Colloidal polymer patterning

Eoin Murray, Philip Born, and Tobias Kraus 

Monodispersed lattices contain a sizable number of particles with uniform diameter. Their well-defined geometry forms the basis for larger patterns. Thus, instead of defining a number of identical substructures during patterning, only their arrangement is controlled the substructure is efficiently defined by the particle geometry. A serial step is replaced by a parallel, low-cost method, namely, the emulsion synthesis of polymer particles. 

Colloidal patterns are excellent templates that can mask parts of a surface during coating processes, provide a porous structure that can be filled with a second compound, or occupy parts of a volume so that pores can later be opened. Depending on the polymer and the other material involved, the templates can subsequently be removed by thermal decomposition or dissolution in an appropriate solvent. The particle surfaces can be tuned using a wide range of chemical functional groups to improve compatibility with different matrices. 

While the production of monodispersed particles takes place in a well-understood process, their deposition in regular arrangements is less well-researched and remains challenging to perform on a large scale. In this chapter, we will describe the state-of-the-art of this field. The preparation of polymer particles via emulsion polymerization and the forces and mechanisms that can contribute to the arrangement of the particles will be described first. Different implementations of particle- 

Gmerating Micro- and Nanopattems on Polymeric Materials. Edited by A. del Campo and E. Arzt Copyright 2011 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32508-5 

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The variety of strategies available to assemble colloidal polymer particles and the manifold applications of particle assemblies has lead to the design of a large range of setups to fabricate colloidal polymer patterns. The fabrication setups can be divided into two main groups setups to produce bulk colloidal assemblies and setups to deposit thin two-dimensional (2D) arrays of particles. 

The prospects are alluring. Colloidal polymer patterning is similar to very well-established painting and coating processes, so that existing equipment could be adapted for the production of coatings and materials with new properties. The polymer latex formulations that form the basis of the process are well-known in industry, and the step to monodispersed particles and controlled deposition seems viable. For applications where molding methods are inapplicable, particle-based polymer patterns could form the basis of industrial processes. 

Fig. VIII-10. (a) Intensity versus energy of scattered electron (inset shows LEED pattern) for a Rh(lll) surface covered with a monolayer of ethylidyne (CCH3), the structure of chemisorbed ethylene, (b) Auger electron spectrum, (c) High-resolution electron energy loss spectrum. [Reprinted with permission from G. A. Somoijai and B. E. Bent, Prog. Colloid Polym. ScL, 70, 38 (1985) (Ref. 6). Copyright 1985, Pergamon Press.]...

Okubo, T, Yokota, N. and Tsuchida, A. (2007) Drying dissipative patterns of dyes in ethyl alcohol on a cover glass. Colloid. Polym. Sci., 285, 1257-1265. 

In addition to recent advances in block co-polymer templating of periodic mesoporous silica and silica colloidal crystal templating of periodic mesopo-rous polymers [79], SAMs have been used for polymer patterning [80]. Mixtures of two strongly incompatible polymers, a polystyrene (PS)-polyvinylpyridine (PVP) blend, were found to phase separate when placed on a... 

Kratohvil JP, Hsu WP, Jacobs MA, Aminabhavi TM, and Mukunoki Y. Concentration-Dependent Aggregation Patterns of Conjugated Bile-Salts in Aqueous Sodium-Chloride Solutions—a Comparison between Sodium Tau-rodeoxycholate and Sodium Taurocholate. Colloid Polymer Sci 1983 261 781-785. 

Fig. 4.27 Sketch of the demixing process observed in a sample containing a colloid polymer mixture at high polymer concentrations at q<03. The corresponding light scattering patterns are indicated as well a gel formation birth , b gel lifetime life , c gel collapse death , d macroscopic phase separation. Redrawn from Verhaegh et al. [107]...

W. Wang, R. Liu, H. Kang, W. Liu, Y. Huang, UV irradiation gradient induced banded texture in photo-polymerized ethyl-cyanoethyl cellulose / poly (acryhc acid) cholesteric hquid crystalhne films and patterns fabrication thereof Colloid Polym. Sci. 289, 371-379 (2011). 

Polymer patterning via colloids is a promising method and a very active field of research. It is currently limited to a small number of geometries, for some of vhich it is the most efficient fabrication approach. Today, particle-based structures are arguably the most efficient source of optical bandgap materials and (via shadowed evaporation) a very promising route to large-area metal nanostructures. 

Bonart R, Hosemann R and McCullough R L (1963) The Influence of Particle Size and Distortions upon the X-ray Diffraction Patterns of Polymers, PoZymer 4 199-211. Vonk C G (1979) A SAXS study of PE fibers, using the two-dimensional correlation function. Colloid Polym Sci 257 1021-1032. 

The effect of a structured surface on the crystallization of hard-sphere colloids has been extensively studied in experiments [87, 88, 89, 90], These experiments indicate that crystallization on a template is induced at densities below freezing. This finding is supported by computer simulations of hard spheres in contact with a patterned substrate, by Heni and Lowen [91], These simulations indicate that surface freezing already sets in 29% below the coexistence pressure. Furthermore the effect of a surface on crystallization has also been studied in mixtures of binary hard-spheres [92, 93] and colloid-polymer mixtures [94, 95, 96], In both systems surface crystallization was found to take place before bulk fluid-solid coexistence. In the systems studied in Refs. [92, 93, 94, 95, 96], depletion forces favor the accumulation of the larger component on the wall, and this should facilitate surface crystallization [97]. 

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