Real-time monitoring the adsorption of sodium dodecyl sulfate on a hydrophobic surface using dual polarization interferometry

• In dilute solution, SDS molecules adsorb at the surface as isotropic layer.
• In higher concentration, SDS aggregate to form hemimicelles and the HMC is 1 mM.
• Competitive formation of micelles and hemimicelles leads to adsorption behaviors.
• The adsorption of SDS at C18 surface obeys two-step process.
• A four-stage adsorption model of SDS at C18 surface was proposed.

The adsorption process of sodium dodecyl sulfate (SDS) at a hydrophobic layer was investigated by dual polarization interferometry (DPI), which provided the real-time information at solid/liquid interface. In dilute solution, the molecules adsorb at the surface as isotropic layer. With the increase in concentration, the molecules aggregate to form hemimicelles and the critical hemimicelles concentration (HMC) is 1 mM. The adsorption of SDS at C18 surface obeys two-step process. The competitive formations of micelles in solution and hemimicelles on C18 surface lead to particular adsorption behavior in higher concentration. We also proposed a four-stage adsorption model of SDS at C18 surface according to bulk concentration.

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