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1.
《Journal of Dispersion Science and Technology》2013,34(5):461-472
The processes of adsorption of two neutral polymers (poly(vinyl pyrrolidone), PVP and poly(vinyl alcohol), PVA) were investigated on liposomes composed of soy lecithin/dicetyl phosphate/cholesterol = 25:2:3 (molar ratio). The liposomes were prepared in buffered solution at pH = 7.4 and mixed with the solution of the measured polymers in the desired polymer/lipid (w/w) ratios. Adsorption was measured by determination of the equilibrium bulk concentration of the polymer. In the case of PVA quantitative adsorption measurements with a specific reagent were possible. Adsorption isotherms were recorded at 25 ± 1°C. It was concluded that adsorbed and unadsorbed PVA molecules are in equilibrium even at low polymer/ lipid ratios. The results were confirmed by dynamic laser light scattering (DLS), and thermal activity monitoring (TAM) experiments. Another group of the liposomes was prepared in 60 mM ammonium sulphate (pH = 5.0) and we filled the vesicles with a test dye, acridine orange (AO) using the pH-gradient (remote loading) method. The AO release property of liposomes was tested with a special vertical diffusion cell after we had made PVA adsorb on their surface in different PVA/lipid (w/w) ratios. 相似文献
2.
The role of initiation in the synthesis of silica/poly(methyl methacrylate) nanocomposite latex particles through emulsion polymerization 总被引:7,自引:0,他引:7
Silica/poly(methyl methacrylate) nanocomposite latex particles have been synthesized by emulsion polymerization of methyl
methacrylate using a nonionic surfactant: nonylphenol poly(oxyethylene) and three different initiators, namely: 2,2′-azobis(2-amidinopropane)
dihydrochloride (AIBA), potassium persulfate (KPS) and azobis(isobutyronitrile) (AIBN), being cationic, anionic and nonionic,
respectively. A silica sol with an average diameter of 68 nm was used as the seed. The polymerization reaction was conducted
under alkaline conditions in order to evaluate the role of the surface charge of the hydrophilic silica on the coating reaction.
AIBA was found to be adsorbed on the silica surface owing to electrostatic interactions of the amidine function of the cationic
initiator with the silanolate groups of the oxide surface, while the anionic and the nonionic initiators did not adsorb on
silica under the same conditions. Nonetheless, whatever the nature of the initiator, polymerization took place on the silica
particles as evidenced by transmission electron microscopy. The extent of interaction between the inorganic surface and the
polymer particles was quantified by means of ultracentrifugation and a material balance. As much as 65% by weight of the total
polymer formed was found to be present at the silica surface using AIBA, while only 40% for KPS and 25% for AIBN was found
to cover the silica particles under alkaline conditions. We demonstrate that by using a cationic initiator and by controlling
the pH of the suspension it is possible to significantly decrease the amount of free polymer. Coating of the silica particles
took place through a kind of in situ heterocoagulation mechanism.
Received: 8 December 2000 Accepted: 22 February 2001 相似文献
3.
Polymer-free and polymer-bearing small unilamellar (SUV) liposomes from dimyristoyl-phosphatidylcholine (DMPC) were prepared
under standardized conditions. Polymer-bearing liposomes were formed by incorporating an uncharged polymer [hydrolyzed poly(vinyl
alcohol) (PVA), poly(vinyl alcohol-co-vinylacetal) (PVA-Al), poly(vinyl alcohol-co-vinyl propional) (PVA-Prol) poly(vinyl
alcohol-co-vinyl butiral) (PVA-Bul) copolymer or poly(vinyl pyrrolidone) (PVP)] into the membrane bilayer of vesicles. The
kinetic (long-term) stability of the liposome dispersions stored in distilled water, in physiological NaCl solution and at
various pH values, respectively, were studied. The physical stability of vesicles was tested by measuring the size and the
zeta potential of liposomes by means of a Malvern Zetasizer 4 apparatus.
