Template Wetting Research Articles

Role of AAO template filling process parameters in controlling the structure ofone-dimensional polymer nanoparticles

Solution template wetting is a common technique used to fabricate elongated polymernanostructures; however, the parameters controlling the resulting morphology remainunclear. The purpose of this investigation was to elucidate the effects of process variableson the types of nanostructures obtained and to understand the physical mechanismsassociated with structure development. 1 wt% polystyrene–THF solutions were infiltratedinto commercial and homemade anodized aluminum oxide (AAO) templates. The wettinginteraction between the AAO template and the polymer solution was examinedthrough contact angle measurements. In general, for moderate dipping times (<18 h), the morphology of the nanopolymer was rod-like at low molecular weights, while tubeswere observed at high molecular weight, even at this low concentration. Nanorods wereobtained for all molecular weights for extended dipping times. The data suggest that phaseseparated layers may grow sequentially from the pore walls and yield nanotubes if thegrowth is interrupted or produce nanorods for unhindered deposition over longperiods.

Template‐assisted fabrication and characterization of photoluminescent polymer nanopillars

AbstractPhotoluminescent nanopillars are fabricated by replication from nanoporous anodic alumina via template wetting using polymer from different chemical families: polyfluorenes, PPV derivatives and thiophenes. The experimental process entails infiltration of a polymeric solution into the pores of the template with an average pore diameter of 225 nm and a pore depth of 500 nm. The geometric features of the resulting structures are characterized with environmental scanning electron microscopy (ESEM). The influence of nanostructure in the photophysical properties of the polymer is investigated by UV‐Vis absorbance and photoluminescence measurements. Polarized Raman spectroscopy characterization is also performed in order to study the different polymer conformation into the nanoporous template. The nanopillars obtained are interesting in many applications such as nanostructured solar cells and polymer light emitting diodes. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Solvent Effects on Template Wetting Nanofabrication of MEH-PPV Nanotubules

Template wetting is simple, solution-based nanofabrication technique that has previously been demonstrated for a number of different polymers. Like other solution-based polymer processing methods, it is reasonable to expect that the choice of solvent will have a significant impact on the properties of the resulting structures. This work examines the impact of wetting solvent on the properties of poly(2-methoxy-5-2′-ethylhexyloxy-1,4-phenylenevinlyene) (MEH-PPV) nanotubules formed using this method. The strength of solvent−polymer interaction was found to positively correspond to the degree of polymer chain alignment in the resulting nanotubules. Alignment was indicated by the level of dichroism observed using polarized FTIR spectroscopy, with no preferential alignment observed when using the poorest solvent (chlorobenzene) and dichroic ratios greater than 10 observed when “good” solvents chloroform and tetrahydrofuran were employed. The degree of alignment in turn correlated to a greater effective conjuga...

High thermal conductivity of polyethylene nanowire arrays fabricated by an improved nanoporous template wetting technique

Generally polymer bulk structures and nanostructures are thermally insulative. In this study, we show that an improved nanoporous template wetting technique can prepare thermally conductive polymer nanowire arrays. The thermal conductivities of the fabricated high-density polyethylene (HDPE) nanowire arrays with diameters of 100 nm and 200 nm, measured by a laser flash method, are about 2 orders of magnitude higher than their bulk counterparts. The estimated thermal conductivity of a single HDPE nanowire is as high as 26.5 W/mK at room temperature. The high orientation of chains of the HDPE nanowires may arise from the integrative effects of shear rate, vibrational perturbation, translocation, nanoconfinement and crystallization. Findings in this study provide useful strategies on enhancing the intrinsic thermal properties of polymer nanostructures.

