Molybdenum nitride fibers or tubes via ammonolysis of polysulfide precursor

Millimeter-sized molybdenum nitride (MoN), in the forms of fiber-like prisms or hollow tubes, has been successfully synthesized via thermal ammonolysis of molybdenum polysulfide precursor. The initial morphology of the precursor is well preserved in the final product. This method could be expanded to preparation of other fiber-like nonmetal ceramics without addition of template. The polysulfide precursor (abbreviated to PS), hydrothermally prepared at 30°C (PS1) or 150°C (PS2), was characterized by various methods for better comprehension of the sulfide-nitride topotactic conversion model.     

"On the fly" continuous generation of alginate fibers using a microfluidic device

In this paper, we introduce a new continuous production technique of calcium alginate fibers with a microfluidic platform similar to a spider in nature. We have used a poly(dimethylsiloxane) (PDMS) microfluidic device embedded capillary glass pipet as the apparatus for fiber generation. As a sample flow, we introduced a sodium alginate solution, and, as a sheath flow, a CaCl2 solution was introduced. The coaxial flows were generated at the intersection of both flows, and the sodium alginate was solidified to calcium alginate by diffusion of the Ca2+ ions during traveling through the outlet pipet. The diameter changes in the sample and sheath flow variations were examined, and the size of alginate fibers was well regulated by changing both flow rates. In addition, we have measured the elasticity of dried fibers. We evaluated the potential use of alginate fibers as a cell carrier by loading human fibroblasts during the "on the fly" fabrication process. From the LIVE/DEAD assay, cells survived well during the fiber fabrication process. In addition, we evaluate the capability of loading the therapeutic materials onto the alginate fibers by immobilized bovine serum albumin-fluorescein isothiocyanate in the fibers.     

Three‐dimensional microfabrication of protein hydrogels via two‐photon‐excited thiol‐vinyl ester photopolymerization

Engineering three‐dimensional (3D) hydrogels with well‐defined architectures has become increasingly important for tissue engineering and basic research in biomaterials science. To fabricate 3D hydrogels with (sub)cellular‐scale features, two‐photon polymerization (2PP) shows great promise although the technique is limited by the selection of appropriate hydrogel precursors. In this study, we report the synthesis of gelatin hydrolysate vinyl esters (GH‐VE) and its copolymerization with reduced derivatives of bovine serum albumin (acting as macrothiols). Photorheology of the thiol‐ene copolymerization shows a much more rapid onset of polymerization and a higher end modulus in reference to neat GH‐VE. This allowed 2PP to provide well‐defined and stable hydrogel microstructures. Efficiency of the radical‐mediated thiol‐vinyl ester photopolymerization allows high 2PP writing speed (as high as 50 mm s^?1) with low laser power (as low as 20 mW). MTT assays indicate negligible cytotoxicities of the GH‐VE macromers and of the thiol‐ene hydrogel pellets. Osteosarcoma cells seeded onto GH‐VE/BSA hydrogels with different macromer relative ratios showed a preference for hydrogels with higher percentage of GH‐VE. This can be attributed both to a favorable modulus and preferable protein environment since gelatin favors cell adhesion and albumin incurs nonspecific binding. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4799–4810     

Directional pyrolytic growth of microscale carbon fibers on electrochemically pretreated polyacrylonitrile-based carbon microfibers

Vapor-grown carbon microfibers were synthesized pyrolytically on electrochemically pretreated polyacrylonitrile-based carbon microfibers (PAN-CFs) without introducing any catalyst. Cyclohexane was used as the carbon source for the growth of fibers in a thermal chemical vapor deposition process (CVD). Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used for the characterization of the fibers. Microscale carbon fibers with about 1 to 2 μm in diameter were formed at 1123 K, while carbon microfibers of about 0.3 μm in diameter were synthesized at 1048 K. A pretreatment at negative potential or sequentially at both positive and negative potentials was found to be a prerequisite for the growth of carbon microfibers in the CVD process. Without electrochemical pretreatment or when only a positive potential was applied, the growth of microscale carbon fibers did not occur. Correspondence: Michael Bron, Analytische Chemie – Elektroanalytik und Sensorik, Ruhr-Universit?t Bochum, Universit?tsstr. 150, 44780 Bochum, Germany     

Facile preparation of antibacterial polymer coatings via thiol-yne click photopolymerization

Novel antibacterial polymer coatings were prepared by a facile thiol-yne click photopolymerization of 1-propargyl-3-alkyl-1,3-diazanyl-2,4-cyclopentadiene bromide ([PAIM]Br) and tetra(3-mercapto-propionate) pentaerythritol (PETMP) (2:1 molar ratio) using 2,2-dimethoxy-2-phenylacetophenone (DMPA) as initiator. The antibacterial activity of the coatings was tested against Staphylococcus aureus (ATCC 292130) and Escherichia coli (ATCC 25922) by the dynamic shake method. The evaluation results revealed the antibacterial polymer coatings exhibited excellent inhibitory activity against S. aureus and E. coli, especially for S. aureus.     

