共查询到10条相似文献,搜索用时 109 毫秒
1.
Monolayers of dioctadecyldimethylammonium bromide (DODA) at the air/water interface were used as model for charged surfaces
to study the adsorption of anionic polyelectrolytes. After spreading on a pure water surface the monolayers were compressed
and subsequently transferred onto a polyelectrolyte solution employing the Fromherz technique. The polyelectrolyte adsorption
was monitored by recording the changes in surface pressure at constant area. For poly(styrene sulfonate) and carboxymethylcellulose
the plot of the surface pressure as function of time gave curves which indicate a direct correlation between the adsorbed
amount and surface pressure as well as a solely diffusion controlled process. In the case of rigid rod-like poly(p-phenylene sulfonate)s the situation is more complicated. Plotting the surface pressure as function of time results in a curve
with sigmoidal shape, characterized by an induction period. The induction period can be explained by a domain formation, which
can be treated like a crystallization process. Employing the Avrami expression developed for polymer crystallization, the
change in the surface pressure upon adsorption of rigid rod-like poly(p-phenylene sulfonate)s can be described.
Received 1st July 2000 and Received in final form 7 December 2000 相似文献
2.
L. Bolotov N. Uchida T. Kanayama 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):271-274
We present results of scanning tunneling spectroscopy (STS) measurements of hydrogen-saturated silicon clusters islands formed
on Si(111)-( 7×7) surfaces. Nanometer-size islands of Si6H12 with a height of 0.2-4 nm were assembled with a scanning tunneling microscope (STM) using a tip-to-sample voltage larger
than 3 V. STS spectra of Si6H12 cluster islands show characteristic peaks originating in resonance tunneling through discrete states of the clusters. The
peak positions change little with island height, while the peak width shows a tendency of narrowing for the tall islands.
The peak narrowing is interpreted as increase of lifetime of electron trapped at the cluster states. The lifetime was as short
as 10-13 s resulting from interaction with the dangling bonds of surface atoms, which prevents charge accumulation at the cluster
islands.
Received 30 November 2000 相似文献
3.
Elastic properties of polyelectrolyte capsules studied by atomic-force microscopy and RICM 总被引:1,自引:0,他引:1
Mechanical properties of polyelectrolyte multilayer capsules were studied using a new method combining atomic-force microscopy and reflection interference contrast microscopy. By measuring the force vs. deformation for poly(styrene sulfonate)/poly(allylamine) capsules the existence of different deformation regimes depending on the applied deformation was shown. The present paper focuses on the small-deformation regime. The elastic response of the deformed capsule was studied as a function of the wall thickness and the capsule size, and showed the theoretically expected variations. The Young modulus obtained from the experiments ranges between 1.3 and 1.9 GPa.Received: 5 August 2003, Published online: 28 October 2003PACS:
46.25.-y Static elasticity - 46.70.De Beams, plates and shells - 82.35.Rs Polyelectrolytes 相似文献
4.
Elasticity of hollow polyelectrolyte capsules prepared by the layer-by-layer technique 总被引:1,自引:0,他引:1
C. Gao E. Donath S. Moya V. Dudnik H. Möhwald 《The European physical journal. E, Soft matter》2001,5(1):21-27
Osmotically induced deformations (invaginations) of polyelectrolyte capsules were observed in poly(styrene sulfonate, sodium
salt) (PSS) solution since PSS of Mw 70 000 is excluded from the capsule interior. It was found that there is a critical osmotic
pressure difference at which the initial spherical capsule shape becomes unstable and invaginations are formed. This critical
osmotic pressure was obtained as a function of the wall thickness and the capsule size. A theoretical model is provided which
describes the relationship between the critical osmotic pressure, the elasticity modulus, the capsule wall thickness, and
the capsule radius. The model was verified by measuring the invagination onset as a function of particle radius and wall thickness.
The elasticity modulus of the PSS/PAH (polyallylamine hydrochloride) polyelectrolyte multilayer was measured as a function
of wall thickness and capsule diameter. The modulus ranges between 500 and 750 MPa, which indicates a relatively strongly
interconnected polyelectrolyte multilayer structure. With higher molecular weight PAH the elasticity modulus of the PSS/PAH
multilayer was slightly enhanced.
Received 25 January 2000 and Received in final form 18 May 2000 相似文献
5.
D.L. Peng T.J. Konno K. Wakoh T. Hihara K. Sumiyama 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):329-332
Cluster-cluster coalescence process of monodispersed Co clusters with mean diameter d = 8.5 and 13 nm deposited a plasma-gas-condensation-type cluster beam deposition system was investigated by in situ electrical conductivity measurements and ex situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and analyzed by percolation concept. The electrical
conductivity measurement and TEM observation indicated that, below temperature T≈ 100°C, the Co clusters in the assemblies maintain their original structure as deposited at room temperature, while that the inter-cluster
coalescence takes place at T > 100°C, although the size distribution and the interface morphology of the clusters showed no marked change at substrate temperatures
T
s≤200°C.
