Dr. Xiao Ma, Deptartment of Bioinformatics, University of Texas Southwestern Medical Center, Dallas, TX752325, USA

Biography: Dr. Xiao Ma received his B.S. in 2004 and M.Sc. in 2007 from Department of Mechanical Engineering of Tsinghua University, and his Ph.D. from Department of Mechanical Engineering of Iowa State University in 2013. Thereafter, he joined Department of Cell Biology/Bioinformatics of University of Texas Southwestern Medical Center as a post-doctoral research fellow. Xiao’s research focused on polymer smart surface/self-assembled materials and biomolecular interaction, nanoscale biosensor and biointerface design using dynamic force spectroscopy and molecular dynamics simulation. Currently, he endeavors to develop adaptive spectral analysis and unsupervised clustering algorithm to elucidate cellular morphodynamics during migration, and investigate GEF and GTPase signaling related cellular mechanotransduction using lateral view high resolution atomic force microscopy and FRET biosensors.

Speech Title: Conformational Transition and Tribological Performance Modulation of Sparsely and Densely Packed Self-Assembled Monolayers under Electrical Stimuli
Abstract: Self-Assembled Monolayers (SAMs) terminated by different functional end groups with distinct coverage densities on substrate exhibit on-demand modulation of their tribological performance under electrical stimuli based on different mechanisms. Here we adopt Molecular Dynamics (MD) simulation to investigate and demonstrate the mechanisms that govern the conformational state and tribological performance of Mercaptocarboxylic Acid (MHA)-terminated and Polyethylene Glycol (PEG)-terminated SAMs in distinct packing densities under electrostatic fields. In the case of sparsely packed MHA terminated SAMs, the major factor controlling the conformational transition and frictional change is the coverage density. The interchain space is large enough to allow lying-down conformational transition under positive potential which lead to an evident decrease of frictional coefficient compared to the negative and neutral potentials. While in the case of densely packed PEG terminated SAMs, the primary factor that leads to the conformational transition and frictional change is the structure of functional end group PEG. The helical “Gauche” transition of the SAMs results in a lower frictional response under positive potential compared with the “All-trans” states of the SAMs under negative and neural potentials. The different mechanisms governing the conformation state and tribological performance of SAMs imply the feasible and versatile application potential in nanotechnology.
Keywords: Self-Assembled Monolayers; Molecular Dynamics simulation; Coverage density; Conformational transition; Tribological performance