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31.
Paul Becher Suzanne E. Trifiletti Pamela C. Petty 《Journal of Dispersion Science and Technology》2013,34(1):53-66
Isotherms for the adsorption of sodium dodecyl benzene sulfonate, sodium POE (4) nonyl phenol sulfate, and POE (25) nonyl phenol, on the hydrophobic crystalline herbicides atrazine and cyanazine were determined. Anionic surfactants were measured at 5°, 25°, and 50° C; the nonionic surfactant at 25° C only. Low degrees of surface coverage were observed; in only one case (atra-zine/NaDBS) was monolayer coverage approached. On the other hand, adsorption was accompanied by a significant increase in negative zeta potential. Although DLVO calculations suggest that this adsorption should lead to stable aggregates, these are of such size that gravitational effects overpower the DLVO terms. 相似文献
32.
Polymer materials with low water uptake exhibit a highly heterogeneous interior characterized by water clusters in the form of nanodroplets and nanochannels. Here, based on our recent insights from computer simulations, we argue that the water cluster structure has large implications for ionic transport and selective permeability in polymer membranes. Importantly, we demonstrate that the two key quantities for transport, the ion diffusion and the solvation free energy inside the polymer, are extremely sensitive to molecular details of the water clusters. In particular, we highlight the significance of water droplet interface potentials and the nature of hopping diffusion through transient water channels. These mechanisms can be harvested and fine-tuned to optimize selectivity in ionic transport in a wide range of applications. 相似文献
33.
To study phase transition kinetics on submillisecond time scale a sensitive ultrafast nanocalorimeter was constructed. Controlled
ultrafast cooling, as well as heating, up to 106K/s was attained. The method was applied for the measurements of the superheating phenomenon in a set of linear polymers:
iPS, PBT, PET, and iPP. A power law relation between the superheating and the heating rate holds in the heating rate range
10-2-104K/s. A limiting superheating of about 10% of the melting temperature was observed at rates above 104-105K/s. This limit depends on annealing conditions before sample melting. The observed superheating limit, as well as the power
law, can be accounted for the internal stresses near the crystalline amorphous interface in semicrystalline polymers induced
by heating, which are related to the thermal expansion gradients inherent in a semicrystalline material. 相似文献
34.
Changing the orientational order in liquid-crystal
elastomers leads to internal stresses and changes of the sample
shape. When this effect is induced by light, due to
photoisomerization of constituent molecular moieties, the
photomechanical actuation results. We investigate quantitatively
how the intensity and the polarization of light affect
photoactuation. By studying dissolved, as well as covalently
bonded azo-dyes, we determine the changes in absorption and the
response kinetics. For the first time we compare the response of
aligned monodomain, and randomly disordered polydomain nematic
elastomers, and demonstrate that both have a comparable
photoresponse, strongly dependent on the polarization of light.
Polarization-dependent photoactuation in polydomain elastomers
gives an unambiguous proof of its mechanism since it is the only
experiment that distinguishes from the associated thermal
effects. 相似文献
35.
This paper investigates finite-stretching corrections
to the classical Milner-Witten-Cates theory for semi-dilute
polymer brushes in a good solvent. The dominant correction to the
free energy originates from an entropic repulsion caused by the
impenetrability of the grafting surface, which produces a
depletion of segments extending a distance μ∝L-1
from the substrate, where L is the classical brush height. The
next most important correction is associated with the
translational entropy of the chain ends, which creates the
well-known tail where a small population of chains extend beyond
the classical brush height by a distance ξ∝L-1/3.
The validity of these corrections is confirmed by quantitative
comparison with numerical self-consistent field theory. 相似文献
36.
Laredo E Prutsky N Bello A Grimau M Castillo RV Müller AJ Dubois P 《The European physical journal. E, Soft matter》2007,23(3):295-303
Thermally stimulated depolarization currents, TSDC, wide-angle X-ray scattering, WAXS, differential scanning calorimetry,
DSC, and polarized light optical microscopy, PLOM, have been used to examine poly(L-lactide)-b -poly(
-caprolactone) diblock copolymers in a wide composition range. Both components are crystallizable and the miscibility in
the amorphous phase has been determined from the behavior of the primary relaxations which are the dielectric manifestation
of the glass transition, and also from the superstructural morphology revealed by PLOM and the compositional dependence of
the melting points as determined by DSC. Distinct segmental mobilities in the amorphous phase which can be well resolved by
TSDC are present; the
mode of the slower component shifts to lower temperatures as the PCL content increases while the glass transition of neat
PCL is present for all compositions. A relaxation times bimodal distribution is apparent for PCL-rich copolymers. The composition
dependence of the multiple glass transitions detected in these weakly segregated copolymers are predicted by the self-concentration
model for a miscible blend made of components with a large Tg contrast. 相似文献
37.
