Four polymer films

The scalar values for the vectorial velocities for the four polymer films that account for the heat transfer and dissipative melting may be calculated as follows ... 

FIG. 20 (a) Density profiles p(z) vs z for e = —2 and four average bulk densities (f> as indicated, (b) Surface excess vs density in the bulk for four choices of e. (c) Profiles for the diagonal components of the pressure tensor and of the total pressure for (p = l.O and e = —2. Insert in (c) shows the difference between P, and Px to show that isotropic behavior in the bulk of the film is nicely obtained, (d) Interfacial tension between the polymer film and the repulsive wall vs bulk density for all four choices of e. Curve is only a guide for the eye [18]. 

Mechanical Properties. The mechanical properties of thin, solvent-cast polymer films were measured on an Instron Tensile Tester according to ASTM standard D882-83. In all cases, tensile values were calculated from the average of at least four measurements obtained from four separate specimens per polymer sample. 

Tetra(o-aminophenyl)porphyrin, H-Co-Nl TPP, can for the purpose of electrochemical polymerization be simplistically viewed as four aniline molecules with a common porphyrin substituent, and one expects that their oxidation should form a "poly(aniline)" matrix with embedded porphyrin sites. The pattern of cyclic voltammetric oxidative ECP (1) of this functionalized metal complex is shown in Fig. 2A. The growing current-potential envelope represents accumulation of a polymer film that is electroactive and conducts electrons at the potentials needed to continuously oxidize fresh monomer that diffuses in from the bulk solution. If the film were not fully electroactive at this potential, since the film is a dense membrane barrier that prevents monomer from reaching the electrode, film growth would soon cease and the electrode would become passified. This was the case for the phenolically substituted porphyrin in Fig. 1. 

Interpreting these results on a detailed molecular basis is difficult because we have at present no direct structural data proving the nature of the split Co(IIl/lI) voltammetry (which seems critical to the electrocatalytic efficacy). Experiments on the dissolved monomeric porphyrin, in CH-C solvent, reveal a strong tendency for association, especially for the tetra(o-aminophenyl)porphyrin. From this observation, we have speculated (3) that the split Co(III/II) wave may represent reactivity of non-associated (dimer ) and associated forms of the cobalt tetra(o-aminophenyl)porphyrins, and that these states play different roles in the dioxygen reduction chemistry. That dimeric cobalt porphyrins in particular can yield more efficient four electron dioxygen reduction pathways is well known (24). Our results suggest that efforts to incorporate more structurally well defined dimeric porphyrins into polymer films may be a worthwhile line of future research. 

For more complex mechanisms, picturesque names such as square, ladder, fence [18] or cubic schemes [20] have been selected. In redox polymer films, additional transport of counterions, solvation, and polymer reconfiguration are important and four-dimensional hyper-cubes are needed to describe the reactions [21]. 

In order to illustrate the utility of model parameter interpretation, a data set containing NIR transmission spectra of a series of polymer films will be used [85]. In this example, films were extruded from seven different polymer blends, each of which was formulated using a different ratio of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) where the blend compositions were 0, 2.5, 5,10, 25, 50 and 100% HDPE. NIR spectra were then obtained for four or five replicate film samples at each blend composition. Figure 12.18 shows the NIR spectra that were obtained. 

Diffuse-reflectance MIRS has found a number of applications for dealing with hard-to-handle solid samples, such as polymer films, fibers, or solid dosage forms. Reflectance MIR spectra are not identical to the corresponding absorption spectra, but sufficiently close in general appearance to provide the same level of information. Reflectance spectra can be used for both qualitative and quantitative analysis. Basically, reflection of radiation may be of four types specular, diffuse, internal, and attenuated total. 

The above theory reveals that the piezoelectricity of polymer film can be classified into four cases at its origin (A) The intrinsic piezoelectricity due to internal strain in the crystal, (B) the intrinsic piezoelectricity due to strain-dependence of spontaneous polarization, (Q the piezoelectricity originated from the polarization charge qp arising from strain-independent persistent polarization P0, and (D) the piezoelectricity from the true charge gt embedded in the film. It must be emphasized that in cases (Q and (D) heterogeneous strain Au = (u — Sl/T) must exist in the film. 

