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1.
The linear viscoelastic behavior of polystyrene (PS) and poly(methylmethacrylate) (PMMA) blends with PS as the matrix and
amounts of PMMA in the range 10–30 wt% was investigated. Transmission electron microscopy (TEM) revealed a complex morphology
which was characterized by the existence of composite particles; the PMMA particles which are enclosed in the PS matrix themselves
carry PS inclusions. In order to explain the G* data of these blends a model is presented which consists of a Palierne model for the composite particles and a Palierne
model for the whole blend, taking into account composite and neat particles. Simulations show the principal relevance of the
assumptions made. Moreover, it is shown that the measurements agree well with the model for the whole measured frequency region
and that the fit parameters, the size of the composite particles and the concentration and size of interior particles are
in reasonable agreement with data available from TEM.
Received: 1 November 1998 Accepted: 5 April 1999 相似文献
2.
Phase separation processes in mixtures of poly-α-methylstyrene-co-acrylonitrile (PαMSAN) and poly-methylmethacrylate (PMMA)
with lower critical solution temperature (LCST) behavior have been studied, focusing on the manifestation of the interface
in oscillatory shear measurements. By using blends of different composition, systems with a droplet-matrix morphology or a
co-continuous structure are generated during the phase separation process. The feasibility of probing this morphology development
by rheological measurements has been investigated. The development of a disperse droplet phase leads to an increase in the
elasticity of the blend at low frequency, showing up as a shoulder in the plot of storage modulus versus frequency. Here,
the droplet growth is unaffected by the shear amplitude up to strains of 0.2; therefore the resulting dynamic data are suitable
for quantitative analysis. In contrast, for blends in which phase separation leads to a co-continuous structure, the storage
modulus shows a power law behavior at low frequency and its value decreases as time proceeds. For the latter systems, effects
of the dynamic measurement on the morphology development have been observed, even for strain amplitudes as low as 0.01. To
probe the kinetics of morphology evolution in droplet-matrix systems, measurements of the time dependence of the dynamic moduli
at fixed frequency should be performed (for a whole series of frequencies). Only from such measurements, curves of the frequency
dependence of the moduli at a well defined residence time can be constructed. From fitting these curves to the emulsion model of Palierne, the droplet diameter distribution
at that particular stage in the phase separation and growth process can be obtained. It is not appropriate to use a simplified
version of the Palierne model containing only the average droplet size, because a morphology with too broad a size distribution
is generated.
Received: 15 February 1999 Accepted: 20 May 1999 相似文献
3.
Interfacial reactions have dominant effects on the morphological and rheological properties of compatibilized polymer blends.
This work aims to investigate the effect of epoxy resin, as a coupling agent, on the interface properties and subsequent influences
on the morphological and rheological properties of polyethylene terephthalate/polyamide66 (PET/PA66) blend. PET/PA66 70/30
blends with different amount of bisphenol A epoxy resin (0, 1, 3, and 5 wt.%) were prepared. SEM micrographs show reduction
in droplet size with increasing epoxy resin concentration, confirming the reactive compatibilizing effect of the epoxy resin.
Reactions at the interface of the PET-EP-PA66 blend are confirmed by FTIR spectra. Shear viscosity results demonstrates that
adding epoxy resin could suppress the interfacial slip at the blend interphase. Obtained results from storage modulus (G′)
curves show the presence of one plateau for the blends at low frequency region; nevertheless, relaxation spectra indicate
the presence of two more relaxation mechanisms than precursors which are related to the shape relaxation of droplets and the
interface relaxation. The presence of the interface relaxation time in the blend without epoxy resin can prove the presence
of reactions between two condensation polymers; however, adding the epoxy resin results in reducing both relaxation time and
interfacial tension and increasing interfacial shear modulus. These observations indicate that the epoxy resin has been successful
to boost the reactions at the interface between two polymers. Fitting the obtained experimental data using Palierne model
indicates that the general Palierne model could describe rheological properties of the blends very well. 相似文献
4.
