共查询到20条相似文献,搜索用时 31 毫秒
1.
Analysis of the electrorheological response of thermotropic solutions of a main-chain liquid crystal polymer (MCLCP) in a
low molar mass nematic solvent is performed at a fixed shear rate as a function of the applied field strength. The Leslie
viscosity coefficient α2 can be obtained by least squares fits to an equation describing the balance between the viscous and electric torques, formulated
via the two dimensional Leslie-Ericksen-Parodi theory. We find that the increment Δα2 on dissolving the MCLCP increases linearly with molecular weight, consistent with earlier light scattering measurements of
the increment in the twist viscosity, Δγ1, and also with previous electrorheological measurements of the increment in the Miesowicz viscosity Δηc.
Received: 1 December 1998 Accepted: 28 April 1999 相似文献
2.
The electrorheological (ER) behavior and stress transient response of dilute solutions of a side-chain liquid-crystalline
polysiloxane (LCP) in 4,4′-n-octylcyanobiphenyl (8CB) is studied. In the flow-tumbling regime of 8CB, i.e. from T = 34–38 °C,
the stress transients of both 8CB and LCP/8CB solutions show oscillatory responses, but with shorter oscillation periodicities
for the solution. In the flow-aligning regime of 8CB, i.e. at 39 and 40 °C, a transformation to flow-tumbling is observed
in the stress transients of the LCP/8CB solution. In both cases, analysis of the transient responses indicates that the change
in Leslie viscosity coefficients on dissolving the LCP are δα2 < 0 and δα3 > 0. The amplitude of the ER response, defined as the viscosity difference between the on and off states, Δη = ηon − ηoff, is only weakly affected by the dissolution of LCP. These rheological results can be interpreted consistently using a modified
version of a hydrodynamic theory by Brochard, provided an additional dissipation mechanism is included, which derives from
the presence of an elastic torque between director rotation and LCP orientation.
Received: 8 September 1999/Accepted: 13 December 1999 相似文献
3.
The dynamic flow behavior of polyamide-6 (PA-6) and a nanocomposite (PNC) based on it was studied. The latter resin contained
2 wt% of organoclay. The two materials were blended in proportions of 0, 25, 50, 75, and 100 wt% PNC. The dynamic shear rheological
properties of well-dried specimens were measured under N2 at T=240 °C, frequency ω=0.1–100 rad/s, and strains γ=10 and 40%. At constant T, γ, and ω the time sweeps resulted in significant
increases of the shear moduli. The γ and ω scans showed a complex rheological behavior of all clay-containing specimens. At
γ=10% the linear viscoelasticity was observed for all compositions only at ω>1 rad/s, while at γ=40% only for 0 and 25 wt%
of PNC. However, the effect was moderate, namely decreasing G′ and G′′ (at ω=6.28 rad/s; γ=50%) by 15 and 7.5%, respectively.
For compositions containing >25 wt% PNC two types of non-linearity were detected. At ω≤ωc=1.4 ± 0.2 rad/s yield stress provided evidence of a 3-D structure. At ω > ωc, G′ and G′′ were sensitive to shear history – the effect was reversible. From the frequency scans at ω > ωc the zero-shear relative viscosity vs concentration plot was constructed. The initial slope gave the intrinsic viscosity from
which the aspect ratio of organoclay particles, p=287 ± 9 was calculated, in agreement with the value calculated from the
reduced permeability data, p=286.
Received: 24 May 2001 Accepted: 27 August 2001 相似文献
4.
