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201.
《国际聚合物材料杂志》2012,61(2):97-106
Functional poly(ester-anhydride) microspheres were prepared using emulsion solvent evaporation (ESE) and phase inversion methods (PIM). The poly(ester-anhydride)s were obtained by polycondensation of sebacic acid (SBA) and oligo(3-allyloxy-1,2-propylene succinate) terminated with carboxyl groups (OSAGE). The effects of various parameters, including: polymer and emulsifier concentrations, stirring speed and molecular weight of polyvinyl alcohol (PVA) used as emulsifier on size, size distribution and morphology of microspheres obtained by ESE technique were examined. The size of microspheres obtained was in the range 2–30 µm and depended mainly on the stirring rate in emulsion formulation process, as well as concentration of polymer solution used. Molecular weight of PVA, and its concentration in aqueous phase, significantly influenced tendency to agglomeration of microparticles formed, but only slightly changed the size of microspheres. The present study demonstrated that the ESE method can be useful to formulate, from functional poly(ester-anhydride)s, small (2–3 µm) or large (20–30 µm) microspheres with relatively narrow size distribution. Such microspheres were loaded with three model compounds (rhodamine B, p-nitroaniline, and piroxicam) with different water solubility and their release characteristics were examined. In the present study microparticles were also obtained by alternative phase inversion method to compare mainly stability of polymers during formulation of microspheres by both techniques. 相似文献
202.
《Journal of the European Ceramic Society》2014,34(4):889-902
Two linear polysiloxanes with vinyl groups regularly distributed in their chains (D2V polymer with a vinyl group at every third and V3 polymer with a vinyl group at each Si atom) were cross-linked with different hydrogensiloxanes (linear difunctional HMMH, linear branched tetrafunctional Q(MH)4, cyclic tetrafunctional D4H) and studied as new precursors to SiCO ceramics. It was found that thermal properties of the cross-linked D2V and V3 polymers are governed mainly by functionality of the initial macromolecule as well as functionality and molecular structure of hydrogensiloxane. Transformation of the systems into ceramics was examined by recording FTIR spectra of the samples obtained after heat treatment of the cross-linked polymers under Ar at several temperatures. Analysis of the products formed at 1 000 °C, allowed establishing that they are a mixture of silicon oxycarbides and a free carbon phase. Lack of pores is a characteristic feature of these materials. 相似文献
203.
The synthesis of monomodal copolymers with poly(ethylene glycol) (PEG) side chains from commercial poly(ethylene glycol) methacrylates (PEGMA) by atom transfer radical polymerization (ATRP) is verified. Two hydroxy-functionalized PEGMA macromonomers (520 g/mol and 360 g/mol) were copolymerized with methyl methacrylate (MMA) using various initial feed (1.5/98.5–50/50 mol.%). The copolymers P(MMA-co-PEGMA) with high degree of polymerization, e.g. 100–275 of repeating units in the backbone including 7–56 PEG side chains, were obtained. The relative reactivity ratios of PEGMA and MMA determined by the Jaacks method indicated slightly faster incorporation of macromonomer into polymeric chain than MMA (rMMA = 0.79; rPEGMA = 1.27). The polymers containing at least 17 mol.% of PEGMA units were water-soluble and exhibited clouding point at temperature in a broad range of 39–70 °C. The temperature-sensitive effect makes these polymers as a potential carriers in drug delivery systems. In the case of copolymers insoluble in water, a three-step procedure, including esterification to ATRP multifunctional macroinitiators, ATRP of tert-butyl methacrylate (tBMA) by grafting from, deprotection of carboxylic groups by removing tert-butyl groups, was applied to extend PEG grafts and expand the content of hydrophilic fraction (32–94 mol.%), what efficiently developed polymer solubility in polar solvents giving possibility for the future biomedical applications. 相似文献
204.
《Carbon》2014
We report a new method to modify electrical properties of carbon nanotubes (CNTs). Single-, double- and multi-wall CNTs were subjected to treatment with a polar interhalogen compound, i.e. iodine monochloride (ICl) for 8 h at room temperature or briefly at 350 °C to assess kinetics and thermodynamics of the reactions. The results showed a powerful p-doping, which enabled us to decrease electrical resistance of the material by more than 60% eventually reaching specific conductivity of 1.24 S m2 g−1. Functionalization of CNTs with halogen atoms resulted in evident changes to the material microstructure and composition. To illustrate viability of this technique for manufacturing highly conductive wires, we have produced an ICl-doped CNT-based USB cable. The tests unequivocally revealed that the cable could be successfully used for power or data transmission on the verge of USB 2.0 capabilities. 相似文献
205.
