Amino-functionalized silicones processed as porous dual covalent/ supramolecular networks for pressure sensing

Polysiloxanes, pendant functionalized with aminopropyl groups and having silanol chain ends, were used as the frameworks to obtain porous networks, in the presence of certain additions. The porosity was achieved by the thermal decomposition gases of ammonium bicarbonate as chemical blowing agent (CBA), in the presence of acetic acid. The latter promotes at the same time covalent cross-linking of the polymer by condensing the silanol chain ends with tetraethoxysilane, thus eliminating the need to add an organometallic catalyst, often used for this purpose. In the presence of CO2 generated during the CBA decomposition, thermally reversible supramolecular ammonium carbamate bridges are also formed between the chains, thus leading to dual covalent/supramolecular cross-linked silicone networks, and increasing the degree of crosslinking. In addition, the presence of the polar groups leads to a rise in the dielectric permittivity of the porous and flexible materials, resulting in a significant increase in the electrical output signal when these are subjected to compression. The materials exhibited stable capacitance variation with a response sensitivity of about 0.01 kPa-1, in the pressure range 0-50 kPa, making them suitable for capacitive pressure sensors.