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1.
The effect of temperature on the interfacial tension for PS/PMMA, PS/PE, and PMMA/PE was measured using the imbedded fiber
retraction method. Interfacial tensions for PS/PMMA, PS/PE, and PMMA/PE were measured over temperature ranges of 160–250 °C,
140–220 °C, and 140–220 °C, respectively. The interfacial tension was found to follow a dependence of 3.6–0.013 T dyn/cm, 7.6–0.051 T dyn/cm and 11.8–0.017 T dyn/cm for PS/PMMA, PS/PE, and PMMA/PE, respectively. Comparison of the data with the mean field theory of Helfand and Sapse
were made; however, a simple linear fit to the data described the temperature dependence in the experimental window as well
as the predictions of the mean field theory.
Received: 6 July 1999 Accepted: 23 March 2000 相似文献
2.
Rheological and mechanical properties of silica colloids: from Newtonian liquid to brittle behaviour
Rheological and mechanical properties of aqueous mono-disperse silica suspensions (Ludox? HS40) are investigated as a function
of particle volume fraction (ϕ
p ranging from 0.22 to 0.51) and water content, using shear rate tests, oscillatory methods, indentation and an ultrasonic
technique. As the samples are progressively dried, four regimes are identified; they are related to the increasing particle
content and the existence and behaviour of the electrical double layer (EDL) around each particle. For 0.22 ≤ ϕ
p ≤ 0.30), the suspensions are stable due to the strong electrostatic repulsion between particles and show Newtonian behaviour
(I). As water is removed, the solution pH decreases and the ionic strength increases. The EDL thickness therefore slowly decreases,
and screening of the electrostatic repulsion increases. For 0.31 ≤ ϕ
p ≤ 0.35, the suspensions become turbid and exhibit viscoelastic (VE) shear thinning behaviour (II), as they progressively
flocculate. For 0.35 ≤ ϕ
p ≤ 0.47, the suspensions turn transparent again and paste-like, with VE shear thinning behaviour and high elastic modulus
(III). At higher particle concentration, the suspensions undergo a glass transition and behave as an elastic brittle solid
(IV, ϕ
p = 0.51). 相似文献
3.
Experimental and numerical studies of natural convection in a single phase, closed thermosyphon were carried out using a
vertical, rectangular enclosure model. Only one vertical plate plays the role of heat transfer surface having 100 mm height
and 100 mm width, and others act as the adiabatic wall made of transparent plexi-glass. The heat transfer surface is separated
into three horizontal zones with an equal height; top 1/3 and bottom 1/3 of the surface are cooling and heating zones, respectively
and intermediate section is an adiabatic zone. Water is used as the working fluid. Variable parameters are distance D between the heat transfer surface and an adiabatic plate opposite to the heat transfer plate, and temperature difference
ΔT between heating and cooling zones. By changing both D and ΔT, three regimes of the natural convection flow; quasi-two-dimensional steady, three-dimensional steady and unsteady flows
are observed by means of thermo-sensitive liquid crystal powder and numerically simulated very well by solving a set of governing
equations.
Received on 17 January 2000 相似文献
4.
The transient recoverable deformation ratio after melt elongation at various elongational rates and maximum elongations was
investigated for pure polystyrene and for a 85 wt.% polystyrene/15 wt.% linear low density polyethylene (PS/LLDPE 85:15) blend
at a temperature of 170 oC. The ratio p of the zero shear rate viscosity of LLDPE to that of PS is p = 0.059 ≈ 1:17. Retraction of the elongated LLDPE droplets back to spheres and end-pinching is observed during recovery.
A simple additive rule is applied in order to extract the contribution of the recovery of the elongated droplets from the
total recovery of the blend. In that way, the recoverable portion of the PS/LLDPE blend induced by the interfacial tension
is determined and compared with the results of a theory based on an effective medium approximation. The effective medium approximation
reproduces well the time scale of the experimental data. In addition, the trends that the recoverable deformation increases
with elongational rate and maximum elongation are captured by the theoretical approach. 相似文献
5.
