The effects of temperature and frequency dispersion on sound speed in bulk poly (vinyl alcohol) poly (N-isopropylacrylamide) hydrogels caused by the phase transition
The effects of temperature and frequency dispersion on sound speed in bulk poly (vinyl alcohol) poly (N-isopropylacrylamide) hydrogels caused by the phase transition
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DOI：
10.1016/j.ultras.2019.05.004
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发表时间：
2020-05-01
期刊：
影响因子：
4.2
通讯作者：
Neogi, A.
中科院分区：
文献类型：
--
作者：
Jin, Y.;Heo, H.;Neogi, A.
聚乙烯醇（PVA）聚N-异丙基丙烯酰胺（PNIPAm）水凝胶是一种热响应型相转移水凝胶，具有体积相变快、热刺激可调等特点，是一种用途广泛的材料。在33摄氏度的低临界溶解温度（LCST）下，水凝胶经历体积相变，这导致弹性模量、粘度、刚度和声速的急剧的非单调变化。在这里，我们报告的温度和频率的依赖性的声音在散装PVA-PNIPAm水凝胶的平面谐振腔测量的装置。本文应用线性响应理论计算频率相关声速。比较发现，标准的飞行时间技术将声速低估了6%，在0.2-0.8 MHz的超声范围内，与频率相关的声速的变化高达200 m/s。PVA-PNIPAm水凝胶中的频率依赖性声速的第一个表征被处理并描绘成与温度相关的相变行为。研究结果可以导致更好的表征机械性能，使用超声光谱，和更高的分辨率在超声成像应用与色散介质。
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 degrees 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.