Fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF-(DOBAA)n-RF]/silica gel nanocomposite, which was prepared by reaction of the corresponding fluorinated oligomer with tetraethoxysilane
and silica gel nanoparticles under alkaline conditions, exhibited no weight loss even at 800 °C equal to the original silica
gel, although the corresponding parent RF-(DOBAA)n-RF oligomer was completely degraded at 600 °C. Thermogravimetric analyses/mass spectra of fluorinated nanocomposite showed that
this nanocomposite decomposed around 280 °C to afford CO2 and H2O as the major evolved gaseous products including some minor fluoro- and hydrocarbons. X-ray photoelectron spectroscopy analyses
also showed that the contents of C, F, and Si atoms in RF-(DOBAA)n-RF/SiO2 nanocomposite after the calcination at 800 °C were similar to those before the calcination. These findings suggest that the
evolved gaseous products should be encapsulated quantitatively into nanometer-size-controlled silica matrices to give the
fluorinated silica gel nanocomposite with no weight loss even at 800 °C equal to the original silica gel. 相似文献
We report here a reversible microchannel surface capture system for stimuli-responsive grafted bioanalytical beads. Poly(N-isopropylacrylamide) (PNIPAAm) was grafted onto polydimethylsiloxane (PDMS) surfaces by a UV-mediated graft polymerization from a photoinitiator that was preadsorbed in the channel wall. The surface grafting density and resulting switchable hydrophilic/hydrophobic properties were controlled by varying the photo-illumination times and/or the initiator concentration. At limiting PNIPAAm-graft densities, the surfaces demonstrated minimal contact angles of 35 degrees below the lower critical solution temperature (LCST) and maximal contact angles of 82 degrees above it. These contact angles could be varied depending on the graft density. The surface grafts are spatially limited to the photo-illuminated region to define where the trap is constructed. The surface traps capture PNIPAAm-grafted nanobeads uniformly above the LCST and facilitate their rapid release as the temperature is reversed to below the LCST. This dual surface trap and injectable chromatography system could be useful in many applications, such as affinity separations, immunoassays, and enzyme bioprocesses, by providing for the controlled capture and release of chromatography beads. 相似文献
This study is based on the assumption that the change in the texture of hazelnut, induced by water sorption or desorption, can be derived from the glass transition. No previous study has investigated the glass transition properties of hazelnuts. This study aimed to investigate the effect of water content on the glass transition and textural properties of a roasted hazelnut product. Water content of the sample was adjusted in various relative humidity conditions, and the mechanical glass transition temperature Tg was investigated using thermal rheological analysis (TRA), a type of thermomechanical analysis. The TRA curve exhibited a clear force drop induced by the glass transition, and mechanical Tg of the samples was determined. Water plasticizing effect caused mechanical Tg to decrease as the water content increased. The reduction in Tg was analyzed using the Gordon–Taylor equation and linear equation, and the critical water contents (water content at mechanical Tg?=?25 °C) were obtained. The fracturing properties of the hazelnut changed from brittle to ductile at the critical water contents. This suggested that the change in the texture of hazelnut can be characterized by the glass transition.
A stimuli-responsive magnetic nanoparticle system for diagnostic target capture and concentration has been developed for microfluidic lab card settings. Telechelic poly(N-isopropylacrylamide) (PNIPAAm) polymer chains were synthesized with dodecyl tails at one end and a reactive carboxylate at the opposite end by the reversible addition fragmentation transfer technique. These PNIPAAm chains self-associate into nanoscale micelles that were used as dimensional confinements to synthesize the magnetic nanoparticles. The resulting superparamagnetic nanoparticles exhibit a gamma-Fe2O3 core ( approximately 5 nm) with a layer of carboxylate-terminated PNIPAAm chains as a corona on the surface. The carboxylate group was used to functionalize the magnetic nanoparticles with biotin and subsequently with streptavidin. The functionalized magnetic nanoparticles can be reversibly aggregated in solution as the temperature is cycled through the PNIPAAm lower critical solution temperature (LCST). While the magnetophoretic mobility of the individual nanoparticles below the LCST is negligible, the aggregates formed above the LCST are large enough to respond to an applied magnetic field. The magnetic nanoparticles can associate with biotinylated targets as individual particles, and then subsequent application of a combined temperature increase and magnetic field can be used to magnetically separate the aggregated particles onto the poly(ethylene glycol)-modified polydimethylsiloxane channel walls of a microfluidic device. When the magnetic field is turned off and the temperature is reversed, the captured aggregates redisperse into the channel flow stream for further downstream processing. The dual magnetic- and temperature-responsive nanoparticles can thus be used as soluble reagents to capture diagnostic targets at a controlled time point and channel position. They can then be isolated and released after the nanoparticles have captured target molecules, overcoming the problem of low magnetophoretic mobility of the individual particle while retaining the advantages of a high surface to volume ratio and faster diffusive properties during target capture. 相似文献
The absolute rate constant of the reaction of O(3P) with toluene was measured by the microwave discharge-fast-flow method to obtain kT = 109.7–2.7/2.303RT l./mole·sec at 100–375°C. This was in good agreement with the rate constant calculated from the combination of the relative rate constant obtained by Jones and Cvetanovic with the recently determined absolute rate constants of the reaction of O(3P) + olefins. The extrapolation of the above Arrhenius plot to 27°C was also in good agreement with the absolute value of kT = 4.5 × 107 l./mole·sec determined recently by Atkinson and Pitts at 27°C. The rate constant of the reaction of chlorobenzene with O(3P), obtained at 238°C as 108.3 l./mole·sec by a competitive method, was smaller than kT by a factor of about two at the same temperature. 相似文献
The cationic polymerization of cis- and trans-ethyl propenyl ethers (EPE, CH3? CH?CH? O? C2H5), initiated by a mixture of hydrogen iodide and iodine (HI/I2 initiator) at ?40°C in nonpolar media (toluene and n-hexane), led to living polymers of controlled molecular weights and a narrow molecular weight distribution (MWD) (M?w/M?n = 1.2–1.3). The geometrical isomerism of the monomer did not affect the living character of the polymerization. 13C NMR stereochemical analysis of the polymers showed that the living propagating end is sterically less crowded than nonliving counterparts generated by conventional Lewis acids (e.g., BF3OEt2). New block copolymers between EPE (cis or trans) and isobutyl vinyl ether were also prepared by sequential living polymerization of the two monomers. 相似文献
Magnetic glyconanoparticles were synthesized via the co-precipitation method. Iron (II) and iron (III) chloride were co-precipitated out of solution by the addition of ammonium hydroxide in an aqueous solution containing carbohydrate stabilizers such as d-gluconic acid, lactobionic acid and Ficoll® at 75-80 °C. Stable magnetic glyconanoparticles were formed in a simple and direct process. Dynamic light scattering and transmission electron microscopy were used to characterize the surface-coated magnetic nanoparticles. In vitro cell viability studies of the glyconanoparticles were conducted with the mouse fibroblast cell lines. The magnetic glyconanoparticles revealed to be non-toxic at a concentration as high as 0.1 mg/mL. 相似文献