ISGS AEROGELS WORKSHOP (St. Petersburg, Russia) August 25, 2019
Transparent and Mechanically Robust Aergoels based on Hybrid Networks
Kazuki NakanishiKazuyoshi Kanamori, Guoqing Zu, Taiyo Shimizu
Institute of Materials and Systems for Sustainability,Nagoya University, Japan
Institute for Integrated Cell-Material Sciences /Department of Chemistry, Graduate School of Science,
Kyoto University, Japan
Institute of Materials and Systems for Sustainability
Low density, transparent, low RI
Low thermal conductivity
What is aerogel?
100 nm
Nano-sized fine porous structure
ρbulk ~ 0.10−0.20 g cm−3
T550nm ~ 90 %/10-mm
λ ~ 12−20 mW m−1 K−1
Excellent thermal insulation of aerogels
Ther
mal
con
duct
ivity
, λ/m
Wm
−1K−
1
Hig
her i
nsul
atio
n
100
90
80
70
60
50
40
30
20
10
0
Superinsulation by aerogels has been expected for more than 80 years !
100 nm
Mesoporous structure consists of weakly connected nanoparticles with 10−20 nm
Mechanically “friable” because of the pore structureHigh-pressure supercritical drying (SCD) is requiredDifficulties in handling and shaping of obtained aerogels
Secondary particles
Primary particles~ 1 nm
10−20 nm
Nanostructure and low mechanical property
Before drying
Duringdrying
Afterdrying
Temporal shrinkage
Aerogel-likeXEROGEL
Spring-back
Gels with high・Strength & flexibility・Hydrophobicity
are needed.
Organogel(e.g. n-hexane)
• Condensation between surface silanols may limit the spring-back.
Si-OH HO-Si → Si-O-Si + H2O
Possibility of ambient pressure drying (APD)
• Gels with low mechanical strength will be damaged.
Si
SiSi
SiSi
OHCH3
O
O
O
O
HO
CH3
CH3
O
CH3
CH3
H3C
Si
Si
Si O
O
O
Si
CH3
R
O
CH3
OO
Hydrophobic methyl groups Enhances “spring-back”
Lower crosslinking density Flexibility
Fewer residual silanols Suppresses irreversible shrinkage
SiCH3
OCH3CH3OOCH3
Methyltrimethoxysilane(MTMS)
Preparation of aerogel-like xerogels without SCD
Polymethylsilsesquioxane (PMSQ)
Polymethylsilsesquioxane(PMSQ)
H+ OH−
Surfactant
H2O, H+ OH−
−H2O, −CH3OH
Hydrolysis at r.t.
Polycondensation at > 60 ˚C
Acetic acidWaterUrea
Surfactant
+
(NH2)2CO + H2O 2NH3 + CO2
PMSQ gel
SiCH3
OCH3CH3OOCH3
SiCH3
OHHOOH
pH
Methyltrimethoxysilane(MTMS) −CH3OH
Avoiding precipitation by• acid-base 2-step reaction for monolithic gel formation• surfactant for suppression of phase separation
One pot process to transparent PMSQ gels
Starting solution
10 mm
CTAC-1 CTAB-1 F127-1
C16H33N+(CH3)3Cl−0.40 g
CTA+Br−0.40 g
EO106PO70EO1061.0 g
Density ~ 0.14 g cm−3
Pore size ~ 50 nm Light transmittance ~ 90 %
MTMS 5 mL, 5 mM HOAc 10 mL, urea 3.0 g, surfactant
• First transparent PMSQ aerogels!• Properties are similar to silica aerogels, except mechanical property
Kanamori et al., Adv. Mater. 19, 1589 (2007), J. Ceram. Soc. Jpn. 117, 1333 (2009), etc.
Obtained PMSQ aerogels
29Si single pulse MAS NMR
SiCH3
OSiSiOOSi
T3
SiCH3
OSiSiOOH or OCH3
T2
800100012001400Tr
ansm
ittan
ce
Wavenumber/cm–1
Linear, branchedSi-O-Si
Cyclic, cageSi-O-Si
Si−OH
C−HCH3C−Si−O
-90-80-70-60-50-40ppm
FTIR
分子レベルの構造Molecular-level structures
T3:T2 = 87:13Condensation degree = 96 %
Optimized aerogel (CTAB system)
h0 h
F127 systemCTAB system
0 0.2 0.4 0.6 0.8 10
2
4
6
8
10
Stre
ss, σ
/MPa
Strain, ε
Uniaxial Compression Test on PMSQ Aerogel
Max. shrinkage: 40 % in linear, 78 % in volume
FF ×9601 s = 16 min1 min = 16 h
Successful ambient pressure drying (Movie)
Thickness = 5 mm
400 500 600 700
20
40
60
80
100
Tran
smitt
ance
(%)
Wavelength/nm
PMSQ xerogelPMSQ aerogelSilica aerogel
PMSQ aerogel Xerogel
Bulk density/g cm−3
Transmittance at 550 nm/%
PMSQ xerogel 0.14 84
PMSQ aerogel 0.13 89
A silica aerogel 0.17 77
Comparable properties between aerogel and xerogel
10-2 10-1 100 101 102 103 104 1050
0.005
0.010
0.015
0.020
0.025
0.030
Nitrogen gas pressure/Pa
Ther
mal
con
duct
ivity
/W m
–1K–1
• Thermal conductivity comparable with silica aerogel• A problem remains: Low bending strength
Thermal conductivity of PMSQ xerogel
PMSQ xerogelSilica aerogelNitrogen gas
(Review) Kanamori, J. Mater. Res. 29, 2773 (2014)
Our new PMSQ aerogels and xerogels
PMSQ aerogel
Xerogel Monolith(Ambient Pressure Drying)
First transparent, superinsulating PMSQ aerogel
“Spring-back” behavior
Granules Composite with fibrous material (Blanket)
Kanamori, Nakanishi, et al., Adv. Mater. 19, 1589 (2007)Hayase, Kanamori, Nakanishi, et al. ACS Appl. Mater. Interfaces 6, 9466 (2014), etc.