Studying molecular interactions via capillary electrophoresis and microscale thermophoresis: A review

The process of choosing the most proper technique for studying the molecular interactions is based on critical factors such as instrumentation complexity, automation, experimental procedures, analysis time, consumables, and cost-value. This review has tracked the use of affinity capillary electrophoresis (ACE) and microscale thermophoresis (MST) techniques in the evaluation of molecular binding among different molecules during the 5 years 2016–2021. ACE has proved to be an attractive technique for biomolecular characterization with high resolution efficiency where small variations in several controlling factors can much improve such efficiency compared to other analytical techniques. Meanwhile, MST has proved its higher sensitivity for smaller amounts of complex non-purified biosamples without affecting its robustness while providing high through output. However, the main motivation to review both techniques in the proposed review was their capability to carry out all experiments without the need for immobilizing one interacting partner, besides a great flexibility in the use of buffering systems. The proposed review demonstrates the importance of both techniques in different areas of life sciences. Moreover, the recent advances in exploiting ACE and MST in other research interests have been discussed.     

In situ fabrication of polyacrylate/nanozirconia hybrid material via frontal photopolymerization

Frontal photopolymerization was applied to fabricate polymer/nanozirconia hybrid material by using acrylates as polymerizable components and tetrabutyl zirconate (TBZ) as the precursor of nanozirconia, respectively. The nanozirconia particles were in-situ generated with the polymerization front traveling and gradiently dispersed in the simultaneously formed polymer rod. The iodonium salt was utilized as photoacid generator to produce protonic acid and drive TBZ into nanozirconia particles. With the frontal polymerization traveling downward, the particle size and concentration of zirconia increased, but layer-resolved conversion of TBZ decreased. The particle size of zirconia could be reduced remarkably by the protection of monoalkyl titanate bearing six long chains. The refractive index of the hybrid rod was found to increase from top to down. The top–down layer-resolved storage modulus of the hybrid rod increased due to nanoparticle filling effect but decreased beyond the depth of 4 cm from the top, which may be ascribed to particle aggregation. This project is supported by the National Natural Science Foundation of China (grant no. 20304019, 60378029).     

Preparation of submicron polypyrrole/poly(methyl methacrylate) coaxial fibers and conversion to polypyrrole tubes and carbon tubes

In an effort to prepare electrically conductive nanofiber and nanotube materials, polypyrrole/poly(methyl methacrylate) coaxial fibers have been prepared using polymer fibers produced from an electrospinning process. Poly(methyl methacrylate) (PMMA) fibers with an average diameter of 230 nm were initially fabricated by electrospinning as core materials. The PMMA fibers were subsequently coated as templates with a thin layer of polypyrrole (PPy) by in-situ deposition of the conducting polymer from aqueous solution. Hollow PPy tubes were produced by dissolution of the PMMA core from PPy/PMMA coaxial fibers. High-temperature (1000 degrees C) treatment under inert atmosphere converted PPy/PMMA coaxial fibers into carbon tubes by complete decomposition of PMMA fiber core and carbonization of the PPy wall. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and FT-IR spectroscopy confirmed the formation of the PPy/PMMA coaxial fibers, PPy tubes, and carbon tubes.     

Polymer nanostructure development of fluorinated and aliphatic monoacrylates in smectic liquid crystals via photopolymerization

To develop viable polymer stabilized liquid crystal systems, it is crucial to understand the factors that affect polymer nanostructure evolution. This work examines the influence of the photopolymerization of aliphatic and fluorinated monoacrylate monomer within a room temperature smectic liquid crystal (LC). Additionally, the effect of LC order on polymerization kinetics, monomer and polymer organization, and the effect of the polymer on LC properties have been examined. Through this work, insight has been gained regarding the impact that the introduction of a fluorinated monoacrylate monomer has on polymerization kinetics, LC organization, and monomer/polymer segregation and organization within a polymer/LC system. Fluorinated moieties lower the surface energy of the monomer to enhance segregation between the smectic layers of the LC as compared with an analogous aliphatic monomer. Additionally, the enhanced segregation significantly increases the polymerization rate in the smectic phase and drives the continued segregation of the fluorinated polymer during and after polymerization. Fluorination also leads to the formation of an ordered polymer nanostructure if polymerized in ordered LC phases. This ordering is particularly evident when the fluorinated monomer is polymerized in the smectic phase in which the monomer is organized between the smectic layers of the LC. In addition, the ordered polymer structure found with the fluorinated monomer in the smectic phase leads to continued birefringence above the clearing point of the LC due to surface interactions between the LC and the ordered fluorinated polymer. The continued birefringence offers an exceptional opportunity to examine how factors such as polymer molecular mass and UV light intensity affect the overall polymer morphology of these polymer/LC systems. As the initiator concentration and UV light intensity are decreased, longer polymer chains form lattice-type morphologies; whereas, shorter polymer chains form smoother morphologies that more closely mirror the texture of the LC smectic phase.     

