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  Elastic, Viscoelastic, and Thermal Characterization of Polymers

Project Example on Elastic/Viscoelastic Characterization: Polydimethylsiloxane (PDMS) is a key polymeric material widely used in biological and biomedical devices. However, PDMS is inherently viscoelastic—its elastic modulus varies with loading rate and over time. This work presents a comprehensive method for the viscoelastic characterization, modeling, and analysis of the bending behavior of PDMS micropillar arrays. Our approach provides a more physically accurate and in-depth conversion model for force measurement applications. The scientific insights gained from this study of PDMS viscoelasticity contribute to the analysis of many other soft polymer materials at the micro/nano scale, which are broadly used in biological and biomedical research.

Project Example on Thermal Characterization: Polymer-based materials have demonstrated significant potential across a wide range of applications, including biomedical devices, photovoltaic solar cells, supercapacitors, and LEDs. Thermal conductivity and thermal diffusivity are critical thermophysical parameters that govern both steady-state and transient heat transport in these materials. However, most polymers are inherently poor thermal conductors, which often necessitates the use of ultra-thin structures in electronic devices. Moreover, techniques available for their thermal characterization remain limited. In this work, we have developed a time-domain fluorescence spectroscopy technique for characterizing the thermophysical properties of polymers. Since many polymers exhibit strong fluorescence excitation, this method offers broad potential for evaluating emerging polymer materials.

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

Time-domain transient fluorescence spectroscopy for thermal characterization of polymers
H. Wu, K. Cai, H. Zeng, W. Zhao, D. Xie, Y. Yue#, Y. Xiong, and X. Zhang
Applied Thermal Engineering, 2018, 138: 403-408
A role for matrix stiffness in the regulation of cardiac side population cell function
Y. Qiu#, A.F. Bayomy, M.V. Gomez, M. Bauer, P. Du#, Y. Yang, X. Zhang, R. Liao
AJP-Heart and Circulatory Physiology, 2015, 308(9): H990-H997
Tunable electrical and mechanical responses of PDMS and polypyrrole nanowire composites
P. Du#, X. Lin, and X. Zhang*
Journal of Physics D: Applied Physics, 2013, 46(19): 195303
Investigation of cellular contraction forces in the frequency domain using a PDMS micropillar-based force transducer
P. Du#, C. Chen, H. Lu, and X. Zhang*
Journal of Microelectromechanical Systems, 2013, 22(1): 44-53
Effect of loading rates on cellular force measurements by polymer micropillar based transducers
P. Du#, X. Zheng#, I-K Lin#, and X. Zhang*
Applied Physics Letters, 2011, 99(8): 083701
Extension of the beam theory for polymer bio-transducers with low aspect ratios and viscoelastic characteristics
P. Du#, I-K Lin#, H. Lu, and X. Zhang*
Journal of Micromechanics and Microengineering, 2010, 20(9): 095016
Viscoelastic characterization and modeling of polymer transducers for biological applications
I-K Lin#, K-S Ou, Y-M Liao, Y. Liu#, K-S Chen, and X. Zhang*
Journal of Microelectromechanical Systems, 2009, 18(5): 1087-1099
Viscoelastic mechanical behavior of soft microcantilever-based force sensors
I-K Lin#, Y-M Liao, Y. Liu#, K-S Ou, K-S Chen, and X. Zhang*
Applied Physics Letters, 2008, 93(25): 251907

Ph.D. Dissertation
Viscoelastic characterization and modeling of PDMS micropillars for cellular force measurement applications
Ping Du, Ph.D. Dissertation, Boston University. (Advisor: Xin Zhang; January 2013)

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