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Interactions between Chitosan and SDS at a Low-Charged Silica Substrate Compared to Interactions in the Bulk: The Effect of Ionic Strength
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.ORCID iD: 0000-0002-2288-819X
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 8, 3814-3827 p.Article in journal (Refereed) Published
Abstract [en]

The effect of ionic strength on association between the cationic polysaccharide chitosan and the anionic surfactant sodium dodecyl sulfate, SDS, has been studied in bulk solution and at the solid/liquid interface. Bulk association was probed by turbidity, clectrophoretic mobility, and surface tension measurements. The critical aggregation concentration, cac, and the saturation binding of surfactants were estimated from surface tension data. The number of associated SDS molecules per chitosan segment exceeded one at both salt concentrations. As a result, a net charge reversal of the polymer-surfactant complexes was observed, between 1.0 and 1.5 mM SDS, independent of ionic strength. Phase separation occurs in the SDS concentration region where low charge density complexes form, whereas at high surfactant concentrations (up to several multiples of cmc SDS) soluble aggregates are formed. Ellipsometry and QCM-D were employed to follow adsorption of chitosan onto low-charged silica substrates, and the interactions between SDS and preadsorbed chitosan layers. A thin (0.5 nm) and rigid chitosan layer was formed when adsorbed from a 0.1 mM NaNO3 solution, whereas thicker (2 nm) chitosan layers with higher dissipation/unit mass were formed from solutions at and above 30 mM NaNO3. The fraction of solvent in the chitosan layers was high independent of the layer thickness and rigidity and ionic strength. In 30 mM NaNO3 Solution, addition of SDS induced a collapse at low concentrations, while at higher SDS concentrations the viscoelastic character of the layer was recovered. Maximum adsorbed mass (chitosan + SDS) was reached at 0.8 times the cmc of SDS, after which surfactant-induced polymer desorption occurred. In 0.1 mM NaNO3. the initial collapse was negligible and further addition of surfactant lead to the formation of a nonrigid, viscoelastic polymer layer until desorption began above a surfactant concentration of 0.4 times the cmc of SDS.

Place, publisher, year, edition, pages
2008. Vol. 24, no 8, 3814-3827 p.
Keyword [en]
sodium dodecyl-sulfate; quartz-crystal microbalance; solid-liquid interface; air-water-interface; x-ray-scattering; anionic surfactant; cationic polyelectrolyte; viscoelastic properties; electrolyte-solutions; air/water interface
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-11138DOI: 10.1021/la702653mISI: 000254647400020Scopus ID: 2-s2.0-42449149169OAI: oai:DiVA.org:kth-11138DiVA: diva2:236334
Note
QC 20100729Available from: 2009-09-22 Created: 2009-09-22 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Interactions Between Biopolymers and Surfactants with Focus on Fluorosurfactants and Proteins
Open this publication in new window or tab >>Interactions Between Biopolymers and Surfactants with Focus on Fluorosurfactants and Proteins
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of this thesis was to obtain a better understanding of the association between surfactants and biopolymers in bulk solutions and at solid/aqueous liquid interface. In order to do this, the interactions between surfactants and biopolymers were investigated with a variety of experimental techniques.

The main focus has been on the interactions between fluorosurfactants and proteins, which are important during electrophoresis of proteins in silica capillaries. Electrophoretic separation of positively charged proteins is often complicated by non-specific adsorption of protein onto capillary wall, while it was found to improve when cationic fluorosurfactants were added into the background buffer. We investigated the interactions between a cationic fluorosurfactant, FC134, and a positively charged protein, lysozyme. By employing Nuclear Magnetic Resonance (NMR) and tensiometry we could conclude that the cationic fluorosurfactant did not associate with positively charged lysozyme in bulk solutions. At the solid/aqueous liquid interface, the adsorption of fluorosurfactants and lysozyme onto silica was studied by the surface force technique (MASIF), ellipsometry, reflectrometry, Quartz Crystal Microbalance (QCM-D) and Atomic Force Microscopy (AFM). Cationic fluorosurfactant FC134 was found to adsorb onto the silica surface in a form of bilayer aggregates, which led to a charge reversal of the originally negatively charged substrate. The adsorption of lysozyme onto silica was also extensive and it corresponded to the more than monolayer coverage. When adsorbing from mixed solutions, the presence of the cationic fluorosurfactant in the solution led to an elimination of the lysozyme in the resulting adsorbed layer. For the lysozyme concentration of 0.2 mg/ml, which is typical for the electrophoretic separation, it was found that adsorption of protein was suppressed by more than 90% when only 30 μM of FC134 was added into the buffer. The presence of the low amounts of residual proteins in the adsorbed layers caused an enhancement of the adsorption of fluorosurfactants, which was attributed to adsorption of the fluorosurfactants between proteins in a form of large vesicles.

