Stearate films

Ba- or Cu-stearate films could be built up to as many as 3000 layers simply by repeated dipping and withdrawal processes (Birdi, 1989, 1999). On the other hand, fatty-acid films or other sources have cracking and fogging tendencies. It was suggested that addition of the Cu ion [10 6M] solved these problems (Birdi, 1999). 

Fig. 28 Cross-sectional areas of different films. Eudragit L 30 D without pigments, film thickness approximately 25 pm (A), Eudragit L 30 D film containing 50% of magnesium stearate, film thickness approx. 25 pm (B), incomplete film formation at higher magnification showing individual latex particles from an Eudragit L 30 D dispersion in the film (C).

The change from calcite to vaterite nucleation on stearate films at low [Ca] suggests that the extent of Ca binding is important for polymorph selection. The nucleation of calcite is favored by the formation of a well-defined Ca-carboxylate layer that mimics the first layer of the (110) face of the unit cell. By contrast, the structural requirements for vaterite formation are less precise. This is consistent with vaterite being the dominant phase on amine monolayers where no Ca binding is present, and suggests that kinetic factors of charge accumulation... 

In two later addresses [73,74] Langmuir added other highly significant observations about the effects of adsorbed films on the wettability of solids. A trimolecular stearate film (prepared by the Langmuir-Blodgett technique) exhibited a contact angle of 55.4° with a white mineral oil, 51.7° with ethyl myristate, 48.7° with carbon tetrachloride, 48° with benzene, 1.5° with n-hexane, and 50° with water. The contact angle of this oil with barium stearate multilayers varied little with the number of monolayers in the film—e.g., it was 52° on a monolayer, 55.4° on three layers, and 55.9° on seven layers. 

ESEM of injector inner surface with smooth stearate film. 

Faulty stearate film with gaps in section. 

On the other hand, the values of the resistance per layer showed a definite increase with the thickness of the film. The specific resistance of the films thus determined from their values of the resistance per layer was ca. 10 fl. This was based on the results of capacity measuranents on some 75 samples. The capacitance measurements thus performed on stearate films (1-10 layers) led to e values between 2.1 and 4.2, with a bulk value of 2.5. 

Figure 4. The same sample as Figure 3, but the dependence of emission of light mass fragments is depicted as a function of position as the edge of the Mn deutero stearate film is moved under the ion beam.

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