Formation Of Nanodroplets Research Articles

Surfactant Concentration Regime in Miniemulsion Polymerization for the Formation of MMA Nanodroplets by High-Pressure Homogenization

This article focuses on the adequate surfactant concentration regime in which MMA droplets are stabilized sufficiently against coalescence during high-pressure homogenization but still no diffusion processes from droplets to micelles take place in the polymerization. Monomer miniemulsions with different surfactant concentrations were prepared with different energy inputs. Emulsions result that depend either on the surfactant concentration or on the energy input of the homogenization process. For both cases, the occupancy of the interface is compared as a function of the droplet size. It is shown that the surfactant concentration needed for the stabilization of a specified interface area decreases with increasing droplet size. For the dependence of droplet size on the energy input, it is shown that more surfactant can be applied before emulsion polymerization starts, but the applicable surfactant concentration is lower than the cmc and also depends on droplet size.

Study of the formation of micro and nano-droplets containing immiscible solutions

There is currently significant interest in the multiple resistance to treatment using drugs (MDR), developed by bacteria and malignant tumors. One of the alternatives to the existing medicines and treatment procedures in fighting MDR is strengthening the effects of cytostatics by improving their delivery methods. Such a method is represented by the generation, transport and use of micro-/nano-droplets which contain medicines. This approach can reduce the medicines consumption by generating micro-droplets which contain drugs incorporated in solvents substances; the micro-/nano-droplets can favour a faster delivery to the targets and a higher drug concentration in them. This paper reports first, results concerning the generation of single micro-droplets containing an inner core (medicine solution in water) and a thin layer of oily liquid covering it. This generation is made one by one and it is, at the moment, not conceived as a method for mass production, or in other words for high population of such droplets. We have generated and measured stratified micro-droplets, each of them containing a solution of Vancomycin in ultrapure water as a core and a surrounding layer of Vitamin A in sunflower oil; the micro-droplets generation was made using a double capillary system. Secondly, micro-/nano-droplets were produced by mixing two immiscible solutions in particular conditions (high rotating speed and/or high pressure difference). For this we have studied the generation of emulsions of Vitamin A diluted in sunflower oil and a solution of Tween 80 surfactant in distilled water. The concentration of surfactant in water was, typically, 4 × 10 −5 M. We have studied the dependence of the droplets dimensions in emulsion on the mixing rotation speed, agitation time and components ratio. The droplets diameters were measured using a light scattering method. It is found that at high enough energy input (high rotation speed, large pressure drop) and relatively small oil/water ratio, droplets diameters smaller than 100 nm were obtained.

Molecular dynamics simulation of formation and control of nanodroplets in piezoelectric nanoejection systems

In this paper, the formation of nanodroplets in piezoelectric nanoejection processes is investigated by non-equilibrium molecular dynamics simulation. By compressing liquid propane molecules with various specific pushing periods of oscillation, the phenomena of liquid thread breakup and droplet formation are simulated. The simulation results revealed that various features aid the piezoelectric nanoejection system. Two breakup shapes including double-cone and long tail structures were found in this process. To analyse the ejection process in detail, 2D contour plots and thermal properties for various pushing periods are shown and discussed in this paper. The results show that the sizes of nanodroplets are linear depending on the pushing periods. The findings show a new control factor and mechanism for nanodroplet formation through piezoelectric nanoejection processes.

Novel Mesogenic Azobenzene Dimer at Air−Water and Air−Solid Interfaces

We have synthesized a novel mesogenic azobenzene molecule and studied its monolayer film properties at air-water interface (Langmuir film) and air-solid interface (Langmuir-Blodgett film). The material, H-shaped dimer bis[5-(4'-n-dodecyloxy benzoyloxy)-2-(4''-methylphenylazo)phenyl] adipate (12D1H) exhibits a smectic C phase between 51 and 48 degrees C on cooling. Surface manometry studies showed the formation of a stable monolayer at the air-water interface. Brewster angle microscopy (BAM) showed that liquid domains coexisting with the gas region at large area transformed to a uniform liquid phase with increasing surface density and finally to a collapsed state. We have carried out atomic force microscope (AFM) studies on Langmuir-Blodgett (LB) films transferred onto freshly cleaved hydrophilic mica substrate. The AFM images showed domains of height of about 3.8 nm, which corresponds to the estimated height of the molecule confirming the formation of monomolecular film. On a hydrophobic silicon substrate, the LB transfer yields a bilayer film, which dewets to form uniform nanodroplets of diameter of about 100 nm and height in the range 10-50 nm. Our analysis indicated that the mechanism involved in the formation of nanodroplets can be attributed to spinodal dewetting. The 12D1H molecule containing an azobenzene group undergoes a trans to cis transformation in the presence of ultraviolet light. Our surface manometry studies showed that the monolayer in the presence of ultraviolet light was more stable with a collapse pressure three times that of the monolayer in the dark.

