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  • 1.
    Abreu, Barbara
    et al.
    Univ Porto, Fac Sci, Dept Chem & Biochem, CIQUP, Rua Campo Alegre, P-4169007 Porto, Portugal..
    Rocha, Jessica
    Univ Porto, Fac Sci, Dept Chem & Biochem, CIQUP, Rua Campo Alegre, P-4169007 Porto, Portugal..
    Ferreira Fernandes, Ricardo Manuel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Regev, Oren
    Ben Gurion Univ Negev, Dept Chem Engn, IL-84105 Beer Sheva, Israel.;Ben Gurion Univ Negev, Ilse Katz Inst Nanotechnol, IL-84105 Beer Sheva, Israel..
    Furo, Istvan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Marques, Eduardo F.
    Univ Porto, Fac Sci, Dept Chem & Biochem, CIQUP, Rua Campo Alegre, P-4169007 Porto, Portugal..
    Gemini surfactants as efficient dispersants of multiwalled carbon nanotubes: Interplay of molecular parameters on nanotube dispersibility and debundling2019In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 547, p. 69-77Article in journal (Refereed)
    Abstract [en]

    Surfactants have been widely employed to debundle, disperse and stabilize carbon nanotubes in aqueous solvents. Yet, a thorough understanding of the dispersing mechanisms at molecular level is still warranted. Herein, we investigated the influence of the molecular structure of gemini surfactants on the dispersibility of multiwalled carbon nanotubes (MWNTs). We used dicationic n-s-n gemini surfactants, varying n and s, the number of alkyl tail and alkyl spacer carbons, respectively; for comparisons, single-tailed surfactant homologues were also studied. Detailed curves of dispersed MWNT concentration vs. surfactant concentration were obtained through a stringently controlled experimental procedure, allowing for molecular insight. The gemini are found to be much more efficient dispersants than their single-tailed homologues, i.e. lower surfactant concentration is needed to attain the maximum dispersed MWNT concentration. In general, the spacer length has a comparatively higher influence on the dispersing efficiency than the tail length. Further, scanning electron microscopy imaging shows a sizeable degree of MWNT debundling by the gemini surfactants in the obtained dispersions. Our observations also point to an adsorption process that does not entail the formation of micelle-like aggregates on the nanotube surface, but rather coverage by individual molecules, among which the ones that seem to be able to adapt best to the nanotube surface provide the highest efficiency. These studies are relevant for the rational design and choice of optimal dispersants for carbon nanomaterials and other similarly water-insoluble materials.

  • 2.
    Chaudhary, Himanshu
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Ferreira Fernandes, Ricardo M.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, Porto, P-4169-007, Portugal.
    Gowda, Vasantha
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Claessens, Mirelle M. A. E.
    Furo, Istvan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Lendel, Christofer
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Intrinsically disordered protein as carbon nanotube dispersant: How dynamic interactions lead to excellent colloidal stability2019In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 556, p. 172-179Article in journal (Refereed)
    Abstract [en]

    The rich pool of protein conformations combined with the dimensions and properties of carbon nanotubes create new possibilities in functional materials and nanomedicine. Here, the intrinsically disordered protein α-synuclein is explored as a dispersant of single-walled carbon nanotubes (SWNTs) in water. We use a range of spectroscopic methods to quantify the amount of dispersed SWNT and to elucidate the binding mode of α-synuclein to SWNT. The dispersion ability of α-synuclein is good even with mild sonication and the obtained dispersion is very stable over time. The whole polypeptide chain is involved in the interaction accompanied by a fraction of the chain changing into a helical structure upon binding. Similar to other dispersants, we observe that only a small fraction (15–20%) of α-synuclein is adsorbed on the SWNT surface with an average residence time below 10 ms

