共查询到20条相似文献,搜索用时 93 毫秒
1.
Production of micron-sized monodispersed composite polymer particles by seeded polymerization utilizing the dynamic swelling method 总被引:1,自引:0,他引:1
In order to develop the seeded polymerization technique utilizing the dynamic swelling method (DSM) proposed by authors for
the production of micron-sized mono-dispersed “composite” polymer particles consisting of two kinds of polymers, the seeded
polymerization for the dispersion of ethyl methacry-late (EMA)-swollen PS particles prepared utilizing DSM was carried out.
Monodispersed PS/poly(ethyl methacrylate) (PEMA) composite particles having 7 μm in diameter were produced by the addition
of NaCl to lower the solubility of EMA in medium and by the addition of CuCl2 as a water-soluble inhibitor to depress the by-production of submicron-sized PEMA particles.
Received: 16 July 1996 Accepted: 10 October 1996 相似文献
2.
Micron-sized mono-dispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles (PS/PBMA=2/1 by weight) having a heterogeneous structure in which many fine
PBMA domains dispersed in a PS matrix near the particle surface were produced by seeded polymerization of n-butyl methacrylate (BMA) of which almost all had been absorbed by 1.8 μm-sized monodispersed PS seed particles utilizing
the dynamic swelling method. The morphology was varied by changing the PS/BMA ratio and polymerization temperature. It was
concluded that the swelling state of 2 μm-sized BMA-swollen PS particles in the seeded polymerization process is one of the
important factors to control the morphology of the composite particles.
Received: 27 November 1996 Accepted: 21 March 1997 相似文献
3.
Micron-sized monodispersed polystyrene (PS)/poly(n-butyl methacrylate) composite particles were produced as follows. First, 1.77 μm-sized monodispersed PS seed particles produced
by dispersion polymerization were dispersed in ethanol/water (1/2, w/w) medium dissolving poly(vinyl alcohol) as a stabilizer.
n-Butyl methacrylate (BMA) monomer dissolving benzoyl peroxide initiator was emulsified in ethanol/water (1/2, w/w) solution
of sodium dodecyl sulfate as emulsifier with ultrasonic homogenizer, and the BMA monomer emulsion was mixed with the PS seed
emulsion. The PS seed particles absorbed with a large amount of BMA (about 150 times weight of the seed particles) for 2 h
to about 10 μm in diameter while keeping good monodispersity and BMA droplets disappeared finally. The seeded polymerization
was carried out at 70 °C after a certain amount of water was added to depress the redissolving of BMA from the swollen particles
into the medium by raising from room temperature to the polymerzation temperature.
Received: 21 February 1996 Accepted: 4 September 1996 相似文献
4.
Glass transition temperature (Tg) of submicron-sized, carboxylated polymer particles dispersed in aqueous media, which were prepared by emulsion copolymerization of styrene, iso-butyl methacrylate, or methyl methacrylate with methacrylic acid, was measured at alkali or acidic pH region with a power compensation-type high sensitive differential scanning calorimeter. The Tg of relatively hydrophilic polymer particles was obviously decreased by the neutralization of the carboxyl groups with KOH, whereas that of hydrophobic polymer particles was not changed though water was absorbed therein. These results indicate that water absorption state, which means not only the amount of water absorption but also the heterogeneity of the ionized carboxylated polymer particles, markedly depends on the hydrophilicity of their base polymers. This strongly supports the formation mechanism of multihollow particles by the stepwise alkali/acid or the alkali/cooling treatments of carboxylated polymer particles proposed by the authors.Part CCLXIX of the series, “Studies on Suspension and Emulsion.” 相似文献
5.
