Physical properties of fatty acids. I. Some dilatometric and thermal properties of stearic acid in two polymorphic forms

Abstract

Summary Purified stearic acid (freezing point 69.20°C., melting point 69.5°C.) when slowly crystallized from benzene at room temperature, yielded transparent monoclinic crystals exhibiting an X‐ray diffraction pattern (long spacing) corresponding to the B‐form of the acid. Crystallization of stearic acid from hot glacial acetic acid resulted in a product exhibiting an X‐ray diffraction pattern (shorter spacing) corresponding to the C‐form of the acid. Rapid chilling of a melted sample of stearic acid likewise yielded a product exhibiting the diffraction pattern characteristic of the C‐forms of the acid. The specific volume, expansion in both solid and liquid states, and melting dilation of stearic acid in both B‐and C‐forms were calculated from dilatometric data. The irreversible transition of stearic acid from the B‐ to the C‐form was rapid and visible at 52.9°C. but also occurred at 35.2°C. when sufficient time was allowed for the transition to occur. The form of stearic acid which was obtained was found to be dependent upon the temperature at which crystallization occurred. When crystallization was carried out at temperatures below the transition point of the acid, the B‐form was obtained, and above the transition point only C‐form of the acid was obtained, irrespective of the solvent used for crystallization. The specific heat of stearic acid was determined, and equations developed for expressing the specific heat of the acid in both solid and liquid states. From the calorimetric data, the heat of fusion, and the entropy of stearic acid were calculated.

Altered phase behavior of the lauric acid–stearic acid binary mixtures in electrospun PVA–PDMS mats

“…Multiple melting events due to the nanoconfinement of LA have also been observed by Mitran et al 70 The transitions of the electrospun mats with a pure LA composition are observed at around 32 1C, which is due to the melting of the LA crystals, and in the case of pure SA two transitions at around 53 1C and 64 1C are observed. The first transition has been attributed to the B to C transformation, as also reported by Singleton et al 71 Interpreting the various thermal transitions observed in the thermograms as polymorphic transitions reported in the literature, we have constructed a binary phase diagram of LA and SA treating the majority components of PDMS and PVA as constituting the medium that accommodates the fatty acid molecules. The phase diagram based on the second heating scan is presented in Fig.…”

Solubility of stearic acid in some halofluorocarbons, chlorocarbons, ethanol, and their azeotropes

“…The pore-size distributions of a large family of silica gels were found by Wheeler (10) to follow approximately a normal distribution.…”

“…The bottle was then immersed in a water bath whose temperature was uniformly raised at 1-2°C /hr, the sample being continuously agitated by the magnetic stirrer. Karl Fischer water analyses, run on samples of several of these solvent samples in the sealed bottles, after six hours immersion showed less than 10 ppm water, so it was concluded that water leakage was not a problem. The temperature at which the last trace of solid disappeared was measured with a thermometer calibrated against a Hewlett-Packard quartz crystal thermometer calibrated at the manufacturer's to within 0.02°C absolute accuracy using NBS techniques.…”

PVA-PDMS-Stearic acid composite nanofibrous mats with improved mechanical behavior for selective filtering applications

“…Singleton et al . 33 , have observed solid-solid transition from B to C at 53 °C. The formation of B or C forms depended upon the choice of solvent (benzene or glacial acetic acid) and temperature of crystallization.…”