Abstract Nanotechnology has been widely used for developing sound absorption materials in air, but studies for underwater applications remain limited. In this study, carboxyl functionalized multi-walled carbon nanotubes (MWCNT-COOH) were added into polydimethylsiloxane (PDMS) with dispersant to enhance the underwater acoustic properties. A water-filled impedance tube was built to determine the underwater sound absorption coefficient in the low frequency range from 1500 Hz to 7000 Hz and under variable hydrostatic pressures. Results demonstrate that pure PDMS is nearly acoustically transparent. With the addition of MWCNT-COOH and under normal pressure (0 MPa), the sound absorption coefficient was marginally improved to 0.3. The coefficient can nonetheless be further increased to above 0.75 with the introduction of both surfactant and MWCNT-COOH. It could be postulated that the trapped micro-voids and uniformly dispersed MWCNT-COOH contributed to the improvement when the pressure is at 0 MPa. Effects of MWCNT-COOH concentrations in a range of 0.1 wt% to 2 wt% were investigated. It was ascertained that the concentrations have only a marginal effect on the sound absorption performance. Tests were also conducted at variable hydrostatic pressure above 0 MPa. Results revealed that underwater sound absorption performance decreased with an increase in the hydrostatic pressure in a range of 0.5 MPa to 1.5 MPa. The drop in performance due the increase of hydrostatic pressure supported the claim that the presence of micro-voids within the material matrix structure contributed to the sound absorption.

中文翻译：

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钢板背衬聚二甲基硅氧烷/碳纳米管复合材料的水下吸声性能

摘要 纳米技术已被广泛用于开发空气中的吸声材料，但对水下应用的研究仍然有限。在这项研究中，将羧基官能化的多壁碳纳米管（MWCNT-COOH）添加到带有分散剂的聚二甲基硅氧烷（PDMS）中以增强水声性能。建立了一个充水阻抗管来确定在 1500 Hz 至 7000 Hz 的低频范围内和可变静水压力下的水下吸声系数。结果表明，纯 PDMS 几乎是透声的。添加MWCNT-COOH并在常压（0 MPa）下，吸声系数略微提高至0.3。尽管如此，通过引入表面活性剂和 MWCNT-COOH，该系数可以进一步增加到 0.75 以上。可以假设，当压力为 0 MPa 时，捕获的微孔洞和均匀分散的 MWCNT-COOH 有助于改善。研究了 0.1 wt% 至 2 wt% 范围内的 MWCNT-COOH 浓度的影响。确定浓度对吸声性能仅具有边际影响。还在 0 MPa 以上的可变静水压力下进行了测试。结果表明，水下吸声性能随着静水压力在 0.5 MPa 至 1.5 MPa 范围内的增加而降低。由于静水压力增加而导致的性能下降支持了材料基体结构中微孔的存在有助于吸声的说法。