The interactions between a positively charged biopolymer chitosan and an anionic surfactant sodium dodecylsulfate (SDS) were studied with respect to the effect of the ionic strength of the background electrolyte, both in the bulk solution and at the silica/liquid interface. It was shown that SDS and chitosan form complexes in the bulk solution, which reverse their charge at higher SDS concentrations. At SDS concentrations above the critical micellar concentration, large aggregates were formed, which were trapped in long-lived nonequilibrium states at both high and low ionic strengths. SDS did not adsorb at the silica/liquid interface by itself. However, by employing QCM-D and ellipsometry we detected an extensive adsorption of SDS on the silica substrate, which has been modified by adsorbed chitosan. The structure of the chitosan layer on the lowly charged silica was strongly affected by the ionic strength of the solution from which the chitosan adsorption took place. The interactions between SDS and the pre-adsorbed chitosan were found to be similar on lowly charged silica and on highly charged mica.

A novel method based on the Bruggeman effective medium approximation was proposed for the evaluation of ellipsometric data characterizing composite adsorbed layers.

Finally, the effect of the adsorbed layer surface roughness on the QCM-D response in liquid was studied with focus on trapped water. It was found that QCM-D effectively senses water, which is mechanically trapped inside topographical structures with the size in nano-meter scale.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 97 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:54
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-4475 (URN)978-91-7178-739-2 (ISBN)
Public defence
2007-09-14, Salongen, KTH Biblioteket, Osquara backe 31, Stockholm, 09:00
Opponent
Supervisors
Note
QC 20100809Available from: 2009-08-30 Created: 2007-08-30 Last updated: 2010-08-09Bibliographically approved
2. Adsorption of biopolymers and their layer-by-layer assemblies on hydrophilic surfaces
Open this publication in new window or tab >>Adsorption of biopolymers and their layer-by-layer assemblies on hydrophilic surfaces
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

