Film compressibility

By coating the compliant electrodes with a thicker but softer layer of polymer gel, the gel can spread out along with the expanding fihn during actuation but bunches at points where the film compresses. If the polymers are imprinted with patterns of electrodes or shades of dots in a variety of shapes, these features can be raised or lowered to fabricate an active camouflage fabric which can change its reflectance for any defence systems and soldiers. 

The particles were spread from ethanolic dispersion. In Figure 3, a characteristic ir-A curve of particles la is shown [75,77]. Film compression first leads to a gradual rise in... 

These assumptions have been expanded upon (Shah and Capps, 1968 Lucassen-Reynders, 1973 Rakshit and Zografi, 1980), especially in regard to the application of the ideal mixing relationship in gaseous films (Pagano and Gershfeld, 1972). It has been pointed out that water may contribute to the energetics of film compression if the molecular structures of the surfactants are sufficiently different (Lucassen-Reynders, 1973). It must be noted that this treatment assumes that the compression process is reversible and the monolayer is truly stable thermodynamically. It must therefore be applied with considerable reservation in view of the hysteresis that is often found for II j A isotherms. 

In addition, it should be noted that none of the compression and expansion cycles for these films are coincident. The considerable hysteresis exhibited during the compression/expansion cycle is evidenced at every compression/expansion rate investigated, and is indicative of a stereoselective kinetic process that must occur upon film compression. Table 3 gives the monolayer stability limits of the amino acid methyl ester films as defined by... 

N-Stearoyltyrosine. The case of N-stearoylserine methyl ester illustrates temperature-dependent enantiomeric discrimination in both monolayers spread from solution and in equilibrium with the bulk phase. Although the IIIA isotherms suggested large differences in the intermolecular associations in homochiral and heterochiral films of SSME, there exist chiral systems in which enantiomeric discrimination as exhibited in film compression properties is much more subtle. N-Stearoyltyrosine (STy) is such a system. 

Fig. 44 Preferred lowest energy conformations of (+)- and meso-diastereomers and the effect of stereochemistry on the mechanism of film compression. Reprinted with permission from Arnett et al., 1989. Copyright 1989 American Chemical Society.

It must be kept in mind that the Goodrich treatment separates out contributions to intermolecular interactions that arise from film expansion. The differences in film expansion are a reflection of conformation and are accounted for in the pure meso- and ( )-films. However, since ( )- and meso-film components do interact, the intramolecular contribution to film compression may be altered. This effect would arise from conformational perturbations as molecules interact, thereby precluding complete separation of inter- and intra-molecular contributions to the thermodynamics of compression. However, these complicating factors can be mitigated by comparing several molecules with varying structures, as has been carried out in this instance. 

As high pressures lead to transition from gas to liquid or to solid phases in the three-dimensional system, a similar state of affairs would be expected in the two-dimensional film compression n versus A isotherms (Figure 4.4), as described in the following text. 

Intermolecular Area and Film Compressibility. Since the observations on film penetration, All, serve to define discontinuities in film structure, the relation of An to intermolecular areas and film compressibility (13, 16) requires some analysis. Does protein penetrate the interface simply because the lipid monolayer is compressible and has available intermolecular areas, or does the protein interact with the lipid ... 

P-A and AV-A studies were carried out with stearic acid films in the presence of Ca2+ and ATP (Figure 3). The P-A curve in the absence of Ca2+ exhibits the typical linear liquid-condensed and solid-condensed regions however, in the presence of 10 4M Ca2+ the liquid-condensed region vanishes. When an equimolar concentration of ATP is present with Ca2+, the P-A curve is almost identical to that obtained without Ca2+. The surface potential for stearic acid in the absence of ATP and added Ca2+ increased gradually with film compression, attaining a maximal value of 230 mv. At a concentration of 5 X lO -W Ca2+, AV increased to a value of 150 mv. and decreased to the original value with film compression. A similar curve was obtained with 10 4M Ca2+... 

PMCG alone or with 2 X 10 r>M Ca2+, the surface potential did not vary with film compression from the initial value of about 20 mv. At a concentration of 10"4M Ca2+ and 2 X 10"r,M PMCG AV remained at first constant with compression, then decreased to —100 mv., and finally returned almost to the initial value. At intermediate concentrations of Ca2+ and the same concentration of PMCG, AV was initially —100 mv., remaining either constant (5 X 10"r>M Ca2+) or increasing (10 4M Ca2+) with film compression. 

The surface potential of the brain lipid film increased linearly with film compression attaining a potential of 375 mvolts at the limiting area... 

An alternative explanation of the NH4OH results suggests itself at maximum film compression, enhanced competition between H+ and NH4+... 

The 1% ethylene-carbon monoxide copolymer was also irradiated in the solid phase (thin film). Compression-molded films were fixed on plates which fitted into the Perkin Elmer 521 infrared spectrophotometer. An infrared spectrum of the polymer could thus be obtained after each period of photolysis without disturbing the film. For photolyses at room temperature and above the plates were mounted in a solid brass cell through which a stream of inert gas could be passed while the cell was being heated. 

Sample Preparation. All polymer samples were prepared from commercial general purpose polystyrene (Monsanto HF-77). The additives were incorporated into the polymer by fluxing on a two-roll laboratory mill at about 350°F. Two types of samples were molded from the milled polymer (a) 50-mil plaques, compression molded at 350°F. (b) 1.5-2.5-mil films, compression molded at 390°F. 

Chen et al. [108] reported that poly(vinyl stearate) (PVS) could be studied only in the dilute regime (77 < 5 mN m-1), as films compressed to higher surface pressures showed continuous relaxation in the surface pressure. Hence,... 

Various process steps were used to determine their Influence on the morphological nature of liquid crystalline copolyester films. Compression molding was used to form quiescent films, while extenslonal deformation above and below the onset of fluidity, as well as shear deformation above the onset of fluidity was used to make non-quies-cent films. It Is a basic result that molecular orientation can only be achieved when the deformation is done while the polymer is In a liquid crystalline melt state. Experimental details are given In the subsection Materials and Processing, while an interpretation is offered in the discussion in the subsection Morphological and Process Consideration. ... 

The second hydrophilic slab extends up to 8 nm and contains a much lower segment density (0.1 to 1 per lipid). It is not observed for low-molecu-lar-weight PSS (Mw 4300 Da) and is hardly observed for low salt. Its thickness decreases on film compression toward 2 nm. Qualitatively this thickness decrease can be understood in terms of residual electrostatic interactions between the surface and the polyelectrolyte tails—on compression surface overcharging is reduced and hence the lowered repulsion (from head+PSS in the first slab) enables condensation of the remaining segments in the adjacent slab. 

Important processing methods vapor phase deposition, spin coating, injection molding, casting, ex-trusion, drawing of oriented films, compression molding, sintering... 

Thermooxidation. Thermooxidation of the films compression molded from the composite was performed at 165°C by measuring oxygen absorption. 

---