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Comparison of different methods to calibrate torsional spring constant and photodetector for atomic force microscopy friction measurements in air and liquid
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.ORCID iD: 0000-0002-5444-7276
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.ORCID iD: 0000-0002-8935-8070
Department of Physical and Analytical Chemistry, Surface Biotechnology, Uppsala University.
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.

Place, publisher, year, edition, pages
2007. Vol. 78, no 9, 093702- p.
Keyword [en]
scanning probe microscopy, lateral force, frequency-response, viscous fluids, cantilevers, surface, monolayers, tip
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7723DOI: 10.1063/1.2779215ISI: 000249787800011Scopus ID: 2-s2.0-34848846232OAI: oai:DiVA.org:kth-7723DiVA: diva2:12833
Note
QC 20100804.Available from: 2007-11-25 Created: 2007-11-25 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Probing Interactions between Bio-Fibre Components
Open this publication in new window or tab >>Probing Interactions between Bio-Fibre Components
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
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:nbn:se:kth:diva-4555 (URN)978-91-7178-796-5 (ISBN)
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
2. Interfacial Properties of Biomacromolecular Model Systems: Surface Forces and Nanotribology
Open this publication in new window or tab >>Interfacial Properties of Biomacromolecular Model Systems: Surface Forces and Nanotribology
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The nanotribology, adhesion and related interfacial properties of biomacromolecular systems have been studied.  The aim was to elucidate the role of physisorbed and chemically grafted bio-polymers implicated as mediators for cellulose based processing and material design.  To that end, model surfaces were prepared and characterized by the versatile techniques quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) in colloidal probe mode.  A prerequisite for the latter in conducting quantifiable force and friction measurements lies in obtaining accurate values for the cantilever spring constants.  An investigation of various recently proposed calibration methods shows that they return essentially the same result, but that the route of Sader et al. is the least strenuous and indeed most reliable.  A novel approach for determining the required frictional detector sensitivity is proposed.

Cellulose model surfaces with varying morphology were evaluated.  For a given surface roughness the adsorption of xyloglucan, a nonionic polysaccharide, leads to a consistent decrease in the friction coefficients for all cellulose substrates, demonstrating that the effects on friction arising from either roughness or chemistry can be decoupled.  Moreover, xyloglucan grafts on gold show biological enzymatic accessibility, and their native affinity towards cellulose is retained, even in an extended brush conformation.

Chitosan, a cationic polysaccharide is also found to mediate lubrication and adhesion of cellulose in a solvent dependent manner, though the mechanisms are unlike those of xyloglucan.  At low pH the most efficient lubrication is achieved due to highly charged chitosan species extending out in the aqueous media, forming a highly hydrated cushion.  Conversely, at high pH the deswelling of the layer results in higher friction.  The same trend is observed between synthetic dual-responsive polyionic grafts on gold where the polymer charge is decisive for the friction properties. Above the lower critical solution temperature where the grafts are fully collapsed and display an attractive force, the friction is slightly reduced due to a nanoscopic flattening at the interface.

Finally, polymer grafts as matrix compatibilizers for bio-degradable cellulose based nano-composite applications were evaluated.  Adhesion is greatly promoted by chain entanglements.  The effect displays a dynamic diffusion based dependence of which the rate is significantly enhanced at a higher temperature close to the melting point of the polymeric layer.  No such adhesion benefit was obtained between ungrafted cellulose and the matrix material.

Abstract [sv]

Nanotribologin, adhesionen samt relaterade gränsskikts egenskaper av biomakromolekylära system har studerats.  Målet var att belysa inverkan av adsorberade samt kemiskt ympade bio-polymerer implicerade som medlare för cellulosa baserad förädling och material design.  För detta ändamål var modell ytor beredda och karakteriserade med de mångsidiga teknikerna kvarts kristall mikro våg med dissipation (QCM-D) och atom krafts mikroskopi (AFM) i kolloidal prob konfiguration.  En förutsättning för den senare i att utföra kvantifierbara kraft och friktionsmätningar ligger i att bestämma noggranna värden för kantilever-fjäderkonstanterna.  En undersökning av olika nyligen föreslagna kalibrerings metoder visar att de ger i huvudsak samma resultat, men att den av Sader et al. är minst krävande och sannerligen den mest tillförlitliga. Ett nytt tillvägagångsstätt för att bestämma den obligatoriska friktions detektor-känsligheten föreslås.