Polyamide-6/poly(epichlorohydrin - co - ethylene oxide) (PA6/ECO) nanocomposites were prepared with 6 wt.% organoclay and different ECO content from 5 to 40 wt.%,
via two-step melt blending process. The effects of organoclay and rubber content on the morphological and rheological properties
of samples have been studied. Samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM),
and rheometry in small amplitude oscillatory shear. XRD results indicate that the nanoclay platelets are partially exfoliated
in both PA6 and ECO phases. The higher rubber content of nanocomposite samples results in higher exfoliation degree of the
nanoclay layers. SEM photomicrographs of samples show that the size of rubber droplets increases by the introducing of nanoclay.
Oscillatory shear measurements show that the storage modulus of nanocomposite samples significantly increases in comparison
with unfilled blends. The formation of physical network is the prime cause of such increase. Moreover, presence of nanoclay
dramatically increases melt yield stress of the samples. Palierne emulsion model has been applied to predict the rheological
behavior of unfilled blends. A quantitative agreement between Palierne model and those of experimental data is found for low
ECO content samples. 相似文献
5.
In this work, the dynamic behavior of poly(methyl methacrylate)/polystyrene blend to which P(S0.5-ran-MMA0.5) was added was studied. Several blend (ranging from 5 to 20 wt% of dispersed phase) and copolymer (up to 20 wt% with respect
to dispersed phase) concentrations were studied. The rheological behavior of the blends was compared to Bousmina’s (Rheol
Acta 38:73–83, 1999) and Palierne’s (Rheol Acta 29:204–214, 1990) generalized models. The relaxation spectra of the blends were also inferred, and the results were analyzed in light of the
analysis of Jacobs et al. [J Rheol 43:1495–1509, 1999]. The relaxation spectra of the blends with smaller dispersed phase (below 10 wt%) and larger copolymer concentrations (above
0.4 wt%) showed the presence of four relaxation times, two corresponding to the blend phases, τ
F
, corresponding to the relaxation of the shape of the dispersed phase of the blend and that can be attributed to the relaxation of Marangoni stresses tangential to the interface between the dispersed phase and
matrix. The experimental values of and were used to infer the interfacial tension (Γ) and the interfacial complex shear modulus (β) for the different blends, Γ decreased with increasing copolymer concentration. β decreased with increasing blend dispersed phase concentration and decreasing copolymer concentration. The predictions of
Palierne’s generalized model were found to corroborate the experimental data once the values of Γ and β, found analyzing the relaxation spectra, were used in the calculations. Bousmina’s model was found to corroborate the data
only for larger dispersed phase concentration.
Paper was presented at the 3rd Annual Rheology Conference, AERC 2006, April 27–29, 2006, Crete, Greece. 相似文献
6.
Edward T. Kopesky Stephen G. Boyes Neil Treat Robert E. Cohen Gareth H. McKinley 《Rheologica Acta》2006,45(6):971-981
Two distinct oligomeric species of similar mass and chemical functionality (M
w≈2,000 g/mol), one a linear methyl methacrylate oligomer (radius of gyration R
g≈1.1 nm) and the other a hybrid organic–inorganic polyhedral silsesquioxane nanocage (methacryl-POSS, r≈1.0 nm), were subjected to thermal and rheological tests to compare the behaviors of these geometrically dissimilar molecules over the entire composition range. The glass transition temperatures of the blends varied monotonically between the glass transition temperatures of the pure oligomer (T
g=−47.3°C) and the pure POSS (T
g=−61.0°C). Blends containing high POSS contents (with volume fraction φ
POSS≥0.90) exhibited enhanced enthalpy relaxation in differential scanning calorimetry (DSC) measurements, and the degree of enthalpy relaxation was used to calculate the kinetic fragility indices m of the oligomeric MMA (m=59) and the POSS (m=74). The temperature dependences of the viscosities were fitted by the free-volume based Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tammann (VFT) framework and a dynamic scaling relation. The calculated values of the fragility from the WLF–VFT fits were similar for the POSS (m=82) and for the oligomer (m=76), and the dynamic scaling exponent was similar for the oligomeric MMA and the POSS. Within the range of known fragilities for glass-forming liquids, the temperature dependence of the viscosity was found to be similarly fragile for the two species. The difference in shape of the nanocages and oligomer chains is unimportant in controlling the glass-forming properties of the blends at low volume fractions (φ
POSS<0.20). However, at higher volume fractions, adjacent POSS cages begin to crowd each other, leading to an increase in the fractional free volume at the glass transition temperature and the observed enhanced enthalpy relaxation in DSC. 相似文献
7.
