We describe the preparation and characterization of uniaxial magnetic gels. Fibril formation of the embedded magnetic particles generates easily detectable magnetic and optical anisotropies. A finite magnetization is frozen‐in and leads to a ferromagnetic‐like response in small homogeneous external magnetic fields. We present, for the first time, frequency dependent measurements of the shear modulus G′. Despite their optical and magnetic anisotropy, the gels are mechanically isotropic.
The time‐dependent G′ for a ferrogel in the parallel orientation in a homogeneous field of 200 mT. 相似文献
Gels of three types of carrageenans (κ‐, ι‐ and λ‐), as well as their composite gels with cellulose, were prepared using an ionic liquid, 1‐butyl‐3‐methylimidazolium chloride (BMIMCl), by a heating‐cooling process. κ‐Carrageenan gave the formation of hard gel while the other two carrageenans gave the formation of softer gels with BMIMCl. The gels were characterized by X‐ray diffraction (XRD), thermal analysis (TGA and DSC), scanning electron microscope (SEM) and compressive testing. The results indicated that, among the three types of carrageenans, κ‐ and ι‐carrageenans gave better miscible gels with BMIMCl, followed by λ‐carrageenan. On the other hand, λ‐carrageenan gave a better miscible composite gel with cellulose and BMIMCl, followed by ι‐ and κ‐carrageenans. The stress‐strain curves indicated that the mechanical properties of the above gel systems on the compressive mode were much better than those of the hydrogels of κ‐ and ι‐carrageenans as well as the cellulose gel with BMIMCl.
The mixed Langmuir monolayers and Langmuir–Blodgett (LB) films of homo‐polystyrene (h‐PS) and the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. When the content of h‐PS is below 80 wt.‐%, the mixed LB films of h‐PS/PS‐b‐P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h‐PS content (80–95%), however, highly uniform and stable necklace‐network structures are observed in the mixed LB films.
Amphiphilic hybrid π‐conjugated polymers that have polyhedral oligomeric silsesquioxanes on their side chains have been successfully synthesized by the Sonogashira–Hagihara polycondensation reaction. The obtained polymers were studied with ultraviolet‐visible absorption and photoluminescence spectra. In these polymers, the π‐conjugation length was extended along the poly(p‐phenylene‐ethynylene) backbone. Furthermore, the content of the POSS substituents can influence the aggregation behavior of the polymers and subsequent luminescent properties.
The effects of temperature and solvent on the β‐phase formation and energy transfer in an Ir(III) complex‐containing polyfluorene were investigated. Efficient energy transfer from polyfluorenes host to Ir complexes guest can be realized at low temperature. The formation of β‐phase was observed both in THF solution at low temperature and as suspended nano‐particles at room temperature. In addition, phosphorescent polymer nanoparticles were prepared successfully and exhibited efficient phosphorescent emission.
The monomer 3‐ethyl‐1‐vinyl‐2‐pyrrolidone ( 3 ) and the homopolymer poly(3‐ethyl‐1‐vinyl‐2‐pyrrolidone) ( 5 ) have been synthesized. Polymer 5 is soluble in water and shows a critical temperature (Tc) of 27 °C. The presence of cyclodextrin causes a slight shift of the Tc. The lower critical solution temperature (LCST) could be varied between 27 and 40 °C by copolymerization with N‐vinyl‐2‐pyrrolidone. A linear correlation between the Tc and the copolymer composition is observed.
A new polyhedral oligomeric silsesquioxane macromer, octakis[N‐(6‐aminopyridin‐2‐yl)undecanamide‐10‐dimethyl‐siloxy]silsesquioxane (POSS‐C11‐Py), containing eight diaminopyridine arms, is able to self‐assemble to form a physically crosslinked polymer‐like structure with good mechanical properties (tensile strength = 46.1 MPa, tensile modulus = 0.58 GPa, elongation = 49.3%) through quadruple hydrogen bonding interactions between these arms. POSS‐C11‐Py is the first organic/inorganic supermolecule possessing polymer‐like mechanical properties as a result of self‐complementary interactions, providing a potential route toward the design and fabrication of polymer‐like supramolecular materials.
The synthesis of poly(β‐alanine) by Candida antarctica lipase B immobilized as novozyme 435 catalyzed ring‐opening of 2‐azetidinone is reported. After removal of cyclic side products and low molecular weight species pure linear poly(β‐alanine) is obtained. The formation of the polymer is confirmed with 1H NMR spectroscopy and MALDI‐TOF mass spectrometry. The average degree of polymerization of the obtained polymer is limited to = 8 by its solubility in the reaction medium. Control experiments with β‐alanine as a substrate confirmed that the ring structure of the 2‐azetidinone is necessary to obtain the polymer.
