Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Grafted Molecular Layers for Control of Surface Properties
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The goal of this thesis work was to develop responsive surface grafted brushlayers for control of surface properties and to gain insights in the molecular mechanisms that control these properties. Three types of grafted layers were investigated, as outlined below. In the first system studied, poly(AAc) was synthesized by a grafting from approach, utilizing a photopolymerization reaction from a macroinitiator cast onto QCM substrates. The responsiveness in terms of frequency change, Δf, of the resulting brushes to changes in bulk pH was studied with QCM. Further, the friction properties of poly(AAc) was elucidated with colloidal probe AFM as a function of pH and counterion valency. High friction (μ=0.27) was found in presence of CaCl2 at high pH (7.5), but not under any other condition explored. It was concluded that the high friction was due to intralayer COO--Ca2+--OOC bridges. QCM-D was utilized for studying viscoelastic properties of growing poly(AAc) films during in situ photopolymerization. By Voigt modeling, the thickness, shear elasticity and shear viscosity were extracted. These parameters were observed to undergo sudden transitions at a critical thickness, and from this thickness the grafting density of the growing poly(AAc) layers was determined. In addition, the sensitivity to changes in Δf and ΔD with respect to the thickness of the poly(AAc) films was investigated, and the results showed that high sensitivity in ΔD is retained at higher film thicknesses than for Δf, and that the sensitivity with respect to noise can significantly alter the thickness that is best suited forthe study of viscoelastic changes in sensor applications. The work with QCM-D also involved the detection of structural variations within a thick brush layer of poly(AAc). Since lower overtones have higher penetration depth, these frequencies sense polymer segments further out in the brush. It was found that the apparent pKa of the poly(AAc) was higher for lower overtones, indicating therelative ease of acid dissociation in segments further out in the polyelectrolytebrush. In the second system studied, phenylethylamine (PEA) was electrografted to flatsurfaces of glassy carbon (GC). The nanomechanical properties, such as topography, deformation, adhesion and dissipation, were investigated using PeakForce quantitative nanomechanical mapping (QNM). One main finding is that globular domains of 40 to 50 nm indiameter appear in the electrografted PEA layer. They are assigned to clusters of PEA formed due to less rapid reactions between radicals and the GC surface compared to reactions with already grafted PEA. The interactions between the PEA layer and a silica sphere were further investigated by surface force measurements. A main finding is that the PEA surfaces were heavily charge regulated due to the limited net charge of the PEA layer compared to that of silica. In the third system studied, the mechanical response of polyelectrolytes as a function of applied load, probing angle and pH was investigated with PeakForce QNM. The used polyelectrolyte was poly(2-dimethylaminoethyl methacrylate)(PDMAEMA) with pKa of 6.5 to 7.5 and grafted to silica nanoparticles. While most research on polyelectrolyte brushes is conducted by employing flat and smooth surfaces, with a roughness on the nanometer scale, real surfaces are rarely ever ideally flat but rather they possess topographic irregularities on nano- and micro-scales, which locally imparts high curvatures. The spherical geometry of the core-shell nanoparticles serves as a model for real surfaces with respect to topographical irregularities of real surfaces. The nanoscale brushes were probed with an ultrasharp AFM tip, providing nanoscale resolution of topography, deformation, adhesion and dissipation. It was found that the mechanical response of the polyelectrolyte corona is dependent on the applied load and the polar angle of the tip-brush interaction. All nanomechanical data show a non-monotonic variation with horizontal position, and the peak values are shifted in magnitude and position as a function of peak force. The effect of pH on deformation was further investigated. The results showed that the brush is more resistant against compression over the centre than it is to deflection at larger horizontal positions, and this effect is amplified by charging the brush. This work provided understanding of the direction dependence of the mechanical properties and is relevant for the design of brush boundary lubricating agents for rough surfaces, where the polymer chains are both being bent and compressed under the influence of load and shear.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012.
Series
Trita-CHE-Report, ISSN 1654-1081 ; TRITA-CHE Report 2012:49
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-103703ISBN: 978-91-7501-502-6 (print)OAI: oai:DiVA.org:kth-103703DiVA: diva2:561332
Public defence
2012-11-09, K2, Teknikringen 28, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20121018

