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CONDENSED PHASE AND INTERFACIAL MOLECULAR SCIENCE
Program
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Principal Investigators
Summary
The CPIMS program at LBNL seeks to expand the fundamental science base that underlies current and future problems in energy sciences, which include both energy production and its environmental impacts. The program is not focused on device-level technologies but rather basic science, with the expectation that any new technological advances are enabled by the long term commitment to uncovering the fundamental principles that control transformations at interfaces, in particular those in aqueous systems. The program supports Department of Energy’s Basic Energy Sciences mission: The Condensed Phase and Interfacial Molecular Science Program at LBNL supports the DOE Basic Energy Sciences mission to better assess, mitigate and control the efficiency, utilization, and environmental impacts of energy use by providing the molecular basis for understanding chemical, physical, and electron-driven processes in aqueous media and at interfaces (see Figure 1).Our studies seek breakthroughs in the fundamental understanding of electron and molecular dynamics at interfaces, solvation in electrolyte solutions and at interfaces, and chemical reactions and transformations in systems often far from equilibrium. These projects are unified by a long term vision .
To address this mission need, the LBNL-based CPIMS program is organized into three subtasks:
Subtask 1. Solvation Dynamics in Confined and Heterogeneous Environments
Subtask 2: Chemical Transformations in Aqueous Solutions and Near Interfaces
Subtask 3. Methods for Addressing Strongly Heterogeneous and Far-from-equilibrium Systems
This diagram shows the integrated subtask structure of the program and its reliance on the experimental and computational resources of BES-user facilities.
The above diagram shows how efforts in the individual subtasks are integrated to achieve our overall program goal of understanding how rare events, fluctuations and fluctuations interfaces govern chemical reactivity in heterogeneous environments.
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<td>Figure 1: The long term objective of our work is to expand the
fundamental science base that underlies current and future problems in
energy sciences, which include both energy production and its
environmental impacts. Our three projects (described below) target
three of the many processes that underlie current and future energy
sciences illustrated by a current example: a prototypical
photo-electrochemical cell. Our work relies on unique computational and
experimental resource at Berkeley Lab.</td>
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<td>Figure 2. TPPE spectrum ultrathin films of NaCl
on Ag(100). Top: Spectrum of sample at 125 K.
Bottom: Spectrum of sample at 50 K. n=1,2,
and 3 correspond to the delocalized IPS, B are
electrons trapped at low coordinated sites, and
C is the new electronic state seen at low
temperature.</td>
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Time resolved spectroscopy is used to understand how molecules influence charge dynamics at solid interfaces (see Figure 2) and at catalytic surfaces. Theory elucidates the dynamics of water and other liquids at solid-liquid interfaces, using coarse grained models to treat universal features and molecular dynamics simulations with force fields developed by electronic structure calculations to treat atomistic details. Our research goal is to determine how molecular dynamics couple with charge dynamics at interfaces. A range of transient spectroscopic techniques are employed to follow the transfer of charges leaving the solid side, the rise and decay of intermediate molecular species from the liquid/adsorbate side, and to probe the evolution of purely interfacial electronic states.
Our Solvation project explores the solvation properties of ions and molecules which play critical roles in electrochemical transport, cloud droplet formation, ion pairing, crystallization, protein folding, corrosion, as well as chemical reactions in solutions and at interfaces.
We are investigating the solvation of electrons at metal interfaces, solutes in bulk liquids and at interfaces and within small clusters. Here theory elucidates experiment through both the construction of coarse-grain models of solvation (see Figure 3) in heterogeneous environments and by first principles calculations of electronic structure. We use nonlinear spectroscopy to measure selected ion absorption at aqueous interfaces, and develop generalized theories of solvation in heterogeneous environments using atomistic and coarse grained simulations.
We seek to develop predictive models of both bulk electrolyte behavior and interfacial phenomena that are essential for future advances in energy research. This subtask addresses the development and application of novel spectroscopic (X-ray absorption, VUV photoionization, nonlinear optics and two photon photoemission) probes of electron solvation in ionic liquids at metal interfaces, contact ion pairing, bulk solvation structure of Li+ ions, interfacial solvation of simple solutes, and micro-solvation in clusters. Theory and simulation establish the basic principles that govern liquid water accommodation of molecular solutes. Future directions include the solvation properties of free radicals, size-selected clusters, and the development of a general field theory of solvation.
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<td>Figure 3: Free energy profile of a hydrophobic solute (5Å in diameter)
crossing through the liquid-vapor interface. The influence of capillary
fluctuations is strongly evident from variations of the average solute
density ρ(z) at heights z more than twice the solute diameter away from the average position of the interface (z=0).</td>
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The Reactions and Transformations project addresses multiphase chemistry, bulk phase dissolution, catalytic reactions, self-assembly dynamics, and transformations at interfaces, glasses and in confined water. This work confronts the complexity of bond breaking and making and seeks to clarify the role of solvent fluctuations and rare events in chemical and multi-phase transformations.
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Subtask 1 addresses the fundamental principles of solvation in heterogeneous systems, with an emphasis on examining how and why solutes are driven to or from an interface. This Subtask focuses on the dynamics and structure of the aqueous "environment" itself, whereas Subtask 2 seeks to elucidate how the aqueous or interfacial "environment" in turn controls molecular reactivity, for instance that of solutes and surfactants. Efforts in Subtask 3 develop new experimental and theoretical tools that will be needed in Subtasks 1 and 2 to gain deeper insight into transient intermediates, confinement and self-assembly. To foster this integrated research structure, each Subtask contains both experiment and theory activities, with each PI contributing to efforts in multiple subtasks.
