About

Michael Fayer is the David Mulvane Ehrsam and Edward Curtis Franklin Professor of Chemistry at Stanford University. He earned his Ph.D. in Chemistry from the University of California at Berkeley in 1974 and his B.S. from the same institution in 1969. His research group studies complex molecular systems using ultrafast multi-dimensional infrared and non-linear UV/Vis methods. A primary focus of his work is understanding the role of mesoscopic structure on the properties of molecular systems, particularly those with structures on length scales of a few nanometers to tens of nanometers. His research encompasses systems such as nanoscopic water environments, room temperature ionic liquids, functionalized surfaces, liquid crystals, metal-organic frameworks, nanoporous silica, polyelectrolyte fuel cell membranes, vesicles, and micelles, with an emphasis on how molecular-level dynamics and intermolecular interactions influence their properties. Fayer's pioneering development of ultrafast measurement techniques allows for real-time observation of molecular processes, providing insights into the relationship between dynamics, structure, and interactions at the molecular level. His work includes studying water confined at nanoscales, dynamics in biological membranes, and the effects of phase changes on molecular behavior, often in collaboration with theoreticians. His contributions significantly advance the understanding of molecular motions and interactions in complex liquids and materials, with broad implications across chemistry, biology, geology, and materials science.

Research topics

• Chemistry
• Materials science
• Chemical physics
• Molecular physics
• Physics

Selected publications

• Partial Desolvation Causes Lithium Structural Transport in Liquid and Gel Polymer Electrolytes.

  ChemRxiv · 2025-09-24 · 1 citations

  articleSenior author

  A deeper understanding of the structural transport mechanism is critical for optimizing lithium diffusion in gel polymer electrolytes (GPEs). We used two-dimensional infrared (2D IR) spectroscopy and polarization-selective pump-probe to investigate lithium solvation structures and desolvation dynamics across the transition from propylene carbonate (PC)/lithium bis(trifluoromethane)sulfonimide (LiTFSI) liquid to GPE containing 60% poly(propylene carbonate). The Li+-PC coordination number (CNLi-PC) decreases from 4 to 2, with a sharp transition at 30% polymer. Li+-solvent residence times, determined from both 2D IR chemical exchange and spectral diffusion observables, increased from ~500 ps in liquids to ~2 ns in gels. We found that the residence time, a metric commonly used to quantify structural transport, fails to capture ionic conductivity trends; instead, the structural step times, defined as residence times normalized by CNLi-PC, accurately predict ionic conductivity. This finding demonstrates that Li+ structural diffusion is driven by partial desolvation, challenging the traditional picture of “ion hopping”.

  PublisherDOI

• Dynamics of Deep Eutectic Mixtures of Tetraethylammonium Halides/Ethylene Glycol Investigated with Ultrafast Infrared Spectroscopy

  The Journal of Physical Chemistry B · 2025-02-27 · 2 citations

  articleSenior authorCorresponding

  Health and environmental risks posed by volatile organic solvents create an incentive to develop safer, less volatile solvents with the appropriate functionality. Deep eutectic solvents and other low-volatility organic mixtures offer a highly tunable alternative through a mixture composition selection. However, a significant gap exists in understanding the relationship between molecular-level properties and the resulting solvation and transport properties. Using ultrafast infrared (IR) polarization-selective pump–probe (lifetimes and orientational relaxation) spectroscopy, we investigated the dynamics of 1:3 molar mixtures of tetraethylammonium bromide (TEABr) and chloride (TEACl) with ethylene glycol (EG) and of pure EG using the anionic vibrational probe, the CN stretch of SeCN–. The very high salt concentrations are in many respects analogous to water-in-salt solutions, e.g., LiBr and LiCl. These ion/water mixtures can have extremely high ratios of ions to solvating neutral molecules, similar to the 1:3TEABr and 1:3TEACl mixtures studied here. In 1:3TEABr/EG and 1:3TEACl/EG solutions, there are far too few EGs to solvate the ions. Therefore, like water-in-salt, 1:3TEABr/EG and 1:3TEACl/EG solutions will have solvent-separated ion pairs, contact ion pairs, and large ion/EG clusters, forming extended ion/solvent networks. The orientational dynamics experiments on 1:3TEABr/EG and 1:3TEACl/EG show striking similarities to experiments from the literature on 1:4 LiBr and LiCl aqueous solutions, even though the cations and solvents in the deep eutectic mixtures are vastly different.

