The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Kazuki Nakanishi - One of the best experts on this subject based on the ideXlab platform.
-
transparent superflexible doubly cross linked polyvinylpolymethylsiloxane aerogel superinsulators via ambient pressure drying
ACS Nano, 2018Co-Authors: Guoqing Zu, Kazuyoshi Kanamori, Taiyo Shimizu, Ayaka Maeno, Hironori Kaji, Jun Shen, Kazuki NakanishiAbstract:Aerogels have many attractive properties but are usually costly and mechanically brittle, which always limit their practical applications. While many efforts have been made to reinforce the aerogels, most of the reinforcement efforts sacrifice the transparency or superinsulating properties. Here we report superflexible polyvinylpolymethylsiloxane, (CH2CH(Si(CH3)O2/2))n, aerogels that are facilely prepared from a single precursor vinylmethyldimethoxysilane or vinylmethyldiethoxysilane without organic cross-linkers. The method is based on consecutive processes involving radical polymerization and hydrolytic polycondensation, followed by ultralow-cost, highly scalable, ambient-pressure drying directly from alcohol as a drying medium without any modification or additional solvent exchange. The resulting aerogels and Xerogels show a homogeneous, tunable, highly porous, doubly cross-linked nanostructure with the elastic polymethylsiloxane network cross-linked with flexible hydrocarbon chains. An outstanding com...
-
silicone based organic inorganic hybrid aerogels and Xerogels
Chemistry: A European Journal, 2017Co-Authors: Taiyo Shimizu, Kazuyoshi Kanamori, Kazuki NakanishiAbstract:Aerogels are attracting increasing attention due to their high thermal insulation ability as well as unique properties such as high porosity, surface area, and transparency. However, low mechanical strengths, originating from their unique porous structure, impede handling, formability, mass production, and extended applications. This minireview focuses on the strengthening of aerogels by several organic-inorganic hybridization strategies. In particular, successful strengthening methodologies, which employ organo-substituted alkoxysilanes as the single precursor for the sol-gel preparations, developed by the authors are highlighted. Moreover, improvements in compressive strength and elasticity lead to monolithic aerogel-like Xerogels through ambient pressure drying. Correlations between structures in different length scales (e.g., molecular, network, and pore structure levels) and resultant mechanical properties are discussed for further understandings and better design toward mechanically improved aerogels/Xerogels and their applications.
-
transparent ethylene bridged polymethylsiloxane aerogels and Xerogels with improved bending flexibility
Langmuir, 2016Co-Authors: Taiyo Shimizu, Kazuyoshi Kanamori, Ayaka Maeno, Hironori Kaji, Kazuki NakanishiAbstract:Transparent, monolithic aerogels with nanosized colloidal skeletons have been obtained from a single precursor of 1,2-bis(methyldiethoxysilyl)ethane (BMDEE) by adopting a liquid surfactant and a two-step process involving strong-acid, followed by strong-base, sol–gel reactions. This precursor BMDEE forms the ethylene-bridged polymethylsiloxane (EBPMS, O2/2(CH3)Si–CH2CH2–Si(CH3)O2/2) network, in which each silicon has one methyl, two bridging oxygens, and one bridging ethylene, exhibiting an analogous structure to that of the previously reported polymethylsilsesquioxane (PMSQ, CH3SiO3/2) aerogels having one methyl and three bridging oxygen atoms. Obtained aerogels consist of fine colloidal skeletons and show high visible-light transparency and a flexible deformation behavior against compression without collapse. Similar to the PMSQ aerogels, a careful tuning of synthetic conditions can produce low-density (0.19 g cm–3) and highly transparent (76% at 550 nm, corresponding to 10 mm thick samples) Xerogels vi...
-
sol gel synthesis of zinc ferrite based xerogel monoliths with well defined macropores
RSC Advances, 2013Co-Authors: Yasuki Kido, Kazuki Nakanishi, Kazuyoshi KanamoriAbstract:Starting from an aqueous solution, porous zinc ferrite-based xerogel monoliths have been prepared via a sol–gel route accompanied by phase separation mediated by propylene oxide in the presence of poly(acrylamide). The Xerogels possess well-defined macropores, and the macroporous morphologies could be easily controlled (macropore size ranges from 0.55 to 1.29 μm) by simply changing the starting composition. As-dried xerogel samples were amorphous under X-ray diffraction, while heat-treatment in air brought about the formation of spinel type ferrite phase, ZnFe2O4. Calcination under Ar atmosphere allowed the crystallization of various iron-based phases/carbon composites (Fe3O4, Fe1-δO, Fe3N, Fe4N, Fe3C, and Fe). Samples heated under Ar flow exhibited hierarchical pore structures, including continuous macropores, in addition to mesopores and micropores embedded in the carbon-containing composite matrices.
