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  Elastic, Viscoelastic and Thermal Characterization of Polymers

Project Example on Elastic/Viscoelastic Characterization: Polydimethylsiloxane (PDMS) is an essential polymeric material widely used in biological and biomedical devices. However, PDMS is inherently viscoelastic, meaning its elastic modulus changes with loading rates and elapsed 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 in-depth and physically accurate conversion model for force measurement applications. The scientific insights gained from this detailed study of PDMS viscoelasticity contribute to the analysis of many other soft polymer materials at micro/nano scales, which are commonly used in biological and biomedical research.

Project Example on Thermal Characterization: In recent years, polymer-based materials have shown great potential in various applications, including biomedical devices, photovoltaic solar cells, supercapacitors, and LEDs. Thermal conductivity and thermal diffusivity are critical thermophysical parameters that determine the steady and unsteady thermal transport performance of these materials. Most polymers are poor thermal conductors, leading to the use of extremely thin structures in electronics, and there are limited techniques available for their thermal characterization. In this work, we have developed a time-domain fluorescence spectroscopy technique to characterize the thermophysical properties of polymers. Given that most polymers exhibit excellent fluorescence excitation, this method offers a wide range of application potentials for new 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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