共查询到20条相似文献,搜索用时 31 毫秒
1.
Sharp JS Vader D Forrest JA Smith MI Khomenko M Dalnoki-Veress K 《The European physical journal. E, Soft matter》2006,19(4):423-432
Optical microscopy and atomic force microscopy were used to study a novel roughness-induced wrinkling instability in thin-film
bilayers of poly(ethylene oxide) (PEO) and polystyrene (PS). The observed wrinkling morphology is manifested as a periodic
undulation at the surface of the samples and occurs when the bilayers are heated above the melting temperature of the semi
crystalline PEO (Tm = 63
) layer. During the wrinkling of the glassy PS capping layers the system selects a characteristic wavelength that has the
largest amplitude growth rate. This initial wavelength is shown to increase monotonically with increasing thickness of the
PEO layer. We also show that for a given PEO film thickness, the wavelength can be varied independently by changing the thickness
of the PS capping layers. A model based upon a simple linear stability analysis was developed to analyse the data collected
for the PS and PEO film thickness dependences of the fastest growing wavelength in the system. The predictions of this theory
are that the strain induced in the PS layer caused by changes in the area of the PEO/PS interface during the melting of the
PEO are sufficient to drive the wrinkling instability. A consideration of the mechanical response of the PEO and PS layers
to the deformations caused by wrinkling then allows us to use this simple theory to predict the fastest growing wavelength
in the system. 相似文献
2.
Blends of poly (ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) diblock copolymer and poly (2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) homopolymer were obtained by solution blending, and the morphologies of PEO dispersed nanoparticles in PPO/PS matrix were observed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The isothermal crystallization kinetics was studied using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Nonisothermal crystallization kinetics was studied using DSC. The results showed that PEO segments were easier to crystallize in the blend than in the copolymer probably due to the interfaces of PPO acting as nucleation sites to promote the crystallization of PEO. The crystallization of PEO blocks destroyed the pre‐existing microdomain structure even though the glass transition temperature of the matrix was much higher than the crystallization temperature. 相似文献
3.
Papadakis CM Darko C Di Z Troll K Metwalli E Timmann A Reiter G Förster S 《The European physical journal. E, Soft matter》2011,34(1):7-8
We have found very slow crystallization in thin films of cylinder-forming poly(isoprene-b -ethyleneoxide) (P(I-b -EO)) diblock copolymers with PEO being the minority block. The film was crystallized at room temperature after melting at
62 °C . Imaging methods were combined with X-ray reflectometry and grazing-incidence small-angle X-ray scattering and diffraction.
Initially, hexagonally packed, amorphous PEO cylinders lie in the film plane. After 148 days, crystallized, finger-like terraces
were observed over the entire film surface. The terrace height is 20% higher than the repeat distance in the as-prepared film.
Thus, at the film surface, the cylinders have been destroyed by crystalline lamellae lying in the film plane. The PEO chain
stems are perpendicular to the substrate surface and are once-folded and fully interdigitated. The substrate-near layers still
consist of the hexagonally packed, amorphous PEO cylinders within the PI matrix. 相似文献
4.
Indekeu Joseph O. Ragil Karine Bonn Daniel Broseta Daniel Meunier Jacques 《Journal of statistical physics》1999,95(5-6):1009-1043
We apply the phenomenological wetting theory of Cahn to fluids with van der Waals forces, and in particular to the wetting of pentane on water. Taking into account explicitly the long-range substrate–adsorbate interaction allows us to reproduce the experimentally observed critical wetting transition, which arises from the vanishing of the Hamaker constant at T53°C. This transition is preceded by a first-order transition between a thin and a thick film at a (much) lower temperature. If long-range forces are neglected, this thin–thick transition is the only wetting transition and critical wetting is missed. Our study focuses on the development of useful theoretical tools, such as phase portraits and interface potentials adapted to systems with van der Waals forces. 相似文献
5.
Crystallization in ultrathin Poly(Ethylene Oxide)/Poly(Methyl Methacrylate) (PEO/PMMA) blend films with thickness of ca. 10 nm was investigated by means of microscopic and in situ spectroscopic methods. It was revealed that the blend films undergo a phase ordering in a humid atmosphere before or during crystallization, with PEO de-mixing with PMMA and segregating to the free film interface on the PMMA layer. The de-mixed PEO chains crystallize into a fractal-like morphology by a diffusion-limited process, and the crystal growth is 1-dimensional with Avrami exponent n ≈ 1, resulting in flat-on crystal lamellae with the PEO chains oriented normal to the film plane. 相似文献
6.
