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Scalable Sensing Membrane for Structural Health Monitoring of Mesosystems
Published in Jayantha Ananda Epaarachchi, Gayan Chanaka Kahandawa, Structural Health Monitoring Technologies and Next-Generation Smart Composite Structures, 2016
Simon Laflamme, Filippo Ubertini
To fabricate a sensor, a waterborne castor oil–based polyurethane dispersion (PUD) is first synthesized by a reaction of isophorone diisocyanate, castor oil, and dimethylol propionic acid (DMPA) as internal surfactant. The DMPA is used to incorporate carboxylic functionality in the prepolymer backbone. Tertiary amine (e.g., triethylamine and TEA) is added to neutralize the carboxylic groups and produce ionic centers, which stabilizes the polymer particles in water. Titania particles are dispersed in the PUD to increase the permittivity and mechanical robustness. An SEC is finally fabricated by sandwiching the dielectric with two conductive electrodes fabricated from a carbon black and SEBS mix. The replacement of electrodes by castor oil–based PUDs is currently being investigated by the authors. Figure 1.10 shows the SEM images of three samples fabricated with various titania content. The uncoated titania particles tend to sink within the matrix, but a closer look at the dense titania region (Figure 1.10b) shows that the particles are well dispersed. This nonuniformity of the dispersion along the thickness of the dielectric does not affect the sensing capabilities of the SEC due to its planar applications. Current research is being conducted by the authors to ameliorate the dispersion of titania along the entire volume of the sensor.
Waterborne polyurethanes: A review
Published in Journal of Dispersion Science and Technology, 2018
Changes in the nature of the polyols, di-isocyanates, and catalysts or other additives allow the user to synthesize different end-polymers. Generally, the properties of the polyurethanes are very good. These include chemical, abrasion, and scratch resistance, as well as flexibility and toughness. Normally, most types of polyurethane systems contain a large percentage of volatile organic compounds (VOCs) and, in some cases, a certain amount of free isocyanate. Organic solvents are toxic and pollute the environment. In the late 1960s, the system of aqueous polyurethane dispersions was introduced.[2] The waterborne polyurethane dispersion is a binary colloidal system in which the polyurethane particles are dispersed in a continuous aqueous medium. The concept of producing water-based polyurethanes is directed toward producing polymers with a high number of hydrophilic groups to obtain water solubility. Polyurethane is completely incompatible with water, which is why a special modification of the backbone is necessary. This idea is executed through the incorporation of hydrophilic monomers containing ionic functionality, including quaternary ammonium, carboxylate, or sulfonate groups. These ionic moieties are known as an internal emulsifier and polyurethane ionomers.[3] There are three major reasons for applying the waterborne polyurethanes. First, the administrative organization has emphasized on the reduction of solvent emission into the atmosphere. Second, the price of these solvents is high. But, perhaps most importantly, the quality of these waterborne polyurethanes has made them highly suitable for a wide range of applications.[4]