Formation of Charged Nanodroplets at Capillary Instability of the Liquid Emitter

The fluctuation excitation mechanism and characteristics of fine dispersive phase in liquid metal ion sources were investigated. The system of standing capillary waves with frequencies of 2–30 MHz develops on the liquid surface during a droplet detachment from the top of the elongated Taylor's cone. The disturbance of a liquid surface modulates the extracting electric field and ion current, whose spectrum of fluctuations has the quasi discrete form. The spectrum of nanoparticle sizes is continuous because of their electrostatic instability upon disruption. The generated nanodroplets of 2–20 nm sizes can be used to coat thin films and create surface quantum structures. The constructed ion source with a penetrable porous electrode can be used to obtain nanoparticles from semiconductor materials. The working substance vapor appears locked inside the container owing to the penetration of the liquid inside the capillaries.

Synthesis of gold-silicon core-shell nanoparticles with tunable localized surface plasmon resonance

Gold-silicon core-shell nanoparticles embedded in silica matrix, evident by transmission electron microscopy and x-ray photoelectron spectroscopy were synthesized by atom beam cosputtering followed by thermal annealing. Optical absorption studies revealed localized surface plasmon resonance (LSPR), which showed regular redshift from 500to583nm with increase in annealing temperature. The observed redshifts in the LSPR peaks are in close agreement with the theoretical calculations assuming Si nanoshells surrounding Au nanoparticles. The Au–Si core-shell formation is explained by Au–Si liquid nanodroplet formation at temperatures higher than the eutectic temperature, followed by phase separation during subsequent cooling.

Elaboration of self-organized magnetic nanoparticles by selective cobalt silicidation

Self-organized magnetic nanoparticles are obtained through selective silicidation of cobalt using a silicon substrate pre-structured with tri-dimensional gold islands as template. On the step bunches array of a vicinal Si(1 1 1) surface, gold deposition results in the formation of nanodroplets aligned along the step bunches. A subsequent cobalt deposition is performed onto this gold islands-covered Si surface, with two silicidation processes investigated: reactive deposition (RD) and solid phase reaction (SPR). The cobalt is converted into a non-magnetic silicide film except where the surface is locally masked by the gold islands, giving rise to cobalt nanomagnets which can be capped by a gold layer. A scanning tunneling microscopy comparative study of RD and SPR processes demonstrates that the former induces strong surface morphology changes while the latter preserves the pristine islands. Magnetic measurements performed with alternating gradient force magnetometry at room temperature are used to demonstrate the presence of ferromagnetic cobalt nanoparticles on SPR-processed samples. These nanomagnets show a clear in-plane anisotropy behavior.

Formation of Interfacial Nanodroplets through Changes in Solvent Quality

We describe the formation of very thin interfacial oil droplets. The oil droplets are composed of decane and have the shape of a spherical cap. They are approximately 1-10 microm across and about 10-500 nm thick. We form these droplets by sequentially exposing a hydrophobic silicon wafer to two solutions of decane, where the second solvent is a poorer solvent than the first. We hypothesize that this method of decorating interfaces with droplets is quite general, and that the method may be useful for the controlled modification of interfaces. Inadvertent application of the method may lead to unanticipated properties of interfaces.