  • 3.
    Dai, Jing
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Ferreira Fernandes, Ricardo Manuel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. Univ Porto, CIQUP, Dept Chem & Biochem, Fac Sci, P-4169007 Porto, Portugal..
    Regev, Oren
    Ben Gurion Univ Negev, Dept Chem Engn, IL-84105 Beer Sheva, Israel.;Ben Gurion Univ Negev, Ilse Katz Inst Nanotechnol, IL-84105 Beer Sheva, Israel..
    Marques, Eduardo F.
    Univ Porto, CIQUP, Dept Chem & Biochem, Fac Sci, P-4169007 Porto, Portugal..
    Furo, Istvan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Dispersing Carbon Nanotubes in Water with Amphiphiles: Dispersant Adsorption, Kinetics, and Bundle Size Distribution as Defining Factors2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 42, p. 24386-24393Article in journal (Refereed)
    Abstract [en]

    Debundling and dispersing single-walled carbon nanotubes (SWNTs) is essential for applications, but the process is not well understood. In this work, aqueous SWNT dispersions were produced by sonicating pristine SWNT powder in the presence of an amphiphilic triblock copolymer (Pluronic F127) as dispersant. Upon centrifugation, one obtains a supernatant with suspended individual tubes and thin bundles and a precipitate with large bundles (and impurities). In the supernatant, that constitutes the final dispersion, we determined the dispersed SWNT concentration by thermogravi-metric analysis (TGA) and UV-vis spectroscopy, and the dispersant concentration by NMR The fraction of dispersant adsorbed at the SWNT surface was obtained by H-1 diffusion NMR Sigmoidal dispersion curves recording the concentration of dispersed SWNTs as a function of supernatant dispersant concentration were obtained at different SWNT loadings and sonication times. As SWNT bundles are debundled into smaller and smaller ones, the essential role of the dispersant is to sufficiently quickly cover the freshly exposed surfaces created by shear forces induced during sonication. Primarily kinetic reasons are behind the need for dispersant concentrations required to reach a substantial SWNT concentration. Centrifugation sets the size threshold below which SWNT particles are retained in the dispersion and consequently determines the SWNT concentration as a function of sonication time.

  • 4.
    Dai, Jing
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ferreira Fernandes, Ricardo Manuel
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Regev, Oren
    Marques, Eduardo
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    The dispersion process of carbon nanotubes sonicated in aqueous solutions of a dispersantManuscript (preprint) (Other academic)
    Abstract [en]

    Single-walled carbon nanotube (SWNT) dispersions are created by sonicating pristine SWNT powders added to aqueous solutions of the dispersant block copolymer Pluronic F127. In those dispersions, the amount of the dispersed SWNT is determined by the combination of TGA and UV-Vis methods, while the dispersant concentration is estimated by 1H NMR spectroscopy. In addition, the amount of dispersant adsorbed at the SWNT surface is obtained by 1H NMR diffusion experiments. A part of the dispersant is taken up by non-dispersed and precipitated particles. Dispersion curves recording the amount of the dispersed SWNT as a function of either the initial dispersant concentration or the final dispersant concentration are obtained at different initial SWNT loadings and sonication times. The results show in detail the way the original SWNT particles are divided into smaller and smaller sizes thereby increasing the available SWNT surface to be covered by dispersant. Centrifugation sets the size-threshold above which SWNT particles are retained in the dispersion which determined the SWNT content as a function of sonication time.

  • 5.
    Fernandes, Ricardo M. Ferreira
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Dispersing Carbon Nanotubes: Towards Molecular Understanding2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Carbon nanotubes (CNTs) exhibit unique and fascinating intrinsic electrical, optical, thermal or mechanical properties that lead to a plethora of potential applications in composite materials, electronics, energy storage, medicine, among others. However, the manipulation of nanotubes is not trivial and there are significant difficulties to overcome before achieving their full potential in applications. Because of their high aspect ratio and strong tube-to-tube van der Waals interactions, nanotubes form bundles and ropes that are difficult to disperse in liquids. In this thesis, the topic of dispersing carbon nanotubes in water was addressed by several experimental methods such as nuclear magnetic resonance (NMR) diffusometry and light/electron microcopy. The main goal was to obtain molecular information on how the dispersants interact with carbon nanotubes.

