Film thickness equivalent

Gas chromatography (GC) employs a gaseous mobile phase, known as the carrier gas. In gas-liquid chromatography (GLC) the stationary phase is a liquid held on the surface and in the pores of a nominally inert solid support. By far the most commonly used support is diatomaceous silica, in the form of pink crushed firebrick, white diatomite filter aids or proprietary variants. Typical surface areas of 0.5-4 m2/g give an equivalent film thickness of 0.05-1 pm for normal liquid/support loadings of 5-50 per cent by mass. 

The thickness of microscopic foam films from F108 was measured by the microinterferometric method (see Section 2.1.1). Fig. 3.32 depicts the dependence of the equivalent film thickness hw on the electrolyte concentration of the higher copolymer F108 (at two concentrations). 

The equivalent film thickness hw initially decreases and then levels off at a constant value. The plateau starts at a critical electrolyte concentration Cei,cr = 3-1 O 3 mol dm 3 NaCl, similar to low molecular mass surfactants. The increase in bulk copolymer concentration raises the plateau (45 1 nm vs. 39 3 nm), but has no marked influence on the sloped branch. The results for the lower copolymer (P85) are very similar. The equivalent film thickness hw initially decreases and above Ceicr = 3-10 2 mol dm 3 NaCl levels off at a constant value of 17 + 1 nm (Ce , = 7-10 5 mol dm 3 P85). 

Fig. 3.32. Equivalent film thickness h vs. electrolyte (NaCl) concentration F108 aqueous solutions ...

The equivalent film thickness hw is larger than the total film thickness, /iTOt, since the refractive index of the adsorption layer is higher than that of water (n, > n2). Allegedly, the electrolyte concentration affects only the aqueous core thickness h2 while the thickness h is constant. According to Duyvis [159] the aqueous core thickness is expressed by Eq. (2.2) (see Chapter 2). 

Fig. 3.36 plots both the experimentally obtained equivalent film thickness (O) and the calculated (Table 3.5) aqueous core thickness ( ) as a function of time. They are monotonously decreasing functions. 

Fig. 3.40. Total disjoining pressure n vs. equivalent film thickness porous plate method aqueous...

The electrostatic interactions may be practically suppressed by increasing the electrolyte concentration (the Debye screening length at 0.1 mol dm 3 NaCl is only 1 nm). Above a critical electrolyte concentration, CeiiCr the equivalent film thickness of such foam films is independent of Cei (Fig. 3.32). At Cei > Cei,cr film thickness is governed by Uvw and n, and the stabilising role of nj( is obvious. 

Fig. 3.41. Total disjoining pressure FI vs. equivalent film thickness hw for aqueous solutions of F108 ...

In order to apply the hole-nucleation theory of bilayer stability of Kashchiev-Exerowa [27] involving quantitative interpretation of the W(C) dependence (probability for observation of black films vs. surfactant concentration), the black films from amniotic fluid should be bilayer films. This is proved experimentally by two dependences Y hw) (Fig. 11.1) and hw(Cei) (Fig. 11.2). As it can be seen in Fig. 11.1, the equivalent film thickness is 8 nm and does not change with the increase in IT (which is the difference between the pressures in the... 

Similarly, the hw(Cei) dependence (Fig. 11.2) indicates the same equivalent film thickness of 8 nm which does not change with further increase in Cei (plateau in the curve). As... 

Figure 1. Surface pressure-area characteristics of DMS-BPAC block copolymers (cf. Table II) on water. Solid lines are region of stable surface pressure, dashed lines represent region where pressure decays with time. Equivalent film thickness (for density of 1.0 g/ml) indicated on axis at top.

Equivalent Film Thickness Refers to an experimentally determined fluid film thickness for which some assumptions about the structure and properties of the film have been made. The experimental technique used should also be stated when using this term. 

Using the film model, calculate the equivalent film thickness. 

Mechanical and thermal characterization of ultra low k dielecteics is very similar to the characterization of dense low k dielectrics however the introduction of porosity requires the development of new characterization techniques in order to understand the pore structure. The dielectric constant, dielectric breakdown and coefficient of diermal expansion can be measured using the same techniques used for dense low k electrics. Modulus and hardness can also be measured by die same techniques, however, if using nanoindentation, measurements firom porous dielectrics may have larger substrate contributions at equivalent film thicknesses. Therefore, the modulus values... 

Figure 15.7 Variation of disjoining pressure with equivalent film thickness at various NaCl concentrations.

A general test for the presence of electrostatic interaction in a film is the influence of the electrolyte concentration. The equivalent film thickness h of foam films from Pluronic F108 aqueous solutions decreases with increasing electrolyte concentration [CgiJ [4]. Above the so-called critical concentration, Ufi — 3x10 mol dm NaCl, h remains constant. There is a plateau in the H ,(Cei) curve. The concentration Cei cr distinguishes the electrostatic interaction from the steric interaction and shows the transition between them. 

The effect of pH on the equivalent film thickness at four different values ofthe... 

DDC) and hydrophilic polyfructose chains (PFC), that is, polyfructose loops of the INUTEC SPl molecules. According to Equation 6.1 the total film thickness (h) differs from the equivalent film thickness (h, ) that is experimentally measured, the difference being hu,corr = 2hi(Wj —1)/(W2—1) [38]. A value of 1.40 is taken for Uj (between 1.42 for bulk dodecane and 1.38 for supersaturated aqueous solutions of inulin [44]). The value of hi is chosen to be 5 nm, based on data from atomic force microscopy and dynamic light scattering measurements [11, 13] h , corr = 12 0.7nm has been obtained. 

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