Monodisperse Highly Ordered and Polydisperse Biobased Solid Foams

165 Pages·2019·9.216 MB·English

by  Sébastien Andrieux

Springer Theses
Recognizing Outstanding Ph.D. Research
Sébastien Andrieux
Monodisperse
Highly Ordered
and Polydisperse
Biobased Solid
Foams
Springer Theses
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é
S bastien Andrieux
Monodisperse Highly
Ordered and Polydisperse
Biobased Solid Foams
Doctoral Thesis accepted by
University of Stuttgart, Stuttgart, Germany
123
Author Supervisor
Dr. Sébastien Andrieux Prof. Cosima Stubenrauch
Institut Charles Sadron(UPR22—CNRS) Institute of Physical Chemistry
Strasbourg, France University of Stuttgart
Stuttgart, Germany
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-030-27831-1 ISBN978-3-030-27832-8 (eBook)
https://doi.org/10.1007/978-3-030-27832-8
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À Alexis Dulaurent
’
Supervisor s Foreword
Many properties of solid foams depend on the distribution of the pore sizes and
their organisation in space. However, these two parameters are very difficult to
controlintraditionalfoamingtechniques.ThePh.D.thesisofSébastienAndrieuxis
dealingwiththisdifficultyandhewasabletoshowthatmicrofluidicscanbeusedto
tune the polydispersity of the foams (mono- vs different polydispersities) and the
spatial organisation of the pores (ordered vs disordered). For this purpose, the
microfluidic flow-focussing technique was modified such that the gas pressure
oscillates periodically which translates into periodically oscillating bubble sizes in
theliquidfoamtemplate.TheliquidfoamsweregeneratedfromChitosansolutions
andthengelledviacross-linkingwithgenipinbeforebeingfreeze-driedtoobtaina
foamedaerogelwithaspecificstructure.Thestudyathandfillstwoscientificgaps.
On the one hand, a novel approach for the generation of foams with controlled
polydispersity is presented. On the other hand, a solid foam consisting of rhombic
dodecahedraisobtained.Thisstructurehasnotyetbeenobservedifonesynthesises
solid foams via foam templating.
The controlled variation of the foam’s structure will allow studying systemati-
cally structure-property relations. Sébastien Andrieux’s important contribution to
thefieldwastoestablishaprotocolforthesynthesisofpolydisperseChitosan-based
solidfoamswithatuneablepolydispersity,whichwillhaveanenormousimpacton
future work in this area. The protocol lends itself to studying the influence of the
pore-size distribution on the mechanical properties of solid foams and is thus a
promisingtoolforgainingadeeperunderstandingofstructure-propertyrelationsof
solid foams. Future work should explore a wider range of polydispersities and
vii
viii Supervisor’sForeword
compare polydisperse foams with different polydispersities but the same average
pore size. Moreover, being fully bio-based, this type of aerogel foams isa suitable
candidateforapplicationsintissueengineering:open-cell,bio-basedscaffoldswith
controllable pore sizes and pore-size distributions are heavily needed as they are
believed to be extraordinary scaffolds for homogeneous and efficient cell growth.
Stuttgart, Germany Prof. Cosima Stubenrauch
July 2018
Abstract
The aim of this work was the synthesis of monodisperse highly ordered bio-based
polymerfoamsandacomparisonwiththeirpolydispersecounterparts.Weusedthe
bio-based and biodegradable polymer chitosan, which we cross-linked with geni-
pin.Thepolymerfoamsweresynthesisedviafoamtemplating,i.e.viaaliquidfoam
whosecontinuousphasecontainsapolymerandcanbesolidified.Inordertoobtain
monodisperse highly ordered polymer foams, one first has to generate monodis-
perse highly ordered liquid foam templates. We did so by using microfluidics,
whichallowstoproducemonodisperseliquidfoamswithbubblesizesfrom200to
800 lm and polydispersities below 5%. The monodisperse foams were collected
outside of the microfluidic channels and left to self-order under the influence of
gravity and confinement.
We studied the kinetics of the cross-linking reaction to find the optimal storage
conditions during cross-linking. Once cross-linked, we freeze-dried the gelled
foams to obtain solid chitosan foams. We compared the morphological properties
of the solid foams with those of the liquid templates in order to test the efficiency
of the developed templating route. We observed how modifying the cross-linking
and drying conditions can strongly affect the morphology of the solid foams. The
main issue was to maintain the key properties of the liquid foam template
throughout the solidification process, namely the bubble size distribution, the
structural order and the density.
We then compared the synthesised monodisperse polymer foams with their
polydispersecounterparts.Althougheasyfoamingmethodsexistforthegeneration
of polydisperse foams, they do not allow the control over the polydispersity. We
thus used microfluidics to generate liquid chitosan foams with tunable polydis-
persities from below 5% up to 26%. Microfluidics allows to match the average
bubble size and density of the polydisperse liquid chitosan foam with those of the
monodispersecounterpart.Aftersolidifyingtheliquidtemplates,weobtainedsolid
foams with controlled polydispersities and studied the influence of the polydis-
persity on the mechanical properties. However, we observed that not the polydis-
persity but the foam density was the main parameter at play. Moreover, the solid
chitosanfoamshadweakmechanicalpropertieswithelasticmodulibelow100 kPa.
ix
x Abstract
To overcome this issue, we incorporated cellulose nanofibres to the original chi-
tosan solution and followed the developed route for foam templating. We had to
adapt the microfluidic parameters to account for the viscosity changes brought
about by the nanofibres. However, we managed to produce monodisperse liquid
foams having the same bubble size, i.e. (cid:1)300 lm, but different amounts of cel-
lulose nanofibres. The cellulose content had a strong influence on the solid foam
morphology in general and on the pore connectivity in particular.