H. Watanabe Tomohiro Sato Motoyuki Hirose Kunihiro Osaki Ming-Long Yao 《Rheologica Acta》1998,37(6):519-527
Dielectric relaxation behavior was examined for 4-4′-n-pentyl-cyanobiphenyl (5CB) and 4-4′-n-heptyl-cyanobiphenyl (7CB) under flow. In quiescent states at all temperatures examined, both 5CB and 7CB exhibited dispersions
in their complex dielectric constant ε*(ω) at characteristic frequencies ω
c
above 106 rad s–1. This dispersion reflected orientational fluctuation of individual 5CB and 7CB molecules having large dipoles parallel to
their principal axis (in the direction of C≡N bond). In the isotropic state at high temperatures, these molecules exhibited no detectable changes of ε*(ω) under flow at
shear rates . In contrast, in the nematic state at lower temperatures the terminal relaxation intensity of ε*(ω) as well as the static
dielectric constant ε′(0) decreased under flow at . This rheo-dielectric change was discussed in relation to the flow effects on the nematic texture (director distribution)
and anisotropy in motion of individual molecules with respect to the director.
Received: 14 April 1998 Accepted: 29 July 1998 相似文献
5.
Hiroshi Watanabe Tomohiro Sato Motoyuki Hirose Kunihiro Osaki Ming-Long Yao 《Rheologica Acta》1999,38(2):100-107
Rheo-dielectric behavior was examined for 4−4′−n-octyl-cyanobiphenyl (8CB) having large dipoles parallel to its principal axis (in the direction of the C≡N bond). In the
quiescent state at all temperatures (T) examined, orientational fluctuation of the 8CB molecules was observed as dielectric dispersions at characteristic frequencies
ωc>106 s−1. In the isotropic state at high T, no detectable changes of the complex dielectric constant ɛ*(ω) were found under slow flow at shear rates ˙γ≫ωc. In the nematic state at intermediate T, the terminal relaxation intensity of ɛ*(ω) was decreased under such slow flow. In the smectic state at lower T, the flow effect became much less significant. These results were related to the flow-induced changes of the liquid crystalline
textures in the nematic and smectic states, and the differences of the rheo-dielectric behavior in these states are discussed
in relation to a difference of the symmetry of molecular arrangements in the nematic and smectic textures.
Received: 1 October 1998 Accepted: 13 January 1999 相似文献
6.
H. Watanabe Kunihiro Osaki Mutsuo Matsumoto Dobrin P. Bossev Cathy E. McNamee Masaru Nakahara Ming-Long Yao 《Rheologica Acta》1998,37(5):470-485
Nonlinear rheological features were investigated for an aqueous solution of tetraethylammonium perfluorooctyl sulfonate (C8F17SO3
–N+(C2H5)4; abbreviated as FOSTEA). In the solution (c=0.045 mol/l; 28.3 g/l), spherical micelles of FOSTEA were connected with each other to form threads of pearl-necklace shape.
These threads were further organized into a transient network to exhibit linear relaxation characteristic of living polymers,
single-mode terminal relaxation widely separated from faster relaxation processes. Nonlinear relaxation experiments against
large step-strains γ(≤8) revealed that the terminal relaxation mode had a γ-insensitive relaxation time but its relaxation
intensity exhibited significant damping (much stronger than that for entangled polymers). In contrast, the relaxation time
and intensity for the fast relaxation modes first increased and then decreased with increasing γ. Under shear flow, the FOSTEA
threads exhibited strong thinning of the viscosity. These nonlinear features of the FOSTEA threads were compared with those
of other threadlike micelles, analyzed on the basis of an empirically introduced constitutive equation, and discussed in relation
to strain/low-induced scission of the living threads.
Received: 20 February 1998 Accepted: 30 July 1998 相似文献
7.
The rheological properties of the near-surface 5CB (4-pentyl-4′-cyanobiphenyl) liquid crystal (LC) under an external electric
field (EEF) are investigated using a dynamic quartz crystal microbalance (QCM). The real-time film-forming process and shearing
response of the EEF-induced absorbed LC liquid are studied. The results indicate that the EEF-induced adsorbed LC is composed
of a bulk liquid layer and a near-surface boundary layer. Within the boundary layer, the nematic 5CB LC presents an anti-electroviscous
effect which may be due to the EEF-induced ordered structure. According to the estimation from QCM measurements, this near-surface
layer is about 100 nm thick under certain electric strength and is irreversible even after the EEF is removed. Based on a
QCM model, the near-surface LC layer presents a decreased and irreversible viscosity as the EEF voltage increases against
the reversible electro-viscous effect of the bulk 5CB liquid crystal measured by rheometer and Raman spectrum measurements.
