Effect Of Chemical Functionalization Research Articles

Functionalization of Multi-Wall Carbon Nanotubes in Chemical Solution of H<sub>2</sub>SO<sub>4</sub>/HNO<sub>3</sub> and its Dispersion in Different Media

The usage of multi-wall carbon nanotubes (MWCNTs) as reinforcement has been limited due to difficulties associated with dispersion of MWCNTs during the processing and poor adhesion between MWCNTs and matrix. In this paper, the effect of chemical functionalization with strong acid on the dispersion of MWCNTs were studied. The functionalization of MWCNTs were performed in chemical solution of sulphuric acid (H2SO4) and nitric acid (HNO3) with ratio of 3:1 and prepared at 80°C for 4 hours. The pristine MWCNTs (PMWCNTs) and acid treated MWCNTs (AMWCNTs) were analyzed using TEM, XRD, FTIR and Pycnometer density. The effect of dispersion of PMWCNTs and AMWCNTs was studied in three different matrices which are in aqueous media (distilled water), metal matrix and polymer matrix. The XRD results determined that the impurities in pristine MWCNTs such as NiZn3 have been removed after the purification process. The presence of carboxylic acid (-COOH) and hydroxyl (-OH) functional groups were determined using FT-IR. Based on the dispersion analysis in aqueous media, PMWCNTs were poor in suspension stability. While, the TEM images showed less agglomeration of the AMWCNTs compared to PMWCNTs and obtained a uniform dispersion in metal matrix (Cu) and polymer (epoxy) matrix composites.

Aggregation induced emission (AIE) active carbazole styryl fluorescent molecular rotor as viscosity sensor

AbstractThe carbazole styryl based fluorescent molecular rotors (FMRs) with different chemical functionalities at C=C bond were synthesized and characterized spectroscopically. These compounds exhibits bright solid state fluorescent and also exhibits aggregation induced emission (AIE) and fluorescent response towards viscosity. Apart from traditional p‐(dialkylamino)‐benzylidene malonitriles motifs, we have used carbazole styryl dyes as viscosity sensors. In this study we have discussed about the effect of chemical functionalities/ substituents on the fluorescent properties, aggregation induced emission (AIE) and viscosity sensitivity. These compounds can find potential applications in biomedical field as fluorescent molecular rotors for viscosity determination.

Characterization at Atomic Resolution of Carbon Nanotube/Resin Interface in Nanocomposites by Mapping sp 2-Bonding States Using Electron Energy-Loss Spectroscopy.

Functionalization is critical for improving mechanical properties of carbon nanotubes (CNTs)/polymer nanocomposites. A fundamental understanding of the role of the CNT/polymer interface and bonding structure is key to improving functionalization procedures for higher mechanical performance. In this study, we investigated the effects of chemical functionalization on the nanocomposite interface at atomic resolution to provide direct and quantifiable information of the interactions and interface formation between CNT surfaces and adjacent resin molecules. We observed and compared electronic structures and their changes at the interfaces of nonfunctionalized and functionalized CNT/polymer nanocomposite samples via scanning transmission electron microscopy and electron energy-loss spectroscopy (EELS) spectrum imaging techniques. The results show that the state of sp 2 bonding and its distribution at the CNT/resin interface can be clearly visualized through EELS mapping. We found that the functionalized CNT/polymer samples exhibited a lower fraction of sp 2 bonding and a lower π*/σ* ratio compared with the nonfunctionalized cases. A good correlation between near-edge fine structures and low-loss plasmon energies was observed.

(Invited) Fluorescent Quantum Defects in Carbon Nanotubes

Fluorescent quantum defects that can be synthetically incorporated into semiconducting carbon nanotubes have opened up exciting new opportunities to imaging, sensing, and single photon generation. In this talk, we will discuss chemical strategies to create this new class of synthetic quantum structures. We will also present new progress in experimentally probing quantum defects and fundamentally understanding the effects of chemical functionalization on low dimensional carbon materials.

Effect of functionalization and charging on resonance energy and radial breathing modes of metallic carbon nanotubes

While changes in resonant Raman scattering measurements are commonly used to measure the effect of chemical functionalization on single-walled carbon nanotubes, the precise effects of functionalization on these spectra have yet to be clearly identified. In this density functional theory study, we explore the effects of functionalization on both the nanotube resonance energy and frequency shifts in radial breathing mode. Charge transfer effects cause a shift in the first Van Hove singularity spacings, and hence resonance excitation energy, and lead to a decrease in the radial breathing mode frequency, notably when the Fermi level decreases. By varying stochastically the effective mass of carbon atoms in the tube, we simulate the mass effect of functionalization on breathing mode frequency. Finally, full density functional calculations are performed for different nanotubes with varying functional group distribution and concentration using fluorination and hydrogenation, allowing us to determine overall effect on radial breathing mode and charge transfer. The results concur well with experiment, and we discuss the importance when using Raman spectroscopy to interpret experimental functionalization treatments.