Summary: Self‐oscillating polymers and nano‐gel particles consisting of N‐isopropylacrylamide and the ruthenium catalyst of the Belousov‐Zhabotinsky reaction have been prepared. In order to clarify the crosslinking effect on the self‐oscillating behavior, the phase transition behaviors were investigated by measuring the transmittance and the fluorescence intensity of the polymer solution and the gel bead suspension. Cooperative effects due to crosslinking will play an important role for the design of nanoactuators.
Chemical structure of poly(NIPAAm‐co‐Ru(bpy)3). 相似文献
It is the general consensus that in Gilch polymerizations the 1,4‐bis(chloromethylene)benzene starting material first changes into p‐quinodimethane intermediates which then act as the real monomers. However, direct observation of these intermediates has not been possible so far. This is because usually the p‐quinodimethane auto‐initiates its rapid radical polymerization instantaneously, keeping its concentration extremely low throughout the whole process. Here it is shown that, when the reaction is carried out at very low temperatures, the formation of p‐quinodimethane still proceeds but chain growth is suppressed. Hence, the concentration of the active monomer reaches a level sufficient for NMR analysis.
The extraordinary mechanical and swelling/deswelling properties of nanocomposite (NC) gels are attributed to their unique organic (polymer)/inorganic (clay) network structure. In this study, poly(N‐isopropylacrylamide) (PNIPA) was successfully separated from an NC gel network by decomposing the clay (hectorite) using hydrofluoric acid (HF). A very low HF concentration (0.2 wt.‐%) was adequate for the decomposition of the clay without causing any damage to PNIPA. The separated PNIPA had a high (=5.5 × 106 g · mol−1). Also, was almost constant regardless of the clay concentration (Cclay = 1–25 × 10−2 mol · l−1), even though the properties of the NC gel varied widely over this Cclay range. Comparisons of NC gels, PNIPA, and SiO2‐NC gels indicated that the clay platelets specifically play an important role in NC gels.
The synthesis of cationic mono‐(6‐O‐(1‐vinylimidazolium))‐ß‐cyclodextrin with toluenesulfonate as the corresponding anion is described. Free‐radical copolymerization of the resulting host–guest complex with N‐isopropylacrylamide or N,N‐diethylacrylamide yielded copolymers showing a temperature‐controlled solubility window in water. The impact of different anionic guests and salt concentrations on solubility behavior was investigated via turbidity measurements.
A high molecular weight ladder polymer based on 5,5′,6,6′‐tetrahydroxy‐3,3,3′,3′‐tetramethylspirobisindane and 1,4‐dicyanotetraflurobenzene has been synthesized by polycondensation under high‐intensity mixing conditions at about 155 °C and cyclic‐free products were obtained in high yield with low molecular weight distribution (1.7–2.3). The reaction could be completed within a few minutes. The polymer properties were characterized by GPC, 1H NMR, 13C NMR, F NMR, FT‐IR, and MALDI‐TOF MS. In addition, the mechanical properties, apparent surface areas and gas permeability are also reported. This procedure can also be used for the synthesis of other ladder polymers by irreversible polycondensations of tetraphenols with activated tetrafluoro aromatics.
Summary: The addition of spermidine (SPD) into turbulent flow as a condensing agent showed the abrupt change of turbulent drag reducing (DR) efficiency of λ‐DNA in turbulent flow for the first time. The resultant asymptote DR efficiency explains the origin of those changes, which can be conclusively verified via the electrophoresis experiment. Despite the different fluid conditions, with and without condensing agent, all λ‐DNA molecules possessed the same half‐cut dimension, implying that the discrete change of DNA conformation can dramatically alter the flow characteristics.
Coil‐globule transition of DNA by spermidine. 相似文献
Addition of commercially available 2‐isocyanatoethyl methacrylate to a water solution of potassium bisulfite unexpectedly yields an anionically charged hydrogel. Structural analysis shows the presence of sulfonato‐blocked isocyanates (with no detectable residual isocyanates), a full polymerization of the vinyl groups, and the appearance of urea functional groups. A mechanism is proposed to explain the gel formation, based on a combination of bisulfite‐initiated free‐radical polymerization, crosslinking by urea bridge formation, and addition of bisulfite ions to isocyanate groups. Some basic physical properties (TGA, swelling) of the gel are presented.
