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H J Coles - One of the best experts on this subject based on the ideXlab platform.
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improving the stability of Organosiloxane smectic a liquid crystal random lasers using redox dopants
Optical Materials, 2015Co-Authors: Ammar A Khan, Damian J Gardiner, Stephen M Morris, Malik M Qasim, Timothy D Wilkinson, H J ColesAbstract:Abstract In this paper, we focus on the development of liquid crystal (LC) visible-light scattering devices for random lasers. These light-scattering devices are based upon binary mixtures that consist of an Organosiloxane smectic A LC and a wide temperature range nematogen LC. Both the temperature range of the smectic A phase and the dielectric anisotropy of the binary mixture are increased compared with that of the neat Organosiloxane compound. In the latter case, the increase in the dielectric anisotropy results in a reduction of the magnitude of the electric field required to induce a clear state. Furthermore, it is found that the electric field threshold continues to decrease with increasing concentration of the nematic compound. For the random laser devices, the Pyrromethene 597 laser dye was added to a mixture that was optimized for scattering and it was found that the absorption properties of the dye becomes unstable in the presence of the electro-hydrodynamic instabilities that are required to generate scattering in the LC cells. This is believed to be due to electro-chemical reactions that occur at the electrodes. To avoid dye degradation and ensure repeatable electro-optic behaviour, a reduction–oxidation (redox) couple is dispersed within the dye-doped binary mixture. It is shown that the addition of redox dopants helps to stabilize the dye in the scattering mixtures, and also increases the long-term repeatability of the scattering behaviour. Finally, we conclude by characterizing the random laser emission of the dye-doped binary mixture and demonstrate improved stability.
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Improving the stability of Organosiloxane smectic A liquid crystal random lasers using redox dopants
Optical Materials, 2015Co-Authors: Aa Khan, Sm Morris, Dj Gardiner, Qasim Malik, Wilkinson Timothy, H J ColesAbstract:This report is focus on the development of liquid crystal (LC) vis ible - light scattering devices for random lasers. These light - scattering devices are based upon binary mixtures that consist of an Organosiloxane smectic A LC and a wide temperature range nematogen LC. Both the temperature range of the smectic A phase and t he dielectric anisotropy of the binary mixture are increased compared with that of the neat Organosiloxane compound. In the latter case, the increase in the dielectric anisotropy results in a reduction of the magnitude of the electric field required to ind uce a clear state. Furthermore, it is found that the electric field threshold continues to decrease with increasing concentration of the nematic compound. For the random laser devices, the pyrromethene 597 laser dye was added to a mixture that was optimize d for scattering and it was found that the absorption properties of the dye becomes unstable in the presence of the electro - hydrodynamic instabilities that are required to generate scattering in the LC cells. This is believed to be due to electro - chemical reactions that occur at the electrodes. To avoid dye degradation and ensure repeatable electro - optic behaviour, a reduction - oxidation (redox) couple is dispersed within the dye - doped binary mixture. It is shown that the addition of redox dopants helps to s tabilize the dye in the scattering mixtures, and also increases the long - term repeatability of the scattering behaviour. Finally, we conclude by characterizing the random laser emission of the dye - doped binary mixture and demonstrate improved stability.This is the author accepted manuscript. The final published version is available at http://www.sciencedirect.com/science/article/pii/S0925346715000816
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Low molar mass Organosiloxane liquid crystals for telecommunication applications
2012Co-Authors: Hu X, Hadeler O, H J ColesAbstract:Mixtures of two proprietary low molar mass Organosiloxane liquid crystals were studied in order to improve their alignment and optimize their electro-optic properties for telecommunication applications. Over a certain concentration range, mixtures exhibited an isotropic-chiral smectic A-chiral smectic C (Iso-SmA*-SmC*) phase sequence leading to exceptionally good alignment. At room temperature, the spontaneous polarization of these samples was reduced from 225 nC cm -2 in the pure SmC* liquid crystal to as low as 75 nC cm -2 in the mixture. Within this concentration range, the ferroelectric tilt angle could be varied between 35° and 15°, while the rise time decreased by 69.4%. The rise times were < 45 μs for moderate electric fields of ± 10 V μm -1 in the SmC* phase and ∼ 4 μs, independent of electric field, in the SmA* phase. At λ = 1550 nm, these mixtures exhibited very large extinction ratios of {\sim} 60 dB for binary switching in the SmC* phase and ∼ 55 dB continuous variable attenuation in the SmA* phase. © 2012 IEEE
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highly anisotropic conductivity in Organosiloxane liquid crystals
Journal of Applied Physics, 2006Co-Authors: Damian J Gardiner, H J ColesAbstract:In this paper, we present the conductivity and dielectric characterization of three homologous series of smectic A siloxane containing liquid crystals. The materials studied include one monomesogenic series, which consists of a 4-(ω-alkyloxy)-4′-cyanobiphenyl unit terminated by pentamethyldisiloxane, and two bimesogenic series, which consist of twin 4-(ω-alkyloxy)-4′-cyanobiphenyls joined via tetramethyldisiloxane or decamethylpentasiloxane. All of the compounds exhibit wide temperature range enantiotropic smectic A phases; the effect of the siloxane moiety is to suppress nematic morphology even in the short chain homologs. We find that these compounds exhibit a highly anisotropic conductivity: the value perpendicular to the director is to up to 200 times that parallel to the director. For the nonsiloxane analog 4-(ω-octyl)-4′-cyanobiphenyl (8CB), this value is approximately 2. It is also found that the dielectric anisotropy is reduced significantly; a typical value is ∼1 compared to 8.4 for 8CB. We propo...
