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Roughness-dependent tribology effects on discontinuous shear thickening
Chiao-Peng Hsu1,2, Shivaprakash N Ramakrishna2, Michele Zanini1
1Laboratory for Interfaces, Soft Matter and Assembly, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland.
Summary
Surface roughness in colloids significantly advances discontinuous shear thickening (DST) onset. This study links nanoscale surface features to particle friction, revealing a tribology-based method for controlling suspension behavior.
Area of Science:
- Colloid and Surface Science
- Materials Tribology
- Rheology of Soft Matter
Background:
- Surface roughness influences colloid properties like dispersibility and interactions.
- Particle-particle friction is increasingly recognized as a key factor in discontinuous shear thickening (DST) of dense suspensions.
- Experimental data on the tribology of nonspherical particle contacts remain scarce.
Purpose of the Study:
- To systematically investigate the impact of nanoscale surface roughness on the rheological and tribological properties of colloids.
- To establish a direct link between surface roughness, particle-particle friction, and the onset of discontinuous shear thickening.
- To explore the potential of an engineering-tribology approach for tuning suspension behavior.
Main Methods:
- Fabrication of a library of all-silica, raspberry-like colloids with varying degrees of surface roughness.
- Rheological measurements to determine the onset of discontinuous shear thickening (DST) as a function of shear rate and solid loading.
- Lateral Force Microscopy (LFM) to directly measure the tribological properties of particle-particle contacts and identify stick-slip friction.
Main Results:
- Increased surface roughness led to an earlier onset of DST, both in terms of shear rate and solid loading.
- Rougher surfaces were observed to suppress continuous thickening phenomena.
- Lateral Force Microscopy confirmed that DST is driven by stick-slip frictional contacts resulting from the interlocking of surface asperities.
Conclusions:
- Nanoscale surface roughness plays a critical role in controlling the discontinuous shear thickening (DST) behavior of dense colloidal suspensions.
- The interlocking of surface asperities, characterized by stick-slip friction, is the primary mechanism behind DST in these systems.
- An engineering-tribology approach, focusing on surface modifications, offers a promising strategy for tailoring the rheological properties of suspensions.
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