Characterizing nanotube–polymer interaction using molecular dynamics simulation

Theoretical characterization of the interaction between Carbon nanotube (CNT) and surrounding polymer is presented in this article using molecular dynamics simulation. Firstly, isolated non-defected and defected CNTs are simulated. The reduction level in Young’s modulus of CNT is analyzed due to the induced vacancy defects in CNT nanostructure. Then, embedded CNT in polymer is simulated focusing on the CNT and polymer interaction. The effect of chemical functionalization on mechanical properties of nanocomposites is discussed at micro level. Stochastic analysis is conducted treating numbers of established covalent bonds between CNT and polymer and their positions as random parameters. Young’s modulus of the interphase region as an intermediate phase between CNT and polymer for continuum modeling is extracted. It is revealed that increasing numbers of transverse covalent bonds between CNT and polymer, Young’s modulus of the nanocomposites decreases arisen from induced vacancy defects in CNT. Although functionalization can improve the interfacial shear strength between CNT and polymer, it has a disadvantage in reducing Young’s modulus of the interphase region leading to weak stress transferring from resin to CNT.

Poly-functional porous-organic polymers to access functionality – CO2 sorption energetic relationships

Poly-functional porous organic polymers are constructed to probe the effect of chemical functionality on the observed Qst for CO2.

Adaptive PEG–PDMS Brushes: Effect of Architecture on Adhesiveness in Air and under Water

The design of multifunctional materials with tailored wetting and adhesion properties under different environmental conditions (dry or wet air, water, or extremely cold conditions/icing) is of paramount importance. It is still a challenging task to produce intelligent materials that are sticky/nonsticky only when it is desired. Controlled surface design based on the understanding of the effects of chemical functionality and polymer architectures can help to solve this problem. In this paper we report on the synthesis of adaptive PEG–PDMS brushes with different architectures (random copolymer and block copolymer) and investigation of their effect on the wettability and adhesiveness in wet and under water conditions. This study contributes to the development of materials with reversibly switchable and adaptive adhesiveness under controlled environmental conditions.

Effect of multiwalled carbon nanotube loading on the properties of Nafion® membranes

Abstract

Effect of chemical functionalization on the mechanical properties of polypropylene hollow fiber membranes

ABSTRACTChemical treatment of polymeric hollow fiber membranes (HFMs) is used to prepare their exterior surfaces for coatings. Typical treatments can cleave both CC and CH bonds of polypropylene, leading to lower mechanical strength of the fibers. This study evaluated the yield strength, maximum strain, ultimate tensile strength, and burst strength of HFMs treated with each of three common oxidizing reagents: ozone as a gas phase system, aqueous solutions of potassium persulfate, and ammonium persulfate for liquid phase systems. The yield strength and ultimate tensile strength of HFMs decreased continuously with increasing ozonation time. Batch treatments with aqueous oxidizing systems showed limiting values of the yield and ultimate tensile strengths with time. Swelling the hollow fibers with methanol prior to oxidation caused less reduction of the mechanical properties after persulfate treatment. Fibers pretreated with methanol showed lower losses of mechanical properties strength with aqueous oxidation systems. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1366–1373

Enhanced dispersion of lignin in epoxy composites through hydration and mannich functionalization

ABSTRACTLignin was used as a biobased fill material to create epoxy composites. Lignin was incorporated into diglycidyl ether of bisphenol A–based epoxy using hydration and Mannich functionalization. The effects of chemical functionalization on the interfacial chemistry of lignin are examined, and the corresponding changes in materials properties are examined. Several types of lignin–epoxy composites were formed through dissolution of lignin in aliphatic amine. Lignin–amine solutions were modified through hydration and the Mannich reaction and were used to cure the epoxy. The resulting composites exhibited two‐phase microstructures containing lignin‐rich agglomerates. Thermomechanical properties were examined using dynamic mechanical analysis, differential scanning calorimetry, and fracture testing. Morphological and chemical changes were examined using scanning electron microscopy and Fourier transform infrared spectroscopy. The hydrated lignin samples showed similar glass transitions and mechanical properties to the neat epoxy samples. Interactions between water and the Mannich functionalized lignin decreased the glass transition temperature and mechanical properties of the highly hydrated Mannich reacted lignin samples because of a plasticization effect. Fracture testing was conducted on the samples and showed that the yield strength and elastic modulus were similar to the neat epoxy, but the fracture toughness decreased in the lignin‐containing specimen. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41263.

