Droplets disintegration

Coulombic explosion The process by which a droplet disintegrates into a number of smaller droplets which occurs when the repulsive forces between charges on the surface of a droplet are greater than the cohesive force of surface tension. 

The mean droplet size, 4. is important because larger droplets move more rapidly toward the central core. Higher inlet oil concentrations increase the probability of coalescence giving rise to an increased mean droplet size. Additionally, careful design to minimize high-shear areas upstream of the hydrocyclooe is important to prevent droplet disintegration. 

In the ion-evaporation model of Iribame and Thomson [11-14], the seqnence of solvent evaporation and electrohydrodynamic droplet disintegration also leads to the production of microdroplets. Gas-phase ions can be generated from the highly-charged microdroplets, at which the local field strength is sufficiently high to allow preformed ions in solution to be emitted into the gas phase (lEV). 

Droplet disintegration is caused by the kinetic energy of the turbulence eddies. Eddies whose size 2 corresponds approximately to the droplet diameter d32) be. z as 32, have the strongest dispersing action. For 2 > d32 the droplet is carried along by the flow and thereby is hardly deformed, whereas for 2 <132 the eddies... 

The critical Weber number We for the droplet disintegration can be obtained from the above relationship. It is the turbulent velocity fluctuations and not the shear rates, which are responsible for the droplet disintegration. Above a critical Weber number the droplet is unstable and breaks up. 

How the droplets produced upon ESI are transformed to the ions observed in the mass spectrum is not yet well xmderstood. As the solvent in the droplets evaporates, the droplets shrink and the ions contained in them accumulate at the surface to minimize coulombic repulsion between the charges. This process can continue until the Rayleigh instability limit is reached, at which the droplets disintegrate ("explode") into smaller droplets (Figure 1.15) that also shrink by solvent loss. Sequential subdivision through coulombic explosion at the Rayleigh limit may be repeated until the... 

A droplet may become charged by other mechanisms such as ionization, preferential adsorption of ions at the interface (electric double layer), and droplet disintegration. 

The time until droplet disintegration results from Eq. (10.42)... 

The flight path until droplet disintegration is calculated using Eq. (10.43), which gives... 

As the droplets are dried, the charge density increases, resulting in droplet disintegration either because of Cordombic forces or by distortion to form a Taylor cone from which ions are released. 

FIGURE 2.13 Taylor cone formation occurs both at the end of the ESI tube and as the droplets disintegrate to release ions. 

Electro hydrodynamic droplet disintegration Coulomb explosion... 

Reinecke, W.G, and Waldman, G.D., An Investigation of Water Droplet Disintegration in the Region Behind Strong Shocks , Presented at 3rd International Conf. on Rain Erosion and Related Phenomena, Hampshire, England, 1970. 

G". Both G and G" are measured as a function of strain amplitude (at constant frequency) and as a function of frequency (at constant strain amplitude in the linear viscoelastic region). Any change is the structure of the multiple emulsion will be accompanied by a change in G and G". For example, if the multiple emulsion droplets undergo swelling by flow of water from the external to the internal phase, G will increase with time. Once the multiple emulsion droplets disintegrate to form an 0/W emulsion, a drop in G is observed. Alternatively, if the multiple emulsion droplets shrink, G decreases with time. 

---