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Organosiloxane liquid crystals for fast switching bistable scattering devices
Journal of Physics D, 2006Co-Authors: Damian J Gardiner, H J ColesAbstract:In this paper, we investigate the dependence of the bistable electro-optic response of Organosiloxane based smectic A liquid crystals on key material properties; the modes are optically scattering ( 1 kHz), respectively. The scattering mode is generated by motion of doped ionic species and is dependent upon the conductivity anisotropy of the liquid crystal; the clear mode occurs through dielectric coupling at frequencies sufficient to inhibit ionic conduction. The pure siloxane liquid crystals exhibit unusually high anisotropic ionic conductivities; the ratio of the components parallel and perpendicular to the director is up to 0.005; for analogous non-siloxane based liquid crystals the value is ~0.5. However, the pure materials possess low dielectric anisotropy compared with similar polar liquid crystals, e.g. 0.8 compared with 8.4. Based upon these observations, we prepare exemplar mixtures of Organosiloxane with 4-(ω-pentyloxy)-4'-cyanobiphenyl (5OCB) as a dielectric additive. These systems show beneficial properties: highly anisotropic conductivity coupled with an increase in the dielectric anisotropy. As a result, the electro-optic responses of these mixtures show a significant improvement upon the pure compounds; for example, for the 49% w/w mixture it is found that the response time of the optically clear mode is significantly reduced, e.g. from 130 ms (at 280 V rms) to 5 ms at an applied voltage of 102 V rms. We conclude that simple mixtures, using an Organosiloxane as the bulk component, have much promise for use in bistable, electro-optic storage and display devices.
Qiang Fang - One of the best experts on this subject based on the ideXlab platform.
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a fluorinated thermocrosslinkable Organosiloxane a new low k material at high frequency with low water uptake
Macromolecular Rapid Communications, 2021Co-Authors: Fengping Liu, Xingrong Chen, Jing Sun, Jiaren Hou, Qiang FangAbstract:In order to obtain low-k material with good comprehensive properties, a trifluoromethyl-containing Organosiloxane with thermocrosslinkable vinyl and benzocyclobutene groups is designed and synthesized through the Piers-Rubinsztajn reaction. After treating at high temperature, the Organosiloxane changed to form a cross-linked polysiloxane (called as c-FSi-BCB). c-FSi-BCB exhibits good dielectric properties with dielectric constant (Dk ) of 2.60 and dielectric loss (Df ) of 1.49 × 10-3 at a high frequency of 5 GHz. Importantly, c-FSi-BCB maintains such good dielectric properties and exhibits low water uptake of below 0.076%, even after immersing it in boiling water for 96 h. c-FSi-BCB also displays good thermostability with a 5% weight loss temperature (T5d ) of 453 °C. These data indicate that this fluorinated Organosiloxane is suitable as the matrix resin for the fabrication of devices used in 5G communication.
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an effective strategy for the preparation of intrinsic low k and ultralow loss dielectric polysiloxanes at high frequency by introducing trifluoromethyl groups into the polymers
Polymer Chemistry, 2020Co-Authors: Fengping Liu, Xingrong Chen, Linxuan Fang, Jing Sun, Qiang FangAbstract:Two new trifluoromethyl-containing Organosiloxanes with cross-linkable styrene groups have been facilely synthesized by the Piers–Rubinsztajn reaction. The homopolymerization of these Organosiloxanes at high temperature gives polysiloxanes, one of which exhibits a dielectric constant (Dk) below 2.53 with an ultralow dielectric loss (Df) of 1.66 × 10−3 at a high frequency of 5 GHz. In contrast, a control non-fluorinated polysiloxane sample with methoxy groups exhibits higher Dk of 2.78 and Df of 2.07 × 10−2. Moreover, the trifluoromethyl-containing polysiloxanes show no obvious change in Dk and Df even after immersing them in boiling water for 96 h. This result is attributed to the low water uptake of the polymers (near to 0.1%). These data indicate that this work provides a facile and effective way for the preparation of intrinsic low-k and low-loss materials used in the microelectronics industry. Based on the good properties, these fluorinated polysiloxanes are suitable as matrix or encapsulation resins for the fabrication of devices used in high-frequency communication.