Allyl-Functionalization enhanced thermally stable graphene/fluoroelastomer nanocomposites

Development of new elastomers with novel functionality has continued since their discovery in order to meet industrial and defense needs in harsh environments. The recent advance of carbon nanomaterials inspired innovative material design strategies and enable more effective production of high-performance elastomers. In this paper, the free radical initiated crosslinking reaction in graphene/fluoroelastomer nanocomposites was studied and the effects of chemical functionalization of graphene nanosheets were analyzed. It indicated that graphene oxide (GO) enhanced fluoroelastomer nanocomposites demonstrated poor high-temperature stability due to the pyrolysis at around 200 °C. In contrast, reduced graphene oxide (RGO) enhanced fluoroelastomer exhibited good thermal stability, but RGO didn't participate in the crosslinking, resulting in very limited improvement in mechanical properties. In this paper, reduced allyl functionalized graphene was studied for the first time to enhance free radical initiated elastomers. The reduced allyl functionalization of graphene was demonstrated to impart superior thermal stability and enhanced mechanical properties to the elastomer matrices. The study of vulcanization kinetics provided insights that the allyl functional groups participated in and accelerated the crosslinking. These results indicated a scalable method to incorporate the advantages of graphene into polymer matrices through free radical reaction. The discovery is very promising to be used in the industry to fabricate gaskets, o-rings, and membranes for high temperature applications.

Chemical functionalization for improving dispersion and interfacial bonding of halloysite nanotubes in epoxy nanocomposites

The effects of chemical functionalization of halloysite nanotubes (HNTs) on dispersion, interfacial interaction, and mechanical properties of epoxy nanocomposites were investigated. HNT-filled epoxy nanocomposites were fabricated and their morphology and mechanical properties were systematically studied; the results were compared with those for neat epoxy resin. Transmission electron microscopic micrographs revealed uniform morphologic dispersion of functional HNTs in the epoxy matrix. The interfacial interaction between functional HNTs and the epoxy matrix was shown by differential scanning calorimetry and scanning electron microscopy analyses. The reaction between the functional amine--terminated groups of HNTs and epoxy monomers improved the dispersion of HNTs and the interfacial adhesion between HNTs and epoxies. The functional HNT-filled epoxy nanocomposites showed improved mechanical properties compared with the as-received HNT-filled nanocomposites. This was attributed to better dispersion and stronger interfacial interaction.

Luminescent carbon nanoparticles: effects of chemical functionalization, and evaluation of Ag+ sensing properties

Luminescent carbon-based nanoparticles, addressed as carbon dots (CDs), were synthesized at relatively low temperature from lactose following an easy and inexpensive procedure. Modification of their surface was done by functionalization with mercaptosuccinic acid (MSA) (CDs–MSA). Transmission electron microscopy images showed regular spherical nanoparticles of 5 nm diameter. Raw and functionalized (CDs–MSA) CDs were highly fluorescent at 448 and 472 nm, with relative high quantum yield (Φ = 0.21 and 0.46 respectively). At the maximum fluorescence of CDs–MSA the intensity was quenched by addition of Ag+ ions by a static mechanism with a Stern–Volmer constant of 3.7 × 103 M−1. The analysis of the emission spectra showed that the CD–MSA complex was stable after this process. The quenching profiles showed that only 44% of the CD–MSA fluorophores are accessible to Ag+. The main figures of merit were detection and quantification limits of 385.8 nM and 1.2 μM respectively, and the precision as relative standard deviation was 1.76%. No interference was observed when other metal ions were present indicating a high selectivity for Ag+ detection. The results showed that CDs–MSA can be used for efficient quantification of Ag+ in silver nanoparticle dissolution.

Poly(lactic acid) composites with poly(lactic acid)‐modified carbon nanotubes

ABSTRACTThis work reports the study of the effect of chemical functionalization of carbon nanotubes on their dispersion in poly(lactic acid). The nanotubes were functionalized by the 1,3‐dipolar cycloaddition reaction, generating pyrrolidine groups at the nanotube surface. Further reaction of the pyrrolidine groups with poly(lactic acid) was studied in solution and in the polymer melt. The former involved refluxing the nanotubes in a dimethylformamide/polymer solution; the latter was carried out by direct melt mixing in a microcompounder. The carbon nanotubes collected after each process were characterized by thermogravimetry and by X‐ray photoelectron spectroscopy, showing evidence of polymer bonded to the nanotube surface only when the reaction was carried out in the polymer melt. The composites with polymer modified nanotubes present smaller average agglomerate area and a narrower agglomerate area distribution. In addition, they show improved tensile properties at low CNT concentration and present lower electrical resistivity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3740–3750

