The surface properties of polymer thin films are important in many industrial applications. The free surface, polymer-substrate interactions and environmental conditions can impart dramatic effects on the properties of thin films. Many researches have studied various polymers and indicated that a surface glass transition temperature (T_g^s) exists at a temperature below or above its bulk glass transition temperature (T_g ). This thesis aims to develop a novel technique to determine this transition temperature using temperature-programmed time-of-flight secondary ion mass spectrometry (ToF-SIMS).

Firstly, ToF-SIMS spectra of polystyrene (PS) films supported on silicon wafers were obtained at various temperatures. Principal component analysis (PCA) of the ToF-SIMS data revealed a t...[ Read more ]

The surface properties of polymer thin films are important in many industrial applications. The free surface, polymer-substrate interactions and environmental conditions can impart dramatic effects on the properties of thin films. Many researches have studied various polymers and indicated that a surface glass transition temperature (T_g^s) exists at a temperature below or above its bulk glass transition temperature (T_g ). This thesis aims to develop a novel technique to determine this transition temperature using temperature-programmed time-of-flight secondary ion mass spectrometry (ToF-SIMS).

Firstly, ToF-SIMS spectra of polystyrene (PS) films supported on silicon wafers were obtained at various temperatures. Principal component analysis (PCA) of the ToF-SIMS data revealed a transition temperature (T_T) at which the surface structure of PS was rearranged. The T_Ts of 120 nm thick PSs with different molecular weights were approximately 30 ℃ lower than their bulk T_g s . As the T_T is dependent on the molecular weight and strongly related to the T_g , it is believed that the T_T determined by ToF-SIMS is related to the T_g^s . Furthermore, the detailed PCA analysis indicated that the phenyl groups of PS tended to move away from the surface at temperatures above T_T , and the results were confirmed by contact angle measurements and X-ray photoelectron spectroscopy (XPS).

Secondly, the mobility of polymer segments at the free surface was further analyzed using poly (2, 3, 4, 5, 6-pentafluorostyrene) (5FPS) at various temperatures. A detailed analysis of ToF-SIMS spectra indicated that the fragmentation processes for PS and 5FPS are very similar, but the pendant groups of 5FPS and PS moved in exactly opposite directions as the temperature increased. The concentration of the end-group ions increased significantly at temperatures above T_T . This information can also be used to determine T_g^s .

In summary, this study demonstrated the capability of ToF-SIMS combined with PCA in determining the surface glass transition temperatures