Vlachos D Kamaratos M Foulias SD Binz S Hupalo M Tringides MC 《J Phys Condens Matter》2012,24(9):095006
We study the Pb growth on both √3 × √3-In and 4 × 1-In reconstructed Si(111) surfaces at room and low temperature (160 K). The study takes place with complementary techniques, to investigate the role of the substrate reconstruction and temperature in determining the growth mode of Pb. Specifically, we focus on the correlation between the growth morphology and the electronic structure of the Pb films. The information is obtained by using Auger electron spectroscopy, low energy electron diffraction, soft x-ray photoelectron spectroscopy, scanning tunneling microscopy and spot profile analysis-low energy electron diffraction. The results show that, at low temperature and coverage ≤12 ML on the Si(111)√3 × √3-In surface, Pb does not alter the initial semiconducting character of the substrate and three-dimensional Pb islands with poor crystallinity are grown on a wetting layer. On the other hand, for the same coverage range, Pb growth on the Si(111)4 × 1-In surface results in metallic Pb(111) crystalline islands after the completion of a double incomplete wetting layer. In addition, the bond arrangement of the adatoms is studied, confirming that In adatoms interact more strongly with the silicon substrate than the Pb ones. This promotes a stronger Pb-Pb interaction and enhances metallization. The onset of the metallization is correlated with the amount of pre-deposited In on the Si(111) surface. The decoupling of the Pb film from the 4 × 1-In interface can also explain the unusual thermal stability of the uniform height islands observed on this interface. The formation of these Pb islands is driven by quantum size effects. Finally, the different results of Pb growth on the two reconstructed surfaces confirm the importance of the interface, and also that the growth morphology, as well as the electronic structure of the Pb film can be tuned with the initial substrate reconstruction. 相似文献
7.
We study the cylinder to sphere morphological transition of diblock copolymers in aqueous solution with a hydrophobic block
and a charged block. We find a metastable undulated cylinder configuration for a range of charge and salt concentrations which,
nevertheless, occurs above the threshold where spheres are thermodynamically favorable. By modeling the shape of the cylinder
ends, we find that the free-energy barrier for the transition from cylinders to spheres is quite large and that this barrier
falls significantly in the limit of high polymer charge and low solution salinity. This suggests that observed undulated cylinder
phases are kinetically trapped structures. 相似文献
8.
《Physica A》2007
The fluid system at the bulk liquid–gas coexistence in a presence of a sinusoidally corrugated substrate exhibits not only the wetting transition, but additionally a first-order, thin–thick transition. The mean-field analysis of this transition based on a simple effective Hamiltonian is valid only in long wavelength limit. In this case the filling transition occurs so close to the wetting temperature, that the behavior of the interface is dominated by fluctuations, therefore the mean-field approach breaks down. We analyze the filling transition with the help of Hamiltonian evaluated from Landau theory. The applicability of our Hamiltonian is not restricted only to the vicinity of the wetting point. We obtain the phase diagram valid beyond the temperature range corresponding to the strong fluctuations regime. It displays more complex dependence on different length scales of the system and includes the old one as a particular case. 相似文献
9.
The phase diagram for diblock copolymer melts is evaluated from lattice-based Monte Carlo simulations using parallel tempering,
improving upon earlier simulations that used sequential temperature scans. This new approach locates the order-disorder transition
(ODT) far more accurately by the occurrence of a sharp spike in the heat capacity. The present study also performs a more
thorough investigation of finite-size effects, which reveals that the gyroid (G) morphology spontaneously forms in place of
the perforated-lamellar (PL) phase identified in the earlier study. Nevertheless, there still remains a small region where
the PL phase appears to be stable. Interestingly, the lamellar (L) phase next to this region exhibits a small population of
transient perforations, which may explain previous scattering experiments suggesting a modulated-lamellar (ML) phase. 相似文献
10.
