Low Degree Of Functionalization Research Articles

Conductivity vs functionalization in single-walled carbon nanotube films

Diazo functionalization is a chemical method that changes the conductance of metallic single-walled carbon nanotubes (SWCNTs) by disrupting the C–C double bonds. Its application to native mixtures of metallic and semiconducting SWCNTs is a promising way of large-scale production of semiconducting SWCNTs for use in electronics. This has been well studied on isolated SWCNTs, but the implications on the conductivity of SWCNT materials are still unclear. Here, we study the conductivity of such functionalized SWCNT films with a progressively decreased metallic/semiconducting ratio in a wide range of temperatures (4–300 K) to unravel the charge transport mechanisms of metallic and semiconducting SWCNT subnetworks to show how these components participate in the total conductivity of the films. At low functionalization degree (below 0.2 mol%), the conductivity is dominated by a subnetwork of metallic SWCNTs through two parallel mechanisms: a Luttinger liquid mechanism and a Variable Range Hopping process. Higher functionalization (over 0.4 mol%) destroys the Luttinger liquid mechanism, and a second parallel Variable Range Hopping process arises, attributed to the conduction through the semiconducting SWCNTs. At these high functionalization degrees, the SWCNT film behaves as a material with the desired semiconducting properties.Graphical abstractWe studied the conductivity of chemically functionalized Single Walled Carbon Nanotube films with a progressively decreased metallic/semiconducting ratio in a wide range of temperatures (4–300 K) to unravel the charge transport mechanisms of metallic and semiconducting SWCNT subnetworks to show how these components participate in the total conductivity of the films.

Ball-Milling Exfoliation of Hexagonal Boron Nitride in Viscous Hydroxyethyl Cellulose for Producing Nanosheet Films as Thermal Interface Materials

Boron nitride nanosheets (BNNS) exfoliated by physical or chemical methods frequently exhibit poor dispersity in common solvents due to incomplete exfoliation and a low degree of functionalization,...

Fatigue resistance of atomically thin graphene oxide

Under cyclic loading, while graphene can suffer from catastrophic brittle fatigue failure, graphene oxide (GO) can be engineered to improve fatigue response and possibly ductile failure. Herein, we study the fatigue response of atomically thin GO using atomistic simulations complemented by atomic force microscopy-based experiments. Analysis of the damage and failure mechanisms demonstrated a notable role of functionalization degree and ratio on the fatigue resistance of GO. In the presence of defects, GO with a low functionalization degree (<15%) exhibited a low defect sensitivity and considerably high fatigue life compared to graphene. Although a reduction in the lifetime was captured for higher functionalization degrees, enhancement in fatigue resistance was observed for epoxy-rich GO, owing to an effective crack arresting mechanism by first epoxy-to-ether transformations of the ether groups and ether-to-epoxy retransformations during loading and unloading phases of a cycle respectively, unearthed using nudged elastic band calculations. Present findings reveal molecular engineering of functional groups as a tool to tune the fatigue resistance of GO and potentially other nanomaterials, paving the way for the design of nanodevices and nanostructured materials with superior durability.

Advancing the boundaries of the covalent functionalization of graphene oxide

The synthesis of a derivatized graphene oxide with a particularly high degree of functionalization is achieved through a facile wet‑chemistry procedure. Graphene oxide is a highly reactive graphene derivative, especially with nucleophiles or dipolarophiles. However the reductive action of nucleophiles, as well as of other reactants or solvents usually prevails over functionalization. Therefore, the reactions of graphene oxide lead almost exclusively into reduced graphene derivatives with low functionalization degree. Here we report that tuning the reaction conditions during functionalization can alter the competition outcome of the two simultaneous reactions in a 1,3 dipolar cycloaddition on graphene oxide. Under these conditions, the cycloaddition pathway was dramatically favoured against the unspecific reduction/oxygen elimination side reactions, affording a selectively and densely functionalized graphene oxide. This property can be exploited for enhancing the interactions with target molecules (very effective immobilization of pharmaceutic compounds, as demonstrated here), as well as in other applications such as in preparing catalysts with high content of active sites by coordinating metal nanoparticles or atoms.

