Self-organization and rigidity in network glasses

Rigidity theory has helped in our understanding of the properties of network glasses. We analyze the connection between rigidity and various non-random features in the network structure. Lack of small rings in the network can lead to a sharper rigidity transition. We review a model of network self-organization that we have proposed, in which the existence of an intermediate phase that is rigid, but stress-free, is predicted. Finally, we discuss recent experiments, in which this intermediate phase may have been observed.     

Self-organization of three-dimensional lead telluride nanoislands under conditions close to thermodynamic equilibrium

Three-dimensional lead telluride (PbTe) nanoislands were grown on (111)BaF₂ substrates by hotwall epitaxy (HWE) from vapor phase under conditions close to thermodynamic equilibrium and their surface morphology was studied by atomic force microscopy in various growth stages, including the initial stage of nucleation and the subsequent evolution of the size and shape of nanoislands. The distributions of island dimensions in the samples grown under various thermodynamic conditions were statistically analyzed. It is shown that the proposed HWE method ensures the formation of dense (∼8 × 10¹⁰ cm⁻²) self-organized arrays of PbTe quantum dots with parameters comparable with those of the quantum dots of the same material grown by molecular beam epitaxy according to the Volmer-Weber mechanism.     

粉体的自组织行为

粉体具有不同于固体、液体和气体的独特物性,并在一定条件下表现出自组织特性。文中介绍了粉体在受迫振动堆积过程中的自组织行为,并对粉体在水平旋转的圆筒中的自组织现象进行了实验观察。     

Reconfigurable, braced, three-dimensional DNA nanostructures

DNA nanotechnology makes use of the exquisite self-recognition of DNA in order to build on a molecular scale. Although static structures may find applications in structural biology and computer science, many applications in nanomedicine and nanorobotics require the additional capacity for controlled three-dimensional movement. DNA architectures can span three dimensions and DNA devices are capable of movement, but active control of well-defined three-dimensional structures has not been achieved. We demonstrate the operation of reconfigurable DNA tetrahedra whose shapes change precisely and reversibly in response to specific molecular signals. Shape changes are confirmed by gel electrophoresis and by bulk and single-molecule F?rster resonance energy transfer measurements. DNA tetrahedra are natural building blocks for three-dimensional construction; they may be synthesized rapidly with high yield of a single stereoisomer, and their triangulated architecture conveys structural stability. The introduction of shape-changing structural modules opens new avenues for the manipulation of matter on the nanometre scale.     

Self-organization in phase separation of a lyotropic liquid crystal into cellular, network and droplet morphologies

Phase separation is one of the most fundamental physical phenomena that controls the morphology of heterogeneous structures. Phase separation of a binary mixture of simple liquids produces only two morphologies: a bicontinuous or a droplet structure in the case of a symmetric or an asymmetric composition, respectively. For complex fluids, there is a possibility to produce other interesting morphologies. We found that a network structure of the minority phase can also be induced transiently on phase separation if the dynamics of the minority phase are much slower than those of the majority phase. Here we induce a cellular structure of the minority phase intentionally with the help of its smectic ordering, using phase separation of a lyotropic liquid crystal into the isotropic and smectic phase. We can control the three morphologies, cellular, network and droplet structures, solely by changing the heating rate. We demonstrate that the kinetic interplay between phase separation and smectic ordering is a key to the morphological selection. This may provide a new route to the formation of network and cellular morphologies in soft materials.     

Self-organization and Social Capital

All forms of capital are created by spending time and effortin transformation and transaction activities. oPhysical capitalis the arrangement of material resources to improve flows offuture income. Social capital is the arrangement of human resourcesto improve flows of future income. Human capital is the knowledgeand skills that individuals bring to the solution of any problem.Social capital is created by individuals spending time and energyworking with other individuals to find better ways of makingpossible the achievement of certain ends that in its absencewould not be possible. The investment in social capital frequentlytakes the form of bargaining over which rules will be adoptedto allocate benefits and costs of collective action. This processis illustrated in this article by focusing on the bargainingover rules that are endogenous to thousands of farmer-ownedirrigation systems throughout the world. When participants arecharacterized by substantial heterogeneities of capabilitiesand interests, the rules that are adopted substantially affectthe distribution of outcomes. If participants are faced withcrosscutting and off-setting differences, however, a configurationof rules can enable participants to generate mutually productiveoutcomes over time. If external agents of change do not takeinto account the delicate balance of interests embedded in socialcapital, when investments in physical capital are undertaken,efforts to improve productivity can have the opposite effect.Institutions that are slowly developed through many years oftough bargaining and trial and error processes may be quicklydestroyed by insensitive overemphasis on physical technology.     

