Stearic acid (C17H35COOH) is a saturated fatty acid and one of the most abundant fatty acids in the environment. It is an important metabolite in the human body and, although being classified as a saturated fatty acid, does not increase the level of LDL cholesterol. Due to its structural characteristics, stearic acid is considered a surface-active agent (SAA). In high concentrations, SAAs are said to form water-soluble aggregates, called micelles. At certain concentrations (pH is particularly important), some fatty acids in solutions have been shown to form lipid vesicles instead of micelles, which is why the solution becomes visibly cloudy. In this work, we attempted to determine if stearic acid could form lipid vesicles. Due to the poor solubility of stearic acid in water, we used a solution of its sodium salt – sodium stearate. Using a neutralisation potentiometric titration, we monitored the change in turbidity of the solution as a function of its pH. The formation of micelles or lipid vesicles requires a certain concentration of the SAA in solution, which must be above the critical micelle concentration (CMC) or above the critical aggregation concentration (CAC). The sodium stearate solution was in insoluble form at room temperature, and even when we prepared a clear solution in which some of the salt had dissolved, its concentration was still below the CMC and CVC. Thus, stearic acid cannot form lipid vesicles at room temperature, but this is not necessarily true for higher temperature conditions.
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