    In dispersions of single-walled carbon nanotubes (SWNTs) in water, only a small fraction of the polymeric dispersant (Pluronic F127) was shown to be adsorbed at the CNT surface. Regarding dynamic features, the residence time of F127 on the SWNT surface was measured to be in the order of hundred milliseconds, and the lateral diffusion coefficient of the polymer along the nanotube surface proved to be an order of magnitude slower than that in the solution. The surface coverage of SWNTs by F127 was also investigated and the competitive adsorption of F127 and the protein bovine serum albumin, BSA, was assessed. F127 was found to bind stronger to the CNT surface than BSA does.

    Low molecular weight dispersants, viz. surfactants, were also investigated. Using carefully controlled conditions for the sonication and centrifugation steps, reproducible sigmoidal dispersibility curves were obtained, that exhibited an interesting variation with molecular properties of the surfactants. Various metrics that quantify the ability of different surfactants to disperse CNTs were obtained. In particular, the concentration of surfactant required to attain maximal dispersibility depends linearly on alkyl chain length, which indicates that the CNT-surfactant association, although hydrophobic in nature, is different from a micellization process. No correlation between dispersibility and the critical micellization concentration, cmc, of the surfactants was found. For gemini surfactants of the n-s-n type with spacer length s and hydrophobic tail length n, the dispersibility of multiwalled carbon nanotubes (MWNTs) also followed sigmoidal curves that were compared to those obtained with single-tailed homologues. The increase in spacer length caused an increase in the dispersion efficiency. The observations indicate a loose type of monolayer adsorption rather than the formation of micelle-like aggregates on the nanotube surface. With the future goal of embedding nanotubes in liquid crystal (LC) phases and thereby creating nanocomposites, the effect of the spacer length on the thermotropic behavior of the gemini 12-s-12 surfactant was investigated. Different mesophases were observed and a non-monotonic effect of the spacer length was found and rationalized within a model of the surfactant packing in the solid state.

    The relative binding strength of simple surfactants to CNTs was assessed by the amount of F127 they displace from the CNT surface upon addition. Anionic surfactants were found to replace more F127, which was interpreted as a sign of stronger binding to CNT. The data collected for all surfactants showed a good correlation with their critical dispersibility concentration that suggests the existence of a surface coverage threshold for dispersing nanotubes.

    On the macroscopic scale, the formation of weakly bound CNT aggregates in homogeneous dispersions was found to be induced by vortex-shaking. These aggregates could quickly and easily be re-dispersed by mild sonication. This counterintuitive behavior was related to the type of dispersant used and of the duration of mechanical agitation and was explained as a result of loose coverage by the dispersant. 

  • 6.
    Fernandes, Ricardo Madeira F.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. University of Porto, Portugal.
    Buzaglo, M.
    Regev, O.
    Furó, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Marques, E. F.
    Mechanical agitation induces counterintuitive aggregation of pre-dispersed carbon nanotubes2017In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 493, p. 398-404Article in journal (Refereed)
    Abstract [en]

    Mechanical agitation is commonly used to fragment and disperse insoluble materials in liquids. However, here we show that when pristine single-walled carbon nanotubes pre-dispersed in water are subject to vortex-shaking for very short periods (typically 10–60 s, power density ∼0.002 W mL−1), re-aggregation counterintuitively occurs. The initial dispersions are produced using surfactants as dispersants and powerful tip sonication (∼1 W mL−1) followed by centrifugation. Detailed imaging by light and electron microscopies shows that the vortex-induced aggregates consist of loose networks (1–102 μm in size) of intertwined tubes and thin bundles. The average aggregate size increases with vortexing time in an apparently logarithmic manner and depends on the dispersant used, initial concentration of nanotubes and size distribution of bundles. The aggregation is, nonetheless, reversible: if the vortex-shaken dispersions are mildly bath-sonicated (∼0.03 W mL−1), the flocs break down and re-dispersal occurs. Molecular insight for the mechanism behind this surprising phenomenon is put forth.

