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Probing Interactions between Bio-Fibre Components
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [sv]

I den här avhandlingen har atomkrafts mikroskopi (AFM) och kvartskristall mikrovåg med dissipation (QCM-D) används för att undersöka interaktioner i bio-fiber modell system av cellulosa och xyloglukan (XG); en naturligt förekommande polysackarid viktig för tillväxt av träd och andra växter. Dessutom har det avgörande momentet av friktionskrafts-kalibrering studerats för att erhålla noggranna och kvantitativa resultat med kolloidal prob AFM.

Fyra olika cellulosa modell ytor med varierande morfologi har utvärderats med kolloidal prob AFM. De normala ytkrafterna för alla undersökta substrat var kvalitativt likadana. Däremot, för en given ytråhet leder adsorption av XG till en konsekvent reduktion av friktions-koefficienterna för alla ytor, vilket antyder att effekten på friktion av antingen ytråhet eller kemi kan separeras. För att kunna undersöka interaktionen mellan enbart cellulosa och xyloglukan ändmodifierades först XG enzymatiskt med en tiol grupp. Dessa makromolekyler ympades sedan till guld, där de bildade ett tiol-bundet borst-liknande lager. QCM-D experiment bekräftade att det ympade lagret var biologiskt tillgängligt för enzymatisk nedbrytning genom användning av växtenzymet endo-xyloglukanas TmNXG1. Friktions-koefficienterna för den orörda ympningen och den enzymexponerade visade samma trend med ytråheten som i fallet med cellulosaytorna. Adhesions mätningar på denna modellyta visade att den ursprungliga specificiteten mellan xyloglukan och cellulosa bevarades.

Ett antal AFM kantilevrar har kalibrerats med olika tekniker för att erhålla både normal- och friktionsfjäder-konstanter med mål att utvärdera den relativa noggrannheten mellan de olika metoderna. Överensstämmelsen var god mellan teknikerna för att bestämma fjäder konstanterna i normalled. Något högre avvikelse mellan teknikerna för att bestämma torsions fjäder konstanterna förekom. Men denna avvikelse leder inte till kvantitativt olika resultat och baserat på behändighet borde den termiska tekniken av Sader et al. tillämpas. Vidare har det viktiga momentet att kalibrera fotodetektorn behandlats, och en ny teknik föreslås för att bestämma detektor-känsligheten genom att kombinera olika metoder. Slutligen beräknades en konverterings faktor, som gör det möjligt att utföra kalibrering av kantilevern i luft, men att själva friktionsmätningen sedan kan utföras i vätska.

Abstract [en]

In this thesis the atomic force microscope (AFM) and quartz crystal microbalance with dissipation (QCM-D) have been used to investigate interactions in bio-fibre model systems containing cellulose and xyloglucan (XG); a naturally occurring polysaccharide important for plant growth. In addition, the crucial element of friction force calibration has been studied to obtain accurate and quantitative results with the colloidal probe AFM.

Four different cellulose model surfaces with varying morphology have been evaluated using colloidal probe AFM. The normal surface forces for all the substrates studied were qualitatively similar. However, for a given surface roughness the adsorption of XG leads to a consistent decrease in friction coefficients for all substrates, suggesting that the effects on friction arising from either roughness or chemistry can be decoupled. To investigate the interaction between cellulose and XG exclusively the xyloglucan chains were enzymatically modified to include a thiol moiety at the chain end. These were further grafted to gold, forming a thiol-bonded xyloglucan brush-like layer. QCM-D experiments confirmed the graft to be biologically accessible to enzyme digestion using the plant enzyme endo-xyloglucanase TmNXG1. The friction coefficients obtained for the neat brush and the enzyme exposed substrate showed the same trend with surface roughness as for the cellulose surfaces. Adhesion measurements on this model surface indicated that the native specificity between xyloglucan and cellulose is retained.

A number of AFM cantilevers have been calibrated by different techniques to obtain both normal and frictional spring constants to evaluate the relative accuracy of the different methods. Good agreement was found between the techniques for obtaining the normal spring constant. Slightly higher deviations between the techniques used in obtaining the torsional spring constant were observed. However these deviations do not lead to quantitatively different results and based on convenience the thermal technique of Sader et al. is preferred. Further the important issue of the photodetector calibration is addressed and a new technique for obtaining the detector sensitivity by combining different methods is proposed. Finally a conversion factor was calculated that allows for the cantilever calibration to be done for example in air while actual friction measurements can be conducted in liquid.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , vi, 35 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 1654-1081
Keyword [en]
AFM, QCM-D, cellulose, xyloglucan, surface forces, friction, colloidal probe, nanotribology, biomimetic, enzymatic, polysaccharide, self assembly, grafting, thiol, spring constant, calibration, photodetector calibration.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4555ISBN: 978-91-7178-796-5 (print)OAI: oai:DiVA.org:kth-4555DiVA: diva2:12834
Presentation
2007-12-06, K1, Kemi, Teknikringen 56, Stockholm, 10:30
Opponent
Supervisors
Note
QC 20101115Available from: 2007-11-25 Created: 2007-11-25 Last updated: 2011-11-23Bibliographically approved
List of papers
1. Friction and forces between cellulose model surfaces: A comparison
Open this publication in new window or tab >>Friction and forces between cellulose model surfaces: A comparison
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2006 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 303, no 1, 117-123 p.Article in journal (Refereed) Published
Abstract [en]