The rheological characterization and modeling of a series of polybutadienes obtained by anionic solution polymerization is
presented in this work. The polybutadienes are synthesized using two different initiators: R,R′,R′′-silyloxyalkyllithium (F1)
and R,R′,R′′-silylalkyllithium (F3). In addition, a polybutadiene obtained with a conventional alkyllithium initiator (n-butyllithium) is used as a reference.
The rheological characterization is carried out under small amplitude oscillatory shear in the stress-controlled mode. Microstructure,
molecular weight, and molecular weight distribution are determined by FTIR and GPC. The vinyl content of the polybutadienes
synthesized using the functionalized initiators is similar to that obtained with n-butyllithium (8–11%). Materials obtained with F1 show a relatively low polydispersity within a narrow molecular weight range
(250,000–300,000 g/mol), while samples obtained with F3 cover a wider range of molecular weights (65,000–670,000 g/mol) and
display higher values of polydispersity. In all cases, a parallel reaction using propylene oxide in the termination step is
done to place a functional group at the chain ends. The effect of this group on the rheological behavior appears to be negligible.
Three rheological models are used and their predictions of the experimental data are compared. The models include the Doi
and Edwards reptation model, expressions using a discrete spectrum of relaxation times based in the rubber-like liquid constitutive
equation and the fractional Maxwell equation in which a given analytical relaxation-spectrum is used. Relevant relations are
obtained between the models' parameters and the molecular properties of these systems, which in turn are related to the presence
of functional groups at the polymer chain ends. 相似文献
8.
Maria Eugenia Romero-Guzmán Angel Romo-Uribe B. Manuel Zárate-Hernández Rodolfo Cruz-Silva 《Rheologica Acta》2009,48(6):641-652
Polyhedral oligomeric silsesquioxane (POSS) are hybrid nanostructures of about 1.5 nm in size. These silicon (Si)-based polyhedral
nanostructures are attached to a polystyrene (PS) backbone to produce a polymer nanocomposite (POSS–styrene). We have solution
blended POSS–styrene of with commercial polystyrene (PS), , and studied the rheological behavior and thermal properties of the neat polymeric components and their blends. The concentration
of POSS–styrene was varied from 3 up to 20 wt.%. Thermal analysis studies suggest phase miscibility between POSS–styrene and
the PS matrix. The blends displayed linear viscoelastic regime and the time–temperature superposition principle applied to
all blends. The flow activation energy of the blends decreased gradually with respect to the matrix as the POSS–styrene concentration
increased. Strikingly, it was found that POSS–styrene promoted a monotonic decrease of zero-shear rate viscosity, η
0, as the concentration increased. Rheological data analyses showed that the POSS–styrene increased the fractional free volume
and decreased the entanglement molecular weight in the blends. In contrast, blending the commercial PS with a PS of did not show the same lubrication effect as POSS–styrene. Therefore, it is suggested that POSS particles are responsible
for the monotonic reduction of zero-shear rate viscosity in the blends. 相似文献
9.