  PublisherDOI

• From Molecular Dynamics to the Conductivity of Sulfuric Acid: Ultrafast Optical Kerr Effect Experiments and Ab Initio Molecular Dynamics Simulations

  Journal of the American Chemical Society · 2025-07-25 · 4 citations

  articleSenior authorCorresponding

  Extensive use of sulfuric acid in technological applications calls for knowledge of its molecular scale properties. Here, we report a study of aqueous sulfuric acid solutions across a broad concentration range using optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments and ab initio molecular dynamics (AIMD) simulations. The OHD-OKE experiments measured the time derivative of the polarizability–polarizability correlation function (PPCF). By comparison of distinct components of the OKE signal to the excess proton identity correlation functions calculated from AIMD simulations, it was found that the experimental t3 components quantitatively agreed with the proton hopping time from one water to another, which suggested that the origin of t3 was associated with proton hopping. The proton hopping distances within the t3 time scale were used to determine the proton hopping diffusion constants at several concentrations. Using information from the literature and the Nernst–Einstein conductivity equation, it was shown that the vehicular mechanism was insufficient to describe the conductivity. The experimental concentration-dependent conductivities were reproduced by adding the AIMD proton hopping contribution to the conductivity, and proton hopping was shown to be the dominant component of the conductivity. Finally, the experimental concentration-dependent function, C3/t3, where C3 is the amplitude coefficient of the third PPCF component, closely tracked the concentration dependence of the hopping component of the conductivity.

  PublisherDOI

• Quantifying the Partitioning of Vehicular and Structural Lithium Transport in Binary Carbonate Electrolytes

  ACS Energy Letters · 2025-10-31 · 4 citations

  articleSenior authorCorresponding

  Lithium-ion batteries use mixed-solvent electrolytes, but the effect of solvent composition on the mechanism of lithium-ion transport is not well understood. Here, we quantify the partitioning between vehicular and structural Li+ transport mechanisms for binary mixtures of dimethyl carbonate (DMC) and propylene carbonate (PC) using a combination of 2D infrared spectroscopy and pulsed-field gradient NMR. The primary transport mechanism varies monotonically, with 65% vehicular transport in pure DMC and only 35% vehicular transport in pure PC. Li+ structural step lengths of 1.2–1.5 Å were determined from the experimental data. The outcomes of this study are compared to previously described molecular dynamics simulations. The results presented here indicate that typical carbonate electrolytes cannot tailor structural transport and that new solvent chemistries may be required to enhance this diffusion pathway.

  PublisherDOI

• Partial Desolvation Causes Lithium Structural Transport in Liquid and Gel Polymer Electrolytes

  Journal of the American Chemical Society · 2025-12-31 · 1 citations

  articleSenior authorCorresponding

  A molecular-level understanding of ion transport is critical for optimizing lithium diffusion in gel polymer electrolytes (GPEs). Using polarization-selective pump-probe and two-dimensional infrared (2D IR) spectroscopy, we quantified lithium solvation structures and desolvation dynamics across the transition from propylene carbonate (PC)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) liquid electrolytes to GPEs containing up to 60% poly(propylene carbonate) (PPC). Lithium ions remain preferentially coordinated by PC across all compositions, but the Li+-PC coordination number (CNLi-PC) decreases from four to two with increasing polymer, exhibiting a sharp transition near 30% PPC. Li+-solvent residence times, extracted independently from 2D IR chemical exchange and spectral diffusion measurements, slow from ∼500 ps in liquids to ∼2 ns in 60% GPEs. Strikingly, we find that the residence time, a metric commonly used to quantify structural transport, fails to capture ionic conductivity trends when the coordination environment changes; instead, we introduce a new descriptor, the structural step times (τss), which is defined as residence times normalized by CNLi-PC, capturing the total rate of parallel dissociation pathways available to a lithium cluster. τss quantitatively predicts ionic conductivity across both liquid and gel electrolytes, even when salt concentration and polymer fraction are varied independently. These findings show that lithium structural diffusion is initiated by partial desolvation events, not through concerted “hopping” between solvation sites, underscoring the need for caution when invoking ion hopping as the structural transport mechanism in common nonaqueous electrolytes.