Cellulosa modell ytor med varierande morfologi utvärderades.   För en given ytråhet leder adsorption av xyloglukan, en icke-jonisk polysackarid, till en konsekvent reduktion av friktions-koefficienterna för alla substraten, vilket demonstrerar att effekten på friktion av antingen ytråhet eller kemi kan separeras.  Därtill visar sig xyloglukan ympningar på guld vara biologiskt enzymatiskt tillgängligt, och deras naturliga affinitet för cellulosa är bevarad, även i en utdragen borst-konformation.

Kitosan, en katjonisk polysackarid visar sig också förmedla smörjning och adhesion av cellulosa på ett lösnings beroende sätt, men mekanismerna är olika de för xyloglukan.  Vid lågt pH uppnås den mest effektiva smörjningen p. g. a. de högt laddade kitosankedjorna som sträcker ut sig i vatten lösningen och formar en högt hydratiserad dyna.  Omvänt, vid högt pH resulterar vattenhaltsminskningen av lagret i en högre friktion.  Samma tendens iakttas mellan syntetiskt dubbel-responsiva polyjoniska ympningar på guld där polymerladdningen är avgörande för friktionsegenskaperna.  Ovanför den lägre kritiska lösningstemperaturen där ympningen är helt kollapsad och uppvisar en attraktiv kraft är friktionen något reducerad        p. g. a. nanoskopisk utjämning vid gränsskiktet.

Slutligen, har polymerympningar som matris-kompatibiliterare för bio-nedbrytbara cellulosa baserade nano-komposit applikationer utvärderats.  Adhesionen är mycket gynnad av kedjeintrasslingar.  Effekten påvisar ett dynamiskt diffusionsbaserat beroende, av vilken takten är signifikant förhöjd vid en högre temperatur nära smältpunkten för polymerlagret.  Ingen sådan adhesionsfördel uppnåddes mellan den rena cellulosan och matrismaterialet.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. vii, 72 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:36
Keyword
afm, surface force, friction, composite material, model surface, quartz crystal microbalance, dissipation, cellulose, xyloglucan, chitosan, colloidal probe, nanotribology, biomimetic, enzymatic, polysaccharide, graft, fiber, thiol, spring constant, calibration, lubrication, polyion, responsive.
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-11002 (URN)978-91-7415-394-1 (ISBN)
Public defence
2009-09-25, FD5, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100804Available from: 2009-09-08 Created: 2009-09-03 Last updated: 2010-08-04Bibliographically approved
3. Lubrication and Surface Properties of Adsorbed Layers of Polyelectrolytes and Proteins
Open this publication in new window or tab >>Lubrication and Surface Properties of Adsorbed Layers of Polyelectrolytes and Proteins
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Friction forces between protein / polyelectrolyte layers, adsorption properties of proteins, and conformational changes due to variation in electrolyte concentration have been investigated. The aim was to obtain better understanding of adsorbed layer properties, with focus on the relation between layer structure and lubrication capabilities. The major techniques used were AFM (atomic force microscope) with colloidal probe for normal force and friction measurements together with QCM-D (quartz crystal microbalance with dissipation) for measurement of adsorption and conformational changes of adsorbed layers.

A comparison between some techniques for calibration of the AFM instrument for friction measurements was made to find the most suitably one for colloidal probe friction measurements in aqueous solutions. It is suggested that the normal and torsional Sader methods are preferred in combination with torsional detector sensitivity measurement, for which one new methodology has been proposed.

Adsorption was studied for bovine serum albumin, cytochrome c, myoglobin and mucin, whereas conformational changes of the adsorbed layer were monitored only for mucin. It was found that it was essential to take into account bulk density and viscosity changes for correct interpretations of QCM data when studying the effect of changes in electrolyte type and concentration on preadsorbed layers of mucin, and also when having different (high) concentrations of proteins in the measuring solution. The adsorbed amount of proteins appears to depend on the strength of the surface attachment, in such a manner that a too high affinity reduces the adsorbed amount.

Friction properties in aqueous solution have been studied for adsorbed layers of PEO45MEMA:METAC co-polyelectrolytes, with varying density of grafted PEO45 side chains and varying charge density, as well as for a naturally occurring polyelectrolyte (chitosan) and the glycoprotein mucin. These polymers were used to cover a wide range of different types of adsorbed layers and interactions to gain a better understanding of friction mechanisms and demands on layer properties for achieving favourable lubrication. It was found that the common features of low friction layers are that no attractive forces are present, and that excluded volume and / or electrostatic forces counteract chain interpenetration under load.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vii, 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:16
Keyword
biochemistry, biomedical engineering
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-4663 (URN)978-91-7178-891-7 (ISBN)
Public defence
2008-03-27, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100903Available from: 2008-03-07 Created: 2008-03-07 Last updated: 2010-09-03Bibliographically approved

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