Systematic Oxidation of Polystyrene by Ultraviolet-Ozone, Characterized by Near-Edge X-ray Absorption Fine Structure and Contact Angle

Klein, Robert J.; Fischer, Daniel A.; Lenhart, Joseph L.

doi:10.1021/la800134u

Cited by 51 publications

(78 citation statements)

References 40 publications

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“…39 NEXAFS spectra of UV-irradiated PS films are consistent with photo-oxidation proceeding from the top surface down through the film, similar to previous studies of PS photo-oxidation. 39,40 Decreasing the bias voltage of the electron yield detector during a NEXAFS (b) UV-exposed lamellar; (c) UV-exposed cylindrical. The polymers are removed by oxygen plasma etching after deposition.…”

Section: Articlesupporting

confidence: 85%

“…38 This observation is consistent with previous demonstrations of block-selective infiltration of TiO 2 using TiCl 4 . 17 NEXAFS spectroscopy provides a surface-sensitive probe of polymer oxidation 39 and confirms the UVinduced formation of oxygen-containing functional groups with stronger Lewis basicity within the PS domain. A comparison of measurements of a ∼20 nm thick UVirradiated (5 min) PS film and an unaltered control sample (both spin-cast on Si substrates) shows the UV-induced formation of spectral peaks associated with the π* orbital of CdO bonds (π* CdO , at photon energy ∼286.4 eV) (Figure 4a).…”

Section: Articlementioning

confidence: 92%

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Chemically Enhancing Block Copolymers for Block-Selective Synthesis of Self-Assembled Metal Oxide Nanostructures

et al. 2012

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We report chemical modification of self-assembled block copolymer thin films by ultraviolet light that enhances the block-selective affinity of organometallic precursors otherwise lacking preference for either copolymer block. Sequential precursor loading and reaction facilitate formation of zinc oxide, titanium dioxide, and aluminum oxide nanostructures within the polystyrene domains of both lamellar- and cylindrical-phase modified polystyrene-block-poly(methyl methacrylate) thin film templates. Near-edge X-ray absorption fine structure measurements and Fourier transform infrared spectroscopy show that photo-oxidation by ultraviolet light creates Lewis basic groups within polystyrene, resulting in an increased Lewis base-acid interaction with the organometallic precursors. The approach provides a method for generating both aluminum oxide patterns and their corresponding inverses using the same block copolymer template.

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Section: Articlesupporting

confidence: 85%

Section: Articlementioning

confidence: 92%

Chemically Enhancing Block Copolymers for Block-Selective Synthesis of Self-Assembled Metal Oxide Nanostructures

et al. 2012

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“…From another two FIB-cut specimen (the two FIB-cut specimen used for Figure 8 were contaminated after the scanning for carbon mapping), we acquired two EELS spectra for Beta-MS by focusing the electron beam on a mesopore region (site 1) and a zeolite domain (site 2), respectively, and one EELS spectra for Beta-C (site 3) (see Figure 9). By comparing the EELS fine structures of the three sites, we learn that site 1 has a 1s π* excitation at 285.1 eV, which is conventionally assigned to large aromatics with high degrees of graphitization [55][56] and does not appear in the EELS spectra of sites 2 or 3 ( Figure 9). Sites 2 and 3 both show a peak of higher energy loss (288.6 eV for site 2 and 288.4 eV for site 3) that is absent from site 1's spectrum.…”

