Complex Surface Structures

The adsorption of concentrated solution of AOT at the hydrophilic solid-solution and air-solution interfaces produced a rather different pattern of behaviour [69]. 

At 2 and 5wt.%, a series of sharp diffraction peaks, characteristic of an adsorbed lamellar structure, were observed (see Fig 10). 

McGillivray et al. [71] have also observed stable layered structures adsorbed at the silicon-solution (and air-solution) interface for didodecyl dimethylammo-nium bromide (DDAB) and the corresponding diundecyl (DUDAB) cationic surfactants, in the concentration range 0.2-2 wt.%. Similar to AOT, the surface structures that are found are highly sensitive to temperature, with the repeat distance decreasing with increasing temperature. A notable difference between these systems and AOT [69] is that for the DDAB and DUDAB, the repeat distances are much larger, 600-1500 A. Furthermore, the observed structures 

The manipulation of the adsorption of surfactants at the air-solution interface by polymers and poly electrolytes has been extensively studied [17], and has 

Further evidence of the charge reversal is demonstrated in that PSS can be adsorbed into the polyDMDAAC-coated surface, and that surface now becomes 

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Van Hove M A, Moritz W, Over H, Rous P J, Wander A, Barbieri A, Materer N, Starke U and Somorjai G A 1993 Automated determination of complex surface structures by LEED Surf. Sc . Rep 19 191-229... 

Van Hove M A 1996 Complex surface structures from LEED Surf. Rev. Lett 3 1271-84... 

Both models have been described theoretically and verified experimentally. Because of the complex surface structure of real samples, no quantification algorithm based on physical models is yet available. 

In the systems characterized by more complex surface structure, consisting of patches of different size and different magnitude of the boundary field, the properties of adsorption isotherms have been found to depend on the... 

Particularly in 2D systems, control over the self-assembly of colloidal templates has offered a versatile way to produce patterned surfaces or arrays with a precision of few nanometres. Diblock copolymer micellar nanolithography (dBCML) is a versatile method that uses homopolymers or block copolymers for the production of complex surface structures with nanosized features [69], In contrast to other approaches like electron-beam lithography (EBL) and photolithography, dBCML does not require extensive equipment. In fact, it is commonly used in the fabrication of data storage devices and photonic crystals, in catalyses [70], and for the design of mesoporous films and nanoparticle arrays [71]. 

Beyond the simple thin surfactant monolayer, the reflectivity can be interpreted in terms of the internal structure of the layer, and can be used to determine thicker layers and more complex surface structures, and this can be done in two different ways. The first of these uses the optical matrix method [18, 19] developed for thin optical films, and relies on a model of the surface structure being described by a series or stack of thin layers. This assumes that in optical terms, an application of Maxwell s equations and the relationship between the electric vectors in successive layer leads to a characteristic matrix per layer, such that... 

As already explained, the as-method of isotherm analysis can be used to derive the external area, a(ext, S), and the pore volume vp(mic, S). Of course the first requirement is to obtain an appropriate standard isotherm on a non-porous alumina. Strictly, the surface chemistry of the reference material should be exactly the same as that of the porous adsorbent, but in practice this is not easy to achieve because of the complex surface structure of active aluminas. As before, standard isotherm data determined on the non-porous Degussa Aluminiumoxid C have been found suitable for the analysis of various isotherms on the porous aluminas (Sing, 1970). 

Phase separation of polymer molecules is clearly one mechanism by which complex surface structures can develop to alter the adhesion. Another method... 

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