Christian Sailer Martin Weber Helmut Steininger Ulrich A. Handge 《Rheologica Acta》2009,48(5):579-588
In this work, we studied the melt rheology of multigraft copolymers with a styrene–acrylonitrile maleic anhydride (SANMA)
terpolymer backbone and randomly grafted polyamide 6 (PA 6) chains. The multi-grafted chains were formed by interfacial reactions
between the maleic anhydride groups of SANMA and the amino end groups of PA 6 during melt blending. Because of the phase separation
of SANMA and PA 6, the grafted SANMA backbones formed nearly circular domains which were embedded in the PA 6 melt with a
diameter in the order of 20 to 40 nm. The linear viscoelastic behaviour of PA 6/SANMA blends at a sufficiently large SANMA
concentration displayed the characteristics of the critical gel state, i.e. the power relations G′ ∝ G′′ ∝ ω
0.5. In elongation, the PA 6/SANMA blend at the critical gel state showed a non-linear strain hardening behaviour already at
a very small Hencky strain. In contrast to neat PA 6, the elasticity of the PA 6/SANMA blends was strongly pronounced, which
was demonstrated by recovery experiments. Rheotens tests agreed with the linear viscoelastic shear oscillations and the measurements
using the elongational rheometer RME. Increasing the SANMA concentration led to a larger melt strength and a reduced drawability.
The occurrence of the critical gel state can be interpreted by the cooperative motion of molecules which develops between
the grafted PA 6 chains of neighbouring micelle-like SANMA domains. 相似文献
6.
An experimental study of transient boiling heat transfer during a cooling of a hot cylindrical block with an impinging water
jet has been made at atmospheric pressure. The experimental data were taken for the following conditions: a degree of subcooling
of ΔT
sub = 20–80 K, a jet velocity of u
j
= 5–15 m/s, a nozzle diameter of d
j
= 2 mm and three materials of copper, brass and carbon steel. The block was initially and uniformly heated to about 250 °C
and the transient temperatures in the block were measured at eight locations in r-direction at two different depths from the surface during the cooling of hot block. The surface heat flux distribution with
time was evaluated using a numerical analysis of 2-D heat conduction. Behavior of the wetting front, which is extending the
nucleate boiling region outward, is observed with a high-speed video camera. A position of wetting region is measured and
it is correlated well with a power function of time. The changes in estimated heat flux and temperature were compared with
the position of wetting region to clarify the effects of subcooling, jet velocity and thermal properties of block on the transient
cooling.
Received on 17 March 2000 相似文献
7.
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
8.
Akinari Minegishi Akihiro Nishioka Tatsuhiro Takahashi Yuichi Masubuchi Jun-ichi Takimoto Kiyohito Koyama 《Rheologica Acta》2001,40(4):329-338
A series of polystyrene (PS) and a small amount of ultra high molecular weight (UHMW) PS blends have been prepared by using
tetrahydrofuran (THF). Matrix PS has an Mw of 423,000 (Mw/Mn= 2.36) and UHMW-PS has either an Mw of 3,220,000 (Mw/Mn= 1.05) or 15,400,000 (Mw/Mn=1.30) in the range of concentration from 0 wt% to 1.5 wt%. The influence of a small amount of UHMW on dynamic viscoelasticity
was investigated. At the frequency lower than 0.001 rad/s, the enhancement of G′ was observed by the incorporation of a small
amount of UHMW. And the degree of enhancement was in the order of Mw of UHMW and its concentration. The measurement of uniaxial elongational viscosity for the blends was performed and the effects
of UHMW on strain-hardening properties were analyzed at equal strain-rate conditions. The concentration of UHMW where the
strain-hardening becomes substantially stronger was determined. To get more insight into the cause of enhancement of strain-hardening
at a certain concentration, the damping function from step-shear stress relaxation was measured. The influence of a small
amount of UHMW on the damping function was found to be small. It was interpreted, from time- and strain-dependency points,
that the enhancement of strain-hardening by a small amount of UHMW was governed by the long relaxation time.