Styrene-methacrylic acid copolymer (P(S-MAA)) nanoparticles having high Tg were produced by a dissolution of submicron-sized P(S-MAA) particles as follows. Submicron-sized P(S-MAA) particles having
various MAA contents were produced by emulsion copolymerization. Secondly, they were treated in a polyoxyethylene nonylphenyl-ether
nonionic emulsifier aqueous solution at pH 13.0 and above 90 °C. The nanoparticles having about 30 nm in diameter were only
produced from the particles having MAA contents around 7 mol%, and above the contents, they were not produced. It seems to
be based on that emulsifier molecules are not adsorbed onto the polymer molecules enough to dissolve them. The effect of MAA
content on such a dissolution behavior was examined using seven kinds of different nonionic emulsifiers having hydrophile-lipophile-balance
values between 12.2 and 18.2 at various temperatures and initial pH.
Received: 12 June 1996 Accepted: 27 August 1996 相似文献
6.
An optical video microscopic technique was used to study hetero-aggregation and selective aggregation phenomena among n-hexadecane oil drops (40–110 μm in diameter) and two types of polystyrene latex particles (6.76 and 30.2 μm, in diameter),
suspended inside an aqueous medium with pH varying between 1.1 and 12.9. A single drop was produced in situ using a micropipette
inside the aqueous phase-filled glass microcapillary (100–160 μm i.d.) containing the particles. Interactions between the
drop and the solid particles and among the solid particles was achieved by movement of the aqueous medium in and out of a
second micropipette. Drop–particle interactions were distinctly different from particle–particle interactions. It was observed
that the latex particles aggregated irreversibly with the oil drop in all cases except two, viz. for 6.76 μm particles at
around neutral pH whereas the irreversibility of aggregation in particle–particle interactions was only seen at the ends of
the pH spectrum. At around neutral pH, the flocs or clusters of small particles were very weak. Visual observations at each
pH are explained on the basis of the classical DLVO (Derjaguin–Landau–Verwey–Overbeek) theory. Partial wetting of particles
surfaces by oil appears to be a key factor in the irreversibility of drop– particle hetero-aggregation. Results indicate that
the display of reversible, irreversible or weak aggregation depends on the location and depth of the secondary minimum and
that the long-range, attractive, London–van der Waals force is responsible for the initial formation of an aggregate.
Received: 4 July 1996 Accepted: 5 December 1996 相似文献
7.
Effect of polymer composition on the production of cationic multihollow polymer particles by the stepwise acid/alkali method 总被引:3,自引:0,他引:3
The effect of the polymer composition on the formation of multihollow structures formed within submicron-sized styrene–butyl
acrylate–dimethylaminoethyl methacrylate terpolymer particles by the “acid/alkali method” proposed by the authors was examined.
The cationic particles were produced by seeded emulsion terpolymerization with 2,2′-azobis(2-amidinopropane) hydrochloride
initiator. The dimethylaminoethyl methacrylate content and the glass-transition temperature of the terpolymer greatly affected
the formation of the multihollow structure.
Received: 3 December 1998 Accepted in revised form: 4 February 1999 相似文献
8.
Adsorption of a well-characterized cationic polyacrylamide (CPAM) onto the surface of a model colloid (monodisperse polystyrene
latex with carboxylic functional groups) was studied over a wide range of pH (4–9) and KCl concentration (c
s
=10-3–0.3 M). The surface charge density of the latex particles with and without adsorbed CPAM was also measured over the same
range of electrolyte compositions. The adsorbed amount of CPAM increases with increase in c
s
and pH. The polyelectrolyte adsorption alters substantially the surface charge density of the latex particles as compared
to the polymer-free case. A large overcompensation of the surface charge by the adsorbed polyelectrolyte is established at
high c
s
and low pH. A qualitative explanation of the observed features is put forward.
Received: 3 December 1996 Accepted: 20 January 1997 相似文献
9.
The effects of nonionic emulsifier on the formation of multihollow structures formed within sub-micron-sized polymer particles by the “acid/alkali method” proposed by the authors were examined. The original acid-swellable particles were produced by seeded emulsion terpolymerization of styrene, butyl acrylate, and dimethylaminoethyl methacrylate. The results indicate that the nonionic emulsifier had a great effect on the formation of multihollow particles. 相似文献
10.
