Liquid-liquid interfaces in interaction with colloidal particles : a Brownian motion study

Samenvatting

Interfaces play a dominant role in the behaviour of many complex fluids and an elegant way to study such interfaces is by absorbing particles in the interface. In the light of biomedical applications, simple fluid-fluid interfaces are an useful start to study the more complex biological interfaces in living organisms. By studying the behaviour of the absorbed particles, information on the properties of the interface can be gathered. This is the reason that particle-laden interfaces have attracted much attention in recent years.This thesis shows a theoretical study of two possible analysis methods to calculate a diffusion coefficient as a measure for the mobility of the particles in the interface. Then the mobility of the micrometer scale particles due to Brownian motion in variable conditions is studied experimentally, with the model system of a water-decane interface. By tuning the ionic strength and pH of the water phase of the model system, the importance of electrostatic interactions between the particles and the interface can be studied.The experimentally derived values for the diffusion coefficients in the experiments are compared to the found values in bulk fluid, indicating a certain correction factor due to the presence of a solid surface or interface. Those values are then compared to the available theoretical models and computed interaction energies. At the water-decane interfaces a fraction of the particles will stay above the interface and the rest will be absorbed by the interface, which is dependent on the ionic strength and pH of the aqueous phase. For both situations the diffusion coefficient of the particles is significantly lower than the diffusion coefficient in bulk. The diffusion coefficient of the particles above the interface is independent of the ionic strength and pH, since the particles are extremely close to the interface (nanometer regime). The diffusion coefficient of the particles trapped at the interface are found to increase with increasing ionic strength, which can be explained by an electrodipping force acting on the charged particles deforming the interface and effectively trapping the particles.

Datum prijs	28 feb. 2014
Originele taal	Engels
Begeleider	S. Cappelli (Afstudeerdocent 1) & Arthur M. de Jong (Afstudeerdocent 2)