Influence of Dodecylammonium Chloride on the Properties of Carrageenan Gels

Abstract

Rheological measurements, confocal laser scanning microscopy, and x-ray diffraction were used to study the influence of dodecylammonium chloride (DDACl) on the gelation of κ- and ι-carrageenans. The increase of DDACl concentration led to the changes of gel structure from nano to macro-scale. At the macroscopic level, two phase regions have been differentiated; one below the surfactant micellar region containing turbid gel and the other in the micellar region characterized by gel collapsing. The effect of monomer DDACl concentration on gel structure at the nano level was detected by rheological measurements. All gel samples exhibited shear thinning behavior, well fitted by power law equation, indicating that they maintain mainly carrageenan rheological properties. The change of flow behavior parameters with increasing DDACl concentration might be ascribed to the formation of surfactant domains inside gel networks. Progressive increase of surfactant concentration caused gradual break down of the gel structure and enhanced ordering of surfactant molecules. In the vicinity of the critical micelle concentration, the appearance of microphase separated domains, visualized by confocal laser scanning microscopy indicated pronounced structural changes of both, κ- and ι-carrageenan gels. X-ray diffraction of collapsed gels revealed the formation of a bilayered surfactant structures in conjunction with the carrageenan chains. The increase of DDACl concentration enhanced ordering and growth of mesostructural domains consisting of stacked bilayers. Both, local ordering of bilayers and regular stacking of lamellae revealed stronger electrostatic interactions between surfactant and carrageenan with higher charge density on chains.

Keywords:

• Biopolymers
• carrageenans
• gelation
• polyelectrolyte
• surfactant

This work was supported from grants (098-0982915-2949 and 178-1780469-3591) of the Ministry of Science, Education and Sports of the Republic of Croatia. The research was conducted within the framework of the Cost Action: D27, Working Group 0006.