The effects of adsorbed polymers on the sedimentation of a homogeneous distribution of colloidal spheres and on the fluid
flow through a bed of particles are investigated theoretically. The Reynolds number is assumed to be small, and the surface
polymer layers are assumed to be thin with respect to the radius of particles and to the surface-to-surface spacing between
neighboring particles. The effects of interaction of the individual particles are taken into explicit account by employing
a fundamental cell-model representation which is known to provide good predictions for the motion of a swarm of spheres within
a fluid in the absence of adsorbed polymers. To solve the Stokes flow equations within and outside the polymer layer a method
of matched asymptotic expansions in a small parameter λ is used, where λ is the ratio of the length scale of the polymer layer
to the particle radius. The results for the sedimentation rate and the pressure drop are expressed in terms of an effective
hydrodynamic thickness (L) of the polymer layer, which are accurate to O(λ2). When the concentration of particles in a suspension or a bed is increased, L becomes larger, meaning the settling velocity decreases or the pressure drop increases. The O(λ) term for L normalized by its value in the limit λ→0 is found to be independent of the polymer segment distribution, the hydrodynamic
inter-actions among the segments, and the volume fraction of the segments. The O(λ2) term for L, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general,
the particle-interaction effects on the motion of polymer-coated particles relative to a fluid can be quite significant.
Received: 28 August 1996 Accepted: 23 January 1997 相似文献
11.
D. A. B. Young 《Colloid and polymer science》2000,278(5):464-468
The persuasive evidence for the role of colloid in the formation of Liesegang rings is nullified by the low diffusion constants
(less than 2 × 10−11 m2 s−1) of sol particles; however, those values were obtained for sols suspended in otherwise homogeneous solutions. The essential
randomness of Brownian motion in such situations is absent in Liesegang experiments, where the large excess of outer electrolyte
diffusing into the gel creates a bias in molecular bombardment resulting in sol particles moving a given distance in fewer
steps, hence in a shorter time. From Einstein's equation (D=x
2/2t) values for D of 2–4 × 10−10 m2 s−1 have been calculated for Liesegang experiments in the literature. It is suggested that such values could well pertain to
sol particles diffusing in the heterogeneous conditions existing in those experiments.
Received: 13 April 1999 Accepted: 16 November 1999 相似文献
12.
The influences of shearing conducted by a Brabender rheometer on phase morphology,thermal and rheological behavior of a commercial impact polypropylene copolymer(IPC) were studied.The crystallization and melting traces show that short-time annealing at 210°C is unable to completely erase the influence of shearing on the samples.When the samples which were treated at a rotation speed of 80 r/min crystallize at a cooling rate of 10 K/min,their 7_cs and corresponding T_ms obviously rise with the increase of shearing time.Furthermore,the POM results reveal that the shearing can lead to the formation of shish-kebab and the shish-kebab amount is proportional to shearing time.The rheological measurement results show that the treated samples exhibit different G’~ωdependences.The ’second plateau’ appears when the sample is treated at a rotation speed of 60 r/min or 80 r/min for 10 min,and linear G’~ωdependence is observed at other rotation speeds.In addition,it is found that the appearance of the ’second plateau’ depends on the shearing time when the rotation speed is fixed. According to SEM observations,it is proposed that the ’second plateau’ of IPC samples should be ascribed to the aggregation of dispersion particles. 相似文献
13.
Isothermal equilibrium adsorption experiments were carried out to study the adsorption of concanavalin A (Con A) on dextran-modified
poly(methyl methacrylate) (PMMA) latex particles. Three PMMA particles with various levels of dextran modification were selected
for study: 0% (designated as D0), 1.24% (D20), and 2.45% (D75) based on total polymer weight. The Langmuir model is applicable
to both D0 and D20 systems, although the data for the D20 system are somewhat scattered. On the other hand, the amount of
Con A adsorbed per gram polymer particles (q*) versus the Con A concentration in water (c*) curve for the D75 system cannot be described by the Langmuir model. The deviation is attributed to the formation of a crosslinked
network structure, caused by specific binding of the dimeric Con A molecules onto two neighboring particles with grafted dextran.
