Physical Chemistry of Gas-Liquid Interfaces

Jennifer A. Faust, James E. House

• Publisher: Elsevier
• Year: 2018
• Print ISBN: 9780128136416
• eBook ISBN: 9780128136423
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

Physical Chemistry of Gas-Liquid Interfaces, the first volume in the Developments in Physical & Theoretical Chemistry series, addresses the physical chemistry of gas transport and reactions across liquid surfaces. Gas–liquid interfaces are all around us, especially within atmospheric systems such as sea spry aerosols, cloud droplets, and the surface of the ocean. Because the reaction environment at liquid surfaces is completely unlike bulk gas or bulk liquid, chemists must readjust their conceptual framework when entering this field. This book provides the necessary background in thermodynamics and computational and experimental techniques for scientists to obtain a thorough understanding of the physical chemistry of liquid surfaces in complex, real-world environments.- 2019 PROSE Awards - Winner: Category: Chemistry and Physics: Association of American Publishers- Provides an interdisciplinary view of the chemical dynamics of liquid surfaces, making the content of specific use to physical chemists and atmospheric scientists- Features 100 figures and illustrations to underscore key concepts and aid in retention for young scientists in industry and graduate students in the classroom- Helps scientists who are transitioning to this field by offering the appropriate thermodynamic background and surveying the current state of research

Chapter 1

Molecular Perspective of Gas–Liquid Interfaces

What Can Be Learned From Theoretical Simulations?

Tsun-Mei Chang University of Wisconsin – Parkside, Kenosha, WI, United States

Abstract

In this chapter, we present an overview of the recent progress of molecular simulations that provide a molecular-level understanding of the properties and processes at gas–liquid interfaces. We first discuss the choices of force fields and simulation methodologies used in these simulations. Next, the analysis of neat gas–liquid interfaces is addressed. The results of various properties, including surface tension, surface potential, diffusion, reorientational dynamics, molecular structures, and orientation, are summarized. We then move on to the adsorption and mass transport of solutes across gas–liquid interfaces, covering the topics of surface propensity, chemical reactivity, and free energy of transport of solutes. Lastly, the outlook and challenges for the future are briefly discussed.

Keywords

Free energy/potential of mean force; Gas–liquid interfacial properties; Interfacial structures; Ion/solute distribution; Ionic liquid; Mass transport; Molecular modeling and simulation; Surface potential

1. Introduction

The molecular properties and chemical processes at gas–liquid interfaces play an essential role in diverse fields of science and technology. Examples include the uptake and release of trace gas molecules by aerosols and oceans, which are fundamental in environmental and atmospheric chemistry.^1,2 The gas–liquid interface of water can serve as a model system for understanding hydrophobic–hydrophilic interactions. The capture of CO₂ and SO₂ using room temperature ionic liquids involves transport and adsorption at the gas–liquid interface.^3,4 All these processes depend critically on the thermodynamic, structural, and dynamical properties of the particular interface under investigation.

Because of the fundamental importance of gas–liquid interfaces, tremendous efforts have been undertaken to describe the interfaces both theoretically and experimentally. Novel experimental techniques such as nonlinear-optical spectroscopy (second harmonic generation [SHG] and sum frequency generation), X-ray diffraction and reflection, and photoelectron spectroscopy have been developed to investigate liquid surfaces.^5–24 These experiments are capable of probing molecules in the surface region and provide insight into chemical processes at the interfaces. From these studies, structural correlations, molecular orientations, surface roughness, and bonding patterns can be characterized. These techniques have also been successfully applied to understand behavior of solutes at gas–liquid interfaces.

It has been more than half a century since the first computational study by Metropolis et al. in the early 1950s.²⁵ With advances in simulation methodologies and computational resources, molecular simulation approaches, including Monte Carlo (MC) and molecular dynamics (MD) techniques, have become indispensable research tools to study liquid interfaces.^26,27 These methods directly provide microscopic information about solvent and solute molecules at the interface given accurate interaction models. Since the late 1980s, molecular simulations have been widely employed to study properties and processes at various interfaces. From these studies, valuable information on the structures, thermodynamics, dynamics, and molecular orientation of liquid interfaces is obtained.^28–36 The simulation techniques have also been applied to examine equilibrium solvation and mass transport of solutes across interfaces, providing detailed descriptions at atomic resolution. In addition, new computational approaches have been developed to model molecular spectra that directly connect with experimental observation.^37–41 These studies have provided useful insight into processes at gas–liquid interfaces.

In this chapter, we present an introduction to molecular simulations at gas–liquid interfaces. The application of these methods to describe structural, thermodynamic, and dynamical properties as well as solute distributions will be discussed. In Section 2, we briefly describe the computational methodologies that are commonly employed for interfacial simulations. The analysis of various interfacial properties at neat gas–liquid interfaces is presented in Section 3. In Section 4, we discuss the adsorption and mass transport of solutes across gas–liquid interfaces. Finally, the conclusions and outlook will be presented in Section 5.

2. Computational Methodologies

The investigation of simple liquids by computer simulations was started in the 1950s.^25,42–45 In the first computational study, Metropolis and coworkers used MC methods to investigate the equation of state of a two-dimensional hard sphere system.²⁵ Even though the model is crude compared to current standards, useful atomic insight was generated. From then on, the tremendous advances in computational resources and development of potential models and methodologies made computer simulation an indispensable research tool in the investigation of gas–liquid interfaces.

In a sense, molecular simulations can be considered as computational experiments. They can provide very accurate results for problems that are not solvable analytically. In a computer experiment, the first task is to construct an accurate description of the potential energy of the system. A potential energy surface gives such a mathematical/numerical function that relates the system energy (of a sing...

Table of contents

• Cover image
• Title page
• Table of Contents
• Developments in Physical & Theoretical Chemistry
• Copyright
• List of Contributors
• Foreword
• Chapter 1. Molecular Perspective of Gas–Liquid Interfaces: What Can Be Learned From Theoretical Simulations?
• Chapter 2. Molecular Simulations of Volatile Organic Interfaces
• Chapter 3. Fluctuations and Adsorption at Liquid–Vapor Interfaces
• Chapter 4. Ionization of Surfactants at the Air–Water Interface
• Chapter 5. Vibrational Spectroscopy of Gas–Liquid Interfaces
• Chapter 6. X-Ray Excited Electron Spectroscopy to Study Gas–Liquid Interfaces of Atmospheric Relevance
• Chapter 7. Liquid Surface X-Ray Scattering
• Chapter 8. Particle Beam Scattering From the Vacuum–Liquid Interface
• Chapter 9. Microfluidics and Interfacial Chemistry in the Atmosphere
• Chapter 10. Gas–Liquid Interfaces in the Atmosphere: Impacts, Complexity, and Challenges
• Chapter 11. New Particle Formation and Growth: Creating a New Atmospheric Phase Interface
• Chapter 12. Characterization of Individual Aerosol Particles
• Chapter 13. Heterogeneous Reactions in Aerosol
• Chapter 14. Interfacial Photochemistry
• Index