Emil J. Samuelsen

The phase transition of two-dimensional squaric acid H2C4O4 studied by neutron scattering

Abstract At Tc = 370 K squaric acid undergoes a phase transition, which was studied in detail by neutron scattering. The transition is essentially two-dimensional with β = 0.137 ± 0.010. Diffuse scattering above Te is found to be anisotropic. From “diffuse crystallography” it is concluded that proton disorder is not the dominant source of diffuse scattering. Individual molecules retain their low-temperature shape in the high-temperature phase.

A Raman Study of Crystalline Glutaric Acid

Glutaric acid C3H6 (COOH)2 is a member of a series of dicarboxylic acids that form infinite molecular chains linked by double hydrogen bonds in the crystalline state. The β-modification shows an anomaly in the lattice vibrational region. At the discontinuous transition to the α-modification the spectra undergo changes indicative of a unit cell reduction and considerable crystalline disorder.

A new assessment of the crystalline structure of undoped and doped aniline oligomers and polymers

Summary form only given. We describe hem the crystalline structure of aniline oligomers and polymers, derived from the aniline dimer p-aminodiphenylamine and aniline. The preparation of the oligomers has been accomplished via a modification of the usual polymerization route to polyaniline. The resulting powders have been successfully fractionated, using diethylether, methanol, tetrahydrofurane and dimethylformamide. The individual fractions differ by their molecular weight and their oxidation state, as has been derived from preliminary U.V. visible and MR spectra and by their solubility behaviour in concentrated sulfuric acid. Differences have been observed also in the chemical reactivity of the different powders. Especially the lower molecular weight materials ( ether/methanol soluble ) are quite reactive and undergo different chemical reactions when treated prolonged during the fractionation schedule. For example, crosslinking and uptake of oxygen are to be expected. The crystalline state of the different fractions depends strongly on the details of the crystallization procedure and on the molecular weight of the materials. Less convienient conditions and higher molecular weights yield samples with less defined crystalline features. Most important is the observation that all the crystalline structures in the undoped powders can be well accounted for by the EB II arrangement, proposed by Pouget et al. On the other hand, the characteristic crystalline arrangement of the doped samples does not show the main features of the ES II crystal arrangement. The ES II structure, reported by Pouget et al., probably results from degradation processes during the preparation of their powders.

X-ray diffraction studies of oriented poly(3-alkylthiophenes)

Abstract Poly(3-hexylthiophene) (PHT) and poly(3-octylthiophene) (POT) were chemically polymerized with FeCl3 in CHCl3 to give a black powder. Remaining FeCl3 was removed by washing and boiling the product in methanol. Free standing 10 μm thick films were cast from CHCl3 solution on a glass substrate. The films were drawn at room temperature by a home made stretching apparatus up to 4 times its initial length. Possible draw ration before the film is torn apart is found to depend on the solubility of the polymer. X-ray diffraction profiles of undrawn films correspond with those reported [1,2]. Films oriented by drawing show a higher degree of crystallinity. X-ray diffraction exposures of drawn polymer films show obvious anisotropy. The diffraction profiles perpendicular and parallel to the draw direction are different, from which models for crystalline polyalkylthiophenes are proposed.

Structure of diphenyltriazole, a potential monomer for a conductive polymer

Abstract The chemical structure of 3,5-diphenyltriazoles indicates that these compounds may have the potential to be monomers for conjugated polymers. Monomeric 4-ethyl-3,5-diphenyl-1,2,4-4H-triazole has been synthetized according to established procedures and single crystals of the compound grown. From X-ray structure determination we find a monoclinic space group Cc, with a = 5.616(4), b = 17.511(4), c = 13.778(3) A , β = 96.30(3)° and Z = 4 . The structure is polar in the ac-plane. The phenyl groups are twisted approximately 90° relative to each other and the molecules are packed in an alternating chain pattern.

Symbiosis of microprocessor and film techniques in X-ray diffractometry

A two-axis X-ray diffractometer run by a microprocessor and equipped with a climbing detector to cover the upper hemisphere was provided with the option of exchanging the point detector with flat or cylindrical film cassettes. By synchronisation of the specimen rotation and the film motion, Weissenberg-type and other exposures are obtained. Various choices of the relative motions may be used to focus the attention on selected parts of the reciprocal space, which may be magnified and reshaped. The importance and convenience of being able to perform film and point detector studies on the same instrument and at any temperature are pointed out.

Automatic diffractometer used as a low-temperature Weissenberg camera

Abstract By exchanging a film for the detector of a diffractometer provided with a lift motion, Weissenberg type exposures may be obtained at all temperatures. Since the diffractometer motions are programmable, the exposures may be magnified and reshaped. Film surveys and detector study details may be obtained on the same instrument.

Crystal Dynamics and Phase Transition of Glutaric Acid

Abstract A crystal-dynamical calculation of the s phase of glutaric acid was performed with Buckingham potentials under consideration of the low frequency internal modes. The overall agreement with experiments is satisfactory and confirms most of the proposed assignment but two bands have to be modified. The eigenvectors show coupling of internal and external motions and thus demonstrate limitations of the rigid-body model. Model calculations suggest a gradual conformational change to explain the observed anomaly of one mode. The site symmetry changes at the transition to the high temperature phase.