Symmetric wetting

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...

For a strong surface field and symmetric wetting conditions, a perforated lamella (PL) phase typically develops in up to four layers of structures, with an exception for the first layer of structures at the favored film thickness. For one layer and all transition regions between terraces a Cy phase was found. 

Walton et al. went on to study the orientation of block copolymers as a function of interaction with blocks when walls are preferential for one of the blocks, parallel orientation forms.In the case of symmetric wetting of preferential walls, unfrustrated spacing occurs for wall spacing h,h = ndg, which is the bulk spatial period do multiplied by the number of layers n. Alternatively, for asymmetric preferential walls (the walls attract opposite blocks), the unfmstrated system forms when the plate spacing corresponds with h = n + Vi)do-This behavior was confirmed experimentally with PS-b-PMMA sandwiched between two walls treated with random copolymers of polystyrene-ran-poly(methyl methacrylate) (PS-r-PMMA) with varying composition and thus varying block interaction. ... 

Several groups have predicted transitions in the orientation from strained paralld lamdlae to distorted perpendicular lamd-lae in a symmetric block copolymer constrained between highly sdective, symmetric wetting walls (i.e., walls made of the same... 

Dreger et al. [72] determined the wetting properties of the sodium salts of symmetrical secondary, secondary, isomeric secondary pentanol sulfates and... 

Metal/molten salt interfaces have been studied mainly by electrocapillary833-838 and differential capacitance839-841 methods. Sometimes the estance method has been used.842 Electrocapillary and impedance measurements in molten salts are complicated by nonideal polarizability of metals, as well as wetting of the glass capillary by liquid metals. The capacitance data for liquid and solid electrodes in contact with molten salt show a well-defined minimum in C,E curves and usually have a symmetrical parabolic form.8 10,839-841 Sometimes inflections or steps associated with adsorption processes arise, whose nature, however, is unclear.8,10 A minimum in the C,E curve lies at potentials close to the electrocapillary maximum, but some difference is observed, which is associated with errors in comparing reference electrode (usually Pb/2.5% PbCl2 + LiCl + KC1)840 potential values used in different studies.8,10 It should be noted that any comparison of experimental data in aqueous electrolytes and in molten salts is somewhat questionable. 

Symmetrical and unsymmetrical benzoins have been rapidly oxidized to benzils in high yields using solid reagent systems, copper(II) sulfate-alumina [105] or Oxone-wet alumina [105, 106] under the influence of microwaves (Scheme 6.32). Conventionally, the oxidative transformation of a-hydroxy ketones to 1,2-diketones is accomplished by reagents such as nitric acid, Fehling s solution, thallium(III) nitrate (TTN), ytterbium(III) nitrate, ammonium chlorochromate-alumina and dayfen. In addition to the extended reaction time, most of these processes suffer from drawbacks such as the use of corrosive acids and toxic metals that generate undesirable waste products. 

Fig. 12. Schematic variation of the order parameter profile /(z) of a symmetric (f=l/2) diblock copolymer melt as a function of the distance z from a wall situated at z=0. It is assumed that the wall attracts preferentially species A. Case (a) refers to the case % %v where non-linear effects are still negligible, correlation length and wavelength X are then of the same order of magnitude, and it is also assumed that the surface "field" Hj is so weak that at the surface it only induces an order parameter 0.2 n if mb is the order parameter amplitude that appears for %=%t at the first-order transition in the bulk. Case (b) refers to a case where % is only slightly smaller than %t, such that an ordered "wetting layer" of thickness 1 [Eq. (76)] much larger than the interfacial thickness which is of the same order as [Eq. (74)] is stabilized by the wall, while the bulk is still disordered. The envelope (denoted as m(z) in the figure) of the order parameter profile is then essentially identical to an interfacial profile between the coexisting ordered phase at T=Tt for (zl). The quantitative form of this profile [234] is shown in Fig. 13. From Binder [6]...

Fig. 18. Log-log plot of the parameter co = l7rwoG j > that controls the behavior of critical wetting [11,220,277,278], vs %/%crit -1, for symmetrical polymer mixtues (NA=NB=N) with chain lengths ranging from N=128 to N=1024, showing the predictions Eqs. (124)-(126). From Werner et al. [266]...

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