José Inés Escalante Daniel Escobar Emma Rebeca Macias Juan Humberto Pérez-López Fernando Bautista Eduardo Mendizábal Jorge E. Puig Octavio Manero 《Rheologica Acta》2007,46(5):685-691
Low-viscosity micellar aqueous solutions of cetyltrimethylammonium bromide (CTAB) undergo a major change in the presence of
the hydrotrope, potassium 1-phenylmethylsulfate (KPhMS), producing a highly viscoelastic entanglement network of polymer-like
micelles. The system studied here shows typical shear banding flow behavior, which tends to disappear with increasing the
hydrotrope-to-surfactant concentration ratio (C
H / C
S). The linear rheological response was analyzed with the model of Granek–Cates, whereas the nonlinear behavior was reproduced
with the Bautista–Manero–Puig (BMP) model. Both models introduce a kinetic equation to account for the breaking and reformation
of the micelles, and they predict the linear and nonlinear rheological data very well.
This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006. 相似文献
10.
N. K. Aluri P. K. G. Pantangi S. P. R. Muppala F. Dinkelacker 《Flow, Turbulence and Combustion》2005,75(1-4):149-172
This numerical investigation carried out on turbulent lean premixed flames accounts for two algebraic – the Lindstedt–Vaos
(LV) and the classic Bray–Moss–Libby (BML) – reaction rate models. Computed data from these two models is compared with the
experimental data of Kobayashi et al. on 40 different methane, ethylene and propane Bunsen flames at 1 bar, where the mean
flame cone angle is used for comparison. Both models gave reasonable qualitative trend for the whole set of data, in overall.
In order to characterize quantitatively, firstly, corrections are made by tuning the model parameters fitting to the experimental
methane–air (of Le = 1.0) flame data. In case of the LV model, results obtained by adjusting the pre-constant, i.e., reaction rate parameter,
CR, from its original value 2.6 to 4.0, has proven to be in good agreement with the experiments. Similarly, for the BML model,
with the tuning of the exponent n, in the wrinkling length scale, Ly = Cl⋅ lx(sL/u′)n from value unity to 1.2, the outcome is in accordance with the measured data. The deviation between the measured and calculated
data sharply rises from methane to propane, i.e., with increasing Lewis number. It is deduced from the trends that the effect
of Lewis number (for ethylene–air mixtures of Le = 1.2 and propane–air mixtures of Le = 1.62) is missing in both the models. The Lewis number of the fuel–air mixture is related to the laminar flame instabilities.
Second, in order to quantify for its influence, the Lewis number effect is induced into both the models. It is found that
by setting global reaction rate inversely proportional to the Lewis number in both the cases leads to a much better numerical
prediction to this set of experimental flame data. Thus, by imparting an important phenomenon (the Lewis number effect) into
the reaction rates, the generality of the two models is enhanced. However, functionality of the two models differs in predicting
flame brush thickness, giving scope for further analysis. 相似文献
11.
Thomas J. Rainey William O. S. Doherty D. Mark Martinez Richard J. Brown Neil A. Kelson 《Transport in Porous Media》2011,86(3):737-751
A one-dimensional pressure filtration model that can be used to predict the behaviour of bagasse pulp has been developed and
verified in this study. The dynamic filtration model uses steady state compressibility parameters determined experimentally
by uniaxial loading. The compressibility parameters M and N for depithed bagasse pulp were determined to be in the ranges 3000–8000 kPa and 2.5–3.0 units, respectively. The model also
incorporates experimentally determined steady state permeability data from separate experiments to predict the pulp concentration
and fibre pressure throughout a pulp mat during dynamic filtration. Under steady state conditions, a variable Kozeny factor
required different values for the permeability parameters when compared to a constant Kozeny factor. The specific surface
area was 25–30% lower and the swelling factor was 20–25% higher when a variable Kozeny factor was used. Excellent agreement
between experimental data and the dynamic filtration model was achieved when a variable Kozeny factor was used. 相似文献
12.
