About

Rosa M. Espinosa Marzal is an Ivan Racheff Professor in the Department of Materials Science and Engineering at the University of Illinois Urbana-Champaign. Her research focuses on interfacial chemistry, colloidal interactions, ionic liquids, hydrogels, and their applications in health, medicine, and energy. She has contributed to understanding the electrical double layer, tribological behavior of ionic liquids, and the mineralization processes in hydrogels, among other topics. Her work involves exploring the fundamental mechanisms at interfaces and interfaces' influence on material properties, with a particular emphasis on biomedical and energy-related applications.

Research topics

• Chemistry
• Chemical physics
• Physics
• Physical chemistry
• Nanotechnology
• Materials science
• Mechanics
• Mechanical engineering
• Composite material
• Computational chemistry
• Inorganic chemistry
• Polymer chemistry
• Engineering

Selected publications

• Thermodynamic effects of solid electrolyte interphase formation from solvation and ionic association in water-in-salt electrolytes

  Open MIND · 2026-02-27

  preprint

  Water-in-Salt-Electrolytes (WiSEs) are a promising class of next-generation electrolytes. Unlike classical dilute electrolytes or more conventional battery electrolytes, WiSEs are characterised by their super-concentrated salt concentration with only a small amount of water, which gives rise to their expanded electrochemical stability window (ESW). The expansion of the ESW is, in part, due to the formation of an inorganic solid electrolyte interphase (SEI) that passivates the anode; this principle is also important in graphite and Li-metal anodes, and beyond Li-ion technologies. The solvation and ionic associations are key descriptors in understanding the expansion of the ESW. Specifically, as reactions which lead to the SEI (or cathode electrolyte interphase, CEI) must occur at the electrode-electrolyte interface, the distribution of reactants and their various solvation environments are critical. This distribution near the interface is referred to as the electrical double layer (EDL), in the absence of reactions. Here we further develop and analyse a recently proposed thermodynamic theory of hydration and ionic associations in the EDL of WiSEs. We parameterize this theory from bulk molecular dynamics simulations and benchmark it against EDL simulations, finding good qualitative agreement. Using this thermodynamic theory, we rationalise changes in the ESW through: changes in the activity in the bulk electrolyte through the Nernst equation, which directly changes the stability of the electrolytes; and thermodynamic changes to the kinetics of these reactions, from the Butler-Volmer equation and coupled ion electron transfer kinetics, through the concentration of reactant species in the Helmholtz layer.

  DOI

• Multi-scale Study of the Lubricious Behaviour of Two Imidazolium-Based Ionic Liquids, [BMIM][PF6] and [BMIM][TFSI]

  Tribology Letters · 2026-03-06

  article
  PublisherDOI

• Lipid self-assembly dependence on hyaluronic acid size reveals biolubrication and osteoarthritic degeneration mechanisms

  Science Advances · 2026-01-14 · 2 citations

  articleOpen accessSenior authorCorresponding

  Hyaluronic acid (HA) and phospholipids (PLs) are key components of joint lubrication. In osteoarthritis (OA), the molecular weight (MW) of HA is reduced, which has been proposed to weaken the anchoring capacity of PL and impair lubrication. This study reveals a different mechanism by directly linking the MW to the structure of HA-PL (hybrid) assemblies and frictional properties. Using mixed-MW HA and PL to model this difference between healthy and OA synovial composition, we found interfacial lamellar structures form under healthy-like conditions, while hybrid vesicles predominate in OA-like conditions. At physiologically relevant shear rates, lamellar assemblies maintain ultralow friction, whereas vesicles are removed, causing a tenfold friction increase. These findings provide mechanistic insight into how HA-PL structural organization controls lubrication. While this simplified system does not capture the biochemical complexity of synovial fluid, this study advances understanding and offers a framework for designing structure-informed therapeutic strategies and biomimetic lubricants.

  PublisherDOI

• Thermodynamic effects of solid electrolyte interphase formation from solvation and ionic association in water-in-salt electrolytes

