Infrared and Raman spectra of three crystal modifications, a, ß, and 7, of oleic acid were investigated. The spectral data of the 7 (low-melting) phase were analyzed on the basis of crystal structure determined by Abrahamsson and Ryderstedt-Nahringbauer. The reversible solid-state phase transition between y and a was followed by the infrared and Raman spectra, and it was concluded that the phase transition was of an order (7)-disorder (a) type accompanied by a conformational disordering in the methyl-sided alkyl segment. Therefore, the y -» a transition was recognized as a new type of interface melting process occurring in layer-formed organic long-chain compounds. The extent of conformational disorder in alkyl chains was compared among various types of disordered crystalline phase. From the spectral feature of phase ß, it was supposed that the subcell structure of this phase differed from the already-known Ox and Tr (or O') type.

Crystallization and crystal structure of the β phase of oleic acid (cis-9-octadecenoic acid) have been investigated with morphological observation, X-ray diffraction, and DSC (differential scanning calorimeter). The morphology of growing crystals of the β phase depends significantly on supercooling. It was found that the β phase could be classified into at least two solid modifications, β1 (mp 16.3 °C) and β2 (mp 16.0 °C). The crystal structure analysis of the β1 phase has been performed. The unit cell belongs to a triclinic system of P1̄, and the asymmetric unit contains two crystallographically independent molecules, A and B. The molecular layer is a unique interdigitated structure, where the methyl group of molecule A and the carboxyl group of molecules B (or vice versa) are located on the same plane. For the conformation around the cis-CC bond, both molecules approximate to trans−cis−trans conformation, the first case for a cis-monounsaturated fatty acid. The methyl and carboxyl side chains together form a T∥ subcell. On the basis of its crystal structure, it was speculated that the β1 phase has a unique surface structure at the (001) face. The factors for the characteristic properties of the β phase were also discussed.

Study of molecular structures with Fourier transform ( I T ) infrared (IR) spectroscopy has been done on polymorphic transformations of three saturated-unsaturated mixed acid triacylglycerols (TAGs): sn-1,3-stearoyl-2-oleoyl glycerol (SOS), sn-1,3-palmitoyl-2-oleoyl glycerol (POP), and sn-1,3-palmitoylstearoyl-2-oleoyl glycerol (POS), in combination with X-ray diffraction and differential scanning calorimetry (DSC). Specific attention has been paid to absorption bands corresponding to methyl end packing, olefinic conformation, subcell structure, and glycerol structure. It was confirmed that the acyl chain packing, mainly expressed in the subcell structure and the olefinic conformation, is rather disordered in the less stable forms such as a! and y. The more ordered packing is revealed in the metastable form of p', which was called pseudo-@' in the authors' previous article.5In the most stable forms of @2 and 81, well-ordered acyl chain packing and the olefinic conformation of the skew-cis-skew' type are revealed. The chain length structure is reflected in the absorption bands of the terminal methyl end packing as well as of the glycerol group. The double chain length structure is revealed in the a! forms of the three TAGs and in p' of POP, whereas the triple chain length structure appears in y, p' except for POP, and j3 forms of the three TAGs. A polarized microprobe FT-IR technique using well-defined crystals was applied to clarify subtle differences between the two @ forms of SOS, which appeared in the subcell structures of the oleoyl chains and the methyl end packing.

