36th International Conference on Science and Technology of Complex Fluids

The Invited Speakers

Whitney Loo

Investigating the Thermodynamics of Single Ion Conducting Polymer Blend Electrolytes Using X-ray and Neutron Scattering

The ongoing development of rechargeable batteries with increased energy density is critical to continue the growth in the electrification of mobile technologies. To achieve these goals, new electrolytes must be developed that possess fast ion transport characterized by high ionic conductivity and high cation transference number (the fraction of ions that carry current), a combination of properties typically not found in a single material. Therefore, we propose to engineer polymer blend electrolytes as suitable electrolyte replacements. In this presentation, we will study blends of ion-containing polymer and ion-conducting polymers and determine how blend composition and polymer molecular weight affects thermodynamics. Through a combined approach leveraging X-ray and neutron scattering, we are able to resolve the nanostructure across a wide range of length-scales ranging from monomer sub-units to inter-chain interactions. By quantitatively fitting the scattering profiles, we can extract thermodynamics parameters and relevant length-scales and show how local charge correlations affect nanoscopic structure. We show that our results qualitatively agree with previously developed theory for similar systems and conclude by suggesting how molecular engineering of these blends can enable precise tuning of the strength of charge correlations and the concentration of charged species to further probe blend thermodynamics.

J. CARLOS RUIZ SUÁREZ

Colloidal Ice Formation in Isochoric Conditions

Water is difficult to freeze. It requires very special help: either very cold water (228 K), or a particle or surface on which ice nucleation can begin at around 273 K. This is the state of affairs. However, by performing dynamic light scattering (DLS), from ambient conditions (room temperature and 1 atm) to the triple point at 250 K and 2100 atm, we discovered an intriguing phenomenon: the formation of colloidal ice at 265 K that diffuse as Brownian particles. Our discovery is in contradiction with the phenomenon mentioned above: the homogeneous nucleation of supercooled water at 228 K. Furthermore, the formation of such colloids produces the compression of the liquid and, consequently (due to the high pressures reached), ice III.

REZA FOUDAZI

Towards Universality in Rheology of Nanoemulsions with Repulsive and Attractive Interdroplet Interactions

The rheology of concentrated nanoemulsions is critical for their formulation in various applications, such as pharmaceuticals, foods, cosmetics, and templating advanced materials. The rheological properties of nanoemulsions depend on interdroplet interactions, Laplace pressure, dispersed phase volume fraction, and continuous phase properties. The interdroplet forces can be tuned by background electrolytes (i.e., charge screening), surfactant type, the excess surfactant micelle concentration, and depletant molecules such as polymer chains. Therefore, one can study nanoemulsions with the same droplet size and volume fraction but in gel, attractive glass, and repulsive glass states. In this research, we investigate model concentrated nanoemulsions which are stabilized by sodium dodecyl sulfate (SDS). To prepare samples in different states, semi-dilute nanoemulsions are prepared, after which evaporating the continuous phase at room temperature leads to concentrated nanoemulsions up to 60% volume fraction. To obtain concentrated nanoemulsions in repulsive glass, attractive glass, and gel states, surfactant concentration is tuned to induce different depletion attractions. Utilizing the existing predictive models for (nano)emulsion rheology reveals a more satisfactory prediction for repulsive systems than systems with attractive interactions. In addition, a master curve is constructed for storage and loss moduli of nanoemulsions with different interdroplet interactions.

ROBERTA ANGELINI

Phase Behaviour of Soft Microgels: A Rheological Perspective

Microgels, a notable class of soft colloids, are composed of particles formed by crosslinked polymer networks. They have attracted significant attention due to their unique properties including deformability, elasticity, and potential interpenetrability [1,2]. Additionally, their responsiveness to environmental stimuli makes them attractive for a wide range of applications. The phase behaviour of microgels has attracted great attention thanks to the large variety of new phenomenology emerging from their ability to pack at very high volume fractions.

