Concept:Dynamic viscosity governs the fluid mobility and spreading kinetics of a liquid adhesive across microscopic substrate asperities during the wetting phase.
Formula / Reaction:$$\text{Spreading Coefficient: } S = \gamma_{S} - (\gamma_{L} + \gamma_{SL})$$
Solution:- While thermodynamic surface energies dictate spreading equilibrium (\(S > 0\)), dynamic viscosity controls the kinetic rate of liquid spreading and gap penetration.
Why other options are incorrect:- Cohesive shear modulus: Measures the mechanical stiffness of the cured solid adhesive.
- Yield tensile strength: A mechanical property of the solid state indicating resistance to plastic deformation.
- Glass transition temperature (\(T_g\)): The temperature at which a polymer transitions between glassy and rubbery states.
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