共查询到20条相似文献,搜索用时 15 毫秒
1.
Two distinct single-chain particles of poly(N-isopropylacrylamide) (PNIPAM) in the state of loose coil and compact globule, have been prepared successfully below and above the lower critical solution temperature (LCST) in extreme dilute aqueous solution by the freeze-drying method, respectively. During the preparation of the compact globular single-chain sample, the surfactant of sodium n-dodecyl sulfate (SDS) was added into the system to prevent aggregation of globular single chains formed at a temperature above the LCST. After all the coil has been transformed into the compact globular particle, the SDS molecules were removed by dialysis. The glass transition temperature (Tg) of the two single-chain samples has been measured by differential scanning calorimetery (DSC) in comparison with that of bulk polymer. It was found that the Tg of the single-chain sample in compact-globule state was very near to that of the bulk polymer, whereas the Tg of the single-chain sample in loose-coil state was approximately 6 K lower than that of the bulk polymer. After treating the sample with repeated DSC cycles, the Tg of the single-chain sample in loose-coil state rose up successively near to that of the bulk polymer. These results have been explained in terms of the effect of entanglement on the mobility of the polymer segments in the two distinct single-chain samples. 相似文献
2.
We have studied the effect of physical ageing in thin supported glassy polystyrene films by using ellipsometry to detect overshooting
in the expansivity-temperature curve upon heating of aged samples. Films with thickness 10-200 nm have been aged at 70°
C and 80°
C (below the bulk glass transition temperature). We observe clear relaxation peaks in the expansivity-temperature curve for
films thicker than 18 nm but not for the 10 nm film. The intensity of the relaxation peak is inversely proportional to the
film thickness, while the temperatures characteristic to the relaxation peak are almost independent of the film thickness.
These observations are successfully interpreted by the idea that the surface layer of the order of 10 nm has liquid-like thermal
properties.
Received 28 October 2002 / Published online: 1 April 2003
RID="a"
ID="a"Present address: Yokohama Research Center, Mitsubishi Chemical Corporation, 1000 Kamoshida-chou, Aoba-ku, Yokohama 227-8502, Japan; e-mail:
kawana@rc.m-kagaku.co.jp 相似文献
3.
Ngai KL 《The European physical journal. E, Soft matter》2002,8(2):225-235
Large increases of mobility of local segmental relaxation observed in polymer films as the film thickness is decreased, as
evidenced by decreases of the glass temperature, are not found for relaxation mechanisms that have longer length scales including
the Rouse relaxation modes and the diffusion of entire polymer chains. We show that the coupling model predictions, when extended
to consider polymer thin films, are consistent with a large increase of the mobility of the local segmental motions and the
lack of such a change for the Rouse modes and the diffusion of entire polymer chains. There are two effects that can reduce
the coupling parameter of the local segmental relaxation in thin films. One is the chain orientation that is induced parallel
to the surface when the film thickness h becomes smaller than the end-to-end distance of the chains and the other is a finite-size effect when h is no longer large compared to the cooperative length scale. Extremely thin ( ≈ 1.5 nm) films obtained by intercalating a
polymer into layered silicates have thickness significantly less than the cooperative length scale near the bulk polymer glass
transition temperature. As a result, the coupling parameter of the local segmental relaxation in such thin films is reduced
almost to zero. With this plausible assumption, we show the coupling model can explain quantitatively the large decrease of
the local segmental relaxation time found experimentally.
Received 1 August 2001 and Received in final form 1 December 2001 相似文献
4.
An original, quantitative, theory of “living” radical copolymerization has been developed proceeding from the current concepts
of its kinetics and mechanism. This theory enables one to calculate both the dependence of monomers' conversion on time and
any statistical characteristics of the chemical structures of the copolymers formed. Expressions have been derived describing
the angular dependence of the scattering amplitude of the copolymerization products. The results of quantitative calculations
of these characteristics have been also presented to exemplify the potentialities of the theory.
Received 13 February 2001 and Received in final form 4 February 2002 相似文献
5.