Ambient effect on optical absorption of Au nanoparticles dispersed within pores of mesoporous SiO2

A gold nanoparticles/monolithic mesoporous silica assembly was synthesized by ultrasonic irradiation of monolithic porous silica presoaked with precursor solution. Subsequent exposure to ambient air (ageing) and then drying at 120°C induce a new optical absorption peak around 470 nm (falling into the range from 460 to 475 nm) which is stable at room temperature, in addition to the normal surface plasmon resonance (SPR) of Au nanoparticles. Further drying results in the decline and disappearance of this peak, accompanied by increase of the normal SPR. If the sample, in which the new peak has disappeared due to long drying at 120°C, is exposed to the ambience once more, this peak will appear again after subsequent drying at 120°C, showing reversibility. Further experiments indicate that ambient ageing for a certain time plays a crucial role in the appearance of the new peak after subsequent drying at 120°C. Increased ageing time increases this peak. In addition, the ambient relative humidity and temperature during exposure are also important to the appearance of this peak. This peak may be associated with Au clusters with a size less than 1.5 nm. Based on the porous structure of the assembly and hydrophilicity of its pore wall, a nanodroplet formation and evaporation model is presented which can well explain all evolution behaviours of this peak. The model predicts the existence of the peak at 470 nm in the Au/silica assembly prepared by methods other than ultrasonic irradiation, which has also been confirmed by further experiments.

The effect of a solvent modifier in the cesium extraction by a calix[4]arene: a molecular dynamics study of the oil phase and the oil–water interface

We report a molecular dynamics (MD) study of the effect of a fluorinated lipophilic alcohol (referred to as "cs3" by Delmau et al, Solvent Extr. Ion Exch., 2005, 23, 23) used as a phase modifier in the solvent extraction of Cs(+) NO(3)(-) by a calix[4]arene. It is shown that adding cs3 to a chloroform phase improves the solvation of all partners of the extraction system, i.e. the free calixarene ligand L, its LCs(+) complex and its counterion. This effect is most pronounced for the NO(3)(-) anion that is H-bonded to the -OH and terminal -CF(2)H protons of cs3. On the average, the dissociated nitrate interacts with 2 to 4 cs3 molecules, whereas the associated nitrate (LCs(+)NO(3)(-) complex) interacts with one cs3 dimer. The remaining modifier molecules are mainly dissolved in the solution as dimers or trimers and, to a lesser extent, as monomers and tetramers. Insights into the question of ion pairing in the organic phase are obtained via free energy perturbation (FEP) calculations, showing that the LCs(+)NO(3)(-) paired complex is more stable than its analogue with the dissociated anion. Furthermore, the nitrate dissociation energy is ca. twice as small in the cs3-modified solution than in a pure chloroform phase. We also simulated chloroform/cs3/water ternary systems, showing that the modifiers are surface active and stabilize the formation of water nanodroplets, while other modifier molecules drag some water to the organic phase. Calixarene complexes also adsorb at the aqueous interface in the presence of modifiers, confirming the importance of interfacial phenomena in the assisted cation extraction process. The microscopic insights obtained by the simulations are consistent with experimental results and allow us to better understand why the extraction is enhanced after addition of modifiers to the organic phase.

Specific Features of Synthesis of Detonation Nanodiamonds

It is demonstrated that the Chapman-Jouguet parameters for high explosives used in nanodiamond synthesis are located in the region of liquid nanocarbon; therefore, the chemical reaction zone of the detonation wave involves formation of carbon nanodroplets, which are later crystallized into nanodiamonds on the segment of the isentrope of expansion of detonation products, passing through the region of stability of nanodiamonds in the pressure range of 16.5–10 GPa and the temperature range of 3400–2900 K. Soot in the resultant mixture is the product of amorphization of nanodroplets rather than graphitization of ultrafine diamonds. The influence of detonation conditions of high-explosive charges in an explosive chamber on nanodiamond synthesis is analyzed.

