Quantifying disorder in colloidal films spin-coated onto patterned substrates

Abstract

Polycrystals of thin colloidal deposits, with thickness controlled by spin-coating speed, exhibit axial symmetry with local 4-fold and 6-fold symmetric structures, termed orientationally correlated polycrystals (OCPs). While spin-coating is a very facile technique for producing large-area colloidal deposits, the axial symmetry prevents us from achieving true long-range order. To obtain true long-range order, we break this axial symmetry by introducing a patterned surface topography and thus eliminate the OCP character. We then examine symmetryindependent methods to quantify order in these disordered colloidal deposits. We find that all the information in the bond-orientational order parameters is well captured by persistent homology analysis methods that only use the centers of the particles as input data. It is expected that these methods will prove useful in characterizing other disordered structures.

Fabrication of Ordered 2D Colloidal Crystals on Flat and Patterned Substrates by Spin Coating

“…51 The grooves act as the preferred location for the deposition of the particles, as the solvent layer ruptures over the substrate pattern protrusions. 57 Consequently, the remaining liquid flows in the grooves, localizing the colloids there. Subsequently, the lateral capillary forces between the particles drive them to form closely packed structures aligned along the grooves.…”

“…It has also been recently shown by Aslam et al that a patterned substrate also eliminates axial symmetry by spin coating and therefore suppresses the formation of OCP structures. 57…”

A Journey Through the Landscapes of Small Particles in Binary Colloidal Assemblies: Unveiling Structural Transitions from Isolated Particles to Clusters upon Variation in Composition

“…To this end, a combined approach merging computational geometry and computational topology has been developed, able to supply a quantitative description of the evolution of patterns generated by L particles in amorphous binary assemblies obtained at the air/water interface at a value of dS/dL slightly above the theoretical threshold for the occurrence of a periodic square packing and for increasing NS/NL [12]. A key element in such a quantitative classification has been represented by the use of persistent homology, a tool applied very recently to the analysis of granular and colloidal assemblies [27,28,29,30]. In particular, the use of persistence diagrams, which allows the study of the characteristics of the “holes” constructed starting from a set of points (a point cloud formed, in the case of colloidal particles, by the centroids of the particles), has revealed the relative weight of hexagonal, square and rhombic arrangements of L particles controllable via the composition of the colloidal suspension [12].…”

Pattern formation in spin-coating of hybrid colloids in different magnetic field configurations

“…However, it has been shown that crystalline order in spin-coated colloids cannot be achieved easily due to the intrinsic symmetries of the process [19]. Alternative paths have been taken in order to modify the classical spin-coating, that is to say: by using patterned substrates [20], and by applying external fields during the process [21][22][23]. Both types of methods show that it is possible to break the axial symmetry that leads to Orientationally Correlated Polycrystals [19].…”

“…Later on, Aslam et al [24] showed that at low concentrations the results were valid for ferromagnetic particles. They have also investigated the behavior of moderately concentrated superparamagnetic colloids in different magnetic fields [20], where they found that the magnetoviscosity in inhomogeneous fields is strongly influenced by the magnetophoretic effect that increases the flows of magnetic fluids in the applied field direction.…”