Hysteresis and non-uniqueness in the speed of onset of instability in curtain coating

The maximum speed of stable coating is determined experimentally by the onset of air entrainment in curtain coating onto a pre-wetted surface over a broad range of dimensionless parameters (Reynolds number: 0.14 <Re <33.02; capillary number: 0.19 <Ca <25.07). We show not only that the substrate speed at the onset of instability is flow-rate dependent for a pre-wetted surface, but that the speed at which instability Occurs is not always unique for a given flow rate