Polymer-assisted preparation of nanoscale films of thermoelectric PbSe and PbTe and of lead chalcogenide-polymer composite films

Polymer films of polyethyleneoxide (PEO) or poly(L-lactide) (PLLA) containing a single-source precursor for either PbSe or PbTe were used to produce films of nanoparticles of these thermoelectric materials. The monomeric homoleptic chalcogenolates lead(II) bis-(2,4,6-trifluoromethylphenylselenolate) Pb[SeC(6)H(2)(CF(3))(3)](2) and lead(II) bis-[tris(trimethylsilyl)silyl-tellurolate] Pb[TeSi(SiMe(3))(3)](2) were used as single-source precursors for the thermolytic formation of the lead chalcogenides. The thickness and the quality of as-obtained thin films depended decisively on the spin-coating conditions, on the polymer, on the precursor concentration in the composite film before thermolysis and on the annealing time. Thin layers of particles of 30-50 nm size and high crystallinity were obtained. They were characterized by X-ray diffraction, thermal analysis and electron microscopy.     

Functional nanoscale additives for ultra-durable powder-coating polymers

Abstract  

Surface-modified titania nanoparticles were prepared and their suitability as additives for the long-term UV-photoprotection of polymer materials was investigated. It was demonstrated that the functionalization of nano-TiO₂ with different fatty acid and phosphonate-based grafting reagents has a beneficial effect on the long-term stability of polyester composites under accelerated weathering conditions. These results are of considerable interest for the development of robust organic–inorganic hybrid systems that can be utilized as transparent but UV-resistant protective layers for outdoor applications.     

Oligopyrenotides: chiral nanoscale templates for chromophore assembly

Getting organized: DNA-like supramolecular polymers formed of short oligopyrenotides serve as a helical scaffold for the molecular assembly of ligands. The cationic porphyrin meso-tetrakis(1-methylpyridin-4-yl)porphyrin interacts with the helical polymers in a similar way as with poly(dA:dT).     

A benchtop method for the fabrication and patterning of nanoscale structures on polymers

A benchtop method for the facile production of nanoscale metal structures on polymers is demonstrated. This approach allows for the design and patterning of a wide range of metallic structures on inexpensive polymer surfaces, affording the fabrication of nanoscaled platforms for use in the design of sensors, actuators, and disposable electronic and photonic devices. Numerous structures, from simple nanowires to multilayered metallic gratings, are demonstrated, with sizes ranging from microns to the nanoscale. The process involves molding a malleable metal film deposited on a rigid substrate such as mica, by the compression of a plastic polymer stamp with the desired pattern against the metal film. While under compression, an etchant is then used to modify the metal. Upon separation of the stamp from the support, micro- to nanoscaled metallic structures are found on the stamp and/or on the substrate. The sizes of the structures formed depend on the sizes of the features on the stamp but can be fine-tuned by about 4-fold through variations in both pressure and duration of etching. Also, depending on the processing, multiple dimension metallic structures can be obtained simultaneously in a single stamping procedure. The metallic structures formed on the stamp can also be subsequently transferred to another surface allowing for the construction of multilayered materials such as band gap gratings or the application of electrical contacts. Using this approach, fabrication of both simple and complex micro- to nanoscaled structures can be accomplished by most any researcher as even the grating structure of commercial compact disks may be used as stamps, eliminating the requirement of expensive lithographic processes to form simple structures.     

"Contact" of nanoscale stiff films

We investigated the contact behaviors of a nanoscopic stiff thin film bonded to a compliant substrate and derived an analytical solution for determining the elastic modulus of thin films. Microscopic contact deformations of the gold and polydopamine thin films (<200 nm) coated on polydimethylsiloxane elastomers were measured by indenting a soft tip and analyzed in the framework of the classical plate theory and Johnson-Kendall-Roberts (JKR) contact mechanics. The analysis of this thin film contact mechanics focused on the bending and stretching resistance of thin films and is fundamentally different from conventional indentation measurements where the focus is on the fracture and compression of the films. The analytical solution of the elastic modulus of nanoscopic thin films was validated experimentally using 50 and 100 nm gold thin films coated on polydimethylsiloxane elastomers. The technical application of this analysis was further demonstrated by measuring the elastic modulus of thin films of polydopamine, a recently discovered biomimetic universal coating material. Furthermore, the method presented here is able to quantify the contact behaviors of nanoscopic thin films, effectively providing fundamental design parameters, the elastic modulus, and the work of adhesion, crucial for transferring them effectively into practical applications.     

