switchable adhesion and friction by stimulus responsive polymer brushes yunlong yu

156 Pages·2017·3.49 MB·English

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SWITCHABLE ADHESION AND FRICTION BY
STIMULUS RESPONSIVE POLYMER BRUSHES
YUNLONG YU
Switchable Adhesion and Friction by
Stimulus Responsive Polymer Brushes
Yunlong Yu
2017
Graduation committee
Chairman
Prof.dr.ir.J.W.M.Hilgenkamp UniversityofTwente
Promotor
Prof.dr.G.J.Vancso UniversityofTwente
Assistant-promotor
Dr.S.J.A.deBeer UniversityofTwente
Members
Prof.dr.X.Zeng ShanghaiAdvancedResearchInstitute,
ChineseAcademyofSciences
Dr.A.C.C.deCarvalhoEsteves EindhovenUniversityofTechnology
Prof.dr.M.M.A.E.Claessens UniversityofTwente
Prof.dr.J.J.L.M.Cornelissen UniversityofTwente
Dr.W.M.deVos UniversityofTwente
The research described in this Thesis was carried out in the Materials Science and
Technology of Polymers (MTP) group, in the MESA+ Institute for Nanotechnology, and in
the Faculty of Science and Technology (TNW) of the University of Twente. This research
was supported by the China Scholarship Council (CSC) and by the Netherlands
OrganizationforScientificResearch(NWO).
Title:SwitchableAdhesionandFrictionbyStimulusResponsivePolymer Brushes
Copyright©2017,YunlongYu,Enschede,theNetherlands
All rights reserved. No part of this Thesis may be reproduced or transmitted by print,
photocopyoranyothermeanswithoutpriorwrittenpermissionoftheauthor.
ISBN: 978-90-365-4280-7
DOI: 10.3990/1.9789036542807
Cover:designedbyGR-Artworks-GenevièveRietveld
PrintedbyIpskampDrukkersinEnschede,theNetherlands
SWITCHABLE ADHESION AND FRICTION BY
STIMULUS RESPONSIVE POLYMER
BRUSHES
DISSERTATION
to obtain
the degree of doctor at the University of Twente,
on the authority of the rector magnificus,
prof. dr. T.T.M. Palstra,
on account of the decision of the graduation committee,
to be publicly defended
on Wednesday, 11th of January 2017, at 14:45h
by
Yunlong Yu
born on 26th of October, 1984
in Shandong, P. R. China
This dissertation has been approved by:
Promotor: Prof. dr. G. J. Vancso
Assistant-promotor: Dr. S.J.A. de Beer
Contents
1.GeneralIntroduction.................................................................................................................1
1.1Introduction.............................................................................................................................1
1.2ContentofthisThesis............................................................................................................2
1.3References...............................................................................................................................3
2.SwitchableAdhesionandFrictionbyStimulusResponsivePolymers..........................5
2.1Polymerbrushes......................................................................................................................5
2.2Surface-initiatedatomtransferradicalpolymerization(SI-ATRP).................................6
2.3Adhesion,adhesionhysteresisandfriction.........................................................................7
2.4Atomicforce microscopy(AFM).........................................................................................8
2.5Stimulusresponsivepolymers..............................................................................................9
2.5.1Temperature...................................................................................................................10
2.5.2Co-(non-)solvency.........................................................................................................11
2.5.3pHandsaltconcentration.............................................................................................12
2.5.4Otherandmulti-stimuli................................................................................................12
2.6Switchableadhesion.............................................................................................................13
2.6.1Adhesionbetweenchemicallyidenticalpolymer films...........................................13
2.6.2Theadhesionbetweenpolymerfilmsandchemicallydifferentcountersurfaces15
2.7Switchablefriction...............................................................................................................16
2.7.1Frictionbetweenchemicallyidenticalpolymerfilms..............................................17
2.7.2Frictionbetweenpolymerfilmsandchemicallydifferentcountersurfaces.........17
2.8Relationbetweenfrictionandadhesion/adhesionhysteresis.........................................19
2.8.1Relationbetweenfrictionandadhesion.....................................................................21
2.8.2Relationbetweenfrictionandadhesionhysteresis...................................................21
2.9Summary................................................................................................................................22
2.10References...........................................................................................................................24
3.StretchingofCollapsedPolymersCausesanEnhancedDissipativeResponseof
PNIPAMBrushesneartheirLCST..........................................................................................31
3.1Introduction...........................................................................................................................32
3.2MaterialsandMethods.........................................................................................................33
3.2.1Materials.........................................................................................................................33
3.2.2Preparationofpolymerbrushes...................................................................................34
3.2.3Characterization.............................................................................................................35
3.3ResultsandDiscussion........................................................................................................38
3.4Conclusions...........................................................................................................................47
II Contents
3.5References.............................................................................................................................47
4.TunableFrictionbyEmploymentofCo-non-solvencyofPNIPAMBrushes.............51
4.1Introduction...........................................................................................................................52
4.2MaterialsandMethods.........................................................................................................53
4.2.1Materials.........................................................................................................................53
4.2.2Brushpreparationandcharacterization......................................................................54
4.3ResultsandDiscussion........................................................................................................55
4.4Conclusions...........................................................................................................................62
4.5Appendix................................................................................................................................63
4.6References.............................................................................................................................67
5.Pickup,MoveandRelease ofNanoparticlesUtilizingCo-non-solvencyofPNIPAM
Brushes............................................................................................................................................71
5.1Introduction...........................................................................................................................72
5.2MaterialsandMethods.........................................................................................................73
5.2.1Materials.........................................................................................................................73
5.2.2Colloidalprobepreparation.........................................................................................74
5.2.3Brushcharacterization..................................................................................................74
5.2.4AFMadhesionforce measurements...........................................................................75
5.2.5Particletransfermeasurements....................................................................................75
5.3ResultsandDiscussion........................................................................................................75
5.4Conclusions...........................................................................................................................80
5.5Appendix................................................................................................................................81
5.6References.............................................................................................................................86
6.Cosolvency-InducedSwitchingoftheAdhesionbetweenPoly(methylmethacrylate)
Brushes............................................................................................................................................89
6.1Introduction...........................................................................................................................90
6.2MaterialsandMethods.........................................................................................................92
6.2.1Materials.........................................................................................................................92
6.2.2Preparationofpolymerbrushes...................................................................................92
6.2.3Characterization.............................................................................................................93
6.3ResultsandDiscussion........................................................................................................95
6.4Conclusions...........................................................................................................................99
6.5References...........................................................................................................................100
7.SubstantiallyEnhancedStabilityAgainstDegraftingofZwitterionicBrushesby
UtilizingPGMA-basedMacro-initiators...............................................................................103
7.1Introduction.........................................................................................................................104
7.2MaterialsandMethods.......................................................................................................106
Contents III
7.2.1Materials.......................................................................................................................106
7.2.2Methods........................................................................................................................106
7.2.3Characterization...........................................................................................................107
7.2.4Stabilitytest..................................................................................................................110
7.3ResultsandDiscussion......................................................................................................110
7.4Conclusions.........................................................................................................................115
7.5Appendix..............................................................................................................................116
7.6Reference.............................................................................................................................121
8.FirstResultsandOutlookon:SpecificAnionEffectsontheHydrationand
TribologicalpropertiesofZwitterionicPMPCBrushes....................................................125
8.1Introduction.........................................................................................................................126
8.2MaterialsandMethods.......................................................................................................128
8.2.1Materials.......................................................................................................................128
8.2.2SynthesisofPGMA-PMPCbrush............................................................................128
8.2.3Characterization...........................................................................................................128
8.2.4Swellingratiomeasurement.......................................................................................129
8.3ResultsandDiscussion......................................................................................................130
8.4Outlook................................................................................................................................134
8.5References...........................................................................................................................135
Summary.......................................................................................................................................137
Samenvatting................................................................................................................................141
Acknowledgements.....................................................................................................................143
CurriculumVitae........................................................................................................................145