Self-consistent modeling of entangled network strands and linear dangling structures in a single-strand mean-field slip-link model 总被引:1,自引:0,他引:1
Linear viscoelastic (LVE) measurements as well as non-linear elongation measurements have been performed on stoichiometrically
imbalanced polymeric networks to gain insight into the structural influence on the rheological response (Jensen et al., Rheol
Acta 49(1):1–13, 2010). In particular, we seek knowledge about the effect of dangling ends and soluble structures. To interpret our recent experimental
results, we exploit a molecular model that can predict LVE data and non-linear stress–strain data. The slip-link model has
proven to be a robust tool for both LVE and non-linear stress–strain predictions for linear chains (Khaliullin and Schieber,
Phys Rev Lett 100(18):188302–188304, 2008, Macromolecules 42(19):7504–7517, 2009; Schieber, J Chem Phys 118(11):5162–5166, 2003), and it is thus used to analyze the experimental results. Initially, we consider a stoichiometrically balanced network,
i.e., all strands in the ensemble are attached to the network in both ends. Next we add dangling strands to the network representing
the stoichiometric imbalance, or imperfections during curing. By considering monodisperse network strands without dangling
ends, we find that the relative low-frequency plateau, G0/GN0G_0/G_N^0, decreases linearly with the average number of entanglements. The decrease from GN0G_N^0 to G
0 is a result of monomer fluctuations between entanglements, which is similar to “longitudinal modes” in tube theory. It is
found that the slope of G′ is dependent on the fraction of network strands and the structural distribution of the network. The power-law behavior of
G
″ is not yet captured quantitatively by the model, but our results suggest that it is a result of polydisperse dangling and
soluble structures. 相似文献
13.
The present work is focused on the rheological properties of two-phase polymer blends in the phase inversion region. A large
number of PS/PMMA- and PSAN/PMMA-blends has been investigated in order to establish a rheological criterion which allows the
quantitative determination of the phase inversion concentration φPI by rheological means. Three rheological criteria based on the viscous and elastic blend properties such as maximum of dynamic
viscosity η′, slope of G′, and maximum of G′ at a constant evaluation frequency have been tested. By correlating the rheological
results to data from quantitative morphological analysis we could prove that the chosen rheological criteria are differently
suitable for the determination of φPI. It has turned out that the G′ criterion is the most robust and most suitable one yielding an excellent correlation with
morphological data. Based on these findings we propose a new simple equation for the prediction of φPI-values.
Received: 14 March 2001 Accepted: 15 May 2001 相似文献
14.
M. García-Morales P. Partal F. J. Navarro F. J. Martínez-Boza C. Gallegos 《Rheologica Acta》2006,45(4):513-524
Knowledge of the kinetics of the manufacturing process of polymer–bitumen blends is of great interest because it provides information on the behaviour of the binder at different stages of the mixing operation, which is useful for the establishment of the optimum processing conditions, involving temperature and operation time. The purpose of this research was to study the evolution of the rheological properties and microstructure of a polymer-modified bitumen during its processing. A 60/70-penetration grade bitumen and recycled EVA/LDPE were mixed under different processing conditions. Measurements of the evolution of viscosity with time, at different temperatures and agitation speeds, were carried out with an experimental device known as ‘rheomixer’, that is, a helical ribbon impeller inside a mixing vessel coupled with the transducer and motor of a conventional rheometer. Under the experimental conditions selected (within the laminar region, Re<10), temperature is the most important processing variable. Hence, low agitation speeds and a processing temperature of around 180°C should be chosen for bitumen modification with the polymer used. 相似文献
15.
Manish K. Tiwari Alexander V. Bazilevsky Alexander L. Yarin Constantine M. Megaridis 《Rheologica Acta》2009,48(6):597-609
Rheological behavior of concentrated suspensions of chemical vapor deposition carbon nanotubes in uniaxial elongation and
simple shear is studied experimentally and theoretically. Nanotubes are suspended in viscous host liquids—castor oil or its
blends with n-decane. The elongational measurements are performed by analyzing self-thinning (due to surface tension effect) liquid threads
of nanotube suspensions. A quasi-one-dimensional model is used to describe the self-thinning process, whereas corrections
accounting for thread nonuniformity and necking are introduced a posteriori. The effects of nanotube concentration and aspect
ratio, viscosity of the suspending liquid, and initial diameter of the self-thinning thread in uniaxial elongation are elucidated.
