Subject highly oriented

The highly oriented molecules in thin organic films such as Langmuir-Blodgett (LB) films and self-assembled monolayers (SAM) [1] are essential for some molecular functions. Non linear optical and opto-electronic properties are two of the most important and interesting functions of these molecular assemblies. In the past more than thirteen years, simulation of the primary process of photosynthesis using such molecular assemblies and its application to molecular photodiodes [2,3] have been one of the main subjects of our laboratory. 

A completely different approach to polymer crystallisation in extended-chain conformation became possible with the coming of a new class of polymers the para-para type aromatic polymers. These polymers possess inherently rigid molecular chains in an extended conformation (Preston, 1975 Magat, 1980 Northolt, 1974, 1980, 1985 Dobb, 1985). Theoretically they should give rise to high orientation in fibre form without the necessity of subjecting the as spun filaments to the conventional drawing process. 

Crazing in anisotropic polymers has seldom been studied by means of optical interferometry. A block copolymer (Isoprene-Styrene) with a highly oriented fibrillar structure, and a PMMA oriented by means of drawing above Tg, have been studied so far. These results are reported in and The same subject has often been studied, however, using other experimental techniques... 

Fig. 7 (a) Two-dimensional SAXS pattern showing a weakly oriented smectic peak for an iPP sampla subjected to a shear pulse with a rate of 1 s" and a strain of 3000% at 180 °C (b) Disappearance of the smectic peak after a steady shear of 0.1 for 10 minutes (c) SAXS pattern with the incident x-ray beam parallel to v x i> showing highly oriented smectic layers (after Li and de Jeu [6])... 

The evolution from highly oriented polymers to in situ composites through PLCs has a common feature in that they all have negative thermal expansivity (as defined in section 8.1.1) in the orientation direction of the order of —10 K in a wide range below and around room temperature. As in oriented flexible polymers, these negative values are attributed to a decrease of the fully extended conformation of the chains induced by thermal vibration [19-21]. Various models and theories have been proposed semi-empirically as well as based on fundamental principles. In the following, a detailed discussion of the subject is presented. 

The majority of results so far available in this Held have been derived from spectra recorded on dispersive instruments. In order to test tl validity of Eq. (1) several independent experiments have been performed in which a highly oriented polyethylene terephthalate film is subjected stepwise to increasingly higher stresses in the stretching machine illustrated in Fig. 1 and FTIR spectra are taken at the relaxed stress levels with unpolarized radiation. In Fig. 4 the wavenumber shifts of the v(0—CH2) absorption band are plotted as a fimctimi of the applied stress for different experiments. From these systematic investigations, however, no linear relationship between the wavenumber shift Av and the plied stress good index of determination (0.98) was obtained for the power function ... 

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