Self-Assembly of Heterogeneously Charged Particles under Confinement

Abstract

Self-assembly—the spontaneous organization of microscopic units into well-defined mesoscopic structures—is a fundamental mechanism for a broad variety of nanotechnology applications in material science. The central role played by the anisotropy resulting from asymmetric shapes of the units and/or well-defined bonding sites on the particle surface has been widely investigated, highlighting the importance of properly designing the constituent entities in order to control the resulting mesoscopic structures. Anisotropy driven self-assembly can also result from the multipolar interactions characterizing many naturally occurring systems, such as proteins and viral capsids, as well as experimentally synthesized colloidal particles. Heterogeneously charged particles represent a class of multipolar units that are characterized by a competitive interplay between anisotropic attractive and repulsive interactions, due to the repulsion/attraction between charged-like/oppositely charged regions on the particle surface. In the present work, axially symmetric quadrupolar colloids are considered in a confined planar geometry; the role of both the overall particle charge and the patch extension as well as the effect of the substrate charge are studied in thermodynamic conditions such that the formation of extended structures is favored. A general tendency to form quasi-two-dimensional aggregates where particles align their symmetry axes within the plane is observed; among these planar self-assembled scenarios, a clear distinction between the formation of microcrystalline gels—branched networks consisting of purely crystalline domains—as opposed to disordered aggregates can be observed based on the specific features of the particle–particle interaction. Additionally, the possible competition of interparticle and particle–substrate interactions affects the size and the internal structure of the aggregates and can possibly inhibit the aggregation process.

Equilibrium structures of anisometric, quadrupolar particles confined to a monolayer

“…IPCs have been observed to form similar structures as the ones encountered here both in simulations 71,72 as well as in experiments. Appendix A: Two particle ground state configurations at particle contact…”

Limiting the valence: advancements and new perspectives on patchy colloids, soft functionalized nanoparticles and biomolecules

“…In particular, numerical investigations on IPC systems with two identical polar patches have shown that an emerging feature of such systems is the formation of planar aggregates either as monolayers closed to a charged substrate 94,95 or as bulk equilibrium phases. 109,110 Close to a homogeneously charged substrate, IPCs with two identical patches form assemblies with well-defined translational and orientational order depending on the charge ratio of the different entities involved, the patch size and the interaction range (see Fig.…”

“…2). 94,95 The features of these assemblies depend on the system parameters and were proven to reversibly respond to changing conditions such as the pH of the solution and the charge of the substrate. 95 It is worth noting that the same morphological features observed in simulations have been found in experimental samples of IPCs sedimented on a glass substrate; 41 however, while all clusters in the same numerical sample have the same spatial and orientational order, experimental IPCs form different particle arrangements within the same sample, probably due to the patch polydispersity.…”

Relaxation dynamics of functionalized colloids on attractive substrates

“…This type of functionalization allows a very detailed control on of colloidal valence, strength, and selectivity of the colloidal bonds. During self-assembly, the chemical nature (or strength) of the patch-patch interaction leads to large energy barriers impeding the formation of equilibrium structures, promoting kinetically trapped structures, such as gels, glasses or polycrystals [1,[21][22][23][24][25]. One route to control the assembly of non-equilibrium structures is the use of flat or patterned substrates [26][27][28][29].…”