Polymeric films thickness

V. Yegnaraman and A.M. Yacynych, Enzyme immobilization on ultramicroelectrodes through electropolymerization effect of polymeric film thickness on the amperometric response of the electrode. Bull. Electrochem., 16 (2000) 21-24. 

Figure 1. Au evaporated glass substrate for estimating the polymerized film thickness on the single probe...

The pursuit of further miniaturization of electronic circuits has made submicrometer resolution Hthography a cmcial element in future computer engineering. LB films have long been considered potential candidates for resist appHcations, because conventional spin-coated photoresist materials have large pinhole densities and variations of thickness. In contrast, LB films are two-dimensional, layered, crystalline soHds that provide high control of film thickness and are impermeable to plasma down to a thickness of 40 nm (46). The electron beam polymerization of CO-tricosenoic acid monolayers has been mentioned. Another monomeric amphiphile used in an attempt to develop electron-beam-resist materials is a-octadecylacryUc acid (8). 

Serious attempts to use LB films in commercial appHcations include the use of lead stearate as a diffraction grating for soft x-rays (64). Detailed discussion on appHcations of LB films are available (4,65). From the materials point of view, the abiHty to build noncentro symmetric films having a precise control on film thickness, suggests that one of the first appHcations of LB films may be in the area of second-order nonlinear optics. Whereas a waveguide based on LB films of fatty acid salts was reported in 1977, a waveguide based on polymeric LB films has not yet been commercialized. 

Media made from woven or nonwoven fabrics coated with a polymeric film, such as Primapor, made by SCAPA Filtration, and Gore-Tex, made by W. L. Gore and Associates, combine the high retentivity charac teristics of a membrane with the strength and durability of a thick filter cloth. These media are used on both continuous and batch filters where excellent filtrate clarity is required. 

Fig. 14. RAIR spectra of a plasma polymerized silica-like film deposited onto a polished aluminum substrate (A) before and (B) after annealing at ISO C for 30 min. Film thickness was about 735 A. Reprinted by permission of Gordon and Breach Science Publishers from Ref. [15].

Lipatov et al. [116,124-127] who simulated the polymeric composite behavior with a view to estimate the effect of the interphase characteristics on composite properties preferred to break the problem up into two parts. First they considered a polymer-polymer composition. The viscoelastic properties of different polymers are different. One of the polymers was represented by a cube with side a, the second polymer (the binder) coated the cube as a homogeneous film of thickness d. The concentration of d-thick layers is proportional to the specific surface area of cubes with side a, that is, the thickness d remains constant while the length of the side may vary. The calculation is based on the Takayanagi model [128]. From geometric considerations the parameters of the Takayanagi model are related with the cube side and film thickness by the formulas ... 

Not much effort has been made, except for the Tafel studies, to establish the empirical kinetics and models of interfacial reactions to obtain thick polymeric films (>100 nm) of industrial interest from different monomers. However, this is much more than the few kinetic studies performed until now to understand the mechanism of chemically initiated polymerization. Electrochemical models still have an advantage in obtaining priority in the industrial production of tailored materials. 

Polymerization at constant current is most convenient for controlling the thickness of the deposited film. Charges of ca. 0.3, 0.2, and 0.08 C cm-2 are required to produce 1 fim of polypyrrole,59 poly(3-methylthio-phene)60 (no data are available for polythiophene), and polyaniline 43 respectively. Although these values can reasonably be used to estimate the thicknesses of most electrochemically formed conducting polymer films, it should be noted that they have considerable (ca. 30%) uncertainties. For each polymer, the relationship between charge and film thickness can... 

In recent years, much attention has been paid to the use of controlled/ living polymerizations from flat and spherical surfaces [121,122],because this allows better control over the MW and MWD of the target polymer. By using these techniques, a high grafting density and a controlled film thickness can be obtained, as such brushes consist of end-grafted, strictly linear chains of the same length and the chains are forced to stretch away from the flat surface. Several research... 

Fig.9 Variation of the rate of polymerization of PUA with the rate at which temperature rises (curve a ) and with the temperature at which (Rp) is measured (curve b A). (Film thickness 10 pm).

Stevenson [99] conducted the first polycondensation experiments with thin polymer melt films of 0.07-5 mm thickness. The experiments were performed on metal surfaces at temperatures between 265 and 285 °C under vacuum. He varied the kind of metal and observed that the behaviour of the polycondensation rate with decreasing film thickness depended on the metal being used. He concluded that the reaction rate increased only on metals soluble in the polymerizing melts... 

Figure 6. Plot of tan 8 vs. temperature for plasma-polymerized ethane formed at 0.5 ton, 20 cmsSTP/min, 5 W, and KHz. Film thickness was 820 A. (9) Measured at 1 KHz and (X) measured at 10 KHz.

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