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Two Dimensional Supramolecular Organisation Of Core-Shell Nanoparticles. A
Computer Simulation Study.
G. Tritsaris 1 , A. G. Vanakaras 1
1 Department of Materials Science, University of Patras, Patras, 26504, Greece.
*a.g.vanakaras@upatras.gr
The so-called core-shell or core-corona particles represent a broad class of systems that have been intensively investigated
during the last few years. Typical systems exhibiting such composite architecture include metal or glass nanoparticles, block
copolymer micelles, and globular dendrimers.
Herein we explore, by means of computer simulations, the molecular organization in two dimensions of two different
classes of core-shell nanoparticles: 1) Janus discs[1], that are composed by a hard internal core decorated with an amphiphilic
halo and 2) half discs[2] that are modeled as hard hemi-discs with their circular periphery decorated with a soft coronal
segment. Simplified intermolecular potentials that mimic the basic molecular features are introduced.
Despite their simplicity the Janus systems exhibit, at high densities, fascinating equilibrium patterns the motif of which
depends critically on the coronal thickness[1]. Furthermore even in the low density regime, where the systems does not
exhibit any long range order, the molecular interactional recognition drives the formation of physical molecular clusters,
either linear and/or branched or cyclic, that resemble random polymeric networks[3].
The ordered (high-density) phases of the half disc systems are characterised by the formation of physical aggregates
(clusters) with well defined and persistent shapes. For particles with thin coronal shells the supramolecular aggregate is
simply a whole disc composed of two half-discs. However, when the coronal thickness exceeds a certain threshold, the
supramolecular aggregate is formed by more than two particles and surprisingly its shape presents an empty interior. These
aggregates, in turn, self-organise in periodic motifs exhibiting open pores and extended coronal overlapping (see figure 1).
The number of molecules per aggregate, the shape and the pore size of the suprmolecular entities in the ordered phases
depend critically on the size of the core relative to the coronal halo. The phase transitions and the molecular organisation in
the resulting phases of such systems are analysed in detail and the molecular forces that drive their fascinating pattern
formation are discussed.
The results of these simulations broaden the rage of known modes of colloidal self assembly in two dimensions[1] and
suggest that 2D semidisc core-shell particles are promising candidates for bottom-up design of precise two-dimensional
porous templates.
Figure 1. Supramolecular organisation of a simulated half-disc system with relatively thick shell. To facilitate visualisation,
the coronal shell has been replaced by a number of flexible chains (green) attached to the circular periphery of the core (dark
grey).
References:
[1] A.G. Vanakaras, Langmuir, 22, 88-93 (2006).
[2] G. Tritsaris and A. G. Vanakaras, to be published.
[3] J. M. Lehn, Progr. Pol. Sci., 30, 814-831 (2005).
Acknowledgment Financial support from the Hellenic Ministry of Education, through the “Pythagoras” research
programme is acknowledged.
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