Interfacial behaviour of surfactants and enzymes: studies at model surfaces

Abstract

This thesis presents results from experimental studies of the interfacial behaviour of surfactants and enzymes at model surfaces. The main technique used throughout the work was ellipsometry.



Studies of surfactant adsorption in static and dynamic wetting situations were performed to investigate adsorption behaviour close to the three-phase contact line (tpl) during dynamic wetting. It was demonstrated for a hydrophobic substrate and a non-ionic surfactant that the dynamic wetting behaviour is strongly affected by surfactant transport over the advancing tpl. This transport route appears to determine the adsorption at the interfaces joining in the tpl and thus also the dynamic wetting tension. It was concluded that the adsorption rate-determining step was the diffusion of surfactant from the bulk solution to the liquid/vapour interface. In contrast to the hydrophobic substrate surfactant carry-over across the tpl to hydrophilic silica substrates was much less efficient. Apparently the reassembly into the surface bilayer/micellar structures which form at the hydrophilic surface is a slower process than simply transferring surfactants from one monolayer at the liquid-vapour interface to another at the hydrophobic solid-liquid interface. Binary surfactant systems comprising cationic and non-ionic surfactants were also studied at hydrophobic solid surfaces in static and dynamic wetting situations. Adsorption isotherms indicated that below the cmc the surface layer consisted almost exclusively of the low solubility non-ionic surfactant. At higher surfactant concentrations the cationic surfactant mixes into the layer. Furthermore, the equilibrium adsorption behaviour was mirrored in the kinetics of desorption. The measured desorption curves indicated a transitional compositional changes and back-diffusion of the non-ionic surfactant due to changes in the concentration gradients of the two components within the diffusion zone. Adsorption and wetting force measurements, measured during substrate immersion were found to correlate to the equilibrium adsorption behaviour.



In a comparison of surfactant adsorption measurements performed by quartz crystal microbalance (QCM) and ellipsometry, the question of consistency and complementary of the two techniques were addressed. It was shown that the frequency shift obtained from the QCM experiments results in an overestimation of the adsorbed mass, due to the presence of water coupled to or trapped within the adsorbed layer. This effect was shown to be larger for a hydrophilic surface than for a hydrophobic substrate consistent with less dense surface layers and/or surface bound water.



In order to facilitate studies of the interfacial behaviour of cellulose active enzymes, different methods for producing model surfaces was assessed and elaborated. The substrates produced by our modified spin-coating procedure fulfilled the demands of being chemically pure, stable in aqueous solutions, smooth and reflecting thereby allowing studies of surfactant and polymer adsorption as well as enzymatic degradation. Investigation of a commercial cellulase mixture at the cellulose model surface, showed that subsequent to an initial adsorption phase the cellulose film began to degrade with time in a concentration dependent manner. In a study where the structure of the enzyme was varied the carbohydrate-binding module (CBM) of the enzyme was shown to play a major role for the binding at the cellulose interface, as well as for the subsequent degradation process. Removing the CBM resulted in a lower adsorption of the cellulase and a slower rate of degradation. Removal of the CBM also resulted in elimination of the pH dependent degradation observed for the native enzyme.

Abstract (Swedish)

Popular Abstract in Swedish

Denna avhandling presenterar resultat från experimentella studier av tensiders och enzymers beteenden vid modellytor. Ellipsometri var den i huvudsak använda tekniken i dessa undersökningar.



Studier av tensidadsorption i statiska och dynamiska vätningssituationer initierades för att undersöka adsorptionsbeteenden i närheten av trefaslinjen under dynamisk vätning. I fallet hydrofob yta och nonjontensid visades att det dynamiska vätningsbeteendet var starkt beroende av tensidtransport, från luft/vätska gränsytan till substratet, via den framskridande trefaslinjen. Denna transportväg föreföll avgöra tensidadsorptionen till gränsytorna vid trefaslinjen och därmed också det dynamiska vätningsbeteendet. Till skillnad från fallet med hydrofob yta, så föreföll adsorptionen till hydrofila ytor inte vara dominerad av transport via trefaslinjen. Uppenbarligen så är formation av bilager eller ytaggregat vid en hydrofil yta långsammare än formation av monolager vid en hydrofob yta. Även binära tensidsystem bestående av katjontensid och nonjontensid vid hydrofoba ytor studerades. Adsorptionsisotermer indikerade att under den kritiska micellkoncentrationen så består det adsorberade lagret i huvudsak av den låglösliga nonjontensiden. Vid högre tensidkoncentrationer sker en inblandning av katjontensid i det adsorberade lagret. Vidare så avspeglades adsorptionsbeteendet vid jämvikt i desorptionskinetiken då tensidkoncentrationen i mätcellen sänktes genom sköljning. De uppmätta desorptionskurvorna indikerade en förändring av ytkompositionen genom diffusion av nonjontensid till ytlagret. Detta som en följd av förändring i koncentrationsgradienterna i diffusionszonen vid ytan för de två tensiderna. Mätning av adsorption och vätningskraft under dynamisk vätning visade överensstämmelse med adsorptionsbeteendet vid jämvikt.



