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1.
Marcelo Do Amaral Steven Van Es Jos M. Asua 《Journal of polymer science. Part A, Polymer chemistry》2004,42(16):3936-3946
The production of high‐solid‐content, low‐viscosity latexes is an active field in both industry and academia. The viscosity of polymer dispersions has a clear dependence on the particle size distribution (PSD). An example is the rule of thumb that a bimodal PSD enables the reduction of the viscosity with respect to monomodal systems. Despite important progress in theoretical work, not much has been done to quantitatively predict the low shear viscosity of aqueous polymer dispersions as a function of the complex PSD. In this work, the capability of a low‐shear‐viscosity equation to quantitatively account for the influence of both the PSD and the physicochemical characteristics of the dispersions is experimentally assessed. An analysis, consistent with theoretical concepts, of the data with semiempirical correlations is proposed. Next, with values of the parameters of the viscosity equation obtained experimentally, the effect of a latex with a 70% solid content on the low shear viscosity is examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3936–3946, 2004 相似文献
2.
The synthesis and comprehensive characterization of a purely sterically stabilized latex with narrow size distribution is
reported. By use of non-ionic initiators no chemically bound surface charges are generated. Stabilization of the particles
is achieved through use of a non-ionic surfactant having a double bond in the hydrophobic part which is chemically bound to
the surface. Analysis of the latex particles thus generated by transmission electron microscopy, disc centrifugation, and
small-angle X-ray scattering (SAXS) reveals that the size distribution is narrow (standard deviation between 6 and 10%). SAXS
furthermore demonstrates that the surfactant is located in a thin layer on the surface. The interaction of the particles is
purely repulsive as shown by the analysis of the turbidity of the latex. The systems obtained herein may serve as model systems
of water-borne purely sterically stabilized colloid particles.
Received: 23 December 1997 Accepted: 18 May 1998 相似文献
3.
High solid content latex: Preparation methods and application 总被引:2,自引:0,他引:2
One of the major challenges in emulsion polymerization over the past two decades was how to increase the solid content of latex products. In contrast to the conventional latex, high solid content (HSC) latex has a large volume fraction of dispersed phase, even larger than 70% in weight. Conventional emulsion polymerization, miniemulsion polymerization, self-emulsification polymerization and concentrated emulsion polymerization were all used to prepare HSC latexes, and many good results have been reported in recent years. Meanwhile, many applications of HSC latexes have also been developed. The present review summarized the progresses in the past few years mainly on the preparation methods and application of HSC latexes. Finally, some research directions as well as prospects were also proposed. 相似文献
4.
A novel class of low-viscosity benzoxazines has been synthesized from melamine and formaldehyde with phenol or bisphenol A. The striking feature of the class of benzoxazines is the subtle combination of their inherently low viscosity at room temperature, good film-forming characteristics and high chemical and thermal stability mainly due to the introduction of melamine into the network of the polymers. The structure of the benzoxazines has been confirmed by proton nuclear magnetic resonance spectroscopy and fourier transform infrared spectroscopy. Thermal properties of polybenzoxazine have been studied by differential scanning calorimetry, dynamic mechanical analysis and thermogravimetric analysis. Transparent polybenzoxazine films were easily obtained under solvent-free conditions, exhibiting significantly improved toughness compared to the conventional polybenzoxazines. Our research may open a new path for overcoming the present drawbacks of polybenzoxazines such as high brittleness, the difficulties in preparing films and poor processibility via tailoring the structures and properties of amine in the benzoxazines. 相似文献
5.
J. M. Peula-Garcia R. Hidaldo-Alvarez F. J. de las Nieves 《Colloid and polymer science》1997,275(2):198-202
The latex agglutination immunoassay technique uses polymer colloids as a carrier for the adsorbed proteins to enhance the
antigen–antibody reaction. Competitive co-adsorption of IgGaCRP and m-BSA proteins on polystyrene latexes with different functionality
(sulfate and sulfonate groups) was carried out looking for the increase in the immunoreactivity and colloid stability of latex–protein
complexes. The preferential adsorption of a protein is also studied, comparing both surface types.
Regarding the application in the development of a diagnostic test system, it is necessary to study the latex–protein complexes
from an electrokinetic and colloid stability point of view.
