Controlled assembly of jammed colloidal shells on fluid droplets

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Original entry: Pratomo Putra (Tom) Alimsijah, APPHY 226, Spring 2009

Another entry on same paper: Controlled Assembly of Jammed Colloidal Shells on Fluid Droplets


Controlled assembly of jammed colloidal shells on fluid droplets

Anand Bala Subramaniam, Manouk Abkarian, and Howard A. Stone, Nature of materials Vol. 4, July 2005


Soft Matter Keywords

Assembly, Colloidal, Shells, Adsorption, Jamming, Armoring, Potential well

Abstract

The paper described a method to use interfacial assembly for producing stable jammed shells. The authors proposed that the energetic barriers to interfacial crystal growth can be overcome by utilizing hydrodynamic flows to deliver colloidal particles. This is different than methods previously reported in that previous approaches reply on bulk emulsification methods. Previous methods require further chemical and thermal treatments and thus restricting the type of materials that can be used.


Soft Matter Discussion

The authors observed that jammed shells will only be adsorbed at high velocities. There is also a well-defined region of capture. This region of capture as shown below (above the thick horizontal line) is where the largest change in flow happens. Particles colliding with the interface are captured when they are above this line.


Fig. 1


The particles are then trapped on the interface in a potential well estimated to be 10^7 kT for micrometer-diameter particles. The shear experienced by the particles from the surrounding fluid is insufficient to dislodge the particle through the interface.


They also found that the jammed armor manufactured this way is intrinsically stable and will not spontaneously coalesce with each other or with an uncovered interface.


Fig. 2 Armored bubbles along gas-water interface. The armored bubbles do not coalesce with each other or with uncovered interface. They seem to be stable indefinitely.


They postulate that this is because of the spontaneous jamming of the particles in the shell causing the systems to undergo shear-induced liquid-to-solid transitions. This causes the droplet to stabilize preventing spontaneous coalescence due to interfacial surface area minimization or shear-induced coalescence.


Without any hydrodynamic flow, the spontaneous adsorption of particles did not happen. Even with the addition of NaCl (up to conc. of 1.0M), the aggregates did not adsorb and cover the droplets. Gentle agitation to prevent particle sedimentation does not cause adsorption. However, more forceful agitation produces partially covered droplets. This shows that the production of colloidal shells on fluid droplets requires specific input of energy to overcome adsorption barriers. In the experiments shown, the energy is the inertia of the hydrodynamic flows.