University of California, Riverside

Wu Group


Research Interests 

Density functional theory for phase-ordering transitions

Colloids display astonishing structural and dynamic properties that can be dramatically altered by modest changes in the solution condition or an external field. This complex behavior stems from a subtle balance of colloidal forces and intriguing mesoscopic and macroscopic phase transitions that are sensitive to the processing conditions and the dispersing environment. Whereas the knowledge on the microscopic structure and phase behavior of colloidal systems at equilibrium is now well-advanced, quantitative predictions of the dynamic properties and the kinetics of phase-ordering transitions in colloids are not always realized. Many important mesoscopic and off-equilibrium colloidal states remain poorly understood. The proposed research aims to develop a new, unifying approach to describe colloidal dynamics and the kinetics of phase-ordering transitions based on accomplishments from previous work for the equilibrium properties of both uniform and inhomogeneous systems and on novel concepts from the state-of-the-art dynamic density functional theory. In addition to theoretical developments, computational research is designed to address a number of fundamental questions on phase-ordering transitions in colloids, in particular those pertinent to a competition of the dynamic pathways leading to various mesoscopic structures, off-equilibrium states, and crystalline phases. By providing a generic theoretical framework to describe equilibrium, metastable as well as non-ergodic phase transitions concurrent with the colloidal self-assembly processes, accomplishments from this work will have major impacts on both fundamental research and technological applications. 

Theory and application of polyelectrolyte complexation

Interaction of polyelectrolytes with oppositely charged substances results in various self-assembled structures commonplace in industrial settings and biology. While there is a large body of experimental work on polyelectrolyte complexes, much lagged behind is a theoretical description of the complex structure and thermophysical properties important for engineering applications or biological functions. The proposed research aims to develop predictive theories that can be used to describe polyelectrolyte complexation from a molecular perspective. The theoretical tools will be applied to examine the role of electrostatics and other non-specific intermolecular interactions in genome packaging and formation of viral capsids.   

The techniques to be employed in this research is built upon recent work in the PI’s group in development and application of classical density functional theory (DFT), which provides a unifying computational tool for describing the microscopic structure and interfacial behavior of complex molecular systems. It has been demonstrated that the DFT captures the local packaging and long-range correlations due to electrostatic interactions and intra-chain structure that are essential for successful description of polyelectrolyte complexes. On the theoretical end, this project will address the effects of molecular topology and solvent-mediated non-electrostatic interactions on complexation of polyelectrolytes with oppositely charged surfaces, macromolecules or surfactants. The theoretical performance will be calibrated with Monte Carlo simulations for simplified models of polyelectrolyte complexes planned in this work and from the literature. In parallel with the theoretical developments, the applied work seeks a quantitative understanding of genome packaging and viral replication in hepatitis B virus. The particular viral system is selected not only for its obvious biomedical implications but also for its well quantified microscopic details already established by microbiologists that make it ideal for a stringent test of emerging molecular modeling techniques. Application of DFT to viral packaging will be in collaboration with experimental groups from the medical schools at the Pennsylvania State University and at the University of Texas. 

Accomplishments from this research will further theoretical descriptions of the structure and thermodynamic properties of complicated polymeric systems from a molecular perspective. The generic techniques will be useful not only for describing the properties of polyelectrolyte complexes per se; they will also have impacts in the broader fields of complex fluids and molecular engineering. In particular, the computational tools developed in this work may have unusual impacts in fundamental research toward understanding the molecular basis of myriad biological processes that entail polyelectrolyte complexation of DNA/RNA chains or unstructured protein domains. Such understanding is essential, for examples, in developing of effective drugs for treatment of virus-induced contagious diseases and in formulation of efficient gene/biopharmaceuticals delivery systems.  

