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  Elastic/Viscoelastic/Thermal Characterization of Polymers

Elastic and Viscoelastic Characterization of Polymers: Polydimethylsiloxane (PDMS) is an important polymeric material widely used in BioMEMS. However, PDMS is an inherently viscoelastic material and its elastic modulus changes with loading rates and elapsed time. This work demonstrates a comprehensive method for the viscoelastic characterization, modeling, and analysis associated with the bending behavior of the PDMS micropillar arrays, providing a more in-depth and physically accurate conversion model for force measurement applications. The scientific insights from the in-depth study of the viscoelasticity of PDMS will contribute to the analysis of many other soft polymer materials at micro/nano scales commonly used in biomedical research.

Thermal Characterization of Polymers: In recent years, polymer-based materials have been studied extensively, and have shown great potentials in biomedical, photovoltaic solar cells, supercapacitors, LEDs and so on. Thermal conductivity and thermal diffusivity are important thermophysical parameters which determine steady and unsteady thermal transport performance. Most polymer materials are poor in thermal transport, and thus extremely thin structures are usually used in electronics, not many techniques are available for thermal characterization. In this work, a time-domain fluorescence spectroscopy technique is developed to characterize thermophysical properties of polymers. Since most polymers have excellent fluorescence excitation, this method provides a wide range of application potentials for newly polymer materials.

Representative Publications (#denotes graduate students/postdocs supervised by X. Zhang; *denotes corresponding author by X. Zhang; +denotes contributed equally.)

H. Wu, K. Cai, H. Zeng, W. Zhao, D. Xie, Y. Yue#, Y. Xiong, and X. Zhang, "Time-domain Transient Fluorescence Spectroscopy for Thermal Characterization of Polymers," Applied Thermal Engineering, 2018, 138: 403-408. [DOI]

P. Du#, X. Lin, and X. Zhang*, "Tunable Electrical and Mechanical Responses of PDMS and Polypyrrole Nanowire Composites," Journal of Physics D: Applied Physics, 2013, 46(19): 195303(8pp). [DOI]

P. Du#, C. Chen, H. Lu, and X. Zhang*, "Investigation of Cellular Contraction Forces in the Frequency Domain Using a PDMS Micropillar-Based Force Transducer," Journal of Microelectromechanical Systems, 2013, 22(1): 44-53. [DOI]

P. Du#, X. Zheng#, I-K Lin#, and X. Zhang*, "Effect of Loading Rates on Cellular Force Measurements by Polymer Micropillar based Transducers," Applied Physics Letters, 2011, 99(8): 083701(3pp). [DOI]

P. Du#, I-K Lin#, H. Lu, and X. Zhang*, "Extension of the Beam Theory for Polymer Bio-Transducers with Low Aspect Ratios and Viscoelastic Characteristics," Journal of Micromechanics and Microengineering, 2010, 20(9): 095016(13pp). [DOI]

I-K Lin#, K-S Ou, Y-M Liao, Y. Liu#, K-S Chen, and X. Zhang*, "Viscoelastic Characterization and Modeling of Polymer Transducers for Biological Applications," Journal of Microelectromechanical Systems, 2009, 18(5): 1087-1099. [DOI]

I-K Lin#, Y-M Liao, Y. Liu#, K-S Ou, K-S Chen, and X. Zhang*, "Viscoelastic Mechanical Behavior of Soft Microcantilever-Based Force Sensors," Applied Physics Letters, 2008, 93(25): 251907(3pp). [DOI]

Ph.D. Dissertation

Ping Du, "Viscoelastic Characterization and Modeling of PDMS Micropillars for Cellular Force Measurement Applications," Ph.D. Dissertation, Boston University. (Advisor: Xin Zhang; January 2013)

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