Ion association and selectivity in synthetic surfactant monolayers

• Grant number: 19/27381-0
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)
• Start date: September 04, 2020
• End date: August 19, 2021
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Physical-Chemistry
• Principal Investigator: Hernan Chaimovich Guralnik
• Grantee: Laura Mortara
• Supervisor: Emanuel Schneck
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: Technische Universität Darmstadt (TU Darmstadt), Germany
• Associated to the scholarship: 18/19838-8 - Decisive forces for the structure and stability of aggregates composed by synthetic surfactants: ion association selectivity to interfaces and vesicle formation, BP.DD

Abstract

The aim of my PhD project (FAPESP 2018/19838-8) is to study the specific ion effect on zwitterionic micelles, and the structure of vesicles of cationic surfactants, comparing the structural differences of the molecules with those of vesicles. We have already studied specific ion effects on zwitterionic DPS (N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) micelles and determined micelle properties like aggregation number and critical micelle concentration (cmc). Using molecular dynamics (MD) simulations we showed that the anion adsorption to the DPS interface is correlated to the degree of anion dehydration. These data are already published. We have also studied the thermodynamics of micellization of DPS in the presence of salts where we could identify the specific ion effects. The cationic surfactants with double alkyl tail 1,3-Dihexadecyl-imidazolium chloride (DHImC) and Dihexadecyl-dimethylammonium chloride (DHDAC) form vesicles in water solutions and were characterized using several techniques. N,N-Didodecyl-N-methyl-3-ammonio-1-propane-sulfonate (DDPS) was also explored and characterized. For DDPS we discovered that the specific ion effect determines vesicle formation in water solutions. Monolayers composed of double-tailed surfactants are interesting systems since they can reveal if specific ion effects are sensitive to differences in interfacial arrangements comparing micelles, vesicles and monolayers. In this project, we aim to understand and quantify the ion distribution in a different surfactant arrangement, i.e., monolayers of DDPS with different salts in the aqueous phase using synchrotron-based total-reflection x-ray fluorescence (TRXF) and grazing-incidence x-ray diffraction (GIXD) and will also use these techniques to understand the tail ordering of cationic surfactants DHDAC and DHImC. These data will give further insights of the systems and an offer an opportunity for me to learn new techniques and complementary views on the same system. (AU)