Program Leader
Principal Investigators
Subtask 1: Solvation Dynamics in Confined and Heterogeneous Environments
Musahid Ahmed, Phillip L. Geissler, Kranthi K. Mandadapu, and Richard J. Saykally
The proposed work in this subtask focuses on elucidating the fundamental principles that control the dynamics of solutes at interfaces. This is accomplished both theoretically and experimentally by a systematic strategy of changing the nature of the interface (solid/solid vs. solid/liquid, liquid/vapor vs. organic monolayer) to better reveal how key structural motifs and solvent environment drive interfacial solvation. Ongoing and past work on the "prototypical" liquid-vapor interface provides the conceptual basis for the proposed studies of solute accommodation in more complex environments of solid-solid grain boundaries, liquid-membrane surfaces and photoelectrochemical interfaces. The long term objective of this Subtask is to fully characterize the molecular forces that drive simple solutes to and from the interface in an effort to lay a robust predictive framework for understanding how the presence of interfaces alter chemical reactions addressed in Subtask 2.
Subtask 2: Chemical Transformations in Aqueous Solutions and Near Interfaces
Musahid Ahmed, Hendrik Bluhm, Teresa Head-Gordon, Richard J. Saykally, and Kevin R. Wilson
The proposed work in this Subtask seeks to elucidate the principles that control reactivity in liquids and in heterogeneous environments with a focus on systems where interface processes are inextricably connected to the overall dynamics. Model systems help to elucidate how reactivity evolves over a broad range of confining length-scales, from nano-confinement that alters solvent properties and dynamics to diffusive and mesoscale confinement in droplets that can alter overall reaction rates and mechanisms. These model systems include hydrophobic monolayers needed to address how surface orientation and interfacial packing impact reactivity. Unique sample environments (liquid jets and droplets) are used to access short lived intermediates and interfacial reactions. This Subtask proposes a specific case study of Diels Alder type reactions under confinement and at an interfaces, using a combined experimental and theoretical approach. Efforts in this Subtask leverage the fundamental insights into interfacial solvation gained in Subtask 1.
Subtask 3: Methods for Addressing Strongly Heterogeneous and Far-from-equilibrium Systems
Phillip L. Geissler, Teresa Head-Gordon, Kranthi K. Mandadapu, and Kevin R. Wilson
This Subtask comprises efforts to establish the chemical methods and insight that will enable
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the team to tackle systems that are profoundly complex in composition
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<td>Figure 4 (A) NanoDESI on microfluidic reactors, (B) Droplet reactor</td>
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Work in all of these projects requires the continual development of new experimental and theoretical tools. A key feature and challenge in describing any complex system is the presence of multiple time and length scales that together ultimately govern average chemical transformations. We are developing microfluidic devices (see Figure 4) to study transient intermediates produced in chemical reactions using X-ray spectroscopy, and are making new measurements of VUV and X-ray spectra of size-selected clusters. Microsolvation in clusters not only enables stringent tests of quantum chemistry but is often used as a simplified model of bulk liquids such as water or methanol.
and heterogeneous. This includes the development of new theoretical approaches for understanding the non-equilibrium dynamics in confined aqueous systems, the transport properties and phase behavior of glasses and the self-assembly of amphiphilic structures. New theoretical and experimental efforts will also focus on the detection of transient intermediates. It is our long-term objective to develop new approaches to more seamlessly connect dynamics that cross disparate scales in order to better understand emergent phenomena. Efforts in this Subtask are designed to develop new methods, which when mature will deepen insight into the science themes covered in Subtasks 1 and 2.
Selected Projects:
Solvation at Hard and Soft Interfaces.
Solvation of a model ion at the interface between liquid water and graphene. (A) Snapshot from a molecular dynamics simulation, with the air/water (upper) and graphene/water (lower) interfaces rendered as smooth surfaces identified from a coarse-graining of the microscopic density field. Note the substantial suppression of capillary fluctuations at the lower interface. (B) Profiles of key thermodynamic quantities as functions of the solute’s distance z relative from the graphene sheet, computed by umbrella sampling. Features at small and large z highlight differences in solvation at the two interfaces. The entropy profile is nearly constant at small z (aside from a drop at the leftmost point, where the solute begins to clash sterically with the graphene sheet), consistent with a reduced significance of interfacial shape fluctuations.
Self-assembly of Solutes.
The "orderphobic" effect: Simulations of assembly of solutes in lipid bilayer interfaces. Pre-transition effects mediated by the order-disorder phase transitions induce forces of interaction between solutes in membrane systems. The solutes nucleate order-disorder interfaces, which lead to assembly of the solutes to reduce the net interfacial energy (left to right).
A New Platform for Multimodal Investigations of Chemical Transformations at Liquid/Vapor Interfaces.
Combined core level and vibrational spectroscopy on surfactants in a Langmuir trough enable the elucidation of the influence of molecule packing, solution chemistry, concentration and pH as well as trace gas concentration on the heterogeneous chemistry of the interface.
Microscale Confinement and Reaction-diffusive Lengths.