Surface force spectroscopy of elastomeric nanoscale films

We studied nanomechanical properties for a series of ultrathin films of elastomeric materials from polyisoprene rubbers and tri‐block styrene‐butadiene‐styrene copolymer, SEBS. As we observed, the Hertzian approximation for elastic mechanical deformation of double layer films can be used for the analysis of force‐distance data at modest indentation depths and film thickness higher than 3 nm. For thinner films, the influence of solid substrate becomes very significant. On the other hand, the applicability of the Hertzian approximation is limited by the rate dependent elastomeric deformation. We demonstrated that Johnson modification of the contact mechanics model that includes a viscoelastic contribution could be utilized to obtain reasonable fitting of loading data for elastomeric materials.     

DNA-templated assembly of nanoscale wires and protein-functionalized nanogap contacts

The use of DNA to template the assembly of nanoscale wires and protein-functionalized nanogap contacts is described: Specifically, the use of DNA to template the assembly of gold nanowires between conventionally patterned gold contacts on a silicon wafer substrate. Also described is the use of DNA to template the assembly of protein-functionalized nanogap gold contacts on a silicon wafer substrate. Of particular significance is the finding that suitably modified gold nanoparticles recognize and bind selectively the protein-functionalized nanogap and are localized there.     

Optimization of electrochemical aspects for epitaxial depositing nanoscale ZnSe thin films

Studies of the electrochemical optimization of ZnSe thin film deposition on polycrystalline Au substrates using electrochemical atomic layer epitaxy are reported. Electrochemical aspects were characterized by means of cyclic voltammetry, differential pulse voltammetry, and coulometry. To study the growth mechanism of the underpotential deposition in the formation of ZnSe, the effects of Zn and Se deposition potentials and a Se-stripping potential were adjusted to optimize the deposition program. The deposit, grown using the optimized program, was proved to be a single-phase ZnSe compound with a strong (220)-preferred orientation by X-ray diffraction analysis, and scanning electronic microscopy observation shows the deposit consisted of nanoscale particles with an average size about 100 nm. The right 1:1 stoichiometric ratio of Zn to Se according to the coulometry suggests that ZnSe is formed.     

Ultra-thin films of conjugated polymers for opto-electronic applications

Ultra-thin films of precursor polymers for poly(benzimidazole) (PBI), poly(benzoxazole) (PBO), or poly(benzthiazole) (PBT) were formed at air/water interface by spreading monomers and then polymerizing on the water surface. These thin films could be deposited onto appropriate substrates such as quartz by using the Langmuir-Blodgett (LB) method of horizontal lifting. Moreover, the heat treatment of the built-up films of the precursor polymers transformed the films into corresponding PBI, PBO, or PBT, which were high-temperature polymers. The resulting films had uniform and controllable thickness. Electronic and opto-electronic properties of these thin films were evaluated in terms of electric conductivities and nonlinear optical properties.     

Fluorescent nanoscale zinc(II)-carboxylate coordination polymers for explosive sensing

Fluorescent nanoscale coordination polymers with cubic morphology and long range ordered structure were fabricated and exhibited efficient sensing for both nitroaromatic explosive and nitromethane due to large surface area to volume ratio and strong binding affinity to explosive molecules.     

A general concept for the preparation of hierarchically structured pi-conjugated polymers

Typical biopolymers exhibit structures and order on different length scales. By contrast, the number of synthetic polymers with a similar degree of hierarchical structure formation is still limited. Starting from recent investigations on the structures of amyloid proteins as well as research activities toward nanoscopic scaffolds from synthetic oligopeptides and their polymer conjugates, a general strategy toward hierarchically structured pi-conjugated polymers can be developed. The approach relies on the supramolecular self-assembly of diacetylene macromonomers based on beta-sheet forming oligopeptides equipped with hydrophobic polymer segments. Polymerization of these macromonomers proceeds under retention of the previously assembled hierarchical structure and yields pi-conjugated polymers with multi-stranded, multiple-helical quaternary structures.     

Selective metal substitution for the preparation of heterobimetallic microporous coordination polymers

The designed synthesis of heterobimetallic microporous coordination polymers (MCPs) is reported by a strategy employing the selective replacement of a single metal in homometallic MCPs with two unique metal coordination environments: octahedral and tetrahedral. This strategy is successful in the preparation of six mixed-metal MCPs, where Co/Zn and Ni/Zn versions of MOF-4, MOF-39, and a Zn-BTEC MCP are reported.     

