## 1 Introduction  
Corrosion is the process of the irreversible surface disintegration of metals or their alloys caused by their interaction with an aggressive environment. Common types of corrosion include rusting, which occurs when iron or steel is exposed to moisture and oxygen, and pitting corrosion, which creates small holes in the metal surface. Preventative actions can be taken to protect materials against corrosion, e.g., applying protective coatings or using corrosion-resistant materials. The corrosion resistance of a material determines its operational lifetime; thus, considerable efforts are made to develop new classes of anti-corrosion layers, including organic-inorganic compounds, to improve material protection against the detrimental effects of the external environment [1]. Siloxane-polyacrylamide-based coatings, Si-PxMA (where x is the type of acrylic monomer: M = methyl, E = ethyl, B = butyl, etc. ), were found to be promising as coatings that provide high corrosion resistance for metals and their alloys while also ensuring good adhesion to the surface [2, 3]. These properties make such a coating an effective barrier that prevents corrosive species from penetrating the material. The anti-corrosion properties can be improved by modifying the composition of the basic hybrid material [4] or by decreasing the length of the alkyl chain in the siloxane-polyacrylamideic sol-gel structure [5], which enhances its reliability and durability when applied in devices working in aqueous media. It has been found that Si-PxMA coatings with short alkyl chains, such as ethyl- and butyl-, have relatively good anti-corrosionproperties, whereas Si-PxMA coatings with longer alkyl chains present rather poor corrosion properties [6; 7]. The goal of our study is to use the Photothermal Radiometry [8; 9] and Beam Deflection Spectroscopy [10; 11; 12] methods for the thermal characterization of Si-PBMA coatings and make a comparison of the advantages and disadvantages of these methods in the investigation of the discussed layers. Photothermal Radiometry is a powerful tool for material characterization and defect detection, offering nondestructive evaluation capabilities across various fields. This method involves the pulsed illumination of a sample with monochromatic radiation and the detection of the consequent thermal radiation emitted by the sample [13; 14; 15]. PTR provides nondestructive, non-contact, reliable, and fast coating characterization with high in-plane and through-plane resolution. It has been applied to determine a coating's thickness, adhesion strength, hardness depth and profile, residual stress, etc. [16; 17]. The PTR method is well known for its applications in the investigation of the parameters of semiconductor materials [18; 19; 20; 21; 22; 23; 24]. Photothermal beam deflection spectrometry is a non-contact technique for advanced material characterization that provides information about the thermal and related properties of materials [25; 26]. It is based on periodic sample illumination and generates temperature oscillations in the sample itself and further in its surroundings by converting the absorbed energy into heat through different radiationless de-excitation processes that occur in the illuminated material. As a result, the refractive index changes, and its gradient is induced in the fluid layer over the sample's illuminated surface, which is sensed by the probe laser beam, causing its deflection and phase change [27; 28; 29]. Beam deflection spectrometry provides the highly sensitive and accurate detection of subtle changes in material properties, including porous [30], amorphous [31], and bulk [32] materials. It is also applicable to thin films, layered structures, and nanomaterials [33]. The potential of beam deflection spectrometry has even been used in pharmaceutical applications [34].