Received 29 November 2000 相似文献
6.
Berret JF Cristobal G Hervé P Oberdisse J Grillo I 《The European physical journal. E, Soft matter》2002,9(4):301-311
We report on the phase behavior and scattering properties of colloidal complexes made from block copolymers and surfactants. The copolymer is poly(sodium acrylate)-b-poly(acrylamide), hereafter abbreviated as PANa-PAM, with molecular weight 5000 g/mol for the first block and 30000 g/mol for the second. In aqueous solutions and neutral pH, poly(sodium acrylate) is a weak polyelectrolyte, whereas poly(acrylamide) is neutral and in good-solvent conditions. The surfactant is dodecyltrimethylammonium bromide (DTAB) and is of opposite charge with respect to the polyelectrolyte block. Combining dynamical light scattering and small-angle neutron scattering, we show that in aqueous solutions PANa-PAM diblocks and DTAB associate into colloidal complexes. For surfactant-to-polymer charge ratios Z lower than a threshold (Z(C) approximately 0.3), the complexes are single surfactant micelles decorated by few copolymers. Above the threshold, the colloidal complexes reveal an original core-shell microstructure. We have found that the core of typical radius 100-200 A is constituted from densely packed surfactant micelles connected by the polyelectrolyte blocks. The outer part of the colloidal complex is a corona and is made from the neutral poly(acrylamide) chains. Typical hydrodynamic sizes for the whole aggregate are around 1000 A. The aggregation numbers expressed in terms of numbers of micelles and copolymers per complex are determined and found to be comprised between 100-400, depending on the charge ratio Z and on the total concentration. We have also shown that the sizes of the complexes depend on the exact procedure of the sample preparation. We propose that the driving mechanism for the complex formation is similar to that involved in the phase separation of homopolyelectrolyte/surfactant systems. With copolymers, the presence of the neutral blocks prevents the macroscopic phase separation from occurring. 相似文献
7.
简述了高聚物薄膜玻璃化转变的复杂性,并结合文章作者的的一些研究结果介绍了扫描力显微术(SFM)在研究高聚物玻璃化转变中的一些方法,包括观察高聚物薄膜形貌的变化,测量其摩擦力、粘附力和弹性模量等物理量的变化,最后指出SFM是研究高聚物薄膜玻璃化转变的有力工具。 相似文献
8.
针尖 样品的距离控制系统是扫描近场红外显微镜的重要组成部分。切变力探测作为一种重要的近场距离控制手段而得到了广泛的应用。介绍了一种对切变力探测系统的改进方法 ,它可以有效地提高石英晶振音叉的品质因数 ,进而提高探测系统对切变力感应的灵敏度。给出了理论分析和实验验证结果 相似文献
9.
Chécot F Lecommandoux S Klok HA Gnanou Y 《The European physical journal. E, Soft matter》2003,10(1):25-35
This paper discusses the self-assembly of block copolymers into vesicular morphology. After a brief state of art of the field,
a system based on an amphiphilic poly(butadiene)-b-poly(-L-glutamic acid) (PB-b-PGA) diblock copolymer in aqueous solution is discussed in detail. The aggregation behavior of this block copolymer has been
investigated by means of fluorescence spectroscopy, dynamic (DLS) and static (SLS) light scattering as well as transmission
electron microscopy (TEM). The diblock copolymer was found to form well-defined vesicles in water. The size of these so-called
polymersomes or peptosomes could be reversibly manipulated as a function of both pH and ion strength. Depending on the pH
of the aqueous solution, the hydrodynamic radii of these vesicles were found to vary from 100 nm to 150 nm. By cross-linking
the 1,2-vinyl double bonds present in the polybutadiene block, the ability to transform a transient supramolecular self-organized
aggregate into a permanent “shape-persistent stimuli-responsive nanoparticle” has been demonstrated.
Received 25 June 2002 and Received in final form 22 October 2002 Published online: 11 March 2003 相似文献
10.
G. Migliorini N. Lee V. Rostiashvili T.A. Vilgis 《The European physical journal. E, Soft matter》2001,6(3):259-270
We study the properties of polyelectrolyte chains under different solvent conditions, using a variational technique. The free
energy and the conformational properties of a polyelectrolyte chain are studied by minimizing the free energy FN, depending on N(N - 1)/2 trial probabilities that characterize the conformation of the chain. The Gaussian approximation is considered for
a ring of length 24 < N < 28 and for an open chain of length 50 < N < 200 in poor- and theta-solvent conditions, including a Coulomb repulsion between the monomers. In theta-solvent conditions
the blob size is measured and found in agreement with scaling theory, including charge depletion effects, expected for the
case of an open chain. In poor-solvent conditions, a globule instability, driven by electrostatic repulsion, is observed.
We notice also inhomogeneous behavior of the monomer-monomer correlation function, reminiscence of necklace formation in poor-solvent
polyelectrolyte solutions. A global phase diagram in terms of solvent quality and inverse Bjerrum length is presented.
Received 7 June 2001 and Received in final form 17 October 2001 相似文献