Table Of ContentElectrospun
Polymer
Nanofibers
Pan Stanford Series on Renewable Energy — Volume 2
Electrospun
Polymer
Nanofibers
editors
Preben Maegaard
Arkadii Arinstein
Anna Krenz
Wolfgang Palz
The Rise of Modern Wind Energy
Wind Power
for the World
Published by
Pan Stanford Publishing Pte. Ltd.
Penthouse Level, Suntec Tower 3
8 Temasek Boulevard
Singapore 038988
Email: [email protected]
Web: www.panstanford.com
British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
Electrospun Polymer Nanofibers
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ISBN 978-981-4745-27-7 (Hardcover)
ISBN 978-1-315-36462-9 (eBook)
Printed in the USA
Contents
Preface
1. In troduc tion i1x
Part I The Necessary Basics 5
2. Nano-objects 7
2.1 What “Nano-objects” Mean? 7
2.2 Physical Properties of Nano-objects Compared
to the Bulk 11
2.2.1 Mechanical Properties 12
2.2.2 Thermodynamic Properties 17
3. Experim2e.n2t.a3l ExSaimzei-nDaetipoenn odfe Enlte Bcterhoaspviuonr Poof lNymaneor - objects 19
Nanofibers 21
3.1 Experimental Examination of Nanofiber Mats 23
3.2 Experimental Examination of Single Nanofiber 26
3.2.1 Atomic Force Microscopy 26
3.2.2 Tensile Test 29
Part II Nano3.f2ib.3e r FRaebsroincaatnicoen M ethod 3370
4. Electrospinning of Polymer Nanofibers 39
4.1 Spinability of Polymer Solution 41
4.2 Hydrodynamics of Electrospinning 46
4.3 Hydrodynamic Instabilities of Spinning Jet 50
4.4 Solvent Evaporation and Polymer Solidification 56
4.5 Post-fabrication Relaxation 64
4.5.1 Experimental Observations 66
4.5.2 Preliminary Estimates 68
4.5.3 Kinetic Equations Describing the
System Evolution 70
4.5.4 Pressure and Velocity Distribution 71
vi Contents
4.5.5 Meniscus Moving (Kinetics of Solvent
Evaporation) 72
4.5.6 Experimental Proof of Post-fabrication
Relaxation 74
4.6 Post-processes in Electrospun Tubular
Nanofibers 75
4.6.1 Formation of Gas Bubbles 76
5. Polymer4 D.6y.n2a mBicusc iknl iSnegm oi-fd Tiluubteu lSaor lNutainoonf Dibuerrin g 78
Electrospinning 85
5.1 Theoretical Model Describing Stretching of
a Polymer Topological Network 87
5.1.1 Initial State of Entangled Semi-dilute
Polymer Solution 87
5.1.2 Axial Stretching of an Entangled
Polymer Network during Electrospinning 88
5.1.3 Radial Contraction of an Entangled
Polymer Network during Electrospinning 92
5.2 Experimental Observations of Polymer System
Evolution under High Stretching 95
5.2.1 Radial Contraction of an Entangled
Polymer Network during Electrospinning 95
5.2.2 Stretch-Induced Phase Separation in
Polymer Solutions 99
5.3 Disentanglement of Polymer Topological
Network in Further Stages of Electrospinning 107
5.3.1 Multiple Necking 108
5.3.2 Short Fiber Fabrication 109
5.3.3 Simulation of Disentanglement
Processes with the Help of a Pulley
System 111
5.3.4 Spontaneous Symmetry Breaking in a
Thermodynamic System of Pulleys 114
5.3.4.1 Mathematical description 115
5.3.4.2 Motion analysis 117
5.3.4.3 The energy balance 121
5.3.4.4 The thermodynamic system 122
5.3.4.5 Numerical simulations 123
Contents vii
Part III Unique Properties of Electrospun Polymer
Nanofibers 125
6. Size-Dependent Behavior 127
6.1 Size-Dependent Behavior of Electrospun
Nanofibers 127
6.1.1 Size-Dependent Behavior in Mechanical
Properties 127
6.1.2 Size-Dependent Behavior in
Thermodynamic Properties 130
6.2 Do Surface Effects Explain the Unique
Elasticity of Polymer Nanofibers? 132
6.3 Concept of Near-Surface Layer 138
6.4 Confinement Concept 140
6.4.1 Physical Model of the Phenomenon 142
7. Explanat6i.o4n.2s of Tthhee oSrizeet-iDcaelp Eesntdimenatt iBoenhsa vior by a 143
Physicist: Some Possible Reasons and Mechanisms 147
7.1 Confinement Mechanism of Electrospun
Polymer Nanofibers Reinforcement 147
7.1.1 Structure of an Amorphous Nanofiber
Polymer Matrix 150
7.1.2 Mathematical Model for Polymer
Nanofiber Elongation 154
7.1.3 Scaling Properties of the
Size-Dependent Elastic Modulus of
Electrospun Polymer Nanofibers 159
7.2 Shifting of Melting Point for Semi-Crystalline
Polymer Nanofibers 164
7.2.1 Theoretical Background 165
7.2.2 Experimental Results and Discussions 169
7.3 Nonequilibrium State of Polymer Matrix Inside
Electrospun Nanofibers 171
7.3.1 Orientation of Polymer Macromolecules
as a Result of Electrospinning 171
7.3.2 Stretching of Polymer Matrix of
Electrospun Nanofibers 177
7.3.3 Orientation versus Stretching under
Confinement 180
viii Contents
Final Remarks 183
Bibliography 185
Index
193
Contents ix
Preface
“By making something absolutely clear, someone will become
confused.”
—Arthur Bloch
Polymer nanofibers fabricated through electrospinning have
attracted much attention recently because of their unique mechanical
and thermodynamic properties compared to the bulk.
Despite the prehistory of electrospinning spanning more than 100
years, the real examination of this process and its adaptation to the
praxis started only 15–20 years ago. Nowadays, the hydrodynamics
of the electrospinning process is well understood, which has enabled
fabrication of polymer nanofibers in a regular and stable way, and
electrospun polymer nanofibers are utilized for many applications.
At the same time, in spite of the aforementioned progress, the
physical reasons for the observed unique properties of polymer
nanofibers are poorly understood. Now it is clear that the unusual
properties of polymer nanofibers cannot be attributed to the surface
effect, and for the explanation of the observed phenomena, the
confinement concept seems the most perspective one. Nevertheless,
the physical mechanisms providing the confinement effect and, as a
result, the appearance of unique properties of polymer nanofibers
require thorough investigation.
This book clarifies (maybe, partially) the physical aspects of the
problem in question, focusing on the analysis of the size-dependent
Arkadii Arinstein
behavior of electrospun polymer nanofibers.
Fall 2017