  • 7.
    Fernandes, Ricardo M.F.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, Porto, Portugal.
    Abreu, Bárbara
    Claro, Bárbara
    Buzaglo, Matat
    Regev, Oren
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Marques, Eduardo
    Dispersing Carbon Nanotubes with Ionic Surfactants under Controlled Conditions: Comparisons and Insight2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 40, p. 10955-10965Article in journal (Refereed)
    Abstract [en]

    A fundamental understanding of the mechanisms involved in the surfactant-assisted exfoliation and dispersion of carbon nanotubes (CNTs) in water calls for well-controlled experimental methodologies and reliable comparative metrics. We have assessed the ability of several ionic surfactants to disperse single and multiwalled carbon nanotubes, resorting to a stringently controlled sonication-centrifugation method for the preparation of the dispersions. The CNT concentration was accurately measured for a wide range of surfactant concentration, using combined thermogravimetric analysis and UV–vis spectroscopy. The obtained dispersibility curves yield several quantitative parameters, which in turn allow for the effects of nanotube morphology and surfactant properties (aromatic rings, chain length, headgroup charge, andcmc) to be assessed and rationalized, both in terms of dispersed nanotube mass and surface area. The data also indicate that the CNT-surfactant association follows patterns that are markedly different from other equilibrium processes governed by hydrophobicity (such as micellization); in particular, the surfactant concentration needed for maximum dispersibility,cs,max, and the number of surfactant molecules per unit CNT area at cs,max are shown to depend linearly on chain length. The results further suggest that the presence of micelles in the exfoliation process is not a key factor either for starting CNT dispersibility or attaining its saturation value.

  • 8.
    Fernandes, Ricardo M.F.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, Porto, Portugal.
    Buzaglo, Matat
    Regev, Oren
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Marques, Eduardo
    Mechanical Agitation Induces Aggregation of Pre-Dispersed Carbon Nanotubes2015Manuscript (preprint) (Other academic)
    Abstract [en]

    Mechanical agitation is typically used to fragment and disperse insoluble materials in a solvent. We report here an aggregation process that, contrary to expectation, is induced by mechanical agitation: when aqueous dispersions of single-walled carbon nanotubes (SWNTs) are subject to vortex-shaking, weakly bound micron-sized aggregates are formed. The SWNT dispersions are prepared by adding various dispersants employing a sonication followed by centrifugation approach. While surfactant adsorption to the SWNTs during sonication results in stabilized exfoliated tubes and thin bundles, we find that vortex-shaking the fresh dispersions for short periods (10-60 s) results in re-aggregation into flocs in the 1-102 µm range. The aggregation is reversible: if the vortexed dispersions are mildly sonicated, the flocs break down and re-dispersal occurs. Imaging at different resolutions shows that the aggregates consist of loose networks of intertwined tubes and bundles. The data further indicate that the average aggregate size increases logarithmically with vortex time and is critically influenced by dispersant type (ionic or nonionic), centrifugation time (prior to vortexing) and initial concentration of dispersed SWNTs. These results are relevant if stabilization or destabilization of dispersions is sought for, i.e., in drug delivery or sensing applications, and could also be of interest for chiral sorting of SWNTs and percolation conductivity.

