Time-of-flight secondary ion mass spectrometry study of the orientation of a bifunctional diblock copolymer attached to a solid substrate.
A block copolymer consisting of a phosphate-containing moiety (poly[2-(methacryloyloxy)ethyl phosphate], PMOEP) and a keto-containing moiety (poly[2-(acetoacetoxy)ethyl methacrylate], PAAEMA) showed good stability after attachment to an APS amine-modified glass slide, as did both of the respective homopolymers. The PAAEMA homopolymer can attach to the APS amine groups via covalent linkages, while the PMOEP homopolymer most likely attaches through electrostatic interactions involving deprotonated phosphate and protonated amine groups. To elucidate the conformation of the block copolymer after attachment, particularly with respect to the PMOEP segment orientation, principal component analysis (PCA) of time-of-flight secondary ion mass spectrometry (ToF-SIMS) spectra of the surface-attached polymer layers was performed. Comparison with the pure homopolymer spectra and interpretation after PCA indicate that the adsorbed conformation is not random. Rather, the copolymer is adsorbed in a conformation that preferentially exposes the PMOEP block toward the outer surface. We thus conclude that the most likely conformation of PMOEP-b-PAAEMA immobilized onto the APS-modified glass slide is via covalent interfacial linkages involving the PAAEMA block with the result that the surface is enriched in PMOEP tails. This in turn implies that under the conditions applied (dry DMF) the covalent coupling of keto groups to the amine groups of the aminated slide is more efficient than the proton transfer required for the generation of electrostatic attractions. This (partially) preferential orientation of the PMOEP-b-PAAEMA copolymer could have significant implications on interfacial interactions such as those involved in nucleation and the subsequent mineralization sequence of events in hydroxyapatite formation. The present study demonstrates that ToF-SIMS is a powerful tool not only for the investigation of the surface composition of adsorbed layers, but also for probing the molecular conformation of such adsorbed block copolymers, though care is required in the PCA analysis of multiple spectra.
Jasieniak
Marek
M
Ian Wark Research Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia.
Suzuki
Shuko
S
Monteiro
Michael
M
Wentrup-Byrne
Edeline
E
Griesser
Hans J
HJ
Grøndahl
Lisbeth
L
D000588:Amines / Q000737:chemistry; D005898:Glass / Q000737:chemistry; D008689:Methacrylates / Q000737:chemistry*; D015394:Molecular Structure; D010710:Phosphates / Q000737:chemistry; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D011109:Polymethacrylic Acids / Q000737:chemistry*; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods; D013053:Spectrophotometry; D014965:X-Rays
C454021:2-(methacryloyloxy)ethyl phosphate; D000588:Amines; D008689:Methacrylates; D010710:Phosphates; D011108:Polymers; D011109:Polymethacrylic Acids; C535266:poly(2-(acetoacetoxy)ethyl methacrylate)