Received: 6 September 2000 Accepted: 11 January 2001 相似文献
9.
Gerald Henry Meeten 《Rheologica Acta》2007,46(6):803-813
Various soft solid suspensions were squeezed at constant force between polished and roughened circular glass plates and the
time-dependence of the interplate separation was measured. The filterability of suspensions was quantified by their desorptivity
S obtained from measurements of capillary suction time. The squeeze flow (SF) of suspensions for which S < 2 μm s−1/2 was largely consistent with rheological theory, which neglected radial filtration: the relative motion between the liquid
and solid phases of the suspension in the radial pressure gradient. Suspensions having S > 2 μm s−1/2 showed SF behavior that was consistent with the presence of radial filtration. 相似文献
10.
M. Khalilian M. Navidbakhsh M. Rezazadeh Valojerdi M. Chizari P. Eftekhari Yazdi 《Experimental Mechanics》2011,51(2):175-182
The unfertilized oocyte is surrounded by a spherical layer called the zona pellucida (ZP). The physical hardness of this layer
plays a crucial role in fertilization and it is largely unknown because of the lack of appropriate measuring and modeling
methods. Recently, considerable biomedical attentions have concentrated on determination of the mechanical properties of oocytes
as a single cell. In order to investigate the biophysical characteristics of mammalian oocytes, a change in the elasticity
of human ZP has been quantitatively evaluated before and after fertilization. Young’s modulus of ZP of metaphase-II (MII)
and pronuclear (PN) stages have been estimated using two different protocols of the micropipette aspiration, step-by-step
and continuous increase in pressure, in combination with proportional theoretical models. Experimental results clearly demonstrated
that after fertilization the mean Young’s modulus of the ZP calculated from the step-by-step aspiration test (MII: 7.34 ± 1.36
kPa vs PN: 13.18 ± 1.17 kPa.) and continuous aspiration test (MII: 2.41 ± 0.75 kPa vs. PN: 4.43 ± 1.66 kPa) significantly
increased, (p < 0.05). Mathematical Evaluation of the results shows that although the results of the two methods are different but both
confirm that the hardening of ZP will increase following fertilization. As can be seen, different experimental methods can
influence the choice of the models and this in turn will lead the mechanical properties to be found. 相似文献
11.
F. Puig N. Gavara R. Sunyer A. Carreras R. Farré D. Navajas 《Experimental Mechanics》2009,49(1):47-55
Background The structural integrity of the alveolar monolayer, which is compromised during lung inflammation, is determined by the balance
between cell–cell and cell-matrix tethering forces and the centripetal forces owing to cell viscoelasticity and contraction.
Dexamethasone is an anti-inflammatory glucocorticoid with protective effects in lung injury.
Aim To determine the effects of Dexamethasone on the stiffness and contractility of alveolar epithelial cells.
Methods Cell stiffness (G′) and average traction exerted by the cell (T) were measured by magnetic twisting cytometry and by traction microscopy, respectively. A549 cells were treated 24 h with
Dexamethasone (1 μM) or vehicle (control). G′ and T were measured before and 5 min after challenge with the inflammatory mediator Thrombin (0.5 U/ml). Changes induced by Dexamethasone
in actin cytoskeleton polymerization were assessed by the fluorescent ratio between F-actin and G-actin obtained by staining
cells with phalloidin and DNase I.
Results Dexamethasone significantly increased G′ and T by 56% (n = 11; p < 0.01) and by 80% (n = 17; p < 0.05), respectively. Dexamethasone also increased F/G-actin ratio from 2.68 ± 0.07 to 2.96 ± 0.09 (n = 10; p < 0.05). The relative increase in stiffness and contraction induced by Thrombin in control cells was significantly (p < 0.05) reduced by Dexamethasone treatment: from 190 to 98% in G′ and from 318 to 105% in T.