D. Starešinić A. Kiš K. Biljaković B. Emerling J. W. Brill J. Souletie H. Berger F. Lévy 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):71-77
Specific heats of the charge-density-wave compounds o-TaS3 and (TaSe4)2I have been measured over the wide temperature interval 10 K-300 K. Both systems exhibit strong non-Debye behavior. Very weak
and broad anomalies are observed at the Peierls transition temperatures. For o-TaS3, the change in the curvature of the specific heat occurs at temperature of 40 K where glass transition has been deduced from
dielectric measurements, and an extended scaling analysis suggests that the glass transition is associated with a dynamical
cross over in length scales. We briefly discuss the characteristics and physical origins of the anomalies at both the Peierls
and glass transitions.
Received 5 April 2002 / Received in final form 28 June 2002 Published online 17 September 2002 相似文献
6.
7.
Herminghaus S 《The European physical journal. E, Soft matter》2002,8(2):237-243
It is discussed how the proximity of a free surface or mobile interface may affect the strain relaxation behavior in a viscoelastic
material, such as a polymer melt. The eigenmodes of a viscoelastic film are thus derived, and applied in an attempt to explain
the experimentally observed substantial shift of the glass transition temperature of sufficiently thin polymer films with
respect to the bulk. Based on the idea that the polymer freezes due to memory effects in the material, and exploiting results
from mode-coupling theory, the experimental findings of several independent groups can be accounted for quantitatively, with
the elastic modulus at the glass transition temperature as the only fitting parameter. The model is finally applied discussing
the possibility of polymer surface melting. A surface molten layer is predicted to exist, with a thickness diverging as the
inverse of the reduced temperature. A simple model of thin polymer film freezing emerges which accounts for all features observed
experimentally so far.
Received 8 August 2001 相似文献
8.
Grohens Y Hamon L Reiter G Soldera A Holl Y 《The European physical journal. E, Soft matter》2002,8(2):217-224
We have measured, the thickness dependence of the glass transition temperature T(g)( h), using ellipsometry at variable temperature, for poly(methyl-methacrylate) (PMMA) of various tacticity in confined geometry. We report that several factors significantly affect T(g)( h): i) polymer microstructure (stereoregularity of PMMA) related to local dynamics; ii) interfacial interactions; iii) conformation of the polymer chains. These results raise many fundamental questions on the origin of the thickness-dependent glass transition. Why and how do the interactions with the substrate significantly affect T(g)( h)? Does T(g)( h) depend on the modifications of conformational parameters of the chains (their entropy)? What is the correlation between local dynamics and T(g)( h) in thin films? The aim of this paper is to summarise these open questions, which should stimulate further investigations in the thin polymer film scientific community. 相似文献
9.
S. Mossa E. La Nave F. Sciortino P. Tartaglia 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):351-355
The equation of state for a liquid in equilibrium, written in the potential energy landscape formalism, is generalized to
describe out-of-equilibrium conditions. The hypothesis that during aging the system explores basins associated to equilibrium
configurations is the key ingredient in the derivation. Theoretical predictions are successfully compared with data from molecular
dynamics simulations of different aging processes, such as temperature and pressure jumps.
Received 7 August 2002 / Received in final form 8 October 2002
Published online 19 December 2002
RID="a"
ID="a"Present address: Laboratoire de Physique Théorique des Liquides, Université Pierre et Marie Curie, 4 place Jussieu, Paris 75005, France e-mail:
mossa@lptl.jussieu.fr 相似文献
10.
P. Peyla C. Misbah 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(2):233-247
Elastic interactions between defects is investigated at the surface of thin layers, a question on which we have given a brief
account [P. Peyla et al. Phys. Rev. Lett. 82, 787 (1999)]. Two isotropic defects do not interact in an unlimited medium, regardless of the spatial dimension, a result
which can be shown on the basis of the Gauss theorem in electrostatics. Within isotropic elasticity theory, defects interact
only (i) if they are, for example, at a surface (or at least if they feel a boundary), or if their action on the material
is anisotropic (e.g. they create a non central force distribution, though the material elasticity is isotropic). It is known that two identical
isotropic defects on the surface of a semi-infinite material repel each other. The repulsion law behaves as 1/r
3(r = defects separation). We first revisit the Lau-Kohn theory and extend it to anisotropic defects. Anisotropy is found to
lead to attraction. We show that in thin films defects may either attract or repel each other depending on the local geometric
force distribution caused by the defect. It is shown that the force distribution (or more precisely the forces configuration
symmetry) fixes the exponent in the power law 1/r
n (e.g. for a four-fold symmetry n = 4). We discuss the implication of this behaviour in various situations. We treat the interactions in terms of the symmetries
associated with the defect. We argue that if the defects are isotropic, then their effective interaction in an unlimited 2D
(or a thin film) medium arises from the induced interaction, which behaves as 1/r
4 for any defect symmetry. We shall also comment on the contribution to the interaction which arises from flexion of thin films.
