PROPERTIES AND STRUCTURES OF SULFONATED SYNDIOTACTIC POLYSTYRENE AEROGEL AND SYNDIOTACTIC POLYSTYRENE/SILICA HYBRID AEROGEL A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirement for the Degree Master of Science Huan Zhang August, 2014
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PROPERTIES AND STRUCTURES OF SULFONATED SYNDIOTACTIC
POLYSTYRENE AEROGEL AND SYNDIOTACTIC POLYSTYRENE/SILICA
HYBRID AEROGEL
A Thesis
Presented to
The Graduate Faculty of The University of Akron
In Partial Fulfillment
of the Requirement for the Degree
Master of Science
Huan Zhang
August, 2014
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PROPERTIES AND STRUCTURES OF SULFONATED SYNDIOTACTIC
POLYSTYRENE AEROGEL AND SYNDIOTACTIC POLYSTYRENE/SILICA
HYBRID AEROGEL
Huan Zhang
Thesis
Approved: Accepted: ____________________________ _____________________________ Advisor Department Chair Dr. Sadhan C. Jana Dr. Robert A. Weiss ____________________________ _____________________________ Faculty Reader Dean of the College Dr. Bryan Vogt Dr. Stephen Z.D. Cheng ____________________________ _____________________________ Faculty Reader Dean of the Graduate School Dr. Nicole Zacharia Dr. George R. Newkome ____________________________ Date
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ABSTRACT
This study focuses on hybrid aerogels of syndiotactic polystyrene (sPS) and silica
where silica concentration is varied and silica condensation conditions are varied to
produce various mesoporous materials. In addition, the study investigates hybrid
materials obtained by coating sulfonated syndiotactic polystyrene on a cellulose filter
paper.
In first part of this study, syndiotactic polystyrene is modified by sulfonation to enable
further chemical modifications. Specifically, sulfonated syndiotactic polystyrene (ssPS) is
coated on macroporous cellulose filter paper using a dip coating process, ssPS is turned
into gel by thermoreversible gelation, and finally aniline is polymerized on ssPS strands
to obtain a hybrid aerogel with electrical conductivity. The aerogels are recoved by
removing the solvents under supercritical conditions. The ssPS aerogels are coated on
cellulose filter materials to derive two benefits: first, to capitalize on the large surface
area of ssPS aerogels and second, to exploit the mechanical strength of the cellulose
filter.
In second part of this study, silane precursor is absorbed inside the macropores of sPS
gels and silica gels are grown under both a two-step reaction and a one-step reaction.
Type A silica aerogel is synthesized by acid-base catalyzed sol-gel method, while type B
silica aerogel is prepared only by acid catalyzed sol-gel process. Type A silica gels
exhibit pearl-necklace structure, while type B silica gels are composed of strand-like
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combination of organic and inorganic materials and their associated surface area and
surface energy offer a number of attractive properties.
The sPS/silica hybrid aerogels are fabricated from different concentrations of sPS in
solution and from different weight ratio of sPS to silica. The sPS/silica hybrid aerogels
exhibit predominant pores located in the mesopore range (2~50 nm), and at higher silica
content, silica particles undergo more aggregation as evident from larger fractions
mesopore size (~15 nm). In contrast to native sPS aerogel, the compressive modulus of
hybrid aerogel is increased up to 100%. In addition, the hybrid aerogels present specific
surface area as high as 693 m2/g, high porosity, fast absorption and high absorption
capacity of crude oil. Type A hybrid aerogels are composed of both fiber-like strands of
sPS and pearl-necklace particles of silica. At low weight ratio of sPS to silica, the silica
forms aggregates on sPS backbones as conformal coating. At higher weight ratio of sPS
to silica, the silica particles not only coated on the polymer backbones, but also filled the
macropores of sPS. Type B hybrid aerogels present fiber-like interpenetrating networks
formed by sPS strands of 50-100 nm and silica strand of 200 nm.
silica particles. In the process, the mesoporous hydrophilic silica particles are combined
with macro- and microporous hydrophobic sPS in single articles. This unique
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ACKNOWLEDGEMENTS
I would like to express my sincere appreciation to my advisor, Prof. Sadhan C. Jana,
for his selfless guidance, and for his perseverance and constant encouragement to
complete this thesis.
I would like to extend my thanks to all my friends in my groups for their support to my
work. I would like to express my deep gratitude to Xiao Wang for her invaluable help
and encouragement to my research.
