高压二氧化碳作用下聚苯乙烯薄膜表面链段运动研究

Surface Chain Segment Dynamics of Polystyrene under High Pressure Carbon Dioxide

采用改进的纳米孔洞愈合法考察了高压二氧化碳作用下聚苯乙烯薄膜表面的链段运动能力。研究表明,在高压二氧化碳作用下,纳米孔洞愈合到平衡深度所需要的时间大大降低,说明表层链段的运动能力大大增加,同时愈合的深度也有所增加,说明二氧化碳同样增加了具有高运动能力的表面层的厚度。利用薄膜表面层的高运动能力,在高压二氧化碳作用下对聚苯乙烯薄膜进行粘结,采用胶带剥离的方法定性地考察了粘结强度,同时采用原子力显微镜考察了粘结面的形貌特征。结果表明,真空及70℃作用下,聚苯乙烯薄膜无粘结,粘结面光滑;在2.07 MPa二氧化碳及70℃下,粘结膜经剥离后表面粗糙度为几个纳米,粘结强度较低;在相同压力的二氧化碳及80oC下,粘结膜经剥离后表面粗糙度为十几个纳米,具有一定的粘结强度。将具有高运动能力表面层厚度与粘结实验相对比,发现当具有高运动能力的表面层厚度超过约7.0 nm时,聚苯乙烯薄膜才具有一定的粘结强度,孔洞愈合法的实验结果能够很好地解释聚合物薄膜在不同条件下的粘结情况。

In this study, chain dynamics of polystyrene surface under high pressure carbon dioxide（CO2） wascharacterized by a modified nanohole recovery method. The results show that, under high pressure CO2, therecovery times for the nanoholes are significantly reduced, which indicates that the moving ability of the surfacechain segment is increased significantly. In addition, the thickness of the surface layer with high mobility isgreatly increased by higher pressure CO2, which was suggested by the decreased remaining depth of thenanoholes after the recovery. Applying this phenomenon, two PS thin films were bonded together at differenttemperatures with the assistance of high CO2 pressure. The bonding strength was qualitatively characterized byseparating the two bonded films with an adhesive tape, which shows that at 70℃ and under vacuum, no bondingoccurres and the separated contact surfaces are smooth. Under 2.07 MPa CO2 and at 70℃, the bonding strength islower, and the contact surface of bilayer sample shows a roughness with several nanometers. While under the sameCO2 pressure and at 80℃, the bonding strength is much higher and after separating, the contact surface of bilayersample has a higher roughness. Associating the thickness of the surface with high mobility under high CO2 pressurewith the bonding experiment results, it could be concluded that the two films could be well bonded only when thethickness of the surface with high mobility is more than 7.0 nm. The nanoholes recovery method could be applied topredict the bonding strength of bilayer samples bonded at different conditions.