Polymer nanostructure development of fluorinated and aliphatic monoacrylates in smectic liquid crystals via photopolymerization

To develop viable polymer stabilized liquid crystal systems, it is crucial to understand the factors that affect polymer nanostructure evolution. This work examines the influence of the photopolymerization of aliphatic and fluorinated monoacrylate monomer within a room temperature smectic liquid crystal (LC). Additionally, the effect of LC order on polymerization kinetics, monomer and polymer organization, and the effect of the polymer on LC properties have been examined. Through this work, insight has been gained regarding the impact that the introduction of a fluorinated monoacrylate monomer has on polymerization kinetics, LC organization, and monomer/polymer segregation and organization within a polymer/LC system. Fluorinated moieties lower the surface energy of the monomer to enhance segregation between the smectic layers of the LC as compared with an analogous aliphatic monomer. Additionally, the enhanced segregation significantly increases the polymerization rate in the smectic phase and drives the continued segregation of the fluorinated polymer during and after polymerization. Fluorination also leads to the formation of an ordered polymer nanostructure if polymerized in ordered LC phases. This ordering is particularly evident when the fluorinated monomer is polymerized in the smectic phase in which the monomer is organized between the smectic layers of the LC. In addition, the ordered polymer structure found with the fluorinated monomer in the smectic phase leads to continued birefringence above the clearing point of the LC due to surface interactions between the LC and the ordered fluorinated polymer. The continued birefringence offers an exceptional opportunity to examine how factors such as polymer molecular mass and UV light intensity affect the overall polymer morphology of these polymer/LC systems. As the initiator concentration and UV light intensity are decreased, longer polymer chains form lattice-type morphologies; whereas, shorter polymer chains form smoother morphologies that more closely mirror the texture of the LC smectic phase.     

Monolayers of diphenyldiacetylene derivatives: Tuning molecular tilt angles and photopolymerization efficiency via electrodeposited Ag interlayer on Au

An electrodeposited Ag adlayer (upd, underpotential deposition) is utilized to improve monolayer photopolymerization of diphenyldiacetylene derivatives (DPDAs) that would otherwise exhibit no polymerization in solid state. Topochemical reaction of diacetylene derivatives via solid-state 1,4-addition yields polydiacetylenes which are of great importance due to properties associated with their ene-yne conjugated backbones. The polymerization efficiency heavily depends on the molecular arrangement in the crystals. For example, crystals of most DPDA derivatives show no activity for topochemical reaction because the bulky phenyl end groups space out the triple bonds and thus DPDAs require relatively large translation and rotation angles for polymerization. In principle, topochemical reaction is viable if molecules are in optimal arrangement. The upd interlayer can be applied to tune the adsorbate-substrate interactions, intermolecular spacing, and the molecular tilt angle by controlling the coverage of the Ag adlayer. It is thus possible to manipulate the molecular arrangement of DPDAs for the subsequent polymerization. Successful photopolymerization of DPDA monolayers is realized from the decrease in nu(C[triple bond]C) intensity by infrared reflectance absorbance spectroscopy, growth of ene-yne pi-pi* transition by UV-vis measurements, and enhanced electrochemical stability by the cathodic desorption protocol. The optimal efficiency of polymerization takes place on upd-modified substrates that can generate approximately 45 degrees tilt angle for DPDA derivatives.     

Enhancing cationic ring‐opening photopolymerization of cycloaliphatic epoxides via dark cure and oxetanes

Due to the longevity of the cationic active centers, cationic ring‐opening photopolymerization can continue after illumination ceases. In addition, substantial reactivity enhancement for epoxides is realized through copolymerization with oxetanes. Here, the separate reactions of epoxide and oxetane moieties were resolved during illumination and subsequent dark cure via real‐time Raman spectroscopy. Using oxetane additives, reactivity and conversion of 3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate (EEC) were improved during illumination and subsequent dark cure through modulation of the initial formulation viscosity and selection of the oxetane secondary functional groups. The largest enhancement in reactivity occurred with secondary groups comprising either aliphatic chains with their flexibility or hydroxyls with their chain‐transfer capacity. In contrast, oxetanes containing UV‐absorbing phenyl rings reduced the initiation efficiency, and difunctional oxetanes suppressed overall conversion through additional crosslinking. Although bulk conversion was directly related to initial formulation viscosity, the impact of the oxetane secondary functional groups was greater. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1436–1445     

