Shaping in the Third Direction; Synthesis of Patterned Colloidal Crystals by Polyester Fabric-Guided Self-Assembly

Abstract

A polyester fabric with rectangular openings was used as a sacrificial template for the guiding of a sub-micron sphere (polystyrene (PS) and silica) aqueous colloid self-assembly process during evaporation as a patterned colloidal crystal (PCC). This simple process is also a robust one, being less sensitive to external parameters (ambient pressure, temperature, humidity, vibrations). The most interesting feature of the concave-shape-pattern unit cell (350 μm × 400 μm × 3 μm) of this crystal is the presence of triangular prisms at its border, each prism having a one-dimensional sphere array at its top edge. The high-quality ordered single layer found inside of each unit cell presents the super-prism effect and left-handed behavior. Wider yet elongated deposits with ordered walls and disordered top surfaces were formed under the fabric knots. Rectangular patterning was obtained even for 20 μm PS spheres. Polyester fabrics with other opening geometries and sizes (~300–1000 μm) or with higher fiber elasticity also allowed the formation of similar PCCs, some having curved prismatic walls. A higher colloid concentration (10–20%) induces the formation of thicker walls with fiber-negative replica morphology. Additionally, thick-wall PCCs (~100 μm) with semi-cylindrical morphology were obtained using SiO2 sub-microspheres and a wavy fabric. The colloidal pattern was used as a lithographic mask for natural lithography and as a template for the synthesis of triangular-prism-shaped inverted opals.

Shaping in the Third Direction; Fabrication of Hemispherical Micro-Concavity Array by Using Large Size Polystyrene Spheres as Template for Direct Self-Assembly of Small Size Silica Spheres

“…Superstructures can be integrated into higher complexity superstructures on larger size scales of hundreds of micrometers by using a polyester fabric [ 34 ], where polystyrene spheres of tens of micrometers can be forced to follow the pattern of the fabric and to self-assemble on a large area ( Figure 7 b,c). After infiltration of the silica spheres and the removal of the polystyrene spheres by calcination, higher complexity superstructures (such as those in Figure 7 d) composed only of silica spheres are obtained.…”

“…A sharper variation of the wavelength with the incident angle can be achieved on very thin colloidal-crystal films (single or bilayer) in transmitted light, for a transmitted angle that is different from the incident angle (non-Bragg diffraction) even when the normal to the substrate is the same with the normal to the film. This phenomenon is known as the super-prism effect [ 33 , 34 ] and it is not caused by the CCs’ shape. They are too thin to have a 3D shape.…”

“…Different optical features for different incident angles could be obtained by shaping CCs with flat surfaces but non-parallel with the substrate: a pyramid [ 35 ], a triangular prism [ 34 ], or a truncated pyramid [ 36 , 37 ] ( Figure 1 c), for example. In these cases, each CCs’ face shows a different diffraction plane family normal to the surface.…”

“…This is the case with so-called “superstructures” which are arrays or patterns of 3D shaped colloidal crystals units ( Figure 1 h). These superstructures can look like convex hemispherical colloidal-crystal arrays as a result of colloidal droplets printed onto a substrate [ 40 , 54 ]; spherical or toroidal-colloidal crystals produced by emulsion or microfluidic techniques arranged as monolayers [ 38 , 55 ]; triangular prisms formed as grids by using a polyester fabric as scaffold [ 34 ]; or aligned and packed cylinders in whose insides sub-micron spheres have crystallized [ 56 ].…”

Design and multilevel structuring of shape memory polymers for pleochroism control

“…Block copolymers can self‐assemble into periodic photonic structures that have different intense colors in the transmitted light due to spontaneous phase separation of chemically different polymer blocks in macromolecules 3,4 . Spontaneous structuring processes of filled polymer compositions are intensified by introducing large polystyrene and small silica spheres into a high molecular weight binder 5 . Liquid or solvent vapors sorption from the environment affects pleochroism.…”