(3gr) Molecular Thermodynamics in Confined Space

Background. Advances in nanotechnology and biotechnology enable people to observe and control matters at nanoscale. Unlike bulk, homogeneous systems, systems at nanoscale are subjected to strong boundary effects, inter-molecular correlations, and abnormal fluctuations, etc. Shrinking system size down to nanoscale incapacitate the direct application of traditional thermodynamics models, which are usually developed for macroscopically homogeneous or periodic systems. Therefore, study of thermodynamics at nanoscale calls for molecular level modification of previous theories or direct molecular simulation of nanoscale systems.

As a chemical engineer, I am interested in understanding the rules that underlie the behavior and functions of various materials under nanoscale or microscale confinement using molecular thermodynamics. My overall research goal is to achieve rationale functional material design based on fundamental knowledge of the structure property-function relationship. I use advanced molecular theories and molecular simulations to probe thermodynamic relationships in various systems. Beyond simulation and theory, working closely with experimental collaborators is indispensable for me because it leads to validation, improvement, and application of theoretical results.

Previous research. One of my previous research directions was on transport of small molecules – both charged ions and neutral waters – in nano-spaces, including slit pores, carbon nanotubes, and biological channels such as aquaporin or dipeptide channels. I developed a molecular theory that can accurately predict ionic transport in nanochannels driven by three different forces: pressure drop, concentration gradient, and electric field. This theory proves to be universally applicable to many systems involving ionic transport in nanochannels. Another aspect of my previous research is soft matter assembly, particularly lipid bilayers. I developed a molecular theory that can describe different lipid structures near a charged substrate. This theory is useful for studying how different factors influence the formation and stability of supported lipid bilayers, which is an important platform for many biomimetic techniques such as biosensors and high performance desalination membranes. At Stanford, I shifted my research to polymer electrolytes and biological tissue. I developed a weak segregation theory that predicts the morphology phase diagram of salt-doped block copolymers, incorporating composition fluctuation effects. This not only improved our basic understanding of the system, but also provided a theoretical guide to design block copolymers that can assemble to desired phases. I also identified a new jamming transition (which we termed “chromatic jamming”) in systems with homotypic repulsion, which is pervasive in many biological systems, such as brains with different neuron types. This finding improved our understanding about jamming in biological systems and is useful for understanding neuron organization in the brain. In addition, cooperating with experimentalists, we found how ion solvation influences charge-transfer reactions at electrode surfaces. This will guide the design of next-generation electrolytes.

Future Research. Based on my previous experience, in the future, I will focus on the behavior of polyelectrolytes under confinement in emerging systems, such as polymer based electrolytes, DNA sequencing based on nanopore, and polyelectrolytes brush modified nanochannels. These studies will apply or adapt advanced theory and simulations in novel systems for energy, biological, and environmental applications.

Teaching Interests

Based on my education and research background, I am most suited to teach classes that are fundamental theories in chemical engineering, such as thermodynamics, physical chemistry, statistical mechanics, and transport phenomenon. I can also teach other relevant engineering courses such as molecular simulation, process modelling, optimization algorithms, and scientific computing, etc. I have served as teaching assistant in both undergraduate and graduate courses such as thermodynamics, bio-separation, and chemical product design. The central goal of my teaching is to improve students’ skills of problem-solving so that they can be well prepared for chemical engineering problems in their future careers. I will illustrate fundamental rules with the help of numerical demonstrations, highlighting the historical and engineering contexts. To help students master and strengthen their understanding of knowledges in the class, I will design homework problems that are based on realistic application aspects.

Selected Publications

1. Kong X.^†, et al. Dendrite suppression by a polymer coating: a coarse-grained molecular study. Advanced Functional Materials, 30(15):1910138, 2020
2. Khariton M.^*, Kong X.^*, et al. Chromatic neuronal jamming in a primitive brain. Nature Physics, acceped, 2020, https://doi.org/10.1038/s41567-020-0809-9
3. Jia M., Kong X.^†, et al. Light-powered directional nanofluidic ion transport in kirigami-made asymmetric photonic-ionic devices. Small, 16(1):1905557, 2020
4. Feng Y., ..., Kong X.^†, et al. Geometric structure-guided photo-driven ion current through asymmetric graphene oxide membranes. Journal of Materials Chemistry A, 7(35):20182, 2019
5. Zhang Y., Li F., Kong X.^*, et al. Photo-induced directional proton transport through printed asymmetric graphene oxide superstructures: A new driving mechanism under full-area light illumination. Advanced Functional Materials, 30(4):1907549, 2019
6. Kong X.^†, et al. An atomistic simulation study on poc/pim mixed-matrix membranes for gas separation. The Journal of Physical Chemistry C, 123(24):15113, 2019
7. Yang J.^*, Hu X.^*, Kong X.^*, et al. Photo-induced ultrafast active ion transport through graphene oxide membranes. Nature Communications, 10(1):1171, 2019
8. Yang A.^*, Zhou G.^*, Kong X., et al. Electrochemical generation of liquid and solid sulfur on two-dimensional layered materials with distinct areal capacities. Nature Nanotechnology, 15:231, 2020
9. Wan J.^*, Xie J.^*, Kong X., et al. Ultrathin, flexible, solid polymer composite electrolyte enabled with aligned nanoporous host for lithium batteries. Nature Nanotechnology, 14:705, 2019

(^†indicates corresponding author; ^* indicates equal contributions)