It was shown that most of these polymers are effective steric stabilizers for the DMPC-liposomes. Among the polymers, the
PVA-Bul and PVA-Prol copolymers and the PVP of high molecular mass exhibited the most efficient stabilizing effect at each
pH studied, indicating that the formation of a relatively thick polymer layer around the lipid bilayers ensures an enhanced
and prolonged physical stability of liposomes. Also, the butiral or propional side chain in the PVA-based copolymers presumably
promotes the anchoring of macromolecules to the vesicles. Using these macromolecules, the colloidal interactions between vesicles
can be modified and so the physical stability of liposomes and the kinetic stability of liposome dispersions can also be controlled.
Received: 20 May 1997 Accepted: 03 September 1997 相似文献
4.
The surfactant effect on the lower critical solution temperature (LCST) of thermosensitive poly(organophosphazenes) with
methoxy-poly(ethylene glycol) and amino acid esters as side groups was examined in terms of molecular interactions between
the polyphosphazenes and surfactants including various anionic, cationic, and nonionic surfactants in aqueous solution. Most
of the anionic and cationic surfactants increased the LCST of the polymers: the LCST increased more sharply with increasing
length and hydrophobicity of the hydrophobic part of the surfactant molecule. The ΔLCSTs (T
0.03M − T
0M), the change in the LCST by addition of 0 and 0.03 M sodium dodecyl sulfate (SDS), were found to be 7.0 and 14.5 °C for the
polymers bearing ethyl esters of glycine and aspartic acid, respectively. The LCST increase of poly(organophosphazene) having
a more hydrophobic aspartic acid ethyl ester was 2 times larger compared with that of the polymer having glycine ethyl ester
as a side group. The binding behavior of SDS to the polymer bearing glycine ethyl ester as a hydrophobic group was explained
from the results of titration of the polymer solutions containing SDS with tetrapropylammonium bromide. Graphic models for
the molecular interactions of polymer/surfactant and polymer/surfactant/salt in aqueous solutions were proposed.
Received: 17 February 2000/Accepted: 25 April 2000 相似文献
5.
A. A. Zaman 《Colloid and polymer science》2000,278(12):1187-1197
In this study a systematic investigation on the adsorption of polyethylene oxide (PEO) onto the surface of silica particles
and the viscosity behavior of concentrated dispersions of silica particles with adsorbed PEO has been performed. The variation
of shear viscosity with the adsorbed layer density, concentration of free polymer in the solution (depletion forces), polymer
molecular weight, and adsorbed layer thickness at different salt concentrations (range of the electrostatic repulsion between
particles) is presented and discussed.
Adsorption and rheological studies were performed on suspensions of silica particles dispersed in solutions of 10−2 M and 10−4 M NaNO3 containing PEO of molecular weights 7,500 and 18,500 of different concentrations. Adsorption measurements gave evidence of
a primary plateau in the adsorption density of 7,500 MW PEO at an electrolyte concentration of 10−2 M NaNO3. Results indicate that the range of the electrostatic repulsion between the suspended particles affects both adsorption density
of the polymer onto the surface of the particles and the viscosity behavior of the system. The adsorbed layer thickness was
estimated from the values of zeta potential in the presence and absence of the polymer and was found to decrease with decreasing
the range of the electrostatic repulsive forces between the particles. Experimental results show that even though there is
a direct relation between the viscosity of the suspension and the adsorption density of the polymer onto the surface of the
particles, variation of viscosity with adsorption density, equilibrium concentration of the polymer, and range of the electrostatic
repulsion cannot be explained just in term of the effective volume fraction of the particles and needs to be further investigated.
Received: 15 February 2000/Accepted: 26 June 2000 相似文献
6.
