Freeze Casting of SDS-assisted Gradient Graphene Composite Foam with Superior Broadband Noise Absorption and Thermal Insulation

Graphene aerogels-based sound absorbers are promising lightweight materials, but their
practical use is still limited because of weak mechanical strength, structural shrinkage,
pore-wall collapse, poor recovery after compression, and difficulty in controlling
connected pores across different length scales. To resolve these issues, we have
developed an SDS-assisted rGO/ANF/PVA composite foam, named rGAPS, using a
simple chemically foamed freeze-casting strategy. The rGAPS composite foams were
fabricated by mixing the GAP suspension with Sodium Dodecyl Sulfate (SDS) powder
under shear mixing to form a stable foam solution, followed by unidirectional freeze
casting, freeze drying, and thermal annealing. During this process, SDS-stabilized
bubbles worked as soft templates, while ice crystals created aligned channels. As a
result, the final rGAPS aerogel showed a hierarchical porous structure containing large
foam-derived macropores, aligned freeze-cast pores, and smaller interconnected pores
within the pore walls. The prepared composite foam exhibited ultralow density, high
porosity of about 99.0–99.6%, and stable porous morphology in both top and side views.
Mechanical tests showed compressible and recoverable behaviour up to 60% strain, with
stable cyclic response over 200 cycles. The acoustic absorption performance of the
rGAPS composite foams was measured using a BSWA SW series impedance tube
equipped with BSWA MPA416 microphones, following the ISO 10534-2:1998 standard.
The acoustic results confirmed strong broadband sound absorption, especially for 30
mm samples. The best directional gradient S3S2S1 of the foam achieved an NRC of 0.73
and a mean SAC of 0.88. The aerogels also showed very low thermal conductivity of
approximately 0.006–0.015 W m⁻¹ K⁻¹, hydrophobic behaviour with a water contact angle
of about 126°, and strain-dependent conductivity up to about 4 S.m⁻¹ under
compression. Overall, the SDS-assisted rGAPS composite foam provides a simple and
effective design for lightweight excellent acoustic absorbers, thermal insulators,
mechanical cushioning materials, and flexible strain-sensing devices.