Organic Molecules as Tools To Control the Growth, Surface Structure, and Redox Activity of Colloidal Quantum Dots

In order to achieve efficient and reliable technology that can harness solar energy, the behavior of electrons and energy at interfaces between different types or phases of materials must be understood. Conversion of light to chemical or electrical potential in condensed phase systems requires gradients in free energy that allow the movement of energy or charge carriers and facilitate redox reactions and dissociation of photoexcited states (excitons) into free charge carriers. Such free energy gradients are present at interfaces between solid and liquid phases or between inorganic and organic materials. Nanostructured materials have a higher density of these interfaces than bulk materials. Nanostructured materials, however, have a structural and chemical complexity that does not exist in bulk materials, which presents a difficult challenge: to lower or eliminate energy barriers to electron and energy flux that inevitably result from forcing different materials to meet in a spatial region of atomic dimensions. Chemical functionalization of nanostructured materials is perhaps the most versatile and powerful strategy for controlling the potential energy landscape of their interfaces and for minimizing losses in energy conversion efficiency due to interfacial structural and electronic defects. Colloidal quantum dots are semiconductor nanocrystals synthesized with wet-chemical methods and coated in organic molecules. Chemists can use these model systems to study the effects of chemical functionalization of nanoscale organic/inorganic interfaces on the optical and electronic properties of a nanostructured material, and the behavior of electrons and energy at interfaces. The optical and electronic properties of colloidal quantum dots have an intense sensitivity to their surface chemistry, and their organic adlayers make them dispersible in solvent. This allows researchers to use high signal-to-noise solution-phase spectroscopy to study processes at interfaces. In this Account, I describe the varied roles of organic molecules in controlling the structure and properties of colloidal quantum dots. Molecules serve as surfactant that determines the mechanism and rate of nucleation and growth and the final size and surface structure of a quantum dot. Anionic surfactant in the reaction mixture allows precise control over the size of the quantum dot core but also drives cation enrichment and structural disordering of the quantum dot surface. Molecules serve as chemisorbed ligands that dictate the energetic distribution of surface states. These states can then serve as thermodynamic traps for excitonic charge carriers or couple to delocalized states of the quantum dot core to change the confinement energy of excitonic carriers. Ligands, therefore, in some cases, dramatically shift the ground state absorption and photoluminescence spectra of quantum dots. Molecules also act as protective layers that determine the probability of redox processes between quantum dots and other molecules. How much the ligand shell insulates the quantum dot from electron exchange with a molecular redox partner depends less on the length or degree of conjugation of the native ligand and more on the density and packing structure of the adlayer and the size and adsorption mode of the molecular redox partner. Control of quantum dot properties in these examples demonstrates that nanoscale interfaces, while complex, can be rationally designed to enhance or specify the functionality of a nanostructured system.

Efficient cyanoaromatic photosensitizers for singlet oxygen production: synthesis and characterization of the transient reactive species

In order to graft cyanoaromatic molecules onto various inert supports, we designed two new cyanoanthracene derivatives of benzo[b]triphenylene-9,14-dicarbonitrile (DBTP, 1), which already demonstrated good photosensitizing properties. We synthesized 3-(N-hydroxypropyl)carboxamido-9,14-dicyanobenzo[b]triphenylene, 3 and 3-(N-N0-Boc-aminohexyl)carboxamido-9,14-dicyanobenzo[b]triphenylene, 4 and compared their photophysical properties in acetonitrile relative to those of the parent compound 1 and its carboxylic derivative 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid, 2. The transient species were analysed and the quantum yields of singlet oxygen production (ΦΔ) determined in acetonitrile. The effect of chemical functionalization can be considered negligible, since absorption spectra, fluorescence emission spectra and fluorescence lifetimes do not significantly change with the substituent. The triplet-triplet absorption spectra and the triplet excited state lifetimes are similar for the whole series. For compounds 1-4 high values of ΦΔ, close to that of the standard sensitizer 1H-phenalen-1-one (PN, ΦΔ ≈ 1), and higher than that of the well-known photosensitizer 9,10-dicyanoanthracene (DCA), are due to very efficient intersystem crossing from the singlet to the triplet excited state and subsequent energy transfer to ground state oxygen ((3)O2). They belong to a class of very efficient photosensitizers, absorbing visible light and stable under irradiation, they may be functionalized without significant changes to their photophysical behaviour, and grafted onto various supports.

