Colloidal Micro- and Nanostructures Assembled on Patterned Surfaces
Read full article onlineFull Article
Colloidal particles are liquid or solid objects with dimensions ranging from a few to several hundred nanometers (and, in a broader sense, up to many micrometers), that are suspended in a solid, liquid, or gas matrix. These particles can show very distinct properties compared to small molecules and macroscopic systems, because of their mesoscopic size with the resulting large surface-to-volume ratio and intermediate dynamics. One of the most common forms of colloids are solid particles suspended in a liquid medium, such as paint and adhesives, and this format will be discussed here. Solid colloid particles are available from many different materials, such as organic compounds (drugs and pigments), polymers, and inorganic materials (ceramics and semiconductors). Depending on the interactions between the particles and of the particles with the suspending medium, the colloids can form aggregates and ordered structures in three dimensions, e.g., colloidal crystals. Such 3-D aggregates may serve as mesoporous materials for filter applications, or if the particle diameter is in the wavelength range of visible light, colloid crystals can diffract and filter light of specific wavelength (photonic bandgap structures).
If the particles additionally interact with a surface, colloid adsorption can take place that leads to planar structures. For such structured surfaces, many current and potential applications exist, such as self-cleaning, superhydrophobic or antireflecting surfaces, adhesion control (like protein adsorption and antifouling), chemo- and biosensors, optical filters and switches, electromechanical devices, microfluidics, and surfaces for separation technology. For such applications, lateral patterning of the colloid layer is often required, which can be achieved via various methods, such as site-selective surface modification or templating with a 3-D mold.
This article provides an overview on the methods and effects that lead to structured colloid assemblies at substrate surfaces. Besides the fundamental interactions in colloidal systems that lead to 3-D and 2-D assembly structures, several techniques are discussed which can be used to build highly ordered particle assemblies with complex lateral structure in a controlled way. The patterning is realized by the application of templates and directing methods during particle deposition, which will be presented in further detail.