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Wang et al. Soft Sci. 2026, 6, 8 Page 13 of 28

Specifically, by placing the bottom of the carbon-based solution container on a cold source and maintaining
a relatively higher temperature at the top, a stable and directional thermal gradient is established across the
sample. The ice crystals would nucleate near the cold interface and grow directionally toward the warmer
region, excluding and confining the carbon-based components between the gaps of the adjacent lamellar ice
crystal array, obtaining carbon-based aerogel with a highly ordered, anisotropic, and layered porous
structure after removing the ice template by sublimation treatment. Moreover, by tuning the key processing
parameters [109] , such as the thermal gradient and freezing rate, the pore size, wall thickness, orientation and
direction of pores can be tailored, enabling the construction of a hierarchically aligned structure spanning
from the micro- to macro-scale. The resulting anisotropic porous architecture produced by directional
freezing methods significantly influences the microwave propagation behaviors. Incident microwaves
undergo multiple internal reflections and scattering at channel walls and heterogeneous interfaces, rather
than penetrating the aerogel directly. This significantly prolongs their propagation path within the aerogel,
increasing opportunities for EM energy dissipation.

Fei et al. prepared carbon-based aerogels by growing cobalt nanoparticles on CNTs within a conductive
framework via directional freeze-casting followed by carbonization [110] . Owing to the unique 3D porous
structure with a large surface area, abundant interfacial defects, and efficient electrical conductivity, the
resulting carbon aerogel exhibited a minimum RL of -27.5 dB and an excellent EAB of 7.4 GHz. Li et al.
prepared honeycomb-like anisotropic porous channels via unidirectional freeze-drying of a chitin
nanofiber/water suspension, while the carbon-based defective microstructure could be effectively tailored by
controlling the carbonization temperature [111] . The resulting aerogels exhibited outstanding microwave
absorption performance for microwaves applied both parallel and perpendicular to the anisotropic channels.
The chitin-derived carbon aerogels were then subjected to controlled compression from 0% to 80% to
investigate the corresponding EM response behaviors , achieving a maximum RL of -40 dB while covering
[112]
the entire X-band region after 60,000 compression-recovery cycles. Furthermore, radial freezing strategies, a
special type of unidirectional freezing, can produce aerogels with unique pore structures containing
numerous interfaces [113,114] , enhancing interfacial polarization and dielectric loss, thereby improving RL
intensity and EAB.

Compared to unidirectional freezing, bidirectional freezing is more attractive for synthesizing aerogels with
ordered and layered microstructures. To achieve broadband absorption, lamellar RGO-based aerogels were
successfully synthesized via bidirectional freezing and subsequent thermal annealing [115] , exhibiting
exceptional microwave absorption with a minimum RL of -72.2 dB at a thickness of 2.1 mm and an EAB of
8.4 GHz within 9.6-18.0 GHz. Liang et al. constructed a Ni nanochain-anchored 3D MXene/RGO aerogel
(NiMR-H) using bidirectional freezing followed by chemical reduction with hydrazine vapor [Figure 5A],
forming dielectric/magnetic heterogeneous interfaces with an oriented pore structure [116] . This aerogel
exhibited an enhanced RL of -75.2 dB with a wide EAB of 7.3 GHz, attributed to improved impedance
matching and magnetic-electric coupling. Moreover, the RL response toward incident microwaves differed
between the parallel and perpendicular directions of the anisotropic aerogel. To explore the interaction
between incident microwaves and the directional macroporous structure, Du [117] measured the EM
parameters at different incident angles [Figure 5B]. Both the complex permittivity and the α value decreased
as the incident wave direction changed from perpendicular (90°) to parallel (0°) to the channels, while
impedance matching increased, due to enhanced microwave propagation along the directional pore
channels. Therefore, the pore orientation affects the trade-off between impedance matching and attenuation,
leading to direction-dependent microwave absorption performance.

The gradient-structured aerogel simultaneously enhances impedance matching and microwave attenuation
by engineering a heterogeneous pore structure. This structure exhibits a continuous spatial gradient in EM