Patchy colloids: state of the art and perspectives

Abstract

Recently, an increasing experimental effort has been devoted to the synthesis of complex colloidal particles with chemically or physically patterned surfaces and possible specific shapes that are far from spherical. These new colloidal particles with anisotropic interactions are commonly named patchy particles. In this Perspective article, we focus on patchy systems characterized by spherical neutral particles with patchy surfaces. We summarize most of the patchy particle models that have been developed so far and describe how their basic features are connected to the physical systems they are meant to investigate. Patchy models consider particles as hard or soft spheres carrying a finite and small number of attractive sites arranged in precise geometries on the particle's surface. The anisotropy of the interaction and the limited valence in bonding are the salient features determining the collective behavior of such systems. By tuning the number, the interaction parameters and the local arrangements of the patches, it is possible to investigate a wide range of physical phenomena, from different self-assembly processes of proteins, polymers and patchy colloids to the dynamical arrest of gel-like structures. We also draw attention to charged patchy systems: colloidal patchy particles as well as proteins are likely charged, hence the description of the presence of heterogeneously distributed charges on the particle surface is a promising perspective for future investigations.

Colloids with valence and specific directional bonding

“…One approach is to decorate the surface of colloidal particles with "sticky patches," made, for example, of synthetic organic or biological molecules and assigned to specific locations [15][16][17][18][19] . Bonding between particles occurs through patch-patch interactions, so that in principle the location and functionality of the patches can endow particles with bonding directionality and valence.…”

Competing ordered structures formed by particles with a regular tetrahedral patch decoration

“…In Figure 5 we have depicted U ⋆ and η (both obtained via simulations) along the isotherm T ⋆ = 0.10 over a relatively large pressure interval, namely P ⋆ ∈ [2,10]. Values for the two quantities are depicted for structures labeled "b", "d", "e", "f", "g", and "h" over the respective ranges of stability; we note that mechanical stability (i.e., a positive compressibility) is guaranteed as long as η increases monotonically with increasing pressure.…”

“…Patchy particles are colloidal entities whose surfaces are decorated by well-defined regions, which differ in their interaction behaviour significantly from the one of the "naked" colloidal surface (for an experimental and theoretical overview see [1] and [2], respectively). Since these regions can be positioned with high accuracy on the particle surface and the spatial extent of the patches can be tuned in suitable chemical or physical synthesis processes, the highly directional and selective interactions of patchy particles have promoted them as very promising entities that are able to self-assemble into larger target units with desired physical properties.…”

The configurational space of colloidal patchy polymers with heterogeneous sequences

“…A beautiful review on the experimental methods to produce patchy particles can be found in the paper of Bianchi et al [12].…”

“…We map the phase space for a range of values of the interaction potential and for two different forms of the interaction potential. We have chosen as subunits patchy particles, because in addition to mimicking the properties of hydrogen bonds, they have a rich ensemble of self-assembling properties [11][12][13].…”