Interfacial micellar structures from novel amphiphilic star polymers.
An amphiphilic heteroarm star polymer containing 12 alternating hydrophobic/hydrophilic arms of polystyrene (PS) and poly(acrylic acid) (PAA) connected to a well-defined rigid aromatic core was studied at the air-water and the air-solid interfaces. At the air-water interface, the molecules spontaneously form pancakelike micellar aggregates which measure up to several microns in diameter and 5 nm in thickness. Upon reduction of the surface area per molecule to 7 nm2, the two-dimensional micelles merged into a dense monolayer. We suggest that confined phase separation of dissimilar polymer arms occurred upon their segregation on the opposite sides of the rigid disklike aromatic core, forcing the rigid cores to adopt a face-on orientation with respect to the interface. Upon transfer onto solid supports the PS chains face the air-film interface making it completely hydrophobic, and the PAA chains were found to collapse and form a thin flattened underlayer. This study points toward new strategies to create large 2D microstructures with facial amphiphilicity and suggests a profound influence of star molecular architecture on the self-assembly of amphiphiles at the air-water interface.
Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA.
Kirsten L
KL
Genson
Joshua
J
Hoffman
Jing
J
Teng
Eugene R
ER
Zubarev
David
D
Vaknin
Vladimir V
VV
Tsukruk
D000180:Acrylic Resins / Q000737:chemistry*; D000388:Air; D008823:Micelles; D008958:Models, Molecular; D015394:Molecular Structure; D010316:Particle Size; D011137:Polystyrenes / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
D000180:Acrylic Resins; D008823:Micelles; D011137:Polystyrenes; D014867:Water; C006903:carbopol 940