de Pablo Group: Jian Qin

Postdoctoral Researcher

de Pablo Group

Contact

  • Phone
    773.834.2912
  • Address

    Searle Laboratory 105

    5735 South Ellis Avenue

    Chicago, IL 60637

  • Email
    qin at uchicago.edu

Research

Dr. Jian Qin is working on multiple projects in Prof. de Pablo's group, including: (1) building theory and simulation models to understand the formation and properties of polyelectrolyte coacervates; (2) understanding phase behavior of salt-doped diblock copolymer melts; (3) developing free energy sampling algorithm for identifying the order-disorder temperature; (4) developing algorithm to optimize directed self-assembly pattern design with evolutionary strategy.

(1) Charged polymers of opposite signs can form complex aggregation in aqueous solutions known as the coacervate phase. The distinguishing feature of the coacervate phase is that it contains a large amount of water, which results in an extremely low interfacical tension while in contact with water. The process of coacervation was initially studied in the co-solution of arabic gums and gelatin, and have been investigated for decades. In this project, Dr. Jian Qin's goal is to understand the phase behavior of coacervation, by using the both coarse-grained simulations and theoretical modeling. The preliminary results have been achieved on the study of interfacial tension between the coacervate phase and the coexisting supernatant water rich phase by using the classical Voorn-Overbeek model, and the manuscript summarizing these is currently being prepared.

(2) Salt-doped block copolymers is a promising lithium-ion conducting membrane solid electrolyte that can be used as electrode separation membranes in lithium-ion batteries, since it nicely combined the mechanical stability and relatively high ion conductivity, both entailed by the micro-phase separation. The project is aimed at studying the morphology and structures of ion-doped block copolymers (e.g., poly-(styrene-ethylene oxide)) by developing an efficient simulation package treating long ranged Coulomb interactions explicitly. The results related to this project is being assembled for publication.

(3) Identifying order-disorder transition temperatures in block copolymer materials accurately is challenging, even for the simplest lamella forming symmetric block copolymers, because of the issue of incommensurability and the presence of many closely-competing metastable phases. Sampling free energy directly would be a very reliable method for achieving this. To get the free energy or effective potential, a sensitive order parameter which delineate the disordered phase and the ordered phase nicely is defined, and an efficient and power free energy sampling technique using EXE-DOS (expanded ensemble density of state simulation) is implemented. The results related to this project is being assembled for publication.

(4) Directed self-assembling offered a suitable avenue for synthesizing large scale devices of feature sizes at the order of tens of nanometers. From the point of view of application, the challenging inverse problem is to design an economic (minimal) pattern to direct materials self-assembly. The approach is to abstract the pattern design into a few parameters, map the problem of designing a target pattern into an optimization problem, then implement a novel yet powerful optimization technique inspired by nature evolution, CMA-ES (covariance matrix adaptation—evolutionary strategy) to find the optimal solution. This project is in collaboration with graduate students Daman, Grant, Yongrui, and Marc (physics department). The preliminary results on this project has been accepted for publication in Soft Matter.

Biography

Dr. Jian Qin received his PhD in 2009 from the Department of Chemical Engineering and Materials Science, under the supervision of Profs. David Morse and Frank Bates, at the University of Minnesota. His thesis work, which he began in 2004, was focused on the field theoretical studies of self-assembly of ABC-type triblock copolymers and on the long-range density fluctuation correlations in binary polymeric systems. During this period he developed a highly efficient pseudo-spectral algorithm with symmetry adapted basis functions to solve the self-consistent field equations that are the standard theoretical tool for understanding the phase behavior of multi-component polymer melts. He also developed a predictive theory that is able to predict the fluctuation-corrected structure factor that is free from ultra-violet divergence, and that supersede the conventional RPA (random phase approximation) treatment. The theory was tested by independent Monte Carlo simulations of symmetric diblock copolymers and has recently been tested by several other model systems.

Prior to his Minnesota experience, he received his MS and BS in 2004 and 2002 respectively from the Department of Materials Science and Engineering at Tsinghua University, both under the supervision of Prof. Dan We. He worked on the dynamics of the magnetic nano-particle near the superparamagnetic limit and analyzing the conductivity of a sandwiched multi-layer spintronic device using the Green's function coupled with the Landauer formula for conductivity.

From 2009 to 2012, Dr. Jian Qin worked as a postdoc in Prof. Scott Milner's group, working on the molecular theory of polymer entanglement, and rheology. During this period, he and Prof. Milner worked out a highly efficient algorithm for analyzing the topological states of ring polymers to facilitate the study of polymer entanglement, and have come up with several non-invasive methods to quantify the polymer entanglement length, the key materials parameter needed to understand polymer rheology. The methodology being developed has been applied to quiescent melts, deformed polymer networks, and stretched linear polymer chains.

Dr. Jian Qin is generally interested in statistical mechanics, molecular simulations, algorithm development, and is particularly interested in the problems in polymers and soft matter physics that are mathematically well-defined.

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