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ABSTRACT:A new material, which can be used in solar energy utilization, is obtained here by adding different weights of poly(vinyl alcohol) (PVA) to the semiconducting material CdS. The effect of this addition was studied by using FT-Raman spectrometer (based on 1500 mW Nd : YAG laser at 1064 nm), UV-Vis-IR (190 -800 nm) spectrophotometer, and X-ray diffractometer. Our experimental results indicated the appearance of several new Raman bands, which have not existed in both CdS and PVA. Some of the bands which are already existing in the Raman spectra of PVA showed an unexpected systematic increase in their intensities after the addition of CdS to the matrix. On the other hand, some of the new Raman bands appeared in special concentrations of PVA only, whereas some of the Raman bands of CdS were found to disappear after adding PVA. Finally, shifts in some bands associated with random increase in their intensities after adding PVA to CdS was detected in the FT-Raman analysis. The experimental evidence given here might be attributed to the occurrence of new bonds, indicating that the produced mixture is a new material. The assignment of the new bands as well as an interpretation of the obtained variations is given here. Our X-ray diffraction data confirmed the interpretation introduced here. Moreover, the UV-Vis spectra confirmed the existence of new absorption bands in the Visible region. The I-V characteristic curve was measured for a selected concentration of the new composite material, showing a remarkable increase in the values of the conduction current of about two orders of magnitude as compared with the pure PVA material.

The conformational changes occurring in isotactic polypropylene during the melting and crystallization processes have been carefully investigated using FT-Raman spectroscopy at temperatures below, at, and above the polymer melting point. Results confirmed the retention of some crystallinity up to þ210 8C, which is 50 8C above the melting point. It was found that, at temperatures just above the melting point (1-10 8C), there is still some short range order of at least 12 monomer units long in certain regions of the melt. At 10 8C above the melting point, the short range order drops below 12 monomer units resulting in the disappearance of the Raman band at 841 cm -1 . Vice versa, the experimental measurements show that the iPP melt system is stable when the persistence length of helical sequences is less than 12 monomer units. As soon as the helix length exceeds 12 units, the 3 1 helix conformation extends quickly and then crystallization occurs. These results are discussed in terms of Imai's microphase separation theory and it agreed very well with it. Also, from our observations for correlation splitting, Raman bands related to conformational states were identified. This analysis indicates the existence of three different conformational states at 808, 830, and 841 cm -1 . The 808 cm -1 band was assigned to helical chains within crystals (representing crystalline phase). The 841 cm -1 band was shown to be composed of a band at 841 cm -1 , assigned to shorter chains in helical conformation with isomeric defects (representing the isomeric defect phase), and a broader band at 830 cm -1 assigned to chains in nonhelical conformation (representing the melt-like amorphous phase). This indicates the detection of a three-phase structure in iPP, where a third phase could be due to the presence of defect regions within the crystalline region, or due to the presence of an amorphous-crystal interphase.

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