Available from: 2012-10-18 Created: 2012-10-18 Last updated: 2012-10-30Bibliographically approved
List of papers
1. Surface-confined photopolymerization of pH-responsive acrylamide/acrylate brushes on polymer thin films
Open this publication in new window or tab >>Surface-confined photopolymerization of pH-responsive acrylamide/acrylate brushes on polymer thin films
Show others...
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 14, 7559-7564 p.Article in journal (Refereed) Published
Abstract [en]

Dynamic acrylamide/acrylate polymeric brushes were synthesized at gold-plated quartz crystal surfaces. The crystals were initially coated with polystyrene-type thin films, derivatized with photolabile iniferter groups, and subsequently subjected to photoinitiated polymerization in acrylamide/acrylate monomer feeds. This surface-confined polymerization method enabled direct photocontrol over the polymerization, as followed by increased frequency responses of the crystal oscillations in a quartz crystal microbalance (QCM). The produced polymer layers were also found to be highly sensitive to external acid/base stimuli. Large oscillation frequency shifts were detected when the brushes were exposed to buffer solutions of different pH. The dynamic behavior of the resulting polymeric brushes was evaluated, and the extent of expansion and contraction of the films was monitored by the QCM setup in situ in real time. The resulting responses were rapid, and the effects were fully reversible. Low pH resulted in full contractions of the films, whereas higher pH yielded maximal expansion in order to minimize repulsion around the charged acrylate centers. The surfaces also proved to be very robust because the responsiveness was reproducible over many cycles of repeated expansion and contraction. Using ellipsometry, copolymer layers were estimated to be similar to 220 nm in a collapsed state and similar to 340 nm in the expanded state, effectively increasing the thickness of the film by 55%.

Keyword
Bioelectric phenomena, Brushes, Chemical reactions, Crystallography, Frequency response, Gold, Molecular beam epitaxy, Monomers, Oxide minerals, Photopolymerization, Polyethylenes, Polymerization, Polymers, Powders, Quartz, Quartz crystal microbalances, Shrinkage, Thick films, Thin films
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-17676 (URN)10.1021/la800700h (DOI)000257468300072 ()2-s2.0-47949088757 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Friction between Surfaces—Polyacrylic Acid Brush and Silica—Mediated by Calcium Ions
Open this publication in new window or tab >>Friction between Surfaces—Polyacrylic Acid Brush and Silica—Mediated by Calcium Ions
2010 (English)In: Journal of Dispersion Science and Technology, ISSN 0193-2691, E-ISSN 1532-2351, Vol. 31, 1285-1287 p.Article in journal (Refereed) Published
Abstract [en]

With this letter, we report how friction can be controlled by inducing physical bonds solely within a polyelectrolyte brush layer, while keeping repulsive interactions between the brush layer and the bare surface that slides above. Our results imply that the nature of the bare surface is of minor importance as long as the repulsive surface interaction is maintained.

Keyword
AFM, boundary lubrication, brush layer, calcium ion, poly(acrylic acid)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-48436 (URN)10.1080/01932691.2010.511973 (DOI)000281904700001 ()2-s2.0-77956758781 (Scopus ID)
Note
QC 20111121Available from: 2011-11-18 Created: 2011-11-18 Last updated: 2017-12-08Bibliographically approved
3. Attractive double-layer forces and charge regulation upon interaction between electrografted amine layers and silica
Open this publication in new window or tab >>Attractive double-layer forces and charge regulation upon interaction between electrografted amine layers and silica
Show others...
2012 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 385, 225-234 p.Article in journal (Refereed) Published
Abstract [en]

Amine functionalities have been introduced on glassy carbon surfaces through electrografting of 4-(2-aminoethyl)benzenediazonium tetrafluoroborate. The grafted layers were characterized by ellipsometry and by nanomechanical mapping in air and aqueous solutions using the atomic force microscopy Peak-Force QNM mode. The layer was found to be 2.5 nm thick with low roughness, comparable to that of the glassy carbon substrate. However, small semi-spherical features were observed in the topographical image, indicating a clustering of the grafted amine compound. The nanomechanical mapping also demonstrated some swelling of the layer in water and pointed toward an important contribution of electrostatic interactions for the tip-surface adhesion. The forces between an aminated glassy carbon surface and a mu m-sized silica particle in aqueous solutions were measured at different ionic strength and pH-values. The results demonstrate that an attractive double-layer force predominates at large separations, and that the surface charge densities increase as the separation between the surfaces decreases. The degree of charge regulation on the aminated glassy carbon is significant. The relatively low surface charge density of the aminated glassy carbon is attributed to significant incorporation of counterions in the water-rich grafted layer.

