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The dispersion process of carbon nanotubes sonicated in aqueous solutions of a dispersant
KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.ORCID-id: 0000-0002-9570-4187
KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.ORCID-id: 0000-0003-1775-8160
Visa övriga samt affilieringar
(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
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.

Nationell ämneskategori
Fysikalisk kemi
Identifikatorer
URN: urn:nbn:se:kth:diva-220693OAI: oai:DiVA.org:kth-220693DiVA, id: diva2:1169902
Anmärkning

QC 20180103

Tillgänglig från: 2017-12-30 Skapad: 2017-12-30 Senast uppdaterad: 2018-01-03Bibliografiskt granskad
Ingår i avhandling
1. Adsorption, aggregation and phase separation in colloidal systems
Öppna denna publikation i ny flik eller fönster >>Adsorption, aggregation and phase separation in colloidal systems
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The thesis presents work regarding amphiphilic molecules associated in aqueous solution or at the liquid/solid interface. Two main topics are included: the temperature-dependent behavior of micelles and the adsorption of dispersants on carbon nanotube (CNT) surfaces. Various NMR methods were used to analyze those systems, such as chemical shift detection, spectral intensity measurements, spin relaxation and, in particular, self-diffusion experiments. Besides this, small angle X-ray scattering (SAXS) was also applied for structural characterization.

 

A particular form of phase transition, core freezing, was detected as a function of temperature in micelles composed by a single sort of Brij-type surfactants. In mixed micelles, that phase transition still occurs accompanied by a reversible segregation of different surfactants into distinct aggregates. Adding a hydrophobic solubilizate shifts the core freezing point to a lower temperature. Upon lowering the temperature to the core freezing point, the solubilizate is released. The temperature course of the release curves with different initial solubilizate loadings is rationalized in terms of a temperature-dependent loading capacity.

 

The behavior of amphiphilic dispersant molecules in aqueous dispersions of carbon nanotubes (CNTs) has been investigated with a Pluronic-type block copolymer as frequent model dispersant. Detailed dispersion curves were recorded and the distribution of the dispersant among different available environments was analyzed. The amount of dispersed CNT was shown to be defined by a complex interplay of several factors during the dispersion process such as dispersant concentration, sonication time, centrifugation and CNT loading. In the dispersion process, high amphiphilic concentration is required because the pristine CNT surfaces made available by sonication must be rapidly covered by dispersants to avoid their re-attachment. In the prepared dispersions, the competitive adsorption of possible dispersants was investigated that provided information about the relative strength of the interaction of those with the nanotube surfaces. Anionic surfactants were found to have a strong tendency to replace Pluronics, which indicates a strong binding of those surfactants.

 

CNTs were dispersed in an epoxy resin to prepare nanotube-polymer composites. The molecular mobility of epoxy was investigated and the results demonstrated the presence of loosely associated CNT aggregates within which the molecular transport of epoxy is slow because of strong attractive intermolecular interactions between epoxy and the CNT surface. The rheological behavior is dominated by aggregate-aggregate jamming.

Ort, förlag, år, upplaga, sidor
KTH Royal Institute of Technology, 2017. s. 62
Serie
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:88
Nyckelord
NMR, chemical shift, spin relaxation, self-diffusion, micelle, core freezing, segregation, solubilization, release, adsorption, binding, surfactant, carbon nanotube, block copolymer, dispersion, competitive adsorption, nanocomposite
Nationell ämneskategori
Fysikalisk kemi
Forskningsämne
Kemi
Identifikatorer
urn:nbn:se:kth:diva-220669 (URN)978-91-7729-647-8 (ISBN)
Disputation
2018-02-09, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20180103

Tillgänglig från: 2018-01-03 Skapad: 2017-12-29 Senast uppdaterad: 2018-01-03Bibliografiskt granskad

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