Plasma-deposited PEG-like films are emerging as promising materials for preventing protein and bacterial attachment to surfaces. To date, there has not been a detailed surface analysis to examine the chemistry and molecular structure of these films as a function of both precursor size and structure. In this paper, we describe radio-frequency plasma deposition of a series of short-chain oligoglymes, dioxane, and crown ethers onto glass cover slips to create poly(ethylene glycol)-like coatings. The resultant films were characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), dynamic contact angle goniometry, and radiolabeled fibrinogen adsorption. Detailed analysis of the high-mass (120-300 m/z) TOF-SIMS oligoglyme film spectra revealed six classes of significant fragments. Two new models are proposed to describe how these fragments could be formed by distinct film-building processes: incorporation of intact and fragmented precursor molecules. The models also provide for the incorporation of hydrocarbon--a species that is not present in the precursors but is evidenced in XPS C(1s) spectra of these films. Two additional models describe the effects of incorporating intact and fragmented cyclic precursors.

The dibutyltin diacetate-catalyzed reaction of (tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane (FTEOS) with dihydroxy-terminated poly(dimethylsiloxane), HO(Me2SiO) n H, has been used to prepare surface-modified siloxane networks. Surface characterization of these elastomers was carried out with electron spectroscopy for chemical analysis (ESCA) and optical and atomic force microscopy (AFM). Surface phase separation occurs as a function of FTEOS concentration. For example, FTEOS-6x compositions (where 6x is the initial SiOEt/SiOH ratio) exhibited micron scale “islands” of fluorinated siliceous phase (FSP) surrounded by a siloxane-rich “sea”. In FTEOS-12x, the FSP formed a continuous layer on the elastomeric network. Differing dynamic contact angle (DCA) analysis protocols with water as the interrogating fluid showed that water contamination affects force vs distance curve (fdc) data on samples up to FTEOS-10x. Intrinsic wetting behavior is reproduced only with a protocol where clean water is used for each DCA cycle. For FTEOS-12x, an FSP monodomain exists characterized by high θadv (135−6°) and low θrec (55−56°), similar to previously reported values for fluoroalkyl side chain polymers. Long-term testing showed that the coatings undergo slow chemical degradation by water, with the rate depending on composition. FTEOS-12x is chemically stable in water due to the continuous FSP overlayer.

Two established techniques have been coupled to allow surfaces to be precision engineered. Electrospray ionization to bring large, complex, intact molecular ions into the gas phase has been interfaced with a radio frequency ͑rf͒ plasma reactor to treat surfaces making them receptive to the deposition of active biomolecules. The new instrument has been designed and used successfully to deposit a number of high molecular weight molecules including the polysaccharide, sodium hyaluronan ͑HA͒, that has an important role in a number of physiological functions. Substrate material is treated using a rf glow discharge plasma chamber, to clean and activate the surface in a controlled manner, then exposed to a beam of multiply charged ions in the gas phase that have been generated using electrospray techniques. The ions are deposited gently onto the substrate and become covalently bound. The molecular integrity and stability of HA surfaces prepared in this way was established using x-ray photoelectron spectroscopy, changes in the observed contact angle, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, and a biological assay-platelet adhesion to the surface.

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Hybrid poly(dimethylsiloxane) networks have been prepared with the ethoxysiloxane mixture “ES40” that acts as a cross-linker and siliceous domain (SD) precursor through sol−gel chemistry. ES40, with an approximate formula (SiO(OEt)2) n , is a mixture of oligo-ethoxysiloxanes that is much less volatile than tetraethoxysilane (TEOS) and provides hybrid elastomeric coatings of reproducible composition. With SiOEt from ES40 and SiOH from HO(Me2SiO) n H, compositions with SiOEt/SiOH ratios from 5 to 35 (ES40-5x−ES40-35x) were prepared. Solid-state 29Si NMR spectroscopy was used to determine the relative amounts of PDMS and SD in the hybrid elastomers. The relative amounts of Q2, (⋮SiO)2 Si(OH)2; Q3, (⋮SiO)3 Si(OH); and Q4, (⋮SiO)4 Si, in the SD were estimated by deconvolution of the 29Si NMR peaks. Both light microscopy and tapping mode atomic force microscopy (TM-AFM) show that PDMS-SD compositions “5x” and higher slowly develop “island-like” surface features while stored at ambient conditions. After 1 month cure, PDMS-SD surface features are ≤1 μm, while after 6 months feature size is broadly distributed up to ∼10 μm. In contrast, surface features developed quickly (24 h) with previously reported PDMS-FSD hybrids, where FSD is fluorinated siliceous domain, from (tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane. AFM experience demonstrates that PDMS-SD surface features are often poorly adherent and easily moved compared to the robust phase-separated surface structure of PDMS-FSD materials. Differing dynamic contact angle (DCA) analysis protocols with water as the interrogating fluid show that water contamination affects force vs distance curve (fdc) data for PDMS-SD hybrids. Intrinsic wetting behavior for PDMS-SD hybrids is reproduced only with a protocol where clean water is used for each DCA cycle. The stability in water of PDMS-SD materials is strongly compositionally dependent. Over a period of 70 days, the ES40-14x composition showed the greatest resistance to mass loss with a mass loss rate of 0.08 wt %/month.

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Surface‐modified siloxane networks were prepared using the dibutyltin diacetate catalyzed reaction of α,ω‐dihydroxy(polydimethylsiloxane), HO(Me2SiO)nH, with tridecafluoro‐1,1,2,2‐tetrahydrooctyl triethoxysilane, [CF3(CF2)5(CH2)2Si(OC2H5)3, FTEOS]. Surface characterization of these elastomers was carried out using electron spectroscopy for chemical analysis (ESCA) and atomic force microscopy (AFM). Surface phase separation occurs as a function of increasing ratio of FTEOS to HO(Me2SiO)nH. Dynamic contact angle (DCA) analysis with water as the interrogating fluid showed that water contamination affects DCA data in the compositional range 4x–8x, where “x” is the ratio of ethoxy groups from FTEOS to OH groups in HO(Me2SiO)nH. Diffusion of polydimethylsiloxane oil species from the coatings is blocked in compositions of 10x or greater. Chemical stability is also enhanced for 10x and 12x compositions.