  • 9.
    Fernandes, Ricardo M.F.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, Porto, Portugal.
    Buzaglo, Matat
    Regev, Oren
    Marques, Eduardo
    Furo, Istvan
    Surface Coverage and Competitive Adsorption on Carbon Nanotubes2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, The Journal of Physical Chemistry C, ISSN 1932-7447, Vol. 119, no 38, p. 22190-22197Article in journal (Refereed)
    Abstract [en]

    The binding strength of dispersants to the surface of carbon nanotubes is of crucial importance for the efficiency of the dispersion process and for potential applications, yet data are scarce on this subject. Here we present the results of diffusion NMR experiments in dispersions of single-walled carbon nanotubes (SWNTs) prepared by either the polymer Pluronics F127 or the protein bovine serum albumin (BSA). The experiments detect the amount of F127 molecules adsorbed onto the SWNT surface. This quantity is recorded (i) in F127-SWNT dispersions to which BSA molecules are added and (ii) in BSA-SWNT dispersions to which F127 molecules are added. The data clearly show that F127 replaces BSA adsorbed at the SWNT surface, while BSA leaves the adsorbed F127 coverage intact. Consequently, F127 binds to the nanotube surface more strongly than BSA. Hence, we provide a way to categorize dispersants by adsorption strength. We also provide evidence showing that the nanotubes dispersed by BSA form loose aggregates where a large part of the surface is not in direct contact with the surrounding liquid. The results are discussed in relation to previous findings in the literature.

  • 10.
    Fernandes, Ricardo M.F.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, Porto, Portugal.
    Dai, Jing
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Regev, Oren
    Marques, Eduardo
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Assessing Surfactant Binding to Carbon Nanotubes via Competitive Adsorption: Binding strength and critical coverage2015Manuscript (preprint) (Other academic)
    Abstract [en]

    The displacement of a nonionic polymeric dispersant, Pluronic F127, adsorbed at the surface of single-walled carbon nanotubes, by low molecular-weight ionic dispersants (surfactants) is studied in aqueous dispersion. The method applied is diffusion NMR spectroscopy that can accurately measure the fraction of F127 molecules adsorbed at the tube surface because of the slow exchange (over the experimental time scale) of F127 between bulk and surface. In a series of surfactants with varying chain length and headgroups, we find that anionic surfactants replace in general more nonionic F127 than do cationic surfactants. The data collected show a strong correlation with the critical dispersibility concentration of the different surfactants, a parameter that signifies the concentration at which one obtains significant dispersed nanotube concentration by ultrasonication. We posit that this finding indicates the existence of a threshold surface coverage for dispersants that constitutes a necessary condition for de-bundling by ultrasonication. The results are discussed in relation to previous findings in the literature. 

  • 11.
    Fernandes, Ricardo M.F.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, Porto, Portugal.
    Wang, Yujie
    Tavares, Pedro
    Nunes, Sandra
    Pais, Alberto
    Marques, Eduardo
    Strong Spacer Length Effects on The Thermal Behavior and Mesophase Formation By Gemini Surfactants2015Manuscript (preprint) (Other academic)
    Abstract [en]

    The self-aggregation properties in aqueous solution of gemini surfactants of the type alkanediyl-α,ω-bis(dodecyldimethylammonium bromides), 12-s-12, have been extensively reported and are known to be significantly influenced by the number of methylene groups, s, of the covalent spacer. In contrast, the thermal behavior of the anhydrous compounds as a function of varying s has not been investigated in a similarly systematic way. Herein, we present the thermal phase behavior of eight compounds of the 12-s-12 family (with s = 2-6, 8, 10 and 12), resorting to differential scanning calorimetry (DSC), polarized light microscopy (PLM) and X-ray diffraction (XRD). We find that compounds with either the shortest spacer, s = 2, or the longest ones—8, 10 and 12—form several smectic liquid-crystalline phases prior to isotropization to the liquid phase, with appearance of oily streaks, focal conics, mosaic and fan-shaped birefringent textures. In sharp contrast, gemini compounds with intermediate spacers, s = 3-6, decompose and do not form any disordered, fluid mesophases. Both the DSC thermodynamic parameters for the phase transitions and d00l spacings obtained from XRD show non-monotonic trends with spacer variation, indicating that there are significant differences in solid-state packing and melting process. Plausible molecular packing arrangements in the solid-state are presented, consistent with the XRD information and geometric considerations, and their influence on the phase behavior trends critically discussed.

