This paper reports a simple spin-coating technique for rapidly fabricating three types of technologically important materials--colloidal crystal, macroporous polymer, and polymeric nanocomposite, each with high crystalline qualities and wafer-scale sizes. Dispersion of monodisperse silica colloids in triacrylate monomers is spin-coated onto a variety of substrates. Shear-induced ordering and subsequent polymerization lead to the formation of three-dimensionally (3D) ordered colloidal crystals trapped inside a polymer matrix. The thickness of as-synthesized colloidal crystal-polymer nanocomposite is highly uniform and can be controlled simply by changing the spin speed and time. Selective removal of the polymer matrix and silica spheres lead to the formation of large-area colloidal crystals and macroporous polymers, respectively. The wafer-scale process is compatible with standard semiconductor microfabrication, as multiple micrometer-sized patterns can be created simultaneously for potential device applications. Normal-incidence transmission spectra in the visible and near-infrared regions show distinct peaks due to Bragg diffraction from 3D ordered structures. The spin-coating process opens a new route to the fundamental studies of shear-induced crystallization, melting and relaxation.

Large-scale fabrication of wafer-size colloidal crystals, macroporous polymers and nanocomposites by spin-coating.

Dip coating is a simple old way of depositing onto a substrate, especially small slabs and cylinders, a uniform thin film of liquid for solidification into a coating. The basic flow is steady, and in it film thickness is set by the competition among viscous force, capillary (surface tension) force and gravity. Thickness and uniformity can be sensitive to flow conditions in the liquid bath and gas overhead. The faster the substrate is withdrawn, the thicker the film deposited. This can be countered by using volatile solutes and combining rapid enough drying with the basic liquid flow. Then the physics grows more complicated, theoretical prediction of process performance more difficult, and control of the process more demanding. Outside product RD actually it is often modified.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400485180

Physics and Applications of DIP Coating and Spin Coating

The never-ending race towards miniaturization of devices induced an intense research in the manufacturing processes of the components of those devices. However, the complexity of the process combined with high equipment costs makes the conventional lithographic techniques unfavorable formany researchers. Through years, nanosphere lithography (NSL) attracted growing interest due to its compatibility with wafer-scale processes as well as its potential to manufacture a wide variety of homogeneous one-, two-, or three-dimensional nanostructures. This method combines the advantages of both top-down and bottom-up approaches and is based on a two-step process: (1) the preparation of a colloidal crystal mask (CCM) made of nanospheres and (2) the deposition of the desired material through the mask. The mask is then removed and the layer keeps the ordered patterning of the mask interstices. Many groups have been working to improve the quality of the CCMs. Throughout this review, we compare the major deposition techniques to manufacture the CCMs (focusing on 2D polystyrene nanospheres lattices), with respect to their advantages and drawbacks. In traditional NSL, the pattern is usually limited to triangular structures. However, new strategies have been developed to build up more complex architectures and will also be discussed.

/pdf/nanosphere-lithography-a-powerful-method-for-the-controlled-4qywmr7pcg.pdf

Nanosphere lithography: a powerful method for the controlled manufacturing of nanomaterials

A mathematical model for atmospheric ice accretion and water flow on a cold surface

A model for the flow of a thin film, with and without solidification, on an arbitrary three-dimensional substrate is presented. The problem is reduced to two simultaneous partial differential equations for the film and solid layer thicknesses. The flow model (with the solidification rate set to zero) is the first such model to describe thin film flow on an arbitrary three-dimensional surface. Various limits are investigated to recover previous models for flow on flat, cylindrical and two-dimensional curved surfaces. With solidification a previous model for accretion on a flat substrate is retrieved. It is shown how the model may be reduced to standard forms, such as solidification on a flat surface, circular and non-circular cylinders, aerofoils and spheres. Numerical solutions are obtained by combining an ADI scheme with a shock capturing method. Results are presented for flow and accretion on a flat surface, aerofoil and sphere.

/pdf/the-flow-and-solidification-of-a-thin-fluid-film-on-an-4w28zdjryu.pdf

The flow and solidification of a thin fluid film on an arbitrary three-dimensional surface

In the spin‐coating process for producing thin films, air flow induced by disk rotation provides a shear stress at the liquid‐air interface which enhances the rate of thinning of the liquid film on the disk. An approximate analysis using Cochran’s classical solution [Proc. Cambridge Philos. Soc. 30, 365 (1934)] for the induced air flow is presented. Regions wherein air flow significantly enhances thinning are delineated. As film thickness becomes very small, in accordance with a dimensionless criterion developed as part of the analysis, the external air flow dominates the centrifugal effect and controls the final rate of thinning. A set of data obtained under conditions appropriate to application of this new theory shows enhanced thinning, but not to the degree predicted.

Stanley Middleman

Papers

The effect of induced air‐flow on the spin coating of viscous liquids