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Interfacial Properties of Biomacromolecular Model Systems: Surface Forces and Nanotribology
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. (Yt- och korrosionsvetenskap, Surface and Corrosion Science)
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 [en]
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: urn:nbn:se:kth:diva-11002ISBN: 978-91-7415-394-1 (print)OAI: oai:DiVA.org:kth-11002DiVA: diva2:233868
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
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: 2017-12-14Bibliographically approved
2. Mediation of the Nanotribological Properties of Cellulose by Chitosan Adsorption
Open this publication in new window or tab >>Mediation of the Nanotribological Properties of Cellulose by Chitosan Adsorption
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2009 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 10, no 3, 645-650 p.Article in journal (Refereed) Published
Abstract [en]

Cellulosic model surfaces functionalized with chitosan, a naturally occurring cationic biomacromolecule, by in-situ adsorption have been studied with an atomic force microscope (AFM) in colloidal probe configuration.  The interaction forces on approach and separation, as well as the nanotribological properties, were shown to be highly pH-dependent and a significant difference in the behaviour was seen before and after chitosan adsorption.  In general, all forces on approach showed a highly repulsive interaction at shorter distances due to deformation of the probe.  At high pH, before chitosan adsorption, a long-range electrostatic repulsion was observed, consistent with DLVO theory.  However at low pH no electrostatic contribution was found before adsorption probably due to charge neutralization of carboxyl groups.  After chitosan adsorption, repulsive forces acting over a much longer distance than predicted by DLVO theory were present at low pH.  This effect was ascribed to chain extension of the chitosan species of which the magnitude and the range of the force increased dramatically with higher charge at low pH.  In all cases, a typical saw-tooth patterned adhesion was present with pull-off events occurring at different separations.  The frequency of these events after chitosan adsorption was greatly increased at longer distances.  Additionally, the adsorbed chitosan markedly reduced the friction where the largest effect was a 7-fold decrease of the friction coefficient observed at low pH.

Place, publisher, year, edition, pages
USA: American Chemical Society, 2009
Keyword
AFM, QCM-D, cellulose, chitosan, nanotribology, surface forces, friction, adhesion, colloidal probe, polysaccharide interactions
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-10998 (URN)10.1021/bm801467w (DOI)000264059400024 ()2-s2.0-65249099501 (Scopus ID)
Note
QC 20100804Available from: 2009-09-02 Created: 2009-09-02 Last updated: 2017-12-13Bibliographically 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: 2017-12-13Bibliographically approved
4. Tunable Nanolubrication between Dual-Responsive Polyionic Grafts
Open this publication in new window or tab >>Tunable Nanolubrication between Dual-Responsive Polyionic Grafts
2009 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 9, no 8, 2984-2990 p.Article in journal (Refereed) Published
Abstract [en]

This study reports on a direct approach of quantitatively probing the nanotribological response of chemically end-grafted polyions.  A combination of quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM), in the now well established colloidal probe mode was utilized to investigate the stimuli-induced lubrication behavior between poly-2-(dimethylamino)ethyl methacrylate (PDMAEMA) grafts on gold.  Force and friction measurements showed reversible transitions of up to an order of magnitude difference induced by varying the solvent conditions.  The greatly enhanced lubrication observed at low pH was attributed to the formation of a repulsive, highly charged, hydrated cushion.  At high pH the friction was significantly increased.  The system turned attractive above the lower critical solution temperature (LCST) with a small friction reduction interpreted as nanoscopic flattening at the interfacial boundary.

Place, publisher, year, edition, pages
USA: American Chemical Society, 2009
Keyword
AFM, QCM-D, responsive polymer, RAFT, thiol, force, friction, colloidal probe, DMAEMA, LCST, lubrication, nanotribology
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-11000 (URN)10.1021/nl901411e (DOI)000268797200031 ()2-s2.0-68949108073 (Scopus ID)
Note
QC 20100804Available from: 2009-09-03 Created: 2009-09-03 Last updated: 2017-12-13Bibliographically approved
5. Adhesion Dynamics for Cellulose Nano-Composites
Open this publication in new window or tab >>Adhesion Dynamics for Cellulose Nano-Composites
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2009 (English)In: ACS applied Materials & Interfaces, ISSN 1944-8252, 2098-2103 p.Article in journal (Refereed) Published
Abstract [en]

The efficiency of poly(ε-caprolactone) (PCL) as a matrix polymer for cellulose nano-composites has been investigated at the macromolecular contact level using atomic force microscopy (AFM) in colloidal probe configuration.  Model cellulose micro-spheres grafted with PCL were prepared via ring-opening polymerization (ROP).  Force measurements between the functionalized particles revealed the adhesion to be highly dependent on contact time due to a diffusion controlled mechanism.  Moreover, an increase of the temperature to 60 °C (close to Tm for the PCL-graft) greatly enhanced the adhesion at the polymer-polymer interface demonstrating the importance of entanglements in the annealing of composite materials.

Keyword
atomic force microscopy, cellulose, surface forces, adhesion, colloidal probe, nano-composites, ring-opening polymerization, surface grafting, poly(ε-caprolactone)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-11001 (URN)10.1021/am900381t (DOI)000271105000002 ()2-s2.0-79955835800 (Scopus ID)
Note
QC 20100730Available from: 2009-09-03 Created: 2009-09-03 Last updated: 2010-12-06Bibliographically approved
6. 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: 2017-12-14Bibliographically approved

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