2011/11/18 by Djamel El Masri, Teun Vissers, Stéphane Badaire +8
Agricultural and Biological Sciences · Chemistry · Materials Science · Medicine · Physics and Astronomy · #Biocrusts and Microbial Ecology #Chemical physics #Chemistry #Colloid #Colloidal crystal #Composite material #Crystallization #Geology #Material Dynamics and Properties #Materials science #Particle (ecology) #Physical chemistry #Sediment #Sedimentation #Spaceflight effects on biology #Suspension (topology) #Volume fraction #cond-mat.soft #physics.space-ph
paper · pdf · doi:10.1039/c2sm07217c
13 pages, 13 figures
arxiv created 2011/11/18 · openalex publication_date 2012/01/01 · arxiv updated 2012/06/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/01
We report qualitatively on the differences between colloidal systems left to evolve in the Earth's gravitational field and the same systems for which a slow continuous rotation averaged out the effects of particle sedimentation on a distance scale small compared to the particle size. Several systems of micron-sized colloidal particles were studied: a hard sphere fluid, colloids interacting via long-range electrostatic repulsion above the freezing volume fraction, an oppositely charged colloidal system close to either gelation and/or crystallization, colloids with a competing short-range depletion attraction and a long-range electrostatic repulsion, colloidal dipolar chains, and colloidal gold platelets under conditions where they formed stacks. Important differences in structure formation were observed between the experiments where the particles were allowed to sediment and those where sedimentation was averaged out. For instance, in the case of colloids interacting via long-range electrostatic repulsion, an unusual sequence of dilute-fluid–dilute-crystal–dense-fluid–dense-crystal phases was observed throughout the suspension under the effect of gravity. This was related to the volume fraction dependence of the colloidal interactions, whereas the system stayed homogeneously crystallized with rotation. For the oppositely charged colloids, a gel-like structure was found to collapse under the influence of gravity with a few crystalline layers grown on top of the sediment, whereas when the colloidal sedimentation was averaged out, the gel completely transformed into crystallites that were oriented randomly throughout the sample. Rotational averaging out of gravitational sedimentation is an effective and cheap way to estimate the importance of gravity for colloidal self-assembly processes.