W. S. Lyoo S. G. Lee J. P. Kim S. S. Han C. J. Lee 《Colloid and polymer science》1998,276(11):951-959
To obtain high molecular weight (HMW) poly(vinyl acetate) (PVAc) with high conversion and high linearity for a precursor
of HMW poly(vinyl alcohol) (PVA), vinyl acetate (VAc) was suspension-poly-merized using a low-temperature initiator, 2,2′-azobis
(2,4-dimethyl-valeronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior and molecular
structures of PVAc and PVA prepared by saponifying PVAc were investigated. On the whole, the experimental results well corres-ponded
to the theoretically predicted tendencies. Suspension polymerization was slightly inferior to bulk polymerization in increasing
molecular weight of PVA. In contrast, the former was absolutely superior to the latter in increasing conversion of the polymer,
which indicated that the suspension polymerization rate of VAc was faster than the bulk one. These effects could be explained
by a kinetic order of ADMVN concentration calculated by initial-rate method and an activation energy difference of polymerization
obtained from the Arrhenius plot. Suspension polymerization at 30 °C by adopting ADMVN proved to be successful in obtaining
PVA of HMW (number-average degree of polymerization (P
n)): (4200–5800) and of high yield (ultimate conversion of VAc into PVAc: 85–95%) with diminishing heat generated during polymerization.
In the case of bulk polymerization of VAc at the same conditions, maximum P
n and conversion of 5200–6200 and 20–30% was obtained, respectively. The P
n, lightness, and syndiotacticity were higher with PVA prepared from PVAc polymerized at lower temperatures.
Received: 10 February 1998 Accepted: 15 April 1998 相似文献
7.
Micron-sized, monodispersed highly styrene-“adsorbed” particles having snow-man shape were prepared by the dynamic swelling
method (DSM) with tightly cross-linked polymer seed particles as follows. First, 3.8 μm-sized monodispersed polystyrene (PS)/
poly(divinylbenzene) (PDVB) (PS/PDVB = 1/10 wt. ratio) composite particles produced by seeded polymerization utilizing DSM
were dispersed in an ethanol/water (6/4, w/w) solution dissolving styrene monomer, and poly(vinyl alcohol) as a stabilizer.
Second, water was subsequently added to the dispersion with a micro-feeder at a rate of 2.88 ml/h at room temperature. The
cross-linked seed particles adsorbed a large amount of styrene onto the surfaces and resulted in mono-dispersed highly styrene-“adsorbed”
snow-man shape particles having about 10 μm in diameter.
Received: 16 April 1998 Accepted: 9 June 1998 相似文献
8.
The temperature dependence of the dimensions of poly(N-isopropylacrylamide) (PNIPAM) adsorbed on two different colloidal silica particles was studied with dynamic light scattering.
The hydrodynamic diameter was measured when the temperature was varied stepwise from 10 to 60 °C. PNIPAM molecules free in
solution undergo a conformational transition at the θ temperature. We have found that PNIPAM adsorbed onto silica particles
also undergoes a transition below the θ temperature. When a small amount of polymer was adsorbed the coil-to-globule transition
at the θ temperature did not occur. Potentiometric titrations showed that the surface charge of the silica particles was not
affected by the polymer adsorption. Sodium dodecyl sulfate (SDS) (100–1200 mg/l) was added to improve the stability. The particles
with a higher zeta potential required a smaller addition of SDS to prevent coagulation compared to the particles with a smaller
surface potential. For low additions of SDS the transition curves of adsorbed PNIPAM were unaffected. For larger additions
of SDS the collapse of PNIPAM was shifted to higher temperatures. When as much as 1200 mg/l SDS was added, two regions with
weak transitions were observed before the collapse. It was also observed that the presence of SDS results in a smaller adsorption
of PNIPAM onto the particles. The addition of SDS strongly increased the magnitude of the electrophoretic mobility of the
polymer–particle unit. From the electrophoretic measurements an electrokinetic layer thickness was calculated and it was found
to be smaller than the corresponding hydrodynamic layer thickness, as obtained by dynamic light scattering.
Received: 14 December 1999/In revised form: 22 February 2000/Accepted: 6 March 2000 相似文献
9.
The phase transition between unimer and micellar phases of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide)
(PEO–PPO–PEO) triblock copolymer Pluronic P105 in aqueous solution has been investigated as a function of temperature using
Fourier transform infrared spectroscopy. The transition of 8 wt% Pluronic P105 in aqueous solution was found to occur at 25 °C.
As temperature increases, PO blocks appear to be stretched conformers with strong interchain interaction, and the formation
of a hydrophobic core in the micellar phase. The EO chains are found to change to a more disordered structure with low-chain
packing density from the unimer phase to the micellar phase. Both the EO and PO blocks exhibit dehydration during the phase
transition.