  ArXiv.org · 2026-02-27

  articleOpen access

  Water-in-Salt-Electrolytes (WiSEs) are a promising class of next-generation electrolytes. Unlike classical dilute electrolytes or more conventional battery electrolytes, WiSEs are characterised by their super-concentrated salt concentration with only a small amount of water, which gives rise to their expanded electrochemical stability window (ESW). The expansion of the ESW is, in part, due to the formation of an inorganic solid electrolyte interphase (SEI) that passivates the anode; this principle is also important in graphite and Li-metal anodes, and beyond Li-ion technologies. The solvation and ionic associations are key descriptors in understanding the expansion of the ESW. Specifically, as reactions which lead to the SEI (or cathode electrolyte interphase, CEI) must occur at the electrode-electrolyte interface, the distribution of reactants and their various solvation environments are critical. This distribution near the interface is referred to as the electrical double layer (EDL), in the absence of reactions. Here we further develop and analyse a recently proposed thermodynamic theory of hydration and ionic associations in the EDL of WiSEs. We parameterize this theory from bulk molecular dynamics simulations and benchmark it against EDL simulations, finding good qualitative agreement. Using this thermodynamic theory, we rationalise changes in the ESW through: changes in the activity in the bulk electrolyte through the Nernst equation, which directly changes the stability of the electrolytes; and thermodynamic changes to the kinetics of these reactions, from the Butler-Volmer equation and coupled ion electron transfer kinetics, through the concentration of reactant species in the Helmholtz layer.

  PublisherOA PDF

• Linking structural and rheological memory in disordered soft materials

  Soft Matter · 2025-01-01 · 6 citations

  articleOpen access

  a generalized memory function using rheo-X-ray photon correlation spectroscopy (rheo-XPCS). Our rheo-XPCS data show that the nanometer scale aggregate-level structure recorrelates whenever the change in recoverable strain over some interval is zero. The macroscopic recoverable strain is therefore a measure of the nano-scale structural memory. We further show that yielding in disordered colloidal materials is strongly heterogeneous and that memories of prior deformation can exist even after the material has been subjected to flow.

  PublisherOA PDFDOI

• Ionic Associations and Hydration in the Electrical Double Layer of Water-in-Salt Electrolytes

  ECS Meeting Abstracts · 2025-07-11

  article

  Water-in-Salt-Electrolytes (WiSEs) are an exciting class of concentrated electrolytes finding applications in energy storage devices because of their expanded electrochemical stability window, good conductivity and cation transference number, and fire-extinguishing properties. These distinct properties are thought to originate from the presence of an anion-dominated ionic network and interpenetrating water channels for cation transport, which indicates that associations in WiSEs are crucial to understanding their properties. Currently, associations have mainly been investigated in the bulk, while little attention has been given to the electrolyte structure near electrified interfaces. Here, we develop a theory for the electrical double layer (EDL) of WiSEs, where we consistently account for the thermoreversible associations of species into Cayley tree aggregates. The theory predicts an asymmetric structure of the EDL. At negative voltages, hydrated Li + dominate and cluster aggregation is initially slightly enhanced before disintegration at larger voltages. At positive voltages when compared to the bulk, clusters are strictly diminished. Performing atomistic molecular dynamics (MD) simulations of the EDL of WiSE provides EDL data for validation and bulk data for parameterization of our theory. Validating the predictions of our theory against MD showed good qualitative agreement. Furthermore, we performed electrochemical impendence measurements to determine the differential capacitance of the studied LiTFSI WiSE and also found reasonable agreement with our theory. Overall, the developed approach can be used to investigate ionic aggregation and solvation effects in the EDL, which amongst other properties, can be used to understand the pre-cursers for solid-electrolyte interphase formation. Figure 1

  PublisherDOI

• Pioneers in Applied and Fundamental Interfacial Chemistry (PAFIC): Nicholas D. Spencer

  Langmuir · 2025-02-25

  editorialOpen access
  PublisherOA PDFDOI

• Electrochemical and Interfacial Insights into Sodium Salt-in-Ionic Liquid Electrolytes

  ECS Meeting Abstracts · 2025-11-24

  articleSenior author

  Given the urgent need to improve energy resilience, our interest in exploring alternative electrolyte chemistries is driven by the limitations of lithium resources and the safety risks associated with organic electrolytes. Sodium-ion batteries, paired with ionic liquid (IL) electrolytes, offer a promising solution due to the abundance of sodium and inherent safety advantages of ILs. ILs—molten salts at room temperature—exhibit exceptional properties such as high electrochemical stability, non-volatility, and non-flammability. However, key aspects of IL-based electrolytes, including the structure of the electrical double layer (EDL), electrochemical behavior, and solid electrolyte interphase (SEI) formation, remain poorly understood. This study investigates the electrochemical and interfacial properties of a salt-in-ionic liquid (SIL) electrolyte, where sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) is dissolved in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]). We employ a multi-technique approach to gain comprehensive insights into the fundamental behavior of this SIL at the interface with a gold surface as the working electrode. Cyclic voltammetry is utilized to determine the electrochemical stability window (ESW), with both anodic and cathodic scans revealing the influence of initial SEI formation on ESW. Electrochemical impedance spectroscopy is used to characterize electrochemical properties of the SEI. To probe interfacial structures at the molecular level, atomic force microscopy (AFM) is employed to study EDL layering and SEI formation in situ, while surface-enhanced infrared absorption spectroscopy (SEIRAS) is used to analyze the enrichment of specific species near the electrode. Furthermore, electrochemical quartz crystal microbalance (EQCM) measurements track mass changes on the electrode, shedding light on SEI formation kinetics. By integrating these techniques, this work advances the understanding of EDL structure and SEI evolution in IL-based electrolytes at the nanoscale, contributing to the design of next-generation batteries beyond lithium-based chemistries.

