Speaker Name: Prof. Bhuvnesh Bharti(Louisiana State University)

Date: 08-04-2026 (Wednusday)

Time: 14:30 PM

Venue: LC102

Abstract: Understanding solid-liquid interfaces is central to problems ranging from nanoparticle assembly and catalysis to the environmental behavior of emerging pollutants. However, most classical models treat interfacial forces and surface properties as stable and time-invariant. In reality, interfaces are dynamic: surface charges fluctuate, ions continuously bind and unbind, and environmental exposure alters surface chemistry over time. These fast and spontaneous processes can strongly influence reactivity, collective interactions, and phase transformations. In this talk, I will first discuss how transient charge and counterion fluctuations at nanoscale solid–liquid interfaces generate interaction mechanisms beyond traditional charge regulation and screening models. Using silica nanoparticles with well-defined surface chemistries and sizes ranging from 20 to 40 nm, we uncover the mechanistic origins of fluctuation-driven forces and show how they impact nanoparticle stability, emergent assembly, and interfacial reactivity. I will then extend these ideas to atmospheric microplastics, whose surfaces also evolve dynamically through environmental weathering. Microplastics are increasingly detected at altitudes relevant to mixed-phase cloud formation, yet their role in atmospheric microphysics remains poorly understood. Through droplet freezing assays and ice nucleation experiments, we demonstrate that model polyethylene microplastics can induce heterogeneous ice nucleation under atmospherically relevant conditions, and that sunlight-driven surface aging alters surface-bound water structure and ice nucleation activity. Across multiple polymer chemistries, we show that interfacial composition and evolution dictate the ice nucleation potential of microplastics. Together, these results highlight dynamic interfacial transformations as a unifying principle governing both nanoscale forces and the environmental impacts of microplastic pollutants.