I would like to express special thanks to Dr. Rong Bai and Dr. Boji Wang for training
me for the instrument
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TABLE OF CONTENTS Page
LIST OF TABLES ............................................................................................................. ix
LIST OF FIGURES ............................................................................................................ x
CHAPTER
I INTRODUCTION ......................................................................................................... 1
II REVIEW OF LITERATURE ....................................................................................... 5
2.1 What is an aerogel? ................................................................................................ 5
1. Critical constant for some solvents [66]. ................................................................. 7
2. Physical properties of cellulose filter and ssPS-coated-filter aerogel. The specimens of radius 24.52 mm were used in measurement. ...................... 28
3. Surface area and average pore size of different materials. .................................... 35
4. Composition and properties of sPS/silica hybrid aerogels .................................... 46
5. Surface areas of native sPS aerogel and hybrid aerogel ........................................ 52
6. Contact angles of water for sPS-0.02-TEOS aerogels ........................................... 54
7. Contact angles of hydrocarbon oil for sPS-0.02-TEOS aerogels……...………...53
8. Crude oil absorption data for all specimens. .......................................................... 57
9. Water absorption data for sPS-0.02-TEOS aerogel. .............................................. 58
10. Surface area of native sPS aerogel, acid-derived silica aerogel and Type B hybrid aerogel. ……………………………………………………….…..63
11. Oil absorption and water absorption data for sPS-0.02-TEOS-3 acid-derived aerogel. ......................................................................................................... 65
x
LIST OF FIGURES
Figure Page
1. Pressure-temperature phase diagrams. Supercritical drying (arrow 1) goes beyond the critical point of the working fluid. The arrow 2 shows ordinary drying, and the arrow 2 shows two phase changes in freeze-drying. ....................... 7
2. Hydrolysis mechanism of alkoxysilanes under acid/base catalyzed conditions .... 10
3. Condensation mechanisms of alkoxysilanes under acid/base catalyzed conditions . ............................................................................................... 11
4. Gel network structure for acid and base catalyzed reactions . ............................... 12
5. Schematic representations of temperature-concentration phase diagrams for sPS and (a) good solvent, (b) bad solvent ....................................................... 14
6. Schematic of polyaniline formation on sulfonated polystyrene ............................ 20
7. Chemical formula of sPS ....................................................................................... 21
8. Schematic view of apparatus used in synthesis of sulfonated sPS ........................ 23
9. Schematic view of dip coater ................................................................................. 24
10. The PANI-coated-filter is shown in graph (a). The cellulose filter shown in graph (b). .............................................................................................................. 25
11. SEM images of the surfaces of cellulose filter (a), sPS-coated-filter aerogel (b), ssPS-coated-filter aerogel (c), and polyaniline-coated-filter aerogel (d) 29
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12. SEM images of the cross-section of cellulose filter (a), ssPS-coated-filter aerogel (b). The internal space of the ssPS-coated-filter aerogel is shown in (c) . 31
13. SEM images of the structure of sPS aerogel (a), ssPS aerogel (b), and polyaniline-coated aerogel (c). ............................................................... 32
14. Nitrogen adsorption-desorption isotherms at 77 K of cellulose filter, ssPS-coated aerogel and polyaniline-coated-filter aerogel. ........................................ 34
15. Pore size distribution of pure filter, ssPS-filter aerogel and polyaniline-ssPS-filter aerogel..................................................................................................... 34
16. TGA traces of sPS and ssPS ................................................................................. 36
17. TGA traces of cellulose filter, ssPS-coated-filter aerogel, and polyaniline-coated-filter aerogel .............................................................. 37
18. The relationship between the voltage and current. ssPS-coated aerogel is shown in graph (a), polyaniline-coated aerogel is shown in graph (b). ............... 39
19. Chemical formula of TEOS. ................................................................................ 42
20.(a) TGA curves of sPS-0.02-TEOS aerogels, (b) TGA curves of sPS-0.04-TEOS aerogels. ................................................................................................ 49
21. The hybrid aerogels before (a) and after (b) heated to 800 0C in the air. From left to right, the concentration of TEOS decrease from zero to 0.7 mol/l. ..... 49
22. SEM images of sPS aerogel (a), hybrid aerogels (b)~(e), and native silica aerogel (f) ................................................................................................................ 51