Multisample preparation methods for the solvent-free MALDI-MS analysis of synthetic polymers

A limitation of any current approach using solvent-free MALDI mass spectrometry is that only one sample at a time can be prepared and transferred to the MALDI-plate. For this reason, multiple-sample preparation approaches for solvent-free MALDI MS analysis of synthetic polymers were developed that are simple and practical. One approach multiplexed sample preparation by simultaneously preparing multiple samples. With this approach, as many as 384 samples could be prepared by addition of analyte, matrix, salt, and 1-mm metal beads to each well of a 384-well disposable bacti plate, capping the plate with the lid and homogenizing all samples simultaneously using a common laboratory vortex device. Besides the time savings achieved by a single vortex step for multiple samples, an additional advantage of this method relative to previously reported solvent-free preparation methods is that the mixing volume per sample is reduced, which allows a reduction in the amount of analyte required. This method, however, still requires the transfer of each homogenized sample to the MALDI plate for subsequent analysis. Here we report a novel approach that combines multiple simultaneous solvent-free sample preparation with automatic sample transfer to the MALDI target plate. This approach reduces the possibility of cross-contamination, the amount of sample and matrix consumed for an analysis, and the time required for preparation of multiple samples. These methods were shown to provide high-quality mass spectra for various synthetic polymer standards with M(n) values to 10 kDa. The methods are efficient in that small sample amounts are required, the sample/salt/matrix ratio is not critical, and the time necessary to achieve sufficient homogenization of multiple samples is less than 5 min.     

Bifunctional catalysts supported on polymers for the preparation of Bisphenol A

This work is relative to attempts for obtaining acid‐thiol supported polymers that may be used as solid bifunctional catalysts, active in the Bisphenol A synthesis. Five approaches are tested with modified sulphonic styrene‐based polymers obtained either by multi‐polymerisation in one or several steps and derivatization. The objective is to get simultaneously sufficient capacity and high selectivity, by using an adequate acid/thiol ratio, and enhanced sites accessibility via an optimisation of the morphology. Reactivity results are favourably compared to those obtained in a homogeneous process.     

Mussel adhesive protein mimetic polymers for the preparation of nonfouling surfaces

A new biomimetic strategy for modification of biomaterial surfaces with poly(ethylene glycol) (PEG) was developed. The strategy exploits the adhesive characteristics of 3,4-dihydroxyphenylalanine (DOPA), an important component of mussel adhesive proteins, to anchor PEG onto surfaces, rendering the surfaces resistant to cell attachment. Linear monomethoxy-terminated PEGs were conjugated either to a single DOPA residue (mPEG-DOPA) or to the N-terminus of Ala-Lys-Pro-Ser-Tyr-Hyp-Hyp-Thr-DOPA-Lys (mPEG-MAPD), a decapeptide analogue of a protein found in Mytilus edulis adhesive plaques. Gold and titanium surfaces were modified by adsorption of mPEG-DOPA and mPEG-MAPD from solution, after which surface analysis by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy confirmed the presence of immobilized PEG on the surface. The ability of modified surfaces to resist cell attachment was examined by culturing 3T3 fibroblasts on the surfaces for up to 14 days. Quantitative image analysis revealed that cell adhesion to mPEG-DOPA and mPEG-MAPD modified surfaces decreased by as much as 98% compared to control surfaces. Modified Ti surfaces exhibited low cell adhesion for up to 2 weeks in culture, indicating that the nonfouling properties of mPEG-DOPA and mPEG-MAPD treated surfaces persist for extended periods of time. This strategy paradoxically exploits the strong fouling characteristics of MAP analogues for antifouling purposes and may be broadly applied to medical implants and diagnostics, as well as numerous nonmedical applications in which the minimization of surface fouling is desired.     

Polylactides - degradable polymers for fibres and films

Modification of a poly(L-lactide) (PLLA) base resin, by treatment with peroxides and compounding with plasticisers, yield resins which can be processed by conventional techniques and equipment to thin blown films, fibres and nonwoven fabrics having properties comparable to those of corresponding PP and PE samples. Film samples have tensile strength between 30 and 50 MPa, elongation at break around 250%, and puncture resistance, measured as dart drop values, of 12 g/μm. Fibres can be spun to filaments or directly to nonvowen fabrics by spun-bond techniques. These fabrics have mechanical properties comparable to polypropylene materials. The polymer products are readily degraded in a compost to carbon dioxide, water and biomass.     

Layer-by-layer assembly for rapid fabrication of thick polymeric films

In the past two decades, layer-by-layer (LbL) assembly has been proven to be a convenient and versatile method to fabricate functional films. However, using traditional dipping LbL assembly to fabricate micrometer-thick films is time consuming. Compared with ultrathin films, micrometer-thick films prepared by LbL assembly possess enhanced mechanical stability, and allow deposition of a significantly increased amount of materials and the integration of multiple functions. These merits of thick films produced by LbL assembly can result in new functions and allow the functions of ultrathin films fabricated by LbL assembly to be optimized. In this tutorial review, the methods for rapid fabrication of thick polymeric films involving LbL assembly are reviewed. The functions of such films that are relevant to their micrometer thickness are discussed.