Search results for "siloxane"
showing 10 items of 121 documents
Dynamic covalent urea bonds and their potential for development of self-healing polymer materials
2019
Self-healing polymer materials have drawn rapidly increasing interest over the last decade, and have been studied and used in an ever-increasing range of applications. Herein, we successfully make the covalent urea bond – a pinnacle of stability due to strong resonance effects – dynamic in nature through mediation of zinc salts. The dynamic covalent character of urea in the presence of zinc ions is confirmed through dissociation reaction experiments and quantum chemical calculations of small-molecule model urea compounds. In line with our experiments, the modelling results suggest that the presence of zinc ions speeds up the reaction of urea dissociation by two orders of magnitude via the f…
Gold nanoparticles grown on a hydrophobic and texturally tunable PDMS-like framework
2021
Mesoporous silicas are among the most suitable high-surface area solids to support small-sized metal clusters and nanoparticles. Unfortunately, the instability of silica in water constitutes a serious impediment for its widespread use and large implementation as a catalytic support for fine chemical synthesis and for biomass upgrading in the context of biorefineries. While end cupping silanols provides a way for delaying framework degradation, further investigations are needed to design more robust, water-resistant supports. Prompted by the success of polydimethylsiloxane (PDMS) in surface coating and water-repellent technologies, we herein explore the transformation of triethoxysilyl-funct…
Ionic liquids versus amine solutions in biogas upgrading: the level of volatile organic compounds
2013
Background: This article provides information related to the occurrence of volatile organic compounds before and after biogas purification, by means of both aqueous amine solutions and ionic liquids. Results & discussion: Encouraging results were obtained. Under the experimental conditions, 1-butyl-3-methylimidazolium acetate ionic liquid appeared to perform at least two-times better than aqueous amines solutions, since it captured 65 wt% of the identified volatile organic compounds, while aqueous amine solutions retained around 35 wt% only. However, in the case of octamethylcyclotetrasiloxane and dichlorobenzene, aqueous amine solutions rendered better purification performance and diminish…
In vitro investigation of the impact of remaining tooth structure on the tensile failure loads of overdenture copings
2019
Background The purpose of this in vitro study was to evaluate the impact of the remaining tooth structure on the retention of overdenture cast metal copings. Material and Methods A freshly extracted intact mandibular human canine (length 25 mm) was selected and endodontically treated. An incisal reduction of 4 mm with no ferrule preparation was performed and a post space of 12 mm was created. By using polyvinyl siloxane duplication material and autopolymerizing polymethylmethacrylate resin, ten resin teeth analogs (control group) were obtained. A second set of ten resin teeth analogs (group 1) was created by preparing on the original natural tooth a 360o ferrule design of 1 mm in height and…
Zwitterionic codeine-derived methacrylate monoliths for enantioselective capillary electrochromatography of chiral acids and chiral bases
2018
Thiol-ene click reaction of N-acetyl-L-cysteine methyl ester to codeine, followed by reaction with allyl isocyanate and hydrolysis to the corresponding zwitterionic chiral selector and its subsequent bonding to the surface of a methacrylate monolith provided a new chiral capillary column for enantiomer separation of chiral acids and chiral bases. First, the epoxy groups of a poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolith were converted into amine residues, followed by reaction with allylglycidyl ether. In this way, a spacer arm was bonded to the surface before coating and cross-linking poly(3-mercaptopropyl methylsiloxane) (PMPMS) via radical addition (thiol-ene click react…
Aggregation-induced heterogeneities in the emission of upconverting nanoparticles at the submicron scale unfolded by hyperspectral microscopy
2018
Transparent upconverting hybrid nanocomposites are exciting materials for advanced applications such as 3D displays, nanosensors, solar energy converters, and fluorescence biomarkers. This work presents a simple strategy to disperse upconverting b-NaYF4:Yb3+/Er3+ or Tm3+ nanoparticles into low cost, widely used and easy-to-process polydimethylsiloxane (PDMS)-based organic–inorganic hybrids. The upconverting hybrids were shaped as monoliths, films or powders displaying in the whole volume Tm3+ or Er3+ emissions (in the violet/blue and green/red spectral regions, respectively). For the first time, hyperspectral microscopy allows the identification at the submicron scale of differences in the …
Interfacial tension of demixed polymer solutions: augmentation by polymer additives
1997
The interfacial tension between phase separated polymer solutions increases pronouncedly upon the addition of asmall amounts of incompatible polymers. This feature is demonstrated by means of measurements with solutions of polystyrene in cyclohexane and the folloowing additives: poly(styrene-block-dimethylsiloxane), polyisobutylene and polydimethylsiloxane. Theoretical considerations based on a correlation between the lenth of the tie lines and the corresponding interfacial tension corroborates this finding
Colorimetric determination of alcohols in spirit drinks using a reversible solid sensor
2018
Abstract A sensor for the colorimetric estimation of the alcoholic content has been developed based on the entrapment of the reagent (4-N,N-dioctylamino)-4‘-trifluoroacetylazobenzene (ETHT 4001) into polydimethylsiloxane (PDMS) modified with tretraethylorthosilicate (TEOS). When exposed to an alcoholic media, the sensor delivers ETHT 4001 so that it reacts with alcohols, resulting in a change in the solution color. The diffusion of the entrapped ETHT 4001 from the polymeric sensor to the working solution depends on the hydrophobicity of both the sensor matrix and the media, while the time of exposure determines whether the reagent reacts with methanol, or with methanol and ethanol. Thus, th…
Synthesis of aldonamide siloxanes by hydrosilylation
1998
Abstract The synthesis of hydrophobic/hydrophilic hybrid polymers based on polydimethylsiloxanes (PDMS) and carbohydrate derivatives involving a hydrosilylation step is reported. Starting with poly(dimethyl- co -hydromethyl)siloxanes (PDMS- co -HMS), O -acetylated N -allylaldonamides of various sugars can be attached to the siloxane backbone using platinum catalysts. The characteristics of different transition metal complexes in the polymer-analogous formation of SiC bonds are investigated. A generalized reaction pathway applicable to several reducing carbohydrates is established to synthesize aldonamide siloxanes in a broad variety of molecular weight and composition. The products obtaine…
The effect of pressure on the liquid–liquid phase equilibrium of two polydisperse polyalkylsiloxane blends
2002
The effect of pressure-induced immiscibility in polymer blends is investigated by experimental and theoretical methods. Experimental data of cloud point curves and critical points are obtained by turbidity measurements. The chosen system is a mixture of polydimethylsiloxane and polyhexylmethylsiloxane which is one of the very few polymer blends exhibiting pressure-induced immiscibility. This unusual behaviour is related to a critical temperature minimum of the critical curve and cloud point isopleths at positive pressure in the temperature–pressure diagram. The effect of the chain length on the critical temperature minimum is investigated here based on theoretical models. The effect of diff…