The ratio of the initial number of Con A molecules to the initial number of active binding sites on the dextran-modified particle
surface plays an important role in determining the structure of flocs formed. The maximum amount of Con A adsorbed on the
particle surface (q
max) is of the order of 10−1 μmol per gram particles and q
max in decreasing order is D75 > D20 > D0. The dissociation constant of the Con A-D20 (or Con A-D75) pair is of the order of
10−1 μmol dm−3 which is 1 order of magnitude smaller than that of the Con A-D0 pair. Thus, the electrostatic interaction between Con A and
D0 is much weaker than the affinity interaction between Con A and D20 (or D75). An empirical model is proposed to qualitatively
explain the q* versus c* data.
Received: 18 June 1998 Accepted in revised form: 24 December 1998 相似文献
14.
M. Fujiwara T. Okano T. -H. Nakashima A. A. Nakamura G. Sugihara 《Colloid and polymer science》1997,275(5):474-479
For a sodium salt of α-sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, critical micellization
concentration (CMC), solubility and degree of counterion binding (β) were determined by means of electrocon-ductivity measurements
at different temperatures (at every 5 °C) ranging from 15 to 50 °C. The phase diagram of 14SFNa in pure water was constructed
from the CMC- and solubility-temperature data, in which the Krafft temperature (critical solution temperature) was found around
0 °C. The changes in the Gibbs energy, ΔG
0
m, enthalpy, ΔH
0
m, and entropy, ΔS
0
m, upon micelle formation as a function of temperature were evaluated taking βvalues into calculation.
Received: 28 August 1996 Accepted: 5 November 1996 相似文献
15.
The preparation of polymer microcapsules of well defined size in the range of 10–50 μm with different shell thickness to
core diameter ratios is described. An aerosol of monodisperse droplets of a homogeneous ternary liquid system which contained
a hydrophobic component and a hydrophilic component dissolved in a high-volatile mutual solvent, was produced by dispersing
with a vibrating-orifice aerosol generator. After the evaporation of the solvent in a nitrogen atmosphere the particles demix
and form a two-phase droplet of core-shell type. These droplets were illuminated with UV light and polymerized to highly monodisperse
microcapsules with a solid polymer shell and a liquid core. The properties of the resulting particles (size, size distribution,
shell thickness, shape and surface characteristics) were investigated by scanning electron microscopy, Raman spectroscopy
on single optically levitated particles, and confocal Raman micro spectroscopy. The microcapsules were highly monodisperse
and have spherical shape.
Received: 24 July 1996 Accepted: 29 August 1996 相似文献
16.
Indentation tests were carried out on a carbon black filled rubber sample on different length scales. The experiments covered
the range from aggregation of particles on the submicron scale up to structures which represent the bulk properties of the
sample on the millimeter scale. The local stiffness was used to visualize the areas investigated; therefore, mechanical images
were obtained for all length scales. So-called “mechanical units” were defined for every scale. The size distribution curves
for the mechanical units were analyzed and they were found to be non-Gaussian-shaped for every scale. Moreover, the distribution
curves of the mechanical units are similar to the distribution curves of particles and aggregates obtained by electron microscopy
reported in the literature. Evaluation by means of fractal analysis led to fractal dimensions for the mechanical units. It
could be shown in the present case that the fractal dimension D≈1.24 of the mechanical units in the range of submicrons up to several hundred microns is in good agreement with that of the
filler aggregates proposed in the literature. Furthermore, D is constant over a wide range of about 6 decades in area scale starting from aggregates up to the size of agglomerates. This
leads to the conclusion that the local arrangement of the filler ensembles seems to be self-similar from the smallest scale
of aggregation of particles up to the largest formation observed by indentation testing on the millimeter scale.
Received: 15 May 2001 Accepted: 18 August 2001 相似文献
17.