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high performance low dielectric polysiloxanes with high thermostability and low water uptake
Materials Chemistry Frontiers, 2018Co-Authors: Xiaoyao Chen, Jing Sun, Jiajia Wang, Qiang FangAbstract:Two novel low dielectric polysiloxanes with high thermostability and low water uptake were developed. These polymers were formed via a thermo-crosslinking reaction of two BCB-containing Organosiloxanes. They exhibited dielectric constants (Dk) of less than 2.60 for frequencies ranging from 0.15 to 30.0 MHz, and good thermostability with a 5% weight loss temperature of up to 460 °C. In particular, the polymer derived from a monomer containing three BCB units displayed a Tg of 350 °C. These polymers exhibited water uptakes of less than 0.20% when they were immersed in boiling water for 72 h. These data reflect that these polysiloxanes are suitable as high performance low dielectric resins in the microelectronics industry.
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a new four arm Organosiloxane with thermopolymerizable trifluorovinyl ether groups synthesis and conversion to the polymer with both low dielectric constant and low water uptake
Macromolecular Chemistry and Physics, 2017Co-Authors: Jing Sun, Jiajia Wang, Yumeng Xin, Kaikai Jin, Yijie Luo, Junfeng Zhou, Yuanqiang Wang, Shijun Zheng, Qiang FangAbstract:A new fluoro-containing four-arm Organosiloxane has been successfully synthesized, which can be easily converted to a cross-linked network, showing water uptake of below 0.12 wt% (maintained in boiling water for 72 h) and dielectric constant of below 2.56 with dissipation factor of near 1.8 × 10−3 at 30 MHz, as well as showing high transparency and good thermostability. These data indicate that this new Organosiloxane is suitable as an adhesive or sealant for the applications in microelectronic industry.
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a novel one pot synthesized Organosiloxane synthesis and conversion to directly thermo crosslinked polysiloxanes with low dielectric constants and excellent thermostability
Polymer Chemistry, 2015Co-Authors: Jiajia Wang, Chao Yuan, Fengkai He, Qiang FangAbstract:A novel Organosiloxane containing a thermally cross-linkable benzocyclobutene group was successfully synthesized through a one-pot Grignard reaction procedure. The Organosiloxane can be easily polymerized or copolymerized to form the oligomers which can be directly converted to cross-linked network structures with excellent thermostability and low dielectric constants, implying that the Organosiloxane has potential application in the electrical and microelectronics industry.
Laurent Gonon - One of the best experts on this subject based on the ideXlab platform.
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Untangling the Condensation Network of Organosiloxanes on Nanoparticles using 2D 29Si–29Si Solid-State NMR Enhanced by Dynamic Nuclear Polarization
2015Co-Authors: Daniel Lee, Guillaume Monin, Nghia Tuan Duong, Michel Bardet, Vincent H Mareau, Laurent Gonon, Isabel Zamanillo Lopez, Gaël De PaëpeAbstract:Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with Organosiloxanes. Information about the surface coverage and the nature, if any, of Organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear 29Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of 29Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D 29Si–29Si correlation experiments, it is shown that the required reaction conditions favor lateral polymerization and domain growth. Moreover, the natural abundance correlation experiments permitted the estimation of 2JSi–O–Si-couplings (13.8 ± 1.4 Hz for surface silica) and interatomic distances (3.04 ± 0.08 Å for surface silica) since complications associated with many-spin systems and also sensitivity were avoided. The work detailed herein not only demonstrates the possibility of using MAS-DNP to greatly facilitate the acquisition of 2D 29Si–29Si correlation spectra but also shows that this technique can be used in a routine fashion to characterize surface grafting networks and gain structural constraints, which can be related to a system’s chemical and physical properties
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untangling the condensation network of Organosiloxanes on nanoparticles using 2d 29si 29si solid state nmr enhanced by dynamic nuclear polarization
Journal of the American Chemical Society, 2014Co-Authors: Daniel Lee, Guillaume Monin, Nghia Tuan Duong, Isabel Zamanillo Lopez, Michel Bardet, Vincent H Mareau, Laurent GononAbstract:Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with Organosiloxanes. Information about the surface coverage and the nature, if any, of Organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear 29Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of 29Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D 29Si–29Si correlation experiments, it ...
