Jp. Kampf et al., Stability and molecular conformation of poly(benzyl ether) monodendrons with oligo(ethylene glycol) tails at the air-water interface, LANGMUIR, 15(1), 1999, pp. 227-233
Room-temperature film balance measurements were used to study the monolayer
stability and molecular conformation of third- through fifth-generation po
ly(benzyl ether) monodendrons with linear oligo(ethylene glycol) tails at t
he air-water interface. All the third- and fourth-generation monodendrons s
tudied formed stable Langmuir films, but the fifth-generation monodendrons
were not stable at 20 degrees C. Monolayers of the smaller dendritic molecu
les experienced a repeatable collapse to a multilayer upon sufficient compr
ession. Longer hydrophilic tails increased the stability of the Langmuir fi
lms. For third- and fourth-generation monodendrons each additional ethylene
oxide repeat unit in the tail increased the collapse pressure by 3.1 and 4
.1 mN/m, respectively. The molecular area of the monodendrons at the air-wa
ter interface increased linearly with molecular weight. Using a simplified
cylindrical model, we determined that the dendritic molecules take a vertic
ally elongated shape at the water surface and become flatter as the generat
ion increases. The diameter-to-height ratio ranged from 1/3 to 2/3 for mono
dendrons of generation three through five.