Conclusion The cytoskeleton remodelling and the increase in cell stiffness and contraction induced by Dexamethasone could account for
its protective effect in the alveolar epithelium when subjected to inflammatory challenge. 相似文献
12.
Edge fracture is an instability of cone-plate and parallel plate flows of viscoelastic liquids and suspensions, characterised
by the formation of a `crack' or indentation at a critical shear rate on the free surface of the liquid. A study is undertaken
of the theoretical, experimental and computational aspects of edge fracture. The Tanner-Keentok theory of edge fracture in
second-order liquids is re-examined and is approximately extended to cover the Criminale-Ericksen-Filbey (CEF) model. The
second-order theory shows that the stress distribution on the semi-circular crack is not constant, requiring an average to
be taken of the stress; this affects the proportionality constant, K in the edge fracture equation −N
2c = KΓ/a, where N
2c is the critical second normal stress difference, Γ is the surface tension coefficient and a is the fracture diameter. When the minimum stress is used, K = 2/3 as found by Tanner and Keentok (1983). Consideration is given to the sources of experimental error, including secondary
flow and slip (wall effect). The effect of inertia on edge fracture is derived. A video camera was used to record the inception
and development of edge fracture in four viscoelastic liquids and two suspensions. The recorded image was then measured to
obtain the fracture diameter. The edge fracture phenomenon was examined to find its dependence on the physical dimensions
of the flow (i.e. parallel plate gap or cone angle), on the surface tension coefficient, on the critical shear rate and on
the critical second normal stress difference. The critical second normal stress difference was found to depend on the surface
tension coefficient and the fracture diameter, as shown by the theory of Tanner and Keentok (1983); however, the experimental
data were best fitted by the equation −N
2c = 1.095Γ/a. It was found that edge fracture in viscoelastic liquids depends on the Reynolds number, which is in good agreement with
the inertial theory of edge fracture. Edge fracture in lubricating grease and toothpaste is broadly consistent with the CEF
model of edge fracture. A finite volume method program was used to simulate the flow of a viscoelastic liquid, obeying the
modified Phan-Thien-Tanner model, to obtain the velocity and stress distribution in parallel plate flow in three dimensions.
Stress concentrations of the second normal stress difference (N
2) were found in the plane of the crack; the velocity distribution shows a secondary flow tending to aid crack formation if
N
2 is negative, and a secondary flow tending to suppress crack formation if N
2 is positive.
Received: 4 January 1999 Accepted: 19 May 1999 相似文献
13.
Effect of melt viscosity of polypropylene on fibrillation of thermotropic liquid crystalline polymer in in situ composite film 总被引:1,自引:0,他引:1
Various grades of polypropylene were melt blended with a thermotropic liquid crystalline polymer, a block copolymer of p-hydroxy benzoic acid and ethylene terephthalate (60/40 mole ratio). The blends were extruded as cast films at different values
of draw ratio (slit width/film thickness). Fibrillation of TLCP dispersed phase with high fiber aspect ratio (length/width)
was obtained with the matrix of low melt flow rate, i.e., high viscosity and with increasing film drawing. Melt viscosities
of pure components and blends measured using capillary rheometer were found to decrease with increasing shear rate and temperature.
Viscosity ratios (dispersed phase to matrix phase) of the systems being investigated at 255 °C at the shear rate ranged from
102 to 104 s−1, were found to lie between 0.04 and 0.15. The addition of a few percent of elastomeric compatibilizers; a tri-block copolymer
SEBS, EPDM rubber and maleated-EPDM, was found to affect the melt viscosity of the blend and hence the morphology. Among these
three compatibilizers, SEBS was found to provide the best fibrillation.
Received: 10 January 2000/Accepted: 24 January 2000 相似文献
14.