  PublisherDOI

• Concentrated aqueous lithium chloride solution dynamics: The role of chemical exchange on anisotropy and vibrational population relaxations

  The Journal of Chemical Physics · 2025-06-04 · 1 citations

  articleSenior author

  Ultrafast polarization-selective pump-probe experiments, conducted on the OD stretch of dilute HOD, are reported for LiCl/H2O solutions ranging from 1-24 to 1-128 (ion pairs-water molecules), 2.3-0.4 m. The results are compared to prior and revised experiments on 1-4 to 1-16 concentrations, 13.9-3.5 m. Vibrational population relaxation and anisotropy decays were measured for hydroxyls hydrogen-bonded to chlorides (HBCs). In contrast to higher salt concentrations, at ≤∼1-32 (1.7 m salt), the HBC population relaxation times and anisotropy decays are concentration independent. 1-32 marks a transition from high concentrations of ion pairs, clusters, and ion networks to concentrations of ion pairs low enough not to affect observable molecular level dynamics. At a concentration of approximately 1-32 and lower salt concentrations, chemical exchange is responsible for HBC anisotropy decay and plays a role in population relaxation. Wavelength-dependent population relaxation was used to obtain lifetime amplitude spectra (LAS), which show distinct species that are not observable with FT-IR. At very high salt concentrations, e.g., 1-6, there are no "pure" water regions, and the LAS has two bands: HBCs and hydroxyls of water oxygens solvating Li+. At lower salt concentrations, there is also a "pure" water band in the LAS. The HBC band shape is concentration independent from 1-4 to 1-128.

  PublisherDOI

• Revealing Lithium Ion Transport Mechanisms and Solvation Structures in Carbonate Electrolytes

  Journal of the American Chemical Society · 2024-12-11 · 25 citations

  articleSenior authorCorresponding

  Optimizing lithium-ion battery (LIB) electrolytes is essential for high-current applications such as electric vehicles, yet experimental techniques to characterize the complex structural dynamics responsible for the lithium transport within these electrolytes are limited. In this study, we used ultrafast infrared spectroscopy to measure chemical exchange, spectral diffusion, and solvation structures across a wide range of lithium concentrations in propylene carbonate-based LiTFSI (lithium bis(trifluoromethanesulfonimide) electrolytes, with the CN stretch of phenyl selenocyanate as the long-lived vibrational probe. Phenyl selenocyanate is shown to be an excellent dynamical surrogate for propylene carbonate in Li+ solvation clusters. A strong correlation between exchange times and ionic conductivity was observed. This correlation and other observations suggest structural diffusion as the primary transport mechanism rather than vehicular diffusion. Additionally, spectral diffusion observables measured by the probe were directly linked to the desolvation dynamics of the Li+ clusters, as supported by density functional theory and molecular dynamics simulations. These findings provide detailed molecular-level insights into LIB electrolytes’ transport dynamics and solvation structures, offering rational design pathways to advanced electrolytes for next-generation LIBs.

  PublisherDOI

• Poly(ether imide) Alumina Nanocomposites: Interphase Properties Determined from Free Volume Element Radius Distributions

  Macromolecules · 2024-06-29

  articleSenior authorCorresponding

  Ultrafast infrared (IR) spectroscopy was used to characterize the free volume element (FVE) radius probability distributions (RPDs) of poly(ether imide) (PEI) alumina nanocomposites. The nanocomposites (0–2 wt %) were prepared with 20 nm diameter spherical Al2O3 nanofillers and a small amount of phenyl selenocyanate (PhSeCN) as IR vibrational probes. Restricted orientation anisotropy method (ROAM), an ultrafast IR technique, was used to measure FVE radii. The results yield RPDs as a function of the nanoparticle concentration. The RPDs were decomposed into bulk PEI and interphase region contributions. The ROAM results demonstrate that the polymer chain packing in PEI nanocomposites is significantly altered from that of pure PEI. The average FVE radius increases with increasing nanofiller content. The RPDs indicate that subensembles with smaller radii are disproportionately affected by the presence of the Al2O3 nanofillers, causing the width of the distribution to narrow. The FVE RPDs for the interface regions reveal a distribution with an average radius ∼0.2 Å larger but significantly narrower than the pure PEI distribution. Finally, the interface volume fraction for each nanocomposite sample was determined from the differences in the RPD curves, and the effective interfacial layer thickness was found to be 19.2 ± 0.5 nm. The results demonstrated that FVE characteristics are strongly affected by the proximity to nanoparticles. The nature of the FVEs in the interfacial regions provides information about the microscopic origin of the polymer nanocomposite material’s properties.

