Two-dimensional solid-phase

Klejdus B, Vitamvasova D and Kuban V. 2001. Identification of isoflavone conjugates in red clover (Trifolium pratense) by liquid chromatography-mass spectrometry after two-dimensional solid-phase extraction. Anal Chim Acta 450 81-97. 

Dahlin, A. R, Bergstroem, S. K., Andren, R E., Markides, K. E., and Bergquist, J., Poly(dimethylsiloxane)-based microchip for two-dimensional solid-phase extraction-capillary electrophoresis with an integrated electrospray emitter tip. Analytical Chemistry, 77, 5356, 2005. 

Fig. 4. Schematic representation of the smectic layering along with their characteristic diffraction patterns for the monolayer (Ai), the partially bilayer (Aj), the bilayer (A2) and the two-dimensional (A) phases. The arrows indicate permanent dipoles, the solid points are Bragg reflections...

Initially, the compression does not result in surface pressure variations. Molecnles at the air/water interface are rather far from each other and do not interact. This state is referred to as a two-dimensional gas. Farther compression results in an increase in snrface pressure. Molecules begin to interact. This state of the monolayer is referred as two-dimensional liquid. For some compounds it is also possible to distingnish liqnid-expanded and liquid-condensed phases. Continnation of the compression resnlts in the appearance of a two-dimensional solid-state phase, characterized by a sharp increase in snrface pressure, even with small decreases in area per molecule. Dense packing of molecnles in the mono-layer is reached. Further compression results in the collapse of the monolayer. Two-dimensional structure does not exist anymore, and the mnltilayers form themselves in a non-con trollable way. 

There appears to be a disparity in terminology of isotherms between the hydrogeology and chemistry literature. While chemistry textbooks describe adsorption isotherms (e.g., Drever, 1988, p. 362 Stumm and Morgan, 1996, p. 521), the hydrogeology literature uses the term sorption isotherms (e.g., Domenico and Schwartz, 1998, p.299 Fetter, 1999, p. 122 Freeze and Cherry, 1979, p.403). Manuals for popular transport codes also describe sorption isotherms (Zheng, 1990, pp.2-9). According to Sposito (1984), the term adsorption includes all reactions on the two-dimensional solid-water interface physical and chemical adsorption and ion-exchange the term sorption refers to all processes that transfer an ion from aqueous to solid phase. 

When the adsorbate-substrate bonds are weak (of the van der Waals type), the properties of the adsorbed monolayer are less dependent on the substrate s atomic structure. In this circumstance, two-dimensional adsorbate phases exhibit lattice-gas-liquid-solid transitions as a function of coverage and temperature changes. 

It should be noted that instabihty leading to dendrite formation can also occur in insoluble surfactant monolayCTs of the type discussed in ChaptCT 4. In this case, supersaturation of a two-dimensional Uquid phase occurs during rapid compression of the monolayer, and the instabihty is the result of mass transfer to the growing solid phase. Vollhaidt (1996) provides examples. 

The concept of the spreading pressure as the appropriate intensive variable for the discussion of surface adsorption was first introduced by Gibbs. However, the Gibbs formulation implies a two-dimensional adsorbed phase which is unnecessarily restrictive. Essentially the same thermodynamic relations may be developed in terms of the surface energy, and this approach has the advantage that it is equally applicable to two-dimensional adsorption on a surface or three-dimensional adsorption in a microporous solid. 

Figure 1.8(a) shows a typical columnar mesophase, consisting of liquidlike columns of molecules arranged in the hexagonal lattice. This mesophase can be referred to as a unidimensional liquid and as a two-dimensional solid. The point group symmetry is Dqyi- Disc-like molecules can also form the nematic mesophase [22] shown in Fig. 1.8(b). As a rule, such a phase is optically uniaxial and negative. The optical axis coincides with the director L. 

High-resolution Si NMR spectra of solids can be obtained using H- Si CPMAS, as demonstrated by Lippmaa et al. in 1981. Si NMR spectroscopy, originally applied to study silicate solutions and silicon-organic compounds in the liquid phase, has since evolved into an important tool for the investigation of various classes of crystalline and amorphous solids. Klinowski and co-workers provided remarkable new insights into the structure and catalytic activity of diverse aluminosilicates employing H, Si, Al and MAS NMR, as well as an array of two dimensional solid state NMR methods. ... 

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