Research Projects

Pilot-wave hydrodynamics, in which a droplet self-propels by bouncing on the waves it generates over a vertically vibrated fluid bath, provides a striking macroscopic analog to quantum behavior. Such systems exhibit features reminiscent of quantum phenomena—quantized orbits, tunneling, and interference—despite being entirely classical and deterministic. While prior studies have explored pilot waves in clean fluids, real-world interfaces are rarely pristine. The presence of surfactants, which modify surface tension and introduce Marangoni stresses, adds a new layer of complexity to the wave–droplet interaction. The rationale for this project lies in exploring how surfactant-induced interfacial rheology modulates pilot-wave memory, stability, and coherence. This will bridge fluid dynamics, interfacial physics, and analog quantum systems, while enabling new directions in soft matter and microscale transport research. Scientific Objectives: To investigate the role of surfactant concentration and type (ionic/nonionic) on droplet bouncing, walking, and orbiting behaviors in pilot-wave systems. To quantify how surfactants alter the wave field properties (damping rate, wavelength, memory length) and affect the coupling strength between droplet and pilot wave. To identify transitions in droplet motion regimes induced by Marangoni stresses and interfacial elasticity. To develop a coupled droplet–wave–surfactant model incorporating nonlinear dynamics, surfactant transport, and interfacial tension gradients. To experimentally construct regime diagrams of droplet dynamics vs. surfactant concentration, vibration frequency, and bath viscosity. To examine analogs of quantum decoherence and environmental coupling in surfactant-modulated pilot-wave systems. Hypothesis & Model: The central hypothesis is that surfactants modulate the pilot-wave memory and stability through surface tension gradients and interfacial viscosity, resulting in qualitative changes in droplet dynamics. We posit that surfactant concentration introduces new control parameters that can lead to bifurcations between bouncing, walking, and orbiting states, and even to “decoherence” effects in quantum analog behavior. A coupled model incorporating a damped, driven wave equation with surfactant-modulated boundary conditions and Marangoni flow feedback will be developed to predict these dynamics. Main Experiments: Construct a vertical oscillatory bath with controlled frequency and amplitude, integrated with a high-speed camera (≥10,000 fps) and synchronized lighting. Introduce bouncing droplets of fixed volume onto the bath with varying surfactant concentrations (CTAB, SDS, Triton X-100). Measure key outputs: walking velocity, coherence time, step size, orbital radii, and trajectory complexity. Perform visualization of wave fields via synthetic Schlieren or dye-advection methods to assess damping, symmetry, and interference patterns. Develop and validate a droplet–wave–interface model via comparison with experimental data. Significance: This study will pioneer the exploration of pilot-wave dynamics in chemically active (surfactant-laden) environments, a domain unexplored in previous literature. Its outcomes could reshape our understanding of interfacial nonlinear dynamics and provide: A testbed to investigate environment-induced decoherence in analog quantum systems. A framework for non-invasive interfacial rheometry, where droplet motion serves as a diagnostic for surface elasticity and Marangoni effects. Design principles for microscale surface walkers or autonomous droplet transport, relevant for lab-on-chip and targeted delivery systems. Foundational insights into how complex interfaces modulate classical wave–particle interactions, enriching fluid dynamics and soft matter physics. By unifying interfacial science, nonlinear wave dynamics, and analog quantum modeling, the project has the potential to make fundamental contributions to both theory and application.