In this study, aqueous suspensions of microgels based on the thermosensitive polymer poly(N-isopropylacrylamide) (PNIPAM) were synthesized and systematically investigated. Changes in key parameters such as temperature, pH, crosslinker content and presence of a second network affect the softness of microgel particles, thereby influencing their structural, dynamical, rheological, and thermodynamic properties [3,4]. Starting from their rheological behaviour, we performed an extensive experimental study with the ultimate goal of understanding the complex phase behaviour of these systems.

RYAN TOOMEY

Effect of confinement on the thermal expansion, crystallization, and density of

poly(lactic-co-glycolic acid) copolymer thin film coatings

It is widely recognized that the bulk properties of semicrystalline polymers can differ significantly from their properties in nanoscale or confined geometries. Confinement impacts crystalline form, chain orientation, and crystallization kinetics. Regarding the latter, most report that the overall crystallization rate is reduced by several orders of magnitude due to hindered mobility or irreversible adsorption at the confining substrate, however crystallization kinetics have also been reported to be stratified in the case of asymmetric confinement. In this talk, I will discuss isothermal crystallization in ultrathin films of poly(D,L-lactic-co-glycolic acid) (PLGA) and the relationship between confinement and thermal relaxation, the glass transition, and melting.

SAMANVAYA SRIVASTAVA

Block Polycatechols: Old Horse, New Tricks

In this presentation, we will discuss our progress in creating robust wet adhesives based on triblock polycatechols. Marine organisms such as mussels and sandcastle worms secrete glue proteins that enable robust wet adhesion and curing – properties that are primarily ascribed to the catecholic 3,4-dihydroxy-l-phenylalanine (DOPA) moieties in the glue proteins. Inspired by these marine adhesives, numerous efforts have endeavored to create synthetic polymers with catechol functionality. However, typical catechol-functionalized polymers possess low catechol density, leading to poor adhesive performance. To address these issues, we engineered triblock polycatechol polymers with high catechol content and precise control over the density and placement of catechol groups. Our approach leverages anionic ring-opening polymerization to synthesize precursor block copolymers, which are then functionalized with thiol-containing catechol groups via thiol-alkene click reactions. By tuning the degree of oxidation of the catechol end blocks into quinones and controlling catechol-quinone crosslinking, we demonstrate swift gelation, resulting in robust hydrogels with shear strength exceeding 10kPa. Moreover, the catechol content, which is controlled by the catechol block length, is shown to dictate the hydrogel curing times and shear strengths. When deployed as wet adhesives, we demonstrate the superiority of our strategy by achieving fast curing and exceptional adhesion on diverse surfaces – outperforming commercially available adhesives and far surpassing conventional catechol-based adhesives.

SEPIDEH RAZAVI

Influence of Colloidal Particle Attributes on the Stability and Dynamics of Interfacial Systems

Presence of complex dispersions composed of fluids, ions, surfactant molecules, and colloidal particles is commonplace in problems relevant to materials discovery and manufacturing. Such multicomponent fluidic systems are often confined by interfaces in processes associated with the water-energy nexus as well, for example, in membrane separations and subsurface energy recovery and storage. To make matters more intricate, fluid interfaces are not static and are constantly subject to external disturbances such as imposed stresses, thermal gradients, and changes in composition. Given the environmental and economic impact of the subject matter, advancing our fundamental quantitative understanding of these complex interfacial systems is crucial for predicting and controlling their behavior in relevant high-tech applications. For instance, the binding of colloidal species to fluid interfaces can be harnessed in tuning the stability of bubbles and droplets. While coarsening through coalescence and Ostwald ripening causes interfacial deformations, understanding the role of interfacial rheology in the resulting stability remains an active area of research. In this presentation, I will discuss findings from our group regarding how particle attributes affect the interfacial microstructure and rheology of fluid interfaces, and their subsequent impact on the performance of particle-stabilized (i.e., Pickering) systems.

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