Thermophysical properties of methacrylic polymer films with guest-host and side-chain azobenzene

The methacrylic polymer films containing azobenzenes with different peripheral substituents in the form of side-chain (P) and guest-host (A) systems were thermally investigated. The azo polymers with thicknesses below 1 μm were deposited on glass substrates using spin coating method. Photothermal radiometry (PTR) and scanning thermal microscopy (SThM) were used for determination of thermophysical properties of polymer samples. The topography of studied compounds was examined by atomic force microscopy (AFM). The results showed the influence of peripheral substituents as well as that of the polymer system on the thermophysical properties of studied azo polymers. Thermal diffusivity (α) extracted from PTR measurements is between 5.56 10⁻⁸ m²s⁻¹ and 11.3‧10⁻⁸ m²s⁻¹ for A samples, 2.76‧10⁻⁸ m²s⁻¹ and 7.62‧10⁻⁸ m²s⁻¹ for P samples depending on the substituent. Likewise, thermal effusivity (ε) changes from 474 Ws^1/2m⁻²K⁻¹ to 532 Ws^1/2m⁻²K⁻¹ for A, and from 473 Ws^1/2m⁻²K⁻¹ to 564 Ws^1/2m⁻²K⁻¹ for P samples. The volumetric heat capacity (C_v) and in-depth thermal conductivity (κ) were calculated on the base of PTR results. Local κ obtained from SThM measurements is between 0.15 Wm⁻¹K⁻¹ and 0.22 Wm⁻¹K⁻¹ due to different substituents and polymer system. Thermal studies performed in this work provide valuable information for engineers designing azobenzene polymer thin films based devices and supplement the knowledge of their thermal behavior in the system.