Shaping the Light: The Key Factors Affecting the Photophysical Properties of Fluorescent Polymer Nanostructures.

To manipulate the functions of nanomaterials more precisely for diverse applications, the controllability and critical influencing factors of their properties must be thoroughly investigated. In this work, the macroscopic and microscopic effects are studied on the photophysical properties of various pyrene-ended poly(styrene-block-methyl methacrylate) nanostructures. Fluorescent polymer nanospheres, nanorods, and nanotubes are prepared by different template-based methods using anodic aluminum oxide membranes. Chain arrangements and conformations are determined as the key factors affecting the photophysical properties of the fluorescent polymer nanostructures. This work not only gives a deeper understanding of the effects on the photophysical properties of polymer nanomaterials influenced by morphologies, chain arrangements, and chain conformations, but also provides a reference for designing proper fluorescent nanostructures for specific applications.

[Abundance of Toxic and Non-toxic Microcystis sp. in Lake Hongze and Its Correlation with Environmental Factors].

In the present study, the eutrophic level of 30 water samples collected from Lake hongze in August 2014 were analyzed, and the abundance of toxic and non-toxic Microcystis sp., together with their spatial distribution, was investigated by quantitative real-time PCR techniques. The results showed that the average concentrations of total nitrogen and total phosphorus were 1.63 and 0.11 mg x L(-1), respectively. The trophic state index ( TSI) ranged from 58.1 to 73.6, and the water quality was in the state of eutrophication based on TSI. Toxic Microcystis was widely distributed in Lake Hongze, and its abundance varied sharply, from 1. 13 x 10(4) to 3.51 x 10(6) copies x mL(-1), and the abundance of total Microcystis ranged from 1.06 x 10(5) to 1.10 x 10(7) copies x m(-1), meanwhile, the proportion of toxic Microcystis in the total Microcystis ranged from 8.5% to 38.5%, with the average value of 23.6%. Correlation analysis indicated that there was a significant positive correlation among total Mirocystis, toxic Microcystis and the toxic proportion (P < 0.01). The abundance of total and toxic Microcystis was significantly positively correlated to chlorophyll a ( Chl-a) concentrations and TSI (P < 0.01), but was negatively correlated to transparency (SD) (P < 0.01). The ratio of toxic Microcystis to total Microcystis was significantly positively correlated to Chl-a, TN, TP and TSI (P < 0.01), but significantly negatively correlated to the ratio of TN to TP and SD (P < 0.01). Therefore, reducing total nitrogen and phosphorus concentrations could not only lower the eutrophication level of Lake Hongze, but also inhibit the competition advantage of the toxic Microcystis over non-toxic Microcystis.

Fabrication of Electrospun Polymer Fibers with Nonspherical Cross-Sections Using a Nanopressing Technique.

The fabrication of electrospun polymer fibers is demonstrated with anisotropic cross-sections by applying a simple pressing method. Electrospun polystyrene or poly(methyl methacrylate) fibers are pressed by flat or patterned substrates while the samples are annealed at elevated temperatures. The shapes and morphologies of the pressed polymer fibers are controlled by the experimental conditions such as the pressing force, the pressing temperature, the pressing time, and the surface pattern of the substrate. At the same pressing force, the shape changes of the polymer fibers can be controlled by the pressing time. For shorter pressing times, the deformation process is dominated by the effect of pressing and fibers with barrel-shaped cross-sections can be generated. For longer pressing times, the effect of wetting becomes more important and fibers with dumbbell-shaped cross-sections can be obtained. Hierarchical polymer fibers with nanorods are fabricated by pressing the fibers with porous anodic aluminum oxide templates.

Fabrication of multicomponent polymer nanostructures containing PMMA shells and encapsulated PS nanospheres in the nanopores of anodic aluminum oxide templates.

Multi-component polymer nanomaterials have attracted great attention because of their applications in areas such as biomedicine, tissue engineering, and organic solar cells. The precise control over the morphologies of multi-component polymer nanomaterials, however, is still a great challenge. In this work, the fabrication of poly(methyl methacrylate)(PMMA)/poly-styrene (PS) nanostructures that contain PMMA shells and encapsulated PS nanospheres is studied. The nanostructures are prepared using a triple solution wetting method with anodic aluminum oxide (AAO) templates. The nanopores of the templates are wetted sequentially by PS solutions in dimethylformamide (DMF), PMMA solutions in acetic acid, and water. The compositions and morphologies of the nanostructures are controlled by the interactions between the polymers, solvents, and AAO walls. This work not only presents a feasible method to prepare multi-component polymer nanomaterials, but also leads to a better understanding of polymer-solvent interactions in confined geometries.

