Surface force studies of association phenomena at solid-liquid interfaces

Sammanfattning: The main topics of this thesis, association phenomena inbulk and at solid-liquid interfaces in polar and non-polarmedia, were studied by a range of methods. Direct forcemeasurements employing the interferometric surface forceapparatus (SFA) was the chief technique. In addition, atomicforce microscopy (AFM), X-ray photoelectron spectroscopy (XPS),small angle neutron scattering (SANS), dynamic light scattering(DLS), turbidimetric and electrophoretic mobility measurementswere also applied. These techniques give complementaryinformation, and together they can provide a rather detailedpicture of the fairly complex systems studied.The first system studied was designed to explore particleinteractions in non-polar media. It consisted of polar or,alternatively, non-polar surfaces immersed in a non-polarmedium, triolein, in some cases containing additives such asphospholipids, polyglycerol polyricinoleate (PGPR), and traceamounts of water. It was investigated how triolein mediates thesurface interactions and how these interactions are affected bythe presence of additives. Triolein adsorbs onto mica surfacesthus producing a barrier against flocculation of the particles.The additives mentioned interact with the surfaces and witheach other, thus altering the surface interactions. Water, forinstance, being strongly polar, preferentially adsorbs ontomica and disturbs the triolein ordering at the mica surfacescausing the barrier against flocculation to vanish. Owing tocapillary condensation of water, a strong adhesion between thesurfaces is instead developed. On the other hand, it could beshown that in the presence of phospholipids, the effect ofwater was opposite: long-range repulsive forces develop due toweakly adsorbed reversed phospholipid aggregates.The second type of system studied contained cationicpolyelectrolytes and oppositely charged surfactants. Suchsystems occur in numerous technological processes: wastewatertreatment and ore recovery as well as laundry and body care.Polyelectrolytes and surfactants associate in bulk solution,and they also adsorb on surfaces. Thus, the relation betweenthe bulk properties of polyelectrolyte-surfactant mixtures andtheir properties at the solid-liquid interface is of greatscientific and industrial interest. The bulk properties ofpolyelectrolyte-surfactant aggregates were characterised byDLS, SANS, turbidimetry and electrophoretic mobilitymeasurements. It was concluded that to a certain extent theinterfacial properties of polyelectrolyte-surfactant aggregatescan be rationalised by considering their bulk properties.However, it was also shown that the presence of a surfaceaffects the association between polyelectrolytes andsurfactants. The chemical composition of adsorbed aggregates isdifferent from that of aggregates in solution, and, moreover,the structure of surface-bound polyelectrolyte-surfactantaggregates changes slowly with time.Keywords:Triolein, phosphatidiylethanolamine,phospholipid, lecithin, capillary condensation, polyglycerolpolyricinoleate, aggregation, adsorption, surface forces,structural forces, mica, polar surface, non-polar surface,polyelectrolyte, surfactant, sodium dodecyl sulphate,polyelectrolyte-surfactant association, turbidity,electrophoretic mobility, AFM, SANS, DLS, SFA.