-
new flexible aerogels and Xerogels derived from methyltrimethoxysilane dimethyldimethoxysilane co precursors
Journal of Materials Chemistry, 2011Co-Authors: Gen Hayase, Kazuyoshi Kanamori, Kazuki NakanishiAbstract:We report new flexible “marshmallow-like” aerogels and Xerogels with a bendable feature from the methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) co-precursor systems. A 2-step acid/base sol–gel process and surfactant are employed to control the phase separation of the hydrophobic networks, which give porous monolithic gels. The obtained gels become softer and more flexible with increasing DMDMS fractions.
Kazuyoshi Kanamori - One of the best experts on this subject based on the ideXlab platform.
-
mechanically strong scalable mesoporous Xerogels of nanocellulose featuring light permeability thermal insulation and flame self extinction
ACS Nano, 2021Co-Authors: Wataru Sakuma, Kazuyoshi Kanamori, Shunsuke Yamasaki, Shuji Fujisawa, Takashi Kodama, Junichiro Shiomi, Tsuguyuki SaitoAbstract:Scalability is a common challenge in the structuring of nanoscale particle dispersions, particularly in the drying of these dispersions for producing functional, porous structures such as aerogels. Aerogel production relies on supercritical drying, which exhibits poor scalability. A solution to this scalability limitation is the use of evaporative drying under ambient pressure. However, the evaporative drying of wet gels comprising nanoscale particles is accompanied by a strong capillary force. Therefore, it is challenging to produce evaporative-dried gels or "Xerogels" that possess the specific structural profiles of aerogels such as mesoscale pores, high porosity, and high specific surface area (SSA). Herein, we demonstrate a structure of mesoporous Xerogels with high porosity (∼80%) and high SSA (>400 m2 g-1) achieved by exploiting cellulose nanofibers (CNFs) as the building blocks with tunable interparticle interactions. CNFs are sustainable, wood-derived materials with high strength. In this study, the few-nanometer-wide CNFs bearing carboxy groups were structured into a stable network via ionic inter-CNF interaction. The outline of the resulting Xerogels was then tailored into a regular, millimeter-thick, board-like structure. Several characterization techniques highlighted the multifunctionality of the CNF Xerogels combining outstanding strength (compression E = 170 MPa, σ = 10 MPa; tension E = 290 MPa, σ = 8 MPa), moderate light permeability, thermal insulation (0.06-0.07 W m-1 K-1), and flame self-extinction. As a potential application of the Xerogels, daylighting yet insulating, load-bearing wall members can be thus proposed.
-
nanocellulose Xerogels with high porosities and large specific surface areas
Frontiers in Chemistry, 2019Co-Authors: Shunsuke Yamasaki, Wataru Sakuma, Hiroaki Yasui, Kazuho Daicho, Tsuguyuki Saito, Shuji Fujisawa, Akira Isogai, Kazuyoshi KanamoriAbstract:Xerogels are defined as porous structures that are obtained by evaporative drying of wet gels. One challenge is producing Xerogels with high porosity and large specific surface areas, which are structurally comparable to supercritical-dried aerogels. Herein, we report on cellulose Xerogels with a truly aerogel-like porous structure. These Xerogels have a monolithic form with porosities and specific surface areas in the ranges of 71-76% and 340-411 m2/g, respectively. Our strategy is based on combining three concepts: (1) the use of a very fine type of cellulose nanofibers (CNFs) with a width of ~3 nm as the skeletal component of the xerogel; (2) increasing the stiffness of wet CNF gels by reinforcing the inter-CNF interactions to sustain their dry shrinkage; and (3) solvent-exchange of wet gels with low-polarity solvents, such as hexane and pentane, to reduce the capillary force on drying. The synergistic effects of combining these approaches lead to improvements in the porous structure in the CNF Xerogels.