Received: 17 September 1998 Accepted in revised form: 10 December 1998 相似文献
10.
H. Ahmad M. S. Rahman M. A. J. Miah A. M. I. Ali 《Colloid and polymer science》2001,279(10):1039-1043
A series of poly(methyl methacrylate)/poly(methyl methacrylate-acrylamide) composite polymer particles was prepared with
varying proportions of acrylamide in the copolymer shell layer. Adsorption behaviors of some biomolecules and specific activity
of adsorbed trypsin were studied. The hydrophobic interaction between the composite polymer particle surfaces and biomolecules
decreased with increasing acrylamide content.
Received: 7 February 2001 Accepted: 16 May 2001 相似文献
11.
Yuanyuan Zhang Xiaobo Huang Bin Duan Lili Wu Shuo Li Xiaoyan Yuan 《Colloid and polymer science》2007,285(8):855-863
Electrospinning of chitosan from its solutions in 2% aqueous acetic acid was studied by adding poly(vinyl alcohol) (PVA) as
a “guest” polymer. Properties of the chitosan/PVA solutions including viscosity, conductivity, and surface tension were measured,
and effects of the polymer concentration, chitosan/PVA mass ratio and processing parameters (applied voltage, flow rate, capillary-to-collector
distance) on the electrospinnability of chitosan/PVA were investigated. Analyses of scanning electron micrographs and transmission
electron micrographs suggested that the chitosan/PVA ultrafine fibers were often obtained along with beads, and chitosan was
located in the elctrospun fibers as well as in the beads. Uniform chitosan/PVA fibers with an average diameter of 99 ± 21 nm
could be prepared from a 7% chitosan/PVA solution in 40:60 mass ratio. Results of Fourier transform infrared spectroscopy
and X-ray diffraction demonstrated that there were possible hydrogen bonds between chitosan and PVA molecules, which could
weaken the strong interaction in chitosan itself and facilitate chitosan/PVA electrospinnability. The electrospun chitosan/PVA
membranes showed higher water uptake and would have potential applications in wound dressings. 相似文献
12.
Micron-sized, monodispersed polystyrene/poly(3,5-xylidine) composite polymer particles were produced by chemical oxidative
seeded polymerization of 3,5-xylidine with 1.37-μm-sized, monodispersed polystyrene seed particles. The chemical oxidative
seeded polymerization was conducted in an aqueous medium at 25 °C in the presence of poly(vinyl alcohol) as a stabilizer using
ammonium persulfate as an oxidant. The composite particles had a multihollow structure.
Received: 30 June 1999/Accepted in revised form: 21 October 1999 相似文献
13.
Ma?gorzata Wi?niewska 《Central European Journal of Chemistry》2012,10(4):1236-1244
The influence of temperature on the adsorption of polyvinyl alcohol (PVA) on a silica surface was studied from 15–35°C. The
structure of the polymer adsorption layer was determined from spectrophotometric, viscosity and thermogravimetric measurements.
The amount of PVA adsorbed, macromolecules’ conformation in solution, thickness of the polymer adsorption layer, and changes
in the heating curve of SiO2 with adsorbed polymer were determined. Temperature influences the PVA chain conformation in solution and the structure of
the polymer adsorption layer. A temperature rise causes relaxation of polymer coils which results in an increase in the linear
dimensions of PVA chains in the solution, the creation of a thicker adsorption layer, and an increase in polymer adsorbed.
Polymer adsorption on the silica surface also causes changes in the heating curve of these systems. The mass losses due to
heating are smallest for the systems obtained at 15°C because the least polymer is adsorbed at this temperature.
相似文献
14.
B. Mahltig J.-F. Gohy R. Jérôme C. Bellmann M. Stamm 《Colloid and polymer science》2000,278(6):502-508
The adsorption of the diblock polyampholyte poly (methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate) from aqueous solution on silicon substrates was investigated as a function of polymer
concentration and pH. Dynamic light scattering and electrokinetic measurements were used to characterize the polyampholyte
in solution. The amount of polymer adsorbed was determined by ellipsometry and lateral structures of the polymer layer were
investigated by scanning force microscopy. The amount of polymer adsorbed was found to be strongly influenced by the pH of
the polymer solution, while the size of the polyampholyte micelles adsorbed on the surface was hardly affected by pH during
adsorption. From investigations by scanning force microscopy well-seperated micelles were seen in the dried monolayers adsorbed
directly from solution. The structures at the surface are correlated to structures in solution, and the adsorbed amount depends
on the relative charge of the micelles and the surface.
