Broadband Dielectric Spectroscopy (BDS) in combination with a nanostructured electrode arrangement – which circumvents the conventional need to evaporate metal electrodes onto soft matter – is used to study the molecular dynamics of several glass forming materials
confined in nanometric (> 5 nm) layers. Other complementary experimental tools employed in this work include spectroscopic vis-Ellipsometry (SE), AC-chip calorimetry (ACC), X-ray reflectrometry (XRR), Differential Scanning Calorimetry (DSC) and Atomic Force Microscopy (AFM). The latter is used to characterize the topography of the samples and to determine their thicknesses. Under the conditions of annealing samples (Tg + 50K) in high oil-free vacuum (10E-6 mbars) for at least 12 h and carrying out measurements in inert (dry nitrogen or argon) atmosphere, it is found for all studied thin layers that the
structural relaxation, and hence the dynamic glass transition – in its mean relaxation times – remains within a margin ±3 K from the respective bulk behaviour. It is revealed, inter alia, that the one-dimensional confinement of thin films introduces restrictions on other (slower) molecular relaxation processes which manifest, depending on the specific system under investigation, as (i) an interruption of the end-to-end (normal mode) fluctuation of the chains, or (ii) a slowing down of the delta-relaxation when the system is cooled towards glass-formation. Furthermore, (iii) evidence is provided to show that the dimensionality of confinement plays a significant role in determining the resulting dynamics. A molecular understanding of these findings is given, and the discussion presented with respect to the
on-going international debate about dynamics in confinement.:1. Introduction
2. The glass transition and chain dynamics
2.1 The phenomenology of the glass transition
2.2 Theories of the glass transition
2.2.1 Free volume theories
2.2.2 Cooperative concepts
2.2.3 Mode-coupling theory
2.3 Dynamics of polymer chains in melt
2.4 The dynamic glass transition in confinement
2.4.1 Experiments: state-of-the-art
2.4.2 Theoretical attempts at explaining dynamics in confinement
3. Sample preparation and experimental techniques
3.1 Thin-film preparation by spin-coating
3.1.1 Films on glass slides
3.1.2 Films on silicon wafers
3.1.3 Reproducibility of sample preparation
3.1.4 Stability of thin film samples
3.1.5 Film thickness determination
3.1.6 Sample annealing experiments
3.2 Use of nanostructured electrodes – a novel approach
3.3 Poly(cis-1,4-isoprene) (PI) in porous media
3.4 Experimental techniques
3.4.1 Broadband Dielectric Spectroscopy (BDS)
3.4.1.1 Polarization
3.4.1.2 Dielectric relaxation
3.4.1.3 Debye relaxation
3.4.1.4 Non-Debye relaxation
3.4.1.5 Dielectric data in the time domain
3.4.1.6 Conductivity contribution
3.4.1.7 The distribution of relaxation times
3.4.1.8 BDS – summary
3.4.2 Spectroscopic Ellipsometry (SE)
3.4.3 AC-chip calorimetry (ACC)
4. Results and Discussion
4.1 Effect of sample geometry on measured dynamics
4.1.1 Introduction
4.1.2 Experimental details
4.1.3 Results and discussion
4.1.4 Summary
4.2 Dynamics of polystyrene in a wide range of molecular weights
4.2.1 Introduction
4.2.2 Experimental details
4.2.3 Results and discussion
4.2.4 Summary
4.3 Molecular dynamics of itraconazole confined in thin supported layers
4.3.1 Introduction
4.3.2 Experimental details
4.3.3 Results and discussion
4.3.4 Summary
4.4 Segmental and chain dynamics in nanometric layers of poly(cis-1,4-isoprene)
4.4.1 Introduction
4.4.2 Experimental details and data analysis
4.4.2.1 Sample preparation
4.4.2.2 Data analysis
4.4.3 Results and discussion
4.4.3.1 1- versus 2-D confinement of poly(cis-1,4-isoprene)
4.4.4 Summary
5 Conclusions
5.1 Dynamics in confinement – a wider perspective
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:11953 |
| Date | 30 October 2014 |
| Creators | Mapesa, Emmanuel Urandu |
| Contributors | Kremer, Friedrich, Colmenero de León, Juan, Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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