-
transparent superflexible doubly cross linked polyvinylpolymethylsiloxane aerogel superinsulators via ambient pressure drying
ACS Nano, 2018Co-Authors: Guoqing Zu, Kazuyoshi Kanamori, Taiyo Shimizu, Ayaka Maeno, Hironori Kaji, Jun Shen, Kazuki NakanishiAbstract:Aerogels have many attractive properties but are usually costly and mechanically brittle, which always limit their practical applications. While many efforts have been made to reinforce the aerogels, most of the reinforcement efforts sacrifice the transparency or superinsulating properties. Here we report superflexible polyvinylpolymethylsiloxane, (CH2CH(Si(CH3)O2/2))n, aerogels that are facilely prepared from a single precursor vinylmethyldimethoxysilane or vinylmethyldiethoxysilane without organic cross-linkers. The method is based on consecutive processes involving radical polymerization and hydrolytic polycondensation, followed by ultralow-cost, highly scalable, ambient-pressure drying directly from alcohol as a drying medium without any modification or additional solvent exchange. The resulting aerogels and Xerogels show a homogeneous, tunable, highly porous, doubly cross-linked nanostructure with the elastic polymethylsiloxane network cross-linked with flexible hydrocarbon chains. An outstanding com...
-
silicone based organic inorganic hybrid aerogels and Xerogels
Chemistry: A European Journal, 2017Co-Authors: Taiyo Shimizu, Kazuyoshi Kanamori, Kazuki NakanishiAbstract:Aerogels are attracting increasing attention due to their high thermal insulation ability as well as unique properties such as high porosity, surface area, and transparency. However, low mechanical strengths, originating from their unique porous structure, impede handling, formability, mass production, and extended applications. This minireview focuses on the strengthening of aerogels by several organic-inorganic hybridization strategies. In particular, successful strengthening methodologies, which employ organo-substituted alkoxysilanes as the single precursor for the sol-gel preparations, developed by the authors are highlighted. Moreover, improvements in compressive strength and elasticity lead to monolithic aerogel-like Xerogels through ambient pressure drying. Correlations between structures in different length scales (e.g., molecular, network, and pore structure levels) and resultant mechanical properties are discussed for further understandings and better design toward mechanically improved aerogels/Xerogels and their applications.
-
transparent ethylene bridged polymethylsiloxane aerogels and Xerogels with improved bending flexibility
Langmuir, 2016Co-Authors: Taiyo Shimizu, Kazuyoshi Kanamori, Ayaka Maeno, Hironori Kaji, Kazuki NakanishiAbstract:Transparent, monolithic aerogels with nanosized colloidal skeletons have been obtained from a single precursor of 1,2-bis(methyldiethoxysilyl)ethane (BMDEE) by adopting a liquid surfactant and a two-step process involving strong-acid, followed by strong-base, sol–gel reactions. This precursor BMDEE forms the ethylene-bridged polymethylsiloxane (EBPMS, O2/2(CH3)Si–CH2CH2–Si(CH3)O2/2) network, in which each silicon has one methyl, two bridging oxygens, and one bridging ethylene, exhibiting an analogous structure to that of the previously reported polymethylsilsesquioxane (PMSQ, CH3SiO3/2) aerogels having one methyl and three bridging oxygen atoms. Obtained aerogels consist of fine colloidal skeletons and show high visible-light transparency and a flexible deformation behavior against compression without collapse. Similar to the PMSQ aerogels, a careful tuning of synthetic conditions can produce low-density (0.19 g cm–3) and highly transparent (76% at 550 nm, corresponding to 10 mm thick samples) Xerogels vi...
James H Small - One of the best experts on this subject based on the ideXlab platform.
-
dialkylene carbonate bridged polysilsesquioxanes hybrid organic inorganic sol gels with a thermally labile bridging group
Chemistry of Materials, 1999Co-Authors: James V Beach, Brigitta M Baugher, Roger A Assink, Kenneth J Shea, Joseph Tran, James H SmallAbstract:In this paper, we introduce a new approach for altering the properties of bridged polysilsesquioxane Xerogels using postprocessing modification of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or chemically after the gel has been processed to a xerogel. These modifications can produce changes in density, solubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic−inorganic materials. Dialkylene carbonate-bridged polysilsesquioxane gels were prepared by the sol−gel polymerization of bis(triethoxysilylpropyl) carbonate (1) and bis(triethoxysilylisobutyl) carbonate (2). Thermal treatment of the resulting nonporous Xerogels and aerogels at 300−350 °C resulted in quantitative decarboxylation of the dialkylene carbonate bridging groups to give new hydroxyalkyl and olefini...