It is widely known that surfaces play an important role in numerous biological processes and technological applications. Thus, being able to modify surface properties provides an opportunity to control many phenomena occurring at interfaces. One way of controlling surface properties is to adsorb a polymer film onto the surface, for example through layer-by-layer (LbL) deposition of polyelectrolytes. This simple but versatile technique enables various polymers, proteins, colloidal particles etc. to be incorporated into the film, resulting in a multifunctional coating. Due to recent legislations and a consumer demand for more environmentally friendly products, we have chosen to use natural polymers (biopolymers) from renewable resources. The focus of this thesis has been on the adsorption of biopolymers and their layer-by-layer formation at solid-liquid interfaces; these processes have been studied by a wide range of techniques. The main method was the quartz crystal microbalance with dissipation monitoring (QCM-D), which measures the adsorbed mass, including trapped solvent and the viscoelastic properties of an adsorbed film. This technique was often complemented with an optical method, such as ellipsometry or dual polarization interferometry (DPI), which provided information about the “dry” polymer or protein adsorbed mass. From this combination, the solvent content and density of the layers was evaluated. In addition, the surface force apparatus (SFA), X-ray photoelectron spectroscopy (XPS), total internal reflection fluorescence (TIRF), and fluorescence resonance energy transfer (FRET) were utilized, providing further information about the film structure, chemical composition, and polymer inter-layer diffusion. Adsorption studies of the glycoprotein mucin, which has a key role in the mucousal function, showed that despite the net negative charge of mucin, it adsorbed on negatively charged substrates. The adsorbed layer was highly hydrated and the segment density on the substrate was low. We showed the importance of characterizing the mucin used, since differences in purity, such as the presence of albumin, gave rise to different adsorption behaviours in terms of both adsorbed amount and structure. The adsorbed mucin layer was to a large extent desorbed upon exposure to the anionic surfactant sodium dodecyl sulfate (SDS). In order to prevent desorption, we demonstrated that a protective layer of the cationic polysaccharide chitosan could be adsorbed onto the mucin layer and that the mucin-chitosan complexes resisted the desorption normally induced by association with SDS. Moreover, the association between chitosan and SDS was examined at the solid-liquid interface, in the bulk, and at the air-water interface. In all these environments chitosan-SDS complexes were formed and a net charge reversal of the complexes from positive to negative was observed when the concentration of SDS was increased. Furthermore, the LbL deposition method could be used to form a multilayer-like film by alternate adsorption of mucin and chitosan on silica substrates. The LbL technique was also applied to two proteins, lysozyme and β-casein with the aim of building a multilayer film consisting entirely of proteins. These proteins formed complexes at the solid-liquid interface, resulting in a proteinaceous layer, but the build-up was highly irregular with an increase in adsorbed amount per protein deposition cycle that was far less than a monolayer.Continuing with chitosan, known to have antibacterial properties we assembled multilayers with an anti-adhesive biopolymer, heparin, to evaluate the potential of this system as a coating for medical implants. Multilayers were assembled under various solution deposition conditions and the film structure and dynamics were studied in detail. The chitosan-heparin film was highly hydrated, in the range 60-80 wt-% depending on the deposition conditions. The adsorbed amount and thickness of the film increased exponential-like with the number of deposition steps, which was explained by inter-diffusion of chitosan molecules in the film during the build-up. In a novel approach, we used the distant dependent FRET technique to prove the inter-layer diffusion of fluorescent-labelled chitosan molecules within the film. The diffusion coefficient was insignificantly dependent on the deposition pH and ionic strength, and hence on the film structure. With the use of a pH sensitive dye buried under seven chitosan-heparin bilayers, we showed that the dye remained highly sensitive to the charge of the outermost layer. From complementary QCM-D data, we suggested that an increase in the energy dissipation does not necessarily indicate that the layer structure becomes less rigid.

Abstract [sv]

