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Uzma K H Bangi - One of the best experts on this subject based on the ideXlab platform.
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A new route for preparation of sodium-silicate-based hydrophobic silica aerogels via ambient-pressure drying.
Science and technology of advanced materials, 2008Co-Authors: Uzma K H Bangi, A. Venkateswara Rao, A. Parvathy RaoAbstract:An in-depth investigation into the synthesis of hydrophobic silica aerogels prepared by the Surface Derivatization of wet gels followed by subsequent drying at ambient pressure is reported. The following sol-gel parameters were examined for their effect on the physical properties of the derived aerogels: number of gel washings with water, percentage of hexane or methanol in silylating mixture, molar ratio of tartaric acid: Na2SiO3, gel aging period, weight% of silica, trimethylchlorosilane (TMCS) percentage, and silylation period. These parameters were varied from 1 to 4, 0 to 100%, 0.27 to 1.2, 0 to 4 h, 1.5 to 8 wt.%, 20 to 40% and 6 to 24 h, respectively. The properties of hydrophobic silica aerogels synthesized by this new route were investigated in terms of bulk density, percentage volume shrinkage, percentage porosity, thermal conductivity and contact angle with water, and by Fourier transform infrared spectroscopy (FTIR). The as-prepared hydrophobic silica aerogels exhibited high temperature stability (up to approximately 435 °C) as measured by thermogravimetric/differential thermal analysis (TGA-DTA). The optimal sol-gel parameters were found to be a molar ratio of Na2SiO3:H2O : tartaric acid : TMCS of 1 : 146.67 : 0.86 : 9.46, an aging period of 3 h, four washings with water in 24 h and the use of a 50% hexane- or methanol-based silylating mixture. Aerogels prepared with these optimal parameters were found to exhibit 50% optical transparency in the visible range, 84 kg m-3 density, 0.090 W mK-1 thermal conductivity, 95% porosity and a contact angle of 146° with water.
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a new route for preparation of sodium silicate based hydrophobic silica aerogels via ambient pressure drying
Science and Technology of Advanced Materials, 2008Co-Authors: Uzma K H BangiAbstract:AbstractAn in-depth investigation into the synthesis of hydrophobic silica aerogels prepared by the Surface Derivatization of wet gels followed by subsequent drying at ambient pressure is reported. The following sol–gel parameters were examined for their effect on the physical properties of the derived aerogels: number of gel washings with water, percentage of hexane or methanol in silylating mixture, molar ratio of tartaric acid: Na2SiO3, gel aging period, weight% of silica, trimethylchlorosilane (TMCS) percentage, and silylation period. These parameters were varied from 1 to 4, 0 to 100%, 0.27 to 1.2, 0 to 4 h, 1.5 to 8 wt.%, 20 to 40% and 6 to 24 h, respectively. The properties of hydrophobic silica aerogels synthesized by this new route were investigated in terms of bulk density, percentage volume shrinkage, percentage porosity, thermal conductivity and contact angle with water, and by Fourier transform infrared spectroscopy (FTIR). The as-prepared hydrophobic silica aerogels exhibited high temperatur...
Vladimir V Popik - One of the best experts on this subject based on the ideXlab platform.
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photo click chemistry strategies for spatiotemporal control of metal free ligation labeling and Surface Derivatization
Pure and Applied Chemistry, 2013Co-Authors: Selvanathan Arumugam, Jason Locklin, Sara V Orski, Ngalle Eric Mbua, Christopher D Mcnitt, Geertjan Boons, Vladimir V PopikAbstract:Three photo-click ligation strategies described in this account provide scientists with efficient and selective tools for Derivatization of various molecules, polymers, and Surfaces. Fast photochemical reactions that are utilized in these techniques permit spatio temporal control of the process. The absence of activating reagents and catalysts, as well as compatibility with aqueous media, makes photo-click ligations suitable for biomedical applications. The first of these approaches relies on the photochemical decarbonylation of cyclopropenones to produce cyclooctynes. The latter undergo rapid catalyst-free strain-promoted azide–alkyne cycloaddition (SPAAC) to azide-tagged substrates. The second method is based on a very fast (>104 M–1 s–1) light-triggered hetero-Diels–Alder reaction and permits efficient Derivatization of substrates bearing vinyl ether moiety. An even faster reaction between photochemically generated naphthoquinone methides (oNQMs) and thiols (~2 × 105 M–1 s–1) serves as a basis for a third method. This thiol photo-click chemistry allows for the selective Derivatization of thiol-functionalized substrates or labeling of free cysteine residues in proteins. The thioether linkage produced by the reaction of oNQMs and a thiol is stable under ambient conditions, but can be cleaved by UV irradiation, regenerating free thiol. This feature permits the removal or replacement of immobilized compounds, as well as traceless substrate release.
