Simple Method for Rheological Determination of Surfactant Layer Thickness, Adsorbed on Soft Rubber Particles

Area of Science:

• Colloid and Surface Science
• Materials Science
• Rheology

Background:

• Natural rubber latex is a critical industrial material, but its soft, deformable, polydispersed particles present rheological prediction challenges.
• Understanding colloidal stability and particle interactions is crucial for optimizing latex applications.

Purpose of the Study:

• To investigate the rheological properties of natural rubber latex at high particle concentrations.
• To analyze the effect of a specific inulin surfactant (INUTEC NRA) on colloidal stability.
• To determine the thickness of the adsorbed surfactant layer and its influence on rheological behavior.

Main Methods:

• Rheological measurements (viscosity, viscoelasticity) at varying latex volume fractions and surfactant concentrations.
• Development of a semi-empirical method to calculate surfactant adsorbed layer thickness from rheological data.
• Dynamic Light Scattering (DLS) for direct measurement of surfactant layer thickness.

Main Results:

• Relative viscosity sharply increases as latex volume fraction approaches maximum packing.
• A novel semi-empirical method determined an adsorbed surfactant layer thickness of approximately 2.8 nm.
• DLS measurements confirmed the surfactant layer thickness at 3.1 nm.
• Natural rubber latex suspensions exhibit predominantly elastic behavior above 0.63 volume fraction.
• Surfactant concentration was identified as the primary factor controlling latex particle stability and elastic modulus.

Conclusions:

• The study successfully determined the adsorbed surfactant layer thickness on natural rubber latex particles.
• The findings highlight the importance of surfactant choice and concentration in controlling latex rheology and stability.
• The developed semi-empirical method offers a valuable tool for characterizing soft particle suspensions.