Formation of dispersed nanostructures from poly(ferrocenyldimethylsilane-b-dimethylsiloxane) nanotubes upon exposure to supercritical carbon dioxide.
While incompatible block copolymers commonly assemble into several established classical or complex morphologies, highly asymmetric poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS-b-PDMS) diblock copolymers can also self-organize into high-aspect-ratio nanotubes with PDMS corona in the presence of PDMS-selective organic solvents. Exposure of these nanotubes on a carbon substrate to supercritical carbon dioxide (scCO2), also a PDMS-selective solvent, appears to promote partial dissolution of the copolymer molecules. At sufficiently high copolymer concentrations, the dissolved molecules subsequently re-organize within the scCO2 environment to form new copolymer nanostructures that redeposit on the substrate upon scCO2 depressurization. Transmission electron microscopy reveals that micelles form under all the conditions examined here, whereas nanotubes coalesce and vesicles develop only at relatively high temperatures. The extent to which the copolymer nanotubes dissolve and the size distribution of the replacement micelles are sensitive to exposure conditions. These results suggest that the phase behavior of PFS-b-PDMS diblock copolymers in scCO2 may be remarkably rich and easily tunable.
Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA.
David J
DJ
Frankowski
Jose
J
Raez
Ian
I
Manners
Mitchell A
MA
Winnik
Saad A
SA
Khan
Richard J
RJ
Spontak
D002245:Carbon Dioxide / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry*; D043942:Nanotubes / Q000737:chemistry; D017646:Organosilicon Compounds / Q000737:chemistry*; D010316:Particle Size; D011312:Pressure; D012833:Siloxanes / Q000737:chemistry*; D013499:Surface Properties
D005296:Ferrous Compounds; D017646:Organosilicon Compounds; D012833:Siloxanes; C509667:poly(ferrocenyldimethylsilane-b-dimethylsiloxane); D002245:Carbon Dioxide