Synthesis of dextran-based chain transfer agent for RAFT-mediated polymerization and glyco-nanoobjects formulation

Glycopolymers based on dextran are frequently prepared via ATRP, whereas the use of RAFT polymerization is strangely limited due to the difficult synthesis of Dextran-based macromolecular chain transfer agent (DexCTA). The aim of this work is to establish a controlled and reproducible methodology for its preparation. Direct esterification of the hydroxyl dextran functions is the most common method. Our study shows that this latter leads to a very low degree of functionalization. As alternative, we report a reproductible multistep strategy consisting of oxidation, amination, and amidation reactions. Various DexCTAs with tunable degree of substitution (respectively 0.025, 0.045, and 0.06) were successfully prepared. As proof of concept, one of the DexCTAs was involved in the photo-mediated RAFT polymerization of hydroxypropyl methacrylate in DMSO to prepare amphiphilic Dex-g-PHPMA glycopolymers, which can self-assemble in water into monodisperse spherical nano-objects. MTT assays revealed the biocompatibility of all dextran derivatives.

Steric and Electronic Effects of Electrochemically Generated Aryl Radicals on Grafting of the Graphite Surface.

Grafting of aryl radicals generated by electrochemical reduction of aryldiazonium salts has been extensively studied on various surfaces. However, there exists two unclear aspects; the first one is the generality of the blocking ability of simple functional groups toward multilayer growth, and the second one is the electronic impact of substituent groups of aryl radicals on grafting efficiency. To address these aspects, we have studied the electrochemical functionalization of graphite using aryldiazonium salts having electron-donating or electron-withdrawing groups at the 3,4,5-positions. Atomic force microscopy investigation of the functionalized surfaces revealed the formation of monolayers for all aryldiazonium salts, and thus, nitro, carboxy, ester, methyl, and methoxy groups at the 3,4,5-positions of the benzene ring suppress polyaryl growth. The degree of grafting estimated by scanning tunneling microscopy imaging and Raman spectroscopy of the functionalized surfaces depends on the electronic state of the aryl radicals, in which the radicals with electron-donating groups show a high degree of functionalization, whereas those with electron-withdrawing groups exhibit a low degree of functionalization. We discuss several possibilities that affect grafting density. Though there are several factors, we hypothesize that one factor to explain the observed reactivity trend is the electronic property of the aryl radicals, namely, the relative position of the singly occupied molecular orbital energy levels of the aryl radicals with respect to the graphite Fermi energy level.

Tuning the functionalization degree of graphene: Determining critical conditions for inhibiting the corrosion promotion activity of graphene/epoxy nanocomposite coatings

Graphene functionalization helps to improve the barrier property of graphene-reinforced coatings, however, it may also increase the electrical conductivity of coatings and result in galvanic corrosion between coating and metal. To demonstrate that fine-tuned functionalization of graphene is vital for its applications in metal protection, reduced graphene oxide (rGO) with various functionalization degree was precisely prepared. Compared with pristine rGO, rGO with a low functionalization degree possesses an enhanced corrosion promotion activity (CPA), and rGO with a high functionalization degree exhibits an inhibited CPA. Critical functionalization degree for inhibiting the CPA of rGO/epoxy nanocomposite coatings was determined.

Proper functional modification and optimized adsorption conditions improved the DNA loading capacity of mesoporous silica nanoparticles

Packaging enough genetic materials is necessary for gene delivery, but functional modification of the carriers may affect their gene loading capacity. In this study, RGD peptide-modified mesoporous silica nanoparticles were synthesized to investigate the influences of functionalization on their DNA adsorption and desorption behaviors. Effects of the functionalization degree of the nanocarriers and the adsorption conditions including DNA concentration, pH, ionic strength and temperature were studied. The DNA adsorption of the nanocarriers were enhanced by reducing pH or adding moderate amounts of ionic salt. Compared with nonfunctional nanoparticles, nanoparticles with low degree of functionalization possessed decreased DNA adsorption capacity but increased adsorption stability. High degree of functionalization resulted in both poor adsorption capacity and stability. Systematic studies showed that the adsorption processes were spontaneous and endothermic, and could be well described by pseudo-second-order kinetic model, Langmuir and Freundlich models. In summary, the DNA loading capacity of mesoporous silica nanoparticles can be improved by proper functionalization and optimized adsorption conditions.

Branched Hydroxyl Modification of SBS Using Thiol-Ene Reaction and Its Subsequent Application in Modified Asphalt

Based on the thiol-ene radical addition reaction, the branched hydroxyl functionalized modified styrene-butadiene-styrene triblock copolymer (SBS-g-OH) was prepared using a commercially available SBS with high molecular weight and low content of 1,2-vinyls as substrate polymer, 2-mercaptoethanol (MCH) as modifying agent, 2,2-azodiisobutyronitrile (AIBN) as initiator, and 1,4-dioxane (DOA) as solvent. By the characterization of Fourier transform-infrared spectroscopy (FT-IR), and 1H nuclear magnetic resonance spectroscopy (1H NMR), the order of reactivity was proved that 1,2-vinyls had a priority to react with MCH at low functionalization degree of SBS-g-OH. A novel reaction kinetics model was set up to only describe the addition reaction between MCH and 1,2-vinyls, but not 1,4-units of PB segments, with this reaction kinetics model, the effect of reaction time, temperature, and initial concentration ratio of MCH to 1,2-vinyls on functionalization degree of SBS-g-OH were investigated, besides the desired o...

