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Surface-confined photopolymerization of pH-responsive acrylamide/acrylate brushes on polymer thin films
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
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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%.

Place, publisher, year, edition, pages
2008. Vol. 24, no 14, 7559-7564 p.
Keyword [en]
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: urn:nbn:se:kth:diva-17676DOI: 10.1021/la800700hISI: 000257468300072Scopus ID: 2-s2.0-47949088757OAI: oai:DiVA.org:kth-17676DiVA: diva2:335721
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Signal Enhancement by Dynamic Polymers in Quartz Crystal Microbalance Applications
Open this publication in new window or tab >>Signal Enhancement by Dynamic Polymers in Quartz Crystal Microbalance Applications
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

 This licentiate thesis presents studies of signal enhancement by dynamic polymers in quartz crystal microbalance (QCM) applications. The aim of the study has been to determine the potential for the use of polymers on QCM sensors for signal enhancement in molecular interaction studies. A method for synthesis of polymer sensor surfaces on QCM substrates was developed based on an iniferter photo polymerization technique. Polymerized poly(acrylic acid) and poly(acryl amide) surfaces were extensively characterized with electron spectroscopy for chemical analysis (ESCA), infrared reflection absorption spectroscopy (IRAS) and atomic force microscopy (AFM). The QCM response dynamics of these surfaces to pH changes was studied and the carboxyl containing surfaces exhibited large, reversible and highly reproducible frequency shifts due to expansion of deprotonated polymer chains. Surface acid dissociation constants (pKa) were determined for poly(acrylic acid) surfaces, carboxymethyldextran surfaces and self-assembled monolayer carboxyl surfaces by means of pH titration in QCM flow-through instrumentation. Surface pKa data was consistent with available literature data. The sensitivity enhancement for molecular interaction studies was investigated for poly(acrylic acid) coated QCM sensors with a model system consisting of immobilized biotin and an anti-biotin Fab fragment. Binding responses of antibiotin Fab to immobilized biotin was revealed to be 11 times higher than the corresponding results for a carboxylated SAM surface.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 41 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:17
Keyword
Signal enhancement, QCM, polyelectrolytes, hydrogel, iniferter, photopolymerization, dynamic polymers
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-10305 (URN)978-91-7415-307-1 (ISBN)
Presentation
2009-05-27, E3, Osquars backe 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2009-05-07 Created: 2009-05-06 Last updated: 2010-10-15Bibliographically approved
2. Grafted Molecular Layers for Control of Surface Properties
Open this publication in new window or tab >>Grafted Molecular Layers for Control of Surface Properties
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:nbn:se:kth:diva-103703 (URN)978-91-7501-502-6 (ISBN)
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

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