β-cyclodextrin and its hyperbranched polymers-induced micro/nanopatterns and tunable wettability on polymer surfaces

This paper reports an efficient strategy to fabricate micro/nanopatterns on the surfaces of polymers for obtaining tunable wettability. Tepee-like bundles as micro/nanopatterns, composed of irregular polygon “podium” and “valley” structures, are formed by adding β-cyclodextrin (β-CD) or its hyperbranched polymers [HBP(β-CD)s] into a polystyrene (PS) matrix in the process of anodized aluminum oxide (AAO) template wetting. The degree and region of micro/nanopatterns are evidently enlarged with the increase of β-CD content or the molecular weight (Mw) of HBP(β-CD). The formation of micro/nanopatterns is mainly dependant on the self-organization of long and flexible aligned nanofiber/nanotube arrays with high aspect ratios, which are generated by the enhanced nanoflow behaviors of β-CD or HBP(β-CD)-containing PS melts in AAO templates. The final topographies of micro/nanopatterns are determined by the dilation stress and the interactions of nanofibers/nanotubes during the template's removal and solvent evaporation process. The static and dynamic water contact angle measurements show that the wettability of micro/nanopatterned surfaces is systematically tuned from being merely hydrophobic to being highly hydrophobic, and to being finally superhydrophobic by simply adjusting the content of β-CD or the Mw of HBP(β-CD) due to the decrease of the contact area fraction of the water droplet and solid polymer. The reported novel method, using nanoparticles or hyperbranched polymers as processing aids to induce micro/nanopatterns and tunable wettability on polymer surfaces, may be extended to various polymeric matrices to realize nanopatterns, and is useful for tailoring artificial superhydrophobic surfaces as well.

Multi-colour emission from dye doped polymeric nanotubes by host–guest energy transfer

Emission chromaticity tuning in polymeric nanotubes was achieved by transfer of excitation energy from a polymer host matrix poly(N-vinylcarbazole) (PVK) to incorporated luminescent chromophore guests (Coumarin 6 and Nile red). Nanotubes were synthesized in densely packed arrays by solution assisted template wetting. Un-doped PVK tubes displayed blue luminescence while Coumarin 6 and Nile red doped tubes exhibited characteristic green and red luminescence with minimal PVK emission, confirming effective host–guest energy transfer. The emission spectral data of single nanotubes, and indicated that, by varying the type and relative concentrations of the dopant dyes, nanotube emission could be tuned from the blue, through green and yellow, to the red and, ultimately, to white, while maintaining excellent color purity.

Effect of wetting solvent on poly(3-hexylthiophene) (P3HT) nanotubles fabricated via template wetting

Template wetting is a simple, solution based nanofabrication method that has been shown effective for a wide range of polymers. Like other solution based polymer processing methods, it is reasonable to expect that the choice of solvent will have a significant impact on the chain orientation in the final solid structure. Here we examine the impact of wetting solvent on the properties of 100 nm diameter poly(3-hexylthiophene) (P3HT) nanotubules made via template wetting. The degree of alignment of the P3HT backbone with the nanotubule axis as observed through dichroism in the FTIR spectrum was observed to depend on the strength of polymer–solvent interaction forces, observed experimentally through thermogravimetric analysis experiments. This solvent effect was not observed in other properties as neither the UV–Vis absorbance nor the hole mobility was observed to depend significantly on the wetting solvent. It is believed that the rigid rod structure and large side chain limited the degree of increase in the effective conjugation length and preventing even the aligned chains from being more tightly packed as would be necessary for an increase in inter-chain π-bond interactions sufficient to impact these performance characteristics of the material.

β-Phase Morphology in Ordered Poly(9,9-dioctylfluorene) Nanopillars by Template Wetting Method.

An efficient method based in template wetting is applied for fabrication of ordered Poly(9,9-dioctylfluorene) (PFO) nanopillars with β-phase morphology. In this process, nanoporous alumina obtained by anodization process is used as template. PFO nanostructures are prepared under ambient conditions via infiltration of the polymeric solution into the pores of the alumina with an average pore diameter of 225 nm and a pore depth of 500 nm. The geometric features of the resulting structures are characterized with environmental scanning electron microscopy (ESEM), luminescence fluorimeter (PL) and micro μ-X-ray diffractometer (μ-XRD). The characterization demonstrates the β-phase of the PFO in the nanopillars fabricated. Furthermore, the PFO nanopillars are characterized by Raman spectroscopy to study the polymer conformation. These ordered nanostructures can be used in optoelectronic applications such as polymer light-emitting diodes, sensors and organic solar cells.