Quantification of genome packaging in HBV nucleocapsids

Hepatitis B virus (HBV) infects more than 2 billion people alive today and is responsible for over 1 million deaths caused by acute and chronic hepatitis and hepatocellular carcinoma every year. Although remarkable progress has been made in understanding the natural history and pathogenesis of HBV infection, effective treatment and eradication of chronic HBV infection remain a tremendous therapeutic challenge. The next biomedical breakthrough towards a cure is awaiting innovative interdisciplinary approaches to examine the detailed mechanism responsible for HBV infection and replication from a molecular perspective. The planned research introduces novel molecular modeling methods combined with in vitro X-ray/neutron scattering experiments to quantify the internal structure of HBV nucleocapsids and electrostatic regulation at various stages of the viral replication. Specific aims include: 1) To determine the density distributions of the genomic nucleic acids and the C-terminal domain (CTD) of the core protein and their potential changes during NC maturation; 2) To elucidate the effect of electrostatic interactions and the CTD phosphorylation state on NC maturation and stability. Theory and experiment will create a synergy because, on the one hand, the scattering experiments provide necessary data for calibration of theoretical predictions and, on the other hand, computational results will further understanding the genome packaging in greater details. Theoretical calculations will also provide information not directly accessible by scattering experiments such as structural and thermodynamic properties pertaining to capsid formation and stability in vivo. By investigating biomolecular interactions within HBV nucleocapsids that underpin the viral replication, accomplishments from this work will help to develop unconventional system-based therapeutics to regulate and ultimately eradicate HBV replication. If successful, the generic nature of the proposed computational and experimental methods ensures that this research will have unusually high impact in understanding the molecular basis of viral morphogenesis and in developing drugs for effective treatment of virus-induced contagious diseases.

Design and synthesis of metal-organic frameworks for efficient hydrogen storage

Design of MOF materials for efficient hydrogen storage requires a good understanding of hydrogen interaction with the substrate at the atomistic scales. Whereas the literature on hydrogen storage is now vast, conventional theory and simulation methods are insufficient to account for the non-classical behavior of hydrogen-MOF interactions that involve hydrogen dissociation/recombination. Novel computational methods are needed for successful description of the quantum effects affiliated with both the local electronic structures of hydrogen atoms near the active sites of the MOF materials and the weak but long-ranged van der Waals interactions among hydrogen molecules within the microscopic pores. The research aims to provide fundamental understanding of multi-body phenomena entailing strongly correlated electronic, atomic and molecular interactions. A synergistic combination of theoretical and experimental investigations may lead to a better design of novel materials for hydrogen storage. 

Condensation and icing at superhydrophobic surfaces

Superhydrophobic surfaces are promising for a wide variety of interesting applications owing to their extremely high water contact angles (typically greater than 150°) and low hysteresis (<5°). Up to date, most published researches on superhydrophobicity are focused on the effects of surface topology on water contact angle by trapping macroscopic air pockets at geometrically heterogeneous surfaces. While the extraordinary water repellency of a superhydrophobic surface can be successfully described by various modifications of Young’s equations, the macroscopic approach is insufficient to describe surface phase transitions affiliated with broader applications of superhydrophobic surfaces including anti-fogging and/or anti-icing. Such broader applications hinge on a better understanding of the surface hydrophobicity that depends on the microscopic details of the substrate and different states of water at inhomogeneous conditions. By bringing together complementary expertise, the proposed collaborative research aims to (i) establish a theoretical framework for describing vapor-liquid condensation, wetting transition and heterogeneous ice formation at superhydrophobic surfaces, (ii) develop practical schemes for fabrication of superhydrophobic surfaces with systematically tailored surface morphologies and chemical properties, (iii) conduct real-time study of condensation on superhydrophobic surfaces by a high-resolution environmental scanning electron microscope with atomic force microscope and cooling stage attachments, and (iv) study icing of supercooled water on superhydrophobic surfaces using a custom-designed experimental system.

More Information 

General Campus Information

University of California, Riverside
900 University Ave.
Riverside, CA 92521
Tel: (951) 827-1012

College Information

Bourns College of Engineering
Wu Group

Tel: (951) 827-2413
Fax: (951) 827-5696