Nanophase separation of polymers exposed to simulated bonding conditions.

Under in vivo conditions, there is little control over the amount of water left on the tooth during dentin bonding. As a result, it is possible to leave the dentin surface so wet that the adhesive actually undergoes physical separation into hydrophobic- and hydrophilic-rich phases. Using tapping mode atomic force microscopy/PhaseImaging technique, nanosized phases with worm-like features were found on the surface of model HEMA/BisGMA dentin adhesives cured in the presence of varying concentrations of water. The phase contrast became evident with the increase of water concentration in the initial adhesive formulation and varied with the ratio of hydrophilic/hydrophobic composition. Oversaturated water droplets of variable sizes may accumulate as micro-voids within the hydrophilic and hydrophobic polymer phases. The phase domains were also identified following ethanol-etching in combination with SEM/AFM techniques.