Surface modification of poly(tetrafluoroethylene) by remote hydrogen plasma

The kinetics of hydrogen plasma in an afterglow region has been simulated to distinguish remote plasma treatment from conventional (direct) plasma treatment. A simulation shows the possibility that remote hydrogen plasma treatment can enhance interaction reactions with hydrogen radicals relative to those with electron and hydrogen ions. Practically, hydrogen substitution processes in the PTFE sheet by remote and direct hydrogen plasma treatments have been investigated by means of contact angle measurement and XPS. The hydrogen plasma makes the surface of the PTFE sheet hydrophilic. The hydrophilicity depends on the sample position as well as the rf power and the plasma exposure time. The sample position strongly influences the hydrophilicity. The remote hydrogen plasma leads to higher hydrophilicity than the direct hydrogen plasma. The F/C atom ratio for the remote hydrogen-plasma-treated PTFE sheet is 0.41 and that for the direct hydrogen-plasma-treated PTFE sheet is 0.60. The main product of the substitution atoms by remote and direct hydrogen plasma treatments is a dihydrogen-substituted carbon unit and reaches 63% and 55% of the total carbon, respectively. The substitution proceeds at least 3.4 nm from the surface of the PTFE sheet. Remote hydrogen plasma treatment especially accomplishes complete substitution (the F/C atom ratio is 0). These experimental results show the accuracy of the simulation regarding the kinetics of the remote hydrogen plasma.