  PublisherDOI

• Shear Thinning and Stress-Dependent Viscosity Activation Volumes: Combining Eyring and Carreau

  Tribology Letters · 2025-07-23 · 1 citations

  articleOpen access

  Abstract The viscosity of fluids and their dependence on shear rate, known as shear thinning, plays a critical role in applications ranging from lubricants and coatings to biomedical and food-processing industries. Traditional models such as the Carreau and Eyring theories offer competing explanations for shear-thinning behavior. The Carreau model attributes viscosity reduction to molecular distortions, while the Eyring model describes shear thinning as a stress-induced transition over an activation energy barrier. This work proposes an extended-Eyring model that incorporates stress-dependent activation volumes, bridging key aspects of both theories. In modifying transition-state theory by using an Evans-Polanyi perturbation analysis, we derive a generalized viscosity equation that accounts for the molecular-scale rearrangements governing fluid flow. The model is validated against computational and experimental data, including shear-thinning behavior of pure squalane and polyethylene oxide (PEO) aqueous solutions. Comparative analysis with Carreau-Yasuda and conventional Eyring models demonstrates excellent accuracy in predicting viscosity trends over a wide range of shear rates. The introduction of stress-dependent activation volumes provides a description of molecular exchange kinetics accounting for structural reorganization under shear. These findings offer a unified framework for modeling shear thinning and have broad implications for designing advanced lubricants, polymer solutions, and complex fluids with tailored flow properties. Graphical Abstract

  PublisherOA PDFDOI

• Ionic Control of Microstructure and Lubrication in Charged, Physically Cross‐Linked Hydrogels

  Advanced Functional Materials · 2025-09-23 · 2 citations

  articleOpen accessSenior authorCorresponding

  Abstract Charged, physically cross‐linked hydrogels provide a versatile platform for designing responsive materials with programmable interfacial properties, with applications in drug delivery, biomedical devices, and biosensing. Here, poly(methacrylamide‐co‐methacrylic acid) hydrogels stabilized by a short‐range attractive, long‐range repulsive potential is investigated. By integrating microstructural, mechanical, and tribological characterization across multiple length and time scales, this work uncovers how salt addition alters not only swelling, but also the microstructure and dynamics, near‐surface stiffness and charge, and ultimately, its lubricity. Friction measurements reveal a velocity‐dependent response with distinct mixed, transition, and elastohydrodynamic regimes. Microscopic friction imaging reveals that adhesive interactions are promoted by salt and play a critical role. Unlike neutral hydrogels, where increased water content correlates with reduced friction, salts introduce additional dissipation mechanisms that can dominate over hydration effects, offering enhanced control of functional behavior. These findings provide new insights into the salt‐induced responsive behavior of poly(methacrylamide‐co‐methacrylic acid) hydrogels‐including lubrication mechanisms‐and challenges conventional interpretations of salt effects in polyelectrolyte systems. This knowledge will inform design principles for synthetic hydrogel interfaces and advance understanding of the functional behavior of hydrogel‐like materials such as biological tissues, whose lubricity‐in salinity conditions similar to those studied here‐is essential to their function.

  PublisherOA PDFDOI

Frequent coauthors

• Mark W. Rutland

  RISE Research Institutes of Sweden

  70 shared

• Tooba Shoaib

  Riphah International University

  65 shared

• Nicholas D. Spencer

  ETH Zurich

  49 shared

• Kangdi Sun

  UNSW Sydney

  49 shared

• Changwoo Do

  Oak Ridge National Laboratory

  49 shared

• Joesph Beller

  University of Tennessee at Knoxville

  42 shared

• Antonella Rossi

  University of Cagliari

  34 shared

• Manfred Heuberger

  Swiss Federal Laboratories for Materials Science and Technology

  30 shared

Labs

• Espinosa-Marzal LabPI