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 different temperatures (0 to 98/spl deg/C) and its subsequent recovery in air (during 4500 h) have been investigated. The hydrophobicity is determined by measuring the static contact angle /spl theta/ between the tangent to a droplet of distilled water and the horizontal surface. The changes in the surface roughness and in the weight of the specimens were determined and correlated with the changes in the contact angle. It has been found that /spl theta/ decreased with increasing conductivity and increasing temperature of the saline solution. After removal from the solution, the higher the conductivity and temperature, the longer it took for /spl theta/ to recover in air. /spl theta/ decreased from 70/spl deg/ to 54/spl deg/ after nylon was subjected for 521 h to a uniform field of 15 kV/sub dc//cm in air. The surface free energy of nylon was determined as a function of time of immersion, the conductivity and temperature of the solution and during the recovery in air. The surface energies calculated for the virgin specimen are in good agreement with the literature. The diffusion coefficient of water into nylon increased from 0.23/spl times/10/sup -12/ m/sup 2//s at 23/spl deg/C to 7.4/spl times/10/sup -12/ m/sup 2//s at 75/spl deg/C. The activation energy was determined to be 59.4/spl plusmn/2.2 kJ/mol. For unaged nylon the surface energies were determined at 23/spl deg/C to be /spl gamma//sub S/=44.7 mJ/m/sup 2/, /spl gamma//sub SD/=29.3 mJ/m/sup 2/, /spl gamma//sub SH/=15.4 mJ/m/sup 2/, W/sub SL/=97.7 mJ/m/sup 2/ and /spl gamma//sub SL/=19.8 mJ/m/sup 2/.