The Invited Speakers

Nature‑Evolved Complex Fluids: Cactus Mucilage as a Sustainable Platform Material

Materials evolved for survival in extreme environments offer a largely untapped design space for complex fluids and soft matter engineering. One such material is the mucilage produced by the prickly pear cactus (Opuntia ficus‑indica), a polysaccharide‑rich hydrogel that enables water retention and resilience in arid climates.

This talk explores cactus mucilage as a naturally occurring complex fluid whose structure–property relationships can be leveraged for engineered water treatment and related applications. We examine how extraction conditions, molecular composition, and solution chemistry govern its colloidal interactions, and functionality as a flocculant and dispersant in aqueous systems.

Through systematic studies spanning natural and industrial water matrices, we evaluate performance using engineering‑relevant metrics such as flocculation kinetics, turbidity removal, and contaminant separation efficiency. Under optimized conditions, cactus‑derived hydrogels demonstrate performance comparable to conventional chemical flocculants across selected regimes, while exhibiting distinct transport and aggregation behaviors characteristic of biodegradable, polymeric complex fluids.

Beyond efficacy, cactus mucilage presents a compelling materials platform from a sustainability and systems perspective. It is non‑toxic, fully biodegradable, biocompatible, and sourced from a drought‑tolerant plant that can be cultivated with minimal inputs—attributes that align performance with environmental responsibility.

Overall, this work illustrates how plant‑derived hydrogels can be rigorously characterized and intentionally engineered, bridging bioinspired soft matter science with practical technologies for water treatment, materials engineering, and emerging biomedical applications.

Nanoparticle-Stabilized Liquid Crystal Droplets:  New Strategies for Optical Detection of Amphiphilic Analytes

Microscale droplets of thermotropic liquid crystals (LC) dispersed in water (i.e., LC-in-water emulsions) provide versatile platforms for the design of droplet-based sensors capable of detecting a wide range of amphiphilic analytes, including surfactants, biosurfactants, and phospholipids, in aqueous environments. However, the broader practical application of LC emulsions has been limited by their poor colloidal stability, as bare (unprotected) LC droplets tend to coalesce over time. In this presentation, we describe our recent efforts to address these limitations through the development of Pickering stabilization strategies using surface-modified nanoparticles adsorbed at LC-water interfaces to prevent droplet coalescence and enhance emulsion stability. Our approach enables the preparation of colloidally stable thermotropic LC emulsions with significantly improved shelf-life, yielding LC droplets that remain stable for periods ranging from at least three months up to one year. Importantly, the nanoparticle-stabilized LC droplets retain their ability to respond to amphiphilic analytes in aqueous solutions by undergoing characteristic LC ordering transitions and “bipolar-to-radial” configurational changes that can be readily observed and quantified in real time using polarized light microscopy. These responses are similar to those observed in bare LC droplets, demonstrating that Pickering stabilization preserves the sensing functionality of the LC emulsions while substantially improving their practical utility. We further demonstrate that the sensitivity and potential selectivity of the stabilized LC droplets can be tuned through the choice of nanoparticle system used to prepare the Pickering LC emulsions. Overall, our results highlight Pickering-stabilized LC emulsions as promising, colloidally stable, and tunable platforms for the development of practical LC droplet-based sensors and biosensors for aqueous analyte detection.

Charge Regulation Effects in Ionizable Colloidal Suspensions.

Charge regulation, driven by acid–base equilibria, strongly influences the electrostatic interactions, aggregation, and structural organization of ionizable colloidal and supramolecular systems. In this work, we investigate the effects of pH and salt concentration on charge dissociation and self-assembly using a hybrid Molecular Dynamics–Monte Carlo simulation framework. The model explicitly accounts for protonation and deprotonation of dissociable groups, allowing us to analyze cooperative charge-regulation effects in charged colloids. Our results show that charge regulation modifies the phase behavior of colloidal suspensions, promoting transitions from ordered to disordered structures and affecting network formation. In addition, preliminary studies on coloidal nanoparticles reveal that electrolyte concentration and intermolecular separation strongly influence the spatial distribution of charge and the effective interactions between neighboring particles. These findings provide insight into the role of pH-responsive electrostatic interactions in soft-matter self-assembly and functional materials design.

TBA