The results for uniaxial elongation are compared with those for simple shear. The correspondence in the results of the shear
and elongational measurements is addressed and interpreted. The results conform to the Herschel–Bulkley rheological constitutive
equation (i.e., power law fluids with yield stress). However, the yield stress in elongation is about 40% higher than in simple
shear flow, which suggests that the original Herschel–Bulkley model need modification with the yield stress being a function
of the second invariant of the deviatoric stress tensor. The present effort is the first to study capillary self-thinning
of Herschel–Bulkley liquids, which are exemplified here by suspensions of carbon nanotubes. 相似文献
16.
A phenomenological model for dispersed systems which exhibit complex rheological behaviour such as shear and time-dependent
viscosity, yield stress, and elasticity is proposed. The model extends the Quemeda model to describe the viscosity function
with a structural parameter λ which varies according to different kinetic orders of particle aggregation and segregation.
The transient stress response is obtained by solving an instantaneous Maxwell model with an assumed shear modulus functionG of the same form as the viscosity function η. Accuracy of the proposed model is verified experimentally with the results
obtained for two oil (creosote)/water emulsions. The model that gives the best fit of experimental data appears to be the
one with kinetic ordersn=m=2. 相似文献
17.
Artur Bartosik 《Flow, Turbulence and Combustion》2010,84(2):277-293
The paper deals with fully developed steady turbulent flow of slurry in a circular straight and smooth pipe. The Kaolin slurry
consists of very fine solid particles, so the solid particles concentration, and density, and viscosity are assumed to be
constant across the pipe. The mathematical model is based on the time averaged momentum equation. The problem of closure was
solved by the Launder and Sharma k-ε turbulence model (Launder and Sharma, Lett Heat Mass Transf 1:131–138, 1974) but with a different turbulence damping function. The turbulence damping function, used in the mathematical model in the
present paper, is that proposed by Bartosik (1997). The mathematical model uses the apparent viscosity concept and the apparent viscosity was calculated using two- and three-parameter
rheological models, namely Bingham and Herschel–Bulkley. The main aim of the paper is to compare measurements and predictions
of the frictional head loss and velocity distribution, taking into account two- and three-parameter rheological models, namely
Bingham and Herschel–Bulkley, if the Kaolin slurry possesses low, moderate, and high yield stress. Predictions compared with
measurements show an observable advantage of the Herschel–Bulkley rheological model over the Bingham model particularly if
the bulk velocity decreases. 相似文献
18.
19.
The most important rheological and mathematical features of the pom–pom model are presently used to compare and improve other
constitutive models such as the Giesekus and Phan-Thien–Tanner models. A pragmatic methodology is selected that allows derivation
of simple constitutive equations, which are suited to possible software implementation. Alterations to the double convected
pom–pom, Phan-Thien–Tanner and Giesekus models are proposed and assessed in rheometric flows by comparing model predictions
to experimental data.
相似文献
Benoit Debbaut (Corresponding author)Email: |
20.
The effect of low-volume fractions of nanoparticles on the morphological processes and the rheological properties of immiscible
blends are dis cussed. For blends of poly-isobutylene and poly-dimethylsiloxane stabilized by silica particles, particles
help to suppress coalescence. Yet, particle bridging of different droplets has also been reported and leads to a slow build
up of a gel-like structure, which could interfere with the morphology evolution under flow. We first investigated the importance
of this effect under relevant conditions. To further assess the relative importance of the different processes in technically
relevant polymer–polymer blends, the effect of carbon black particles on morphological processes—coalescence and break-up—in
polyamide and ethylene–ethylene–metylacrylate copolymers will be studied using rheological methods. It will be shown that
particles affect coalescence and break-up, suggesting that the effect of particles is linked to their effect on interfacial
dynamics. 相似文献