  • 12.
    Ferreira Fernandes, Ricardo Manuel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Univ Porto, Portugal.
    Buzaglo, Matat
    Shtein, Michael
    Bar, Ilan Pri
    Regev, Oren
    Marques, Eduardo F.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Lateral Diffusion of Dispersing Molecules On Nanotubes As Probed by NMR2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 1, p. 582-589Article in journal (Refereed)
    Abstract [en]

    Noncovalent dispersion of carbon nanotubes is essential to most applications but still poorly understood at the molecular level. The interaction of the dispersing molecule with the nanotube, wrapping or nonwrapping, still awaits consensus. Herein, we have studied by H-1 NMR diffusometry some features of molecular dynamics in the system of carbon nanotubes dispersed by triblock copolymer Pluronics F127 in water. The diffusional decays obtained at different diffusion times, Delta, are not single-exponential and have a complex Delta-dependent profile, ultimately implying that the polymer is observed in two states: free (in unimeric form) and nanotube-bound. Fitting a two-site exchange model to the data indicates that at any instant, only a small fraction of polymers are adsorbed on the nanotubes, with polydisperse residence times in the range of 100-400 ms. Most significantly, we further provide an estimate of D = (3-8) x 10(-12) m(2) s(-1) the coefficient of lateral diffusion of the polymer along the nanotube surface, which is an order of magnitude slower than the corresponding self-diffusion coefficient in water. The emerging picture is that of a nonwrapping mode for the polymer-nanotube interaction.

  • 13.
    Ferreira Fernandes, Ricardo Manuel
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. Univ Porto, Dept Chem & Biochem, CIQUP, Fac Sci, P-4169007 Porto, Portugal..
    Dai, Jing
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Regev, Oren
    Ben Gurion Univ Negev, Dept Chem Engn, IL-84105 Beer Sheva, Israel.;Ben Gurion Univ Negev, Ilse Katz Inst Nanotechnol, IL-84105 Beer Sheva, Israel..
    Marques, Eduardo F.
    Univ Porto, Dept Chem & Biochem, CIQUP, Fac Sci, P-4169007 Porto, Portugal..
    Furo, Istvan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Block Copolymers as Dispersants for Single-Walled Carbon Nanotubes: Modes of Surface Attachment and Role of Block Polydispersity2018In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 45, p. 13672-13679Article in journal (Refereed)
    Abstract [en]

    When using amphiphilic polymers to exfoliate and disperse carbon nanotubes in water, the balance between the hydrophobic and hydrophilic moieties is critical and nontrivial. Here, we investigate the mode of surface attachment of a triblock copolymer, Pluronics F127, composed of a central hydrophobic polypropylene oxide block flanked by hydrophilic polyethylene oxide blocks, onto single-walled carbon nanotubes (SWNTs). Crucially, we analyze the composition in dispersant of both the as-obtained dispersion (the supernatant) and the precipitate-containing undispersed materials. For this, we combine the carefully obtained data from H-1 NMR peak intensities and self-diffusion and thermogravimetric analysis. The molecular motions behind the observed NMR features are clarified. We find that the hydrophobic blocks attach to the dispersed SWNT surface and remain significantly immobilized leading to H-1 NMR signal loss. On the other hand, the hydrophilic blocks remain highly mobile and thus readily detectable by NMR. The dispersant is shown to possess significant block polydispersity that has a large effect on dispersibility. Polymers with large hydrophobic blocks adsorb on the surface of the carbonaceous particles that precipitate, indicating that although a larger hydrophobic block is good for enhancing adsorption, it may be less effective in dispersing the tubes. A model is also proposed that consistently explains our observations in SWNT dispersions and some contradicting findings obtained previously in carbon nanohorn dispersions. Overall, our findings help elucidating the molecular picture of the dispersion process for SWNTs and are of interest when looking for more effective (i.e., well-balanced) polymeric dispersants.