DABCO-functionalized polysulfones as anion-exchange membranes for fuel cell applications: Effect of crosslinking

A series of DABCO-functionalized polysulfones were synthesized and characterized. The effect that crosslinking has on the membrane properties containing different degrees of functionalization was evaluated. These polymers showed good thermal stability below the fuel cell operation temperature, T < 100 °C, reflected by the TOD, TFD, and thermal durability. The water uptake increased as the percentage of DABCO groups increased and the crosslinked membranes showed lower capacity to absorb water than the non-crosslinked ones favoring thus the dimensional stability of the first ones. Membranes in the chloride form containing low degree of functionalization exhibited the highest tensile strength values. The ionic conductivity of non-crosslinked membranes varied as a function of the functionalization degree until a value of around 100% achieving a maximum value at 86%. However, the crosslinked ones showed satisfactory ionic conductivities for values higher than 100%. The behavior of these polymeric materials in alkaline solutions revealed a great alkaline stability necessary to be used as solid electrolytes in fuel cells. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1326–1336

Synthesis and antimicrobial evaluation of cationic low molecular weight amphipathic 1,2,3-triazoles

A library of 28 small cationic 1,4-substituted 1,2,3-triazoles was prepared for studies of antimicrobial activity. The structures addressed the pharmacophore model of small antimicrobial peptides and an amphipathic motif found in marine antimicrobials. Eight compounds showed promising antimicrobial activity, of which the most potent compound 10b displayed minimum inhibitory concentrations of 4–8μg/mL against Streptococcus agalacticae, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Enterococcus faecalis. The simple syntheses and low degree of functionalization make these 1,4-substituted 1,2,3-triazoles interesting for further optimizations.

Graphene Oxide: A One- versus Two-Component Material.

The structure of graphene oxide (GO) is a matter of discussion. While established GO models are based on functional groups attached to the carbon framework, another frequently used model claims that GO consists of two components, a slightly oxidized graphene core and highly oxidized molecular species, oxidative debris (OD), adsorbed on it. Those adsorbents are claimed to be the origin for optical properties of GO. Here, we examine this model by preparing GO with a low degree of functionalization, combining it with OD and studying the optical properties of both components and their combination in an artificial two-component system. The analyses of absorption and emission spectra as well as lifetime measurements reveal that properties of the combined system are distinctly different from those of GO. That confirms structural models of GO as a separate oxygenated hexagonal carbon framework with optical properties governed by its internal structure rather than the presence of OD. Understanding the structure of GO allows further reliable interpretation of its optical and electronic properties and enables controlled processing of GO.

Core phosphine-functionalized amphiphilic nanogels as catalytic nanoreactors for aqueous biphasic hydroformylation

Amphiphilic phosphine-functionalized nanogel particles were synthesized by aqueous polymerization-induced self-assembly insuring a well-defined architecture as well as a narrow size distribution (average diameter of ca. 90nm in water). They were successfully applied as ligands for the biphasic hydroformylation of 1-octene catalyzed by rhodium, yielding TOFs in the 350–650h−1 range and a linear to branched aldehyde ratio of 3.5. Embedding the phosphine ligands within a cross-linked structure did not strongly impede mass transfer toward the active centers, as proved by fast metal coordination and a catalytic activity tantamount to that of higher chain mobility micelles or core-cross-linked micelles that have phosphine moieties located on flexible linear arms. However, this extended cross-linking reduced particle swelling and transfer to the organic phase, affording a significantly lowered Rh loss. For all the architectures, a low functionalization degree was preferable to achieve high activity, the selectivity remaining essentially unchanged.

Grafting Low Contents of Branched Polyethylenimine onto Carbon Fibers to Effectively Improve Their Interfacial Shear Strength with an Epoxy Matrix

The mechanical properties of carbon fiber (CF) reinforced composites are greatly dependent on the interfacial strength between the CFs and matrix. To improve the interfacial adhesion of carbon fiber/epoxy composites, branched polyethylenimine (PEI) is grafted onto the CFs treated in a mixed acid at optimized process time. The chemical compositions and bonds of functionalized CFs are characterized by thermal gravimetric analysis, Fourier‐transform infrared, and X‐ray photoelectron spectroscopy. The surface structures and morphologies of various CFs are analyzed by Raman spectroscopy and scanning electron microscopy, respectively. Microbond test is adopted to evaluate the interfacial shear strength (IFSS) between the CFs and epoxy matrix. The results show that the CFs modified by low molecular weight PEI are better than those modified by high molecular weight PEI. The IFSS of PEI modified CFs can reach a maximum of 107.2 ± 14.3 MPa at a low functionalization degree compared with 78.1 ± 11.6 MPa of unmodified CFs. The branched structure and high density of active amine groups on the PEI chains are responsible for the improved interfacial strength.

