Coalescence of Repelling Colloidal Droplets: A Route to Monodisperse Populations
Forskningsoutput: Tidskriftsbidrag › Artikel i vetenskaplig tidskrift
Abstract
Populations of droplets or particles dispersed in a liquid may evolve through Brownian collisions, aggregation, and coalescence. We have found a Set of conditions under which these populations evolve spontaneously toward a narrow, size distribution. The experimental system of poly(methyl methacrylate) (PMMA) nanodroplets dispersed in a solvent (acetone) + nonsolvent (water) mixture. These droplets carry electrical charges, located on the ionic end groups of the macromolecules. We used timeresolved Small angle Xray scattering to determine their size distribution. We find that the droplets grow through coalescence events the average radius < R > increases logarithmically with elapsed time While the relative width sigma(R)/< R > of the distribution decreases as the inverse square root of < R >. We interpret this evolution as resulting from coalescence events that are hindered by ionic repulsions between. droplets. We generalize this evolution through a simulation of the Smoluchowski kinetic equation, with fa kernel that takes into account the interactions. between droplets. In the case of vanishing or attractive interactions, all droplet encounters lead to coalescence. The corresponding,kernel leads to the wellknown "selfpreserving" particle distribution Of the coalescence process, where sigma(R)/< R > increases to a plateau Value. However, for droplets that interact through longrange ionic repulsions, "large + small" droplet encounters are. more suceessful at. coalescence than, "large + large" encounters. We show that the corresponding kernel leads to a particular scaling of the dropletsize distributionknown as the "secondscaling law" in the theory of critical phenomena, where sigma(R)/< R > decreases as 1/root < R > and becomes independent of the initial distribution. We argue that this Scaling explains the narrow size distributions of colloidal dispersions that have been synthesized through aggregation processes.
Detaljer
Författare  

Enheter & grupper  
Forskningsområden  Ämnesklassifikation (UKÄ) – OBLIGATORISK

Originalspråk  engelska 

Sidor (fråntill)  56895700 
Tidskrift  Langmuir 
Volym  29 
Utgåva nummer  19 
Status  Published  2013 
Publikationskategori  Forskning 
Peer review utförd  Ja 