-
dialkylenecarbonate bridged polysilsesquioxanes hybrid organic inorganic sol gels with a thermally labile bridging group
Journal of the American Chemical Society, 1999Co-Authors: James V Beach, Brigitta M Baugher, Roger A Assink, Kenneth J Shea, Joseph Tran, James H SmallAbstract:In this paper, we introduce a new approach for altering the properties of bridged polysilsesquioxane Xerogels using post-processing modification of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or by chemical means after the gel has been processed to a xerogel. These modifications can produce changes in density, volubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic-inorganic materials. Dialkylenecarbonate-bridged polysilsesquioxane gels were prepared by the sol-gel polymerization of bis(triethoxysilylpropyl)carbonate (1) and bis(triethoxysilylisobutyl)-carbonate (2). Thermal treatment of the resulting non-porous Xerogels and aerogels at 300-350 C resulted in quantitative decarboxylation of the dialkylenecarbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilsesquioxane monolithic Xerogels and aerogels that can not be directly prepared through direct sol-gel polymerization of organotrialkoxysilanes.
Mark H. Schoenfisch - One of the best experts on this subject based on the ideXlab platform.
-
photoinitiated nitric oxide releasing tertiary s nitrosothiol modified Xerogels
ACS Applied Materials & Interfaces, 2012Co-Authors: Daniel A Riccio, Peter N Coneski, Scott P Nichols, Angela D Broadnax, Mark H. SchoenfischAbstract:The synthesis of a tertiary thiol-bearing silane precursor (i.e., N-acetyl penicillamine propyltrimethoxysilane or NAPTMS) to enable enhanced NO storage stability at physiological temperature is described. The novel silane was co-condensed with alkoxy- or alkylalkoxysilanes under varied synthetic parameters (e.g., water to silane ratio, catalyst and solvent concentrations, and reaction time) to evaluate systematically the formation of stable xerogel films. The resulting Xerogels were subsequently nitrosated to yield tertiary RSNO-modified coatings. Total NO storage ranged from 0.87 to 1.78 μmol cm–2 depending on the NAPTMS concentration and xerogel coating thickness. Steric hindrance near the nitroso functionality necessitated the use of photolysis to liberate NO. The average NO flux for irradiated Xerogels (20% NAPTMS balance TEOS xerogel film cast using 30 μL) in physiological buffer at 37 °C was ∼23 pmol cm–2 s–1. The biomedical utility of the photoinitiated NO-releasing films was illustrated by their ...
-
nitric oxide releasing s nitrosothiol modified Xerogels
Biomaterials, 2009Co-Authors: Daniel A Riccio, Benjamin J Privett, Kevin P. Dobmeier, Heather S. Paul, Evan M. Hetrick, Mark H. SchoenfischAbstract:The synthesis, material characterization, and in vitro biocompatibility of S-nitrosothiol (RSNO)-modified Xerogels are described. Thiol-functionalized xerogel films were formed by hydrolysis and co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and methyltrimethoxysilane (MTMOS) sol-gel precursors at varying concentrations. Subsequent thiol nitrosation via acidified nitrite produced RSNO-modified Xerogels capable of generating nitric oxide (NO) for up to 2 weeks under physiological conditions. Xerogels also exhibited NO generation upon irradiation with broad-spectrum light or exposure to copper, with NO fluxes proportional to wattage and concentration, respectively. Xerogels were capable of storing up to approximately 1.31 micromol NO mg(-1), and displayed negligible fragmentation over a 2-week period. Platelet and bacterial adhesion to nitrosated films was reduced compared to non-nitrosated controls, confirming the antithrombotic and antibacterial properties of the NO-releasing materials. Fibroblast cell viability was maintained on the xerogel surfaces illustrating the promise of RSNO-modified Xerogels as biomedical device coatings.
