Capillary Suspension Rheology and Stability

Capillary suspensions are defined by a small volume of an immiscible secondary fluid introduced to a particle–fluid suspension, triggering the formation of liquid bridges that interconnect particles into a network. The resulting capillary forces dominate van der Waals or electrostatic interactions, elevating yield stress and imparting solid-like behaviour even at low particle loadings. Two distinct microstructure regimes emerge: the pendular state, in which the secondary fluid preferentially wets individual particles to create isolated bridges, and the capillary state, where clusters of particles surround droplets of the secondary fluid. These networks confer remarkable tunability of rheological properties. By varying the volume fraction and surface chemistry of the secondary fluid, researchers can modulate yield stress across orders of magnitude, control shear-thinning responses and manipulate viscoelastic moduli. Stability of capillary suspensions is governed by the robustness of liquid bridges under shear and ageing. Factors such as contact-angle hysteresis, surface roughness and evaporation of bridging fluid critically influence long-term structure and flow behaviour. The capacity to design suspensions with tailored flow thresholds, minimal sedimentation and reversible restructuring has unlocked applications ranging from printable electronics through lightweight porous composites to health-oriented food formulations. Emerging studies continue to probe the interplay between microstructure and macroscopic flow, seeking routes to dynamically reconfigurable materials and processing strategies that exploit capillary networks under complex deformation.

Research from Nature Portfolio

Recent studies have harnessed the capillary suspension paradigm to revolutionise functional pastes for printed electronics. An innovative formulation achieved high-purity conductive films by introducing minute quantities of a secondary fluid to silver or nickel suspensions. The imposed capillary network granted extreme shear-thinning behaviour suited to fine-line printing, while the secondary fluid fully evaporated during sintering, yielding metal layers with conductivity far exceeding conventional formulations. Other foundational work has elucidated the non-monotonic variation of viscosity and yield stress as a function of secondary fluid dosage. Using confocal microscopy, researchers identified three microstructural states—dispersive, clustered and cellular—that correlate with rheological transitions. This framework has provided predictive control over flow properties by mapping dosing to structure, informing the rational design of capillary-driven networks across material systems.

Capillary Suspension Rheology and Stability publication trend

The graph below shows the total number of articles in capillary suspension rheology and stability across all publications each year (not limited to Nature Index journals).

Technical terms

Capillary suspension: A ternary fluid–fluid–solid system in which small volumes of an immiscible liquid create capillary bridges that form a particle network.
Pendular state: A regime in which the secondary fluid preferentially wets particles, producing discrete bridges between particle pairs.
Capillary state: A regime characterised by clusters of particles surrounding droplets of the secondary fluid, forming a more isotropic network.
Yield stress: The critical stress required to initiate flow in a structured fluid.
Percolating network: A continuous particle framework spanning the suspension, responsible for imparting solidity.
Liquid bridge: A curved meniscus of secondary fluid that connects adjacent particles through capillary forces.
Wettability: The propensity of a liquid to spread on or adhere to a solid surface, quantified by the contact angle.

References

1. Highly conductive, printable pastes from capillary suspensions. Scientific Reports (2016).
2. Multiple Effects of the Second Fluid on Suspension Viscosity. Scientific Reports (2015).
3. How bulk liquid viscosity shapes capillary suspensions. Journal of Colloid and Interface Science (2024).
4. Preparation and yielding behavior of pendular network suspensions. Journal of Rheology (2017).
5. Lightweight Porous Glass Composite Materials Based on Capillary Suspensions. Materials (2019).