The anti-electroviscous effect of the near-surface 5CB layer is also proved by an improved boundary lubrication property tested
on a tribometer. The coefficient of friction of 5CB LC after a preliminary induction of EEF is the lowest one compared to
those without EEF and during the application of EEF. The unique anti-electroviscous property of near-surface 5CB LC revealed
in this article suggests a potential method to actively reduce shear resistance in boundary lubrication and in microfluidics. 相似文献
8.
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
9.
Mohammadhassan Vasheghani Ehsan Marzbanrad Cyrus Zamani Mohamed Aminy Babak Raissi Toraj Ebadzadeh Hadi Barzegar-Bafrooei 《Heat and Mass Transfer》2011,47(11):1401-1405
Thermal conductivity of α-Al2O3 was measured using hot wire method. α-Al2O3 (20 nm in size) was synthesized by microwave method for which, the results were compared with commercially available γ-Al2O3. Thermal conductivity of nanofluids was investigated considering, it is dependency on Al2O3 phase. It was observed that by adding 3 wt% of nano γ-Al2O3 and α-Al2O3 to the engine oil, thermal conductivity increases by 37 and 31%, respectively. The corresponding viscosity increase for the
same amount of nano γ-Al2O3 and α-Al2O3 were 36 and 38%, respectively. It was concluded that the differences in thermal conductivity originate from higher specific
surface area of γ-Al2O3 compared to the α-Al2O3 which is the result of porosity difference, obtained during the synthesis process. 相似文献
10.
David M. Boudreau H. Henning Winter C. Peter Lillya Richard S. Stein 《Rheologica Acta》1999,38(6):503-513
Orientational changes in monodomains of flow-aligning liquid crystals, 4-n-pentyl-4′-cyanobiphenyl and N-(4-methoxybenzylidene)-4-butylaniline, were studied during shear and recovery in a linear shearing device fitted to an optical
microscope. Planar alignment (director in the shear plane) allows the study of twist effects and was generated by strong planar
anchoring at the walls with orientations in a range of 0–90° with the shear direction. While being held back by the anchoring
walls, shear caused the bulk director to rotate towards a steady-state alignment angle in the shear direction (Leslie angle
θL). The transient director rotation was observed with conoscopy. It was found that increasing the initial alignment towards
the vorticity direction increased the measured θL. Upon stopping the flow, the bulk director returned to its initial state. With initial alignment orientation changing from
parallel to perpendicular to the flow direction, the rate of the twist-driven recovery process increases. This rate increase
is not seen in the splay-driven recovery which is constant and consistently faster than twist-driven recovery at all orientations
studied.
Received: 10 December 1998/Accepted: 7 June 1999 相似文献
11.
Mahmoud Rajabian Ghassem Naderi Charles Dubois Pierre G. Lafleur 《Rheologica Acta》2010,49(1):105-118
Transient elongational rheology of two commercial-grade polypropylene (PP) and the organoclay thermoplastic nanocomposites
is investigated. A specifically designed fixture consisting of two drums (SER Universal Testing Platform) mounted on a TA
Instruments ARES rotational rheometer was used to measure the transient uniaxial extensional viscosity of both polypropylene
and nanoclay/PP melts. The Hencky strain rate was varied from 0.001 to 2 s − 1, and the temperature was fixed at 180°C. The measurements show that the steady-state elongational viscosity was reached at
the measured Hencky strains for the polymer and for the nanocomposites. The addition of nanoclay particles to the polymer
melt was found to increase the elongation viscosity principally at low strain rates. For example, at a deformation rate of
0.3 s − 1, the steady-state elongation viscosity for polypropylene was 1.4 × 104 Pa s which was raised to 2.8 × 104 and 4.5 × 104 Pa s after addition of 0.5 and 1.5 vol.% nanoclay, respectively. A mesoscopic rheological model originally developed to predict
the motion of ellipsoid particles in viscoelastic media was modified based on the recent developments by Eslami and Grmela
(Rheol Acta 47:399–415, 2008) to take into account the polymer chain reptation. We show that the orientation states of the particles and the rheological
behavior of the layered particles/thermoplastic hybrids can be quantitatively explained by the proposed model. 相似文献
12.
