Fluid interfaces, nanoparticles

We have considered the case of a fluid wedge that can deform under the action of the disjoining pressure. Our simulations show that the extent of deformation of the meniscus (or fluid interface) increases with increase in the volume fraction of nanoparticles/micelles, when a decrease in the diameter of micelles and with a decrease in the capillary pressure resisting the deformation is smaller. The resulting deformation of the meniscus causes the contact line to move so that it displaces the fluid that does not contain the micelles (oil) in favor of the fluid that contains it (aqueous surfactant solution). 

In brief, the investigation of ferrofluids through Raman spectroscopy permits to access the physical and chemical properties of both solid and liquid phases. Comparison between the Raman spectra obtained from liquid water and the Raman spectra obtained from the uncoated and coated nanoparticles dispersed as ferrofluid provides information about the interface nanoparticle surface-carrier liquid [63]. The onset of the hematite phase in core magnetite dispersed as magnetic fluids was followed by Raman spectroscopy, and the results showed that the laser intensity at which the phase-transition takes place was higher for nanoparticles in the colloid than that for the same core as powder samples [69]. 

Vekas, L., Rasa, M., and Bica, D., Physical properties of magnetic fluids and nanoparticles from magnetic and magneto-rheological measurements, J. Colloid Interface Sci., 231, 247, 2000. 

The structure of CdSe nanoparticles segregated to the fluid interface as shown by confocal microscopy (Fig. 4a) has been investigated ex situ with scanning force microscopy (SFM) and transmission electron microscopy (TEM) methods. All results point to a monolayer of nanoparticles with liquidlike ordering at the interface (Fig. 4b,c) [46],... 

Similarly, Lan et al. [7] developed a one-step microfluidic method for fabricating nanoparticle-coated patchy particles. A coaxial microfluidic device was employed to produce Janus droplets composed of curable phase and non-curable phase. The results showed that nanoparticles were dispersed either in the continuous fluid or the non-curable phase fluid. The nanoparticles (30 nm or 300-500 nm) were adsorbed onto the interface between these phases, and the curable phase was solidified by UV-irradiated polymerization. Thus, the patchy microparticles asymmetrically coated by nanoparticles were synthesized. They also employed Si02, TS-1, and fluorescent polystyrene nanoparticles as the coating materials to demonstrate the validity of the method. The microfluidic approach exhibited excellent controllability in morphology, monodispersity, and size for the nanocomposites. The morphology of the particles could be controlled from less than a hemisphere to a sphere by adjusting the flow rate ratio of the two dispersed phases. The method can be applied to other nanoparticles with specific surface properties. 

Monolayers of nanoparticles at liquid-fluid interfaces have attracted considerable attention over several decades [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17]. Among others, the examinations focused on thin-layer preparation [10, 18, 19, 20, 21, 22, 23], emulsion stabilisation [15, 24] and particle characterisations [25, 26, 27]. The Stober silica (synthesised by controlled hydrolysis of tetraethylorthosilicate in ethanol in the presence of ammonia and water) [28] has many advantageous properties for model investigations. The nearly spherical particles show a narrow size distribution and are compact above a certain particle size (around 20 nm diameter) [29]. The particles, on the one hand, show partial wettability and, on the other hand, form a weakly cohesive two-dimensional dispersion at the water-air interface [10, 14]. All that makes them suitable to determine the total repulsive interparticle energies in a film balance by measuring the effective surface tension of the monoparticulate layer [30, 31, 32, 33, 34, 35, 36]. 

Heat transport in suspensions of Au-core silica-shell nanoparticles was reported to depend on the composition of the solvent i.e., solvent penetration into the porous silica shell changed the thermal conductivity of the shell significantly [40]. Ge et al. have emphasized the role of the nanoparticle/surfactant/fluid interfaces on thermal transport from nanoparticles to the surrounding fluid [41]. In aqueous suspensions, these interface effects are relatively weak because the thermal conductance of the nanoparticle/water interface is large. 

N. Aubry and P. Singh, Physics underlying controlled self-assembly of micro- and nanoparticles at a two-fluid interface using an electric field, Phys. Rev. E, 11, 056302, 2008. 

F. Bresme and M. Oettel, Nanoparticles at fluid interfaces, J. Phys. Condens. Matter, 19,413101, 2007. 

Nanoparticle assembly at a fluid-fluid interface can be categorized as a dynamic self-assembled system, since the nanoparticles are small and thus have less to contribute to interfadal stabilization relative to miaoparticles. As... 

Lynch, I. et al. (2007) The nanoparticle-protein complex as a biological entity a complex fluids and surface science challenge forthe 21st century. Advances in Colloid and Interface Science, 134—135, 167-174. 

Inorganic nanoparticles themselves can be assembled into mesoscopic structures. Dinsmore et al. proposed an approach for the fabrication of solid capsules from colloidal particles with precise control of size, permeability, mechanical strength, and compatibility (Fig. 2.9).44 This unusual mesoscopic structure is called colloidosome and is prepared through emulsion droplets at a water-oil interface. Following the locking together of the particles to form elastic shells, the emulsion droplets were transferred to a fresh continuous-phase fluid identical to that contained inside the droplets. The resultant structures are hollow, elastic shells whose permeability and elasticity can be precisely controlled. 

Abstract. Surface pressure/area isotherms of monolayers of micro- and nanoparticles at fluid/liquid interfaces can be used to obtain information about particle properties (dimensions, interfacial contact angles), the structure of interfacial particle layers, interparticle interactions as well as relaxation processes within layers. Such information is important for understanding the stabilisation/destabilisation effects of particles for emulsions and foams. For a correct description of II-A isotherms of nanoparticle monolayers, the significant differences in particle size and solvent molecule size should be taken into account. The corresponding equations are derived by using the thermodynamic model of a two-dimensional solution. The equations not only provide satisfactory agreement with experimental data for the surface pressure of monolayers in a wide range of particle sizes from 75 pm to 7.5 nm, but also predict the areas per particle and per solvent molecule close to the experimental values. Similar equations can also be applied to protein molecule monolayers at liquid interfaces. 

In a solution, nanoparticles interact with each other in a number of ways. Widely separated nanoparticles may be brought into contact by Brownian motion. As they approach each other, electrostatic, van der Waals forces, and hydrogen bonding, in addition to Brownian motion, can cause two nanoparticles to rotate with respect to each other, and collide. Evidently, under some conditions, the collisions that result in fusion are those that involve two nanoparticles in appropriate orientations to form a coherent (or semicoherent) interface. Particle rotation in the absence of a fluid has been modeled computationally (Zhu and Averback 1996), implying that oriented assembly-based crystal growth can also occur in dry systems. 

A number of interesting properties are associated with the critical state. One of these is that the density of the liquid and of the vapor becomes identical, and for this reason the interface between the two phases disappears. Supercritical fluid technology is a relatively new approach to obtain micro- and nanoparticles. For pharmaceutical applications, supercritical carbon dioxide (SC-CO2) is most widely used because of its low and easily accessible critical temperature and pressure (31.2 °C ... 

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