Wed November 12th 2014
16:00 – 17:00
ZH286
Seminar Spreading of volatile droplets containing non-ionic polyoxyethylene alkyl ether surfactants: Correlative relationships between spreading parameters and properties of surfactants and surfaces
Victoria Dutschk

Details:

Surface wetting as a physical phenomenon has been known for a long time. It is ability of a liquid to keep contact with a solid surface resulting from intermolecular interactions. In the phase boundary liquid-solid ¬– the three-phase contact (TPC) line – moves relative to an adjacent solid surface, a dynamic contact angle can be observed. The dynamic contact angle as a function of time can significantly differ from the static contact angle. A unified approach to a theoretical description and measurement of dynamic contact angels does not exist.
For many applications, surfactants are introduced into the aqueous phase to increase the rate and uniformity of wetting. Despite their enormous importance, there is a lack of data in the literature about the spreading dynamics of aqueous surfactant solutions. The knowledge of how surfactant adsorption at the surfaces involved affects the spreading mechanism and dynamics is also limited. To explain and predict the behaviour of aqueous surfactant solutions on the solid-liquid interface, information of their dynamic behaviour at the liquid-vapour interface is absolutely necessary.
In these studies, dynamic three-phase contact (TPC) angles of aqueous non-ionic surfactant solutions (CnEOm) were measured in the pre- and micellar concentration ranges on polymer surfaces of different hydrophobicity. A special emphasis was put on possible evaporation effects at ambient humidity that was varied between 40 and 80%.
The interpretation of the experimental data and the observed spreading regimes were analysed in the frame of Blake-Haynes model for the TPC line velocity. The analysis is based on the assumption that the droplet keeps its spherical cap shape during wetting and evaporation processes. According to this assumption, from three geometric parameters measured – the droplet volume V, TPC radius r and TPC angle  only two are independent. Similarly, only two of the observed rate processes – evaporation rate (dV/dt), spreading rate (dr/dt) and contact angle change rate (d/dt) can be independent. The role of relative humidity, surfactant type and concentration as well as substrate surface energy on the spreading velocity dr/dt and the evaporation rate dV/dt is discussed. The interaction between the two processes (spreading and evaporation) is analyzed.
Additionally, some practical examples of industrial applications (personal care products, detergents, specialty chemicals in textile applications, stress corrosion cracking) based on the wetting dynamics of surfactants solutions are illustrated.
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The 10th Complex Motion in Fluids 2020
Max Planck Gesellschaft
MCEC
Twente
Centre for Scientific Computing
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