Self-organization of porphyrin structures on Si

The system produced by deposition of aqueous solution (10^− 3–10^− 6 M) of mesotetra(4-sulfonatophenyl)porphine (TPPS₄) on Si was studied. The morphology of self-organized structures of TPPS₄ was investigated by atomic force microscopy (AFM). The rod- and fiber-like structures of 250–1000 nm width and 30–200 nm height have been found on glass substrates and crystalline Si (c-Si). The aggregation state of TPPS₄ was determined by analysis of optical absorption of aqueous solutions in a visible spectral range and spectroscopic ellipsometry of TPPS/Si samples in the region 1–5 eV. The deposition of aqueous solution of metal-free TPPS₄ and Fe-TPPS₄ was examined. The difference in the adsorption of TPPS₄ on c-Si, porous Si and glass substrates was discussed. The self-ordered ring effect caused inhomogeneous distribution of Fe-TPPS₄ on the c-Si surface. From optical studies, it was found that in TPPS/Si samples formed from aqueous solution of TPPS₄ of high acidity the optical response of J-aggregates was dominant. In contrast, the fine structure in the optical spectra of the samples Fe- TPPS₄/Si corresponded to the excitation of monomers in aqueous solution independently on the pH-value of deposited aqueous solutions. The dependence of spectra for TPPS/Si samples on substrate type, orientation of c-Si, and acidity of aqueous solution was discussed in order to clarify the mechanism of porphyrin adsorption on Si.     

Self-organization of nickel atoms in silicon

We present experimental evidence for self-organization of nickel microparticles in silicon under certain thermodynamic conditions of nickel diffusion doping. The concentration and distribution of the microparticles in silicon are very uniform. Additional anneals lead to self-ordering of the impurity microparticles.     

Chip-based bioassay using bacterial sensor strains immobilized in three-dimensional microfluidic network

A whole-cell bioassay has been performed using Escherichia coli sensor strains immobilized in a chip assembly, in which a silicon substrate is placed between two poly(dimethylsiloxane) (PDMS) substrates. Microchannels fabricated on the two separate PDMS layers are connected via perforated microwells on the silicon chip, and thus, a three-dimensional microfluidic network is constructed in the assembly. Bioluminescent sensor strains mixed with agarose are injected into the channels on one of the two PDMS layers and are immobilized in the microwells by gelation. Induction of the firefly luciferase gene expression in the sensor strains can be easily carried out by filling the channels on the other layer with sample solutions containing mutagen. Bioluminescence emissions from each well are detected after injection of luciferin/ATP mixtures into the channels. In this assay format using two multichannel layers and one microwell array chip, the interactions between various types of samples and strains can be monitored at each well on one assembly in a combinatorial fashion. Using several genotypes of the sensor strains or concentrations of mitomycin C in this format, the dependence of bioluminescence on these factors was obtained simultaneously in the single screening procedure. The present method could be a promising on-chip format for high-throughput whole-cell bioassays.     

Ultrathin graphite foam: a three-dimensional conductive network for battery electrodes

We report the use of free-standing, lightweight, and highly conductive ultrathin graphite foam (UGF), loaded with lithium iron phosphate (LFP), as a cathode in a lithium ion battery. At a high charge/discharge current density of 1280 mA g(-1), the specific capacity of the LFP loaded on UGF was 70 mAh g(-1), while LFP loaded on Al foil failed. Accounting for the total mass of the electrode, the maximum specific capacity of the UGF/LFP cathode was 23% higher than that of the Al/LFP cathode and 170% higher than that of the Ni-foam/LFP cathode. Using UGF, both a higher rate capability and specific capacity can be achieved simultaneously, owing to its conductive (～1.3 × 10(5) S m(-1) at room temperature) and three-dimensional lightweight (～9.5 mg cm(-3)) graphitic structure. Meanwhile, UGF presents excellent electrochemical stability comparing to that of Al and Ni foils, which are generally used as conductive substrates in lithium ion batteries. Moreover, preparation of the UGF electrode was facile, cost-effective, and compatible with various electrochemically active materials.     