Rheology and flow-induced morphology were studied in immiscible polypropylene (PP)/polystyrene (PS) blends with a droplet–matrix
microstructure. Two reactive precursors, maleic anhydride grafted PP and amino terminated PS, were added during the melt-mixing
process to form a graft copolymer. The effects of both the amount of compatibilizer and the shear history on the rheological
and morphological behavior were investigated systematically. Small amplitude oscillatory experiments and scanning electron
microscopy were used to study the phase morphology. Shear history has an important effect on the morphology of the uncompatibilized
blends. The droplet size refines with increasing shear rate. The decrease of this effect with increasing degrees of in situ
compatibilization is mapped out. The results are discussed in terms of interfacial tension and the interfacial coverage. It
turns out that most of the conclusions that were previously obtained on physically compatibilized blends are also valid for
chemically compatibilized ones. 相似文献
15.
In this paper, a non-isobaric Marangoni boundary layer flow that can be formed along the interface of immiscible nanofluids
in surface driven flows due to an imposed temperature gradient, is considered. The solution is determined using a similarity
solution for both the momentum and energy equations and assuming developing boundary layer flow along the interface of the
immiscible nanofluids. The resulting system of nonlinear ordinary differential equations is solved numerically using the shooting
method along with the Runge-Kutta-Fehlberg method. Numerical results are obtained for the interface velocity, the surface
temperature gradient as well as the velocity and temperature profiles for some values of the governing parameters, namely
the nanoparticle volume fraction φ (0≤φ≤0.2) and the constant exponent β. Three different types of nanoparticles, namely Cu, Al2O3 and TiO2 are considered by using water-based fluid with Prandtl number Pr =6.2. It was found that nanoparticles with low thermal conductivity,
TiO2, have better enhancement on heat transfer compared to Al2O3 and Cu. The results also indicate that dual solutions exist when β<0.5. The paper complements also the work by Golia and Viviani (Meccanica 21:200–204, 1986) concerning the dual solutions in the case of adverse pressure gradient. 相似文献
16.
Rheological behavior of polymer/layered silicate nanocomposites are strongly dependent not only upon their microstructure
but also upon the interfacial characteristics. Different phase morphology (intercalated or exfoliated) of polymer/clay is obtained according to interfacial characteristics between polymer chains and clay. In intercalated structure,
the presence of randomly oriented anisotropic stacks of silicate layers is responsible for the enhancement of both moduli.
The PS/clay nanocomposites exhibit a slight enhancement at low frequency because of its simple intercalated structure and
little interaction. On the other hand, the PS-co-ma/clay nanocomposites have a similar intercalated structure but exhibit a distinct plateau-like behavior at low frequency
since the PS-co-ma has a strong attractive interaction with the silicate layers. Finally, PE-g-ma/clay nanocomposites display an exfoliated structure, which exhibit both a distinct plateau-like behavior at low frequency
and enhanced moduli at high frequency. Percolation structure as well as large interfacial area between polymer chains and
clay are responsible for the rheological behavior.
Received: 20 March 2000 Accepted: 11 September 2000 相似文献
17.
Benjamín M. Marín-Santibáñez José Pérez-González Lourdes de Vargas 《Rheologica Acta》2010,49(2):177-189
The nonlinear rheological behavior of short glass fiber suspensions has been investigated in this work by rotational rheometry
and flow visualization. A Newtonian and a Boger fluid (BF) were used as suspending media. The suspensions exhibited shear
thinning in the semidilute regime and weaker shear thinning in the transition to the concentrated one. Normal stresses and
relative viscosity were higher for the BF suspensions than for the Newtonian ones presumably due to enhanced hydrodynamic
interactions resulting from BF elasticity. In addition, relative viscosity of the suspensions increased rapidly with fiber
content, suggesting that the rheological behavior in the concentrated regime is dominated by mechanical contacts between fibers.