Adsorption of lysozyme on hyaluronic acid functionalized SBA-15 mesoporous silica: a possible bioadhesive depot system.

Silica-based ordered mesoporous materials are very attractive matrices to prepare smart depot systems for several kinds of therapeutic agents. This work focuses on the well-known SBA-15 mesoporous silica and lysozyme, an antimicrobial protein. In order to improve the bioadhesion properties of SBA-15 particles, the effect of hyaluronic acid (HA) functionalization on lysozyme adsorption was investigated. SBA-15 samples having high (H-SBA) and low (L-SBA) levels of functionalization were analyzed during the three steps of the preparations: (1) introduction of the -NH2 groups to obtain the SBA-NH2 samples; (2) functionalization with HA to obtain the SBA-HA matrices; (3) adsorption of lysozyme. All silica matrices were characterized through N2-adsorption/desorption isotherms, small-angle X-ray scattering, transmission electron microscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The whole of the experimental data suggests that a high level of functionalization of the silica surface allows for a negligible lysozyme adsorption mainly due to unfavorable electrostatic interactions (H-SBA-NH2) or steric hindrance (H-SBA-HA). A low degree of functionalization of the silica surface brings about a very good performance toward lysozyme adsorption, being 71% (L-SBA-NH2) and 63% (L-SBA-HA) respectively, compared to that observed for original SBA-15. Finally, two different kinetic models--a "pseudo-second order" and a "intraparticle diffusion"--were compared to fit lysozyme adsorption data, the latter being more reliable than the former.

Tracer Diffusion in Heterogeneous Polymer Networks

The diffusion of linear polymer chains in swollen polymer networks is studied with different extents of spatial heterogeneity of their crosslinking density. Structural heterogeneity is imparted to these gels by photo‐crosslinking of polymer precursor chains in semidilute solution, which comprise either just one batch of precursors, yielding gels with just a little spatial heterogeneity, or mixtures of two different batches of precursors, one with high and one with low degree of functionalization with crosslinkable moieties, yielding gels with more pronounced heterogeneity. In addition, heterogeneous gels are also prepared from crosslinkable precursor chains and defined fractions of pre‐crosslinked microgel particles that serve as doped‐in nanometer‐scale domains of high local crosslinking density. The resulting gels are probed by static light scattering and shear rheology, and the self‐diffusion of fluorescent linear tracer chains within the gels is studied by fluorescence recovery after photobleaching. The outcome of these investigations is that spatial heterogeneity of a given crosslinking density in swollen polymer networks decreases their ability to store mechanical deformation energy, but has no marked impact on the above‐micrometer‐scale diffusivity of linear tracer chains. image

Degradation Studies of Functionalized Polyphenylene Oxide for Anion Exchange Membrane

Anion exchange membranes (AEM) have garnered increased attention in recent years due to their potential use in energy conversion and storage devices. Fuel cells (FC) utilizing AEMs as the exchange media are expected to be less costly than the standard proton exchange membrane fuel cells due to the use of a less noble catalyst1. AEMs are also attractive for use in metal air batteries, which have much higher theoretical energy densities than the current generation of lithium ion batteries2. The use of an anion exchange membrane in a metal air battery would eliminate the need for liquid electrolyte, reducing the size and weight of the cell.Anion exchange membranes reported in the literature to date suffer from chemical instability in alkaline environments, which are found in both AEMFCs and metal air batteries. The chemical instability is primarily a result of the degradation of the cationic moieties responsible for the transfer of the hydroxide ions.For this work AEMs based on functionalized polyphenylene oxide (PPO) were synthesized. PPO was selected because it is commercially available, inexpensive, and demonstrates good stability in alkaline environments3,4. AEMs were made by functionalizing PPO with quaternary ammonium groups; dimethylhexylamine, dimethyldecylamine, or trimethylamine. For each of these groups a membrane was synthesized with a high and low degree of functionalization. The resulting AEMs were studied for physical and electrochemical properties and compared against a commercially available AEM.The conductivity of the membranes equilibrated in solutions between 1 and 10M potassium hydroxide and at different humidity levels was determined through electrochemical impedance spectroscopy. The equilibrium concentration of water and base within the membranes was studied. The mechanical properties of the membranes were determined with Dynamic Mechanical Analysis.Degradation of the polymers was monitored by immersing the membranes in solutions between 1 and 10M potassium hydroxide at elevated temperature. The conductivity of the membranes was measured over time to determine loss in electrical properties. Membranes were also tested in situ in anion exchange membrane fuel cells and zinc air batteries.We found that membranes based on the trimethylamine demonstrated the highest conductivity while those based on dimethyldecylamine demonstrated the greatest stability.The membranes in lower molarity solutions were found to become more brittle over time. Thin layer chromatography was conducted on the solutions in which the membranes were held during degradation studies. The results indicated that polyols were forming, indicating that the cationic groups cause the polymer to undergo a SN2 reaction. Figure 1: AEMs studied in this report: a) PPO-TMA, b) PPO-DMHA, b) PPO-DMDA Acknowledgement We gratefully acknowledge the support of ZAF Energy Systems for their support of this work.

