(Invited) Graphene Oxide-Based Membranes: Viscoelastic Properties and Application to Broadband Microspeakers

Abstract

Graphene and graphene derivatives have attracted attention as materials for acoustic transduction [1-3]. Graphene oxide (GO) membranes and borate cross-linked graphene oxide (X-GO) membranes combine high stiffness, low mass density, and high loss coefficient. We show [4] that these mechanical properties are ideal for efficient, broadband, electro-acoustic transduction, where the acoustic diaphragm should be light, stiff, and internally damped. We present a quantitative comparison of the figure of merit, (E/ρ 3)1/2, where E is Young's modulus and ρ is the mass density, and the material performance index, tan δ (E/ρ 3)1/2, where tan δ is the loss coefficient. GO and X-GO exhibit high figures of merit, comparable to that of wood and exceeding that of aluminum and thermoplastics. The material performance indices of GO and X-GO exceed that of wood, thermoplastics, and aluminum. The latter are common diaphragm materials in acoustic transducers. For acoustic applications, it is important to understand the frequency dependent viscoelastic response. The complex modulus G = G' + iG'' of GO and X-GO membranes was measured by dynamic mechanical analysis and analyzed by the application of the time-temperature superposition (TTS) principle of polymer rheology. We find that X-GO shows a more than 30% increase in storage modulus G’ over the frequency range of 1 to 10 kHz, exceeding 55 GPa at 10 kHz. There is a reduction in loss coefficient tan δ = G''/G' for X-GO of ≈30% over the same frequency range, reaching tan δ = 0.04 at 10 kHz, which is approximately one order of magnitude larger than that of aluminum. A quantitative comparison of microspeaker performance was conducted at a fixed diaphragm mass m = 15-20 g and 14 mm x 8 mm size, including GO, X-GO, oak wood, polyethylene terephthalate (PET), aluminum, and titanium. Scanning laser measurements confirm pistonic operation of X-GO membranes. Microspeaker sound pressure level response was measured in both time and frequency domains. X-GO diaphragms exhibit 45% higher damping than aluminum membranes in microspeaker assemblies. Consequently, X-GO membranes enable the upshift of loudspeaker breakup frequency by 1/6 to 1/2 octave above speakers assembled with oak wood, PET, aluminum and titanium membranes. GO based materials are thus found to be an exceptional material for electro-acoustic transduction. References: [1] Q. Zhou, A. Zettl, Appl. Phys. Lett. 102, 223109 (2013). [2] A. U. Khan, G. Zeltzer, G. Speyer, Z. K. Croft, Y. Guo, H. Nagar, V. Artel, A. Levi, C. Stern, D. Naveh, G. Liu, Adv. Mat. 33, 2004053 (2021). [3] H. Tian, T.-L. Ren, D. Xie, Y.-F. Wang, C.-J. Zhou, T.-T. Feng, D. Fu, Y. Yang, P.-G. Peng, L.-G. Wang, L.-T. Liu, ACS Nano 5, 4878 (2011). [4] K. Hu, R.E.Gaskell, W. Cardenas, H. Wei, Y.-C. Huang, M. Cerruti, T. Szkopek, Adv. Func. Mat. 2107167 (2021). Figure 1

A Review of Acoustic Devices Based on Suspended 2D Materials and Their Composites

“…In some cases, the synthesized GO diaphragms have Young's modulus exceeding 30 GPa, which can be further enhanced by cross-linking with borate ion, polyethylene imine, or other chemical groups to form cross-linked GO (X-GO) films, achieving a Young's modulus higher than 80 GPa. [112,119] Additionally, the unique viscoelastic properties of GO and X-GO result in a higher damping ratio compared to other traditional speaker diaphragms such as metal diaphragms. It is indicated that the damping ratio of microspeakers with GO and X-GO diaphragms is respectively 39% and 46% higher than those with aluminum diaphragms.…”