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Forced versus Spontaneous Spreading of Liquids
A Mohammad Karim1, S H Davis2, H P Kavehpour1
1Department of Mechanical and Aerospace Engineering, Complex Fluids and Interfacial Physics Laboratory, University of California at Los Angeles , Los Angeles, California 90095, United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|September 20, 2016
Summary
This study reveals distinct behaviors for liquid spreading and forced plate motion at gas-liquid interfaces. Hydrodynamic theory and molecular kinetic theory apply to separate systems, offering new experimental guidelines.
Area of Science:
- Fluid dynamics
- Surface science
- Physical chemistry
Background:
- Understanding contact angle dynamics is crucial for predicting fluid behavior at interfaces.
- Existing theories often generalize phenomena without distinguishing between different experimental setups.
Purpose of the Study:
- To investigate and differentiate the macroscopic advancing contact angle behavior in free liquid spreading versus forced plate motion.
- To determine the applicability of hydrodynamic theory (HDT) and molecular kinetic theory (MKT) to these distinct systems.
Main Methods:
- Experimental measurement of macroscopic advancing contact angle (θA) as a function of contact line speed (U).
- Comparison of results from two distinct experimental configurations: free drop spreading and forced plate motion through a gas-liquid interface.
Main Results:
- Significant differences observed in the measured θA versus U curves between the two experimental setups.
- Demonstration that HDT accurately describes one system, while MKT accurately describes the other.
- Identification of a previously unrecognized distinction in the applicability of these theories.
Conclusions:
- The behavior of contact angle with speed is configuration-dependent.
- HDT and MKT are not universally applicable but are specific to either free spreading or forced motion scenarios.
- Provides practical rules of thumb for experimentalists to anticipate theoretical applicability based on their setup.
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