Читать книгу Flexible Thermoelectric Polymers and Systems - Группа авторов - Страница 24

Some composites particularly the dispersion of inorganic nano‐fillers in polymer matrix can exhibit high thermoelectric properties [28, 29]. There can be three different structures for a two‐phase composite (Figure 1.17). The resistivity (ρ _c) of the composites depends on the volume fractions and the resistivity of the two phases. When the two phases α and β are in series, the resistivity of the composite is given by,

Figure 1.17 Structures of a composite with two phases of α and β (a) in series, (b) in parallel, and (c) one phase dispersed in another phase.

(1.18)

where χ _α and χ _β are the volume fractions of the α and β phases, respectively, and ρ _α and ρ _β are the resisitivities of the two phases, respectively. The resistivity of the composite is dominated by the phase of higher resistivity.

When the two phases of α and β are parallel, the conductivity (σ _c) of the composites is related to the conductivities of the two phases by the following equation,

(1.19)

The phase with higher conductivity will be the dominant one for the conductivity of the composite.

If a composite has a structure of the α phase dispersed in the β phase, the α phase is the dispersed phase and the β phase is the matrix. The resistivity of the composite depends on the relative resistivities of the two phases. If the α phase is more resistive than the β phase, ρ _α > 10 ρ _β, the resistivity of the composite is given by

(1.20)

If the α phase is less resistive than the β phase, ρ _α < (1/10)ρ _β, the resistivity of the composite is given by

(1.21)

The Seebeck coefficient of the composites is also related to the microstructure of the two phases. When the α and β phases are in series, the Seebeck coefficient (S _c) of the composite is given by,

(1.22)

where S _α and S _β are the Seebeck coefficients of the α and β phases, respectively, and κ _α and κ _β are the thermal conductivities of the two phases, respectively. When the two phases are in parallel, the Seebeck coefficient of the composite is given by

(1.23)