Data: 03 de dezembro - quinta-feira.
Local: Mini-auditório do IQ
Título: "Complex salts: Controlling love and hate".
Prof. Dr. Lennart Piculell, Lund University, Sweden.
Docente responsável: Watson Loh.
Complex salts: Controlling love and hate
Physical Chemistry, Department of Chemistry, Lund University
Nature offers two strong intermolecular attractions that operate in water: the hydrophobic interaction, and the electrostatic attraction between + and -.
The hydrophobic interaction is the mechanism by which surfactants, lipids and other amphiphilic molecules self-assemble into aggregates of varying shape and size, the details of which depend on both the molecular properties and the environment. Charged amphiphilic molecules build up aggregates of a high total charge in water; the simplest example is a surfactant micelle. Conventional charged micelles are water soluble, but by using charged polymers, polyions, as their counterions, we can use the strong electrostatic attraction to bring the aggregates out of water. They then form concentrated systems that only swell in water, but do not dissolve completely. These surfactant ion-polyion compounds are the complex salts that I will talk about.
Concentrated complex salts in water can form a number of interesting organized, liquid-crystalline structures, where small spherical, long rod-like, or infinite sheet-like surfactant aggregates pack in a regular fashion. For a number of years, our group has studied this self-assembly behavior systematically. Our main questions have been fundamental, but always with an eye on complex salts as interesting soft materials with potential applications:
· How do we control the structures of complex salts in water?
· How do we control their maximum water uptake, or solubility?
· What are the important similarities and differences in behavior between complex salts and conventional ionic surfactants (with monovalent counterions)?
Most recently, we have developed a method to coat surfaces with a thin layer of complex salt. Such a surface layer is robust, and does not dissolve in water. It also takes up water from normal humid air. So, we have here a responsive surface coating that changes its liquid crystalline structure in air when the humidity is changed, and in water when we introduce various solutes in the water. These materials can also take up - or release - other molecules from air or water. We can now use all our accumulated knowledge on complex salts in the design of the structure, and "responsivity", of these surface coatings.
1. Lennart Piculell: Understanding and exploiting the phase behavior of mixtures of oppositely charged polymers and surfactants in water. Langmuir, 2013, 29, 10313−10329.
2. Charlotte Gustavsson, Joaquim Li, Karen J. Edler and Lennart Piculell: Water-responsive internally structured polymer-surfactant films on solid surfaces. Langmuir, 2014, 30, 12525−12531.
3. Charlotte Gustavsson, Marc Obiols-Rabasa, and Lennart Piculell: Water-insoluble surface coatings of polyion-surfactant ion complex salts respond to additives in a surrounding aqueous solution. Langmuir 2015, 31, 6487-6496.