Electrical Detection of DNA Hybridization Based on Enzymatic Accumulation Confined in Nanodroplets

Electrical monitoring of DNA hybridization is one way to reduce the cost and size of the DNA chip reader in comparison with the more classical optical detection. Within electrical methods, electrochemical detection shows very high performances in terms of accuracy and sensitivity, especially when an enzymatic accumulation is used to amplify the signal. However, signal multiplexing for miniaturized systems based on both enzymatic accumulation and electrochemical detection remains challenging due to the Brownian diffusion of the detected product of the enzymatic reaction. We present here a DNA chip with electrical detection based on the following sequence: (i) hybridization of nucleic acids and washing in a liquid layer as usual, (ii) formation of independent nanodroplets on each detection site, (iii) enzymatic accumulation in each droplet avoiding cross-contamination between neighboring sites, and (iv) electrochemical detection of the product accumulated during the enzymatic reaction. The simple and fast transition from the liquid layer (hybridization step) to an array of nanodroplets (enzymatic accumulation and detection steps) was performed through the filling of the hybridization chamber with a solution containing the enzymatic substrates, the drawing of this solution, and the simultaneous creation of droplets thanks to retention areas based on circular rims or hydrophilic rings. Using this approach, hybridization is achieved in a liquid layer as usual, followed by the enzymatic accumulation in nanodroplets to avoid the cross-talk between neighboring sites. Moreover, working in droplets enables a fast increase in the concentration of the product generated by the enzymatic reaction and thus an improvement of the detection limit of the system.

Electron hole liquid in silicon single quantum wells

We have carried out photoluminescence measurements on the two dimensional electron hole liquid in perfectly crystalline Si quantum wells with SiO 2 barriers. The condensation of excitons in an EHL is strongly enhanced in 2D geometry. Formation of liquid nanodroplets with size varying with laser power is seen. Carriers are submitted to a quantum confinement regime for sufficiently small thickness. We present a model taking into account 2D many-body effects and the increase of the Coulomb interaction due to the dielectric mismatch between the Si well and the dielectric barrier. Results are in good agreement with photoluminescence measurements.

Two-dimensional electron-hole liquid in single Si quantum wells with large electronic and dielectric confinement.

We report a luminescence study of the electronic properties of the 2D electron-hole liquid in crystalline Si quantum wells with SiO2 dielectric barriers. The Fermi-Dirac condensation of e-h pairs into a metallic liquid is strongly enhanced by spatial localization. We present experimental evidence for the formation of liquid nanodroplets, with size increasing with e-h pair density. The quantum confined regime is observed for well width below 15 nm. The data are analyzed in a confinement model that takes account of the band-gap renormalization by 2D many-body effects and the increase of the Coulomb interactions due to the dielectric mismatch between the Si well and the SiO2 barriers.

Modelling of mass-transfer induced instabilities at liquid–liquid interfaces based on molecular simulations

Interfaces and especially mass transfer across interfaces are of great importance in many fields of chemical engineering. Interfacial convection, which is generally called the Marangoni effect, may improve mass transfer across interfaces quite drastically and has not been investigated adequately in detail. In order to investigate the influence of mass transfer on a liquid–liquid interface molecular computer simulations have been performed. Since many molecules have to be considered for a significant modelling of the interface, cubic lattice systems have been chosen for the simulation which proceeds according to the Monte-Carlo scheme. The parameters that describe the thermodynamic and transport properties resemble those of realistic standard EFCE test systems for extraction. Results of various Monte-Carlo simulations show that under certain conditions mass transfer across interfaces induces the formation of nano droplets in the close vicinity of the interface. The different combinations of the nano droplet behaviour due to attractive or repulsive long-range forces together with the characteristics of coalescence may lead to different macroscopic interfacial instabilities such as spontaneous emulsification or eruptions. Based on diffusive and thermodynamic properties of the chosen lattice system a first stability criterion which allows the prediction of the onset of nano droplet formation is developed. The theoretical results compare well with experimental observations at a single drop and in a two-phase cell where the instabilities are investigated optically via Schlieren optics.

An ambience-induced optical absorption peak for Au/SiO 2 mesoporous assembly

In this Letter, we report that a new optical absorption around 470 nm (varying from 465 to 475 nm) occurs for the gold nanoparticles/monolithic mesoporous silica assembly, after exposure to ambient air (aging) and subsequent drying at 120 °C. Ambient ageing for a certain time plays a crucial role in appearance of this peak after subsequent drying at 120 °C. This new peak may be associated with Au clusters with size less than 1.5 nm. A nanodroplet formation and evaporation model is presented, which can qualitatively explain all evolution behaviours of this peak under different treatment conditions