The presence of protein on the surface latex shifts the iso-electric point (i.e.p.) of the latex–protein complexes to pH values
near the i.e.p. of the protein which is the majority. Thus by the adsorption of m-BSA we can obtain complexes with the i.e.p.
near pH 5 and, therefore, with a significant electrostatic repulsion at neutral pH.
Due to the higher surface charge density of the sulfonate latexes there is a higher adsorption of both proteins, which can
provide a better colloidal stability (by the adsorption of m-BSA) and a better immunoreactivity (by the adsorption of IgG).
Received: 27 March 1996 Accepted: 1 September 1996 相似文献
6.
The purpose of this paper is to apply the classical DLVO theory to explain the colloid stability of two model colloids with
similar size and different sign and value of the surface charge. For this comparison the hydrodynamic interaction and the
presence of hydration forces (extended DLVO theory) have been taken into account. The experimental stability factor and the
experimental doublet rate constant in diffusion conditions were compared with those evaluated theoretically. The mathematical
treatment permits an easy evaluation and interpretation of the different adjustable parameters such as the Hamaker constant,
diffuse layer potential and the hydration layer thickness. The theoretical and experimental comparison shows that the “extended
DLVO theory” only permits to explain the stability curves Log[W]/Log[KBr] in a semiquantitative way by using, for the evaluation of the total interaction potential V
T, a value of the Hamaker constant (A) similar to the classical theoretical one for polystyrene particles dispersed in water. In the case of the anionic latex,
it was necessary to admit the presence of a hydration layer of a thickness similar to the radius of the hydrated/dehydrated
counterion. On the other hand, by using the experimental doublet rate constant in diffusion conditions, we obtain a lower
value of the Hamaker constant (A), but within the range of the A values usually found in previous studies.
Received: 8 September 1997 Accepted: 8 January 1998 相似文献
7.
A series of P[N-isopropylacrylamide (NIPAM)] latexes with different contents of cyano groups were successfully prepared by either seeded
or shot-growth polymerizations of an aqueous solution containing acrylonitrile (AN) onto a seed P[NIPAM] latex, respectively, and further characterized by FT-IR, 1H-NMR, elemental analysis, as well as by quasielastic light scattering (QELS) and scanning electron microscopy (SEM). All
prepared surface-cyanofunctionalized P[NIPAM] latexes exhibited the same range of lower critical solution temperature (LCST) as a pure P[NIPAM] latex. The shot polymerization process proved more efficient at yielding cyano derivatized latexes than the seeded
polymerization technique. The amount of incorporated cyano groups onto the particles was determined with a good correlation
both by 1H-NMR and elemental analysis. The higher the amount of initially introduced AN monomer in the reaction mixture, the more cyano
groups were incorporated onto the particles. The surface of the particles with high content of cyano groups appeared quite
rough by SEM in comparison with that of the pure P[NIPAM] particles.
Received: 25 February 1998 Accepted: 23 June 1998 相似文献
8.
Martin Albrecht 《Theoretical chemistry accounts》2002,107(2):71-79
A local-orbital-based ab initio approach to calculate correlation effects on quasi-particle energies in insulating solids
is presented. The use of localized Wannier-type Hartree–Fock orbitals allows correlation effects to be efficiently assessed.
First a Green's function approach based on exact diagonalization is introduced and this is combined with an incremental scheme,
while subsequently different levels of perturbative approximations are derived from the general procedure. With these methods
the band structure of LiF is calculated and good agreement with experiment is found. By comparing the different approximations
proposed, including the exact diagonalization procedure, their relative quality is established.
Received: 25 June 2001 / Accepted: 31 August 2001 / Published online: 19 December 2001 相似文献
9.
10.
This article reports the colloidal and physicochemical characterization of crosslinked poly (N-isopropylmethacrylamide) (poly[NIPMAM]) latexes. The latex particles were first characterized by determining the lowest critical
solubility temperature by measuring the optical density variation as a function of temperature. In addition, the electrophoretic
mobility behaviors of all latexes were examined as a function of pH and temperature. Finally, the colloidal stability was
investigated by determining the critical coagulation concentration and the critical flocculation temperature, and the corresponding
results were discussed by taking into account both the effect of salinity and temperature on the solvency of poly[NIPMAM].
Received: 25 March 1999 Accepted: 5 May 1999 相似文献
11.
