[Paper Review] Drop Impact Dynamics of Complex Fluids: A Review

Phalguni Shah, Michelle Driscoll|arXiv (Cornell University)|Dec 18, 2020

Fluid Dynamics and Heat Transfer77 references4 citations

TL;DR

This review synthesizes recent advances in the drop impact dynamics of complex fluids—specifically polymeric fluids and particulate suspensions—highlighting how non-Newtonian rheology alters impact outcomes such as delayed spreading, solidification, and bouncing. It emphasizes the synergy between high-speed imaging, local stress measurements, and constitutive modeling to bridge bulk rheology and localized flow behavior under extreme shear rates.

ABSTRACT

The impact of fluid drops on solid substrates has widespread interest in many industrial coating and spraying applications, such as ink-jet printing and agricultural pesticide sprays. Many of the fluids used in these applications are non-Newtonian, that is they contain particulate or polymeric additives that strongly modify their flow behaviour. While a large body of experimental and theoretical work has been done to understand the impact dynamics of Newtonian fluids, we as a community have much progress to make to understand how these dynamics are modified when the impact fluid has non-Newtonian rheology. In this review, we outline recent experimental, theoretical, and computational advances in the study of impact dynamics of complex fluids on solid surfaces. Here, we provide an overview of this field that is geared towards a multidisciplinary audience. Our discussion is segmented by two principal material constitutions: polymeric fluids and particulate suspensions. Throughout, we highlight promising future directions, as well as ongoing experimental and theoretical challenges in the field.

Motivation & Objective

• To synthesize experimental, theoretical, and computational progress in non-Newtonian drop impact dynamics.
• To identify key challenges in understanding localized, high-strain-rate flows in complex fluids beyond bulk rheology.
• To connect impact phenomena to constitutive modeling by highlighting discrepancies and opportunities in current data.
• To explore the role of particle shape and substrate heterogeneity in modifying impact outcomes.
• To advocate for systematic, multi-scale experiments combining high-speed imaging and local stress measurements.

Proposed method

• Systematic review of experimental, theoretical, and computational studies on drop impact of polymeric fluids and particulate suspensions.
• Use of high-speed imaging to capture transient dynamics such as splashing, spreading, and solidification at strain rates up to ~1.67×10³ s⁻¹.
• Integration of particle image velocimetry (PIV) and local stress measurements to resolve spatially and temporally heterogeneous flows.
• Comparison of impact outcomes across varying Weber (We) and Reynolds (Re) numbers to map regime transitions.
• Analysis of contact-line dynamics and shear-thickening behavior in suspensions with anisotropic particles.
• Incorporation of bulk rheological data with free-surface impact data to inform and refine constitutive models.

Experimental results

Research questions

• RQ1 How does non-Newtonian rheology alter the spreading, splashing, and rebound behavior of impacting drops compared to Newtonian fluids?
• RQ2 What role do particle shape and aspect ratio play in modifying impact dynamics, particularly in shear-thickening suspensions?
• RQ3 How do substrate properties such as wettability, roughness, and compliance influence the impact outcomes of complex fluids?
• RQ4 To what extent can localized stress and velocity measurements during impact improve constitutive modeling of complex fluids?
• RQ5 What are the dominant physical mechanisms behind phenomena like delayed spreading and solidification in complex fluid impacts?

Key findings

• Drop impact on complex fluids induces strain rates approaching 1.67×10³ s⁻¹, exceeding the operational limits of many conventional rheometers.
• Non-Newtonian fluids exhibit unique behaviors such as solidification, delayed spreading, and bouncing—phenomena absent in Newtonian drop impact.
• Suspensions with high particle volume fractions (e.g., φ = 49%) can exhibit partial shear jamming upon impact, leading to solid-like responses.
• Elongated particles significantly alter shear-thickening thresholds and ranges, expanding the parameter space for exotic impact outcomes.
• Contact-line dynamics play a critical role in both particulate and polymeric fluid impacts, influencing spreading and rebound behavior.
• Combining high-speed imaging with PIV and local stress measurements enables multi-scale resolution of flow heterogeneity during impact.