I en jämförande mätning av tensidadsorption med kvartskristallmikrovåg (QCM) och ellipsometri, undersöktes om de två teknikerna ger samma resultat. Resultaten visade att QCM-mätningar överskattar den adsorberade massan på grund av att tekniken inkluderar vatten bundet till den adsorberade tensidfilmen. Denna effekt var större för den hydrofila ytan än för den hydrofoba ytan.



En modellyta av cellulosa tillverkades med avsikt att användas i undersökningar av cellulosaaktiva enzymers gränsytebeteende. Ytan som tillverkades genom att spinna ut en cellulosafilm på ett kiselsubstrat, uppfyllde kraven på kemisk renhet, stabilitet i vattenlösning och användbarhet i ellipsometristudier. Cellulosaytans möjligheter demonstrerades genom mätning av tensid- och polymeradsorption så väl som enzymatisk nedbrytning av ytan. En kommersiell enzymblandnings beteende vid cellulosaytan undersöktes. Vid tillsats av enzym skedde initialt adsorption av enzym följt av nedbrytning av ytan. Nedbrytningshastigheten visade ett starkt beroende av enzymkoncentrationen, med snabbare nedbrytning vid högre enzymkoncentration. I en studie av ett enzym i olika varianter, visades att enzymets kolhydratbindande modul (CBM) spelar en viktig roll i enzymets inbindning till cellulosaytan och den påföljande nedbrytningen. Enzymet utan CBM visade an lägre adsorption till ytan samt lägre nedbrytningshastighet. Även nedbrytningens pH beroende, observerat för det ursprungliga enzymet, eliminerades för enzymet utan CBM.

• author: Eriksson, Olaspers Jonny
• supervisor: [unknown] [unknown]
• opponent: Prof Arnebrant, Thomas, Malmö högskola
• organization: Physical Chemistry
• publishing date: 2004
• type: Thesis
• publication status: published
• subject: Physical Chemistry
• keywords: Surface and boundary layery chemistry, gränsskikt, enzymatic degradation, cellulase, model film, cellulose, QCM, ellipsometry, surfactant, three-phase contact line, adsorption, wetting, Ytkemi
• pages: 122 pages
• defense location: Hörsal B, Kemicentrum, Lund
• defense date: 2004-02-13 10:15:00
• ISBN: 91-7422-043-8
• language: English
• LU publication?: yes
• additional info: Article: Paper IWetting effects due to surfactant carryover through the three-phase contact lineJonny Eriksson, Fredrik Tiberg and Boris ZhmudLangmuir 2001, 17, 7274 Article: Paper IIAdsorption and wetting at hydrophobic surfaces by cationic and cationic / non-ionic surfactant solutionsJonny Eriksson, Boris Zhmud and Fredrik TibergManuscript Article: Paper IIIA comparative study of surfactant adsorption on model surfaces using the quartz crystal microbalance and the ellipsometerJohan Stålgren, Jonny Eriksson and Katrin BoschkovaJournal of Colloid and Interface Science 2002, 253, 190 Article: Paper IVModel cellulose films on silica – preparation, characterisation and applicationsJonny Eriksson, Martin Malmsten, Fredrik Tiberg, Thomas Hønger Callisen and Ture DamhusSubmitted to Journal of Colloid and Interface Science Article: Paper VEnzymatic degradation of model cellulose filmsJonny Eriksson, Martin Malmsten, Fredrik Tiberg, Thomas Hønger Callisen, Ture Damhus and Katja S. JohansenSubmitted to Journal of Colloid and Interface Science Article: Paper VIModel cellulose films exposed to H. insolens glucoside hydrolase family 45 endo-cellulase – the effect of the carbohydrate-binding moduleJonny Eriksson, Martin Malmsten, Fredrik Tiberg, Thomas Hønger Callisen, Ture Damhus and Katja S. JohansenSubmitted to Journal of Colloid and Interface Science
• id: e8cdd5c6-e9df-442b-985a-fec651a4f6dc (old id 466603)
• date added to LUP: 2016-04-04 11:42:16
• date last changed: 2018-11-21 21:06:39