The modification of magnesium implants with functional organic molecules is important for increasing the biological acceptance and for reducing the corrosion rate of the implant. In this work we evaluate by a combined experimental and theoretical approach the adsorption strength and geometry of a functional self-assembled monolayer (SAM) of hydrolyzed (3-aminopropyl)triethoxysilane (APTES) molecules on a model magnesium implant surface. In time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) only a minor amount of reverse attachment was observed. Substrate-O-Si signals could be detected as well as other characteristic APTES fragments. The stability of the SAM upon heating in UHV was investigated additionally. Density-functional theory (DFT) calculations were used to explore the preferred binding mode and the most favorable binding configuration of the hydrolyzed APTES molecules on the hydroxylated magnesium substrate. Attachment of the molecules via hydrogen bonding or covalent bond formation via single or multiple condensation reactions were considered.

(M.S. Killian, S. Seiler, V. Wagener, R. Hahn, C. Ebensperger, B. Meyer, P. Schmuki, ACS Appl. Mater. Interfaces 2015, 7, 9006.)

Electrode layers based on electroactive polymer poly(3,4-ethylenedioxythiophene) (Pedot) and carbon in the form of: i) carbon nanotubes (CNTs) or ii) graphene oxide (Gox) were deposited on platinum and fluorinated tin oxide substrates. Electrochemical synthesis was performed in the solution containing monomer and: i) carbon nanotubes and poly (sodium 4-styrenesulfonate (PSS) or ii) graphene oxide. Potentiostatic electrodeposition was carried out in a conventional three electrodes cell configuration (Pt counter electrode and Ag/AgCl reference electrode) with deposition charges between 0.2 to 0.4 C·cm^-2. The formation process allows to form 50 nm to 4 micrometer thick layers.

The samples were then analyzed with two mass spectrometry techniques, secondary ion mass spectrometry (SIMS) and glow discharge mass spectrometry (GD-MS). In both cases Ar⁺ ion bombardment was applied for depth profile analysis. SIMS analysis was performed on SAJW-05 [1] apparatus equipped with Physical Electronics 06-350E ion gun. Sputtering with 5 keV Ar⁺, 100 µm diameter ion beam was performed over 2 x 2 mm area of the samples with 15% electronic gate. Registered were negative secondary ions: 1 (H^-), 12 (C^-), 16 (O^-), 32 (S^-,O₂^-), 79 (C_xH_y^-), 44 (CS^-), 152 (SnO₂^-), 211 (PtO^-) and positive ions: 1 (H⁺).12 (C⁺), 16 (O⁺), 23 (Na⁺), 32 (S⁺, O₂⁺), 120 (Sn⁺), 195 (Pt⁺).

GD-MS analysis was performed in ~0.1 Torr Ar, 1.5 Kv DC glow discharge and SMWJ-01 [2] spectrometer was used. Positive ion currents of similar masses as chosen in SIMS were registered.

Obtained results allow us to monitor uniformity of obtained layers and their atomic composition related to technological parameters of their formation. Results allow us also to compare the techniques: SIMS and GD-MS. Discussion of the results concerns different sputtering conditions and sensitivity of the two techniques.

Acknowledgements

Authors (PK and MM) thank The National Centre for Research and Development Poland for project No PBS1/A9/9/2012 founded in years 2012 – 2015. MW and AD acknowledge the financial support from Norway Grants in the Polish-Norwegian Research Programme (Small Grant Scheme) operated by the National Centre for Research and Development, grant No POL-NOR/209673/9/2013.

References

[1] P. Konarski, A. Mierzejewska; Appl. Surf. Sci. 203–204, 354–358 (2003).

[2] P. Konarski, K. Kaczorek, M. Ćwil, J. Marks; Vacuum 81, 1323-1327 (2007).

Glass fiber reinforced plastic (GFRP) has been widely used as a replacement of metal owing to its high strength and toughness without sacrificing its lightweight. Basically, mechanical behavior of GFRP is highly dependent on the interphase of glass fiber and polymer matrix. Thus, analyzing the interphase of GFRP is critical for evaluating its quality. Our previous study regarding glass fiber reinforced polycarbonate (PC) composites reported that oligomer distributions within the composites can be clarified by applying principal component analysis (PCA) to ToF-SIMS spectrum image data [1]. However, PCA scores and pixel resolutions were not clear enough to identify the PC oligomer distribution around the interphase of glass fiber and polymer matrix whose thickness is estimated to be a few 100 nm [2].

In this study, glass fiber reinforced PC with deuterium-labeled PC oligomer was prepared as a definite indicator of PC oligomer and isotopic images were observed by TRIFTII (Physical Electronics) and NanoSIMS50L (CAMECA) to investigate the detailed distribution of PC oligomer around the interphase between the glass fiber and the polymer matrix.

References

[1] Y. Kajiwara, H Nagashima, S. Nagai and S. Aoyagi, e-J. Surf. Sci. Nanotech., 13, 47 (2015).

[2] S.-L. Gao, E. Mäder, Composites: Part A, 33, 559 (2002).