InkJet Printable Self-Cleaning Materials

Self-cleaning polymeric materials can be a very advantageous solution for covering solar cells, whose service life and efficiency can be enhanced by preventing accumulation of dust and filth that can cause the loss of incident light through scattering or light absorption, on cell covers. Sulfonated Polyethersulfone (SPES), a totally amorphous polymer, is characterized by excellent thermal and UV resistance, optical features, chemical stability, oxidation resistance, as well as by good mechanical properties and easy processability, i.e. for the production of films. Ionic Liquids (I.Ls.), a class of molten salts, have excellent thermal stability and their physical-chemical properties can be modulated changing the nature of the cation or anion. Modulating cationic apolar groups can dramatically influence the tendency of I.L. towards efficient ion packing and, in turn, its hydrophobic features, e.g. the longer the alkyl chains, the more hydrophobic the salt. In this work, SPESs with different concentrations of sulfonic acid moiety, expressed as degree of sulfonation (DS), were successfully synthesized via homogeneous synthesis using a sulfonated co-monomer. The wetting properties of SPES were modulated by introducing different cationic apolar groups, substituted by alkyl chains characterized by increasing length, through a novel ionic exchange reaction between the K+ cation of the sulfonic moiety of SPES and the cation of imidazolinium based I.Ls. The hydrophobic properties of SPESs treated with I.Ls. were found to improve with the DS of SPES, i.e. with the number of K+ ions available for substitution by the hydrophobic I.Ls. cations, obtaining contact angles up to 130° (θ), leading therefore to self-cleaning surfaces. Several techniques were used to characterize the films obtained: thermal properties were characterized by Differential Scanning Calorimetry (DSC); wettability and morphology were studied by static contact angle measurement (SWCA), Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Easy processability of SPES due to its viscosity and surface energy makes it a good material for the production of films through InkJet printer technology, a very simple and economic deposition technique.