Effect of Electrostatic Interactions in Wormlike Micelles of Surfactants Based on Betaine and Charged Tertiary Amine with the Same Hydrophobic Groupsстатья
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Дата последнего поиска статьи во внешних источниках: 5 июня 2024 г.
Аннотация:The viscoelastic properties and structure of solutions of mixed wormlike micelles based on a zwitterionic surfactant, oleylamidopropyldimethylcarboxybetaine (OAPB), and positively charged oleylamidopropyldimethylamine (OAPA) have been studied at different ratios between the components. At a small fraction of the cationic surfactant, OAPA, the solution exhibits viscoelastic properties characteristic of semidiluted solutions of entangled wormlike micelles, the presence of which has been confirmed by cryogenicelectron microscopy data. It has been found that, as the molar fraction of the charged surfactant increases to0.1, the viscosity and relaxation time of the solutions decrease by a factor of three, and the values of the storagemodulus remain unchanged at short stress action times. The studied surfactants have a similar structure;therefore, when replacing zwitterionic OAPB molecules by positively charged OAPA molecules, the mainfactor of variations in the properties and structure is the enhancement of the electrostatic repulsion on themicelle surface. It has been shown that this factor leads to a decrease in the average length of micelles and anincrease in their number, which have a weak effect on the rheological properties of the system as long as thelength of the micelles is larger than the length of the subchains in the network. With an increase in the molarfraction of OAPA from 0.1 to 0.5, the viscosity and relaxation time drop drastically by several orders of magnitude and the viscoelastic response of the solution is lost; i.e., the network is destroyed. This transition froma semidilute solution to a dilute one is explained by a decrease in the length of the wormlike micelles and theformation of spherical ones. Cryogenic electron microscopy images have confirmed the formation of a mixture of long and short wormlike micelles with spherical micelles at an OAPA molar fraction of 0.5.