Cationic drag reducing surfactants are suitable means for reducing the energy costs in city district heating and cooling
systems. Water used in these systems is usually a treated water, however, the loss of water due to the leakage is often supplied
by water from the municipal network and thus the content of ions in the system may increase. That is why the influence of
ions present in water and temperature on viscosity curves has been investigated and the effect of both on Shear Induced Structure
(SIS) is shown here. We have proved that SIS is not an indispensable condition for the surfactant ability of drag reduction.
Received: 7 August 1997 Accepted: 29 April 1998 相似文献
12.
Agustín Urretabizkaia Jos M. Asua 《Journal of polymer science. Part A, Polymer chemistry》1994,32(9):1761-1778
The kinetics of the high solids content emulsion terpolymerization of vinyl acetate, methyl methacrylate, and butyl acrylate were investigated. The effect of feed flow rate, total amount of emulsifier, distribution of emulsifier between the initial charge and the feed, concentration of initiator, and solids content on the time evolution of the conversion, terpolymer composition, and total number of polymer particles were investigated. The experimental results were analyzed by means of a mathematical model that incorporated the main features of the system. © 1994 John Wiley & Sons, Inc. 相似文献
13.
Latexes as dispersions of poly(methyl methacrylate-co-butyl methacrylate) copolymeric nanoparticles within water were produced by microemulsion polymerization of the respective
comonomers. Polymer yield, number-average and weight-average molecular weights, polydispersity index, and the glass-transition
temperature of the copolymer produced were 50%, 8.8 × 104, 2.54 × 105, 2.87, and 45 °C. Scanning tunneling microscopy (STM) images of the latex nanoparticles and film formation on highly oriented
pyrolitic graphite (HOPG) were obtained with a 2 V sample bias and a tunneling current of 20 pA. The STM pictures revealed
that the particle size was 18 ± 3 nm. There was no film formation in the case of dehydration at room temperature. There was
some coalesence of particles when the HOPG surface was preheated at 55 °C, while complete film formation was achieved when
the latexes were annealed at 55 °C in an oven for about 10 min.
Received: 23 August 1999 Accepted: 17 January 2000 相似文献
14.
D. Van Dyck 《Mikrochimica acta》2002,138(3-4):153-180
With the resolution becoming sufficient to reveal individual atoms, HREM is now entering the stage where it can compete with
X-ray methods to quantitatively determine atomic structures of materials without much prior knowledge, but with the advantage
of being applicable to aperiodic objects such as crystal defects. In our view the future electron microscope will be characterised
by a large versatility in experimental settings under computer control such as the illumination conditions (TEM-STEM), CBED,
detecting conditions (diffraction, image, ptychography) and many other tunable parameters such as focus (g), voltage, spherical aberration (C
s
), beam tilt, etc. Since modern detectors can detect single electrons, also the counting statistics is known. The only limiting
factor in the experiment will be the total number of electrons that interact with the object during the experiment due to
the limitations in the exposure time or in the object damage. However, instrumental potentialities will never be exploited
fully if not guided by an experimental strategy. Here intuitive guidelines can be very deceptive. For instance an image made
with the best electron microscope (C
s
= 0) at the best focus (g = 0) from the best object (phase object) would show no contrast at all. Hence, questions such as what is the best C
s
, focus, object thickness, etc. can only be answered properly if done using a method of experiment design. 相似文献
15.
Viscosities of exhaustively deionized aqueous suspensions of colloidal silica spheres are measured with coexisting ion-exchange
resins using an Ubbelohde-type viscometer. The reduced viscosities of small silica spheres (56.3 nm in diameter) with and
without resins decrease as the sphere concentration increases. However, the former are larger than the latter especially at
low sphere concentrations. The reduced viscosities of other silica spheres, 81.2, 103, 110 and 136 nm in diameter, with resins
decrease as the sphere concentration increases, whereas those without resins increase especially at low sphere concentrations.
The significant effect of the extent of deionization upon the viscometric properties supports the important role of the extended
electrical double layers formed around the colloidal spheres.
Received: 28 October 1999 Accepted: 24 December 1999 相似文献
16.
