Growth micromorphology of stearic acid crystals

Abstract

Growth and micromorphology of stcaric acid crystals grown by solvent evaporation method has been studied. The cffect of the solvent and the rate of evaporation of the solvent on the growth micromorphology has been investigated. The formation of spherulitic growth features, rhombic platelets of B-and C forms having growth spirals associated wii,h solution channels and twinned crystals involving B-B, C-C, and B-C forms is observed. The complexity of the twins involving the B-and C forms is discussed. iritroduetioiiCharacterization of the growth of long chain organic molecular crystals can be understood t o a certain extent from similar studies on hydrocarbon molecules having a simpler structure such as n-alkanes etc. Fatty acids and fatty alcohols also play a n important role in such studies, as these molecules have a different niolecular species at one end of the molecular chain compared t o the n-alkanes. The growth and niicroniorphology of these materials has been the study since a long time (e. g. MULLER; AMELINCKX ; VERMA ; DANIEL; BOISTELLE ; SATO 1977). This article reports a systematic study on the crystallization of stearic acid employing different solvents. Certain aspects related t o spherulitic growth and the formation of twinned crystals is considered. Experinleiit a1Stcaric acid (99% pure) obtained from Loba Chemicals, India is used as the starting matcrial. Crystallization is carried out by solvent evaporation method. The solvents employed are (i) acetom, (ii) benzene, (iii) toluene and (iv) xylene. Characteristics of growth is investigated at different levels of supersaturation and growth rates. The rate of evaporation of the solvent is varied over wide limits i.e., 4 x -0.1 cm3 . min-'. Growth at high-and low levels of supersaturation is characterized by dendritic, spherulitic growth forms in addition t o lozenge shaped platelets and thin platelets 52 Observations and discussion

Experimental validation of the modified Avrami model for non-isothermal crystallization conditions

“…1A). 5,7,20,[44][45][46][47] Stearic acid crystals are rhombic shaped 32,33,48 (Fig. 1B) and trihydroxystearin appears as Maltese crosses (Fig.…”

“…1B) crystallizes into two-dimensional rhombic platelets. 9,32,33 Trihydroxystearin (Fig. 1C) forms 3-dimensional spherulitic crystals.…”

Self decoration: Case ofn-octacosane hydrocarbon crystals

“…Such a change in the morphology can be caused by the presence of water as impurity in the solvent. For example, morphology o f stearic acid crystals greatly differ, when crystallized from 2% water containing acetone (Swamy et al 1985) and pure acetone (Prasad 1985). It thus explains the different morphologies (hemispherical) of the deposits (DLF) noticed.…”

Activation Energy of Crystallization for Trihydroxystearin, Stearic Acid, and 12-Hydroxystearic Acid under Nonisothermal Cooling Conditions

“…Three systems, 12HSA, stearic acid, and trihydroxystearin, were chosen to be modeled to determine the activation energy of nucleation due to their molecular similarities and different dimensionalities of crystal growth. Upon crystallization, 12HSA forms 1-D nanofibers, ,− stearic acid forms 2-D platelets, − and trihydroxystearin forms 3-D spherulitic crystals. , …”