Mechanically tunable three-dimensional elastomeric network/air structures via interference lithography

We show how to employ an interference lithographic template (ILT) as a facile mold for fabricating three-dimensional bicontinuous PDMS (poly(dimethylsiloxane)) elastomeric structures and demonstrate the use of such a structure as a mechanically tunable PDMS/air phononic crystal. A positive photoresist was used to make the ILT, and after infiltration with PDMS, the resist was removed in a water-based basic solution which avoided PDMS swelling or pattern collapse occurring during the ILT removal process. Since the period of the structure is approximately 1 microm, the density of states of gigahertz phonons are altered by the phononic PDMS/air crystal. Brillouin light scattering (BLS) was employed to measure phononic modes of the structure as a function of mechanical strain. The results demonstrate that the phononic band diagram of such structures can be tuned mechanically.     

Direct mechanical measurements reveal the material properties of three-dimensional DNA origami

The application of three-dimensional DNA origami objects as rigid mechanical mediators or force sensing elements requires detailed knowledge about their complex mechanical properties. Using magnetic tweezers, we directly measure the bending and torsional rigidities of four- and six-helix bundles assembled by this technique. Compared to duplex DNA, we find the bending rigidities to be greatly increased while the torsional rigidities are only moderately augmented. We present a mechanical model explicitly including the crossovers between the individual helices in the origami structure that reproduces the experimentally observed behavior. Our results provide an important basis for the future application of 3D DNA origami in nanomechanics.     

Numerical experiments on paper-fluid interaction — permeability of a three-dimensional anisotropic fibre network

The effect of paper structure on flow characteristics of various fluids is one of the most important, fundamental problems in papermaking, coating, and printing. A computer code based on a cellular automaton model, in particular the lattice-gas Boltzmann model, has been developed to simulate flow numerically in a random fibre network. As a preliminary investigation, a numerical experiment has been conducted on the three-dimensional permeability of an interpenetrable fibre network. It was found that the in-plane permeability and the z-directional (thickness direction) permeability are very sensitive to the distribution of fibre segments in the z-direction. At a constant porosity, the z-directional permeability increases and the in-plane permeability decreases with increasing z-directional fibre orientation.     

界面法制备三维网状PPy-PEDOT共聚物膜及电容性能

制备具有多电子传输与多孔有序的结构电极是电化学储能技术创新发展的两个重要策略。本工作采用一种界面电化学聚合新法合成聚吡咯-聚3,4-乙撑二氧噻吩(PPy-PEDOT)共聚物薄膜材料。采用FTIR,XPS,EDX,SEM与电化学充放电测试对PPy-PEDOT共聚物膜的化学组成、分布、微观形貌及电容性能进行表征与测试。结果表明:PPy-PEDOT共聚物膜由PPy与PEDOT按一定比例组成,且分布均匀;SEM测试表明共聚物膜具有正反两面各异的特殊形貌,且有机相一侧呈三维网状多孔层状结构。电化学充放电测试表明,PPy-PEDOT共聚物膜表现出优异的超级电容器电极材料的特性,具有较高的比电容,较快的充放电速率与较好的循环稳定性。PPy与PEDOT共聚后实现二者性能互补,提高了共聚物膜的导电性,电荷迁移速率及稳定性,同时三维网状多孔层状结构也有助于充放电过程中电子离子的迁移,使得共聚物膜的储能性能显著提高。     

Highly flexible frontside-illuminated dye-sensitized solar cells using three-dimensional network TiO2 nanowires

Here we report a highly flexible frontside-illuminated dye-sensitized solar cell (FIDSSC) using Ti foils as the substrates. The laser-drilled microhole arrays (LDMAs) on Ti foil substrates as the photoanode provided an efficient pathway for the diffusion of liquid electrolyte, which would be particularly favorable for frontside illumination of FIDSSC designs. The three-dimensional (3D) network TiO2 nanowires (NWs) were directly grown on the Ti substrate with LDMAs via a simple hydrothermal method. Platinized Ti sheet was used as the counter electrode in the FIDSSC. The mechanical properties of the novel structured device were measured. It was shown that as-synthesized large-scale 3D network TiO2 NWs with a diameter of about 20-30 nm and a length of about 6 microm can prevent crack from generating efficiently when bended to an extreme angle of 120 degree. Furthermore, we demonstrated that the effects of the different bending angles on the performance of the 3D network TiO2 NWs-based FIDSSCs were slight, indicating NWs preferable advantages for the fabrication of flexible DSSCs. The results showed that the FIDSSC achieved an efficiency of 0.72% under front illumination of AM 1.5 simulated one sun light (100 mWcm(-2)).