Phoretic self-assembly of active colloidal molecules

We simulate the self-assembly of active colloidal molecules from binary mixtures of spherical particles using a Brownian dynamics algorithm. These particles interact via phoretic interactions, which are determined by two independently tunable parameters, surface activity and surface mobility. In systems composed of equal-size particles, we observe the formation of colloidal molecules with well-defined coordination numbers and spatial arrangement, which also display distinct dynamic functions, such as resting, translating, and rotating. By changing the size ratio to 2 : 1 between the two species,we further observe the formation of colloidal molecules with new structures arising from breaking the size symmetry. By tuning the mutual interactions between the smaller species via their surface mobility, we are able to control their spacing as well as the coordination number of the colloidal molecules. This study highlights the importance of tuning surface parameters and size asymmetry in controlling the structure and the active dynamics of colloidal molecules.     

Inversionless amplification by anisotropic molecules

Switching from opaque via transparent to a strongly amplifying state is shown to be possible for molecular media without a change in the noninverted population of their energy levels.     

宏观分子自组装:一条架在分子和结构体之间的桥梁

文章介绍了一种新的分子自组装现象 :宏观分子自组装 .由一种新型的两亲性超支化多臂共聚物在丙酮中直接自组装形成厘米长度、毫米直径的宏观多壁螺旋管 .并对宏观管子的精细结构、性能进行了详细描述 ,同时阐述了宏观分子自组装机理 .宏观分子自组装现象的发现将分子自组装的研究领域推进到了宏观尺度范围 .     

Two-dimensional self-assembly of DNA base molecules on Cu(111) surfaces

We present scanning tunneling microscope images of the self-assembled nucleic-acid base molecules on the surfaces of Cu(111). The images reveal that the chemical inertness of the Cu(111) substrate allows the molecules to diffuse over the surface to self-assemble themselves spontaneously into their own unique structure: adenine into one-dimensional (1D) molecular chains, thymine into 2D islands, guanine into 2D square lattices, and cytosine into 1D zig-zag molecule-cluster networks. We find that molecular orbital calculations reproduce some of the observed self-assembly, and suggest that base-base interaction induced by hydrogen bonding is essential to this phenomenon.     

Modelling non-equilibrium self-assembly from dissipation

Non-equilibrium self-assembly is ubiquitous in physico-chemical and biological systems, and manifests itself at different scales, ranging from the molecular to the cosmological. The formation of microtubules, gels, cells and living beings among many others takes place through self-assembly under nonequilibrium conditions. We propose a general thermodynamic non-equilibrium model to understand the formation of assembled structures such as gels and Liesegang patterns and at the same time able to describe the kinetics and the energetics of the structure formation process. The model is supported for a global mechanism to obtain self-assembled structures from building blocks via activation, deactivation, assembly, and disassembly processes. It is proposed that the resulting structures can be characterised by a structural parameter. Our model may contribute to a better understanding of non-equilibrium self-assembly processes and give deeper insight as to how to obtain a specific structural architecture to materials, such as hydrogels which are of great importance in the design of advanced devices and novel materials.     

Photo-oxidation of polyhydroxyl molecules on TiO2 surfaces: from hole scavenging to light-induced self-assembly of TiO2-cyclodextrin wires

First-principles calculations are carried out to study photo-oxidation of glucose, as a prototype of polyhydroxyl carbohydrates and alcohols, on TiO2 surfaces. We reveal the microscopic mechanisms for the separation and transfer of photogenerated electrons and holes at the TiO2-molecule interface as detailed from hole trapping, deprotonation, to the formation of an electron-hole recombination center. These revealed mechanisms further lead to the understanding of the light-induced self-assembly mechanism for TiO2-cyclodextrin nanowires.     

Reflection of light from an anisotropic film on an anisotropic substrate

The ellipsometric equations are presented for a reflecting film system consisting of an anisotropic layer and an anisotropic substrate with the principal axes of the dielectric tensor in the plane of incidence of the sample. Linear Drude approximations are obtained for the angular dependences of the ellipsometric parameters.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 102–107, May, 1991.     

Kinetic effects in the self-assembly of pure and mixed tetradecyl and octadecylamine molecules on mica

The self-assembly of tetradecylamine (C14) and of mixtures of tetradecyl and octadecylamine (C18) molecules from chloroform solutions on mica has been studied using atomic force microscopy (AFM). For pure components self-assembly proceeds more slowly for C14 than for C18. In both cases after equilibrium is reached islands of tilted molecules cover a similar fraction of the surface. Images of films formed by mixtures of molecules acquired before equilibrium is reached (short ripening time at room temperature) show only islands with the height corresponding to C18 with many pores. After a long ripening time, when equilibrium is reached, islands of segregated pure components are formed.     

