Friction of Polymers: from PDMS Melts to PDMS Elastomers

Area of Science:

• Polymer Physics
• Surface Science
• Rheology

Background:

• Understanding polymer melt slip behavior on surfaces is crucial for predicting flow in microdevices and coatings.
• Previous studies have explored slip phenomena, but the local nature of interfacial friction in polymer melts requires further investigation.

Purpose of the Study:

• To characterize the slip behavior of polydimethylsiloxane (PDMS) polymer melts on weakly adsorbing, grafted PDMS surfaces.
• To determine if the interfacial Navier's friction coefficient is a local quantity and independent of polymer molecular weight.

Main Methods:

• Experimental characterization of polymer melt flow on end-grafted PDMS chains on silica surfaces.
• Measurement of slip lengths at high shear rates.
• Comparison of deduced interfacial shear stresses with friction stress data for cross-linked PDMS elastomers.

Main Results:

• Observed slip lengths proportional to bulk fluid viscosity at high shear rates, consistent with Navier's interfacial equation.
• Demonstrated that the interfacial Navier's friction coefficient is a local quantity, independent of polymer molecular weight.
• Confirmed the local character of the friction coefficient by comparing interfacial shear stresses and relating it to monomer-monomer friction.

Conclusions:

• The slip behavior of PDMS melts on grafted surfaces is governed by a local interfacial friction coefficient.
• This friction coefficient is independent of polymer molecular weight, providing fundamental insights into polymer-surface interactions.
• Findings support the applicability of Navier's interfacial equation for describing polymer melt slip under specific conditions.