Three-dimensional block copolymer nanostructures by the solvent-annealing-induced wetting in anodic aluminum oxide templates.

Block copolymers have been extensively studied over the last few decades because they can self-assemble into well-ordered nanoscale structures. The morphologies of block copolymers in confined geometries, however, are still not fully understood. In this work, the fabrication and morphologies of three-dimensional polystyrene-block-polydimethylsiloxane (PS-b-PDMS) nanostructures confined in the nanopores of anodic aluminum oxide (AAO) templates are studied. It is discovered that the block copolymers can wet the nanopores using a novel solvent-annealing-induced nanowetting in templates (SAINT) method. The unique advantage of this method is that the problem of thermal degradation can be avoided. In addition, the morphologies of PS-b-PDMS nanostructures can be controlled by changing the wetting conditions. Different solvents are used as the annealing solvent, including toluene, hexane, and a co-solvent of toluene and hexane. When the block copolymer wets the nanopores in toluene vapors, a perpendicular morphology is observed. When the block copolymer wets the nanopores in co-solvent vapors (toluene/hexane = 3:2), unusual circular and helical morphologies are obtained. These three-dimensional nanostructures can serve as naontemplates for refilling with other functional materials, such as Au, Ag, ZnO, and TiO2 .

Curved polymer nanodiscs by wetting nanopores of anodic aluminum oxide templates with polymer nanospheres.

Although nanostructures with diverse morphologies have been fabricated, it is still a great challenge to prepare anisotropic two-dimensional (2-D) nanostructures, especially non-planar disc-like nanostructures. In this work, we develop a simple method to prepare curved polymer nanodiscs with regular sizes by wetting polymer nanospheres in the nanopores of anodic aluminum oxide (AAO) templates. Polystyrene (PS) nanospheres are first fabricated by using a non-solvent-assisted template wetting method. By annealing the PS nanospheres in the nanopores of AAO templates, curved PS nanodiscs can be produced. The length and morphology of the curved PS nanodiscs can be controlled by the wetting conditions such as the annealing temperatures and times. For some stacked nanospheres, the annealing process can result in the formation of helix-like nanostructures. To demonstrate the universality of this work, this approach is also applied to poly(methyl methacrylate) (PMMA), another common polymer, and similar results are obtained.

Porous polymer nanostructures fabricated by the surface-induced phase separation of polymer solutions in anodic aluminum oxide templates.

We study the formation of porous polymer nanostructures fabricated by the surface-induced phase separation of polymer solutions in anodic aluminum oxide (AAO) templates. Poly(methyl methacrylate) (PMMA) and tetrahydrofuran (THF) are used to investigate the evolution process of the surface-induced phase separation. With the longer immersion time of the AAO template in the polymer solution, the size of the solvent-rich droplet is increased by the coarsening process, resulting in the formation of porous polymer nanostructures. The coarsening mechanism is further evaluated by changing the experimental parameters including the immersion time, the polymer concentration, the polymer molecular weight, and the solvent quality. Under conditions in which polymer solutions have higher viscosities, the coarsening process is slowed down and the formation of the porous nanostructures is prohibited. The prevention of the porous nanostructures can also be realized by adding water to the PMMA/THF solution before the immersion process.

Solvent-annealing-induced nanowetting in templates: towards tailored polymer nanostructures.

We study the solvent-annealing-induced nanowetting in templates using porous anodic aluminum oxide membranes. The morphology of polystyrene and poly(methyl methacrylate) nanostructures can be controlled, depending on whether the swollen polymers are in the partial or complete wetting regimes, which are characterized by the spreading coefficient. When the swollen polymers are in the partial wetting regime, polymers wet the nanopores by capillary action, resulting in the formation of polymer nanorods. When the swollen polymers are in the complete wetting regime, polymers form wetting layers in the nanopores, resulting in the formation of polymer nanotubes. The solubility parameters of polymers and solvents are also used to predict the wetting behavior of swollen polymers in cylindrical geometry.