Confinement Chemically Patterned Surfaces

In thin film, the relation between film thickness (h) and the size of TFCD, specifically its lateral diameter (2r) is well estabhshed by Fournier et al. [46] and The total energy of FCD results from a balance between the elastic energy density of LC, AFei, and the surface energy at both the air and substrate interfaces 

By minimizing F with respect to r, h is found to be linearly proportionate to r as shown 

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The second key observation is that the intersections between a twin boundary and a crystal surface represent chemically activated sites (and mechanically soft areas) (Novak and Salje 1998a, 1998b). It appears safe to assume that similarly activated sites exist also at the intersection of APBs and dislocations with the surface (e.g. Lee et al. 1998, Hochella and Banfield 1995). Besides the obvious consequences for the leaching behaviour of minerals, these key observations lead to the hypothesis of confined chemical reactions inside mesoscopic patterns. The idea is as follows as the surface energy is changed near mesoscopic interfaces, dopant atoms and molecules can be anchored near such interfaces. Some particles will diffuse into the mineral and react with... 

Precisely this latter situation arises if the confining solid surface is endowed with a chemical pattern that is both nanoscopic in size and hnite in extent. Such chemical patterns may be created by lithographic methods [179]. Atomic beams have been employed to produce hexagonal nemostruc-tures [180]. Other methods capable of creating cliemically nanostnictured substrate surfaces involve microphase separation in diblock copolymer films [181] or the use of forc( microscopy to locally oxidize silicon surfaces [182]. 

Surface forces tend to be inherently important for capillary-driven microfluidic devices as surface area-to-volume ratios are rather high and surface tension-induced interfacial curvature is significant enough to promote capillary wicking. For chemically patterned devices depending on hydrophobic/hydrophilic confinement in particular, the capillary number must be sufficiently low (i.e., Ca 1) in order to maintain fluid confinement within intricate geometry implying AF < ylw [1],... 

Wang, Q., Nath, S. et al. (2000a) Symmetric diblock copolymer thin films confined between homogeneous and patterned surfaces simulations and theory. Journal of Chemical Physics, 112,9996-10011. 

Recently, researchers paid more attention to the guided self-assembly of block copolymer thin films on a patterned surface. The patterned surface means the surface of a constrained situation is chemically or physically modified to form a pattern with specific property and size. A series of exquisite structures are found in the microphase separation of block copolymer under the patterned surface. In the theoretic work of Wu and Dzenis [43], they designed two kinds of patterned surface to direct the block copolymer self-assembly (Fig. 15.7). The self-assembled structures are found strongly influenced by the commensurability of polymer bulk period and pattern period. With mismatched patterns on two surfaces, both MC simulation [44] and SCFT researching [45] predicted the titled lamellae and perforated lamellae structures for symmetric diblock copolymers. Petrus et al. carried out a detailed investigation on the microphase separation of symmetric and asymmetric diblock copolymers confined between two planar surfaces using DPD simulation [46,47]. It is found that various nonbulk nanostructures can be fabricated by the nanopatterns on the surfaces. 

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