  • 14.
    Ferreira Fernandes, Ricardo Manuel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Dai, Jing
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Regev, Oren
    Marques, Eduardo
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Block copolymers adsorbed on single-walled carbon nanotubes. Block polydispersity and the modes of surface attachmentManuscript (preprint) (Other academic)
    Abstract [en]

    1H NMR peak intensities, 1H NMR diffusion measurements and TGA experiments were used to clarify the fate of the dispersing molecules, block copolymer Pluronic F127, during preparation of single-walled carbon nanotube (CNT) dispersions and their state in the created dispersions. In the dispersions, a fraction of the F127 molecules is adsorbed to the CNT surface. The mode of adsorption is the attachment and significant immobilization of the hydrophobic polypropylene oxide (PPO) block to the CNT surface and, as a result, the 1H NMR signal from the attached PPO blocks is lost. On the other hand, the hydrophilic polyethylene oxide (PEO) blocks remain highly mobile and thereby detectable by NMR. The F127 is revealed to exhibit significant block polydispersity. Molecules with large PPO blocks become enriched upon the surface of that fraction of the initial CNT powder that does not become dispersed. The molecular motions involved in creating the observed NMR features are clarified.

  • 15.
    Lousada, Cláudio M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Technology.
    Fernandes, Ricardo M. F.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Tarakina, Nadezda V.
    Soroka, Inna L.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Synthesis of copper hydride (CuH) from CuCO3·Cu(OH)2 – a path to electrically conductive thin films of Cu2017In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, no 20, p. 6533-6543Article in journal (Refereed)
    Abstract [en]

    The most common synthesis methods for copper hydride (CuH) employ hard ligands that lead to the formation of considerable amounts of metallic Cu as side-product. Here we explore a synthesis method for CuH(s) through the reaction of CuCO3 center dot Cu(OH)(2)(s) with hypophosphorous acid (H3PO2) in solution, via the formation of the intermediate Cu(H2PO2)(2)(aq) complex. The reaction products were characterized with XRD, FTIR and SEM at different reaction times, and the kinetics of the transformation of Cu(H2PO2)(2)(aq) to CuH(s) were followed with NMR and are discussed. We show that our synthesis method provides a simple way for obtaining large amounts of CuH(s) even when the synthesis is performed in air. Compared to the classic Wurtz method, where CuSO4 is used as an initial source of Cu2+, our synthesis produces CuH particles with less metallic Cu side-product. We attribute this to the fact that our reaction medium is free from the hard SO42- ligand that can disproportionate Cu(I). We discuss a mechanism for the reaction based on the known reactivity of the reagents and intermediates involved. We explored the possibility of using CuH(s) for making electrically conductive films. Tests that employed water-dispersed CuH particles show that this compound can be reduced with H3PO2 leading to electrically conductive thin films of Cu. These films were made on regular office paper and were found to be Ohmic conductors even after several weeks of exposure to ambient conditions. The fact that the synthesis reported here produces large amounts of CuH particles in aqueous media, with very little impurities, and the fact that these can then be converted to a stable electrically conductive film can open up new applications for CuH such as for printing electrically conductive films or manufacturing surface coatings.

  • 16. Nadiv, R.
    et al.
    Fernandes, Ricardo M. F.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Ochbaum, G.
    Dai, Jing
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Buzaglo, M.
    Varenik, M.
    Biton, R.
    Furo, Istvan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Regev, O.
    Polymer nanocomposites: Insights on rheology, percolation and molecular mobility2018In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 153, p. 52-60Article in journal (Refereed)
    Abstract [en]