IntroductionInthispaper,weshallconsiderthefollowingsingularboundaryvalueproblems (BVP)u″ g(t)f(u) =0 , 0 <t<1 ,αu(0 ) -βu′(0 ) =0 , γu(1 ) δu′(1 ) =0 ,(1 )whereα ,β,γ ,δ≥ 0 ,ρ:=βγ αγ αδ>0 ,f∈C([0 ,∞ ) ,[0 ,∞ ) ) ,gmaybesingularatt=0and/ort=1 .Thisproblemarisesnaturallyinthestudyofradiallysymmet… 相似文献
13.
Jalil Moghadasi Fakhri Yousefi Mohammad Mehdi Papari Mohammad Ali Faghihi Ali Asghar Mohsenipour 《Heat and Mass Transfer》2009,45(11):1453-1466
It is the purpose of this paper to extract unlike intermolecular potential energies of five carbon dioxide-based binary gas
mixtures including CO2–He, CO2–Ne, CO2–Ar, CO2–Kr, and CO2–Xe from viscosity data and compare the calculated potentials with other models potential energy reported in literature. Then,
dilute transport properties consisting of viscosity, diffusion coefficient, thermal diffusion factor, and thermal conductivity
of aforementioned mixtures are calculated from the calculated potential energies and compared with literature data. Rather
accurate correlations for the viscosity coefficient of afore-cited mixtures embracing the temperature range 200 K < T < 3273.15 K is reproduced from the present unlike intermolecular potentials energy. Our estimated accuracies for the viscosity
are to within ±2%. In addition, the calculated potential energies are used to present smooth correlations for other transport
properties. The accuracies of the binary diffusion coefficients are of the order of ±3%. Finally, the unlike interaction energy
and the calculated low density viscosity have been employed to calculate high density viscosities using Vesovic–Wakeham method. 相似文献
14.
We have investigated the rheological changes in two particulate-filled dental composite resin cements during the curing process
using a Micro-Fourier Rheometer (MFR). In the MFR, the sample was sandwiched between two parallel plates, and pseudorandom
small amplitude squeezing was applied by oscillating the upper plate over a range of frequencies. Fourier transforms of the
displacement signal and the resulting time dependent force signal enabled the rapid determination of the dynamic properties
G′ and G′′ over the frequency range 2π–200π rad/s . This technique permitted us to follow changes in the rheological properties of
the resin cements through the setting period. A typical result was that G′ increased from 2×103 Pa to 2×105 Pa after about 120 s, and that G′′ changed from 4×103 Pa to 4×104 Pa over the same period at frequency 40π rad/s. We also found that the dental composite resin cements show linear viscoelastic
behaviour over a range of strain amplitudes before curing, but the response becomes distinctly non-linear at the later stages
of curing for strain amplitudes γ>0.067%. 相似文献
15.
The mean value theorem of integral calculus guarantees that the apparent viscosity η
a
can easily be converted into the correct viscosity η. For ordinary liquids there is a direct identity between η
a
and η but the apparent shear rate (or apparent shear stress) has to be shifted to the representative shear rate γ˙^ (or representative shear stress τ^). A model free approximation scheme is introduced which implies a constant shift factor. The corresponding approximation
for η is acceptable for liquids most commonly encountered. For plastic fluids the relation between η and η
a
is more complex since it involves a function depending upon α; the yield stress relative to the maximum stress within the
viscometer. Using the same approximation scheme as before the shift factor will involve α as well. The corresponding approximation
of η is shown to be acceptable for the whole range of α.
