Anisotropic film

Research Focus Synthesis of anisotropic films using polymerizable aromatic acrylate... 

Originality While the preparation of anisotropic films using acrylate intermediates... 

The fragments of macromolecules with ordered cholesterol group sequences, that are formed in bad solvents, may serve as nuclei of supermolecular order in films, obtained from these solvents. Structural and optical studies have shown that PChMA-11 films produced by solvent evaporation display different properties those obtained from chloroform and toluene solutions (small relaxation times, see Table 17) are optically isotropic, and those obtained from heptane solutions (large relaxation times, see Table 17) are optically anisotropic, what reflects the differences in conformational state of polymeric chains in these films. Contrary to the optically isotropic films, a high degree of side branch ordering characterizes optically anisotropic films, which is confirmed by X-ray studies. The observed difference of LC polymer structure in the bulk is thus the consequence of their different conformational state in solution this reveals some possibilities for the control of LC polymer structure at the initial steps of mesophase nucleation in solutions. 

Finally, transient potential/current waveforms may be used for polymerization. Cyclic voltammetric growth has mostly been used to carry out mechanistic studies. The use of pulsed current or potential is not a common practice. Recently, however, pulsed-current methods28 29 have been used by Mitchell and coworkers to produce more ordered anisotropic films. The use of transient waveforms adds another dimension to electropolymer growth, because the oxidation/reduction of the polymer according to Equation 2.2 will occur during growth, and the effect of this on the polymerization process must be considered. 

The anisotropic films exhibited two glass transitions whose temperature location and ACp agree well with values reported by Menzcel and Wunderlich (J12,itQ.). The first heat DSC scan of the EK60ca film shows a broad endotherm above the first glass transition roughly corresponding to the vaporization of about 3 wt% triflouroacetic acid. The presence of 3 wt% residual solvent was confirmed by thermogravimetric analysis (TGA). 

Ellipsometry at noble metal electrode/solution interfaces has been used to test theoretically predicted microscopic parameters of the interface [937]. Investigated systems include numerous oxide layer systems [934-943], metal deposition processes [934], adsorption processes [934, 944] and polymer films on electrodes [945-947]. Submonolayer sensitivity has been claimed. Expansion and contraction of polyaniline films was monitored with ellipsometry by Kim et al. [948]. Film thickness as a function of the state of oxidation of redox active polyelectrolyte layers has been measured with ellipsometry [949]. The deposition and electroreduction of Mn02 films has been studied [950] below a thickness of 150 nm, the anodically formed film behaved like an isotropic single layer with optical constants independent of thickness. Beyond this limit, anisotropic film properties had to be assumed. Reduction was accompanied by an increase in thickness, which started at the ox-ide/solution interface. 

A third approach to underfilling involves applying an insulative thermoplastic preform (film) prior to attaching the device. Under pressure and heat, the preform softens and flows around the solder bumps, then solidifies quickly on cooUng. The devices may then be solder reflowed to make the connections or the preform may be formulated to flow and encapsulate the solder during solder reflow. Table 5.6 lists some commercially available preforms used as underfills. Anisotropic film adhesives have also been used as underfill preforms, in which case z-direction conductive paths are formed beneath the solder bumps at the same time that the rest of the insulating film flows and cures around the bumps. Anisotropic paste adhesives can be similarly used (Figure 5.11). 

Electrically conductive adhesives are being used to interconnect flip-chip devices in smart cards resulting in thinner and smaller structures. Flip-chip silicon devices that have been thinned to several mils may be connected to a substrate with silver-filled paste epoxy or with anisotropic film adhesive instead of solder, then embedded and laminated to form a card that is less than 40-mils thick. Requirements for adhesives used in smart cards, in many respects, are more severe than those for other commercial applications. Besides having to withstand high humidity and temperature extremes, smart cards must take the continued abuse of human handling, repeated bending, exposure to human sweat and salt residues, and exposure to ultraviolet radiation from sunlight. 

Plastic products with biaxial orientation (such as the wall of a PET carbonated drink bottle) have a greater resistance to puncturing than initially isotropic or uniaxially oriented film, because there is no weak direction in the plane of the film. In such anisotropic films, the value of cr — rr to cause thinning is larger than [Pg.245]

For optical anisotropic films, three refractive indices, n, Uy, and n, along three principal axes have to be taken into consideration. The x-axis is the direction showing the maximum refractive index within the film plane in general, the y-axis is the direction perpendicular to the x-axis within the film plane, and the z-axis is the thickness direction that is normal to the x-y plane. 

The manufacture of cellulose blown films from NNMO solution [48] was mentioned in Section 3.5.2 and mechanical values of a more anisotropic film as well as a more balanced type are included in Table 3.4 demonstrating the versatility of the process. 

FC-212B/ Hitachi Anisotropic film 180°C, 145 psi, 20 sec Fhp-chip underfill and electrical connections... 

Alternately, flip-chip devices or TAB devices may be connected using an anisotropic film adhesive which, with moderate heat and pressure, forms electrical connections between the bumps or leads of the device and the conductor pads on the panel. In using an anisotropic film adhesive, the film is first attached to the glass at 80°C-100°C under pressure of 50-100 N/cm (based on bump area) for 3-5 seconds. The protective... 

Wang et al. (1979) studied amorphous Gd-Co films by means of electron diffraction and found that the radial distribution functions are significantly different for the perpendicular anisotropic and in-plane anisotropic films. Wang et al. and also Nishihara et al. (1979) conclude from their results that the perpendicular anisotropy is associated with a predominance of Gd-Co pairs. This would agree with the pseudo-dipolar model of Chaudhari and Cronemeyer (1975) where the cross term predominates in their expression for given by... 

Yamamoto and Ishida [115] have obtained the following expressions for reflectances in the case of an anisotropic film on an isotropic substrate within the Abeles thin-film approximation (1.5.5°) ... 

For the external reflection in a three-phase system, air-ultrathin anisotropic film-substrate, the components of absorbance As(y), Apiy, and A (j) can be calculated by Mielczarsky s approximate formulas, which are frequently used in practice [123, 124] due to their simple form ... 

It is noteworthy that for inorganic films the linear approximation (1.98) is valid only in the extremely narrow range of the layer thicknesses [126] (see discussion of this phenomenon in Section 3.3.4). To apply Eqs. (1.97) and (1.98) to anisotropic films, one should substitute 2 by ly in the formulas for -component and by etx and 2z in the first and second terms of the formulas for / -component, respectively. 

This so-called Sperline relationship has been verified in a series of in situ and ex situ studies of surfactant adsorption phenomena (see Refs. [169, 170] for examples and references). The corrected formula (1.114) is also applicable to ex situ ATR spectra [171] and adsorption onto a film-coated IRE [172]. The extension of Eq. (1.114) to anisotropic films is discussed by Eringelli [173]. Pitt and Cooper [174] represented Eq. (1.114) as... 

Note (Section 3.11.5) that for anisotropic films the optimum conditions can be different. 

Figure 3.18. Simulated AR of ( ) vjoy, (o) vtox> and (A) vlqj bands in IRRAS spectra of 10-nm inorganic anisotropic film on (a) Bap2 (03 = 1.5), (b) ZnSe (ns = 2.4), (c) Si (03 = 3.4), and (d) Ge (ns = 4.0) as function of angle of incidence. Optical parameters of film material are shown in Table 3.3 ni = 1.0. Adapted, by permission, from K. Yamamoto and H. Ishida, Appl. Spectrosc. 48, 775 (1994), p. 779, Fig. 5. Copyright 1994 Society for Applied Spectroscopy.

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