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Wednesday, 11. June 2014 15:23 Age: 3 yrs

Tunable Assembly of Heterogeneously Charged Colloids

Category: Scientific Highlights

Published in Nano Letters

ABSTRACT:

The self-assembly of colloidal particles is a route to designed materials production that combines high flexibility, cost effectiveness, and the opportunity to create ordered structures at length scales ranging from nano- to micrometers. For many practical applications in electronics, photovoltaics, and biomimetic material synthesis, ordered mono- and bilayers are often needed. Here we present a novel and simple way to tune via external parameters the ordering of heterogeneously charged colloids into quasi two-dimensional structures. Depending on the charges of the underlying substrate and of the particles, a rich and versatile assembly scenario takes place, resulting from the complex interplay between directional attractive and repulsive particle?particle and particle?substrate interactions. Upon subtle variations of the relative charge of the system components, emerging via pH modification, reversible changes either from extended aggregates to a monomeric phase or from triangular to square domains are observed.

 

Figure:

Analysis of the particle−particle energy, ecc, for simplified,
fully two-dimensional, isolated units of the microcrystalline domains
observed when ZwZp > 0. Left/right: Neutral/charged IPCs are forced
to be arranged into a g-triangle/square configuration, and the energy
of the central particle (colored in red) is reported as a function of
small angular rotations of this particle (defined by the angle ω) with
respect to the equilibrium orientation; in the snapshot, the continuous
arrow indicates the equilibrium orientation (ω = 0°), while the dotted
arrow defines the angle ω. The corresponding internal energy of the
central particle for neutral/charged IPCs in its equilibrium orientation
in a g-triangle/square configuration is also reported for comparison.
Note that in the grain-like patterns observed in the simulations the
orientational vectors of two neighboring IPCsin contrast to the
idealized scenario considered hereare not fully horizontal, as shown
in Figure 3 of the Supporting Information.

Bianchi E., Likos C.N., Kahl G. (2014), Tunable Assembly of Heterogeneously Charged Colloids, Nano Lett. 14, 3412–3418. DOI:10.1021/nl500934v, OpenAccess

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