H. W. Kammer 《Ionics》2018,24(12):3815-3826
Impedance spectra of linear and cross-linked poly(ethylene oxide) (PEO) are analyzed in a wide range of temperature. Dielectric responses differ at low and high temperature due to tendency of PEO to crystallization below melting temperature. Extent of crystallization depends on cross-linking density. The network in PEO with high cross-linking density is rigid and morphology transition shifts to very low temperature. Debye-like relaxation appears at low temperature similar as in ionic liquids. Onset of polarization relaxation shifts to higher temperature with increasing mesh size that is coupling of electric and structural relaxation appears. This is also nicely reflected by scaled conductivity. It demonstrates that the structure in cross-linked systems is a superposition of chemical and physical networks. They relax separately at low temperature and frequency under condition of sufficient rigidity. 相似文献
11.
An analysis is given of the behavior of an interface above a stepped substrate in the presence of an external pinning potential for the lattice solid-on-solid (SOS) interface model in 2D. Step-free energy including step-step interaction free energy is calculated, for large step separation. It is found it vanishes at temperatures lower thanT
w
(wetting transition temperature), which is different from the case having only one step on a substrate where, as it is well known, step-free energy vanishes at the wetting transition. 相似文献
12.
系统地研究了亚微米聚苯乙烯微球在气-液界面的组装机理.聚苯乙烯微球在介质对流的带动下会到达悬浮液的表面并在气-液界面组装,气-液界面处聚苯乙烯微球间由弯液面产生的毛细管力是组装的推动力.界面处聚苯乙烯微球在干燥过程中其润湿性发生了转变,由完全润湿到部分润湿并最终变成不润湿,相应的聚苯乙烯微球与分散介质间接触角也逐渐增大.研究表明,只有接触角达到或超过某数值θ′critical时,才能够出现气-液界面组装现象.考虑到PS胶粒晶体的表面是“规则”粗糙的表面,由Wenzel公式知θ′critical大于测量值θ=22°.聚苯乙烯微球润湿性的转变是界面组装发生和持续进行的关键性因素.
关键词:
自组装
胶粒晶体
聚苯乙烯微球
润湿性 相似文献
13.
系统地研究了亚微米聚苯乙烯微球在气-液界面的组装机理.聚苯乙烯微球在介质对流的带动下会到达悬浮液的表面并在气-液界面组装,气-液界面处聚苯乙烯微球间由弯液面产生的毛细管力是组装的推动力.界面处聚苯乙烯微球在干燥过程中其润湿性发生了转变,由完全润湿到部分润湿并最终变成不润湿,相应的聚苯乙烯微球与分散介质间接触角也逐渐增大.研究表明,只有接触角达到或超过某数值θ′critical时,才能够出现气-液界面组装现象.考虑到PS胶粒晶体的表面是“规则”粗糙的表面,由Wenzel公式知θ′critical大于测量值θ=22°.聚苯乙烯微球润湿性的转变是界面组装发生和持续进行的关键性因素.
关键词:
自组装
胶粒晶体
聚苯乙烯微球
润湿性 相似文献
14.
Kenneth S. Alexander François Dunlop Salvador Miracle-Solé 《Journal of statistical physics》2011,142(3):524-576
We study the solid-on-solid interface model above a horizontal wall in three dimensional space, with an attractive interaction
when the interface is in contact with the wall, at low temperatures. There is no bulk external field. The system presents
a sequence of layering transitions, whose levels increase with the temperature, before reaching the wetting transition. 相似文献
15.
We present a detailed study of free polymer surfaces and their effects on the measured glass transition temperature (Tg) of thin polystyrene (PS) films. Direct measurements of the near-surface properties of PS films are made by monitoring the embedding of 10 and 20 nm diameter gold spheres into the surface of spin-cast PS films. At a temperature T = 378K( > Tg), the embedding of the spheres is driven by geometrical considerations arising from the wetting of the gold spheres by the PS. At temperatures below Tg ( 363K < T < 370K), both sets of spheres embed 3-4 nm into the PS films and stop. These studies suggest that a liquid-like surface layer exists in glassy PS films and also provide an estimate for the lower bound of the thickness of this layer of 3-4 nm. This qualitative idea is supported by a series of calculations based upon a previously developed theoretical model for the indentation of nanoscale spheres into linear viscoelastic materials. Comparing data with simulations shows that this surface layer has properties similar to those of a bulk sample of PS having a temperature of 374 K. Ellipsometric measurements of the Tg are also performed on thin spin-cast PS films with thicknesses in the range 8nm < h < 290nm. Measurements are performed on thin PS films that have been capped by thermally evaporating 5 nm thick metal (Au and Al) capping layers on top of the polymer. The measured Tg values (as well as polymer metal interface structure) in such samples depend on the metal used as the capping layer, and cast doubt on the general validity of using evaporative deposition to cover the free surface. We also prepared films that were capped by a new non-evaporative procedure. These films were shown to have a Tg that is the same as that of bulk PS (370±1 K) for all film thicknesses measured (> 7 nm). The subsequent removal of the metal layer from these films was shown to restore a thickness-dependent Tg in these samples that was essentially the same as that observed for uncapped PS films. An estimate of the thickness of the liquid-like surface layer was also extracted from the ellipsometry measurements and was found to be 5±1 nm. The combined ellipsometry and embedding studies provide strong evidence for the existence of a liquid-like surface layer in thin glassy PS films. They show that the presence of the free surface is an important parameter in determining the existence of Tg reductions in thin PS films. 相似文献
16.
