Frequency-tunable acoustic absorption in anisotropic graphene aerogels via morphological engineering of internal...

The development of high-efficiency acoustic attenuation media has been significantly advanced by the integration of graphene derivatives and carbon nanotubes, taking advantage of their superior chemical and mechanical attributes. Nevertheless, a primary obstacle in engineering these materials involves the precise morphological control of low-dimensional nanostructures-specifically regarding the prevention of random restacking and the achievement of uniform directional alignment within the porous framework. Furthermore, systematic investigations into the acoustic properties of pure graphene aerogels-specifically regarding how flake dimensions and loading influence the barrier effect and structural anisotropy-remain largely unexplored. To address these challenges, this research demonstrates a systematic approach to engineering anisotropic graphene-based aerogels featuring frequency-tunable acoustic absorption through synergistic modulation via bidirectional freeze-casting. By employing the Ice-Segregation-Induced Self-Assembly (ISISA) process, the study successfully fabricated highly ordered, vertically and horizontally aligned lamellar networks. Morphological investigations revealed a distinct structural divergence: aerogels based on large graphene flakes formed continuous, streamlined micro-channels with minimal structural resistance, whereas variants utilizing smaller flakes developed a high density of internal structural barriers, or septa. The superior performance of these structures is driven by intensified visco-thermal energy dissipation and multiple scattering effects, both of which are facilitated by increased tortuosity and internal air-flow resistance. Furthermore, by manipulating the spatial orientation of the framework relative to the incident sound vector, we proposed a mechanism to explain how the barrier effect sustains enhanced absorption in transverse modes compared to longitudinal ones. These findings establish a robust structure-property relationship between microscopic precursor dimensions and macroscopic hierarchical architecture, offering a new paradigm for high-performance, multifunctional carbon-based noise insulators.