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Polymer nanocomposites: insights on rheology, percolation, jamming and molecular mobility
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-1775-8160
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0002-9570-4187
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(English)Manuscript (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.

National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-220695OAI: oai:DiVA.org:kth-220695DiVA: diva2:1169904
Note

QC 20180103

Available from: 2017-12-30 Created: 2017-12-30 Last updated: 2018-01-03Bibliographically approved
In thesis
1. Adsorption, aggregation and phase separation in colloidal systems
Open this publication in new window or tab >>Adsorption, aggregation and phase separation in colloidal systems
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. 62 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:88
Keyword
NMR, chemical shift, spin relaxation, self-diffusion, micelle, core freezing, segregation, solubilization, release, adsorption, binding, surfactant, carbon nanotube, block copolymer, dispersion, competitive adsorption, nanocomposite
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-220669 (URN)978-91-7729-647-8 (ISBN)
Public defence
2018-02-09, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20180103

Available from: 2018-01-03 Created: 2017-12-29 Last updated: 2018-01-03Bibliographically approved

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