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photoreactive polymer brushes for high density patterned Surface Derivatization using a diels alder photoclick reaction
Journal of the American Chemical Society, 2012Co-Authors: Selvanathan Arumugam, Jason Locklin, Sara V Orski, Vladimir V PopikAbstract:Reactive polymer brushes grown on silicon oxide Surfaces were derivatized with photoreactive 3-(hydroxymethyl)naphthalene-2-ol (NQMP) moieties. Upon 300 or 350 nm irradiation, NQMP efficiently produces o-naphthoquinone methide (oNQM), which in turn undergoes very rapid Diels–Alder addition to vinyl ether groups attached to a substrate, resulting in the covalent immobilization of the latter. Any unreacted oNQM groups rapidly add water to regenerate NQMP. High-resolution Surface patterning is achieved by irradiating NQMP-derivatized Surfaces using photolithographic methods. The Diels–Alder photoclick reaction is orthogonal to azide–alkyne click chemistry, enabling sequential photoclick/azide-click Derivatizations to generate complex Surface functionalities.
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patterned Surface Derivatization using diels alder photoclick reaction
Journal of the American Chemical Society, 2011Co-Authors: Selvanathan Arumugam, Vladimir V PopikAbstract:The utility of photochemically induced hetero-Diels–Alder reaction for the light-directed Surface Derivatization and patterning was demonstrated. Glass slides functionalized with vinyl ether moieties are covered with aqueous solution of substrates conjugated to 3-(hydroxymethyl)-2-naphthol (NQMP). Subsequent irradiation via shadow mask results in an efficient conversion of the latter functionality into reactive 2-napthoquinone-3-methide (oNQM) in the exposed areas. oNQM undergoes very facile hetero Diels–Alder addition (kD-A ≈ 4 × 104 M–1s–1) to immobilized vinyl ether molecules resulting in a photochemically stable covalent link between a substrate and a Surface. Unreacted oNQM groups are rapidly hydrated to regenerate NQMP. The click chemistry based on the addition of photochemically generated oNQM to vinyl ether works well in aqueous solution, proceeds at high rate under ambient conditions, and does not require catalyst or additional reagents. This photoclick strategy represents an unusual paradigm in ...
Selvanathan Arumugam - One of the best experts on this subject based on the ideXlab platform.
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photo click chemistry strategies for spatiotemporal control of metal free ligation labeling and Surface Derivatization
Pure and Applied Chemistry, 2013Co-Authors: Selvanathan Arumugam, Jason Locklin, Sara V Orski, Ngalle Eric Mbua, Christopher D Mcnitt, Geertjan Boons, Vladimir V PopikAbstract:Three photo-click ligation strategies described in this account provide scientists with efficient and selective tools for Derivatization of various molecules, polymers, and Surfaces. Fast photochemical reactions that are utilized in these techniques permit spatio temporal control of the process. The absence of activating reagents and catalysts, as well as compatibility with aqueous media, makes photo-click ligations suitable for biomedical applications. The first of these approaches relies on the photochemical decarbonylation of cyclopropenones to produce cyclooctynes. The latter undergo rapid catalyst-free strain-promoted azide–alkyne cycloaddition (SPAAC) to azide-tagged substrates. The second method is based on a very fast (>104 M–1 s–1) light-triggered hetero-Diels–Alder reaction and permits efficient Derivatization of substrates bearing vinyl ether moiety. An even faster reaction between photochemically generated naphthoquinone methides (oNQMs) and thiols (~2 × 105 M–1 s–1) serves as a basis for a third method. This thiol photo-click chemistry allows for the selective Derivatization of thiol-functionalized substrates or labeling of free cysteine residues in proteins. The thioether linkage produced by the reaction of oNQMs and a thiol is stable under ambient conditions, but can be cleaved by UV irradiation, regenerating free thiol. This feature permits the removal or replacement of immobilized compounds, as well as traceless substrate release.
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photoreactive polymer brushes for high density patterned Surface Derivatization using a diels alder photoclick reaction
Journal of the American Chemical Society, 2012Co-Authors: Selvanathan Arumugam, Jason Locklin, Sara V Orski, Vladimir V PopikAbstract:Reactive polymer brushes grown on silicon oxide Surfaces were derivatized with photoreactive 3-(hydroxymethyl)naphthalene-2-ol (NQMP) moieties. Upon 300 or 350 nm irradiation, NQMP efficiently produces o-naphthoquinone methide (oNQM), which in turn undergoes very rapid Diels–Alder addition to vinyl ether groups attached to a substrate, resulting in the covalent immobilization of the latter. Any unreacted oNQM groups rapidly add water to regenerate NQMP. High-resolution Surface patterning is achieved by irradiating NQMP-derivatized Surfaces using photolithographic methods. The Diels–Alder photoclick reaction is orthogonal to azide–alkyne click chemistry, enabling sequential photoclick/azide-click Derivatizations to generate complex Surface functionalities.
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patterned Surface Derivatization using diels alder photoclick reaction
Journal of the American Chemical Society, 2011Co-Authors: Selvanathan Arumugam, Vladimir V PopikAbstract:The utility of photochemically induced hetero-Diels–Alder reaction for the light-directed Surface Derivatization and patterning was demonstrated. Glass slides functionalized with vinyl ether moieties are covered with aqueous solution of substrates conjugated to 3-(hydroxymethyl)-2-naphthol (NQMP). Subsequent irradiation via shadow mask results in an efficient conversion of the latter functionality into reactive 2-napthoquinone-3-methide (oNQM) in the exposed areas. oNQM undergoes very facile hetero Diels–Alder addition (kD-A ≈ 4 × 104 M–1s–1) to immobilized vinyl ether molecules resulting in a photochemically stable covalent link between a substrate and a Surface. Unreacted oNQM groups are rapidly hydrated to regenerate NQMP. The click chemistry based on the addition of photochemically generated oNQM to vinyl ether works well in aqueous solution, proceeds at high rate under ambient conditions, and does not require catalyst or additional reagents. This photoclick strategy represents an unusual paradigm in ...
A. Parvathy Rao - One of the best experts on this subject based on the ideXlab platform.
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A new route for preparation of sodium-silicate-based hydrophobic silica aerogels via ambient-pressure drying.
Science and technology of advanced materials, 2008Co-Authors: Uzma K H Bangi, A. Venkateswara Rao, A. Parvathy RaoAbstract:An in-depth investigation into the synthesis of hydrophobic silica aerogels prepared by the Surface Derivatization of wet gels followed by subsequent drying at ambient pressure is reported. The following sol-gel parameters were examined for their effect on the physical properties of the derived aerogels: number of gel washings with water, percentage of hexane or methanol in silylating mixture, molar ratio of tartaric acid: Na2SiO3, gel aging period, weight% of silica, trimethylchlorosilane (TMCS) percentage, and silylation period. These parameters were varied from 1 to 4, 0 to 100%, 0.27 to 1.2, 0 to 4 h, 1.5 to 8 wt.%, 20 to 40% and 6 to 24 h, respectively. The properties of hydrophobic silica aerogels synthesized by this new route were investigated in terms of bulk density, percentage volume shrinkage, percentage porosity, thermal conductivity and contact angle with water, and by Fourier transform infrared spectroscopy (FTIR). The as-prepared hydrophobic silica aerogels exhibited high temperature stability (up to approximately 435 °C) as measured by thermogravimetric/differential thermal analysis (TGA-DTA). The optimal sol-gel parameters were found to be a molar ratio of Na2SiO3:H2O : tartaric acid : TMCS of 1 : 146.67 : 0.86 : 9.46, an aging period of 3 h, four washings with water in 24 h and the use of a 50% hexane- or methanol-based silylating mixture. Aerogels prepared with these optimal parameters were found to exhibit 50% optical transparency in the visible range, 84 kg m-3 density, 0.090 W mK-1 thermal conductivity, 95% porosity and a contact angle of 146° with water.
Stuart L Cooper - One of the best experts on this subject based on the ideXlab platform.
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Surface properties and hemocompatibility of alkyl siloxane monolayers supported on silicone rubber effect of alkyl chain length and ionic functionality
Biomaterials, 1999Co-Authors: James H Silver, Jui Che Lin, Florencia Lim, Vassiliki A Tegoulia, Manoj K Chaudhury, Stuart L CooperAbstract:Self-assembled monolayers of alkylsiloxanes supported on poly(dimethylsiloxane) (PDMS) rubber were used as model systems to study the relation between blood compatibility and Surface composition. The inner lumen of PDMS tubes were first treated with an oxygen plasma. The resultant oxidized Surfaces were post-derivatized by reaction with alkyltrichlorosilanes to form the monolayer films. The alkyl chain lengths used were slightly longer than in a previous study, and this may alter the phase-state of the monolayer from liquid-like to crystalline. The chemical properties of the monolayer were controlled by varying the chemical composition of the alkyltrichlorosilanes used. Terminal functionalities included -CH3, -CF3, -COOH, -SO3H and -(CH2CH2O)4OH. Surface Derivatization was verified with static contact angle measurements and X-ray photoelectron spectroscopy. Blood compatibility was evaluated using a canine ex vivo arterio-venous series shunt model. Surfaces grafted with hydrophobic head groups such as -CH3 and -CF3 were significantly less thrombogenic than the Surfaces composed of ionic head groups such as -COOH and -SO3H. Surfaces enriched in -(CH2CH2O)4OH had an intermediate thrombogenicity. Silastic pump grade tubing and polyethylene tubing, used as controls, were found to be the least thrombogenic of all the Surfaces tested.
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Surface properties and hemocompatibility of alkyl siloxane monolayers supported on silicone rubber effect of alkyl chain length and ionic functionality
Biomaterials, 1999Co-Authors: James H Silver, Jui Che Lin, Florencia Lim, Vassiliki A Tegoulia, Manoj K Chaudhury, Stuart L CooperAbstract:Self-assembled monolayers of alkylsiloxanes supported on poly(dimethylsiloxane) (PDMS) rubber were used as model systems to study the relation between blood compatibility and Surface composition. The inner lumen of PDMS tubes were "rst treated with an oxygen plasma. The resultant oxidized Surfaces were post-derivatized by reaction with alkyltrichlorosilanes to form the monolayer "lms. The alkyl chain lengths used were slightly longer than in a previous study, and this may alter the phase-state of the monolayer from liquid-like to crystalline. The chemical properties of the monolayer were controlled by varying the chemical composition of the alkyltrichlorosilanes used. Terminal functionalities included }CH 3 , }CF 3 , }COOH, }SO 3 H and }(CH 2 CH 2 O) 4 OH. Surface Derivatization was veri"ed with static contact angle measurements and X-ray photoelectron spectroscopy. Blood compatibility was evaluated using a canine ex vivo arterio-venous series shunt model. Surfaces grafted with hydrophobic head groups such as }CH 3 and }CF 3 were signi"cantly less thrombogenic than the Surfaces composed of ionic head groups such as }COOH and }SO 3 H. Surfaces enriched in }(CH 2 CH 2 O) 4 OH had an intermediate thrombogenicity. Silastic pump grade tubing and polyethylene tubing, used as controls, were found to be the least thrombogenic of all the Surfaces tested. ( 1999 Elsevier Science Ltd. All rights reserved.