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CONDENSED PHASE AND INTERFACIAL MOLECULAR SCIENCE
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: 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.
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 interfaces govern chemical reactivity in heterogeneous environments. 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.
Kevin R. Wilson
Phillip L. Geissler
Kranthi K. Mandadapu
Richard J. Saykally
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 the team to tackle systems that are profoundly complex in composition 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.
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.
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.
A branched quadrupole trap used to collide and merge droplets to initiate a bimolecular chemical reaction. Droplet size and composition can be obtained in situ using Raman and fluorescence spectroscopy. Single droplet mass spectrometry (via paper spray ionization) is used to monitor reaction products. Arrays of droplets (100's) can be trapped and ejected one by one to examine long time heterogeneous reactions (e.g. the heterogeneous reaction of citric acid with gas phase OH radicals.
The Effects of Nanoconfinement on Diels-Alder type Reactions.
Prototypical conditions for chemical reactions in hydrophobic and hydrophilic confinement of water using graphene and graphene oxide studies respectively.