RESUMO
The influence of the dispersion states of the nanofillers on the dewetting behavior of the polymer thin film was investigated. Polyhedral oligomeric silsesquioxanes (POSS) with various substituents were added into polystyrene (PS) thin films as the nanofillers. The dewetting rate of the films drastically changed with the surface substituents of POSS additives. Neutron reflectivity measurements indicated that the difference of the dewetting rate was associated with the dispersion state of POSS additives in the films. POSS with phenethyl groups (PhPOSS), which homogeneously dispersed into the films, resulted in the decrease of the glass transition temperature of PS and the enhancement of the dewetting of the films. POSS with a fluoroalkyl group (CpPOSS-R f) segregated to the film surface and showed the retardation of the dewetting by the decrease of the surface energy of the film. POSS with hydroxyl groups (CpPOSS-2OH) segregated to the film surface and film-substrate interface and led to the elimination of the dewetting, suggesting the importance of the interfacial segregation for the inhibition of dewetting. These results revealed the strong relationship between the dispersion state of the nanofillers and the dewetting of the nanofilled films.
RESUMO
Polyhedral oligomeric silsesquioxane (POSS) meets increasing interest as a building unit for inorganic-organic hybrid materials. The incorporation of cyclopentyl-substituted POSS (CpPOSS) into polystyrene (PS) thin films led to an inhibition of dewetting. In this paper, the dispersion state of CpPOSS in the CpPOSS/PS hybrid films and, furthermore, the relationships between the structure and dewetting inhibition effect are discussed. Structural analysis of the hybrid films revealed that CpPOSS segregated to the film surface and crystallized. The segregation of CpPOSS to the surface changes the surface free energy and spreading coefficient of the film. Interfacial structure was also roughened by the segregation of CpPOSS, which can contribute to the inhibition of dewetting by pinning the contact line of the PS film with the substrate. The inhibition of dewetting can be attributed to the modification of the film surface and interface by the segregation of CpPOSS.
RESUMO
Super-hydrophilic polymer brushes were prepared by surface-initiated atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) on initiator-immobilized silicon wafers. The graft density was estimated to be 0.22 chains nm based on the linear relationship between and the layer thickness. The contact angle against water was very low, and air bubbles in water hardly attached onto the brush surface, indicating a super-hydrophilic surface. Neutron reflectivity measurements of the poly(MPC) brush showed that the grafting polymer chains extended a fair amount in the vertical direction from the substrate in a good solvent such as water, while they shrunk in a poor solvent. Frictional properties of the poly(MPC) brushes were characterized by sliding a glass ball probe in air and various solvents under a load of 0.49 N at a sliding velocity of 90 mm min. An extremely low friction coefficient of the poly(MPC) brush was observed in humid atmosphere because water molecules adsorbed into the brush layer acted as a lubricant.