  PublisherDOI

• Pendant Group Functionalization of Cyclic Olefin for High Temperature and High‐Density Energy Storage

  Advanced Materials · 2024-05-20 · 37 citations

  articleOpen access

  High-temperature flexible polymer dielectrics are critical for high density energy storage and conversion. The need to simultaneously possess a high bandgap, dielectric constant and glass transition temperature forms a substantial design challenge for novel dielectric polymers. Here, by varying halogen substituents of an aromatic pendant hanging off a bicyclic mainchain polymer, a class of high-temperature olefins with adjustable thermal stability are obtained, all with uncompromised large bandgaps. Halogens substitution of the pendant groups at para or ortho position of polyoxanorborneneimides (PONB) imparts it with tunable high glass transition from 220 to 245 °C, while with high breakdown strength of 625-800 MV/m. A high energy density of 7.1 J/cc at 200 °C is achieved with p-POClNB, representing the highest energy density reported among homo-polymers. Molecular dynamic simulations and ultrafast infrared spectroscopy are used to probe the free volume element distribution and chain relaxations pertinent to dielectric thermal properties. An increase in free volume element is observed with the change in the pendant group from fluorine to bromine at the para position; however, smaller free volume element is observed for the same pendant when at the ortho position due to steric hindrance. With the dielectric constant and bandgap remaining stable, properly designing the pendant groups of PONB boosts its thermal stability for high density electrification.

  PublisherOA PDFDOI

• Effects of Nanoconfinement on Dynamics in Concentrated Aqueous Magnesium Chloride Solutions

  The Journal of Physical Chemistry B · 2024-05-24

  articleSenior authorCorresponding

  Water behavior in various natural and manufactured settings is influenced by confinement in organic or inorganic frameworks and the presence of solutes. Here, the effects on dynamics from both confinement and the addition of solutes are examined. Specifically, water and ion dynamics in concentrated (2.5–4.2 m) aqueous magnesium chloride solutions confined in mesoporous silica (2.8 nm pore diameter) were investigated using polarization selective pump–probe and 2D infrared spectroscopies. Fitting the rotational and spectral diffusion dynamics measured by the vibrational probe, selenocyanate, with a previously developed two-state model revealed distinct behaviors at the interior of the silica pores (core state) and near the wall of the confining framework (shell state). The shell dynamics are noticeably slower than the bulk, or core, dynamics. The concentration-dependent slowing of the dynamics aligns with behavior in the bulk solutions, but the spectrally separated water-associated and Mg2+-associated forms of the selenocyanate probe exhibit different responses to confinement. The disparity in the complete reorientation times is larger upon confinement, but the spectral diffusion dynamics become more similar near the silica surface. The length scales that characterize the transition from surface-influenced to bulk-like behavior for the salt solutions in the pores are discussed and compared to those of pure water and an organic solvent confined in the same pores. These comparisons offer insights into how confinement modulates the properties of different liquids.

  PublisherDOI

Recent grants

• Investigations of Concentrated Salt and Acid Solutions Using Ultrafast Nonlinear Spectroscopy

  NSF · $650k · 2023–2026

• Dynamics in Complex Molecular Condensed Matter Systems

  NSF · $772k · 2003–2008

• Dynamics of Ions and Molecules in Concentrated Electrolyte and Acid Solutions

  NSF · $700k · 2020–2024

• Dynamics and Structure in Complex Molecular Systems

  NSF · $627k · 2012–2015

• NIH Grant R01GM061137

  NIH · $3.2M · 2013

Frequent coauthors

• Dana D. Dlott

  49 shared

• Ilya J. Finkelstein

  The University of Texas at Austin

  40 shared

• K. D. Rector

  Los Alamos National Laboratory

  40 shared

• Roger F. Loring

  Cornell University

  35 shared

• Andrei Tokmakoff

  University of Chicago

  33 shared

• Kyungwon Kwak

  31 shared

• Jeffrey R. Hill

  Brigham Young University

  31 shared

• Aaron M. Massari

  University of Minnesota

  30 shared

Education

• Ph. D. , Chemistry

  University of California Berkeley

  1974