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Influence of Salt and Rinsing Protocol on the Structure of PAH/PSS Polyelectrolyte Multilayers
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
Eotvos Lorand University, Institute of Chemistry, Budapest, Hungary.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0001-7496-1101
2010 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 22, 17048-17057 p.Article in journal (Refereed) Published
Abstract [en]

A quartz crystal microbalance (QCM) and dual polarization interferometry (DPI) have been utilized to study how the structure of poly(allylamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) multilayers is affected by the rinsing method (i.e., the termination of polyelectrolyte adsorption). The effect of the type of counterions used in the deposition solution was also investigated, and the polyelectrolyte multilayers were formed in a 0.5 M electrolyte solution (NaCl and KBr). From the measurements, it was observed that thicker layers were obtained when using KBr in the deposition solution than when using NaCl. There different rinsing protocols have been studied: (i) the same electrolyte solution as used during multilayer formation. (ii) pure water, and (iii) first a salt solution (0.5 M) and then pure water. When the multilayer with PAH as the outermost layer was exposed to pure water, an interesting phenomenon was discovered: a large change in the energy dissipation was measured with the QCM. This could be attributed to the swelling of the layer, and from both QCM and DPI it is obvious that only the outermost PAH layer swells (to a thickness of 25-30 nm) because of a decrease in ionic strength and hence an increase in intra- and interchain repulsion. whereas the underlying layers retain a very rigid and compact structure with a low water content. Interestingly, the outermost PAH layer seems to obtain very similar thicknesses in water independent of the electrolyte used for the multilayer buildup. Another interesting aspect was that the measured thickness with the DPI evaluated by a single-layer model did not correlate with the estimated thickness from the model calculations performed on the QCM-D data. Thus, we applied a two-layer model to evaluate the DPI data and the results were in excellent agreement with the QCM-D results. To our knowledge. this evaluation of DPI data has not been done previously.

Place, publisher, year, edition, pages
2010. Vol. 26, no 22, 17048-17057 p.
Keyword [en]
quartz-crystal microbalance, charge-density, growth regime, ionic-strength, polymer-films, thin-films, water, protein, adsorption, thickness
National Category
Chemical Sciences Physical Chemistry
URN: urn:nbn:se:kth:diva-13937DOI: 10.1021/la102351fISI: 000283837800058ScopusID: 2-s2.0-78650355862OAI: diva2:328465
EU, European Research Council, PERG02-GA-2007-2249Swedish Research Council

QC 201150721 Uppdaterad från submitted till published(20110104). Tidigare titel: The Influence of Salt on the Structure of PAH/PSS polyelectrolytemultilayers

Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2015-07-21Bibliographically approved
In thesis
1. Structures of Polyelectrolyte Multilayers and Preasorbed Mucin: The Influence of Counterions
Open this publication in new window or tab >>Structures of Polyelectrolyte Multilayers and Preasorbed Mucin: The Influence of Counterions
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus in this thesis has been to gain a fundamental understanding of how different type of salts affect preadsorbed polyelectrolytes, both natural and synthetic. The knowledge from the fundamental work is then applied on a commercial system to investigate if the efficiency can be enhanced.

We built thin films using the synthetic polyelctrolytes by using layer-by layer (LbL) deposition. The formed film is commonly known as a polyelectrolyte multilayer. The LbL method allows the incorporation of proteins, polymers, polyelectrolytes with different functions and so on within the film, thus achieving multilayers with different functions.

The major measuring technique used within this thesis is the quartz crystal microbalance with dissipation (QCM-D), which measures mass adsorbed on a surface including the trapped solvent and the viscoelastic properties of an adsorbed film. The QCM-D measurements were complemented with an optical technique, dual polarization interferometry (DPI), which measures the change in refractive index and thickness. From these parameters the dry mass and relative water content of the film can be calculated. The Atomic Force Microscopy (AFM) further gave information about forces acting between preadsorbed films.

We investigated the effect of salt on synthetic polyelectrolyte poly(allylamine hydrochloride)/poly(sodium 4-styrenesulfonate) built with the LbL technique, thus forming polyelectrolyte multilayers. We concluded that the multilayer build-up was linear and that the internal structure of the multilayer is of a compact and rigid nature. However, the type of rinsing protocol (termination of adsorption by: salt, water and salt first followed by water) has a significant effect on the outer layer of the formed multilayer. Interestingly, the structural changes only applied when poly(allylamine hydrochloride) was at the outermost layer and the most significant when water was used. We suggest that it is only the top layer that swells due to the removal of counterions resulting in increased intrachain repulsion. We further performed two-layer model calculations with the Voight model to confirm the QCM-D results as well as a novel two layer model simulation for the DPI data in order to resolve the thickness. The model calculations were in good agreement with each other thus we concluded that only the outer layer swells for this particular multilayer system.

In a related experiment we studied the adsorption of bovine submaxillary mucin (BSM), which has an important mucousal function, to different thiol modified gold surfaces as well as the effect of electrolytes (NaCl, CaCl2, LaCl3) on preadsorbed mucin to a hydrophobic thiol-modified Au surface. The salt induced an expansion at low concentrations; higher concentrations resulted in a compaction. Increasing the valence of the counter ion resultedin a compaction at low concentrations. The structural change of preadsorbed BSM was reversible for NaCl, partially reversible for CaCl2 and irreversible for LaCl3. Interestingly, the swelling of BSM could not be fully understood by using the QCM-D and thus AFM force curves of the same system were taken and the results showed that NaCl does decrease the tail length due to the effective screening of charged sites within the BSM molecule. Increasing the valence resulted in a notable compaction already at very low concentrations suggesting that the ions bind to the anionic sites on BSM.

In the last work we attempted to combine the gained knowledge from the previous studies by using the LbL-buildup on an actual commercial health care application. The above-mentioned mutlilayer were used to coat polystyrene wells in order to increase the binding of immunoglobulin (IgG). The main goal was to increase the sensitivity of the conventional enzymelinked immunosorbent spot assay (ELISpot) and subsequently the modified polystyrene wells were used with the ELISpot test with human peripheral blood mononuclear cells (PBMC) to measure the cytokine response. We suggested that the main driving force for adsorption for IgG on a PAH terminated multilayer is electrostatic attraction, whereas on PSS terminated multilayer the driving force is hydrophobic. Further, we suggested that IgG  does not overcharge the surface and the linearity of the multilayer build-up is not altered when IgG is incorporated within the multilayer structure. We concluded that the cytokine response (spots) on the built multilayers regardless thickness or adsorbed IgG is significantly less than the regular polyvinyldiene fluoride (PVDF) backed ELISpot wells. We suggested that due to the compact and rigid nature of the PAH/PSS multilayer structure it is unable to form the kind of three-dimensional antibody-binding support found in the PVDF membrane. PSS terminated PAH/PSS multilayer did not induce any cytokine response whereas PAH terminated did, which suggests that PSS totally covers the surface from the cells point of view.


Place, publisher, year, edition, pages
Stockholm: KTH, 2010. ix, 51 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2010:18
National Category
Physical Chemistry
urn:nbn:se:kth:diva-13182 (URN)978-91-7415-639-3 (ISBN)
Public defence
2010-06-11, E1, Lindstedtsvägen 3, entréplan, KTH, Stockholm, 10:00 (English)
QC20100705Available from: 2010-06-01 Created: 2010-06-01 Last updated: 2010-07-05Bibliographically approved

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