Four different cellulose model surfaces, and one silica surface, have been studied by means of atomic force microscopy (AFM). The normal interactions have been found to consist of a longer range double layer force with a short range steric interaction, the nature of which is extensively discussed. Both the surface charge and range of the steric force depend on the type of cellulose substrate used, as does the magnitude of the adhesion. Studies of friction reveal that surface roughness is the determining factor for the friction coefficient, with which it increases monotonically. The absolute value, however, is determined by the surface chemistry. All studied cellulose surfaces show similar behavior in response to xyloglucan addition.

Keyword
AFM; cellulose; surface forces; colloid probe; xyloglucan; nanotrilology; friction
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-7721 (URN)10.1016/j.jcis.2006.06.070 (DOI)000241079500015 ()2-s2.0-33748919455 (Scopus ID)
Note
QC 20100804Available from: 2007-11-25 Created: 2007-11-25 Last updated: 2011-09-02Bibliographically approved
2. Comparison of different methods to calibrate torsional spring constant and photodetector for atomic force microscopy friction measurements in air and liquid
Open this publication in new window or tab >>Comparison of different methods to calibrate torsional spring constant and photodetector for atomic force microscopy friction measurements in air and liquid
2007 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 78, no 9, 093702- p.Article in journal (Refereed) Published
Abstract [en]

A number of atomic force microscopy cantilevers have been exhaustively calibrated by a number of techniques to obtain both normal and frictional force constants to evaluate the relative accuracy of the different methods. These were of either direct or indirect character-the latter relies on cantilever resonant frequencies. The so-called Sader [Rev. Sci. Instrum. 70, 3967 (1999)] and Cleveland [Rev. Sci. Instrum. 64, 403 (1993)] techniques are compared for the normal force constant calibration and while agreement was good, a systematic difference was observed. For the torsional force constants, all the techniques displayed a certain scatter but the agreement was highly encouraging. By far the simplest technique is that of Sader, and it is suggested in view of this validation that this method should be generally adopted. The issue of the photodetector calibration is also addressed since this is necessary to obtain the cantilever twist from which the torsional force is calculated. Here a technique of obtaining the torsional photodetector sensitivity by combining the direct and indirect methods is proposed. Direct calibration measurements were conducted in liquid as well as air, and a conversion factor was obtained showing that quantitative friction measurements in liquid are equally feasible provided the correct calibration is performed.

Keyword
scanning probe microscopy, lateral force, frequency-response, viscous fluids, cantilevers, surface, monolayers, tip
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-7723 (URN)10.1063/1.2779215 (DOI)000249787800011 ()2-s2.0-34848846232 (Scopus ID)
Note
QC 20100804.Available from: 2007-11-25 Created: 2007-11-25 Last updated: 2010-09-03Bibliographically approved
3. Top-Down Grafting of Xyloglucan to Gold Monitored by QCM-D and AFM: Enzymatic Activity and Interactions with Cellulose
Open this publication in new window or tab >>Top-Down Grafting of Xyloglucan to Gold Monitored by QCM-D and AFM: Enzymatic Activity and Interactions with Cellulose
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2008 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 9, no 3, 942-948 p.Article in journal (Refereed) Published
Abstract [en]

This study focuses on the manufacture and characterisation of model surfaces consisting of end grafted xyloglucan (XG), a naturally occurring polysaccharide, onto a gold substrate.  The now well-established XET-technology was utilised for enzymatic incorporation of a thiol moiety at one end of the xyloglucan backbone.  This functionalised macromolecule was subsequently top-down grafted to gold, forming a thiol-bonded xyloglucan brush-like layer. The grafting was monitored in-situ with QCM-D and a significant difference in the adsorbed/grafted amount between unmodified xyloglucan and the thiol-functionalised polymer was observed.  The grafted surface was demonstrated to be accessible to enzyme digestion using the plant endo-xyloglucanase TmNXG1.  The nanotribological properties towards cellulose of the untreated crystal, brush modified surface and enzyme exposed surfaces were compared with a view to understanding the role of xyloglucan in friction reduction.  Friction coefficients obtained by the AFM colloidal probe technique using a cellulose functionalised probe on the xyloglucan brush showed an increase of a factor of two after the enzyme digestion and this result is interpreted in terms of surface roughness.  Finally, the brush is shown to exhibit binding to cellulose despite its highly oriented nature.

Place, publisher, year, edition, pages
USA: American Chemical Society, 2008
Keyword
AFM, QCM-D, xyloglucan, enzymatic, graft, thiol, nanotribology, surface force, friction, colloidal probe, self assembly, model polysaccharide surface, brush layer, polysaccharide interactions
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-10999 (URN)10.1021/bm701214e (DOI)000253926400026 ()2-s2.0-41949124066 (Scopus ID)
Note
QC 20100804Available from: 2009-09-02 Created: 2009-09-02 Last updated: 2010-11-15Bibliographically approved

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