Biopolymer-assisted self-assembly of ZnO nanoarchitectures from nanorods

We have investigated three-dimensional (3-D) architectures–microspheres and radial structures–based on biopolymer-assisted self-assembly from one-dimensional ZnO nanorods. The developed method is simple, rapid and cost-effective and can be used for self-assembly of different complex superstructures. A possible model of 3-D architectures self-assembled with biopolymer assistance is presented using minimum energy considerations. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy, micro–Raman spectroscopy and cathode luminescence investigations show that the novel 3-D architectures are built from high-purity ZnO nanorods with a wurtzite structure. The resulting radial structures show an intense ultraviolet (UV) cathode luminescence emission suggesting applications as UV light emitting diodes or lasers. Their structural characteristics endow them with a broad area of applications and offer a possibility to be used as fundamental low-dimensional building units. These building units open opportunities for the self-assembly of multifunctional nanostructured systems with applications in bioscience and nanomedicine, electronics and photonics.     

Rotationally symmetric scattering from anisotropic media

It is reported that the rotationally symmetric distributions of the spectral density and the spectral degree of coherence of the scattered field in the far zone can be produced by appropriate choices of the effective radius and the correlation length of the scatterer, when a polychromatic plane light wave is incident upon a Gaussian-correlated, quasi-homogeneous, anisotropic medium. The necessary and sufficient conditions are presented. Our results are illustrated by numerical examples.     

Field emission from self-assembly structure of carbon-nanotube films

Chemical vapor deposited (CVD) carbon nanotube (CNT) arrays were immersed in ethanol to make shrunk structures with separate nanotube “walls” for better field emission properties, such structures decreased the screening effects and reduced the turn-on electric field at 10 μA/cm² from 1.68 to 1.23 V/μm. The field enhancement factor was calculated to increase by 23% according to Fowler–Nordheim (F–N) equation. The number of emission sites also increased and their distribution was more uniform.     

Highly spin-polarized atoms and molecules from rotationally state-selected molecules

It is shown that large nuclear polarizations in isolated molecules may be created via the hyperfine interaction following excitation to selected rotational states |JM>. Explicit time-dependent nuclear polarization expressions for pulsed rotational excitation are presented for the case of one nuclear spin I, and for the case of two nuclear spins I1 and I2 in the hierarchical coupling limit. Photodissociation of the polarized molecules allows the production of polarized atoms, on short time scales if pulsed, at densities close to the parent molecule density.     

Encapsulation of dye molecules into mesoporous polymer resin and mesoporous polymer-silica films by an evaporation-induced self-assembly method

Polymer resin and polymer-silica films with highly ordered mesostructure have been used as host materials to encapsulate DCM (4-(dicyanomethylene) -2-methyl-6-(4-dimethylaminostyryl)-4h-pyran), a kind of fluorescent dye, through evaporation-induced self-assembly method (EISA). After encapsulation, the composites show significant blue-shift in photoluminescence (PL) spectra. Particularly, by changing the excitation wavelength, the samples show different emission bands. These phenomena are related to the mesostructure and the positions of DCM molecules in the host.     

Zero reflection from layered anisotropic metamaterial structures

Mathematical formulation for analysis of electromagnetic wave scattering from multilayer anisotropic homogeneous metamaterial structures with general tensors is presented. The result is reflection and transmission matrices formulas. Then, closed form formulas are extracted for structures with diagonal tensors. We try to find structures with exact zero reflection for general incident waves. New cases with zero and low reflection are introduced.     

Scattering from an anisotropic cylindrical dielectric shell

The electromagnetic scattering from an anisotropic cylindrical dielectric shell is formulated by using the wave functions for anisotropic media and the boundary-value method. The cylindrical shell is assumed to be infinite in length, and it is illuminated by a plane wave or a cylindrical wave from a line source. The problem is two-dimensional and the solutions to both types of polarization (TE and TM) are presented. Numerical results for the effects of various geometrical and electrical parameters on the bistatic radar cross section are presented.     

Emission studies on ZnO-inverse photonic crystals derived from self-assembly

Photonic crystals fabricated from the colloidal spheres of polymethyl methacrylate (PMMA) using the inward-growing self-assembly technique were subsequently in-filled with zinc oxide (ZnO) prepared by the sol-gel process. The polymer template was removed by heat treatment and chemical method to get ZnO-inverse photonic crystal. The structural quality of the inverse photonic crystal obtained by the chemical method was found to be superior to that obtained by heat treatment. The ZnO-inverse photonic crystal obtained by the chemical method was further treated at an elevated temperature to ensure the crystalline nature of ZnO. Laser-induced emission studies on ZnO-inverse photonic crystals were carried out at an excitation wavelength of 325 nm. The emission spectra showing UV and visible bands at collection angle of 45° from the direction of excitation helped to establish the role of crystalline ZnO.