Poly absorbance spectra

Fig. 1. Comparison of amide V VCD for an identical sample of poly-L-lysine in D20 as measured on the UIC dispersive instrument (top) and on the ChirallRFT-VCD instrument (at Vanderbilt University, kindly made available by Prof. Prasad Polavarapu). Sample spectra were run at the same resolution for the same total time ( 1 h) in each case. The FTIR absorbance spectrum of the sample is shown below. VCD spectra are offset for sake of comparison. Each ideal baseline is indicated by a thin line, the scale providing a measure of amplitude. Noise can be estimated as the fluctuation in the baseline before and after the amide V, which indicates the S/N advantage of the single band dispersive measurement.

Heating of an H2S-exposed film of CdAr (deposited from pH 7 subphase) above 70°C was accompanied by an increase in particle size from 2.5 to 3.4 nm (48). Washing of an H2S-exposed CdAr (deposited at pH 6) film with CHC13 caused a red shift in the absorbance spectrum of the CdS corresponding to an increase in particle size (58,64). LB films containing M2+ ions have been prepared with poly-... 

A) The absorbance spectrum of poly-y-methyl-L-glutamate in the a-helical form, with an assignment of its three constituent transitions. (B) The far-UV CD spectrum of the same compound, deconvoluted on the assumption that the shapes of the absorbance and dichroic bands are directly related (broken lines). The solid line is the observed spectrum and the filled circles the sum of the three bands. In general, the sign of a CD band may be either positive or negative, and its intensity does not necessarily follow that of the absorbance band. (From Holzwarth and Doty, 1965.)... 

Figure 21.5. (a) In-phase and (b) quadrature spectra of the DIRLD spectra of a composite sample of poly(Y-benzyl-L-glutamate) and polypropylene (c) static absorbance spectrum of the sample. (Reproduced from [6], by permission of the Society for AppUed Spectroscopy copyright 1991.)... 

With h 6) - 1/sin 0)5(0 — Oq), one obtains the same result as given by (4.58), which implies that the anisotropy of the/factor cannot be derived from the intensity ratio of the two hyperfine components in the case of a single crystal. It can, however, be evaluated from the absolute/value of each hyperfine component. However, for a poly-crystalline absorber (0(0) = 1), (4.66) leads to an asymmetry in the quadrupole split Mossbauer spectrum. The ratio of l-Jh, as a function of the difference of the mean square amplitudes of the atomic vibration parallel and perpendicular to the y-ray propagation, is given in Fig. 4.19. 

The absorption and emission of radiation in the near ultraviolet (UV) and visible regions of the electromagnetic spectrum are associated with electronic (and associated vibronic) transitions involving n- and/or n-electron systems of molecules. Synthetic and natural polymers absorb in the UV region and particularly strong absorption spectra are recorded for polymers containing aromatic and heteroaromatic groups (e.g., poly(styrenes), poly(vinyl naphthalenes), poly(vinyl carbazoles)). 

Finally, two related studies can be mentioned here. It was noted that when a quartz plate was immersed overnight in a solution of Pb(C104)2 and poly(vinyl alcohol) through which H2S had been bubbled, a film formed on the plate parallel with formation of a colloidal PbS sol [47]. The film was extremely thin (maximum absorbance of <0.015 at 400 nm). The absorption spectrum of this film was similar to that of the PbS sol and consisted of several absorption peaks with an absorption onset of ca. 630 nm (1.97 eV). It is not clear that this is the true bandgap onset, for the same reasons as discussed previously (weak absorption close to the bandgap). The XRD crystal size of the precipitate was ca. 3 nm. 

Fig. 14.5 Infrared spectrum of poly(vinyl chloride) (a) transmittance and (b) absorbance.

Studies of the triplet-triplet absorption spectrum of P1VN 59) and P2VN 60-61> in degassed fluid solution have shown that triplet annihilation is still important at room temperature. The triplet absorbance of dilute poly(vinylnaphthalene) solutions is only 0.05-0.2 times as large as that of the corresponding ethylnaphthalene solution having the same concentration of naphthyl groups. While quantitative data on kMXX at room temperature are unavailable, the ordinary triplet decay rate kx has been extensively studied for monochromophoric compounds. 

Poly(vinylidene fluoride) PVDF2, has been studied by absorbance subtraction in order to isolate the spectral features of the different phases in particular, the difference spectra were used to interpret the structure of phase III212). The spectrum of the unoriented phase-III sample before annealing is shown in Fig. 15. The spectrum after annealing at 160 °C for 20 hr is also shown with the difference... 

Coleman et al. 2471 reported the spectra of different proportions of poly(vinylidene fluoride) PVDF and atactic poly(methyl methacrylate) PMMA. At a level of 75/25 PVDF/PMMA the blend is incompatible and the spectra of the blend can be synthesized by addition of the spectra of the pure components in the appropriate amounts. On the other hand, a blend composition of 39 61 had an infrared spectrum which could not be approximated by absorbance addition of the two pure spectra. A carbonyl band at 1718cm-1 was observed and indicates a distinct interaction involving the carbonyl groups. The spectra of the PVDF shows that a conformational change has been induced in the compatible blend but only a fraction of the PVDF is involved in the conformational change. Allara M9 250 251) cautioned that some of these spectroscopic effects in polymer blends may arise from dispersion effects in the difference spectra rather than chemical effects. Refractive index differences between the pure component and the blend can alter the band shapes and lead to frequency shifts to lower frequencies and in general the frequency shifts are to lower frequencies. 

The conjugation length of poly(3-alkylthiophene)s can be determined from the absorption maximum in the electronic spectrum. Whereas regioregular (i.e., head-tail) poy(3-octylthiophene) (POT) displays a maximum at 442 nm in CHCl3/Freon-113 solution, the absorbance maximum of 504 is blue shifted by 114 to 328 nm. This blue shift could arise from a particularly low molecular weight. 

The absorption spectrum for a typical stabilizer of this type, 2-hydroxy-4-dodecyloxybenzophenone, is shown in Figure 8 (10) along with that of poly (ethylene—CO). Over the near ultraviolet range, the absorption coefficient of the stabilizer is much greater than that of the polymer, and even at low concentrations the stabilizer will absorb most of the light, thereby protecting the polymer. 

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