Time evolution of the size distribution of nano-sphere droplets in the hexadecane-in-water miniemulsion stabilized by nonionic surfactants

Time evolutions of the droplet size distribution in miniemulsions, which is constituted of water/n-hexadecane/nonionic surfactants, were investigated by using light scattering techniques. A hard-sphere model is applied to cha racterize the polydispersity of miniemulsion droplets. Measuring the relati ve scattering intensity as a function of the volume fraction of dispersed p hase, the variance of the droplets size distribution, sigma (2), was evalua ted. Miniemulsions developed gradually from monodisperse systems (sigma (2) congruent to 0.02) to polydisperse ones (sigma (2) greater than or equal t o 0.13) over 12 days after preparation. sigma (2) increased rapidly in the early stage, and ceased to develop at about 6 days after preparation. The z -average hydrodynamic radius of miniemulsion droplets grew with time over t he whole time range. The change with time of the total droplet number of mi niemulsion is in agreement with that predicted by Smoluchowski's theory for diffusion-controlled coagulation. Although the characteristic coagulation time obtained here was much larger than that estimated by Smoluchowski's th eory, the qualitative agreement between the theory and the experimental res ults obtained here is good. At the earlier stage of the destabilization pro cess of miniemulsions, the growth mechanism of droplets may be explained in terms of a diffusion-controlled coagulation.