Received: 13 September 1999 Accepted in revised form: 8 December 1999 相似文献
15.
The adsorption of poly(vinyl alcohol) (PVOH) from aqueous solutions to a silicon-supported fluoroalkyl monolayer is described. Thickness, wettability, and roughness of adsorbed films are studied as a function of polymer molecular weight, degree of hydrolysis (from the precursor, poly(vinyl acetate)), polymer concentration, salt type and concentration, and temperature. The data suggest a two-stage process for adsorption of the polymer: physisorption due to a hydrophobic effect (decrease in interfacial free energy) and subsequent stabilization of the adsorbed layer due to crystallization of the polymer. Adsorption of lower-molecular-weight polymers results in thicker films than those prepared with a higher molecular weight; this is ascribed to better crystallization of more mobile short chains. Higher contents of unhydrolyzed acetate groups on the poly(vinyl alcohol) chain lead to thicker adsorbed films. Residual acetate groups partition to the outermost surface of the films and determine wettability. Salts, including sodium chloride and sodium sulfate, promote adsorption, which results in thicker films; at the same time, their presence over a wide concentration range leads to formation of rough coatings. Sodium thiocyanate has little effect on PVOH adsorption, only slightly reducing the thickness in a 2 M salt solution. Increased temperature promotes adsorption in the presence of salt, but has little effect on salt-free solutions. Evidently, higher temperatures favor adsorption but cause crystallization to be less thermodynamically favorable. These competing effects result in the smoothest coatings being formed in an intermediate temperature range. 相似文献
16.
Martin Albrecht Peter Reinhardt Jean-Paul Malrieu 《Theoretical chemistry accounts》1998,100(1-4):241-252
A size-consistent ab initio formalism to calculate correlation corrections to ionization potentials as well as electron affinities
of periodic systems is presented. Our approach is based on a Hartree-Fock scheme which directly yields local orbitals without
any a posteriori localization step. The use of local orbitals implies non-zero off-diagonal matrix elements of the Fock operator,
which are treated as an additional perturbation and give rise to localization diagrams. Based on the obtained local orbitals,
an effective Bloch Hamiltonian is constructed to second order of perturbation theory with all third-order localization diagrams
included. In addition, the summation of certain classes of diagrams up to infinite order in the off-diagonal Fock elements
as well as the Epstein-Nesbet partitioning of the full Hamiltonian are discussed. The problem of intruder states, frequently
encountered in many-body perturbation theory, is dealt with by employing the theory of intermediate Hamiltonians. As model
systems we have chosen cyclic periodic structures up to an oligoethylene ring in double-zeta basis; however, the theory presented
here straightforwardly carries over to infinite periodic systems.
Received: 30 April 1998 / Accepted: 27 July 1998 / Published online: 7 October 1998 相似文献
17.
The reentrant behavior of Poly(vinyl alcohol) (PVA)–borax aqueous semidilute solutions with a PVA concentration of 20 g/l
and borax concentrations varies from 0.0 to 0.20 M was investigated using dynamic light scattering (DLS) and dynamic viscoelastic
measurements. Two (fast and slow modes) and three (fast, middle, and slow) relaxation modes of PVA semidilute aqueous solutions
without and with the presence of borax, respectively, were observed from DLS measurements. The fast and middle relaxation
modes were q
2-dependent (q is the scattering vector) characteristic of diffusive behavior; however, the slow modes were q
3-dependent, characteristic of intraparticle dynamics. The experimental results showed that the slow relaxation mode dominates
the DLS relaxation. The DLS slow mode relaxation time, τs, and the viscoelastic modulus G′(ω) and G′′(ω) data had a similar trend and demonstrated reentrant behavior as the borax concentration was increased from 0.0 to 0.20 M,
i.e. τs, G′(ω), and G′′(ω) fluctuated with increasing borax concentration. The excluded-volume effect of polymers, charge repulsion among borate
ions bound on PVA molecules, and intermolecular cross-linking didiol–borate complexation caused an expansion of the polymer
chain; however, the screening effect of free Na+ ions on the negative charge of the borate ions bound on PVA and intramolecular cross-linking didiol–borate complexation led
to a shrinkage of the polymer chain. The reentrant behavior was the consequence of the balance between expansion and shrinkage
of the PVA–borate complex.
