Chemical Surface Modification of Polycarbonate to Increase Hydrophilicity

Abstract

Polycarbonate, commonly used in glasses lenses, is prone to fogging. Fogging can be reduced by modifying the structure of polycarbonate to be more hydrophilic, ideally superhydrophilic with a contact angle less than 10°. Many chemicals were tested to see if they could increase the polarity of polycarbonate. Polycarbonate was partially submerged in pure chemicals for 2 hours at room temperature to determine its chemical compatibility. Compounds with aromatic rings, like aniline, altered the appearance of polycarbonate. Amines qualitatively reduced the contact angle when compared to untreated polycarbonate. p-Phenylenediamine (PPD) is an aromatic amine commonly used in hair dyes. Polycarbonate was submerged in PPD solution, heated, rinsed in DI water, and dried with air. Contact angles were taken using the sessile method on an optical tensiometer. Temperature, reaction time, concentration, solvent, and oxidation levels were varied to determine optimal reaction conditions. Using 0.01 wt% PPD at 80 ℃ for 2 hours, contact angles were reduced to 33°, but PPD dyed polycarbonate and left a residual polymer on its surface. Alternatively, polycarbonate was submerged in poly(ethylene imine) (PEI) solution, heated, rinsed in DI water, and dried with air. Afterwards, polycarbonate was submerged in poly(acrylic acid-co-maleic acid) (PAA-MAA) solution, heated, rinsed in DI water, and dried with air. PEI introduced more amine groups than PPD, and PAA-MAA uses those amine groups to expose more polar carboxylic acid groups. PEI and PAA-MAA were tested by varying reaction conditions such as temperature, reaction time, and concentration to optimize hydrophilicity. Using 1 wt% PEI at 100 ℃ for 30 minutes and 1 wt% PAA-MAA at 100 ℃ for 90 minutes, contact angles were reduced to 3° and preserved transparency. Using the two-step method with PEI and PAA-MAA, the surface of polycarbonate became superhydrophilic and retained transparency.