Abstract
Micellar systems consisting of a surfactant and an additive such as an organic salt or an acid usually self-organize as a series of worm-like micelles that ultimately form a micellar network. The nature of the additive influences micellar structure and properties such as aggregate lifetime. For ionic surfactants such as sodium dodecyl sulfate (SDS), CMC decreases with increasing temperature to a minimum in the low-temperature region beyond which it exhibits the opposite trend. The presence of additives in a surfactant micellar system also modifies monomer interactions in aggregates, thereby altering CMC and conductance. Because the standard deviation of β was always lower than 10%, its slight decrease with increasing temperature was not significant. However, the absolute value of Gibbs free enthalpy, a thermodynamic potential that can be used to calculate the maximum of reversible work, increased with increasing temperature and caffeic acid concentration. Micellization in the presence of caffeic acid was an endothermic process, which was entropically controlled. The enthalpy and enthropy positive values resulted from melting of “icebergs” or “flickering clusters” around the surfactant, leading to increased packing of hydrocarbon chains within the micellar core in a non-random manner. This can be possibly explained by caffeic acid governing the 3D matrix structure of water around the micellar aggregates. The fact that both enthalpy and entropy were positive testifies to the importance of hydrophobic interactions as a major driving force for micellization. Micellar systems allow the service life of some products to be extended without the need to increase the amounts of post-harvest storage preservatives used. If a surfactant is not an allowed ingredient or food additive, carefully washing it off before the product is consumed can avoid any associated risks. In this work, we examined the influence of temperature and SDS concentration on the properties of SDS–caffeic acid micellar systems. Micellar properties can be modified with various additives to develop new uses for micelles. This allows smaller amounts of additives to be used without detracting from their benefits.
Highlights
Hydroxycinnamic acids are phenolic compounds of the phenylpropanoid family that occur naturally as secondary metabolites in plants
We examined the properties of micellar systems consisting of caffeic acid and sodium dodecyl sulfate (SDS)
The critical micelle concentration (CMC) of the SDS–caffeic acid micellar system was determined from specific conductance versus surfactant concentration curves
Summary
Hydroxycinnamic acids are phenolic compounds of the phenylpropanoid family that occur naturally as secondary metabolites in plants. Because these phenolic compounds are ubiquitous in plants, they are usual components of the animal and human diet, albeit in widely variable proportions around the world. They can be absorbed in the gastrointestinal tract, they are partially excreted unchanged or in derivative forms via urine and faeces [5]. Because these phenolic compounds are ubiquitous in influence fruit quality through a number of sensory properties such as flavour [7], colour [8] or plants, they are usual components of the animal and human diet, albeit in widely variable proportions texture [9]. We examined the properties of micellar systems consisting of caffeic acid and SDS
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