23. Pore size distribution of two series of hybrid aerogels. ....................................... 52
24. Images of aerogels exposed to water. (a) 0.7 mol/l silica aerogel, sank to the bottom of water and collapsed under a tender touch. (b) sPS-0.04-TEOS-0.7 aerogel, floated on the surface of water, kept a strong structure after immersed in the water using a external force. .................. 54
25. (a) Compressive moduli of hybrid aerogels. (b) compressive stress-strain curves of selected hybrid aerogel. ........................................................................ 56
26. Images of sPS-0.04-TEOS-0.7 aerogel and sPS-0.04-TEOS-0.1 aerogel at different time during oil absorption test, sPS-0.04-TEOS-0.7 aerogel : (a): 1s, (b) 15s, (c) 30s; sPS-0.04-TEOS-0.1 aerogel : (d): 1s, (e) 15s, (f) 30s. .................................................................................................................. 59
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27. Image (a) and (b) show the hybrid aerogel and native sPS aerogel before and after oil absorption test. Image (c) and (d) show the hybrid aerogel before and after water absorption test ................................................................ 59
28. (a) TGA curves of Type B hybrid aerogels, (b) The Type B hybrid aerogels before and after heated to 800 0C in the air. ........................................................ 62
29. SEM images of acid-derived silica aerogel (a) and Type B hybrid aerogel (b). .. 63
30. Pore size distribution of native sPS aerogel, acid-derived silica aerogel and type B hybrid aerogel……… …………...63
31. Image (a) and (b) show Type B hybrid aerogel before and after oil absorption test. Image (c) and (d) show Type B hybrid aerogel before and after water absorption test ......................................................................................... 66
1
CHAPTER I
INTRODUCTION
Aerogels are highly porous, low density, solid state materials with three dimensional
network structures. The network structures are produced first in the starting gels and
aerogels are derived by removing the liquid component from gels under supercritical
conditions. Aerogels attract significant academic and industrial interest owing to its
extremely low density, high porosity, and high surface area. However, their applications
are limited due to some of their inherent defects. For example, silica aerogels are fragile
and friable materials. The structure of native silica aerogel can be easily crushed by a
stress of 31 kPa [1]. Accordingly, many strategies emerged in last decades to tailor the
network structures and to obtain reinforcement.
Aerogels have been made from polymers [ 2 3 4 5 ], transition metals [ 6 7 8 9 ], and
montmorillonite clay/polymer composites [10,11]. Since first reported in the 1930s [12],
silica aerogels have became most widely used and extensively studied due to versatile
chemistry and remarkable properties, e.g., density ~3-350 mg/cm3 [13,14], high porosity
(>95%), large surface area (ca. 1000 m2/g), low thermal conductivity (0.004-0.03
W/mˑK), low dielectric constant (1.1-2.2) [15,16], and low index of refraction (~1.05) [17]
2
Due to these interesting properties, silica aerogels found many potential applications in
thermal insulation, energy media, molecular separation, high energy physics, to name a
few [14],[1819202122]. Two unfavorable properties limit the applications of silica aerogels –
first, the hygroscopic nature and second, the inherent fragility of the silica networks. The
network structures of silica aerogels are formed by the condensation reaction between
"Si-OH" groups. However, not all Si-OH groups are fully condensed. Thus, silica
aerogels can be easily destroyed by placing a small drop of water on its surface [23,24].
The hygroscopic silica particles absorb water into its pores. The capillary stress causes
compressive stress and crushes the networks [25]. A native silica aerogel derived from
tetramethoxysilane (TMOS) with a density of 0.12 g/mL can be completely shattered into
dust under a small load of 31 kPa [1]. This is due to weak network structures formed by
many "pearl necklaces" that are tied together by a limited number of "Si-O-Si" bonds at
the necks of the secondary silica particles.
Many effective methods of reinforcement of silica aerogel have been developed. The
most straightforward way is to increase the total number of connecting points between
the secondary particles by increasing the density [26]. In addition, strengthening the neck
region using multifunctional particles, and reinforcing the network with nanofibers
showed large increases in mechanical strength [27282930313233]. It is reported [34,35] that silica
aerogels can be effectively strengthened by a conformal coating of polymer on silica
backbone. In this context, one can capitalize on the unique properties of silica aerogels if
silica aerogels are efficiently packaged in another porous material and the carrier porous
material provides mechanical integrity.
3
Since first reported by Daniel et al. in 2005 [36], syndiotactic polystyrene (sPS)
aerogel has also attracted significant interest. sPS aerogel is a highly porous, high surface
area and low density material obtained from physical sPS gel by replacing the liquid
component with a gas by supercritical drying or freeze drying methods. The network
structures of sPS aerogel are composed of three-dimensional polymeric strands, and the
connectivity of network is obtained from the intermolecular physical bonding at the
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