171 research outputs found
Self-assembly of colloidal molecules due to self-generated flow
The emergence of structure through aggregation is a fascinating topic and of
both fundamental and practical interest. Here we demonstrate that
self-generated solvent flow can be used to generate long-range attractions on
the colloidal scale, with sub-pico Newton forces extending into the
millimeter-range. We observe a rich dynamic behavior with the formation and
fusion of small clusters resembling molecules, the dynamics of which is
governed by an effective conservative energy that decays as . Breaking the
flow symmetry, these clusters can be made active
Forces between Colloidal Particles in Aqueous Solutions Containing Monovalent and Multivalent Ions
The present article provides an overview of the recent progress in the direct
force measurements between individual pairs of colloidal particles in aqueous
salt solutions. Results obtained by two different techniques are being
highlighted, namely with the atomic force microscope (AFM) and optical
tweezers. One finds that the classical theory of Derjaguin, Landau, Verwey, and
Overbeek (DLVO) represents an accurate description of the force profiles even
in the presence of multivalent ions, typically down to distances of few
nanometers. However, the corresponding Hamaker constants and diffuse layer
potentials must be extracted from the force profiles. At low salt
concentrations, double layer forces remain repulsive and may become long
ranged. At short distances, additional short range non-DLVO interactions may
become important. Such an interaction is particularly relevant in the presence
of multivalent counterions.Comment: Submitted on 30th of May 2016 as invited article to Curr. Opinion
Colloid Interf. Sci. Edited by W. Ducker and P. Claesson. 15 Pages, 7 Figures
82 reference
Melting and Freezing Lines for a Mixture of Charged Colloidal Spheres with Spindle-Type Phase Diagram
We have measured the phase behavior of a binary mixture of like-charged
colloidal spheres with a size ratio of 0.9 and a charge ratio of 0.96 as a
function of particle number density n and composition p. Under exhaustively
deionized conditions the aqueous suspension forms solid solutions of body
centered cubic structure for all compositions. The freezing and melting lines
as a function of composition show opposite behavior and open a wide, spindle
shaped coexistence region. Lacking more sophisticated treatments, we model the
interaction in our mixtures as an effective one-component pair energy
accounting for number weighted effective charge and screening constant. Using
this description, we find that within experimental error the location of the
experimental melting points meets the range of melting points predicted for
monodisperse, one component Yukawa systems made in several theoretical
approaches. We further discuss that a detailed understanding of the exact phase
diagram shape including the composition dependent width of the coexistence
region will need an extended theoretical treatment.Comment: 25 pages, 4 figure
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