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Ferreira Fernandes, Ricardo ManuelORCID iD iconorcid.org/0000-0003-1775-8160
Alternative names
Publications (10 of 12) Show all publications
Abreu, B., Rocha, J., Ferreira Fernandes, R. M., Regev, O., Furo, I. & Marques, E. F. (2019). Gemini surfactants as efficient dispersants of multiwalled carbon nanotubes: Interplay of molecular parameters on nanotube dispersibility and debundling. Journal of Colloid and Interface Science, 547, 69-77
Open this publication in new window or tab >>Gemini surfactants as efficient dispersants of multiwalled carbon nanotubes: Interplay of molecular parameters on nanotube dispersibility and debundling
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2019 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 547, p. 69-77Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
ACADEMIC PRESS INC ELSEVIER SCIENCE, 2019
Keywords
Gemini surfactant, Carbon nanotube, Exfoliation, Dispersion efficiency, Molecular structure, Spacer length, Tail length, Adsorption, Hydrophobicity
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-252363 (URN)10.1016/j.jcis.2019.03.082 (DOI)000466826600007 ()30939346 (PubMedID)2-s2.0-85063650726 (Scopus ID)
Note

QC 20190718

Available from: 2019-07-18 Created: 2019-07-18 Last updated: 2019-07-18Bibliographically approved
Ferreira Fernandes, R. M., Dai, J., Regev, O., Marques, E. F. & Furo, I. (2018). Block Copolymers as Dispersants for Single-Walled Carbon Nanotubes: Modes of Surface Attachment and Role of Block Polydispersity. Langmuir, 34(45), 13672-13679
Open this publication in new window or tab >>Block Copolymers as Dispersants for Single-Walled Carbon Nanotubes: Modes of Surface Attachment and Role of Block Polydispersity
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2018 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 45, p. 13672-13679Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-239775 (URN)10.1021/acs.langmuir.8b02658 (DOI)000450695000023 ()30335395 (PubMedID)2-s2.0-85056155151 (Scopus ID)
Note

QC 20190108

Available from: 2019-01-08 Created: 2019-01-08 Last updated: 2019-01-09Bibliographically approved
Dai, J., Ferreira Fernandes, R. M., Regev, O., Marques, E. F. & Furo, I. (2018). Dispersing Carbon Nanotubes in Water with Amphiphiles: Dispersant Adsorption, Kinetics, and Bundle Size Distribution as Defining Factors. The Journal of Physical Chemistry C, 122(42), 24386-24393
Open this publication in new window or tab >>Dispersing Carbon Nanotubes in Water with Amphiphiles: Dispersant Adsorption, Kinetics, and Bundle Size Distribution as Defining Factors
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 42, p. 24386-24393Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-239095 (URN)10.1021/acs.jpcc.8b06542 (DOI)000448754300065 ()2-s2.0-85054962387 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20181121

Available from: 2018-11-21 Created: 2018-11-21 Last updated: 2019-08-20Bibliographically approved
Nadiv, R., Fernandes, R. M. F., Ochbaum, G., Dai, J., Buzaglo, M., Varenik, M., . . . Regev, O. (2018). Polymer nanocomposites: Insights on rheology, percolation and molecular mobility. Polymer, 153, 52-60
Open this publication in new window or tab >>Polymer nanocomposites: Insights on rheology, percolation and molecular mobility
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2018 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 153, p. 52-60Article in journal (Refereed) Published
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. 

Place, publisher, year, edition, pages
Elsevier Ltd, 2018
Keywords
Nanocomposites, NMR diffusion, Rheology, Aggregates, Carbon nanotubes, Diffusion, Elasticity, Molecules, Solvents, X ray scattering, Yarn, Macroscopic systems, Molecular mobility, Pi interactions, Polymer nanocomposite, Rheological behaviors, Rheological property, Slow diffusion, Polymer matrix composites
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-236679 (URN)10.1016/j.polymer.2018.07.079 (DOI)000445783300007 ()2-s2.0-85053160650 (Scopus ID)
Funder
Swedish Research Council, CA15107
Note

Export Date: 22 October 2018; Article; CODEN: POLMA; Correspondence Address: Nadiv, R.; Department of Chemical Engineering, Ben-Gurion University of the NegevIsrael; email: roeynadiv@gmail.com; Funding details: NORTE-01-0145-FEDER-000028; Funding details: UID/QUI/00081/2013; Funding details: POCI-01-0145-FEDER-006980; Funding details: CA15107; Funding details: Aichi Science and Technology Foundation; Funding details: COST, European Cooperation in Science and Technology; Funding details: FCT, Fuel Cell Technologies Program; Funding text: The authors are grateful for excellent technical support by Dr. Jürgen Jopp (Light microscopy). The authors are grateful for excellent technical support by Carmen Tamburu and Prof. Uri Raviv (SAXS). The authors acknowledge useful discussions with Dr. Gleb Vasilyev. This article is based upon work from COST action CA15107 (MultiComp), supported by COST (European Cooperation in Science and Technology) and the Swedish Research Council VR. RF also acknowledges the CIQUP and the Science and Technology Foundation (FCT), Portugal , and FEDER/COMPETE for financial support through grants UID/QUI/00081/2013 , POCI-01-0145-FEDER-006980 and NORTE-01-0145-FEDER-000028 . Appendix A