Visualization of individual fibers and their interactions under flow allowed the detection of aggregates, which arise from
adhesive contacts. The orientation states of the fibers were quantified by a second order tensor and fast Fourier transforms
of the flow field images. Fully oriented states occurred for shear rates around 20 s − 1. Finally, the energy required to orient the fibers was higher in step forward than in reversal flow experiments due to a
change in the spatial distribution of fibers, from isotropic to planar oriented, during the forward experiments. 相似文献
18.
The effect of mixing particles of different size on the electrorheological response under steady shear flow 总被引:2,自引:0,他引:2
The effect of mixing particles of different sizes on the electrorheological response of suspensions under steady shear flow
was investigated. Two sizes, 15 μm and 50 μm, of monodisperse spherical sulfonated poly(styrene-co-divinylbenzene) particles were used. Several electrorheological fluids were made containing different proportions of small
and large particles dispersed in silicone oil, but with constant overall particulate concentration. It was found that the
mixed size system produced the highest electrorheological response under the shear rates used (10 s−1 to 500 s−1), which is the opposite trend to previous studies of bimodal systems with larger size ratios.
Received: 21 December 2000 Accepted: 29 March 2001 相似文献
19.
The modified imbedded disc retraction method for measurement of interfacial tension in polymer melts
The imbedded disc retraction method is used to estimate interfacial tension in LLDPE/PS system with PS as the imbedded disc.
Shape evolution of a disc of one material (PS) imbedded into the matrix of another material is observed (LLDPE). Three to
five repetitions at three different temperature levels are observed. The Newtonian model of Rundqvist et al. (1996) for the
imbedded disc retraction is modified to include elastic effects. The modified model is derived assuming uniaxial extension,
starting with the lower convected Maxwell model. Both the original model and modified imbedded disc retraction model are used
in data analysis. The mean values of interfacial tension at 190 °C, 200 °C, and 210 °C are 6.8 ± 0.7 mN/m, 3.9 ± 0.3 mN/m,
and 3.7 ± 0.2 mN/m, respectively. A method of estimating whether elastic effects will significantly affect the estimated interfacial
tension value during retraction for the given polymer pair is provided.
Received: 6 August 1999 Accepted: 2 January 2001 相似文献
20.
Divya Chopra Marianna Kontopoulou Dimitris Vlassopoulos Savvas G. Hatzikiriakos 《Rheologica Acta》2002,41(1-2):10-24
We investigated the thermo- rheological behavior of high glass transition, high molecular weight and small dynamic asymmetry
blends of poly(styrene-co-maleic anhydride) (SMA) and poly (methyl methacrylate) (PMMA) with varying amounts of maleic anhydride (MA) content, namely
8 wt%, 14 wt% and 32 wt%, in the SMA component. The phase separation (binodal) temperature of each blend was determined rheologically
using a combination of dynamic frequency and temperature sweeps in parallel plate geometry; it was marked by a change in slope
of the elastic modulus and the occurrence of a peak in tan δ in temperature sweeps. Failure of the time-temperature superposition
principle and observation of two peaks in the Cole-Cole plots corroborated these findings. The blends displayed lower critical
solution temperature (LCST) behavior with the critical temperatures exhibiting a non-monotonic dependence on the MA content.
From rheological and thermal measurements it was concluded that SMA/PMMA blends containing 14% MA were more miscible than
those containing 8% or 32% MA, a finding attributed to the compositional dependence of the interplay between SMA-SMA and SMA-PMMA
interactions in the different samples. MA also influenced the dynamic asymmetry and pretransitional concentration fluctuations.
The phase diagrams corresponding to each blend were modeled using a two-parameter temperature dependent interaction parameter,
based on the concept of generalized Gibbs free energy of mixing. The fitted values of interaction parameter were in good agreement
with values calculated explicitly using the Flory-Huggins theory.
Received: 16 February 2001 Accepted: 11 July 2001 相似文献