PDMS/TiO2 and PDMS/SiO2 Nanocomposites: Mechanical Properties’ Evaluation for Improved Insulating Coatings

Abstract

The use of nanoparticles (NPs) as reinforcements in polymeric coatings allows for direct interaction with the polymeric chains of the matrix, resulting in a synergistic process through physical (electrostatic forces) and chemical interactions (bond formation) for the improvement of the mechanical properties with relatively low weight concentrations of the NPs. In this investigation, different nanocomposite polymers were synthesized from the crosslinking reaction of the hydroxy-terminated polydimethylsiloxane elastomer. Different concentrations (0, 2, 4, 8, and 10 wt%) of TiO2 and SiO2 nanoparticles synthesized by the sol-gel method were added as reinforcing structures. The crystalline and morphological properties of the nanoparticles were determined through X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The molecular structure of coatings was through infrared spectroscopy (IR). The crosslinking, efficiency, hydrophobicity, and adhesion degree of the study groups were evaluated with gravimetric crosslinking tests, contact angle, and adhesion tests. It was observed that the crosslinking efficiency and surface adhesion properties of the different nanocomposites obtained were maintained. A slight increase in the contact angle was observed for the nanocomposites with 8 wt% compared to the polymer without reinforcements. The mechanical tests of indentation hardness and tensile strength following the ASTM E-384 and ISO 527 standards, respectively, were performed. As the nanoparticle concentration increased, a maximum increase of 157% in Vickers hardness, 71.4% in elastic modulus, and 80% in tensile strength was observed. However, the maximum elongation remained between 60 and 75%, ensuring that the composites did not become brittle.

A Novel In Situ Sol-Gel Synthesis Method for PDMS Composites Reinforced with Silica Nanoparticles

“…Variations in species concentration between the two particle types are crucial as they will coexist with PDMS during in situ synthesis. Unlike previous studies where sol-gel by-products were eliminated through thermal treatments or filtration for chemical characterization [ 29 ], this analysis required the identification of all present species to identify those that will not be removed during the in situ process.…”

“…To ascertain the physicochemical characteristics of the components that constituted the polymeric composites, the synthesis of SiO 2 nanoparticles was conducted by employing the Stöber method [ 26 , 27 ] and a previously developed methodology in our research group [ 28 , 29 ] for both acidic and alkaline media.…”

“…The in situ synthesis of PDMS-%SiO 2 nanocomposites was carried out utilizing the sol-gel method and the crosslinking reaction of the hydroxyl-terminated PDMS matrix using magnetic and ultrasonic stirring techniques, as detailed in prior publications [ 28 , 29 ]. The synthesis initiates with a solution of acetone and the PDMS with a 1:0.6 weight ratio (PDMS: C 3 H 6 O).…”

“…Mechanical stirring was applied to homogenize the solution for 1 h. TEOS was added according to the desired nanoparticle concentration (0%, 5%, 10%, and 15% by weight). The reported particle concentration values were derived from the weight particle yields obtained during the SiO 2 sol-gel synthesis process and previous research [ 29 ]. Through this in situ synthesis, the concentration represented a categorical variable that denotes a relative number of particles incorporated within the composite.…”

Synthesis of a water-based TEOS–PDMS sol–gel coating for hydrophobic cotton and polyester fabrics

“…12 Additionally, TEOS–PDMS coatings can be used for the protection of concrete-based cultural heritage buildings, automotive coatings, and insulating coatings. 13–15…”