Teflon AF Composite Materials in Membrane Separation and Molecular Recognition in Fluorous ...

207 Pages·2013·4.68 MB·English

TEFLON AF COMPOSITE MATERIALS IN MEMBRANE SEPARATION AND
MOLECULAR RECOGNITION IN FLUOROUS MEDIA

by
Hong Zhang
BS, Nanjing University, 2005

Submitted to the Graduate Faculty of the
Dietrich School of Arts and Science
in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy

University of Pittsburgh
2013

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UNIVERSITY OF PITTSBURGH
Dietrich School of Arts and Sciences

This dissertation was presented

by

Hong Zhang

It was defended on
November 26th, 2013
and approved by
Dennis P. Curran, Professor, Department of Chemistry
Robert M. Enick, Professor, Department of Chemical and Petroleum Engineering
David H. Waldeck, Professor, Department of Chemistry
Dissertation Advisor: Stephen G. Weber, Professor, Department of Chemistry

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TEFLON AF COMPOSITE MATERIALS IN MEMBRANE SEPARATION AND
MOLECULAR RECOGNITION IN FLUOROUS MEDIA
Hong Zhang, PhD
University of Pittsburgh, 2013

The unique nature of fluoropolymers makes them potentially valuable in partitioning based
separations and sensing. Molecular diffusion and partitioning determine the selectivity of a
chemical separation or sensor based on a polymer film. Unlike in the liquid phase where
diffusion and partitioning can be estimated by empirical methods, the physical properties
including fractional free volume (FFV) as well as dynamics of polymer chains significantly
impact diffusion and partitioning. Therefore, this work is focused on developing a fundamental
understanding of solute transport behavior across Teflon AF 2400 composite films in liquid
phase.
Three types of Teflon AF 2400 (AF) composite films including AF/FC-70,
AF/fluorophilic silica nanoparticles (FNPs), and AF/FNP/FC-70 were investigated for the
selective transport of fluorinated molecules against their hydrocarbon counterparts. AF films
alone have a large FFV that, in the presence of liquids, absorbs them making the AF films less
fluorous. AF/FC-70 films show lower FFV, less sorption of CHCl , and restore the
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fluorophilicity of the film with an increase in transport selectivity. AF/FNP composites
containing ≥ 50 wt% FNP show a significant increase of FFV, sorption of CHCl , increased
3
solute permeability, and decreased transport selectivity. AF/FNP/FC-70 composites represent a
novel type of composite film: the soft AF/FC-70 phase which is not dimensionally stable by
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itself is well supported by the FNPs. The AF/FC-70 phase in the three-component film shows
low CHCl sorption, and high solute permeability as well as transport selectivity.
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Molecular recognition-based extractions based on fluorocarbon matrices should be highly
selective. To gain a quantitative understanding of noncovalent interactions in fluorocarbons, the
association of perfluorodecanoic acid with pyridine and quinazoline (separately) was
investigated via isothermal titration calorimetry (ITC). Thermodynamic data show the formation
of complexes with acid:base (HA:B) stoichiometry greater than 1:1. Proton transfer occurs as
follows: HA B + HA  HA AHB+. The high, favorable free energy of complex formation
2 2
between organic compounds and perfluorinated molecular receptors can serve as the driving
force to improve molecular receptor-based extraction and sensing in fluorous media.