S. A. Mezzasalma 《Colloid and polymer science》2001,279(1):22-32
The contribution of a solid phase to the low-shear viscosity of a solid–liquid dispersion, i.e., the specific viscosity,
ηSP, is investigated theoretically by applying a variational procedure. The Fuchs stability ratio has been interpreted as a general
steady-state equilibrium constant for aggregation and has been extended to a functional form which describes the motion of
two Brownian units in a dispersion. Application of the Euler–Lagrange equation under the validity of an adiabatic-like approximation
for the Hamiltonian (approximately Brownian kinetic energy and inertial potential field) yields a constraint that involves
specific viscosity, solid volume fraction, φ, interparticle energy and correlation functions of the dispersed phase. The Einstein
formula is found as the limit of the Saito equation when an infinitely dilute hard-sphere suspension is considered, while
a general closed form expression, ηSP=ηSP(φ), is proposed for a concentrated suspension. It depends on the particle coordination number and affinity, returns the low
density expansion predicted by effective-medium-type theories for the viscosity, and can be represented as the sum of two
dominant contributions, associated respectively with the first peak of the radial distribution function and the second peak
of the total correlation function. Application to experimental data, concerning latex particles in cis-decalin and interacting silica–water systems, is presented and discussed.
Received: 31 March 2000/Accepted: 13 July 2000 相似文献
17.
Agustín Urretabizkaia Gurutze Arzamendi María J. Unzu Jos M. Asua 《Journal of polymer science. Part A, Polymer chemistry》1994,32(9):1779-1788
A method for the calculation of the optimal monomer addition policies for polymer composition control in emulsion terpolymerization is developed. The method is applied to reactors with and without limited heat removal capacity. A mathematical model that incorporates the main features of the vinyl acetate/methyl methacrylate/butyl acrylate high solids content emulsion terpolymerization system allows the calculation of the composition of the initial charge of the reactor and the time-dependent monomer addition rates required. © 1994 John Wiley & Sons, Inc. 相似文献
18.
A comparison of the swelling behaviour of copolymer and interpenetrating network microgel particles 总被引:1,自引:0,他引:1
A comparison of the swelling behaviour of two types of hydrogel particles, namely, random poly[(acrylic acid)-co-(acrylamide)] [P(AAc-co-AAm)] particles and PAAc/PAAm interpenetrating network (IPN) particles, has been made using temperature and pH as the triggers.
Both types of particles were synthesised by inverse microemulsion polymerisation. The conversion yield of AAc was found to
be around 60 wt% due to the partition of this monomer between the aqueous and organic phases. The AAc content was thus lower
in the final particles than in the initial composition. Both types of hydrogel particle exhibit an upper critical solution
temperature associated with the breakage of the polymer–polymer hydrogen bonds. The maximum swelling ratio occurred in both
cases at approximately equimolar AAc and AAm content of the particles. A sharper swelling transition was observed for the
PAAc/PAAm IPN particles. This is because of the co-operative nature of the interactions between the PAAc and PAAm chains,
the so-called “zipper effect”. A very much higher swelling ratio was obtained using pH as the trigger compared to using temperature.
This difference in behaviour is related to the relative strengths of the forces involved in the particle swelling. Electrostatic
repulsion forces, associated with the AAc dissociation with increasing pH, are much stronger than the hydrogen bonds.
Received: 18 August 1999/Accepted: 28 August 1999 相似文献
19.
Sj. van der Wal 《Chromatographia》1985,20(5):274-278
Summary Three new organic modifier solvent systems for reversed-phase HPLC are recommended which can increase the speed of analysis up to twofold over conventional modifier systems, without a significant sacrifice in general selectivity. 相似文献
20.
We discuss the classical dynamics of a CH-stretching and an OH-stretching vibration coupled to a hindered rotation around
a CC (OC) bond of a CH3 group or an OH group. Our model is based on a two-dimensional system, in which zero angular momentum is assumed. The model
is further simplified by considering only kinetic coupling between the CH (OH) stretching and the hindered rotation. Through
numerical calculations, a new set of states is found, which originates from n:1 resonances between the internal rotation frequency and the stretching frequency, n being associated to the order of symmetry (n = 3 and 6 for the cases investigated). We also present a perturbative approach based on the Lie series method, which provides
insight into these nonadiabatic states.
Received: 28 April 1999 / Accepted: 21 September 1999 / Published online: 15 December 1999 相似文献