A Study of the Relation between Bicontinuous Microemulsions and Oil/Water Nano-emulsion Formation

Oil/water (O/W) nano-emulsions have been formed in the system water/C16E6/mineral oil by the phase inversion temperature (PIT) method. The relation between the phase equilibria observed at the hydrophilic−lipophilic balance (HLB) temperature or the PIT (i.e., the nature, number, and relative volume fractions of the involved phases), the droplet sizes, and polydispersities of the resulting emulsions have been determined. Milky white emulsions were obtained when, at the HLB temperature, a three-phase equilibrium formed by water (W), shear-birefringent microemulsion (D), and oil (O) was observed. However, bluish transparent O/W nano-emulsions with droplet sizes as low as 40 nm were formed in a narrow range of oil-to-surfactant ratios in which a D or W + D phases were the initial equilibrium phases. In the W + D equilibria, droplet sizes were independent from the water content, indicating that nanodroplet formation is mainly controlled by the structure of the D phase. These results suggest that the main requirement for bluish transparent O/W nano-emulsion formation is the complete solubilization of the oil component in a bicontinuous microemulsion, independent of whether the initial phase equilibrium is single or multiphase.

Understanding how the liquid-metal ion source works

There is some interesting physics in how the liquid-metal ion source (LMIS) works. This short review describes our current understanding, covering the following topics. Distinction between the real Taylor-Gilbert cone and Taylor's mathematical cone. Thermodynamic origin of the pressure-difference formula. Shape of an operating LMIS: the cusp-on-a-cone as expected shape and as an electrically driven vena contracta. Onset behaviour and Taylor's slender-body formula. Ion energy distributions, and interpretation in terms of surface processes and space-charge. Swanson's proof that the emission mechanism is field evaporation. Predicting the low-current Ga LMIS apex radius as 1.5 nm. The low-current Ga LMIS as a device driven by a negative pressure of order 40 atm. Re-examination of Mair's formula for LMIS current/voltage characteristics, and the role of space-charge. Cusp length as a function of emission current: theory and modelling. Emitter stability and control mechanisms: space-charge stabilisation, inertial/geometrical stabilisation, pressure-change destabilisation. Secondary emission phenomena: electrons, neutrals and photons. The high-temperature anomaly in the ion energy distribution, and a possible explanation. Instability and the formation of microdroplets and nanodroplets. Numerical modelling of basic LMIS behaviour: current/voltage characteristics for sources with and without viscous drag; modelling of cusp length and limiting half-angle; modelling of time-dependent effects. Current research tasks.

Diffusion Processes of Interacting Brownian Particles in Blockcopolymer‐Microemulsion Transient Networks

AbstractQuasielastic light‐scattering and pulsed field gradient NMR were used to investigate the effects of a triblock copolymer and a α‐ω telechelic ionomer on the interaction potential and transient network formation of nanodroplets in w/o microemulsions. The NMR self diffusion measurements yield a crossover from restricted polymer diffusion to free self diffusion. The relation between the copolymer self diffusion and the dynamic properties of the transient network are explained in the framework of reversibly cross linked polymer chains. Quasi‐elastic light‐scattering, only sensitive to the correlations between the waterdroplets, yields three diffusive processes, which are due to fast collective diffusion and slowly decaying correlations, controlled by the specific interactions of the hydrophilic and hydrophobic blocks with the water and oil phases.

Rheology of mesogels

The effect of triblock copolymers (polyoxyethylene-polyisoprene-polyoxyethylene) on the interaction potential and network formation of nanodroplets in w/o microemulsions, I-e- on the formation of « mesogels », has been studied by flow- and oscillatory shear measurements. Frequency dependent storage and loss moduli, the zero shear viscosity and the terminal relaxation times were determined which agree well with predictions from scaling laws for homopolymer solutions ; lifetimes of network crosslinks were deterrrined from the transition of Newtonian to viscoelastic behaviour that agree with the characteristic time constant which correspond to the crossover from restricted to free diffusion of the copolymer. The activation energy of viscous flow at large copolymer concentrations shows a logarithmic concentration dependence from which a power law dependence of the viscosity against copolymer concentration can be derived if an Arrhenius relation for the temperature dependent viscosity is assumed.