Received 7 October 2002 Published online 4 June 2003
RID="a"
ID="a"e-mail: chaouqi.misbah@ujf-grenoble.fr 相似文献
11.
U. Schneider R. Brand P. Lunkenheimer A. Loidl 《The European physical journal. E, Soft matter》2000,1(1):67-73
The Nagel scaling and the modified scaling procedure proposed recently by Dendzik et al. have been applied to broadband dielectric data on two glass-forming liquids (glycerol and propylene carbonate) and three
plastic crystals (ortho-carborane, meta-carborane, and 1-cyano-adamantane). Our data extend the upper limit of the abscissa
range to considerably higher values than in previously published analyses. At the highest frequencies investigated, deviations
from a single master curve show up which are most pronounced in the Dendzik scaling plot. The loss curves of the plastic crystals
do not scale in the Nagel plot, but they fall onto a separate master curve in the Dendzik plot. In addition, we address the
question of a possible divergence of the static susceptibility near the Vogel-Fulcher temperature. For this purpose, the low-temperature
evolution of the high-frequency wing of the dielectric loss peaks is investigated in detail. No convincing proof for such
a divergence can be deduced from the present broadband data.
Received 14 June 1999 and Received in final form 4 October 1999 相似文献
12.
S. Moreno R.G. Rubio G. Luengo F. Ortega M.G. Prolongo 《The European physical journal. E, Soft matter》2001,4(2):173-182
The complex dielectric permittivity has been measured for three poly(ethylenglycol)-b-poly(propylenglycol)-b-poly(ethylenglycol)
copolymers with different content of poly(ethylenglycol) (15%, 33% and 80%), and increasing degree of crystallinity (0%, 10%
and 20%, respectively). Only the non-crystalline sample shows the normal mode relaxation together with the segmental (α-relaxation)
and the Johari-Goldstein (β-relaxation) modes. The crystalline samples show also polarization contributions due to the existence
of interfaces between the crystallites and the amorphous phase. The relaxation times of the (α and normal modes can be described
by a VFT equation with the same value of T0. There is a slowing-down of the segmental mode due to the presence of crystallites. The temperature dependence of the α and
β relaxations in the copolymers is very similar to that found in pure PPG, while there are significant differences in the
case of the normal mode of the non-crystalline sample. The size of the cooperatively rearranging regions CRR, and the width
of the glass transition region increase slightly with the degree of crystallinity. The temperature dependence of the size
of CRRs is compatible with the prediction of fluctuation theory. No systematic effect of the degree of crystallinity on the
β-relaxation has been found. Near T
g the β-relaxation time is close to the primitive time of the coupling model.
Received: 31 May 2000 相似文献
13.
14.
Hartmann L Gorbatschow W Hauwede J Kremer F 《The European physical journal. E, Soft matter》2002,8(2):145-154
The molecular dynamics in thin films (18 nm-137 nm) of isotactic poly(methyl methacrylate) (i-PMMA) of two molecular weights
embedded between aluminium electrodes are measured by means of dielectric spectroscopy in the frequency range from 50 mHz
to 10 MHz at temperatures between 273 K and 392 K. The observed dynamics is characterized by two relaxation processes: the
dynamic glass transition (α-relaxation) and a (local) secondary β-relaxation. While the latter does not depend on the dimensions
of the sample, the dynamic glass transition becomes faster (≤2 decades) with decreasing film thickness. This results in a
shift of the glass transition temperature T
g to lower values compared to the bulk. With decreasing film thickness a broadening of the relaxation time distribution and
a decrease of the dielectric strength is observed for the α-relaxation. This enables to deduce a model based on immobilized
boundary layers and on a region displaying a dynamics faster than in the bulk. Additionally, T
g was determined by temperature-dependent ellipsometric measurements of the thickness of films prepared on silica. These measurements
yield a gradual increase of T
g with decreasing film thickness. The findings concerning the different thickness dependences of T
g are explained by changes of the interaction between the polymer and the substrates. A quantitative analysis of the T
g shifts incorporates recently developed models to describe the glass transition in thin polymer films.
