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排序方式: 共有119条查询结果,搜索用时 15 毫秒
1.
Jane?Jin John?C.?Achenbach Shiping?ZhuEmail author Yingfu?Li 《Colloid and polymer science》2005,283(11):1197-1205
The influences of polymer-related properties such as molecular weight, charge density, counter ion, and hydrophilic block
on the complexation of polyelectrolytes and a fluorescein-labeled oligonucleotide (ON) were investigated. A series of well-defined
and well-controlled 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) polymers and block copolymers were prepared using living anionic and radical polymerization
methods. Fluorescence measurement was used to reveal the effects of polymer molecular weight, charge density, and counter
ion type on the complexation. PolyDMAEMA samples having double molecular weights of the chosen oligonucleotide gave the optimal
complexation performance. Kinetic studies showed that high-molecular weight/high-charge density polymer samples produced very
stable complexes. The fully charged polyDMAEMA displayed the strongest binding with the ON. These complexes were therefore
less sensitive to the changes in the environment. PolyDMAEMA–DMSQ samples had slightly higher complexation ability than polyDMAEMA–MCQ
(DMSQ: dimethylsulfate quat; MCQ: methylchloride quat). Both poly(DMAEMA-b-HEMA) and poly(DMAEMA–MCQ-b-PEG) block copolymers
showed good complexation ability and steric stability [HEMA: 2-hydroxyethyl methacrylate; PEG: poly(ethylene glycol)]. PEG,
but not HEMA block, enhanced the effectiveness of polyDMAEMA–MCQ binding with the ON. 相似文献
2.
Résumé La courbe représentant, en fonction de la concentrationc, la tension interfaciale entre le toluène et une solution aqueuse d'un copolymère á blocs amphiphile á séquence hydrophile polyélectrolyte (polystyrène-b-polyvinyl-2-pyridine quaternisée au bromure d'éthyle) est foncièrement différente de celle que l'on obtient avec les détergents classiques.Les longues séquences polyélectrolytes ancrées á l'interface y établissent entre les deux phases une différence de potentiel électrique bien supérieure á celle que l'on obtient avec les détergents classiques. Il en résulte que le système reste éloigné de l'équilibre thermodynamique. Comme les énergies d'activation des processus d'adsorption et de désorption sont de nature différente, les courbes (,c) etablies en concentration croissante et décroissante sont non seulement distinctes, mais de caractères différents.
Summary Plotting the water toluene interface tension against the concentrationc, one gets quite different behaviours using classical detergents (Sodium laurylsulfate) or ampholytic block copolymers with polyelectrolytic hydrophilic sequence. (polystyrene-b-polyvinyl-2-pyridine quaternized with ethylbromid).These polyelectrolytic sequences build at the interface a much larger electric potential drop than usual detergents do. It follows that the system keeps far away from the thermodynamic equilibrium. Since adsorption and desorption processes have activation energies of different natures, it turns out that the (,c) curves are quite different in characters if constructed in growing or fallingc values.
Zusammenfassung Kurven, welche die Wasser-Toluol-Grenzflächenspannung als Funktion der Konzentrationc wiedergeben, sind für gewöhnliche Tenside und für Ampholytblock-Copolymere mit einer polyelektrolytartigen Sequenz, völlig verschiedenDie polyelektrolytartige Sequenz bildet an der Grenzfläche einen weitaus größeren elektrischen Potentialsprung als gewöhnliche Tenside. Daraus folgt, daß man dem thermodynamischen Gleichgewicht fern bleibt, und, da Ad- und Desorptionsprozesse unterschiedliche Aktivationsenergien besitzen, sind die (,c) Kurven mit steigenden und fallendenc-Werten völlig verschieden.相似文献
3.
A review of the synthesis and properties of ionenes is presented. Particular attention is paid to the electrical and related properties of conductive teteracyano-p-quinodimethane (TCNQ) complex salts of ionenes containing ammonium or sulfonium groups in the main chain and to their chemical stability. The recent work on preparation of such ionenes with inorganic and organic counterions which show interesting linear and nonlinear optical properties is also discussed. It is shown that in the solid state ionenes act as a kind of a matrix fixing, in a chemically controlled way, positions and distribution of different kinds of counterions. Because the reaction of counterion exchange is easy in the case of ionenes it provides a convenient way to prepare a broad class of polyelectrolytes with many different properties. 相似文献
4.
M. J. Tiera V. A. De Oliveira H. D. Burrows M. Graça Miguel M. G. Neumann 《Colloid and polymer science》1998,276(3):206-212
The binding of the cations thallium(I), calcium(II) and terbium(III) to methyl methacrylate– methacrylic acid copolymers
with different fractions of acid groups (x) has been studied in aqueous solution at various pH values using the fluorescence of covalently bonded 9-vinyl anthracene
as a probe. In all cases, the extent of binding increases as a function of the charge of the polymer with either increasing
fraction of carboxylic acids or of pH. However, differences are observed in the behavior of the three cations. With Tl(I),
quenching of the anthracene group fluorescence is observed, indicating that the thallium(I) approaches the probe and suggesting
that the alkylanthracene is probably in a relatively polar region. Binding constants have been determined from anthracene
quenching data and from studies with the fluo-rescent-probe sodium pyrenetetra-sulfonate. Good agreement is obtained between
the two methods, and values for the binding constants increase from 250 to 950 M-1 as x increases from 0.39 to 1. It is suggested that the cation is held in the polyelectrolyte domain, partly by Debye–Hückel effects
and partly by more specific interactions. Stronger binding is found with calcium(II) and terbium(III), and in this case increases
in fluorescence intensity are observed on complexation due to the anthracene group being in a more hydrophobic region, probably
as a result of conformational changes in the polymer chain. In the former case the stoichiometry of the interaction was determined
from the fluorescence data to involve two carboxylate groups bound per calcium. Association constants were found using murexide
as an indicator of free calcium to vary from 8400 to 37 000 M-1 as x increases from 0.39 to 1. It is suggested that in this case specific calcium(II)–carboxylate interactions contribute to the
binding. With terbium(III), a greater increase in the probe fluorescence intensity was observed than with calcium, and it
is suggested that the interaction with the polymer is even stronger, leading to a more pronounced conformational change in
the polymer. It is proposed that the terbium(III) interacts with six carboxylic groups on the polymer chain, with three being
coordinated and three attracted by electrostatic interactions.
