Out‐of‐Equilibrium Self‐Assembly of Binary Mixtures of Nanoparticles

Abstract

The self-assembly of nanoparticles is one of the most promising techniques currently used to develop advanced materials. [1,2] The distinct properties of the nanoparticles can be integrated into assemblies of nanometer-scale building blocks, which leads to novel superstructures with unique collective properties. Most recent studies have focused on assemblies of single-component systems, such as semiconducting, [3][4][5][6][7][8][9][10][11] magnetic, [12][13][14][15][16] and metal nanocrystals. [17][18][19][20][21][22][23][24][25] The study of multicomponent materials, i.e., assemblies of mixtures of nanoparticles, has received very little attention despite their role in the development of metamaterials, [26] materials with properties arising from the controlled interactions between different nanoparticles in an assembly. Previous studies of assemblies of multicomponent nanocrystals have usually resulted in amorphous materials. [27][28][29][30] This is because of the lack of directional forces or low diffusivity of the nanoparticles during the assembly process itself. [26] An exception is the work reported by Redl et al. where mixtures of PbSe semiconducting quantum dots and Fe 2 O 3 magnetic nanocrystals were assembled into ordered three-dimensional arrays. [26] This was achieved by carefully controlling the solvent vapor pressure, thereby adjusting the rate of evaporation during the drying process. Redl et al. showed how the final superlattice crystal structure can be tuned by the size ratio of the two nanoparticle components. In the present study, an attempt is made to model and understand the physical mechanisms of the assembly of binary mixtures of nanoparticles. For this, the model presented by Rabani and co-workers [31,32] is adopted and extended to describe the drying-mediated self-assembly of binary mixtures of nanoparticles. This out-of-equilibrium problem requires the dynamic treatment of three coupled phase transformations: the evaporation of the solvent (drying), the formation of domains (coarsening), and ordering within the domains (formation of superlattices). In the language of statistical mechanics the present paper treats the dynamics of the three coupled phase transformations, two are described by a conserved order parameter and one by a non-conserved order parameter.[33]Three cases of the self-assembly of binary mixtures of nanoparticles under homogeneous and heterogeneous evaporation conditions are studied. The cases differ only in the interactions between the different nanoparticle species. For the case where the interactions between all the nanoparticles are equal, the dynamics of the model presented here and the resulting selfassembled morphologies are well described by the simplified single-component model. [31,32] However, in the other two cases studied, where the cross interactions are smaller/larger than the interactions between identical particles, it is found that the coarsening of the nanoparticle domains is strongly coupled to the superlattice formation within each domain. Furthermo...

Colloidal Assembly: The Road from Particles to Colloidal Molecules and Crystals

“…This approach is different from a previous strategy for isotropic binary colloids, in which the formation of ionic crystal structures is controlled based on size differences. [183] Using oppositely charged particles, the aim is to manipulate the particle interaction, [184] which would penalize the formation of odd- numbered rings that existed in other structural motifs, thereby making the diamond structure more favorable.…”

Coerced mechanical coarsening of nanoparticle assemblies

“…Self-organisation in colloidal nanoparticle systems gives rise to a panoply of intricate patterns [10][11][12][13][14][15] and the dynamics of the self-organisation process have been investigated 11,[14][15][16] . In one case, a quench-and-observe strategy has been used to ascertain the value of the coarsening exponent, γ for the time-dependent growth of clusters of PbSe nanoparticles 11 .…”

Synthesis of Copper Dendrite Nanostructures by a Sonoelectrochemical Method

“…Our experimental results seem to be consistent with predictions made by Rabani and co-workers. [13] By using a coarse-grained lattice gas model that explicitly accounts for the evaporating solvent, they demonstrated how the nanoparticle size and/or nanoparticle concentration and/ or different substrates determine the various morphologies of the final structures.…”

“…[2] We have used a model developed by Rabani and co-workers to explain the formation of the dendrites upon varying the various sonoelectrochemical parameters. [13] Keywords: copper · dendrimers · nanostructures · polyvinyl alcohol · sonoelectrochemistry Abstract: Copper dendrites have been prepared by a sonoelectrochemical process from an aqueous solution of Cu 2 + in the presence of polyvinyl alcohol. A SEM image of the morpholohy of the copper formed on the electrode after one electric pulse is presented.…”