Received 12 August 2001 and Received in final form 16 November 2001 相似文献
15.
Ellison CJ Kim SD Hall DB Torkelson JM 《The European physical journal. E, Soft matter》2002,8(2):155-166
Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine
the effects of decreasing film thickness on glass transition temperature, T
g, the relative strength of the glass transition, and the relative rate of physical aging below T
g in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state
of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine)
(P2VP) differs from that in the rubbery state with a transition at T
g. Positive deviations from bulk T
g are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T
g are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence
intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength
of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful
information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when
used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of
physical aging in films as thin as 10 nm.
Received 21 August 2001 相似文献
16.
17.
The process of growth of an individual cavity in a viscoelastic adhesive layer has been investigated experimentally. The formation
of cavities was caused by the application of a negative pressure on a very confined layer with a flat-ended probe. The cavities
appeared in the bulk of the adhesive layer and were observed for a range of values of applied stress approximately ten times
higher than the shear modulus of the adhesive layer. Depending on the loading rate, the shape of the growing cavity changed
from a flat disc to a more spherical shape. Furthermore, the growth rate of the cavity radius was consistent with a constant
strain rate at the edge of the cavity, which suggests a constant level of stress at the edge of the cavity.
Received 5 June 2002
RID="a"
ID="a"Current address: Ethicon, Johnson & Johnson, Route 22 West, P.O. Box 151, Somerville, NJ 08876-0151, USA.
RID="b"
ID="b"e-mail: costantino.creton@espci.fr 相似文献
18.
Raegen AN Dalnoki-Veress K Wan KT Jones RA 《The European physical journal. E, Soft matter》2006,19(4):453-459
We present a novel method of probing adhesion energies of solids, particularly polymers. This method uses the axi-symmetric
deformation of a thin spincast polymer membrane brought into contact with a flat substrate to probe the work of adhesion.
The use of a thin membrane minimizes uncertainty in the radius of contact, while the use of spincast films provides very smooth
surfaces by means of a very simple method. The experimental profile of the deformed membrane shows good agreement with the
expected logarithmic profile. The experimental setup enables the measurement of Young's modulus and the solid-solid work of
adhesion for thin films. The value obtained for Young's modulus of polystyrene (PS) was found to be in agreement with other
conventional measurement techniques. In addition, measurement of the work of adhesion at the PS/silicon oxide interface was
possible. The apparatus is well suited to studying the dependence of Young's modulus, work of adhesion and fracture energy
on membrane thickness, temperature, pulling rate, and ageing of the interface, and can readily be modified to study biologically
relevant samples. 相似文献
19.
The dynamic and static properties of a supercooled (non-entangled) polymer melt are investigated via molecular-dynamics (MD) simulations. The system is confined between two completely smooth and purely repulsive walls. The
wall-to-wall separation (film thickness), D, is varied from about 3 to about 14 times the bulk radius of gyration. Despite the geometric confinement, the supercooled
films exhibit many qualitative features which were also observed in the bulk and could be analyzed in terms of mode-coupling
theory (MCT). Examples are the two-step relaxation of the incoherent intermediate scattering function, the time-temperature
superposition property of the late time α-process and the space-time factorization of the scattering function on the intermediate
time scale of the MCT β-process. An analysis of the temperature dependence of the α-relaxation time suggests that the critical
temperature, T
c, of MCT decreases with D. If the confinement is not too strong ( D≥10monomer diameter), the static structure factor of the film coincides with that of the bulk when compared for the same distance,
T - T
c(D), to the critical temperature. This suggests that T - T
c(D) is an important temperature scale of our model both in the bulk and in the films.
Received 12 September 2001 相似文献
20.
L. Bellon S. Ciliberto C. Laroche 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):223-231
A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements
show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant
ε. A temporary stop of cooling produces a downward relaxation of ε. Two main features are observed (i) when cooling is resumed
ε goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) (ii) upon reheating ε keeps the memory of all the cooling
stops (Advanced memory). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally
the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.
Received 24 September 2001 and Received in final form 20 November 2001 相似文献