Michal Sitarz Monika Kwoka Elisabetta Comini Dario Zappa Jacek Szuber 《Nanoscale research letters》2014,9(1):43
In this paper we investigate the surface chemistry, including surface contaminations, of SnO2 nanowires deposited on Ag-covered Si substrate by vapor phase deposition (VPD), thanks to x-ray photoelectron spectroscopy (XPS) in combination with thermal desorption spectroscopy (TDS). Air-exposed SnO2 nanowires are slightly non-stoichiometric, and a huge amount of C contaminations is observed at their surface. After the thermal physical desorption (TPD) process, SnO2 nanowires become almost stoichiometric without any surface C contaminations. This is probably related to the fact that C contaminations, as well as residual gases from air, are weakly bounded to the crystalline SnO2 nanowires and can be easily removed from their surface. The obtained results gave us insight on the interpretation of the aging effect of SnO2 nanowires that is of great importance for their potential application in the development of novel chemical nanosensor devices. 相似文献
206.
《Electrochimica acta》2001,46(1-2):243-249
A new concept based on an identical transducer principle and structure for both (bio-)chemical and physical sensors is presented. For all sensors, the field effect is used as transducer principle. In this approach, the same chemical sensor is employed also as a physical sensor. A novel design of a temperature sensor on the basis of a differential arrangement of two identical ISFETs operating in different working points is demonstrated. A multifunctionality of the sensor system is achieved by means of different sensor arrangements and/or operation modes. Thus, the number of the obtained (bio-)chemical and physical quantities, like ion concentration, temperature, flow rate can be higher than the number of the sensors applied. A hybrid sensor module, for the pH, penicillin and temperature determination is realised and its performance has been investigated. 相似文献
207.
《Journal of the European Ceramic Society》2005,25(7):1081-1087
The removal of wax from an unfired ceramic shell system without cracking or dimensional alterations is a key stage within the investment casting process. The effect of autoclave steam on polymer and fibre modified investment casting mould behaviour has been investigated. The polymer modified system exhibited a higher mechanical strength in the green dry state, but that strength significantly reduced when subjected to a simulated autoclave “wet” condition, giving a 38% reduction in a flat bar section and a 45% reduction in an edge test. It is suggested that this is related to the softening of the latex particles when they are in contact with steam. In comparison the fibre modified system showed a much lower reduction in strength when subjected to “wet” conditions. Calculating the adjusted fracture load (AFL) bearing capacity for the extra shell thickness of the fibre system showed that the fibre system outperforms the polymer system when the samples were tested “wet”, showing a 33% increase in a flat bar section and an increase of over 150% in the more vulnerable edge region. The results suggest that the effect of moisture must be taken into account when studying the shell behaviour under autoclave conditions. 相似文献
208.
《Chemical engineering science》2002,57(22-23):4763-4778
It is shown that chaos analysis provides valuable tools to improve the design and operation of multiphase reactors, the most useful tools being the system's attractor and the Kolmogorov entropy. Applications of chaos analysis are based upon examining the attractor shape and/or on a characterization of the attractor by the Kolmogorov entropy. Examples are given by the characterization of regimes and regime transitions, scale up, control of the bubble pattern in the reactor to influence selectivity and conversion of chemical reactions, and the development of a tool to early detect agglomeration in fluidized beds. 相似文献
209.
Studies were carried out using novel magnetic carrier particles in a magnetically stabilized fluidized bed (MSFB) to determine the degree of liquid phase mass transfer enhancement achievable over a range of magnetic field strengths. The carrier particles, beads of κ-carrageenan incorporating magnetite, ranging in size from 0.25 to 1 mm are used for enzyme immobilization. Results using a 113 mm diameter column showed that a more than five-fold increase in liquid velocity could be achieved when a current of 40 A was applied to a single magnetic coil. The “escape” velocity of the particles from the bed was found to be proportional to the magnetic field intensity squared. The effect was further increased (almost doubled) by inserting a steel rod into the centre of the bed. 相似文献
210.
《Diamond and Related Materials》2000,9(11):1856-1861
The paper is a contribution to the characterization of bonding in carbon films. C is unique in establishing different kinds of CC bonds that are described in terms of variously hybridized s and p electron states of its VB (Valence Bond). On this basis, the idea is put forward that the sp hybridization of C in different environments is best characterized if the s- and p-partial density of states (DOS) are independently mapped. This is made possible by sampling the occupied DOS via probes that are selective with respect to the angular momentum symmetry of electron states, such as X-ray excited VB emission (s-selective) and C KVV (K Valence Valence) Auger emission (p-selective). The VB electronic structure appears to be well-characterized in this way. Systems made of purely sp2 or purely sp3-hybridized carbons are unambiguously singled out while for systems where the two hybridizations coexist, the ability to reveal changes in the relative amount of sp2 and sp3 hybridized carbons is demonstrated. 相似文献