Abstract
Materials with well-defined architectures are heavily sought after in view of their diverse technological applications. Among the desired target architectures, lamellar phases stand out for their exceptional mechanical and optical features. Here we show that charged colloids, decorated on their poles with two oppositely charged regions possess the unusual ability to spontaneously assemble in different morphologies of (semi-)ordered, layered particle arrangements which maintain their structural stability over a surprisingly large temperature range. This remarkable capacity is related to a characteristic bonding mechanism: stable intra-layer bonds guarantee the formation of planar aggregates, while strong inter-layer bonds favor the stacking of the emerging planar assemblies. These two types of bonds together are responsible for the self-healing processes occurring during the spontaneous assembly. The resulting phases are characterized by parallel, densely packed, particle layers connected by a relatively small number of intra-layer particles. We investigate the properties of the (semi-)ordered phases in terms of static and dynamic correlation functions, focusing in particular on a novel hybrid crystal-liquid phase that prevails at intermediate temperatures where the inter-layer particles form a mobile, fluid phase.
Highlights
Most of the present strategies for the fabrication of materials with desired physical properties and/or specific responses to external stimuli rely on the self-assembly of mesoscopic target architectures from suitably designed building blocks.[1,2] Among the desired target structures, layered phases rank at a very prominent position due to their outstanding features.[3]
In contrast to many of the layer-forming systems, the lamellar solid formed by inverse patchy colloids32 (IPCs) systems so far[37,38] combines three important features: (i) it is an equilibrium phase, (ii) it is assembled in pure one-component systems and (iii) it is characterized by a non-close-packed structure, i.e. the colloidal monolayers are not stacked in direct contact on the top of each other
Most of the results presented in this contribution are obtained in Molecular Dynamics (MD) simulations in the microcanonical (NVE) ensemble, using the velocity Verlet integration algorithm.[40]
Summary
The formation of colloidal two-dimensional structures has been observed in systems of particles with heterogeneously charged surfaces, referred to as inverse patchy colloids[32] (IPCs). In contrast to many of the layer-forming systems, the lamellar solid formed by IPC systems so far[37,38] combines three important features: (i) it is an equilibrium phase, (ii) it is assembled in pure one-component systems and (iii) it is characterized by a non-close-packed structure, i.e. the colloidal monolayers are not stacked in direct contact on the top of each other The latter feature is a consequence of the characteristic bonding mechanism between IPCs that is responsible for the internal stability of the layers: bonds between IPCs form via an equator–patch contact when the particle axes lie within the planes, exposing thereby their equatorial belts to the neighboring layers. No significant differences between the results obtained via the different algorithms were observed
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