Metastable multilayer

At present, it must be recognized that adsorption hysteresis may be generated in a number of different ways. In the context of the assessment of mesoporosity, we have seen that there are two major contributing factors (a) on the adsorption branch, the development of a metastable multilayer and the associated delay in capillary condensation (b) on the desorption branch, the entrapment of condensate through the effect of network-percolation. 

Stratification of asymmetric aqueous films from NaDoS, CTAB and a commercial surfactant (alpha-olefin sulphonate) solutions at C > Ccmc on a decane substrate have been studied by Bergeron and Radke [236], They found three transitions by thickness in the metastable multilayer films. They observed also stratified CTAB aqueous films on glass. The n(/i) isotherms of stratified films were analysed considering also the oscillatory structural component of disjoining pressure. 

The behaviour reported above has to be reconciled with the other well known properties of multilayers of cadmium stearate and cadmium arachidate. One possible picture is that these materials deposit in a hex-atic structure which, for a multilayer, represents a metastable state. The upper part of the multilayer, where the molecules are free to move, tends... 

MnAl also goes through an Ll0 transformation with an anisotropy on the order of I07ergs/cm3 when in the metastable x phase. By depositing MnAl/Ag multilayers at relatively low temperatures the formation of ferromagnetic x phase is observed as seen in the x-ray diffraction (XRD) patterns in Fig. 14. 

A different approach was adopted by Saam and Cole (1975), who attempted to explain the hysteresis exhibited by a cylindrical pore in terms of the regimes of stability, metastability and instability of the multilayer film. The applicability of the Saam-Cole theory has been explored in some detail by Findenegg et al. (1994), Lewandowski et al. (1991) and Michalski et al. (1991). 

On the basis of the Saam-Cole-Findenegg approach, we are now able to revise the ideal isotherm for capillary condensation. A more realistic isotherm for the physisorption of a vapour in an assemblage of uniform cylindrical mesopores is shown in Figure 7.5. Here, C represents the limit of metastability of the multilayer (of thickness fc) and M the point at which the three phases (multilayer, condensate and gas) all coexist. Along MC the multilayer and gas are in metastable equilibrium. 

Figure 1.32a. Schematic representation of the adsorption (1) - (3) and desorption (4) - (6) of a fluid from the gaseous phase in a cylindrical pore with radius a-l (1) stable adsorbed film with radius a - t (2) multilayer adsorbed film at the unstabillty limit r (3) completely filled capillary (4) unsymmetrical state of a partially filled pore at the metastability limit r (5) further desorption at the metastability limit r (6) stable film with radius r. " "...

The better understanding of the mechanisms of stability incomplex dermatological emulsions stabilized by surfactants and amphiphiles has enabled the development of a rapid microscopic method for evaluation of potential emulsifiers. The method is based on the observation that good emulsifier blends that stabilize emulsions by the formation of multilayers of stable gel phase also swell spontaneously in water at ambient temperature and this process can be observed microscopically. Mixtures that do not form gel phase or form metastable gels only after a heating and cooling cycle cannot be observed to swell spontaneously at ambient temperature. ... 

The multilayer surface alloy formed by Li adsorption on Al(lOO) is exceptional in that substitution of 1/2 ML A1 by Li occurs in both the first and third A1 layers. An unexpected feature of this structure is that the registry of Li atoms in the first and third layers is such that they are staggered along the surface normal direction, as in the Al3Ti-type bulk alloy structure, rather than collinear, as in the expected CusAu-type bulk alloy structure known to be adopted by the metastable, AlsLi bulk alloy. DPT calculations for this system lead to the novel prediction that the AlaLi bulk alloy has a stacking fault at the surface, such that it can be described as an AlaTi-type surface on a CuaAu-type bulk. 

It is a process for adhering two multilayers, especially a substrate and deposited smface layer. The process involves bombarding layered samples with doses of ion radiation in order to promote mixing at the interface, and generally serves as a means of preparing electrical jrmctions, especially between non-equilibrium or metastable alloys and intermetallic compoimds. Ion implantation equipment can be used to achieve ion beam mixing. 

With a few notable exceptions (Sections 3.3 and 3.4), vesicles are metastable in aqueons solntion energy is reqnired to dissolve the molecular components in water and indnce the formation of vesicles, and eventually the vesicles flocculate and precipitate as hydrated multilayers. The energy reqnired to obtain vesicles is usually provided by heat, stirring, nltrasonication, extrusion, or combinations of these. 

Before deposition of the material to form multilayers, the stability of the monolayer must be considered. The solid monolayer phase of most LB materials is formed at surface pressures above the equilibrium spreading pressure (ESP) of the material the ESP being defined as the pressure at which the monolayer and stable solid or liquid phases are in thermodynamic equilibrium. Consequently, the deposition of most LB materials occurs from a metastable state. This often presents no practical problems, since the approach to thermodynamic equilibrium is extremely slow. However, for some materials a loss of pressure or area is observed below the collapse pressure 11. These materials approach thermodynamic... 

Amorphous networks, 4-5 nAmorphous solid synthesis via ultrathin-film multilayer composites analysis of solid-state reaction mechanisms, 357,358/ application to synthesis of metastable ternary compounds, 366 control of crystallization of amorphous aUoy, 360,363,365-367/ control of formation of homogeneous amorphous alloy, 360,361-36 differential scanning calorimetric procedure, 359-360 grazing measurement procedure, 359 lugb-angje XRD procedure, 359 length sddes vs. course of solid-state reactions, 360,361-362/363 quantitative analysis of interdiffiision reaction, 356-357... 

Rh(llO)- (1x2) LEED yes 1.345 93C3 missing-row reconstmction with multilayer relaxation metastable reconstmction after desorption of O from Rh(110)-p2mg(2x2)-2O... 

FIGURE 4.2 Reduction sweep (2.1 to -0.4 V, 10 mV s ) for a multilayer hydrous oxide-coated gold electrode in 1.0 mol dm NaOH solution at 25°C the film was grown in-situ by extended polarization, 90 min. at 2.30 V. (From Springer Science + Business Media Cyclic voltammetry responses of metastable gold electrodes in aqueous media, L.D. Burke, J.M. Moran, and RF. Nugent. J. Solid State Electrochem., 2003, 7, 529. With permission.)... 

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