Multi-scale modeling and synthesis of polyester ionomers

Simulations of microphase separation are carried out using the dissipative particle dynamics (DPD). By varying the concentration and temperature of resin solutions we explore mesomorphologies supported by the all-atom models. We found that for a low degree of functionalization the homogeneously distributed ionomers self-assemble into spherical micelles at solid loads below 31 wt%, subject to the activation energy barrier for the gradual growth of pre-micellar aggregates. Computed optimum aggregation numbers exhibit sensitivity to both the temperature-dependent interfacial tension and the ionic content and compare well with the experimental observations.

Distribution of functional groups in periodic mesoporous organosilica materials studied by small-angle neutron scattering with in situ adsorption of nitrogen

Periodic mesoporous materials of the type (R′O)3Si-R-Si(OR′)3 with benzene as an organic bridge and a crystal-like periodicity within the pore walls were functionalized with SO3H or SO3− groups and investigated by small-angle neutron scattering (SANS) with in situ nitrogen adsorption at 77 K. If N2 is adsorbed in the pores the SANS measurements show a complete matching of all of the diffraction signals that are caused by the long-range ordering of the mesopores in the benzene-PMO, due to the fact that the benzene-PMO walls possess a neutron scattering length density (SLD) similar to that of nitrogen in the condensed state. However, signals at higher q-values (>1 1/Å) are not affected with respect to their SANS intensity, even after complete pore filling, confirming the assumption of a crystal-like periodicity within the PMO material walls due to π–π interactions between the organic bridges. The SLD of pristine benzene-PMO was altered by functionalizing the surface with different amounts of SO3H-groups, using the grafting method. For a low degree of functionalization (0.81 mmol SO3H·g−1) and/or an inhomogeneous distribution of the SO3H-groups, the SLD changes only negligibly, and thus, complete contrast matching is still found. However, for higher amounts of SO3H-groups (1.65 mmol SO3H·g−1) being present in the mesopores, complete matching of the neutron diffraction signals is no longer observed proving that homogeneously distributed SO3H-groups on the inner pore walls of the benzene-PMO alter the SLD in a way that it no longer fits to the SLD of the condensed N2.

Isohexide Derivatives from Renewable Resources as Chiral Building Blocks

The combination of rapidly depleting fossil resources and growing concerns about greenhouse gas emissions and global warming have stimulated extensive research on the use of biomass for energy, fuels, and chemicals.[1] Although biobased chemicals have the potential to reduce the amount of fossil feedstock consumed in the chemical industry today, the most abundant type of biobased feedstock, that is, carbohydrates, is often unsuitable for current high-temperature industrial chemical processes. Compared to hydrophobic aliphatic or aromatic feedstocks with a low degree of functionalization, carbohydrates such as polysaccharides are complex, overfunctionalized hydrophilic materials. One approach to overcome these drawbacks is to reduce the number of functional groups, resulting in more stable, industrially applicable bifunctional biobased building blocks,[2] such as furan-2,5-dicarboxylic acid,[3] levulinic acid,[4] and isosorbide.[5] Isosorbide (1,4:3,6-dianhydrosorbitol) is a rigid bicyclic diol that is derived from sorbitol and can ultimately be obtained from glucose-based polysaccharides such as starch and cellulose.[6] Apart from isosorbide, in which the hydroxyl groups on C2 and C5 are in the exo and endo positions, respectively, two other isohexides are known (Figure 1): the symmetrical endo-endo isomer isomannide (1,4:3,6-dianhydromannitol) and the exo-exo isomer isoidide (1,4:3,6-dianhydroiditol), derived from d-mannitol and l-iditol, respectively.