Wetting, substrate geometry

Is There an Optimal Substrate Geometry for Wetting (at the Microscopic Scale) ... 

In the wetting and dewetting kinetics studies described earlier, the solid substrate was a flat and smooth surface. However, the sohd deformation due to the action of the vertical component of the hquid surface tension may be expected to act in any geometry. For example, viscoelastic braking is involved in the sliding of a liquid drop on a tilted rubber track [32],... 

Unique Process Requirements. The fabrication of TFML interconnections involves a repetitive sequence of thin-film processes to deposit and pattern conductor and dielectric layers. Many processes used in IC fabrication, such as vacuum deposition of metals, photolithography, wet and dry etching, and newly emerging processes (such as laser etching and deposition), may be used in the fabrication of TFML interconnections. However, the geometries and substrates required for packaging impose a number of unique requirements on conventional thin-film processes. 

The outlined problems correspond to the most typical system where three phases, e.g. liquid, gas and solid, are brought in contact. Additional wetting geometries can occur when the liquid phase consists of two subphases, e.g. mixture of incompatible polymer liquids, and/or the substrate surface exhibits variations in chemical composition. In these cases, the interfacial interactions will strongly interfere with the phase separation inside the film. Laterally ordered polymer films might be formed due to the preferential wetting of the patterned substrate by one of the liquid phases. 

The wetting balance technique is a variant of the maximum pull (or detachment) method used to measure liquid-vapour surface tensions (Keene 1993). It is nowadays widely employed in the electronics industry to quantify wetting of solders, but has also been used for wetting studies in metal/ceramic systems (Naidich and Chuvashov 1983b, Nakae et al. 1989, Rivollet et al. 1990). As compared to the sessile drop method which needs planar substrates, solids of various geometry can be studied by this technique. 

In many cases it is necessary to synthesize porous materials in a well-defined preordered shape or within confined geometries, which introduces a pathway to fabricate hierarchically ordered porous materials. The techniques mentioned above have been shown to be capable of producing structured and well-ordered templates [61] within capillaries [50], thin plates [62], micromolds [63], or photoresist patterns [64,65]. Spatial adjustment of the surface functionality on the substrate and its wetting properties can yield patterned colloidal films [66,67]. Finally, confining the particle dispersion itself by printing techniques produces micropatterned arrays [68]. This was also shown to work without the necessity of preceding surface patterning steps [69]. 

Director modes are, as opposed to biaxial fluctuations, excited very easily in the nematic phase, where their Hamiltonian is purely elastic, whereas in the isotropic phase they are characterized by a finite correlation length. This implies that their wetting-induced behavior should be quite the inverse of that of biaxial modes. Thus, in the disordering geometry, the director modes are forced out of the substrate-induced isotropic boundary layer into the nematic core (see Fig. 8.6 bottom). The lowest mode is a Goldstone mode. In the paranematic phase a few lowest director modes are confined to the nematic boundary layer, whereas the upper ones extend over the whole sample and are more or less the same as in the perfectly isotropic phase. 

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