Det är välkänt att ytor spelar en viktig roll i många biologiska processer och tekniska tillämpningar. Att kunna modifiera en ytas egenskaper ger därför en möjlighet att kunna kontrollera många fenomen som sker på ytor. Ett sätt att kontrollera ytegenskaperna är genom att adsorbera en polymerfilm på ytan, till exempel genom att växelvis adsorbera olika polyelektrolyter (LbL-teknik). Denna enkla men mångsidiga teknik möjliggör att många olika material kan införlivas i filmen, vilket resulterar i en multifunktionell beläggning. På grund av dagens lagstiftning och konsumenters ökade efterfrågan på miljövänliga material beslutade vi oss för att använda biologiska polymerer (biopolymerer) i detta projekt. Fokus i den här avhandlingen har varit på adsorption av biopolymerer och deras LbL-formation på gränsytan vätska-fast fas, där adsorptionsförloppet och det adsorberade skiktet bestående av biopolymerer studerats med en mängd olika tekniker. Huvudtekniken var kvartskristallmikrovåg med energidissipations-registrering (QCM-D), som mäter massan inklusive inkorporerat vatten, samt de viskoelastiska egenskaperna hos ett adsorberat skikt. Som komplement till denna teknik användes ofta optiska metoder, till exempel ellipsometri och ”dubbel polarisationsinterferometri (DPI)”, två tekniker som endast mäter massan av de adsorberade biopolymererna. Genom denna kombination av metoder kunde massan av inkorporerat vatten i filmen och filmens densitet bestämmas. Dessutom användes ytkraftsapparaten (SFA), röntgenfotoelektronspektrometri (XPS), och fluorescens-spektroskopiteknikerna TIRF och FRET i några undersökningar för att erhålla information om skiktens struktur, kemiska sammansättning och polymerernas diffusion inom skiktet.Adsorptionsstudier av glycoproteinet mucin, som har en central roll i funktionen av slemhinnan, avslöjade att trots att mucinet har en negativ nettoladdning adsorberade det ändå på negativt laddade substrat. Det adsorberade lagret var väldigt hydratiserat och hade en låg andel mucin i direkt kontakt med ytan. Vi påvisade vikten av att noga undersöka mucinet som användes, eftersom olika renhet, till exempel i form av förekomsten av albumin gav upphov till olika adsorptionsbeteende gällande både adsorberad mängd och struktur. En stor andel av det adsorberade mucinlagret desorberade när det exponerades för den anjoniska tensiden natriumdodecylsulfat, SDS. Vi visade att ett skyddande lager av den katjoniska polysackariden chitosan kunde adsorberas på mucinet och att mucin-chitosan-komplexen inte desorberade när SDS tillsattes. Därtill studerades växelverkan mellan chitosan och SDS på gränsytan vätska-fast fas, i bulken och på luft-vattengränsytan. Komplex av chitosan-SDS bildades i samtliga miljöer och en nettoladdningsomsvängning från positiv till negativ observerades när koncentrationen av SDS ökades.Vidare kunde LbL-tekniken nyttjas för att skapa ett multilagerlikt skikt genom att alternerande adsorbera mucin och chitosan på kiseldioxidsubstrat. Denna teknik användes även med två proteiner, lysozym och β-kasein, med målet att skapa ett multilager bestående av endast proteiner. Dessa proteiner bildade komplex på gränsytan vätska-fast fas i form av ett blandat proteinlager, men uppbyggnaden var väldigt oregelbunden med en ökning i adsorberad mängd per proteindeponeringscykel som var avsevärt mindre än ett monolager.Inom området för biomaterial utgör de antibakteriella och antihäftande egenskaperna hos chitosan respektive heparin en lovande blandning för beläggningar av medicinska implantat. Baserat på detta konstruerade vi multilagerfilmer av chitosan och heparin med olika deponeringslösningar och undersökte dynamiken och filmens struktur i detalj. Chitosan-heparin-filmen var starkt hydratiserad, bestående av cirka 60-80 vikt-% vatten beroende på deponeringsbetingelserna. Den adsorberade mängden och tjockleken på filmen ökade nästan exponentiellt med antal deponeringar, vilket förklarades med chitosanets förmåga att diffundera genom filmen under uppbyggnaden. Med ett nytt angreppssätt använde vi FRET för att bevisa diffusionen av fluorescerande färgmärkt chitosan i filmen under uppbyggnaden. Diffusionskoefficienten var i princip oberoende av pH och jonstyrka under deponeringen och följaktligen av filmens struktur. Genom att använda ett pH-känsligt färgämne begravt under sju biskikt av chitosan-heparin visade vi att färgämnet i hög grad påverkades av laddningen på det yttersta lagret. Från QCM-D-data lade vi fram teorin om att en ökning av energidissipationen för ett lager inte nödvändigtvis indikerar att lagrets struktur har blivit mindre styvt.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 69 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:49
Keyword
Layer-by-layer, multilayer, adsorption, biopolymers, Chitosan, Heparin, Mucin, Albumin, Lysozyme, β-casein, SDS, QCM-D, Ellipsometri, DPI, TIRF, FRET, SFA, layer structure, solvent content, vertical diffusion, exponential growth, solid-liquid interface, deposition conditions
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-11058 (URN)978-91-7415-419-1 (ISBN)
Public defence
2009-10-09, hörsal F3, KTH, Lindstedtsvägen 26, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20100729Available from: 2009-09-21 Created: 2009-09-14 Last updated: 2011-09-20Bibliographically approved

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