Sandwiched film technique

Figure 14. The region of OD stretching fundamental in the spectrum of HDO in Nafion 125 (sodium form, 95% H, 5% D). The top spectrum was obtained by the sandwiched film technique, the others by the vapor equilibrium technique. The point-by-point spectrum was recorded with 3-min time lapses between points to minimize...

Figure 15. Plot of the frequency of the B component of OD stretching of HDO in Nafion 125 as a function of water content. Key [], sandwiched film technique o, vapor equilibrium technique.

In situ electron transport measurements on conducting polymers are commonly made by using a pair of parallel-band electrodes bridged by the polymer [Fig. 9(A)].141142 Other dual-electrode techniques in which the polymer film is sandwiched between two electrodes [Fig. 9(B)],139,140 rotating-disk voltammetry [Fig. 9(C)],60,143 impedance spectroscopy,144,145 chronoamperometry,146 and chronopotentiometry147 have also been used. 

The schematic model of the film deposited by the technique is shown in Figure 45. A single-stranded DNA layer is sandwiched between two aliphatic amine monolayers. Thus, the technique can be useful for our objectives, for it allows depisition of single-stranded DNA on practically any substrate and does not demand a large quantity of DNA, since only one monolayer will be deposited. Nevertheless, there is a question of whether DNA in such a structure will hybridize. In fact, the film contains a single-stfanded DNA monolayer between two amine monolayers, and it is questionable whether the upper amine monolayer will prevent hybridization with complementary DNA stfands. 

The technique of vertical dipping for construction of multilayer LB films containing metal ions is depicted in Figure 3.5.2. Centrosymmetric bilayers, with metal ions sandwiched between the polar head groups in the film, are deposited onto vertically mounted substrates passed down and then up through the metal/surfactant monolayer at the air/water interface. The structure of the film is represented by the bis chelate coordination of the carboxylate function of the fatty acid around a divalent metal ion. This type of structure has been determined for a number of metal ions including Cd, Co, Mn, Pb and Zn (24 and ref. within). The structure of CoSt (25), inferred from infrared (IR) and XRD studies, is depicted in Figure 3.5.3a (25). Centrosymmetric films, where the area of the film transferred to the substrate... 

Linear-dichroic spectra of SA monolayers prepared from mixtures of OTS and a cyanine-dye surfactant established the absence of dimerization and the orientation of the chromophore parallel to the substrate [183]. In contrast, the same cyanine dye underwent sandwich-type dimer formation in LB films and had its chromophore oriented perpendicular to the water surface [192]. These results highlight an important difference between LB and SA monolayers. Parameters which determine monolayer formation on an aqueous subphase are also responsible for the orientation and organization of the surfactants therein. Furthermore, the configuration of the surfactants is retained regardless of the structure of the substrate to which the floating monolayer was subsequently transferred to by the LB technique. Conversely, in SA monolayers, surfactant organization is primarily dependent upon the nature of the substrate [183]. 

A similar technique can be used to study the rheological properties of liquid films. Figure 4 shows the formation of a W/O/W emulsion film with two, identical aqueous phases (such as in water-in-oil emulsions) at the tip of the capillary. A pre-requisite of the experiment is that the surface of the capillary must be well wetted by the film phase, i.e., it should be hydrophobic in this case. First, an aqueous drop is formed inside the oil (film liquid) and the aqueous phase is in the bottom of the cuvette. Then, the level of the aqueous phase is slowly increased. As the oil/water interface passes the drop, a cap shaped oil film, bordered by a circular meniscus, covers the drop. This film can be studied in equilibrium and in dynamic conditions, similar to the single interfaces (See above). The technique can be used to study films from oil or aqueous phase which can be sandwiched between identical or different liquid or gas phases. 

The classical experimental setup developed for fe polarization reversal implies a singledomain fe sample sandwiched between two electrodes [28], While conventional domain inversion techniques use equal sized electrodes covering the polar faces of fe templates, nanodomain inversion occurs under totally different conditions when the bottom electrode is a uniform plate and the upper one is a point contact. Two different kinds of the upper switching mobile nanoelectrodes may be considered afm tip (and/or array of tips) and electron drop formed using electron beam exposure. When a voltage stress is applied to the nanoelectrode, both the electric field intensity and its spatial distribution strongly differ in fe thin films (thin fe crystals) and bulk fe crystals. 

Autoradiography is a technique for detecting radioactively labelled species in a gel, paper or thin layer by sandwiching a sheet of photographic film next to the support medium and allowing the radioactive emissions to expose the film. After developing the film, the positions and intensities of the radioactive sources are shown by areas of blackening on the film. 

The values of CBF differ slightly since they were obtained by different techniques vertical films in a frame put into a horizontal X-ray diffractometer [341,342] and horizontal film (Fig. 2.21) in a synchrotron ray diffractometer [343], The data presented in the above table confirm the concepts established from previous investigation about the structure of both types of black films a sandwich model of two adsorption layers of amphiphile molecules with an aqueous core in between (for CBF) and bilayer of amphiphile molecules in which molecules of the solvent are incorporated (for NBF). The bilayer structure of NBF has been confirmed [344] for films from aqueous solutions of C]2E6 obtained in the measuring cell shown in Fig. 2.21. Their thickness of 6 nm found is less than the double length of the amphiphile molecule. 

The thickness of horizontal filns of n-decane sandwiched between two water (or aqueous electrolyte) droplets has been determined by a light reflectance technique. The films were stabilised by three surfactants an xyx block copolymer of poly(ethyleneoxide) and poly(12-hydroxystearic) acid soya bean lecithin Arlacel 83 (sorbitan sesquioleate). Results obtained for two and three component mixtures of the surfactants were compared with those for the single surfactants. The results showed that, provided sufficient polymer is present in the film, the thickness is determined by the longest oleophilic chain, namely the poly(12-hydroxystearic) acid. 

A dispersed sample may also be obtained by means of an aerosol sampling device. A suitable technique is to form a sandwich of plastic film particles and 20 nm thick carbon. The underlying plastic may then be washed away with solvent and the specimen examined after shadowing 159,160,162]. 

---