Electrorheology of suspensions containing interfacially active constituents

Area of Science:

• Materials Science
• Rheology
• Nanotechnology

Background:

• Electrorheological (ER) fluids exhibit significant changes in viscosity under an applied electric field.
• Current theories attribute ER effects to the dielectric and conductive properties of core/shell particles.

Purpose of the Study:

• To investigate the effect of sulfonated polyhedral oligomeric silsesquioxane (s-POSS) on the electrorheological behavior of sulfonated-polystyrene (s-PS) particle suspensions in PDMS.
• To explore the underlying mechanisms and compare the findings with existing ER fluid theories.

Main Methods:

• Preparation of s-PS/PDMS suspensions with varying concentrations of s-POSS.
• Measurement of electrorheological properties, including yield stress.
• Dielectric relaxation studies to analyze the electrical properties of the suspensions.

Main Results:

• Addition of s-POSS to s-PS/PDMS suspensions increased yield stress by over 200%.
• Yield stress scaled with the square of the applied electric field (τy ∝ E²).
• Dielectric relaxation studies revealed a new relaxation peak in the s-POSS/s-PS/PDMS system, absent in s-POSS/PS/PDMS suspensions, correlating with ER behavior.

Conclusions:

• The addition of s-POSS significantly enhances the electrorheological performance of s-PS/PDMS suspensions.
• The observed phenomena, particularly the new dielectric relaxation peak, suggest that current theories do not fully explain the behavior of these ER fluids.
• Further research is needed to develop more comprehensive models for this class of materials.