The exterior of a cross-linked polymer gel resembles a polymer brush. Such gel including its brush can be swollen by a good solvent. The detachment of the solvent–vapor (L–V) interface from the brush is controlled by the adsorption of polymer segments onto this interface and is to a very good approximation not influenced by long-range van der Waals contributions. A wetting transition in this system coincided with the adsorption–desorption transition for chains onto such L–V interface and has various unusual features. There are several indications that in practice this system should feature a second-order wetting transition. 相似文献
17.
The evolution of two-dimensional (2D) strained InAs wetting layers on GaAs(0 0 1), grown at different temperatures by molecular beam epitaxy, was studied by in situ high-resolution scanning tunneling microscopy. At low growth temperature (400 °C), the substrate exhibits a well-defined GaAs(0 0 1)-c(4 × 4) structure. For a disorientation of 0.7°, InAs grows in the step-flow mode and forms an unalloyed wetting layer mainly along steps, but also in part on the terrace. The wetting layer displays some local c(4 × 6) reconstruction, for which a model is proposed. 1.2 monolayer (ML) InAs deposition induces the formation of 3D islands. At a higher temperature (460 °C), the wetting layer is obviously alloyed even at low InAs coverage. The critical thickness of the wetting layer for the 2D-to-3D transition is shifted to 1.50 ML in this case presumably since the strain is reduced by alloying. 相似文献
18.
利用我国返回式实验卫星在空间微重力条件下进行了GaSb熔滴与GaP,BN和GaAs等材料的润湿性能的研究,分析了熔滴与基片之间的界面相互作用,并与重力场下实验结果进行了对比.实验表明,重力因素对润湿性存在影响,空间微重力条件下测得的GaSb熔滴与GaP及BN基片的接触角比地面测量的大.对凝固后的熔滴与基片之间的组织分析显示,重力场下,液固界面的相互作用较强,存在较宽的过渡区,这与地面浮力对流有利于物质输运密切相关.实验结果还表明,空间微重力环境下熔体凝固的组织比重力场下要均匀.
关键词:
微重力
润湿性
液/固界面 相似文献
19.
We develop an efficient simulation scheme to study a model suspension of equally sized colloidal hard spheres and nonadsorbing ideal polymer coils, both in bulk and adsorbed against a planar hard wall. The many-body character of the polymer-mediated effective interactions between the colloids yields a bulk phase diagram and adsorption phenomena that differ substantially from those found for pairwise simple fluids; e.g., we find an anomalously large bulk liquid regime and, far from the bulk triple point, three layering transitions in the partial wetting regime prior to a transition to complete wetting by colloidal liquid. 相似文献
20.
The carrier induced refractive index change and linewidth enhancement factor α due to ground-state (GS) and excited-state (ES) transitions have been compared by measuring the optical gain spectra from an InAs/GaAs quantum dot (QD) laser structure. It is shown that the ES transition exhibits a reduced α-factor compared to the value due to the GS transition. This result can be explained by the α-factor due to the ES transition having a smaller increase from the non-resonant carriers in the combined state of the wetting layer and InGaAs strain reducing layer than the α-factor increase due to the GS transition, since the relaxation time for carriers from the combined state of the wetting layer and InGaAs strain reducing layer to the ES is shorter than to the GS. The result reported here shows another advantage of using ES QD lasers for optical communication, in addition to their higher modulation speed. 相似文献