based nanofuel droplets exhibit internal boiling induced atomization. A time scale analysis considering orthokinetic NP aggregation, evaporation lifetime, and bubble growth rate is presented to elucidate the mechanism of such internal boiling. The theoretical non-dimensional time scale (τ*) so coined is extended to estimate the minimum value of the droplet size necessary for exhibiting boiling. The analysis shows excellent agreement with the experimental observations. Furthermore, we propose a unique three-dimensional regime map to correlate the breakup modes with droplet sizes, PLR, and heating rates.

Rheological Characterization of Mixed Surfactant Films at Droplet Interfaces via Micropipette Aspiration.

Cationic and anionic surfactant mixtures can form viscous films that dominate the rheology and stability of micrometer-sized droplet suspensions. In this work, we use micropipette aspiration to study the mechanical properties of mixed surfactant surface films of anionic sodium dodecyl sulfate (SDS) and cationic dodecylamine hydrochloride (DAH) on alkane and lipid droplets. For octane droplets, SDS was found to decrease the surface tension until a minimum of 5 ± 1 mJ/m2 was reached after the critical micelle concentration (cmc). The surface viscosity of the droplets was found to be on the order of 10-3 mN s/m at an SDS concentration of 10 mM. An addition of 0.2 mM of DAH was found to increase this viscosity to a peak of 0.24 ± 0.01 mN s/m. Similar to octane, the surface tension of dodecane decreased to a value of 7.7 ± 0.4 mJ/m2 at SDS concentrations above cmc. Unlike with octane, however, the dodecane droplets had a significant surface viscosity of 0.37 ± 0.01 mN s/m when only the 10 mM SDS film was present. An addition of DAH caused a decrease in this viscosity initially, before rising to a peak viscosity of 0.45 ± 0.01 mN s/m at a DAH concentration of 0.15 mM. We speculate that the peaks in viscosities were the result of the completions of a phase change associated with microcrystalline SDS/DAH grains growing in the film at the surface of the droplets. Fluorescence microscopy and visual observations provided further evidence that these films can show rigid microcrystalline-like structure. Further work done with soybean oil in the same conditions and with a lipid film, simulating biological lipid droplets, confirmed that lipid droplets behave rheologically similar to alkanes in the presence of these mixed surfactant and lipid films. These results imply that droplet mechanics may be heavily influenced by the presence of microcrystalline grains in the oil-water systems with complex surfactant mixtures.