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TABLE OF CONTENTS
PREFACE ................................................................................................................................... XX
1.0 INTRODUCTION ........................................................................................................ 1
1.1 FLUOROUS MEDIA .......................................................................................... 1
1.2 TEFLON AF FAMILY ....................................................................................... 3
1.2.1 Free Volume of Teflon AFs .......................................................................... 5
1.2.2 Gas Transport and Pervaporation .............................................................. 8
1.2.3 Liquid Phase Transport ............................................................................. 15
1.3 MOLECULAR RECOGNITION ..................................................................... 18
1.4 OBJECTIVE AND MOTIVATION ................................................................ 21
2.0 PROPERTIES AND TRANSPORT BEHAVIOR OF
PERFLUOROTRIPENTYLAMINE (FC-70)-DOPED AMORPHOUS TEFLON AF 2400
FILMS ... .................................................................................................................................. 25
2.1 INTRODUCTION ............................................................................................. 25
2.2 EXPERIMENTAL ............................................................................................. 28
2.2.1 Materials ...................................................................................................... 28
2.2.2 Film Preparation and Morphological Characterization ......................... 29
2.2.3 Film Density Measurement and Fractional Free Volume ....................... 30
2.2.4 Dynamical Mechanical Analysis ................................................................ 31
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2.2.5 Sorption and Desorption of Chloroform in FC-70-doped Teflon AF 2400
Films….. ...................................................................................................................... 32
2.2.6 Transport of Solutes Through Films ......................................................... 33
2.2.7 Determination of Solute Diffusion Coefficients (D) and Partition
Coefficients (K) ........................................................................................................... 34
2.2.8 Recycling of Teflon AF 2400 ...................................................................... 36
2.3 RESULTS AND DISCUSSION ........................................................................ 37
2.3.1 Characterization of FC-70-doped Teflon AF 2400 Films ........................ 37
2.3.2 Density and Free Volume of FC-70-doped Teflon AF 2400 Films ......... 38
2.3.3 Sorption of Chloroform in Doped Films ................................................... 43
2.3.4 Dependence of Permeability Coefficients (P), Diffusion Coefficients (D),
and Partition Coefficients (K) on Film Composition .............................................. 46
2.3.5 Transport Selectivity of FC-70-doped Teflon AF Films Based on
Different Substitutions ............................................................................................... 57
2.3.6 Recycling of Teflon AF 2400 ...................................................................... 58
2.4 CONCLUSION .................................................................................................. 59
2.5 ACKNOWLEDGEMENT ................................................................................ 60
3.0 PROPERTIES AND TRANSPORT BEHAVIOR OF TEFLON AF 2400
NANOCOMPOSITE FILMS ..................................................................................................... 61
3.1 INTRODUCTION ............................................................................................. 61
3.2 EXPERIMENTAL ............................................................................................. 63
3.2.1 Materials ...................................................................................................... 63
3.2.2 Surface Modification and Characterization of Silica Nanoparticles ..... 64
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3.2.3 Preparation of the Composite Films ......................................................... 65
3.2.4 Morphological, Mechanical, Sorption, and Transport Properties of the
Composite Films ......................................................................................................... 66
3.2.5 Film Density Measurement and Apparent Fractional Free Volume
(aFFV) ...................................................................................................................... 70
3.2.6 Radius of Gyration (R ) of Teflon AF 2400 .............................................. 71
g
3.3 RESULTS AND DISCUSSION ........................................................................ 72
3.3.1 Fluorophilic Nanoparticle Characterization ............................................ 72
3.3.2 Morphology of Teflon AF Composite Films ............................................. 75
3.3.3 Density and Apparent Free Volume of Teflon AF/FNP Composite
Films….. ...................................................................................................................... 78
3.3.4 T , C at T , and modulus of Teflon AF/FNP Composite Films and R
g p g g
of Teflon AF ................................................................................................................ 79
3.3.5 Sorption of Chloroform in Teflon AF/FNP Composite Films ................ 82
3.3.6 Solute Permeability (P) and Selectivity through Teflon AF/FNP
Composite Films ......................................................................................................... 83
3.3.7 Mechanical Properties of Teflon AF/FNP/FC-70 Composite Films ....... 86
3.3.8 aFFV of Teflon AF/FNP/FC-70 Composite Films .................................. 86
P
3.3.9 aFFV Characteristics Differ in 2- and 3-component Films ................... 87
P
3.3.10 Transport Properties of Teflon AF/FNP/FC-70 Composite Films ......... 89
3.4 CONCLUSION .................................................................................................. 92
3.5 ACKNOWLEDGEMENT ................................................................................ 93
4.0 PREPARATION AND APPLICATIONS OF POROUS TEFLON AF 2400 ...... 95
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4.1 INTRODUCTION ............................................................................................. 95
4.2 EXPERIMENTAL ............................................................................................. 98
4.2.1 Materials ...................................................................................................... 98
4.2.2 Preparation and Characterization of Porous Teflon AF 2400 Films ..... 98
4.2.3 Transport of Solutes through Films ........................................................ 100
4.2.4 Preparation, Characterization, and Transport of Fluorescent
Nanoparticles Across Porous Teflon AF 2400 Films ............................................ 101
4.2.5 Immobilization of Fluorous Tag on Porous Teflon AF 2400 Matrix ... 104
4.2.6 Porous Teflon AF Templated Synthesis of Porous Poly(styrene-
divinylbenzene) ......................................................................................................... 104
4.3 RESULTS AND DISCUSSION ...................................................................... 105
4.3.1 Characterization of Porous Teflon AF 2400 Films ................................ 105
4.3.2 Transport Properties of Krytox Filled Porous Teflon AF 2400 Films . 111
4.3.3 Size-based Separation of Nanoparticles .................................................. 113
4.3.4 Porous Teflon AF 2400 Films as Microarray Substrate ........................ 122
4.3.5 Porous Teflon AF 2400 Templated Synthesis of Porous Hydrocarbon
Polymer Matrix ........................................................................................................ 125
4.4 CONCLUSION ................................................................................................ 127
4.5 ACKNOWLEDGEMENT .............................................................................. 128
5.0 ISOTHERMAL TITRATION CALORIMETRY OF
PERFLUORODECANOIC ACID WITH PYRIDINE AND QUINAZOLINE IN AN
ORGANIC, A SEMI-FLUORINATED AND A PERFLUORONATED SOLVENT ........ 129
5.1 INTRODUCTION ........................................................................................... 129
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5.2 EXPERIMENTAL ........................................................................................... 131
5.2.1 Materials .................................................................................................... 131
5.2.2 Isothermal Titration Calorimetry (ITC) ............................................... 131
5.2.3 Analysis of Isothermal Titration Calorimetry Data ..............................132
5.3 RESULTS AND DISCUSSION ...................................................................... 135
5.3.1 Effects of Solvent and Temperature on the Dimerization of PFDA ..... 135
5.3.2 Thermodynamics of PFDA-quinazoline Complex Formations in FC-77,
HFE-7500, and 1-chloropentane ............................................................................. 138
5.3.3 Thermodynamics of PFDA-pyridine Complex Formations in FC-77,
HFE-7500, and 1-chloropentane ............................................................................. 144
5.3.4 Discussion................................................................................................... 149
5.4 CONCLUSION ................................................................................................ 154
5.5 ACKNOWLEDGEMENT .............................................................................. 155
6.0 SUMMARY AND FUTURE DIRECTIONS ................................................... 156
APPENDIX A ............................................................................................................................ 158
APPENDIX B ............................................................................................................................ 162
BIBLIOGRAPHY ..................................................................................................................... 179
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LIST OF TABLES

