Fission of droplets

Gomez, A. Tang, K. Charge and Fission of Droplets in Electrostatic Sprays. Phys. Fluids 1994, 6,404-414. 

Gomez, A. and Tang, K. (1994). Charge and fission of droplets in electrostatic sprays, Phys. Fluids, 6,404. 

The basic model as outlined above (often described as fusion and fission of droplets in W/O microemulsions) has been generally used for explaining reactions leading to, for example, polymerization of monomers and reduction of metal ions to metal particles. Natarajan et al. [160] who proposed a stochastic model for ultrafine metal particle synthesis from metal salts by the above method worked out some fusion-fission rules as summarized below ... 

Solvent Evaporation from Charged Droplets Causes Coulomb Fissions of Droplets... 

Percolation in microemulsions and concomitant microstructural changes are the focal points of this review. A complete understanding of percolation phenomena in reverse microemulsions will require an understanding of droplet interactions and the associated thermodynamics of droplet fusion, fission, aggregation to form clusters of varying fractal... 

Fig. 11.5. Diagram illustrating the components of an ESI source. A solution from a pump or the eluent from an HPLC is introduced through a narrow gage needle (approximately 150 pm i.d.). The voltage differential (4-5 kV) between the needle and the counter electrode causes the solution to form a fine spray of small charged droplets. At elevated flow rates (greater than a few pl/min up to 1 ml/min), the formation of droplets is assisted by a high velocity flow of N2 (pneumatically assisted ESI). Once formed, the droplets diminish in size due to evaporative processes and droplet fission resulting from coulombic repulsion (the so-called coulombic explosions ). The preformed ions in the droplets remain after complete evaporation of the solvent or are ejected from the droplet surface (ion evaporation) by the same forces of coulombic repulsion that cause droplet fission. The ions are transformed into the vacuum envelope of the instrument and to the mass analyzer(s) through the heated transfer tube, one or more skimmers and a series of lenses.

Fig. 11.13. Illustration of droplet jet fission. The average number of charges on a droplet, the radii of the droplets [pm], and the timescale of events are assigned. The inset shows a drawing of droplet jet fission based on an actual flash microphotograph. Reproduced from Ref. [49] by permission of the authors.

On the contrary, it may be argued that the electric field strength locally necessary to evaporate ions from a droplet cannot be attained because of the prior fission of the droplet due to crossing the Rayleigh limit. [23,90]... 

API-electrospray ionization involves three stages. First, there is the formation of charged droplets. Once the droplets are formed, solvent evaporation and droplet fission occur. Droplet fission is due to an increase in charge repulsion at the surface of the droplet as the solvent evaporates. Once the droplets become small enough (<10 nm), it is believed that charge repulsion produces ion evaporation from the surface of the droplet. Thus, ions are transferred from the solution to the gas phase. Factors affecting the production of the desired ions include analyte concentration, flow rate, matrix content, and analyte surface activity. In... 

As a consequence, the droplet breaks up into a stream of smaller droplets, each one continuing to shrink by evaporation until the Rayleigh stability limit is reached again. The process of droplet fission is repeated several times and it is called uneven fission or droplet jet fission [5,6],... 

The droplet size and size distribution seems to be controlled by a Fokker-Planck type dynamic rate equilibrium of droplet fusion and fission processes, i.e., the primary droplets are much smaller directly after sonication, but colloidally unstable, whereas larger droplets are broken up with higher probability. This also means that miniemulsions reach the minimal droplet sizes under the applied conditions (surfactant load, volume fraction, temperature, salinity, etc.), and therefore the resulting nanodroplets are at the critical borderline between stability and instability. This is why miniemulsions directly after homogenization are called critically stabilized [19,20]. Practically speaking, miniemulsions potentially make use of the surfactant in the most efficient way possible. 

Also in the inverse case, the droplet size throughout the miniemulsification process runs into an equilibrium state (steady-state miniemulsion) which is characterized by a dynamic rate equilibrium between fusion and fission of the... 

The formation of a miniemulsion requires high mechanical agitation to reach a steady state given by a rate equilibrium of droplet fission and fusion. 

For percolating microemulsions, the second and the third types of relaxation processes characterize the collective dynamics in the system and are of a cooperative nature. The dynamics of the second type may be associated with the transfer of an excitation caused by the transport of electrical charges within the clusters in the percolation region. The relaxation processes of the third type are caused by rearrangements of the clusters and are associated with various types of droplet and cluster motions, such as translations, rotations, collisions, fusion, and fission [113,143]. 

It is reasonable and widely accepted that the back-transfer process of proteins and other solutes is governed by an interfacial process and by a coalescence of the reverse micelles at the oil-water interface. According to the previous report, alcohol promotes the fusion/fission of the reverse micelles [11]. Such a modification in the dynamic property of reverse micellar droplets also affects the coalescence of the droplets and the bulk aqueous solution, and in this study results in an assistance in the release of proteins from the droplets. However, besides the alcohol addition, the appropriate pH and salt concentration in the recovery aqueous phase is required for protein release from the droplets into the recovery phase. The salt concentration leads to an osmotic effect and results in a swelling of the droplets in the presence of alcohol. The swelling droplets would... 

In both the procedures, by varying to, the dimensions of the synthesised particles can be altered. The pictorial representations of the above protocols are illustrated in Fig. 6.2. As can be seen, the internal phenomenon of droplet fusion followed by fission takes place. The materials formed during fusion by reaction get distributed among the droplets upon fission. By probability, some droplets may remain empty which is more in dilute solution of the reactants. The occurrence of the process of fusion and fission has been established by the TRFQ (time-resolved fluorescence quenching method [ 18-20]). The internal dynamics of the disperse particles essentially guide the formation characteristics of nanoparticles. 

Equation (170) may be derived by the method used by Behnken et al. (B4) in their study of particle growth processes. The primary difference is that one must account for fission of cells, a possibility not considered in the work cited. Similar equations, but not containing the growth terms, have been considered by Valentas (VI) in his study of droplet breakup and coalescence phenomena in agitated, two-phase systems. Note that if fission always results... 

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