National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-103356 (URN)10.1016/j.jcis.2012.06.071 (DOI)000308511600028 ()2-s2.0-84865385259 (Scopus ID)
Note

QC 20121012

Available from: 2012-10-12 Created: 2012-10-11 Last updated: 2017-12-07Bibliographically approved
4. Nanomechanical mapping of a high curvature polymer brush grafted from a rigid nanoparticle
Open this publication in new window or tab >>Nanomechanical mapping of a high curvature polymer brush grafted from a rigid nanoparticle
Show others...
2012 (English)In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 8, no 32, 8312-8320 p.Article in journal (Refereed) Published
Abstract [en]

Analysis of interaction forces when probing a silica core-polyelectrolyte brush shell nanoparticle, adsorbed on a silica substrate and bathed by aqueous electrolyte solution, with an ultrasharp atomic force microscopy (AFM) tip provides a spatially resolved map of heterogeneous mechanical properties across the nanoparticle. The deformation of the brush is mainly compressive when probed directly above the nanoparticle centre and mainly deflective when probed at a finite horizontal distance away from the centre. The brush is significantly stiffer against compression than against deflection, and ionization of the brush has a greater stiffening effect against compression than deflection. Whereas a height image of the core-shell nanoparticle was unremarkable, showing a monotonic decrease in height with increasing horizontal distance from the centre, brush deformation, energy dissipation and adhesion displayed local minima over the centre and maxima at a finite horizontal distance away from the centre, corresponding to a position near the rigid core nanoparticle edge. The different response to brush deformation depending on the angle of probing is relevant to the interactions of brush-decorated macroscopic surfaces with submicrometer roughness and to the interactions of brush-decorated nanoparticles with ultrafine structures in their environments.

Keyword
Transfer Radical Polymerization, Polyelectrolyte Brushes, Frictional Forces, Solid-Surfaces, Interface, Afm, Lubrication, Microscopy, Dynamics, Particle
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-101138 (URN)10.1039/c2sm26086g (DOI)000306855000009 ()2-s2.0-84864452225 (Scopus ID)
Note

QC 20120823

Available from: 2012-08-23 Created: 2012-08-23 Last updated: 2017-12-07Bibliographically approved
5. Determination of grafting density of poly(acrylic acid) in a grafting: from approach using quartz crystal microbalance with dissipation
Open this publication in new window or tab >>Determination of grafting density of poly(acrylic acid) in a grafting: from approach using quartz crystal microbalance with dissipation
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-103712 (URN)
Note

QS 2012

Available from: 2012-10-18 Created: 2012-10-18 Last updated: 2012-10-30Bibliographically approved
6. Frequency and dissipation measurements of in situ grafted poly(acrylic acid): a study of sensitivity and signal-to-noise ratio from thin to thick viscoelastic regime
Open this publication in new window or tab >>Frequency and dissipation measurements of in situ grafted poly(acrylic acid): a study of sensitivity and signal-to-noise ratio from thin to thick viscoelastic regime
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-103711 (URN)
Note

QS 2012

Available from: 2012-10-18 Created: 2012-10-18 Last updated: 2012-10-30Bibliographically approved
7. Acid dissorciation constant gradients in a thick viscoelastic film determined by dissipation monitoring using quartz crystal microbalance
Open this publication in new window or tab >>Acid dissorciation constant gradients in a thick viscoelastic film determined by dissipation monitoring using quartz crystal microbalance
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-103709 (URN)
Note

QS 2012

Available from: 2012-10-18 Created: 2012-10-18 Last updated: 2012-10-30Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Dunér, Gunnar
By organisation
Applied Physical Chemistry
Chemical Sciences

Search outside of DiVA

GoogleGoogle Scholar

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 929 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf