Two-dimensional assemblies of soft repulsive colloids confined at fluid interfaces

Abstract

Colloidal systems are an excellent example of a materials class for which interrogating fundamental questions leads to answers of direct applied relevance. In our group, we in particular focus on two-dimensional assemblies of micro-and nano-particles confined at the interface between two fluids, e.g., oil-water. Here, we review our work on systems interacting through soft repulsive forces of different origin, i.e., electrostatic and steric. By starting from the paradigmatic case of charged colloids at an interface, we show how they are both offering great opportunities as model systems to investigate the structural and mechanical response of materials and as versatile patterning tools for surface nanostructuring. We then move to the case of deformable particles interacting via steric contacts. We first examine microgel particles, which we also demonstrate as very promising models for structural investigations and robust elements for tunable nanolithography. We conclude by briefly discussing the case of particles comprising a hard inorganic core and a deformable polymer shell, which maintain some of the advantageous features of microgel particles, but also enable the realization of two-dimensional functional materials. This article offers our perspective on a very active field of research, where many interesting developments are expected in the near future.

Microgels Adsorbed at Liquid–Liquid Interfaces: A Joint Numerical and Experimental Study

“…In general, fluid interfaces constitute ideal settings where nanocomposites and colloidal particles can accumulate and self-assemble. [12][13][14][15][16][17] Recently, microgels have also been experimentally explored under these conditions, [18][19][20][21][22] where the colloid-polymer duality of such particles 2 strongly manifests. Indeed, their internal polymeric structure allows them to spread and flatten at the interface in order to maximize their area, reduce non-favourable contacts between the two liquids and thus lower their surface tension.…”

Structural and Thermodynamic Peculiarities of Core-Shell Particles at Fluid Interfaces from Triangular Lattice Models

“…Metal or semiconducting nanoparticles find numerous applications in catalysis, optics, biomedicine, environmental science, etc.. In order to prevent the charge-neutral nanoparticles from aggregation, recently various types of core-shell particles (CSNP) have been produced [1,2]. In the CSNPs, the hard, typically metal or semiconducting nanoparticle with a diameter ranging from a few tens to a few hundreds of nanometers is covered by a soft polymeric shell.…”

“…This energetic cost, or the softness of the shells, can be controlled in particular by crosslinking of the polymeric chains. The shell-to core diameter ratio in majority of the experiments varies from about 1.1 to about 4 [2][3][4][5]. Since the shell thickness can be controlled independently of the core diameter, and the effective interactions between the CSNPs depend on the thickness and the architecture of the shells, the desired effective interactions can be obtained by choosing different protocols for the synthesis.…”

“…Properties of the CSNPs have been intensively studied not only in the bulk, but also at fluid interfaces [1][2][3][4][5][6][7][8][9][10][11][12]. It turned out that while in the bulk the effective interaction consists of the hard core followed by the soft repulsive shoulder, at fluid interfaces strong capillary attraction can be present for separations larger than the shell diameter, in addition to the above mentioned repulsive interactions at shorter distances [2][3][4].…”

“…Experimental results show that the CSNPs at fluid interfaces can form interesting patterns, depending on the properties of the particles and on the fraction of the interface area covered by them [2][3][4]. For small area fraction, highly ordered arrays of hexagonally packed particles are typically observed.…”