A. Tulpar, "Studies on the Adsorption/Depletion...", Oct.3.07, 14:40

Faculty of Engineering and Natural Sciences
FENS SEMINARS

 “Studies on the Adsorption/Depletion of Surfactants and Polymers to/from Surfaces and Their effects on Colloidal Forces”

Ayşen Tulpar, Department of Chemistry, Koç University

Abstract: This talk will consist of three parts. The first part is on the adsorption of surfactant molecules at the solid-aqueous interface by electrostatic forces. This is a systematic study to see the effect of the magnitude of surface charge density and the distribution of charges on the adsorption of surfactants. We fabricate solid-liquid interfaces with a controlled and fixed density of surface charge. We create these fixed-charge surfaces by adsorption to gold of mixed monolayers (SAMs) of -functionalized thiols from solution before the surface is exposed to the aqueous surfactant, sodium dodecyl sulfate (SDS), solution. The monolayer components are S(CH2)11OH and S(CH2)11N+(CH3)3. The mole fraction of S(CH2)11N+(CH3)3 on the mixed SAM dictates the surface charge density. Surface plasmon resonance and atomic force microscopy are employed to measure the adsorption isotherms and surfactant organization on surfaces, respectively.  

In the second part of the talk, the use of artificial block copolymers of amino acids for controlling surface forces will be discussed.  Block copolymers of a strongly adsorbing anchor block and a non-adsorbing tail block stabilize colloidal particles by forming brushes on surfaces.  In this research, the anchor block used is poly-L-glutamic acid and the tail block is poly-L-proline end-capped with his-patch thioredoxin. We have measured the adsorption of this fusion protein on c-plane alumina surfaces with ellipsometry. The forces between an -alumina particle and a c-plane alumina surface have been determined by atomic force microscopy.

The third part of the talk is on depletion and structuring behavior of charged spherical particles and micelles (i.e., macro-ions) between two similarly charged surfaces.  The structuring behavior of the particles can be deduced from the force profiles between two surfaces, which display an oscillatory character with an amplitude that decays with separation.  In this work, we measure the force between a silica particle and a silica plate in aqueous solutions of macro-ions by atomic force microscopy. The nanoparticles are Ludox silica and the micelles are composed of sodium dodecylsulfate (SDS). 

October 3rd , 2007, 14:40, FENS G035