Droplet kinetics parameters

All the factors discussed here make miniemulsion polymerization kinetics very complicated, as shown by the rather scattered values of the kinetic parameters a, P, y and 8 obtained from the relationships Np [S] [I] and Rp [S] [I] (e.g., see Table 5.1 in this section and Table 1 in reference 11). The parameter Np is the number of latex particles per unit volume of water, Rp is the rate of polymerization, and [S] and [I] are the concentrations of surfactant and initiator in water, respectively. As expected, the rate of polymerization in common miniemulsion polymerization systems increases with increasing concentration of surfactant or initiator [11]. As to the influence of the concentration of costabilizer (hexadecane) on the miniemulsion polymerization kinetics, the experimental results reported in the literature are not conclusive [12]. The rate of polymerization may decrease with increasing concentration of hexadecane or this effect may be insignificant in nuniemul-sion polymerization. These conflicting observations can be attributed to the different concentrations of monomer in the monomer droplets and the varying droplet sizes (or droplet numbers) when the level of hexadecane used in stabilizing the miniemulsion is varied. 

Table 9.7. Parameters obtained from droplet kinetics of polymers...

Liquid-liquid multiphasic catalysis with the catalyst present in the ionic liquid phase relies on the transfer of organic substrates into the ionic liquid or reactions must occur at the phase boundary. One important parameter for the development of kinetic models (which are crucial for up-scaling and proper economic evaluation) is the location of the reaction. Does the reaction take place in the bulk of the liquid, in the diffusion layer or immediately at the surface of the ionic liquid droplets ... 

With the above-described heat transfer model and rapid solidification kinetic model, along with the related process parameters and thermophysical properties of atomization gases (Tables 2.6 and 2.7) and metals/alloys (Tables 2.8,2.9,2.10 and 2.11), the 2-D distributions of transient droplet temperatures, cooling rates, achievable undercoolings, and solid fractions in the spray can be calculated, once the initial droplet sizes, temperatures, and velocities are established by the modeling of the atomization stage, as discussed in the previous subsection. For the implementation of the heat transfer model and the rapid solidification kinetic model, finite difference methods or finite element methods may be used. To characterize the entire size distribution of droplets, some specific droplet sizes (forexample,.D0 16,Z>05, andZ)0 84) are to be considered in the calculations of the 2-D motion, cooling and solidification histories. 

It can be considered from the scheme that one has to distinguish between the foam kinetics, i.e. the rate of generation of foam under well defined conditions (air input and mechanical treatment) and the stability and lifetime of a foam once generated. The foam kinetics is also sometimes termed foamability in the literature. These quantities can be related to interfacial parameters such as dynamic surface tension, i.e. the non-equilibrium surface tension of a newly generated surface, interfacial rheology, dynamic surface elasticity and interfacial potential. In the case of the presence of oily droplets (e.g. an antifoam, a... 

The aim of this first section is to describe the rupturing mechanisms and the mechanical conditions that have to be fulfilled to obtain monodisperse emulsions. A simple strategy consists of submitting monodisperse and dilute emulsions to a controlled shear step and of following the kinetic evolution of the droplet diameter. It will be demonstrated that the observed behavior can be generalized to more concentrated systems. The most relevant parameters that govern the final size will be listed. The final drop size is mainly determined by the amplitude of the applied stress and is only slightly affected by the viscosity ratio p. This last parameter influences the distribution width and appears to be relevant to control the final monodispersity. 

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