Annealing was carried out in air into an open joule furnace; the temperature was monitored with a K-type thermocouple. Samples were kept separated from the furnace walls by ceramic spacers. An uncoated quartz substrate was annealed at the same time. The thermal treatment did not cause any alteration in the substrate optical properties.UPS and XPS were performed in a ultrahigh vacuum analysis chamber (base pressure < 1 10 ±6 Pa) equipped with an electrostatic hemispherical analyzer. An Mg-anode source (1253.6 eV) was used for XPS, while He I (21.2 eV) and He II (40.8 eV) resonance lines were utilized for UPS. The overall energy resolution was about 1 eV in XPS and 0.1 eV in UPS. The Fermi level was identified by UPS measurement on a metallic sample. The sputtering of the films was performed by Ar ions (1.5 keV, 3.5±4.2 lA, 30 min each at 1 10 ±4 Pa). The AFM characterization was performed using a Digital Instruments Multimode Nanoscope IIIa atomic force microscope operated in tapping mode and equipped with single-crystal silicon tips. The average crystallite (grain) sizes of the samples were extracted from AFM images using software developed in our laboratory.UV-vis transmittance measurements were obtained with a JAS-CO 7850 spectrophotometer, while the optical gap values were extracted from transmittance measurements using the Tauc Polymer-based composite materials with functional organic molecules such as organic dyes have often been made by dispersing functional molecules in amorphous polymers or amorphous regions of crystalline polymers. However, such composite materials combined with functional organic molecules in the crystalline regions of polymers have not been developed hitherto, since the unit cell of most polymers has been considered to have insufficient space to store functional organic molecules. Nevertheless, the clathration of functional organic molecules within polymer crystalline regions has the advantages of preventing them from coagulation and making it possible to control their arrangement by regulating the orientation of the polymer crystalline regions. In this paper, we demonstrate the first examples of composite materials formed from organic dyes and the crystalline regions of a polymer and control of the dye-molecule orientation, both of which can be accomplished by technically simple methods. COMMUNICATIONS

To clarify the influence of cis-unsaturation on solid-state structures of triacylglycerols (TAGs), the crystal structures of three crystalline phases (alpha, beta' and beta) of triolein [C3H5(OCOC17H33)3] were investigated by powder X-ray diffractometry and IR and Raman spectroscopy. The influence on the structural change of the alpha phase in the course of cooling was also studied. With respect to the subcell structure and conformational order of hydrocarbon chains in the beta and beta' phases, triolein resembles saturated TAGs; trans-zigzag hydrocarbon chains are adopted in the T(parallel) subcell for the beta phase and in the O(perpendicular) subcell for the beta' phase. The influence of cis-unsaturation was most obvious in the structure of the alpha phase and its temperature dependence. The alpha phase of triolein does not form the ordinary hexagonal subcell but a rather loose distorted subcell, which hardly changes in cooling, forming a striking contrast to the hexagonal-->pseudohexagonal subcell transformation found in the alpha phase of saturated TAGs.

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Two reversible solid-state phase transitions of erucic acid (cis-13-docosenoic acid), the γ f R and γ1 f R1 phase transitions, have been followed by vibrational spectroscopy (IR and Raman) and X-ray diffraction. The crystal structure analyses of the higher temperature phases, R and R1, have been performed. The symmetry of crystal lattices remains unchanged during the both transitions, i.e., the γ and R phases belong to a monoclinic system (P2 1 /a) and the γ1 and R1 phases belong to a triclinic one (P1 h). At the γ f R transition point, the subcell structure of the methyl-terminal chains is reconstructed, accompanying a large conformational change of cis-olefin groups. On the γ1 f R1 transition, the inclination manner of hydrocarbon chains changes, while there are no significant changes in the subcell structure and the conformation of cis-olefin groups. The conformational disorder at methyl terminals increases continuously for the γ1 f R1 transition, contrary to an abrupt occurrence at the γ f R transition. The unit cell volume also increases gradually in the γ1 and R1 phases and shows no prominent changes at the γ1 f R1 transition, while a stepwise increase takes place at the γ f R transition. The important factors for transition behaviors are discussed on the basis of the crystal structures.

A photoresponsive polymeric material, in which [2]rotaxane units with α-cyclodextrin threading onto an azobenzene derivative is used as a topological cross-link for the main chains of the polymeric material in aqueous media, was achieved.[2]Rotaxane structures were found to act as movable links in the polymer network, and the mechanical properties of the material were enhanced to show a rupture strain of 2800%. The materials were reversibly deformed by irradiation with UV or visible light in aqueous media, which caused photoisomerization of the azobenzene moiety and changed the structure of the [2]rotaxane linker, leading to deformation of the polymer network. Surprisingly, the dry materials, which had been uniaxially extended in air, showed a faster response than the hydrogel. The orientation of the polymeric network in the materials enables the efficient response. This dry material (5.6 mg) performed 5.6 μJ of mechanical work within 10 s, which is approximately 50 times higher than that achieved in our previous work.