Changes In Molecular Arrangement Research Articles

Phase transitions in p- n-propyloxybenzylidene- p-amino benzoic acid: A DSC Study

The compound, p- n-propyloxy benzylidene p-amino benzoic acid ( 3 BABA), exhibits a nematic liquid crystalline phase at temperatures above ≈190°C. Phase transitions in 3BABA have been studied in the temperature range 25°C≤T≤300°C by differential scanning calorimetry. The following interesting features have been observed: 1. 1. the transitions involving the crystalline phases are very complex, 2. 2. there is a gradual transformation of some of the metastable crystalline phases into more stable ones, 3. 3. the transition(s) occurring while cooling the nematic can follow one of the two paths, one leading directly to a crystalline phase through a very sharp transition, and the other leading to the crystalline phase through an intermediate phase P 1 of unknown nature which is an unusual occurrence. These features may be related, to the change in molecular arrangement from closed dimer to open n-mers while cooling the nematic, and the resulting formation of crystalline phases with almost comparable free energies. The transition entropy, ΔS NI(1.40R 0) for the nematic-isotropic transition is very large compared to that of ordinary nematics(N o). This is thought to be due to the unusually pronounced short range orders in the fibre-type nematic phase(N f) of 3BABA, which are not present in N o phases.

Observation of structural change in organic monolayer film by penning ionization electron spectroscopy: Fe-phthalocyanine on graphite

Structures of Fe-phthalocyanine adsorbed on a graphite substrate (cleavage plane) were studied by Penning ionization electron spectroscopy (PIES). The structural change, disordered layer → closely packed monolayer → island, was observed upon heating the film deposited on the substrate held at 123 K. For the monolayer and island structures, molecules were found to be oriented flat to the substrate. It was concluded that PIES was a useful technique to probe the change in molecular arrangement during order-disorder transformation in monolayer films.

Studies of the Heat of Reaction during Vulcanization of Rubber

Abstract The results of experiments indicate that an addition of accelerators caused the change of molecular arrangement of the rubber hydrocarbon. This discovery is of a great value in explaining the mechanism of acceleration, which is different from physical, chemical, and physico-chemical theories proposed heretofore.