Table 1-1. Properties of Teflon AFs. .............................................................................................. 4 
Table 1-2. Radius of free volume elements (Å) in Teflon AF 2400 from various methods. .......... 6 
Table 1-3. Structures Sorption of organic liquids in Teflon AFs at 25 oC. ................................... 15 
Table 2-1. Storage Modulus of FC-70-doped Teflon AF Films at 20.0 oC. ................................. 42 
Table 2-2. Summary of the Physical and Chemical Properties of FC-70-doped Teflon AF Films
at 20.0 oC. ...................................................................................................................................... 43 
Table 2-3. Comparison of Permeability Coefficients through Fresh Pure Teflon AF Film and
Chloroform-soaked Pure Teflon AF Film at 20.0 oC. ................................................................... 44 
Table 2-4. Solute Partition Coefficients (FC-70/CHCl3) at 20.0 oC. ........................................... 51 
Table 2-5. Structures Properties of the Fresh Teflon AF 2400 Films and Recycled Teflon AF
2400 Film. ..................................................................................................................................... 59 
Table 3-1. A summary of physical, mechanical, chemical, and transport properties of composite
Teflon AF films at 20.0 ± 1.0 oC. ................................................................................................. 77 
Table 4-1. Selective transport of octafluorotoluene over toluene through porous Teflon AF 2400
based supported liquid membranes at 20.0 ± 1.0 oC. .................................................................. 112 
Table 4-2. Zeta-potential of fluorescent silica nanoparticles in ethanol. .................................... 119 
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