Preservation of the biofunctionality of DNA and protein during microfabrication

Microfabrication processes, especially in silicon, are not compatible with biomolecules. Silicon and metal-based materials having crystalline structures are manipulated under harsh conditions with acids, bases, and organic solvents at high temperature. In comparison, organic biomolecules such as DNA and proteins have complex, three-dimensional structures and are sensitive to denaturation, oxidation, hydrolysis, and thermal destruction. Here, we report on the integration of DNA and the biotin-binding protein NeutrAvidin into microfabrication processes by using a novel approach based on a gold passivation mask. Our data show that this passivation method preserves approximately 84% of the biofunctionality of DNA and approximately 30% of that of NeutrAvidin under harsh process conditions. This novel technology enables the integration of DNA, proteins, and potentially other biological molecules into mass scalable microfabrication processes for biomedical devices, biochips, biosensors, and microelectromechanical systems with biomolecules (BioMEMS).     

Continuous silica coatings on glass fibers via bioinspired approaches

Simple methods for producing continuous inorganic coatings on fibers have application in multiple technologies. The application of bioinspired strategies for the formation of particulate inorganic materials has been widely investigated and provides routes to inorganic materials under environmentally benign conditions. In this work, we describe the formation of stable and continuous inorganic coatings on glass fibers via the polymerization of silica in the presence of biopolymers. The formation of both organic and inorganic coatings was investigated via X-ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray analysis. The simple route to silica coatings presented herein could be interesting for the development of functional hybrid fibrous materials suitable for catalytic and sensor applications, given the homogeneous nature of the silica films and the benign conditions employed for film formation.     

Reversible hydrophobization and lipophobization of cellulose fibers via trifluoroacetylation

The surface modification of cellulose fibers with trifluoroacetic anhydride (TFAA) was studied using the heterogeneous cellulose/TFAA/pyridine/toluene system. The degree of substitution (DS) of the ensuing trifluoroacetylated fibers ranged from 0.04 to 0.30. This treatment conferred a high degree of both hydrophobicity and lipophobicity on the fibers' surface, even at low DS values. Both the dispersive and the polar contributions to the surface energy were drastically reduced. However, the original cellulose hydrophilicity could be readily restored through hydrolysis, by treating the modified fibers with neutral water.     

Improved diffusion Monte Carlo for bosonic systems using time-step extrapolation "on the fly"

A diffusion Monte Carlo algorithm employing "on the fly" extrapolation with respect to the time step is implemented and demonstrated simulating realistic systems. Significant advantages are obtained when using on the fly extrapolation, leading to reduced systematic and statistical errors. The sound theoretical basis of extrapolation on the fly is discussed and compared to justifications for the a posteriori extrapolation.     

"Click" on tubes: a versatile approach towards multimodal functionalization of SWCNTs

Organic functionalization of carbon nanotube sidewalls is a tool of primary importance in material science and nanotechnology, equally from a fundamental and an applicative point of view. Here, an efficient and versatile approach for the organic/organometallic functionalization of single-walled carbon nanotubes (SWCNTs) capable of imparting multimodality to these fundamental nanostructures, is described. Our strategy takes advantage of well-established Cu-mediated acetylene-azide coupling (CuAAC) reactions applied to phenylazido-functionalized SWCNTs for their convenient homo-/heterodecoration with a number of organic/organometallic frameworks, or mixtures thereof, bearing terminal acetylene pendant arms. Phenylazido-decorated SWCNTs were prepared by chemoselective arylation of the CNT sidewalls with diazonium salts under mild conditions, and subsequently used for the copper-mediated cycloaddition protocol in the presence of terminal acetylenes. The latter reaction was performed in one step by using either single acetylene derivatives or equimolar mixtures of terminal alkynes bearing either similar functional groups (masked with orthogonally cleavable protecting groups) or easily distinguishable functionalities (on the basis of complementary analytical/spectroscopic techniques). All materials and intermediates were characterized with respect to their most relevant aspects/properties by TEM microscopy, thermogravimetric analysis coupled with MS analysis of volatiles (TG-MS), elemental analysis, cyclic voltammetry (CV), Raman and UV/Vis spectroscopy. The functional loading and related chemical grafting of both primary amino- and ferrocene-decorated SWCNTs were spectroscopically (UV/Vis, Kaiser test) and electrochemically (CV) determined, respectively.