Crosslinking vs. interdiffusion rates in melamine-formaldehyde cured latex coatings: A model for waterborne automotive basecoat

Characterisation of Electrical and Stiffness Properties of Conductive Textile Coatings with Metal Flake-Shaped Fillers

Two conductive formulations containing different types of micron-sized metal flakes (silver-coated copper (Cu) and pure silver (Ag)) were characterised and used to form highly electrically conductive coatings (conductors) on plain and base-coated woven fabrics, the latter in an encapsulated construction. With e-textiles as the intended application, the fabric stiffness, in terms of flexural stiffness and sheet resistance (R_sh), after durability testing (laundering and abrasion) was investigated and related to user friendliness and long-term performance. Bare and encapsulated conductors with increasing amounts of deposited solids were fabricated by adjusting the knife coating parameters, such as the coating gap height (5, 20, 50, and 200 μm), which reduced the R_sh, as determined by four-point probe (4PP) measurements; however, this improvement was at the expense of increased flexural stiffness of the coated fabrics. The addition of a melamine derivative (MF) as a cross-linker to the Cu formulation and the encapsulation of both conductor types gave the best trade-off between durability and R_sh, as confirmed by 4PP measurements. However, the infrared camera images revealed the formation of hotspots within the bare conductor matrix, although low resistances (determined by 4PP) and no microstructural defects (determined by SEM) were detected. These results stress the importance of thorough investigation to assure the design of reliable conductors applied on textiles requiring this type of maintenance.

Smart polymer nanoparticles for high-performance water-borne coatings

Poly(butyl methacrylate) nanoparticles encapsulating a silica precursor, tetraethoxysilane (TEOS), were synthesized by a two-step emulsion polymerization process. We show that TEOS remains mostly unreacted inside the nanoparticles in water but acts both as a plasticizer and cross-linker in films cast from the dispersions. The diffusion-enhancing plasticizing effect is dominant at annealing temperatures closer to the glass-transition temperature of the polymer, and sol-gel cross-linking reactions predominate at higher temperatures. By choosing an appropriate annealing temperature, we were able to balance polymer interdiffusion and silica cross-linking to obtain films with good mechanical properties and excellent chemical resistance. The hybrid cross-linked films produced from these novel "smart" nanoparticles can be used in water-borne environmentally friendly coatings for high-performance applications.

Synthesis and pH-Selective Adsorption of Latex Particles onto Photolithographically Patterned Silane Layers

Surface structures of charged latex particles on patterned surface layers were obtained by a colloidal self-assembly process. The laterally patterned silane layers were prepared on silica surfaces by vapor phase and solution deposition of silanes in combination with photolithography. The monodisperse latex particles used in the self-assembly experiments were synthesized by emulsion polymerization to yield poly-n-butylmethacrylate spheres (217 nm diameter) and poly-n-butylacrylate microgels (155 nm). Both particle types possessed a high surface concentration of free carboxylic acid groups as quantified by polyelectrolyte titration under shear flow. Depending on the pH, the particles assembled onto the hydrophobic surface regions (pH 9) or onto the hydrophilic regions (pH 5). Highest selectivity and pattern quality was obtained with permanently positively charged silane layers (quaternary ammonium salts) onto which the negatively charged colloid particles adhered strongly by Coulomb interaction.