Chapter 1
General Introduction
1.1 Introduction
Stimulus-responsive polymers1 are defined as “polymers that undergo relatively large and
abrupt, physical or chemical changes in response to small modifications in the
environmental conditions”. Recently, there has been quickly growing interest in developing
‘smart’ surface-coatings by using stimulus-responsive polymers, while they can be applied
for varying the surface wettability2 and in drug delivery,3 chemical-sensing4 and tribology
control.5 In these applications, the conformational state and/or the chemical structure of the
polymers is strongly altered due to the adjustment in the surroundings, such as
temperature,6 light radiation7 or electric field,8 which results in a change in the macroscopic
propertiesofthesurfacecoating.
There are different methods to decorate a surface with polymers. Polymers can be
physisorbed9 or covalently bonded to the surface via their side-chains.10 Moreover,
hydrogels can be prepared, which can swell by solvent absorption by many times their
initial size.11 Furthermore, so-called polymer brushes can be formed.12 In a polymer brush,
the polymers are attached with one end to the surface at a density that is high enough for
the polymers to stretch away from the surface.13 The latter is caused by steric hindrance by
the surrounding polymers and can be enhanced by solvent absorption when the brush is
keptinagoodsolvent.
In this Thesis, we will present different polymer brush coatings that have been used to
control adhesion and friction. When polymers are triggered to change their conformation or
chemical structure by an external stimulus, the interaction, e.g. the van der Waals forces,
electrostatic forces, forces due to hydrogen bonding etc., between surfaces that are coated
with these polymers will also change. Generally, when a stimulus causes the effective
interaction to become more attractive, the surfaces will be more strongly bound and make
more intimate contact, such that adhesion and friction will increase, while the opposite is
true when the stimulus results in more repulsive interactions.5b, 6b, 14 However, as we will
discuss in more detail in this Thesis, there are important exceptions for which the inverse
can occur.12b,15 In our research we systematically study the relation between the degree of
solvation of the macromolecules in the brush and the friction and adhesion. Our results
show that the relation between brush swelling and its tribomechanical properties is rather
complex, and that it can depend on the specific interactions in the contact. Our careful
characterization will allow for the development of e.g. smart tweezers5e and gloves,16 pick
upandreleasetools.17