Wetting Dynamics of Liquid Polymers

Promovendus/a: Yichuan Zhang

Promotor(en): Prof. dr. ir. David Seveno, Prof. dr. Joël De Coninck

Our works studied the wetting dynamics of liquid polymers on substrates with flat and fiber geometries, and the results were compared to the hydrodynamic approach (HD) and the molecular-kinetic theory (MKT). First, the spreading dynamics of high-viscosity industrial molten polymers on flat substrates were studied. Both HD and MKT models showed excellent agreements with the experimental data. However, it led to an ambiguity in identifying the dominant channel of energy dissipation (viscous dissipation for HD or frictional dissipation for MKT). These industrial molten polymers are mixtures of short and long polymer chains, and it was hypothesized that the short and long polymer chains play different roles in the spreading process. In order to validate this hypothesis, wetting dynamics of polymer mixtures with different ratios of low-molecular-weight and high-molecular-weight liquids on fiber substrate were then studied. The results suggested that there was a transition region between MKT and HD regimes, and the surface segregation of short molecular chains may happen during the spreading process. Then it aimed to explore the MKT/HD transition interval and experiments were implemented at high temperature, since the viscosities of polymer liquids can be fine-tuned by varying the temperature. The results indicated that the MKT/HD transition was in a very short viscosity interval, in which the fiber roughness played an important role in the identification of the dominant channel of dissipation.