Loss and recovery of hydrophobicity, surface energies, diffusion coefficients and activation energy of nylon

The loss of hydrophobicity of nylon 6/6 caused by immersion in saline water for up to 336 h at different conductivities (0.005 to 100 mS/cm) and diffe rent temperatures (0 to 98 degrees C) and its subsequent recovery in air (d uring 4500 h) have been investigated. The hydrophobicity is determined by m easuring the static contact angle theta between the tangent to a droplet of distilled water and the horizontal surface. The changes in the surface rou ghness and in the weight of the specimens were determined and correlated wi th the changes in the contact angle. It has been found that theta decreased with increasing conductivity and increasing temperature of the saline solu tion. After removal from the solution, the higher the conductivity and temp erature, the longer it took for theta to recover in air. theta decreased fr om 70 degrees to 54 degrees after nylon was subjected for 521 h to a unifor m field of 15 kV(dc)/cm in air. The surface free energy of nylon was determ ined as a function of time of immersion, the conductivity and temperature o f the solution and during the recovery in air. The surface energies calcula ted for the virgin specimen are in good agreement with the literature. The diffusion coefficient of water into nylon increased from 0.23x10(-12) m(2)/ s at 23 degrees C to 7.4x10(-12) m(2)/s at 75 degrees C. The activation ene rgy was determined to be 59.4 +/- 2.2 kJ/mol. For unaged nylon the surface energies were determined at 23 degrees C to be gamma(S) = 44.7 mJ/m(2), gam ma(SD) = 29.3 mJ/m(2), gamma(SH) = 15.4 mJ/m(2), W-SL = 97.7 mJ/m(2) and ga mma(SL) = 19.8 mJ/m(2). These symbols have their usual meanings and are def ined in the text.