Collective motion of active particles in environmental noise

We study the collective motion of active particles in environmental noise, where the environmental noise is caused by noise particles randomly diffusing in two-dimensional space. We show that active particles in a noisy environment can self organize into three typical phases: polar liquid, band, and disordered gas states. In our model, the transition between band and disordered gas states is discontinuous. Giant number fluctuation is observed in the polar liquid phase. We also compare our results with the Vicsek model and show that the interaction with noise particles can stabilize the band state to very low noise condition. This band structure could recruit most of the active particles in the system, which greatly enhances the coherence of the system. Our findings of complex collective behaviors in environmental noise help us to understand how individuals modify their self-organization by environmental factors, which may further contribute to improving the design of collective migration and navigation strategies.     

Dielectric properties of a wide-temperature ferroelectric phase in a fluorinated compound

ABSTRACT

A broad-frequency dielectric spectroscopy (100 Hz to 10 MHz) was used to investigate newly synthesized fluorinated compound. This compound exhibits a wide-temperature ferroelectric phase. Due to the fact that the compound does not crystallize at temperatures available in our DSC equipment, additional measurements were done at the very low temperatures (down to ?100 °C) to find the crystallization temperature. Finally, we did not manage to crystallize the investigated compound. Compound under studies seems to be overcooled. Observed dielectric modes are described and their parameters are shown in this paper. Additionally, DC field influence on dielectric response is shown and analyzed here. Both modes observed at the low temperature are recognized as the molecular ones.     

PMMA-b-QPDMAEMA的合成及其抗菌活性

以α-溴代丙酸乙酯为引发剂,CuCl/二乙烯三胺为催化剂,采用ATRP法制得5个不同分子量的聚甲基丙烯酸甲酯-聚甲基丙烯酸二甲氨乙酯嵌段共聚物(PMMA-b-PDMAEMA, P¹~P⁵); P¹~P⁵经溴代辛烷季铵化合成了5个聚季铵盐(Q¹~Q⁵),其结构和性能经¹H NMR, FT-IR, GPC和DSC表征。结果表明：P⁴和Q⁴的玻璃化转变温度分别为109.67 ℃和117.95 ℃。采用平板活菌计数法研究了Q¹~Q⁵对金黄色葡萄球菌(S. aureus)和大肠杆菌(E. coli)的抗菌活性。结果表明：Q¹~Q⁵对S. aureus的抗菌活性优于E. coli,其MIC值分别为300 mg·L^-1, 250 mg·L^-1, 275 mg·L^-1, 225 mg·L^-1和150 mg·L^-1。     

Benzil Photoperoxidations in Polymer Films and Crosslinking by the Resultant Benzoyl Peroxides in Polystyrene and Other Polymers

Benzil (BZ) can be converted almost quantitatively to benzoyl peroxide (BP) in aerated polymer films upon irradiation at >400 nm (i.e., the long-wavelength edge of the n→π* absorption band of BZ, where BP does not absorb). Here, we summarize results for the photoperoxidation of BZ structures with molecular oxygen, principally in glassy polymer matrices. Some of the polymers are doped directly with BZ or its derivatives, and others, contain covalently attached BZ pendant groups from which BP groups are derived. While the decomposition of low-molecular-weight BP doped into polymer films (such as those of polystyrene (PS)) results in a net decrease in polymer molecular weight, thermal decomposition of pendant BP groups is an efficient method for chain crosslinking. Crosslinking of PS films doped with a molecule containing two covalently linked BZ or BP groups proceeds in a similar fashion. Free radicals from the covalently attached BP allow grafting of new monomers, as well. Additionally, the use of radiation filtered through masks has been used to create patterns of polymers on solid surfaces. Crosslinking of photodegradable poly(phenyl vinyl ketone) with BP structures obtained by photoperoxidation of BZ structures for the preparation of photodegradable polymer networks is described as well. In sum, the use of BZ and BP and their derivatives offers simple and convenient routes for modifying polymer chains and, especially, for crosslinking them. Specific applications of each use and process are provided. Although applications with PS are featured here, the methodologies described are amenable to a wide variety of other polymers.     