Quantification of Carbon Nanomaterials in Vivo

A diverse array of carbon nanomaterials (NMs), including fullerene, carbon nanotubes (CNTs), graphene, nanodiamonds, and carbon nanoparticles, have been discovered and widely applied in a variety of industries. Carbon NMs have been detected in the environment and have a strong possibility of entering the human body. The safety of carbon NMs has thus become a serious concern in academia and society. To achieve strict biosafety assessments, researchers need to fully understand the effects and fates of NMs in the human body, including information about absorption, distribution, metabolism, excretion, and toxicity (ADME/T). To acquire the ADME data, researchers must quantify NMs, but carbon NMs are very difficult to quantify in vivo. The carbon background in a typical biological system is high, particularly compared with the much lower concentration of carbon NMs. Moreover, carbon NMs lack a specific detection signal. Therefore, isotopic labeling, with its high sensitivity and specificity, is the first choice to quantify carbon NMs in vivo. Previously, researchers have used many isotopes, including ¹³C, ¹⁴C, ¹²⁵I, ¹³¹I, ³H, ⁶⁴Cu, ¹¹¹In, ⁸⁶Y, 99mTc, and ⁶⁷Ga, to label carbon NMs. We used these isotopic labeling methods to study the ADME of carbon NMs via different exposure pathways in animal models. Except for the metabolism of carbon NMs, which has seldom been investigated, significant amounts of data have been reported on the in vivo absorption, distribution, excretion, and toxicity of carbon NMs, which have revealed characteristic behaviors of carbon NMs, such as reticuloendothelial system (RES) capture. However, the complexity of the biological systems and diverse preparation and functionalization of the same carbon NMs have led to inconsistent results across different studies. Therefore, the data obtained so far have not provided a compatible and systematic profile of biosafety. Further efforts are needed to address these problems. In this Account, we review the in vivo quantification methods of carbon NMs, focusing on isotopic labeling and tracing methods, and summarize the related labeling, purification, bio-sampling, and detection of carbon NMs. We also address the advantages, applicable situations, and limits of various labeling and tracing methods and propose guidelines for choosing suitable labeling methods. A collective analysis of the ADME information on various carbon NMs in vivo would provide general principles for understanding the fate of carbon NMs and the effects of chemical functionalization and aggregation of carbon NMs on their ADME/T in vivo and their implications in nanotoxicology and biosafety evaluations.

The influence of carbon nanotube functionalization route on the efficiency of dispersion in polypropylene by twin-screw extrusion

The joint effect of chemical functionalization and polymer melt blending conditions on carbon nanotube dispersion in polypropylene, as well as its influence on the electrical and mechanical properties of the resulting composites were investigated. Melt blending was performed using a prototype twin screw extruder enabling sampling along the barrel. The carbon nanotube dispersion was assessed by optical and scanning electron microscopy. The functionalization reaction was tailored for compatibility with the polymer, and characterized by X-ray photoelectron spectroscopy. In particular, nanotubes covalently bonded to polypropylene showed distinctive dispersion ability, while the carbon nanotube dispersion remained stable even after re-melting. However, the polypropylene-functionalized nanotubes produced composites with higher electrical resistivity, possibly due to the insulating effect of the polymer bonded to the nanotubes surface.

Methane and carbon dioxide adsorption on edge-functionalized graphene: A comparative DFT study

With a view towards optimizing gas storage and separation in crystalline and disordered nanoporous carbon-based materials, we use ab initio density functional theory calculations to explore the effect of chemical functionalization on gas binding to exposed edges within model carbon nanostructures. We test the geometry, energetics, and charge distribution of in-plane and out-of-plane binding of CO(2) and CH(4) to model zigzag graphene nanoribbons edge-functionalized with COOH, OH, NH(2), H(2)PO(3), NO(2), and CH(3). Although different choices for the exchange-correlation functional lead to a spread of values for the binding energy, trends across the functional groups are largely preserved for each choice, as are the final orientations of the adsorbed gas molecules. We find binding of CO(2) to exceed that of CH(4) by roughly a factor of two. However, the two gases follow very similar trends with changes in the attached functional group, despite different molecular symmetries. Our results indicate that the presence of NH(2), H(2)PO(3), NO(2), and COOH functional groups can significantly enhance gas binding, making the edges potentially viable binding sites in materials with high concentrations of edge carbons. To first order, in-plane binding strength correlates with the larger permanent and induced dipole moments on these groups. Implications for tailoring carbon structures for increased gas uptake and improved CO(2)/CH(4) selectivity are discussed.