Living polymers are formed by reversible association of primary units (unimers). Generally the chain statistical weight involves
a factor σ < 1 suppressing short chains in comparison with free unimers. Living polymerization is a sharp thermodynamic transition
for σ ≪ 1 which is typically the case. We show that this sharpness has an important effect on the kinetics of living polymerization
(one-dimensional association). The kinetic model involves i) the unimer activation step (a transition to an assembly-competent
state); ii) the scission/recombination processes providing growth of polymer chains and relaxation of their length distribution.
Analyzing the polymerization with no chains but unimers at t = 0 , with initial concentration of unimers M ≳ M
* (M* is the critical polymerization concentration), we determine the time evolution of the chain length distribution and find
that: 1) for M
* ≪ M ≪ M
*/σ the kinetics is characterized by 5 distinct time stages demarcated by 4 characteristic times t1, t2, t3 and t*; 2) there are transient regimes (t
1 ≲ t ≲ t
3) when the molecular-weight distribution is strongly non-exponential; 3) the chain scissions are negligible at times shorter
than t2. The chain growth is auto-accelerated for t
1 ≲ t ≲ t
2 : the cut-off chain length (= polymerization degree 〈n〉w
N
1 ∝ t
2 in this regime. 4) For t
2 < t < t
3 the length distribution is characterized by essentially 2 non-linear modes; the shorter cut-off length N1 is decreasing with time in this regime, while the length scale N2 of the second mode is increasing. (5) The terminal relaxation time of the polymer length distribution, t*, shows a sharp maximum in the vicinity of M*; the effective exponent
is as high as ∼ σ-1/3 just above M*. 相似文献
38.
D. Vignolles A. Audouard V. N. Laukhin J. Béard E. Canadell N. G. Spitsina E. B. Yagubskii 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):383-388
The oscillatory magnetoresistance spectrum of the
organic metal (BEDO)5Ni(CN)4. 3C2H4(OH)2 has
been studied up to 50 T, in the temperature range from 1.5 K to
4.2 K. In high magnetic field, its Fermi surface corresponds to a
linear chain of quasi-two-dimensional orbits coupled by magnetic
breakdown (MB). The scattering rate consistently deduced from the
data relevant to the basic α and the MB-induced β
orbits is very large which points to a significant reduction of
the chemical potential oscillation. Despite of this feature, the
oscillations spectrum exhibits many frequency combinations. Their
effective masses and (or) Dingle temperature are not in agreement
with either the predictions of the quantum interference model or
the semiclassical model of Falicov and Stachowiak. 相似文献
39.
The 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) doped polymer films were prepared with Polypyrrole (PPy) and Polyvinyl alcohol (PVA) polymers by solution-casting. The change in structure and chemical composition of samples was identified by XRD and FTIR respectively. The UV–visible spectroscopy demonstrates the optical characteristics and band gap properties of sample. The homogeneous morphology of sample for higher wt% of PTCDA was examined by atomic force microscopy (AFM). The differential scanning calorimetry (DSC) results demonstrate the decrease in melting temperature (Tm) and degree of crystallinity (χc%) of polymeric organic semiconductor. The mechanical property demonstrates the high tensile strength and improved plasticity nature. Impedance spectroscopy was evaluated to determine the conductivity response of polymeric organic semiconductor. The highest DC conductivity (2.08×10−3 S/m) was obtained for 10 wt% of PTCDA at 140 °C. The decrease in activation energy (Ea) represents the non-Debye process and was evaluated from the slope of ln σdc vs. 103/T plot. 相似文献
40.
K.Kesavan Chithra M.Mathew S.Rajendran 《中国化学快报》2014,25(11):1428-1434
Poly(ethylene oxide), poly(vinyl pyrrolidone)(PEO/PVP), lithium perchlorate salt(Li Cl O4) and different plasticizer based, gel polymer electrolytes were prepared by the solvent casting technique. XRD results show that the crystallinity decreases with the addition of different plasticizers. Consequently, there is an enhancement in the amorphousity of the samples responsible for the process of ion transport. FTIR spectroscopy is used to characterize the structure of the polymer and confirms the complexation of plasticizer with host polymer matrix. The ionic conductivity has been calculated using the bulk impedance obtained through impedance spectroscopy. Among the various plasticizers, the ethylene carbonate(EC) based complex exhibits a maximum ionic conductivity value of the order of2.7279 10 4S cm 1. Thermal stability of the prepared electrolyte films shows that they can be used in batteries at elevated temperatures. PEO(72%)/PVP(8%)/Li Cl O4(8%)/EC(12%) has the maximum ionic conductivity value which is supported by the lowest optical band gap and lowest intensity in photoluminescence spectroscopy near 400–450 nm. Two and three dimensional topographic images of the sample having a maximum ionic conductivity show the presence of micropores. 相似文献