氧等离子体改性聚乙烯表面的疏水性过回复机制

用200 W射频容性耦合氧等离子体处理低密度聚乙烯(LDPE)表面1 min, 研究了老化温度及时间对LDPE表面成分、 形貌和润湿性的影响. 扫描电子显微镜结果表明, 等离子体改性LDPE表面出现纳米凸点织构, 在60和90 ℃老化24 h后纳米凸点织构特征基本保持稳定. X射线光电子能谱分析表明, 等离子体改性LDPE表面经60 ℃老化24 h后, C—C含量由76.9%增至83.0%, C—O, CO和O—CO含量分别由16.4%, 2.2%和4.5%降至13.1%, 1.9%和2.0%. 经90 ℃老化24 h后, C—C含量较60 ℃老化表面增至84.1%, C—O含量分别降至10.1%, CO和O—CO含量分别增至3.1%和2.7%. 等离子体改性LDPE表面接触角由97.2°降至42.3°, 经60 ℃老化24 h后接触角增至95.9°, 经90 ℃老化24 h后接触角增至104.2°, 等离子体改性LDPE表面发生“疏水性过回复”. 根据含有粗糙因子的接触角随时间演变模型, 得到了具有纳米凸点织构LDPE表面在不同老化温度下的可移动极性基团所占面积分数(\begin{array}{c}{f}_m^p\end{array})、 固定极性基团所占面积分数(\begin{array}{c}{f}_{\mathit{im}}^p\end{array})和特征时间常数(τ)3个成分重构参数, 解释了“疏水性过回复”现象.

Mechanism of Hydrophobic Over-recovery on Polyethylene Surface Modified by Oxygen Plasma†

Low density polyethylene(LDPE) surface was modified by oxygen capacitively coupled plasma(CCP) under a radio frequency(RF) power of 200 W for an exposure time of 1 min. The aging process of the plasma-modified LDPE was studied at aging temperatures of 60 and 90 ℃ for an aging time of 24 h. The morphology with the nanonodules was obtained on the as-modified LDPE surface under 200 W for 1 min and was stable on the post-aged LDPE surface at 60 and 90 ℃ after 24 h. The plasma modification under 200 W for 1 min introduced lots of polar oxygen-containing groups on the as-modified LDPE surface. The aging process at 60 ℃ after 24 h aroused the decrease of the polar oxygen-containing groups on the post-aged LDPE surface and lower oxygen-containing group content appeared on the post-aged surface at 90 ℃. The as-modified hydrophi-lic surface with the contact angle of 42.3° underwent the hydrophobic recovery into hydrophobicity on the post-aged surface with the contact angle of 95.9° at 60 ℃ after 24 h similar to the original LDPE surface with 97.2°, and further hydrophobic over-recovery into higher hydrophobicity of the post-aged surface with the contact angle of 104.2° at 90 ℃ after 24 h than the original surface. Based on the time-dependent contact angle model for the aging of the rough surface containing different wetting patches, the surface restructuring on the plasma-modified LDPE surface experiencing the hydrophobic over-recovery during aging process was quantitatively analysized.