The stoichiometry, stability, and structure of the inclusion complex between the photosurfactants, 2-[4-(4-alkylphenylazo)
phenoxy]ethyltrimethylammonium bromides (alkyl=ethyl, and butyl, where the abbreviations are EZ and BZ, and ZT for both, respectively),
and γ-cyclodextrins (γ-CDx) in aqueous solution have been studied by the induced circular dichroism (ICD) and UV/VIS spectra
as well as the potentiometric titration method. It is shown that the trans-ZT/γ-CDx systems form not only 1:1 (EZ) or 2:2 (BZ) but also 2:1 (ZT:γ-CDx) inclusion complexes. On the contrary, the steric
hindrance of cis-ZT destabilizes the inclusion so that there is only 1:1 complex formation with γ-CDx. The thermodynamic discussion suggests
that the stability of ZT complex is governed by the hydrophobic and the van der Waals interaction between the photosurfactants
and cyclodextrins. However, the van der Waals interaction is more predominant in the trans-ZT/α-CDx system than in the β- and γ-CDx’s except for (BZ/γ-CDx)2 system. Moreover, the alkylchain-length dependence of the free energy changes of complex formation of ZT and CDx are less
than those of micellization of ZT because the cavity depth of CDx is limited to incorporate all hydrophobic parts of ZT. Finally,
the iso-equibrium temperature is estimated by the compensation plot of thermo-dynamic parameters.
Received: 29 August 1996 Accepted: 13 November 1996 相似文献
18.
I. Papaefstathiou U. Bilitewski M. D. Luque de Castro 《Fresenius' Journal of Analytical Chemistry》1997,357(8):1168-1173
A spectrophotometric method for the determination of acetaldehyde in liquid, semi-solid and solid food samples, employing
the coupling of a continuous flow configuration to a pervaporation unit, has been proposed. It is based on the reaction of
the analyte with fuchsin in acidic medium and subsequent formation of a coloured product (alkylsulphonic acid chromophore)
with sodium sulphite, which was monitored spectrophotometrically. Variable sensitivity was obtained by altering the pervaporation
temperature and the thickness of the membrane. The detection limits went down to 4.2 μg/mL and the precision was between 1.2
and 3.6%.
Received: 5 August 1996/Revised: 16 October 1996/Accepted: 18 October 1996 相似文献
19.
I. Papaefstathiou U. Bilitewski M. D. Luque de Castro 《Analytical and bioanalytical chemistry》1997,357(8):1168-1173
A spectrophotometric method for the determination of acetaldehyde in liquid, semi-solid and solid food samples, employing
the coupling of a continuous flow configuration to a pervaporation unit, has been proposed. It is based on the reaction of
the analyte with fuchsin in acidic medium and subsequent formation of a coloured product (alkylsulphonic acid chromophore)
with sodium sulphite, which was monitored spectrophotometrically. Variable sensitivity was obtained by altering the pervaporation
temperature and the thickness of the membrane. The detection limits went down to 4.2 μg/mL and the precision was between 1.2
and 3.6%.
Received: 5 August 1996/Revised: 16 October 1996/Accepted: 18 October 1996 相似文献
20.
Experiments were carried out to investigate the effects of surface charge density on emulsion kinetics and secondary particle
formation in emulsifier-free seeded emulsion polymerization. Three monodisperse seed latices with different surface charge
densities were prepared from styrene/NaSS comonomers using the two-stage shot-growth process. After purification of the seed
latices, they were used in seeded emulsion polymerization of methyl methacrylate. The initial rate of poly-merization and
the average number of radicals per particle for the high-charged seed latex system were lower than that of the low-charged
case. The low rate of polymerization resulted from the low rate of radical adsorption in the beginning of the reaction due
to the electrical repulsion between seeds and oligomeric radicals. In this case, because of the secondary particles, particle
size distribution became bimodal. The low rate of radical adsorption and the formation of secondary particles reduced the
average number of radicals per particle. The rate of polymerization (R
p) increased, but the rate of polymerization per particle (R
p/N
p) decreased.
Received: 9 December 1996 Accepted: 7 March 1997 相似文献