Wetting pattern formation

Surface reconstruction of the PS-PMMA brush in selective solvents gave rise to pattern formation which was investigated by SPM, wetting experiments and XPS. The obtained morphologies depended on the thickness of the brush and its composition [283, 284] (Fig. 9.31). 

Fig. 6 Illustration of surface energy effects on the self-assembly of thin films of volume symmetric diblock copolymer (a). Sections b and c show surface-parallel block domains orientation that occur when one block preferentially wets the substrate. Symmetric wetting (b) occurs when the substrate and free surface favor interactions with one block B, which is more hydrophobic. Asymmetric wetting (c) occurs when blocks A and B are favored by the substrate and free surface, respectively. For some systems, a neutral substrate surface energy, which favors neither block, results in a self-assembled domains oriented perpendicular to the film plane (d). Lo is the equilibrium length-scale of pattern formation in the diblock system...

While the demixing patterns in Fig. 1.2 are conceptually simple and exhibit only one characteristic length scale, more complex phase morphologies are obtained by the demixing of a multi-component blend [16]. With more than two polymers in a film, the pattern formation is (in addition to the factors discussed in the previous section) governed by the mutual wetting behavior of the components. Two different scenarios are shown in Fig. 1.4 [ 17]. While both films in Fig. 1.4(a) and (b) consist of the same three polymers, their mutual interaction was modulated by preparing the films under different humidity conditions [15],... 

Abstract Some aspects of self-assembly of quantum dots in thin solid films are considered. Nonlinear evolution equations describing the dynamics of the fihn instability that results in various surface nanostructures are analyzed. Two instability mechanisms are considered the one associated with the epitaxial stress and the other caused by the surface-energy anisotropy. It is shown that wetting interactions between the film and the substrate transform the instability spectrum from the long- to the short-wave type, thus yielding the possibility of the formation of spatiaUy-regular, stable arrays of quantum dots that do not coarsen in time. Pattern formation is analyzed by means of ampbtude equations near the insta-bibty threshold and by numerical solution of the strongly nonlinear evolution equations in the small-slope approximation. 

The analysis of the conditions (56) and (57) shows that the short-wave instability of the film surface that can lead to pattern formation can occur only if the film thickness is above a threshold value determined only by the surface-energy anisotropy and the wetting length, namely, for... 

Two-parameter model was used for simulation of the patterns formation during the wetting process. General form of the model is... 

Figure 14.5 Stripe pattern formation by dip coating, (a-d) Schematic illustration of the formation of an aligned nanoparticles-stripe pattern by vertical deposition. During raising the substrate slowly (a, b) the water evaporates and the wet contact line breaks up into aggregates of nanoparticles (b, c). (e) Optical microscopy image of the waterfront, leading to ID stripes across the entire substrate, formed both for silver (f) and gold (g) nanoparticles. (Images taken from Ref 46.) Abbreviation-. ID, onedimensional.

M. Brinkmann, S. Graaf, and F. Biscarini, Mechanism of nonrandom pattern formation of polar-conjugated molecules in a partial wetting regime, Phys. Rev. B, 66,165430[l-8] [2002]. 

B. Mesoscopic Pattern Formation in Simply Cast Polyion Complex Under Wet Conditions... 

In the disc method, the powder is compressed by a punch in a die to produce a compacted disc, or tablet. The disc, with one face exposed, is then rotated at a constant speed without wobble in the dissolution medium. For this purpose the disc may be placed in a holder, such as the Wood et al. [Ill] apparatus, or may be left in the die [112]. The dissolution rate, dmldt, is determined as in a batch method, while the wetted surface area is simply the area of the disc exposed to the dissolution medium. The powder x-ray diffraction patterns of the solid after compaction and of the residual solid after dissolution should be compared with that of the original powder to test for possible phase changes during compaction or dissolution. Such phase changes would include polymorphism, solvate formation, or crystallization of an amorphous solid [113],... 

Graphs of relative permeability are generally similar in pattern to that shown in Figure 5.10. As shown, some residual water remains in the pore spaces, but water does not begin to flow until its water saturation reaches 20% or greater. Water at the low saturation is interstitial or pore water, which preferentially wets the material and fills the finer pores. As water saturation increases from 5 to 20%, hydrocarbon saturation decreases from 95 to 80% where, to this point, the formation permits only hydrocarbon to flow, not water. Where the curves cross (at a saturation... 

Figure 66D was obtained for the same CdTe(lll) crystal after electrochemical reduction at -2.0 V for 2 minutes. Transitions for both Cd and Te are evident, and the Cd/Te peak height ratio is similar to that observed by other workers for stoichiometric CdTe [393,394]. In addition, well-ordered (1 X 1) LEED patterns (Fig. 67) were observed on both the CdTe(lll)-Cd and CdTe(lll)-Te faces. This is in contrast to CdTe surfaces prepared by ion bombardment, where postbombardment annealing was required to produce a LEED pattern, and the annealing appeared to result in formation of a reconstructed surface. In summary, well-ordered, clean, and unreconstructed CdTe surfaces have been produced using a wet etching/electrochemical treatment. 

Electrolysis of MF/TBAP solution produces methoxide (CH30 ), formate anion (HC02 ), and CO [15], The voltammograms of MF/TBAP solutions with gold electrodes are quite similar to those of the y-BL solutions in Figure 1. Scheme 3 describes the reduction pattern of MF based on the above product distribution. In wet MF/TBAP solutions, both formate and methoxide are formed, and it is clear that, as in the case of wet y-BL solutions, H20 is predominantly... 

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