New keynote: “Controlling Nanoparticle Generated in Reactive Flows: Limits of In-Situ Approaches and Emerging Hybrid Strategies”

In the context of the 37th Canadian Materials Science Conference held at Université Laval on May 4-7, 2026, our work has been highlighted through a keynote talk by Dr. José Morán with the title above and the abstract given below.

Abstract

Controlling nanoparticle properties—including morphology, chemical composition, crystallinity, and size—is central to the engineering of functional materials with tailored performance, such as enhanced thermal and electrical conductivity, optical response, mechanical resistance, and sensing capability. Gas-phase reactive flows, including flames and spark-discharge ablation, have emerged as versatile and scalable platforms for nanoparticle synthesis. In these systems, operating conditions such as flow rate, precursor composition, and thermodynamic state are commonly adjusted to influence particle formation. These approaches are compared here in terms of their respective advantages and limitations for nanomaterial production.

Despite significant progress, in-situ control remains fundamentally constrained by the strongly coupled and nonlinear nature of the underlying physicochemical processes. Competing mechanisms—including nucleation, surface growth, coagulation, and transport—evolve on overlapping time and length scales, making it difficult to isolate individual effects and achieve deterministic control. In particular, controlling aggregation and aggregate morphology, such as fractal-like structures, remains highly challenging. We review representative approaches from the literature, critically assess their capabilities and limitations, and propose a revised perspective. Specifically, we argue that in-situ strategies should prioritize robust process-level objectives, such as maximizing nanoparticle yield, and minimizing energy consumption, rather than attempting fine control of detailed particle morphology. As an illustrative case, we present experimental measurements of spark-discharge ablation of copper, demonstrating that appropriate electrical control can simultaneously enhance nanoparticle production rate and process energy efficiency.

In contrast, ex-situ approaches in aerosol processing, such as thermal treatment in tube furnaces, enable improved control over nanoparticle morphology through decoupling of growth mechanisms. For example, residence time at elevated temperature can drive the transition from fractal aggregates to spherical particles. However, these methods are often energy intensive and offer limited control over local structural features such as partial sintering or internal morphology. To address these limitations, we propose a new route based on nanosecond pulsed laser processing of aerosol nanoparticles, enabling localized and time-resolved control of particle properties. This approach introduces micrometer-scale spatial resolution and nanosecond temporal resolution, opening the possibility of selectively modifying nanoparticle size, morphology, and crystallinity in-flight. While related approaches have been explored in liquid-phase systems, such strategies remain largely unexplored for gas-phase nanoparticle synthesis. Preliminary numerical simulations are presented to describe the governing energy and mass transfer processes. The results indicate that laser fluence is a key parameter tuned to achieve two primary control regimes: (i) size reduction via evaporation and (ii) morphology modification through laser-induced sintering. This hybrid strategy suggests a pathway toward decoupled, high-precision control of nanoparticle properties in reactive flow systems.