Guillaume Monin - One of the best experts on this subject based on the ideXlab platform.
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Untangling the Condensation Network of Organosiloxanes on Nanoparticles using 2D 29Si–29Si Solid-State NMR Enhanced by Dynamic Nuclear Polarization
2015Co-Authors: Daniel Lee, Guillaume Monin, Nghia Tuan Duong, Michel Bardet, Vincent H Mareau, Laurent Gonon, Isabel Zamanillo Lopez, Gaël De PaëpeAbstract:Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with Organosiloxanes. Information about the surface coverage and the nature, if any, of Organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear 29Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of 29Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D 29Si–29Si correlation experiments, it is shown that the required reaction conditions favor lateral polymerization and domain growth. Moreover, the natural abundance correlation experiments permitted the estimation of 2JSi–O–Si-couplings (13.8 ± 1.4 Hz for surface silica) and interatomic distances (3.04 ± 0.08 Å for surface silica) since complications associated with many-spin systems and also sensitivity were avoided. The work detailed herein not only demonstrates the possibility of using MAS-DNP to greatly facilitate the acquisition of 2D 29Si–29Si correlation spectra but also shows that this technique can be used in a routine fashion to characterize surface grafting networks and gain structural constraints, which can be related to a system’s chemical and physical properties
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untangling the condensation network of Organosiloxanes on nanoparticles using 2d 29si 29si solid state nmr enhanced by dynamic nuclear polarization
Journal of the American Chemical Society, 2014Co-Authors: Daniel Lee, Guillaume Monin, Nghia Tuan Duong, Isabel Zamanillo Lopez, Michel Bardet, Vincent H Mareau, Laurent GononAbstract:Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with Organosiloxanes. Information about the surface coverage and the nature, if any, of Organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear 29Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of 29Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D 29Si–29Si correlation experiments, it ...
Vincent H Mareau - One of the best experts on this subject based on the ideXlab platform.
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Untangling the Condensation Network of Organosiloxanes on Nanoparticles using 2D 29Si–29Si Solid-State NMR Enhanced by Dynamic Nuclear Polarization
2015Co-Authors: Daniel Lee, Guillaume Monin, Nghia Tuan Duong, Michel Bardet, Vincent H Mareau, Laurent Gonon, Isabel Zamanillo Lopez, Gaël De PaëpeAbstract:Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with Organosiloxanes. Information about the surface coverage and the nature, if any, of Organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear 29Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of 29Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D 29Si–29Si correlation experiments, it is shown that the required reaction conditions favor lateral polymerization and domain growth. Moreover, the natural abundance correlation experiments permitted the estimation of 2JSi–O–Si-couplings (13.8 ± 1.4 Hz for surface silica) and interatomic distances (3.04 ± 0.08 Å for surface silica) since complications associated with many-spin systems and also sensitivity were avoided. The work detailed herein not only demonstrates the possibility of using MAS-DNP to greatly facilitate the acquisition of 2D 29Si–29Si correlation spectra but also shows that this technique can be used in a routine fashion to characterize surface grafting networks and gain structural constraints, which can be related to a system’s chemical and physical properties
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untangling the condensation network of Organosiloxanes on nanoparticles using 2d 29si 29si solid state nmr enhanced by dynamic nuclear polarization
Journal of the American Chemical Society, 2014Co-Authors: Daniel Lee, Guillaume Monin, Nghia Tuan Duong, Isabel Zamanillo Lopez, Michel Bardet, Vincent H Mareau, Laurent GononAbstract:Silica (SiO2) nanoparticles (NPs) were functionalized by silanization to produce a surface covered with Organosiloxanes. Information about the surface coverage and the nature, if any, of Organosiloxane polymerization, whether parallel or perpendicular to the surface, is highly desired. To this extent, two-dimensional homonuclear 29Si solid-state NMR could be employed. However, owing to the sensitivity limitations associated with the low natural abundance (4.7%) of 29Si and the difficulty and expense of isotopic labeling here, this technique would usually be deemed impracticable. Nevertheless, we show that recent developments in the field of dynamic nuclear polarization under magic angle spinning (MAS-DNP) could be used to dramatically increase the sensitivity of the NMR experiments, resulting in a timesaving factor of ∼625 compared to conventional solid-state NMR. This allowed the acquisition of previously infeasible data. Using both through-space and through-bond 2D 29Si–29Si correlation experiments, it ...