Received: 26 March 1999/Accepted in revised form: 3 September 1999 相似文献
18.
Convectional, sedimentary, and drying dissipative patterns were observed at room temperature on a cover glass, a watch glass,
and a Petri dish during the course of dryness of aqueous suspensions of colloidal polymer complexes of poly(acrylic acid)
(HPAA) with poly(ethylene glycol) (PEG) and poly(vinyl pyrrolidone) (PVP). With increase in the molecular weight of the polymer
component, the complexes showed from transparent solution stable colloidal dispersion and the sticky aggregates. HPAA25K + PVP25K
complex showed bluish colors and the colloidal crystal suspension. Size of the macroscopic broad rings of HPAA25K + PEG decreased as molecular weight of PEG increased. Furthermore,
the size increased sharply as the polymer concentration increased in the complex systems HPAA25K + PVP25K. Characteristic
microscopic patterns appeared for HPAA + PEG and HPAA + PVP complexes. 相似文献
19.
Morphology and mechanical properties of poly(vinyl alcohol) and starch blends prepared by gelation/crystallization from solutions 总被引:1,自引:0,他引:1
In an attempt to produce biodegradation materials, poly(vinyl alcohol) (PVA)–starch (ST) blends were prepared by gelation/crystallization
from semidilute solutions in dimethyl sulfoxide (Me2SO) and water mixtures and elongated up to 8 times. The content of mixed solvent represented as Me2SO/H2O (volume percent) was set to be 60/40 assuring the greatest drawability of PVA homopolymer films. The PVA/ST compositions
chosen were 1/1, 1/3, and 1/5. The elongation up to 8 times could be done for the 1/1 blend but any elongation was impossible
for blends whose ST content was beyond 50%. When the blends were immersed in water at 20 or 83 °C, the solubility became considerable
for an undrawn blend with 1/5 composition and a drawn 1/1 blend with λ=8. To avoid this phenomenon, cross-linking of PVA chains
was carried out by formalization under formaldehyde vapor. Significant improvement could be established by the cross-linking
of PVA chains. For the 1/1 blend, the amount of ST dissolved in water at 23 °C was less than 3% for the undrawn state and
25% for the drawn film. The decrease in the ST content was enough for use as biodegradation materials. Namely, the water content
relating to the biodegradation in soil is obviously different from such a serious experimental condition that a piece of blend
film was immersed in a water bath. At temperatures above 0 °C, the storage modulus of the formalization blends became slightly
higher than those of the nonformalization blends. The Young's modulus of the drawn films with a draw ratio of 8 times was
2 GPa at 20 °C.
Received: 23 June 2000 Accepted: 30 October 2000 相似文献
20.
Summary As a first step in a study on the interaction between polymers and hydrophobic colloids we investigated in detail the adsorption of polyvinyl alcohol (PVA) on aqueous silver iodide sols. The adsorption is irreversible. Adsorption isotherms are of the highaffinity type. The amount adsorbed increases with molecular weight and with the fraction of acetate groups in the PVA chain. The effective thickness of the adsorbed layer was determined viscosimetrically and independently checked by an electrophoretic method. Double layer studies enabled the determination of the occupancy of the first layer on the surface by polymer segments. It was found that even at maximal coverage with polymer this layer is still about 30% void. The combination of these data enabled the assessment of the polymer segment distribution. It was found that with not too low coverages the distribution isHoeve- like. The distribution, thus obtained reflects itself in the flocculation of AgI sols by PVA.Presented at the 25th Colloid-Meeting in Munich, October 13–15, 1971 相似文献