(7bt) From Soft Materials to Soft Circuits

Conjugated polymers possess outstanding properties including high electrical conductivity (in the doped state), tunable band gap, and the ability to emit and absorb a wide spectrum of light. Hence, they are widely used for applications including artificial skin, organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), energy storage devices, and flexible sensors. Recent investigations also show that conjugated polymers display great potential to exhibit high thermal conductivity, and thus are promising candidates for next-generation soft heat transfer materials. In this poster, I will present my PhD research focusing on three branches of conjugated polymer study. First is the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films possessing ultrahigh conductivity and mobility, complemented by theoretical modeling based on Boltzmann transport and wafer scale device fabrication of radio frequency AC to DC rectifier. Second is achieving record high cross-plane thermal conductivity (>10x common polymers) using undoped poly(3-hexylthiophene) (P3HT) thin films along with theoretical modeling. Third, is the fabrication of chemical sensing devices, using various nanostructured PEDOT and related copolymers, and the integration of the sensing devices in printed circuit boards (PCBs). Oxidative chemical vapor deposition (oCVD) is used as the synthesis method for the aforementioned polymers. As a solvent free method, oCVD circumvented the problem of low solubility of conjugated polymers and compatible issue between substrate and the solvent. In addition, the unique growth mechanism of oCVD P3HT synthesis essentially enhances the thermal conductivity. oCVD also makes it easy to pattern the polymer film during device fabrication, and provides conformal coating on nanostructured scaffolds. In addition to my three primary focus areas, side projects during my doctoral research include collaborative work with Eni S.p.A on large-scale flexible photovoltaic fabrication; collaborative work with the Department of Electrical Engineering and Computer Science at MIT on flexible energy harvesting device fabrication; DFT calculations and machine learning assisted monomer selection for light emitting polymers.

Research Interests:

1. Material development:

Material synthesis and study for conjugated polymers and other soft semiconductors, with special focus on their thermal,electrical, and optical properties, and the related theoretical modeling.

2. Flexible circuit development:

Fabrication of flexible electronics and circuits using newly discovered high performance soft materials. The targeted applications include energy harvesting, photovoltaic, energy storage, flexible sensor, and soft robotics.

3. Machine learning assisted material design:

The main goal is using machine learning (ML) as a powerful tool to facilitate the process of conjugated polymer discovery. There are two stages of the project: 1. predicting interested properties of new conjugated polymers using known experimental data, and additional knowledge; 2. generating new molecular structures from the ML algorithms. The results of ML can guide the experiments. And the experimental results, in turn, will improve the development of the ML algorithms.

Teaching Interests:

I would be happy to teach chemical engineering core classes, including transport phenomena, thermodynamics, reaction engineering and numerical methods. Other classes such as polymer chemistry and polymer physics also fit my background. I had experience working as a teaching assistant with Professor Deen and Professor Braatz teaching graduate level analysis of transport phenomena at MIT.

I would also be happy to design and teach new classes, such as metallic/semiconducting polymers, chemical and biological sensors, solid state physics for chemical engineers, or applications of machine learning in chemical engineering.

Selected Publications:

[1] Karen K. Gleason and Xiaoxue Wang “Oxidative Chemical Vapor Deposition for Conjugated Polymers: Theory and Applications”, invited chapter for the fourth edition of the Handbook of Conducting Polymers, CRC Press/Taylor & Francis, to be submitted in December 2017, anticipated publication in late 2018

[2] Xiaoxue Wang, Xu Zhang, Lei Sun, Dongwook Lee, Sunghwan Lee, Yang Shao-Horn, Mircea Dinca, Tomas Palacios and Karen K. Gleason “Ultrahigh Electrical Conductivity of oCVD PEDOT Thin Films and the Wafer Scale Fabrication of the 13.6MHz Rectifiers based on the PEDOT-Si Diode”, to be submitted

[3] Yanfei Xu†, Xiaoxue Wang†, Jiawei Zhou, Elizabeth Lee, Karen K. Gleason and Gang Chen “High Thermal Conductivity of Amorphous oCVD Grown P3HT” († authors contributed equally), to be submitted

[4] Xiaoxue Wang, Sema Ermez, Hilal Goktas, Silvija Gradečak and Karen Gleason “Room Temperature Sensing Achieved by GaAs Nanowires and oCVD Polymer Coating”, Macromolecular Rapid Communications (2017)

[5] Minghui Wang†, Xiaoxue Wang†, Priya Moni†, Andong Liu, Do Han Kim, Won Jun Jo, Hossein Sojoudi and Karen K Gleason “CVD Polymers for Devices and Device Fabrication”(†contributed equally), Advanced Materials, 29.11 (2017): 1604606

[6] Xiaoxue Wang, Asli Ugur, Hilal Goktas, Nan Chen, Minghui Wang, Noa Lachman, Estelle Kalfon-Cohen, Wenjing Fang, Brian L Wardle and Karen K Gleason “Room Temperature Resistive Volatile Organic Compound Sensing Material based on a Hybrid Structure of Vertically Aligned Carbon Nanotubes and Conformal oCVD/iCVD Polymer Coatings” ACS Sensors, 1.4 (2016): 374-383.

[7] Xiaoxue Wang, Sichao Hou, Hilal Goktas, Peter Kovacik, Frank Yaul, Arun Paidimarri, Nathan Ickes, Anantha Chandrakasan, Karen Gleason "Small-area, Resistive Volatile Organic Compound (VOC) Sensors using Metal-polymer Hybrid Film based on Oxidative Chemical Vapor Deposition (oCVD)." ACS Applied Materials and Interfaces, 7.30(2015): 16213–16222

Proposal Writing Experience:

[1] “Improving oCVD PEDOT Properties: Transparent, Conducting, and Flexible Electrodes for Photovoltaics” full proposal for Eni S.p.A under the supervision of Professor Karen Gleason, 2016. 2-year financial support awarded beginning in September, 2017

[2] “oCVD/iCVD Structural Electronics Gas Sensor” full proposal for Analog Devices under the supervision of Professor Karen Gleason and Professor Brian Wardle, 2016. 1-year financial support awarded beginning in January, 2018

[3] “oCVD Polymers for Next Generation Flexible Photovoltaic” pre-proposal for Eni S.p.A under the supervision of Professor Karen Gleason, 2016

[4] “Surface Modification to Reduce Nanoparticle Diffusion Through Flexible Polymers” white paper for Semiconductor Research Corporation under the supervision of Professor Karen Gleason, 2014

Invited Talk:

Wang, Xiaoxue et al“ Novel Resistive Volatile Organic Compound (VOC) Sensors” , invited talk in Nano-Engineered Composite aerospace Structures (NECST) Consortium all-day industry meeting, June 2016