Vacuum ultraviolet photochemistry of polymers

Skurat, V. E.

doi:10.1016/s0168-583x(03)00636-0

Cited by 65 publications

(57 citation statements)

References 9 publications

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“…Deuteration does not significantly change the electronic orbitals and electronic bonds in the material. During VUV photons irradiation, optically allowed electronic singlet-singlet transitions are predominant at wavelengths of about 140 nm and above (Skurat 2003). Chemical transformations are mainly caused by reactions of these excited singlet states, which are very similar in both a-C:H and a-C:D materials.…”

Section: Mass Measurementmentioning

confidence: 99%

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Vacuum ultraviolet photolysis of hydrogenated amorphous carbons

Alata

Cruz-Díaz

Muñoz

et al. 2014

A&A

119

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Context. The interstellar hydrogenated amorphous carbons (HAC or a-C:H) observed in the diffuse medium are expected to disappear in a few million years, according to the destruction time scale from laboratory measurements. The existence of a-C:H results from the equilibrium between photodesorption, radiolysis, hydrogenation and resilience of the carbonaceous network. During this processing, many species are therefore injected into the gas phase, in particular H 2 , but also small organic molecules, radicals or fragments. Aims. We perform experiments on interstellar a-C:H analogs to quantify the release of these species in the interstellar medium. Methods. The vacuum ultraviolet (VUV) photolysis of interstellar hydrogenated amorphous carbon analogs was performed at low (10 K) to ambient temperature, coupled to mass-spectrometry detection and temperature-programed desorption. Using deuterium isotopic substitution, the species produced were unambiguously separated from background contributions. Results. The VUV photolysis of hydrogenated amorphous carbons leads to the efficient production of H 2 molecules, but also to small hydrocarbons. Conclusions. These species are formed predominantly in the bulk of the a-C:H analog carbonaceous network, in addition to the surface formation. Compared with species made by the recombination of H atoms and physisorbed on surfaces, they diffuse out at higher temperatures. In addition to the efficient production rate, it provides a significant formation route in environments where the short residence time scale for H atoms inhibits H 2 formation on the surface, such as PDRs. The photolytic bulk production of H 2 with carbonaceous hydrogenated amorphous carbon dust grains can provide a very large portion of the contribution to the H 2 molecule formation. These dust grains also release small hydrocarbons (such as CH 4 ) into the diffuse interstellar medium, which contribute to the formation of small carbonaceous radicals after being dissociated by the UV photons in the considered environment. This extends the interstellar media environments where H 2 and small hydrocarbons can be produced.

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Section: Mass Measurementmentioning

confidence: 99%

“…It decreases during irradiation. This decrease is explained not only by consumption (depletion) of CH 3 and CH 2 groups, but also by accumulation of conjugated photolysis products, which are able to "protect" the deeper layers by a mechanism of electronic energy transfer (e.g., Skurat 2003).…”

Section: H 2 Quantum Yieldmentioning

confidence: 99%

Vacuum ultraviolet photolysis of hydrogenated amorphous carbons

Alata

Cruz-Díaz

Muñoz

et al. 2014

A&A

119

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“…This can be explained as follows: C C bonds are formed by the abstraction of hydrogen, known as the dominant mechanism during VUV irradiation of hydrocarbon polymers. [11,12,19,21,22,28,34,35] For example, the main primary reaction involved in the VUV photolysis of LDPE is the following:…”

Section: Near-surface Structural Changes Of Irradiated Polymersmentioning

confidence: 99%

“…In the case of BOPP, unsaturation may also result from polymer chain scission, accompanied by the formation of lower molecular weight products: [12,22,34,35] ð13Þ ð14Þ…”

Section: Near-surface Structural Changes Of Irradiated Polymersmentioning

confidence: 99%

Vacuum Ultraviolet Photolysis of Hydrocarbon Polymers

Truica-Marasescu

Wertheimer

2005

Macro Chemistry & Physics

108

131

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Summary: The wavelength‐dependent vacuum ultraviolet (VUV) photolysis of several polymers, low density polyethylene (LDPE), biaxially oriented poly(propylene) (BOPP), atactic polystyrene (PS), and poly(methyl methacrylate) (PMMA), was studied by irradiation in vacuum with the well‐characterized emissions from four different resonant or excimer VUV sources. These lamps comprise radiofrequency (r.f.) discharges in different noble gases, such as krypton, xenon (at low pressures, producing near‐monochromatic resonant line radiations), xenon excimer (at “high” pressure), and a deuterium/argon mixture (producing a broad‐band emission). VUV‐induced mass loss (ablation or etching) was monitored in situ by quartz crystal microbalance measurements. Following irradiation, samples were analysed by ATR‐FTIR and XPS, to evaluate near‐surface structural changes (e.g., creation of unsaturation, cross‐linking) resulting from the VUV‐initiated bond scissions and radical‐creation reactions. PMMA was the most readily ablatable polymer, whereas the mass loss of BOPP was higher than that of LDPE, regardless of the irradiation wavelength, λ. All polymers were found to form double bonds, with the exception of PS, which is rather stable, probably due to energy dissipation by fluorescence.Formation of double bonds in a) vinyl‐, b) vinylidene‐, and c) vinylene‐like unsaturated groups, as a function of the radiation dose, D, for KrL (▪), XeL (▴), and D2Ar‐irradiated (•) PMMA.magnified imageFormation of double bonds in a) vinyl‐, b) vinylidene‐, and c) vinylene‐like unsaturated groups, as a function of the radiation dose, D, for KrL (▪), XeL (▴), and D2Ar‐irradiated (•) PMMA.

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“…At 157 nm PTFE has a strong absorbance. [32] The corresponding electronic transition is mainly assigned to the excitation of C-C bonds, [33] which leads to a photo-dissociation of the C-C single bond, [34] indicating a decomposition of the polymer into monomers and to carbon by defluorination, which is expected as the photon energy at 157 nm is higher than the binding energy of a carbon to fluorine bond. [35] This is also expressed in the XPS C1s level spectra in Figure 6(b).…”

Section: Sample Production and Characterizationmentioning

confidence: 99%