超疏水材料表面液-气界面的稳定性及演化规律

超疏水表面功能材料在防污、流动减阻等领域具有重要应用,其中液–气界面的稳定性是关系到该种材料性能发挥的关键因素。微结构液–气界面的稳定性主要体现在浸润状态转变过程,浸润状态恢复过程和气泡形态演化过程三个方面。在压强变化、气体扩散等多种因素作用下,液–气界面会发生失稳现象,并以不同的形态变化方式进行演化发展。该文首先总结了三类液–气界面稳定性问题。在不同的演化阶段,液–气界面具有不同的位置和形状,体现出不同的稳定性。然后,分别针对液滴系统和水下浸没系统,考虑了几种主要的影响因素,综述了目前国内外关于超疏水微结构液–气界面稳定性研究的主要进展,总结液–气界面的演化机制。最后,展望了该领域中存在的主要科学问题。     

Skin formation in drying a film of soft matter solutions:Application of solute based Lagrangian scheme

When a film of soft matter solutions is being dried, a skin layer often forms at its surface, which is a gel-like elastic phase made of concentrated soft matter solutions. We study the dynamics of this process by using the solute based Lagrangian scheme which was proposed by us recently. In this scheme, the process of the gelation(i.e., the change from sol to gel) can be naturally incorporated in the diffusion equation. Effects of the elasticity of the skin phase, the evaporation rate of the solvents, and the initial concentration of the solutions are discussed. Moreover, the condition for the skin formation is provided.     

Block copolymer morphologies confined by square-shaped particle:Hard and soft confinement

The self-assembly of diblock copolymers confined around one square-shaped particle is studied systematically within two-dimensional self-consistent field theory(SCFT).In this model,we assume that the thin block copolymer film is confined in the vicinity of a square-shaped particle by a homopolymer melt,which is equivalent to the poor solvents.Multiple sequences of square-shaped particle-induced copolymer aggregates with different shapes and self-assembled internal morphologies are predicted as functions of the particle size,the structural portion of the copolymer,and the volume fraction of the copolymer.A rich variety of aggregates are found with complex internal self-assembled morphologies including complex structures of the vesicle,with one or several inverted micelle surrounded by the outer monolayer with the particle confined in the core.These results demonstrate that the assemblies of diblock copolymers formed around the square-shaped particle in poor solvents are of immediate interest to the assembly of copolymer and the morphology of biomembrane in the confined environment,as well as to the transitions of vesicles to micelles.     

Soft x-ray spectroscopy for probing electronic and chemical states of battery materials

The formidable challenge of developing high-performance battery system stems from the complication of battery operations, both mechanically and electronically. In the electrodes and at the electrode–electrolyte interfaces, chemical reactions take place with evolving electron states. In addition to the extensive studies of material synthesis, electrochemical, structural, and mechanical properties, soft x-ray spectroscopy provides unique opportunities for revealing the critical electron states in batteries. This review discusses some of the recent soft x-ray spectroscopic results on battery binder,transition-metal based positive electrodes, and the solid-electrolyte-interphase. By virtue of soft x-ray's sensitivity to electron states, the electronic property, the redox during electrochemical operations, and the chemical species of the interphases could be fingerprinted by soft x-ray spectroscopy. Understanding and innovating battery technologies need a multimodal approach, and soft x-ray spectroscopy is one of the incisive tools to probe the chemical and physical evolutions in batteries.     

Micromagnetic simulation of Sm–Co/α-Fe/Sm–Co trilayers with various angles between easy axes and the film plane

Hysteresis loops and energy products have been calculated systematically by a three-dimensional(3D) software OOMMF for Sm–Co/α-Fe/Sm–Co trilayers with various thicknesses and β, where β is the angle between the easy axis and the field applied perpendicular to the film plane. It is found that trilayers with a perpendicular anisotropy possess considerably larger coercivities and smaller remanences and energy products compared with those with an in-plane anisotropy.Increase of β leads to a fast decrease of the maximum energy product as well as the drop of both remanence and coercivity. Such a drop is much faster than that in the single-phased hard material, which can explain the significant discrepancy between the experiment and the theoretical energy products. Some modeling techniques have been utilized with spin check procedures performed, which yield results in good agreement with the one-dimensional(1D) analytical and experimental data, justifying our calculations. Further, the calculated nucleation fields according to the 3D calculations are larger than those based on the 1D model, whereas the corresponding coercivity is smaller, leading to more square hysteresis loops and better agreement between experimental data and the theory.