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Liu et al. Soft Sci. 2025, 5, 7 https://dx.doi.org/10.20517/ss.2024.69 Page 5 of 25

The layered structure includes randomly multilayered structures, gradient distribution structures,
[65]
sandwich-like structures, alternating multilayered structures, and “brick and mortar” structures, etc. . By
varying the EM characteristics and thickness of each layer in the multilayer absorber, frequency-tunable EM
absorption performance and wide EAB can be achieved [20,66] . Usually, an EM reflection layer, an EM
adsorption interlayer, and a surface impedance matching layer contribute to a multilayered structure.
Although some EMW may enter the EMI adsorption material from the surface impedance matching layer,
the EM loss occurs only in the interlayer . In addition, the development of multilayered structures
[67]
improved the interfacial polarization by creating a special multi-reflection/multi-absorption
mechanism [24,57,65] .

Segregated structure
CPCs with conventional structures, in which the conductive fillers are randomly distributed, used for EM
absorption often require a high conductive filler loading to meet the required EMI shielding effectiveness
(EMI SE). However, extensive conductive fillers not only increase the fabricating cost but also reduce the
[68]
mechanical properties of the CPCs . It has been proven that the creation of separated structure is a
successful approach to realize high EM absorption at low filler loading [69,70] .

In the segregated structure, because of the volume exclusion effect of polymer microcells, the conductive
network was condensed to a dense state, where conductive fillers are enriched in the interface or one
polymer phase . This would lower the percolation threshold, improve the EMI SE of the material, and help
[18]
create optimized conductive pathways at low filler loadings [68,69,71] . In addition, the electron leaping,
interfacial polarization, and interfacial reflection/scattering for EMW could all increase with the
development of multiple interfaces in EMW shielding materials. Therefore, by regulating the arrangement
of conductive fillers and creating multi-interfaces, the segregated structure is a successful strategy to fulfill
the EMI shielding .
[48]

RESEARCH PROGRESS OF POLYMER-BASED EMW ABSORBERS
Conductive polymer-based EMW absorbers
Conductive polymers are made up of repeating structural units joined by single and double bonds to
produce conjugate bonds. Electrical conductivity benefits from their unique π-conjugated structure.
Conductive polymers have been regarded as promising EM absorbing materials in past decades because of
their lightweight, ease of synthesis, good stability and conductivity [27,55,72] . The composites based on
intrinsically conductive polymers, including polypyrrole (PPy) and polyaniline (PANI), offer advantages in
terms of ease of processing, corrosion resistance, high electrical and TC, good dielectric properties [18,40,73] .
They can easily achieve impedance matching and optimized conductivity by adjusting their EM
characteristics [48,72,74] .

Conductive polymers are dielectric loss materials that release EM energy through micro- or macro-current
and polarization loss. However, relying solely on dielectric loss rarely satisfies the requirements for EMW
absorption. Therefore, combining several loss mechanisms is often used for constructing high-performance
EMW absorbers [75-77] .

PANI
PANI has low density, low cost, simple synthesis, tunable conductivity, good thermal stability, reversible
redox reaction, ease of doping, nontoxicity, and environmental stability [73,78] . It can be coupled to other
materials through in-situ polymerization to create composites with core-shell structures that construct rich
heterogeneous interfaces and improve the conductance loss and impedance matching [55,79] . Intrinsic PANI
[29]