Surface Morphologies: Transient and Equilibrium Shapes

Many different well defined surface morphologies of crystalline materials have been studied in the past 50 years. One of the important and most interesting objectives has been to elucidate the physical origin of the anisotropic surface free energy and, in more recent time, the energetics of surface defects, such as monatomic steps and kinks, which are thermally generated at steps. Changes in surface morphology related to phase transitions, such as faceting or surface roughening, have also attracted much attention. Kinetic experiments dealing with non-equilibrium structures and transient shapes, have lead to quantitative transport properties, for example, surface diffusion coefficients. Fully equilibrated structures, such as 2D and 3D equilibrium crystal shapes, have been imaged to extract the orientation dependent step and surface free energies, even at various temperatures. New imaging techniques with atomic resolution (notably scanning tunneling microscopy) applied to transient as well as equilibrium structures have provided more data of increased accuracy in kinetics and defect/surface energetics. The present paper is an attempt of a brief review of this rapidly advancing field, emphasizing more recent results.     

Spontaneous relativistic two-photon decay rate mathematical expression in helium-like systems

Using a laser-induced fluorescence method a detailed analysis of profiles of the ¹¹⁴Cd 326.1 nm line perturbed by argon was performed which revealed deviations from the ordinary Voigt profile. These deviations are shown to be consistent with fits of experimental profiles to an asymmetric Voigt profile. Coefficients of the pressure broadening, shift and collision-time asymmetry are determined and compared with those calculated in the adiabatic approximation for different interaction potentials. Received 19 July 2000     

Elastic properties of polymer-doped dilute lamellar phases: A small-angle neutron scattering study

We investigate experimentally, using small-angle neutron scattering the elastic properties of polymer-doped dilute lamellar phases. In our system the polymer is water-soluble but nevertheless partially adsorbs onto the negatively charged surfactant bilayers. The effective polymer-mediated interaction between bilayers is less repulsive than the weakly screened electrostatic interaction that prevails at zero polymer content. It even becomes attractive in some regions of the phase diagram. Small-angle neutron scattering allows us to measure directly the Caillé exponent η characterizing the bilayer fluctuations in lamellar (smectic A) phases, and thus indirectly estimate the compression modulus as a measure of the strength of the bilayer-bilayer interactions. The compression modulus appears to be vanishing at a point located on the lamellar-lamellar phase separation boundary, a candidate critical point. Received: 7 August 2000     

Ultrathin self-assembled polyelectrolyte multilayer membranes

The paper is concerned with ultrathin membranes prepared upon alternating layer-by-layer adsorption of cationic and anionic polyelectrolytes on a porous substructure. The formation of the polyelectrolyte multilayer membranes is characterised and the transport of gases, liquid mixtures and ions across the membranes is studied. In particular, the use of the membranes for alcohol/water separation under pervaporation conditions, and for the separation of mono- and divalent ions is described. It is demonstrated that upon a suitable choice of polyelectrolytes and substructures, and a careful optimisation of preparation and operation conditions, membranes can be tailored exhibiting an excellent separation capability. Received 4 September 2000     

Adsorption of hydrophobic polyelectrolytes at the air/water interface: Conformational effect and history dependence

We present an experimental study of the adsorption of hydrophobic highly charged polyelectrolytes on a neutral and hydrophobic surface, the air/water interface. The polymer was a randomly sulphonated polystyrene with charge fractions between 0.3 and 0.9 and the adsorbed layers were characterised by Langmuir through measurements, ellipsometry and X-ray reflectivity. The adsorption rate is always very slow and the resulting layers are very thin (< 3 nm). A maximum of adsorption with the charge fraction is observed which we relate to the conformation of the chains in solution. We show that adsorption is partially irreversible, strongly hysteretic and that the state of an adsorbed layer depends on its history. Received 16 June 2000     

A Composite Polymer Film with both Superhydrophobicity and Superoleophilicity

Summary: A composite film composed of porous polyurethane (PU) and polystyrene (PS) microspheres with both superhydrophobicity and superoleophilicity has been prepared. In this film, the dual‐scale structure enhances both the hydrophobicity and oleophilicity of the surface material. The composite film with such an ‘intelligent’ wettability property can be utilized to separate oil and water systems efficiently.

The composite film can be used to separate diesel oil and water.     

Confocal Raman Microspectroscopy: Calculation of Corrected Depth Profiles of Wet‐Chemically Modified Polymer Films

Summary: A mathematical approach developed to correct depth profiles of wet‐chemically modified polymer films obtained by confocal Raman microscopy is presented which takes into account scattered contributions originated from a diffraction‐limited laser focal volume and the refractive index of the sample. The method is demonstrated in both virtual and real samples where it is shown that considerable differences between apparent and corrected depth profiles exist at the surface, especially when profiles with strong concentration gradients are dealt with or an instrument with poor depth resolution is used.

Comparison of depth profiles obtained by simple normalization (solid line) and normalization after correction of the data with respect to diffraction effects.     

Synthesis of Highly Hydrophilic Polyaniline Nanowires and Sub‐Micro/Nanostructured Dendrites on Poly(propylene) Film Surfaces

Summary: Polyaniline (PANI) nanowires and sub‐micro/nanostructured dendrites are synthesized and immobilized on PP‐g‐PAA film surfaces via routine oxidative polymerization of aniline under different conditions, where grafting poly(acrylic acid) (PAA) served as a template and dopant, and SDS as a surfactant. The immobilized PANI enhances the surface hydrophilicity of the poly(propylene) (PP) films, and a superhydrophilic surface is obtained in this way. The mechanism of forming different morphologies of PANI and of correspondingly obtaining a superhydrophilic surface are briefly discussed.

FESEM image shows the PANI sub‐micro/nanostructured dendrites immobilized on the surfaces of PP films. The modified surface is highly hydrophilic with a water contact angle of 3°.     

多模短波长激光在圆形球面腔中的传输

用数值积分方法求解了在圆柱坐标中的横向多模菲涅尔(Fresnel)积分方程.在初始复数光场振幅取均匀分布和随机分布的条件下对圆形球面共焦腔、稳定腔和平面腔的TEM_n0模进行了计算分析.计算结果表明,球面腔单一模的数值结果同解析解的结果符合较好,多种模同时存在时的结果不仅符合多模空间分布特性而且其基模是主要的.     

‘Click’ Chemistry in Polymer and Materials Science

The modification of polymers after the successful achievement of a polymerization process represents an important task in macromolecular science. Cycloaddition reactions, among them the metal catalyzed azide/alkyne ‘click’ reaction (a variation of the Huisgen 1,3‐dipolar cycloaddition reaction between terminal acetylenes and azides) represents an important contribution towards this endeavor. They combine high efficiency (usually above 95%) with a high tolerance of functional groups and solvents, as well as moderate reaction temperatures (25–70 °C). The present review assembles recent literature for applications of this reaction in the field of polymer science (linear polymers, dendrimers, gels) as well as the use of this and related reactions for surface modification on carbon nanotubes, fullerenes, and on solid substrates, and includes the authors own publications in this field. A number of references (>100) are included.