X-Ray and Neutron Reflectometry Study of Glow-Discharge Plasma Polymer Films

Abstract

Radio-frequency glow-discharge plasma polymer thin films of allylamine (AA) and hexamethyldisiloxane (HMDSO) were prepared on silicon wafers and analyzed by a combination of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray reflectometry (XRR), and neutron reflectometry (NR). AFM and XRR measurements revealed uniform, smooth, defect-free films of 20-30 nm thickness. XPS measurements gave compositional data on all elements in the films with the exception of hydrogen. In combination with XRR and NR, the film composition and mass densities (1.46 and 1.09 g cm(-)(3) for AA and HMDSO, respectively) were estimated. Further NR measurements were conducted with the AA and HMDSO films in contact with water at neutral pH. Three different H(2)O/D(2)O mixtures were used to vary the contrast between the aqueous phase and the polymer. The amount of water penetrating the film, as well as the number of labile protons present, was determined. The AA film in contact with water was found to swell by approximately 5%, contain approximately 3% water, and have approximately 24% labile protons. The HDMSO polymer was found to have approximately 6% labile protons, no thickness increase when in contact with water, and essentially no solvent penetration into the film. The difference in the degree of proton exchange within the films was attributed to the substantially different surface and bulk chemistries of the two films.

An X-ray and neutron reflectometry study of ‘PEG-like’ plasma polymer films

“…This film, therefore, allows for greater water adsorption and diffusion throughout its bulk when compared with the 20 W film with the greater mass density. The level of water absorption in these films is far higher than we have observed in previous NR and XRR studies of amine-containing plasma-polymerized allylamine films [24]. In comparing our previous study of an allylamine plasma polymer film that had a water contact angle of 558 and a fitted mass density of 1.46 g cm 23 , it absorbed only 3% v/v water compared with 40% v/v for the 50 W di(ethylene glycol) dimethyl ether plasma polymer film, which has a similar water contact angle of 668 and a significantly lower mass density of 0.99 g cm 23 .…”

Type I Collagen Grafting on Titanium Surfaces Using Low-temperature Glow Discharge

“…It has been proposed to use amine groups to solve the problem of non-specific bioadhesion, as they serve as ideal attachment vehicles between biomaterials and cells 17) . To graft amine groups onto biomaterials, allylamine (AA) radio-frequency GDP was developed to produce thin films with amine groups on biopolymer surfaces 16,18) . Then, in 2007, Stine et al first used glutaraldehyde (GA) as a bifunctional linker to covalently couple proteins on aminated silicon surfaces 19) .…”

Probing the Interfacial Structure of Bilayer Plasma Polymer Films via Neutron Reflectometry

“…[30,39,40] For the AA PP films, the main elemental components of the films are carbon, nitrogen and oxygen. The carbon content differs slightly from the monomer, but the nitrogen content is less than half that of the AA monomer.…”

“…The SLD obtained for the PP films in this study are similar to those reported in the literature. [28,30,31] For the single layer HMDSO, AA, and DG PP films the structural model consists of a thin transition layer between the silicon substrate and the layer describing the majority of the PP film, except for the HM10 PP which can be described by a single layer. The remainder of the film (for all PP) possesses a uniform SLD and is very smooth at the air-film interface.…”

“…Interestingly, the film density and plasma glow discharge load power correlation seen in the HMDSO PP films is the opposite of what was observed in the DG PP system (lower power ¼ higher mass density), but is consistent with our previous reports on HMDSO and DG PP's. [30,31] The significant difference in the HMDSO bilayer broadening between the high and low power depositions can therefore be attributed to a significantly greater mass density and a higher degree of unsaturation/crosslinking for the high power film, which would result in less ablation/mixing during deposition of the dDG PP topcoat film.…”