The effects of temperature and frequency dispersion on sound speed in bulk poly (vinyl alcohol) poly (N-isopropylacrylamide) hydrogels caused by the phase transition

Y Jin; H Heo; E Walker; A Krokhin; T Y Choi; A Neogi

doi:10.1016/j.ultras.2019.05.004

The effects of temperature and frequency dispersion on sound speed in bulk poly (vinyl alcohol) poly (N-isopropylacrylamide) hydrogels caused by the phase transition

Ultrasonics. 2020 May:104:105931. doi: 10.1016/j.ultras.2019.05.004. Epub 2019 May 11.

Authors

Y Jin¹, H Heo², E Walker³, A Krokhin⁴, T Y Choi⁵, A Neogi⁶

Affiliations

¹ Department of Mechanical and Energy Engineering, University of North Texas, 3940 North Elm Suite F101, Denton, TX 76207, USA.
² Department of Mechanical and Energy Engineering, University of North Texas, 3940 North Elm Suite F101, Denton, TX 76207, USA; Department of Physics, University of North Texas, P.O. Box 311427, Denton, TX 76203, USA.
³ Echonovus Inc., 1800 South Loop 288 STE 396 #234, Denton, TX 76205, USA.
⁴ Department of Physics, University of North Texas, P.O. Box 311427, Denton, TX 76203, USA.
⁵ Department of Mechanical and Energy Engineering, University of North Texas, 3940 North Elm Suite F101, Denton, TX 76207, USA. Electronic address: tae-youl.choi@unt.edu.
⁶ Department of Physics, University of North Texas, P.O. Box 311427, Denton, TX 76203, USA; Advanced Materials and Manufacturing Processes Institute, University of North Texas, 3940 North Elm Street, Box Q, Discovery Park Annex, Denton, TX 76207, USA. Electronic address: arup.neogi@unt.edu.

PMID: 32156431
DOI: 10.1016/j.ultras.2019.05.004

Abstract

Bulk Poly (Vinyl Alcohol) (PVA) Poly (N-isopropyl acrylamide) (PNIPAm) hydrogel, one of the thermally responsive phase transitive hydrogels, is a versatile material due to its sharp volumetric phase transition and anomalous behaviors with facile tunability by thermal stimulation. At the lower critical solution temperature (LCST) of 33 °C, the hydrogels undergo a volumetric phase transition that causes drastic, non-monotonic change in the elastic modulus, viscosity, stiffness, and speed of sound. Here, we report the temperature and frequency dependence of the speed of sound in bulk PVA-PNIPAm hydrogel as measured by means of a planar resonant cavity. The linear response theory is applied for calculation of frequency dependent speed of sound. Comparisons find standard time of flight techniques underestimate the speed of sound by up to 6%, with variation in the frequency dependent speed of sound reaching as high as 200 m/s in the ultrasonic range of 0.2-0.8 MHz. The first characterization of frequency dependent speed of sound in PVA-PNIPAm hydrogel is addressed and delineated into its phase transition behaviors as connected to temperature. The findings can lead to better characterization of mechanical properties using ultrasonic spectroscopy, and higher resolution in ultrasonic imaging applications with dispersive media.

Keywords: Dispersion; PVA PNIPAm; Speed of sound; Ultrasonic spectroscopy.