-
Nitric oxide-releasing S-nitrosothiol-modified Xerogels
Biomaterials, 2009Co-Authors: Daniel A Riccio, Benjamin J Privett, Kevin P. Dobmeier, Heather S. Paul, Evan M. Hetrick, Mark H. SchoenfischAbstract:Abstract The synthesis, material characterization, and in vitro biocompatibility of S-nitrosothiol (RSNO)-modified Xerogels are described. Thiol-functionalized xerogel films were formed by hydrolysis and co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and methyltrimethoxysilane (MTMOS) sol–gel precursors at varying concentrations. Subsequent thiol nitrosation via acidified nitrite produced RSNO-modified Xerogels capable of generating nitric oxide (NO) for up to 2 weeks under physiological conditions. Xerogels also exhibited NO generation upon irradiation with broad-spectrum light or exposure to copper, with NO fluxes proportional to wattage and concentration, respectively. Xerogels were capable of storing up to ∼1.31 μmol NO mg−1, and displayed negligible fragmentation over a 2-week period. Platelet and bacterial adhesion to nitrosated films was reduced compared to non-nitrosated controls, confirming the antithrombotic and antibacterial properties of the NO-releasing materials. Fibroblast cell viability was maintained on the xerogel surfaces illustrating the promise of RSNO-modified Xerogels as biomedical device coatings.
-
fluorinated xerogel derived microelectrodes for amperometric nitric oxide sensing
Analytical Chemistry, 2008Co-Authors: Jae Ho Shin, Benjamin J Privett, Justin M Kita, Mark R Wightman, Mark H. SchoenfischAbstract:An amperometric fluorinated xerogel-derived nitric oxide (NO) microelectrode is described. A range of fluorine-modified xerogel polymers were synthesized via the cohydrolysis and condensation of alkylalkoxy- and fluoroalkoxysilanes. Such polymers were evaluated as NO sensor membranes to identify the optimum composition for maximizing NO permeability while providing sufficient selectivity for NO in the presence of common interfering species. By taking advantage of both the versatility of sol−gel chemistry and the “poly(tetrafluoroethylene)-like” high NO permselective properties of the Xerogels, the performance of the fluorinated xerogel-derived sensors was excellent, surpassing all miniaturized NO sensors reported to date. In contrast to previous electrochemical NO sensor designs, xerogel-based NO microsensors were fabricated using a simple, reliable dip-coating procedure. An optimal permselective membrane was achieved by synthesizing Xerogels of methyltrimethoxysilane (MTMOS) and 20% (heptadecafluoro-1,1,...
James V Beach - One of the best experts on this subject based on the ideXlab platform.
-
dialkylene carbonate bridged polysilsesquioxanes hybrid organic inorganic sol gels with a thermally labile bridging group
Chemistry of Materials, 1999Co-Authors: James V Beach, Brigitta M Baugher, Roger A Assink, Kenneth J Shea, Joseph Tran, James H SmallAbstract:In this paper, we introduce a new approach for altering the properties of bridged polysilsesquioxane Xerogels using postprocessing modification of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or chemically after the gel has been processed to a xerogel. These modifications can produce changes in density, solubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic−inorganic materials. Dialkylene carbonate-bridged polysilsesquioxane gels were prepared by the sol−gel polymerization of bis(triethoxysilylpropyl) carbonate (1) and bis(triethoxysilylisobutyl) carbonate (2). Thermal treatment of the resulting nonporous Xerogels and aerogels at 300−350 °C resulted in quantitative decarboxylation of the dialkylene carbonate bridging groups to give new hydroxyalkyl and olefini...
-
dialkylenecarbonate bridged polysilsesquioxanes hybrid organic inorganic sol gels with a thermally labile bridging group
Journal of the American Chemical Society, 1999Co-Authors: James V Beach, Brigitta M Baugher, Roger A Assink, Kenneth J Shea, Joseph Tran, James H SmallAbstract:In this paper, we introduce a new approach for altering the properties of bridged polysilsesquioxane Xerogels using post-processing modification of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or by chemical means after the gel has been processed to a xerogel. These modifications can produce changes in density, volubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic-inorganic materials. Dialkylenecarbonate-bridged polysilsesquioxane gels were prepared by the sol-gel polymerization of bis(triethoxysilylpropyl)carbonate (1) and bis(triethoxysilylisobutyl)-carbonate (2). Thermal treatment of the resulting non-porous Xerogels and aerogels at 300-350 C resulted in quantitative decarboxylation of the dialkylenecarbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilsesquioxane monolithic Xerogels and aerogels that can not be directly prepared through direct sol-gel polymerization of organotrialkoxysilanes.