Available from: 2018-11-13 Created: 2018-11-13 Last updated: 2018-11-13Bibliographically approved
Fernandes, R. M. .., Dai, J., Regev, O., Marques, E. & Furo, I. (2015). Assessing Surfactant Binding to Carbon Nanotubes via Competitive Adsorption: Binding strength and critical coverage.
Open this publication in new window or tab >>Assessing Surfactant Binding to Carbon Nanotubes via Competitive Adsorption: Binding strength and critical coverage
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2015 (English)Manuscript (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. 

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-176436 (URN)
Note

QC 20180103

Available from: 2015-11-04 Created: 2015-11-04 Last updated: 2018-01-03Bibliographically approved
Fernandes, R. M. F. (2015). Dispersing Carbon Nanotubes: Towards Molecular Understanding. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Dispersing Carbon Nanotubes: Towards Molecular Understanding
2015 (English)Doctoral 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. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. p. xii, 77
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:60
Keywords
carbon nanotubes, dispersion, surfactants, polymers, adsorption, liquid crystals, nuclear magnetic resonance, self-diffusion
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-176443 (URN)978-91-7595-713-5 (ISBN)
Public defence
2015-11-26, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:10 (English)
Opponent
Supervisors
Note

This Ph.D thesis was completed under the Thesis Co-supervision Agreement between KTH Royal Institute of Technology and the University of Port. QC 20151105

Available from: 2015-11-04 Created: 2015-11-04 Last updated: 2015-11-04Bibliographically approved
Fernandes, R. M. .., Abreu, B., Claro, B., Buzaglo, M., Regev, O., Furo, I. & Marques, E. (2015). Dispersing Carbon Nanotubes with Ionic Surfactants under Controlled Conditions: Comparisons and Insight. Langmuir, 31(40), 10955-10965
Open this publication in new window or tab >>Dispersing Carbon Nanotubes with Ionic Surfactants under Controlled Conditions: Comparisons and Insight
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2015 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 40, p. 10955-10965Article in journal (Refereed) Published
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.

Keywords
CNT, dispersion, surfactants, TGA
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-176435 (URN)10.1021/acs.langmuir.5b02050 (DOI)26390187 (PubMedID)2-s2.0-84944128629 (Scopus ID)
Note

QC 20151105

Available from: 2015-11-04 Created: 2015-11-04 Last updated: 2019-10-02Bibliographically approved
Rocha, J., Fernandes, R. M. .., Regev, O., Furo, I. & Marques, E. (2015). Gemini Surfactants as Dispersants of Multiwalled Carbon Nanotubes: a Systematic Study on the Role of Molecular Structure.
Open this publication in new window or tab >>Gemini Surfactants as Dispersants of Multiwalled Carbon Nanotubes: a Systematic Study on the Role of Molecular Structure
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2015 (English)Manuscript (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.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-176438 (URN)
Note

QS 2015

Available from: 2015-11-04 Created: 2015-11-04 Last updated: 2015-11-04Bibliographically approved
Fernandes, R. M. .., Buzaglo, M., Regev, O., Furo, I. & Marques, E. (2015). Mechanical Agitation Induces Aggregation of Pre-Dispersed Carbon Nanotubes.
Open this publication in new window or tab >>Mechanical Agitation Induces Aggregation of Pre-Dispersed Carbon Nanotubes
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2015 (English)Manuscript (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.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-176437 (URN)
Note

QS 2015

Available from: 2015-11-04 Created: 2015-11-04 Last updated: 2015-11-04Bibliographically approved
Fernandes, R. M. .., Wang, Y., Tavares, P., Nunes, S., Pais, A. & Marques, E. (2015). Strong Spacer Length Effects on The Thermal Behavior and Mesophase Formation By Gemini Surfactants.
Open this publication in new window or tab >>Strong Spacer Length Effects on The Thermal Behavior and Mesophase Formation By Gemini Surfactants
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2015 (English)Manuscript (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.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-176440 (URN)
Note

QS 2015

Available from: 2015-11-04 Created: 2015-11-04 Last updated: 2015-11-04Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1775-8160

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