Dr. Yun Liu's Openings

Openings

• NRC postdoctoral position (limited to U.S. citizens only). Please contact me if you are interested. Information about NRC postdoc can be found here.

1. Controlling protein aggregation/clustering by understanding protein interactions.  

Protein aggregation/clustering are ubiquitous phenomena in many fundamental research areas as well as industrial products. For examples, prefibrillar intermediates and amyloids, which are protein aggregates from small to large length scale, are responsible for many diseases including Alzheimer's and Parkinson's diseases. In addition, protein phase separation is known to be the major contributing factors in cataract development. With respect to pharmaceutical medicines, dissociable aggregates can affect the shelf life and transportation methods. The interactions between protein molecules in solvents are the decisive driving forces for the aggregation. Although this field has gain much attention recently, there is still a lack of systematical understanding of the interaction between proteins. Both prototypical proteins, such as lysozyme, and proteins from pharmaceutical companies, such as antibodies, will be investigated to understand the non-specific and specific interactions between proteins. During the research, small angle neutron scattering (SANS) and neutron spin echo (NSE) will be both used to understand the dynamics from tens of picosecond to hundreds of nanoseconds and structures from about 1 nm to 300 nm. Both computer simulations and statistical mechanic theories will be used to interpret data. The objective of this project is to link the interaction to the formation of clusters or aggregates at equilibrium conditions or at the early stage of aggregations.

2. In-situ study of time-resolved structural changes in soft matter materials under oscillatory electric fields

The self-assembly of colloid particles in solution assisted by external fields is an important and exciting field directed toward the synthesis of novel materials. The understanding of the instantaneous response of the structural evolution in nanometer to micrometer length scale under the time-dependent external fields, such as oscillatory electric field, can foster thorough understanding of the driven forces for controlled self-assembly. To complete this work, we will utilize various scattering tools, such as small angle neutron scattering (SANS) and ultra-small angle neutron scattering (USANS), available at Center for Neutron Research at NIST (NCNR) that can probe the length scale from about 1 nm to about 10 microns. Different time-resolved neutron scattering techniques, such as TISANE and time slicing, will be used to understand the time dependence. The combined scattering tools available at NCNR provide unique opportunity to study the dynamic response of a material in details. Results of this work will be of immediate interest to the community and are expected to be high impact. The main goal of the current project is to establish detailed structure properties of colloidal particles such as proteins and DNAs in solutions at various concentrations under a time-dependent external field.

3. Understanding the mechanisms of the gel/glass transition of a system with a strong short-range attraction perturbed by a long-range repulsion  

Gelation and glass transition of colloidal particles interacting with a short-range attraction are common phenomena people encounter in everyday life. When the attraction strength is tuned large enough either by changing temperature or adding extra component into the system, the system can be immobilized into a state whose spatial structure is similar to a liquid state while the dynamics of particles are frozen. Despite the long time effort to understand the gelation/glass transition, the physical mechanisms that drive the transition are still debated. Recent interests in model systems with both a short-range attraction and a long-range repulsion have added more complexity. Since a long-range repulsion is universal between small charged particles such as proteins, there is growing interest to fully understand how this additional long-range repulsion affects the glass transition. In this project, we would like to study a few selected model systems and control the repulsion range and strength to systematically understand the gel/glass transition and other related phenomenon such as the crystallization that typically competes with gel/glass transition. Small angle neutron scattering (SANS) and Neutron Spin Echo will be used to understand both the structure properties and short-time dynamics of the system undergoing the gel/glass transition.

4. Understanding the structure and dynamics of adsorbed molecules on materials surface  

Molecular adsorption on material surface is ubiquitous in many biological systems and pharmaceutical products such as water adsorption on protein or DNA, and protein adsorption on different surfaces. It is also important for many applications such as gas sequestration, energy storage, and molecular sieving. The detailed understanding of the interaction of molecules on surface could greatly enhance our capability of controlling adsorption behavior of important systems, leading to breakthroughs in new types of material and improving the manufacture procedures to increase shelf life of pharmaceutical products. We are interested in studying adsorption behavior of small molecules on surface of porous media including metal-organic frameworks (MOFs), activated carbon, porous silica materials to systematically understand how small molecules such as water, hydrogen gas, methane, acetylene, carbon dioxide, small drug molecules, DNA segments, interact with difference surfaces. We will utilize the state-of-the art neutron scattering instruments available at NIST Center for Neutron Research to investigate the structure and dynamic of adsorbed molecules on the surface.