(Invited) Synthesis and Characterization of Photoluminescent Polymer Micro- and Nanopillar Arrays

Photoluminescent micro- and nanopillars are fabricated by replication from macroporous silicon and nanoporous anodic alumina via template wetting using different conducting polymers. The geometric features of the resulting structures are characterized through environmental scanning electron microscopy. The influence of the porous dimension in the photophysical properties of the polymeric structures is investigated by absorption and emission measurements. By means of micro-X-ray diffraction we analyze the amorphous-crystalline nature of the fabricated structures. These structures can be interesting as hole conducting donors in different applications such as nanostructured solar cells and polymer light emitting diodes.

Characterization of conjugated polymer/anodic aluminum oxide nanocomposites fabricated via template wetting

Solution-based template wetting is demonstrated as an effective means of producing semiconductor–insulator nanocomposites. The properties of such nanocomposites formed by incorporating two commonly investigated semiconducting polymers, poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene (MEH-PPV) and poly(3-hexylthiophene-2,5-diyl) (P3HT), along with their blend, into nanoporous aluminum oxide (AAO) are investigated electronically and spectroscopically. Significant improvement in hole mobility of amorphous MEH-PPV in a nanocomposite with AAO while such improvement is absent when the crystalline P3HT is utilized to fabricate the AAO nanocomposites. Spectral evidence indicates that increased molecular order is responsible for this observation. Carrier mobility intermediate to the homopolymer nanocomposites was observed in composites fabricated from an MEH-PPV:P3HT blend and an AAO membrane. Spectral evidence indicates that these two polymers phase segregate in the composite.

Highly fluorescent TPA-PBPV nanofibers with amplified sensory response to TNT

Well-aligned nanofibers were prepared from a conjugated polymer, poly(triphenylamine-alt-biphenylene vinylene) (TPA-PBPV), using a solution-assisted template wetting technique. TPA-PBPV was also coated on the surface of electrospun polyacrylonitrile (PAN) nanofiber nonwoven membrane. The extremely large surface area, highly porous fibrous structure, optical scattering and evanescent-wave guiding effect imparted these one-dimensional (1D) nanofibrous materials with highly improved sensory ability to 2,4,6-trinitrotoluene (TNT) vapors and higher quenching efficiency than that of the neat TPA-PBPV films. The results suggest that nanofibrous structures could be a promising strategy to improve the sensory efficiency of fluorescent chemosensors.

Nano‐lightsticks: polymer nanotubes with embedded chemiluminescent dopants

AbstractAligned arrays of perylene doped poly(methyl methacrylate) nanotubes are synthesized by solution assisted template wetting. Optical studies yield well resolved absorption and photoluminescence spectra consistent with good dopant dispersion throughout the host material. True color photoluminescence images of tubes also reveal uniform, characteristic bright blue, perylene emission. Blue perylene chemiluminescence is observed from nanotubes on exposure to a mixture of aqueous hydrogen peroxide and oxalyl chloride in hexane with a rapid emission decay being consistent with a fast reaction between reagents and dopants. Finally, by monitoring the behavior of individual nanotubes, it is shown that single tubes may act as nanoscale chemiluminescent light sources.

Highly Anisotropic Luminescence from Poly(9,9-dioctylfluorene) Nanowires Doped with Orientationally Ordered β-Phase Polymer Chains

We quantitatively assess the nature and extent of emissive polymer chain organization within individual poly(9,9-dioctylfluorene) nanowires fabricated by solution-assisted template wetting. A minority fraction of planar, extended β-phase polymer chains occurs within the nanowires, which dominates their luminescence behavior. Nanowires exhibit pronounced optical birefringence and detailed polarized optical microscopy analysis indicates preferential axial alignment of polymer chains. Polarization-resolved near-field photoluminescence imaging and spectroscopy methods are employed to probe local spatial variations in light emission intensity along individual nanowires. Data indicate strong axially polarized nanowire emission, with locally measured dichroic ratios up to 8.9, consistent with preferential axial alignment of emissive β-phase polymer chains. To visualize the extent of β-phase chain alignment within a typical nanowire, we generated image maps of the orientational order parameter, ⟨P2⟩, from measured near-field emission intensity image data. Numerous domains of long-range order up to 2 μm in size with ⟨P2⟩ values ranging from 0.47 to 0.76 are identified, indicating extensive axial alignment of emissive β-phase chains within the nanowires. Poly(9,9-dioctylfluorene) nanowires exhibiting micrometer-scale order make them attractive elements for future subwavelength organic opto-electronic devices.

