Magnetic Susceptibility of Alkali n-Butyrates and Isovalerates Near their Melting Points

J. J. Duruz, A. R. Ubbelohde
1975 Proceedings of the Royal Society A  
Various physical properties of alkali carboxylates can be used to study precursor effects immediately below or above their melting points. The present paper describes unusual pre-transition behaviour observed in the magnetic susceptibility of molten ^-butyrates and iso valerates. This takes the form of a transitory enhancement of diamagnetic susceptibility, by nearly 10 % in some cases, when the isotropic melt is cooled through the clearing point and into the mesophase region while a magnetic
more » ... while a magnetic field (up to 1 T( 104 G)) is applied. No corresponding changes are observed on taking the salt through the same tem perature range but in the inverse direction. Again, no corresponding change is observed with an alkali carboxylate which shows no mesophase melting transition. Present findings can be accounted for on the assumption of cluster formation in the molten salts as these approach their upper melting points, which is also indicated by other evidence. The (transient) enhancement of molecular diamagnetism in this region of tem perature may also indicate transient perturbations in the actual cation-anion binding near the transition temperature. I n t r o d u c t io n Previous X-ray studies (Duruz & Ubbelohde 1972) on the mesophases of sodium w-butyrate and sodium isovalerate indicated that, although closely similar in many respects, this pair of salts exhibits contrasting features, notably with respect to the tem perature dependence of the Tong-spacings'. These differences are due to a different mode of packing of alkane chains between the layers of ions (electrostatic sandwiches). Such contrast in behaviour and structure of these organic ionic mesophases suggested investigations by different physical means into other possible anomalies of behaviour. The present paper describes the response of both kinds of salts to applied magnetic fields. Experience with other types of substances had suggested th a t the molecular magnetic susceptibility might give useful information on the nature of the mole cular and ionic interactions in various states of these salts, in particular through the dependence of the magnetic susceptibility on temperature and on transitions between different physical states. Magnetic field-induced orientation of anisotropic liquid crystals has so far mainly [ 39 ]
doi:10.1098/rspa.1975.0010 fatcat:nkhlckquobgvhgn4bxj2nhsvjm