    The integration of carbon nanotubes (CNTs) into a polymer matrix strongly affects the rheological behavior that in turn may hamper the overall performance of the resulting composite. Research in this topic has focused on bulk rheological properties, while here we employ NMR diffusion experiments to explore the mobility (diffusivity) of epoxy molecules when loaded with CNTs. Rheology and light microscopy indicate percolation of CNT aggregates. Those aggregates cage a substantial amount of epoxy molecules while small angle X-ray scattering indicates some rearrangement of epoxy molecules in the vicinity of the nanotubes. NMR diffusion experiments distinguish between the slow diffusion of the caged molecules and that of the free ones, and relate the fraction of the former to the macroscopic system viscosity. The demonstrated surface-induced slowing-down of diffusion is attributed to strong intermolecular π-π interactions among the epoxy molecules, and between them and the CNT surface. These findings demonstrate the utility of NMR diffusion experiments as an additional method applied to nanocomposites. 

  • 17. Nadiv, Roey
    et al.
    Ferreira Fernandes, Ricardo Manuel
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ochbaum, Guy
    Dai, Jing
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Buzaglo, Matat
    Varenik, Maxim
    Biton, Ronit
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Regev, Oren
    Polymer nanocomposites: insights on rheology, percolation, jamming and molecular mobilityManuscript (preprint) (Other academic)
    Abstract [en]

    Carbon nanotubes (CNTs) loading in a polymer matrix strongly affect the rheological behavior and in turn hamper the overall performance of the composite. The majority of the research in this topic has focused on bulk rheological properties, while here we employ NMR diffusion experiments to explore the mobility (diffusivity) of epoxy molecules when loaded with CNTs. Rheology and light microscopy indicate percolation, or jamming events of CNT aggregates, caging a substantial amount of epoxy molecules while small angle X-ray scattering indicates rearrangements of epoxy molecules in the vicinity of the nanotubes. NMR diffusion experiments distinguish between the diffusion of the caged molecules and that of the free ones, and relate the fraction of the former to the system viscosity. These findings demonstrate the utility of NMR diffusion experiments as an additional method applied to the rheological behavior of polymer mixtures.

  • 18. Rocha, Jessica
    et al.
    Fernandes, Ricardo M.F.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, Porto, Portugal.
    Regev, Oren
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Marques, Eduardo
    Gemini Surfactants as Dispersants of Multiwalled Carbon Nanotubes: a Systematic Study on the Role of Molecular Structure2015Manuscript (preprint) (Other academic)
    Abstract [en]

    Surfactants have been widely used as non-covalent dispersants of carbon nanotubes and yet a deeper and systematic understanding of the role of their molecular properties on dispersibility still awaits consensus. Herein, we report on the dispersibility of multiwalled carbon nanotubes (MWNTs) using a set of dicationic gemini surfactants of the n-s-n type, where both the length of the covalent spacer (s) that bridges the two cationic headgroups and the length of the tails (n) are systematically varied. Thus, 12-s-12 gemini with s = 2, 6, and 12 are studied together with 16-s-16 (s = 2 and 12). In addition, the single-tailed homologues dodecyltrimethylammonium bromide, DTAB (n = 12), and cetyltrimethylammonium bromide, CTAB (n = 16), are employed for comparisons. High precision dispersion curves (dispersed NT vs. surfactant concentration) are presented, obtained through a well-controlled sonication/centrifugation procedure combined with an accurate determination of MWNT concentration. The gemini amphiphiles, despite being double-tailed and double-charged, are found to be less effective dispersants than CTAB and roughly as effective as DTAB. Among the gemini, the following pattern emerges as concerning dispersion behavior. (i) The tail length, n, is less influential than spacer length, s, in dispersing ability, implying that the spacer hydrophobicity rather than that of the tail may govern the affinity for the nanotube surface. (ii) In the 12-s-12 series, the surfactant concentration needed for maximum MWNT dispersibility depends linearly on s, while it is known that the neat cmc depends non-monotonically on s. (iii) Similarly to single-tailed ionic surfactants, the presence of micelles has no direct effect on the dispersion behavior. In combination, these observations also point to an adsorption mechanism that does not involve the formation of micelle-like aggregates on the nanotube surface but rather coverage by individual dispersant molecules.

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