Received: 7 February 2000/Accepted: 15 February 2000 相似文献
16.
Experimental studies on drag reduction and rheology of mixed cationic surfactants with different alkyl chain lengths 总被引:2,自引:0,他引:2
Zhiging Lin Lu Chou Bin Lu Yi Zheng H. Ted Davis L. E. Scriven Y. Talmon Jacques L. Zakin 《Rheologica Acta》2000,39(4):354-359
Experimental studies of the effects of mixtures of cationic surfactants on their drag reduction and rheological behaviors
are reported. Cationic alkyl trimethyl quaternary ammonium surfactants with alkyl chain lengths of C12 and C22 were mixed at different molar ratios (total surfactant concentrations were kept at 5 mM with 12.5 mM sodium salicylate (NaSal)
as counterion). Drag reduction tests showed that by adding 10% (mol) of C12, the effective drag reduction range expanded to 4–120 °C, compared with 80–130 °C with only the C22 surfactant. Thus mixing cationic surfactants with different alkyl chain lengths is an effective way of tuning the drag reduction
temperature range. Cryo-TEM micrographs revealed thread-like micellar networks for surfactant solutions in the drag reducing
temperature range, while vesicles were the dominant microstructures at non-drag reducing temperatures. High extensional viscosity
was the main rheological feature for all solutions except 50% C12 (mol) solution, which also does not show strong viscoelasticity. It is not clear why this low extensional viscosity solution
with relatively weak viscoelasticity is a good drag reducer.
Received: 3 November 1999/Accepted: 5 January 2000 相似文献
17.
Hiroshi Watanabe Ming-Long Yao Kunihiro Osaki Toshiyuki Shikata Hirokazu Niwa Yotaro Morishima 《Rheologica Acta》1999,38(1):2-13
Nonlinear rheology was examined for concentrated suspensions of spherical silica particles (with radius of 40 nm) in viscous
media, 2.27/1 (wt/wt) ethylene glycol/glycerol mixture and pure ethylene glycol. The particles were randomly and isotropically
dispersed in the media in the quiescent state, and their effective volume fraction φeff ranged from 0.36 to 0.59. For small strains, the particles exhibited linear relaxation of the Brownian stress σB due to their diffusion. For large step strains γ, the nonlinear relaxation modulus G(t,γ) exhibited strong damping and obeyed the time-strain separability. This damping was related to γ-insensitivity of strain-induced
anisotropy in the particle distribution that resulted in decreases of σB/γ. The damping became stronger for larger φeff. This φeff dependence was related to a hard-core volume effect, i.e., strain-induced collision of the particles that is enhanced for
larger φeff. Under steady/transient shear flow, the particles exhibited thinning and thickening at low and high γ˙, respectively. The thinning behavior was well described by a BKZ constitutive equation using the G(t,γ) data and attributable to decreases of a Brownian contribution, σB/γ˙. The thickening behavior, not described by this equation, was related to dynamic clustering of the particles and corresponding
enhancement of the hydrodynamic stress at high γ˙. In this thickening regime, the viscosity growth η+ after start-up of flow was scaled with a strain γ˙t. Specifically, critical strains γd and γs for the onset of thickening and achievement of the steadily thickened state were independent of γ˙ but decreased with increasing φeff. This φeff dependence was again related to the hard-core volume effect, flow-induced collision of the particles enhanced for larger
φeff.
Received: 26 June 1998 Accepted: 9 December 1998 相似文献
18.