Fabrication of segmented nanofibers by template wetting of multilayered alternating polymer thin films

Segmented polystyrene (PS) and poly-methyl methacrylate (PMMA) nanofibers were fabricated by wetting nanoporous alumina templates with multilayered polymer thin films. The order and thickness of the polymers within the thin films affected the resulting nanofiber morphology, PS and PMMA segment properties, and created unique core-shell structure in the PMMA segments. The core-shell structure suggests a complex wetting phenomenon. Fabrication of polymer nanostructures by wetting of layered thin films opens the arena of multifunctional, one-dimensional, polymer nanostructures with segments having individual and specific functionalities.

Poly(9,9‐dioctylfluorene) Nanowires with Pronounced β‐Phase Morphology: Synthesis, Characterization, and Optical Properties

High aspect ratio, luminescent poly(9,9-dioctylfluorene) nanowires are synthesized by template wetting. Optical spectroscopic characterization indicates the formation of a significant fraction of the polymer β-phase. The results indicate that the wires essentially act as self-doped 1D nanostructures in which the PFO β-phase dominates the luminescence behavior following optical, electrochemical or electrical excitation.

Polyfluorene nanowires with pronounced axial texturing prepared by melt-assisted template wetting

Poly(9,9-dioctylfluorene) conjugated polymer nanowires were fabricated by melt-assisted wetting of porous anodic alumina templates. Analysis by high-resolution transmission electron microscopy and X-ray diffraction suggested that the polymer molecules were axially textured within the nanowires. Polarized optical microscopy images of single nanowires exhibited a pronounced optical birefringence consistent with internal axial alignment of the polymer molecules. Polarization-resolved photoluminescence images and spectra were acquired following near-field optical addressing of single nanowires. This data revealed that nanowire luminescence was markedly anisotropic with a preferred axial polarization of wire emission.

Organic Tube/Rod Hybrid Nanofibers with Adjustable Segment Lengths by Bidirectional Template Wetting

AbstractSegmented nanotubes and nanorods exhibiting a variation in their composition along their long axes represent a new and exciting class of nanomaterials. It is shown that bidirectional template wetting enables the integration of functional and complex polymeric materials into segmented nanofibers. First, a template is wetted under conditions in which a solid polymeric thread with adjustable length fills a pore segment starting from one template surface. Subsequently, a second wetting step starting from the opposite template surface yields segmented nanofibers. The exploitation of different wetting mechanisms results in the formation of tube/rod hybrid nanofibers.

Control over the hydrophobic behavior of polystyrene surface by annealing temperature based on capillary template wetting method

The wetting behavior of water droplets was studied on tunable nanostructured polystyrene (PS) surfaces fabricated by temperature-induced capillary template wetting. The surface morphology of PS varied with the annealing temperature. Contact angle (CA) measurements showed that the wettability of polystyrene surfaces could be tuned from hydrophobic (CA = 104°) to superhydrophobic (CA = 161°) by rendering different morphologies, which could be explained by two distinct wetting modes, i.e., the Wenzel and Cassie–Baxter wetting state. Meanwhile, the critical annealing temperature inducing wetting transition between the Wenzel state and Cassie–Baxter state was obtained. This approach could be easily extended to produce superhydrophobic surfaces on other thermoplastic polymers.

Synthesis of Pentacene Nanotubes by Melt-Assisted Template Wetting.

Synthesis of Pentacene Nanotubes by Melt-Assisted Template Wetting.

Synthesis of Pentacene Nanotubes by Melt-Assisted Template Wetting

We report on convenient synthesis of pentacene nanotubes with good uniformity for key parameters such as tube length (≈15 μm), outer diameter (≈350 nm), and wall thickness (≈40 nm). We also report on electrical contacting of single nanotubes. Preliminary two-terminal electrical characterization of single tube devices yields resistivities ∼ 5 × 105 Ω·m.