Received: 10 June 1997 Accepted: 24 October 1997 相似文献
5.
M. Nierlich L.L.B. F. Boue L.L.B. A. Lapp L.L.B. R. Oberthür I.L.L. 《Colloid and polymer science》1985,263(12):955-964
We have studied salt free semi dilute polyelectrolyte solutions by small angle neutron scattering. Specific labelling associated with an extrapolation method has allowed the separation of the form factor of a single polyelectrolyte chainS
1(q) and the structure factorS
2(q). Two lengths are deduced from these two factors: the persistence lengthb
t which characterizes the electrostatic interactions along the chain by a fitting ofS
1(q) with calculation of the scattering function for a wormlike chain, and fromS
2(q),q
m
–1
which characterizes the interactions between chains. These two lengths vary in the same way with the concentration of polyions (b
t C
p
–1/2
,q
m
–1
C
p
–1/2
) and a constant relation exists between them: only one length is then necessary to describe the structure of polyelectrolyte soltuion on this semidilute concentration range.Laboratoire Commun CEA-CNRS. 相似文献
6.
It was found that the interface effects in viscous capillary flow influenced the process of viscosity measurement greatly,and the abnormal viscosity behaviors of polyelectrolytes as well as neutral polymers in dilute solution region were ascribed to interface effect.According to this theory,we have reviewed the previous viscosity data of derivatives of poly-2- vinylpyridine reported by Maclay and Fuoss first.Then,the abnormal viscosity behaviors of a series of sodium polystyrene sulfonate samples with various molecular weights in dilute aqueous solutions were studied further.The solute adsorption behaviors and structural information of polymers have been discussed carefully. 相似文献
7.
B. Guilleaume M. Ballauff G. Goerigk M. Wittemann M. Rehahn 《Colloid and polymer science》2001,279(9):829-835
We consider the analysis of a rodlike synthetic polyelectrolyte in solution by anomalous small-angle X-ray scattering (ASAXS)
in order to elucidate the correlation of the counterions with the highly charged macroion. ASAXS can be applied to these systems
because the absorption edge of typical counterions, for example, bromine or iodine ions can be attained by synchrotron radiation.
Model calculations using the Poisson–Boltzmann cell model show that ASAXS furnishes two terms caused by the anomalous dispersion
of the counterions. The leading terms is a cross-term between the ordinary scattering amplitude of the polyelectrolyte and
the real part of the scattering length f ′ of the counterions. A second term refers solely to the anomalous contribution of the counterions, i.e., to f ′ and f ′′ ( f ′′: imaginary part of scattering length). Preliminary data obtained from rodlike synthetic macroions having iodine counterions
corroborate the theoretical deductions. They demonstrate that ASAXS is capable of furnishing information that is not available
by the ordinary SAXS experiment.
Received: 11 December 2000/Accepted: 22 February 2001 相似文献
8.
Subba Reddy ChV Jin AP Zhu QY Mai LQ Chen W 《The European physical journal. E, Soft matter》2006,19(4):471-476
A sodium ion-conducting polymer electrolyte based on polyvinyl pyrrolidone (PVP) complexed with NaClO4 was prepared using the solution-cast technique. The cathode film of V2O5 xerogel modified with polyvinyl pyrrolidone was prepared using the sol-gel method. Investigations were conducted using X-ray
diffractometry (XRD), Fourier transformation infrared (FT-IR) spectroscopy. The ionic conductivity and transference number
measurements were performed to characterize the polymer electrolyte for battery applications. The transference number data
indicated that the conducting species in these electrolytes are the anions. Using the electrolyte, electrochemical cells with
a configuration Na/(PVP + NaClO4)/V2O5 modified by (PVP) were fabricated and their discharge profiles studied. 相似文献
9.
Butyl modified poly(allylamine)s with butyl substitution degrees of 15%to 70%were prepared.The polymers show pH sensitive property and lower critical solution temperature(LCST)behavior.The LCST appears at lower temperature,lower pH and lower polymer concentration for the polymer with higher butylated degree.The binding of native lysozyme with the polymers depends on the hydrophobicity of the polymers at the pH range that the protein and the polymer carry the same positive charges.The increase of polymer hydrophobicity can increase the binding with lysozyme,but the self-aggregation of the polymer decreases the binding.The bound lysozyme molecules can recover their native activity completely after the dissociation of the complexes.Compared with native lysozyme,the denatured one which exposes the hydrophobic residues can increase the binding with the polymer and form stable complex nanoparticles. 相似文献
10.
Surfaces functionalized with polystyrene particles and polyelectrolytes were used to investigate the morphological and adhesion properties of composite substrates. Atomic force microscopy (AFM) studies showed that surfaces with non-homogeneous topography have non-homogeneous adhesion properties. In addition, the homogeneity of the adhesion properties is dependent upon the chemical species used to functionalize the surface. Force volume (FV) imaging was utilized to map the adhesion of the fabricated substrates with high-resolution. The FV studies revealed that the hydrophobicity of the surface is not uniform despite the fact that the surface was functionalized with the same polyelectrolyte. The analysis methodology we report here opens the possibility to design better surfaces for future tissue engineering applications. 相似文献