Section: Resultsmentioning

confidence: 99%

Investigating the Influence of Mesoporosity in Zeolite Beta on Its Catalytic Performance for the Conversion of Methanol to Hydrocarbons

et al. 2015

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Hierarchically porous zeolite Beta (Beta-MS) synthesized by a soft-templating method contains remarkable intra-crystalline mesoporosity, which reduces the diffusion length in zeolite channels down to several nanometers and alters the distribution of Al among distinct crystallographic sites. When used as a catalyst for the conversion of methanol to hydrocarbons (MTH) at 330 o C, Beta-MS exhibited a 2.7-fold larger conversion capacity, a 2.0-fold faster reaction rate, and a remarkably longer lifetime than conventional zeolite Beta (Beta-C). The superior catalytic performance of Beta-MS is attributed to its hierarchical structure, which offers full accessibility to all catalytic active sites. In contrast, Beta-C was easily deactivated because a layer of coke quickly deposited on the outer surfaces of the catalyst crystals, impeding access to interior active sites. This difference is clearly demonstrated by using electron microscopy combined with electron energy loss spectroscopy to probe the distribution of coke in the deactivated catalysts. At both low and high conversions, ranging from 20% to 100%, Beta-MS gave higher selectivity towards higher aliphatics (C 4 -C 7 ) but lower ethene selectivity compared to Beta-C. Therefore, we conclude that a hierarchical structure decreases the residence time of methylbenzenes in zeolite micropores, disfavoring the propagation of the aromatic-based catalytic cycle. This conclusion is consistent with a recent report on ZSM-5 and is also strongly supported by our analysis of soluble coke species residing in the catalysts.Moreover, we identified an oxygen-containing compound, 4-methyl-benzaldehyde, in the coke, which has not been observed in the MTH reaction before.

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“…[38][39][40] In the present study, however, we varied the X-ray incidence angle at a constant value of the entrance grid bias.…”

Section: Methodsmentioning

confidence: 99%

NEXAFS Depth Profiling of Surface Segregation in Block Copolymer Thin Films

et al. 2010

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NEXAFS spectroscopy was used to probe the surface composition and under-water surface reconstruction of thin films of comb-like diblock copolymers with cylindrical and spherical microphases. The polymers consisted of a polystyrene block, and a second block prepared from a styrenic monomer grafted with fluoroalkyl-tagged poly(ethylene glycol) side chains. Compositional depth profiling of the microphase separated block copolymer films, in the top 1-3 nm of the film, was performed to understand the role of block copolymer microstructure and self-assembly on surface composition. Using experimentally determined concentration profiles, the surface concentration of phenyl ring carbon atoms was quantified and compared with those of homopolymer and random copolymer controls. The carbon atoms from the relatively high surface energy phenyl groups were depleted or excluded from the surface, in favor of the low surface-energy fluoroalkyl groups. While it is expected that block copolymer surfaces will be completely covered by a wetting lamellar layer of the lower surface energy block, a significant amount of the higher surface energy polystyrene block was found to be present in the surface region of the cylinderforming block copolymer. Evidently, the spontaneous formation of the cylindrical polystyrene microdomains in the near-surface region compensated for the lowering of the free energy that could have been achieved by completely covering the surfaces with a lamellar layer of the lower surface energy fluorinated block. All surfaces underwent molecular reconstruction after immersion in water. The experimental concentration depth profiles indicated an increased surface depletion of phenyl ring carbon atoms in the water-immersed thin films, due to the tendency of hydrophilic PEG side groups to be present at the polymer-water interface. Such a detailed characterization of the outermost layers of the block copolymer surfaces was possible because of the exceptional depth resolution of the NEXAFS depth profiling technique.

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Systematic Oxidation of Polystyrene by Ultraviolet-Ozone, Characterized by Near-Edge X-ray Absorption Fine Structure and Contact Angle

Cited by 51 publications

References 40 publications

Chemically Enhancing Block Copolymers for Block-Selective Synthesis of Self-Assembled Metal Oxide Nanostructures

Chemically Enhancing Block Copolymers for Block-Selective Synthesis of Self-Assembled Metal Oxide Nanostructures

Investigating the Influence of Mesoporosity in Zeolite Beta on Its Catalytic Performance for the Conversion of Methanol to Hydrocarbons

NEXAFS Depth Profiling of Surface Segregation in Block Copolymer Thin Films

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