We report a computational study on the spontaneous self-assembly of spherical particles into twodimensional crystals. The experimental observation of such structures stabilized by spherical objects appeared paradoxical so far.We implement patchy interactions with the patches point-symmetrically (icosahedral and cubic) arranged on the surface of the particle. In these conditions, preference for self-assembly into sheet-like structures is observed. We explain our findings in terms of the inherent symmetry of the patches and the competition between binding energy and vibrational entropy. The simulation results explain why hollow spherical shells observed in some Keplerate-type polyoxometalates (POM) appear. Our results also provide an explanation for the experimentally observed layer-by-layer growth of apoferritin - a quasi-spherical protein. © 2012 American Institute of Physics.

Ethayaraja Mani

Department Of Chemical Engineering

APOFERRITIN

Computational studies

Experimental observation

INHERENT SYMMETRY

LAYER-BY-LAYER GROWTH

Polyoxometalates

Sheet-like

Sheet-like structure

SPHERICAL OBJECTS

Spherical particle

Spherical shell

Two-dimensional crystals

VIBRATIONAL ENTROPY

Binding energy

Self assembly

Spheres

POLYOXOMETALATE I

TUNGSTEN DERIVATIVE

article

chemical structure

chemistry

conformation

surface property

Thermodynamics

Vibration

Models, Molecular

Molecular Conformation

Surface Properties

Tungsten compounds

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Sheet-like assemblies of spherical particles with point-symmetrical patches.

Journal of Chemical Physics

Non-spherical patchy particles are potential candidates as building blocks for the design of target colloidal structures via spontaneous self-organization. We report a facile scheme to synthesize non-spherical particles with patchy electrostatic interactions. In this method, charged spherical latex particles such as polystyrene (PS) are deformed unequally at an oil-water interface due to heating and partial swelling. The spherical particles then evolve into non-spherical shapes such as 'acorn-like' and 'idly-like'. We explain the mechanism of differential deformation by comparing the heat of viscous dissipation and the interfacial energies. Furthermore, if oppositely charged additives such as the cetyltrimethylammonium bromide (CTAB) surfactant or silica nanoparticles are present in water (subphase), electrostatic attraction leads to adsorption of these species on the PS surface exposed to water. As a result, one side of the particles is selectively functionalized, while the other side remains unaltered. As the latex particles are negatively charged initially, this method yields particles that are non-spherical in shape and with negative charges on one side and positive charges on the other side. The degree of shape deformation and patch coverage can be varied by choosing different surface active additives. We extend this approach to curved interfaces and demonstrate a high throughput emulsion based approach for the synthesis of such particles. Self-assembly of these particles shows interesting structures such as linear, branched polymeric or worm-like chains and micelle-like spherical aggregates. These shape anisotropic particles with orientation specific interactions that mimic bio-macromolecular systems can be further explored for self-assembly into hierarchical mesoscale structures. This journal is © The Royal Society of Chemistry 2016.

Soft Matter

Synthesis of non-spherical patchy particles at fluid-fluid interfaces: via differential deformation and their self-assembly

We report a simple strategy to produce single and multipatch particles via the conventional dip-coating process. In this method, a close-packed monolayer of micron-sized silica particles is first formed at air-polymer solution interface, followed by dip coating of particles on a glass substrate. The simultaneous deposition of both polymer and particles on the substrate gives rise to a thin polymer layer and a monolayer of silica particles. Sonication of the substrate leads to the formation of a polymeric patch on one side of the particles. The patch shape depends on the aging of the polymer film prior to sonication. With aging time the patch evolves from ring-like to disk-like. This technique allows easy control of patch width by varying the concentration of polymer in the solution. We further show that the number of patches on the particle can be increased by controlling the concentration of silica particles at the interface such that surface coverage is less than that required for the formation of a close-packed monolayer. The single and multipatch particles are characterized by scanning electron and optical microscopy for the patch size, shape, and number distribution. The as-synthesized particles are used as a model to study self-assembly of colloids with electrostatic repulsion and patchy hydrophobic attractions due to polymeric patches. We find the formation of doublets and finite-sized clusters due to patchy interactions. Dip coating can be automated to produce large quantities of patchy particles, which is one of the major limitations of other methods of producing patchy particles. © 2015 American Chemical Society.

Langmuir

Synthesis of single and multipatch particles by dip-coating method and self-assembly thereof

Journal	Journal of Chemical Physics
ISSN	00219606
Open Access	Yes