This paper concerns the regularity of a capillary graph (the meniscus profile of liquid in a cylindrical tube) over a corner
domain of angle α. By giving an explicit construction of minimal surface solutions previously shown to exist (Indiana Univ. Math. J. 50 (2001), no. 1, 411–441) we clarify two outstanding questions.
Solutions are constructed in the case α = π/2 for contact angle data (γ1, γ2) = (γ, π − γ) with 0 < γ < π. The solutions given with |γ − π/2| < π/4 are the first known solutions that are not C2 up to the corner. This shows that the best known regularity (C1, ∈) is the best possible in some cases. Specific dependence of the H?lder exponent on the contact angle for our examples is
given.
Solutions with γ = π/4 have continuous, but horizontal, normal vector at the corners in accordance with results of Tam (Pacific J. Math. 124 (1986), 469–482). It is shown that our examples are C0, β up to and including the corner for any β < 1.
Solutions with |γ − π/2| > π/4 have a jump discontinuity at the corner. This kind of behavior was suggested by numerical work
of Concus and Finn (Microgravity sci. technol. VII/2 (1994), 152–155) and Mittelmann and Zhu (Microgravity sci. technol. IX/1 (1996), 22–27). Our explicit construction, however, allows us to investigate the solutions quantitatively. For example,
the trace of these solutions, excluding the jump discontinuity, is C2/3. 相似文献
19.
Yoshihiro Ueda Tohru Nakamura Shuichi Kawashima 《Archive for Rational Mechanics and Analysis》2010,198(3):735-762
This paper is concerned with the asymptotic stability of degenerate stationary waves for viscous gases in the half space.
We discuss the following two cases: (1) viscous conservation laws and (2) damped wave equations with nonlinear convection.
In each case, we prove that the solution converges to the corresponding degenerate stationary wave at the rate t
−α/4 as t → ∞, provided that the initial perturbation is in the weighted space
L2a=L2(\mathbb R+; (1+x)a dx){L^2_\alpha=L^2({\mathbb R}_+;\,(1+x)^\alpha dx)} . This convergence rate t
−α/4 is weaker than the one for the non-degenerate case and requires the restriction α < α*(q), where α*(q) is the critical value depending only on the degeneracy exponent q. Such a restriction is reasonable because the corresponding linearized operator for viscous conservation laws cannot be dissipative
in L2a{L^2_\alpha} for α > α*(q) with another critical value α*(q). Our stability analysis is based on the space–time weighted energy method in which the spatial weight is chosen as a function
of the degenerate stationary wave. 相似文献
20.
The time-dependent transformation of an ionically charged lamellar phase (L
α-phase) into a vesicle phase under the influence of shear is investigated using rheological and conductivity measurements.
The L
α-phase consists of the zwitterionic surfactant tetradecyldimethylaminoxide (C14DMAO), hexanol, oxalic acid and water. The experiments were carried out on the L
α-phase in a well defined state. It was prepared by a special route from the neighbouring L
3-phase that consists of 100 mM C14DMAO, 250 mM hexanol and 5 mM oxalicdiethylester (OEE). The OEE hydrolyses in the L
3
-phase to oxalic acid and ethanol. The result is a virgin L
α-phase which consists of stacked bilayers and which has not been exposed to shear. When this low-viscous phase is subjected
to shear it is transformed into a highly viscous vesicle phase. The transformation of the L
α-phase into vesicles under constant shear was monitored by recording the viscosity and conductivity with time. It is observed
that at least three different time constants can be distinguished in the transformation process. The conductivity passes through
a minimum (τ1) in the direction of shear. The viscosity first passes through a minimum (τ2) and then over a maximum (τ3). It is concluded that τ1 belongs to the complete alignment of the bilayer parallel to the wall, τ2 to the beginning of the break-up of the bilayers to the vesicles and τ3 to the complete transformation of the L
α- to the vesicle phase. When the shear rate was varied, it was noted that the product of the time constants and shear is constant.
Received: 30 June 1999/Accepted: 30 August 1999 相似文献