Because the oxidation potential of the polymer is lower than that of the monomer, the polymer is electrochemically oxidized into a conducting state, kept electrically neutral by incorporation of the electrolyte anion as a counter-ion. This is an essential since precipitation of the unoxidized, insulating polymer would stop the reaction. Both coulometric measurements and elemental analysis show approximately one counter-ion per four repeat units. An important feature is the fact that the polymerization is not reversible whereas the oxidation of the polymer is. If the polymer film is driven cathodic then it is reduced towards the undoped state. At the same time neutrality is maintained by diffusion of the counter-ions out of the film and into the electrolyte. This process is reversible over many cycles provided that the film is not undoped to the point where it becomes too insulating. It is possible to use it to put new counter-ions into the film, allowing the introduction of ions which are too nucleophilic to be used in the synthesis. The conductivity of the film for a given degree of oxidation depends markedly on the counter-ion, varying by a factor of up to 105. 

The experimental results described above show that the gas-permeability properties of thin glassy polymer films (submicrometer in thickness) are more time- or history-dependent than much thicker films (the bulk state for example, 50 pm or thicker) seem to be. This is manifested in terms of physical aging over a period of 1 year and more. The observed permeability values for the current thin films are all initially greater than the reported bulk values but approach or become less than these values after a few days or weeks, depending on the thickness. After a year, the thin films may be as much as four times less permeable than the reported bulk values. Selectivity increases with aging time, as might be expected from a densification process. 

Fig. 14 A/SjC>eq vs. /s>eq for PEO, PTFiF, PMA and PVAc up to es>max for all four polymers, with the symbols identical to those in Fig. 13 (A). The same plots for PMMA and PtBMA are shown in (B), where the open symbols stand for 17 < 2 mN nr1 and the filled symbols for n > 2 mN nr1. The solid and dashed curves are the same as in Fig. 4, and the surface pressure increases counterclockwise, starting from 77 = 0, Limit I, in Fig. 4. PMMA shows a discontinuous change with can be explained by the coalescence of PMMA patches existing as a heterogeneous film prior to the monolayer state. Error bars, not shown for clarity, are 0.5% and 5% for/s>eq and A/SjC>eq, respectively...

As in the earlier section, we briefly present the static properties first. The results obtained with pH 2 water (with 10 mM HC1) as the subphase are displayed in Fig. 22, where TI-A and es - A isotherms for all four polymer monolayers are plotted together in each. With the exception of PHcMA, the TI-A isotherms of the polymer monolayers are nearly identical and they are consistent with the expected isotherms of condensed films. Each isotherm is shown in two regions the dilute regime where 77 < 1 mN m 1 (open sym-... 

In Fig. 24 a polar plot with all four polymers is displayed. PHcMA (C4 side chain) follows the profile of an almost purely elastic surface film whereas chains with longer side chains follow that of progressively more viscous pro-... 

By the process described above, a plasma film could be obtained that had high enough electrical conductivity to allow direct electrodeposition of copper. The bulk resistivity of film measured by a four-point probe was 2.6 x 10 " ohm-cm for the copper-containing polymer film when deposition was stopped after 18 min at HOW. This value is critical if a uniform electrolytic deposit is to be obtained. For safety, deposition was carried out until a total film thickness of 150nm was obtained, giving a nearly pure metallic layer thick enough to allow subsequent electroplating. 

The T-dependences of the steady state photocurrent (J j) at E= 1.33 x 10 V/cm in four samples with thicknesses from 120 nm to 5700 nm (a range of nearly fifty) are compared in Fig. VD-2. The thinnest sample (120 nm) exhibits the weakest T-dependence initially decreases but remains nearly constant below about 80 K, behavior which is similar to that obtained from transient experiments in the sub-ns regime. When thicker films are used, the dependence of on T increases. By fitting the low temperature data to a thermally activated form, exp( - A/kgT), the activation energy can be obtained for samples with various thicknesses. As shown in Fig. VD-2, A increases with the thickness of the semiconducting polymer film. 

Wang, Y., Zhao, J., Si, J., Ye, P., Fu, X., Qiu, L., and Shen, Y. (1995). Dynamic studies of degenerate four-wave-mixing in an azobenzene-doped polymer film with an optical pump. /. Chem. Phys. 103, 5357-5361. 

Brignon, A., Sillard, R, and Huignard, J.-P. (1996). Vector phase conjugation in CrV YAG b four-wave mixing with linearly-polarized pump beams. Appl. Phys. B 63, 537-540. fvlohajerani, E. and Mitchell, G. R. (1993). Temperature optimisation of optical phase conjugation in dye doped polymer films. Opt. Commun. 97, 388-396. 

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