Today’s MenuApplications
http://www.emg-pr.com/en/prfitem.aspx?id=3024Transparent insulating windows
Daylighting insulating windows/wallsMonolithGranules
Composites House/buildingwall insulation
Next objective of our research
We’ve got cool materials … But…what about
bending strength?
Chemical design of the network for better
mechanical properties
Bridged polymethylsiloxanes: 2nd generation
1,2-Bis(MethylDiEthoxysilyl)ethane(BMDE-ethy)
Si
CH3
H5C2OH5C2O
Si
CH3
CH2−CH2
OC2H5
OC2H5
Bridged PolyMethylSiloxane(Ethy-BPMS and Ethe-BPMS)
Shimizu, Kanamori, Nakanishi, et al., Langmuir 32, 13427 (2016) and Langmuir 33, 4543 (2017).
1,2-Bis(MethylDiEthoxysilyl)ethene(BMDE-ethe)
Si
CH3
H5C2OH5C2O
Si
CH3
CH=CHOC2H5
OC2H5
=CH=CHCH2−CH2O
Ethe-BPMSEthy-BPMSPMSQ
Experimental for Ethe-BPMS
Polyoxyethylene 2-ethylhexyl ether (EH-208), n ~ 8
Tetramethylammoniumhydroxide (TMAOH)
BMDE-ethe EH-208 5 mM Nitric acid
10 min at r.t.
TMAOH aq.
Gelation & aging at 60 °C or 80 °C
30 s
Solv. exch. with methanol, IPA
CO2 SCD14 MPa, 80 °C, 10 h
BMDE-ethe
This synthetic process was first developed for VTMS system:Shimizu, Kanamori, Nakanishi, et al. Chem. Mater. 28, 6860 (2016).
Almost the same for Ethy-BPMS.
0.10 M 0.30 M 0.60 M 0.90 M 1.2 M 1.5 MCTMAOH = 0.050 M
Tgel = 80 °C
BMDE-ethe EH-208 5 mM NA TMAOH aq.
0.50 mL0.50 mL0.50 mL0.50 mL
Transparency of aerogels is changed depending on CTMAOH.
Shrinkage does not change.
Ethe-BPMS aerogels (base concentration varied)
[H2O]/[BMDE-ethe] ~ 35
ρbulk = 0.14 g cm−3
T550nm = 83 %/10 mm
Ethe-BPMS
Ethe-BPMS Ethy-BPMS PMSQρbulk/g cm−3 0.14 0.15 0.14
T550nm/% 83 78 86
PMSQ
Ethy-BPMS
Mechanical comparison among similar networks
=CH=CHCH2−CH2O
Ethe-BPMSEthy-BPMSPMSQ
Three-point bending Uniaxial compression
Modulus and bending strength are higher for Ethe-BPMS and Ethy-BPMS.
Bending strain at break is higher for PMSQ.
► Similar behaviors between Ethe-BPMS and PMSQ
► Spring-back of Ethy-BPMS is slower (more viscoelastic)
Mechanical comparison among similar networks
Bending strain, ε/%
Stre
ss, σ
/MPa
Stre
ss, σ
/MPa
Compressive strain, ε/%
Stress relaxation for 1 h after 50 % uniaxial compression
Higher stress relaxation in Ethy-BPMS Similar behaviors in Ethe-BPMS and PMSQ
Stress relaxation upon compression
Rel
ativ
e st
ress
, σ/σ
0
Time, t/s
Preparation of Ethy-BPMS xerogels by APD
ρbulk 0.18 g cm−3
T550nm 77 %/10 mm0.19 g cm−3
76 %/10 mm
Aerogel Xerogel
Research on APD of Ethe-BPMS is ongoing. No thermal conductivity data yet. High precursor cost is an important issue for
industrialization (for most bridged precursors).
• PVSQ aerogels have been prepared by two-step acid base in an amphiphilic solvent
• Vinyl groups in the network are available for functionalization and strengthening.
SiCH=CH2
OCH3CH3OOCH3
VTMS
Liq. surfactant as solvent
H+ OH−
Uniform pore structure
Polyvinylsilsesquioxane (PVSQ)
Shimizu, Kanamori, Nakanishi, et al., Chem. Mater. 28, 6860 (2016)
EH-208n ρbulk = 0.17 g cm−3
T550nm = 62 %/10 mm
300 nm
SiCH=CH2
OCH3CH3OOCH3
VTMS
Liq. surfactant as solvent
H+ OH−
Wet Gel
“Vulcanization” with radical initiator
SiO
O OSiSi
O
OSi
Si
OSiO
Si
O
O
O O Si
Si
OO
Si
OSi
O
Si
OO
O
SiO
O
O
Si O
O
With AIBN in 2-propanol
at 60 ˚C
SiO
O OSiSi
O
OSi
Si
OSiO
Si
O
O
O O Si
Si
OO
Si
OSi
O
Si
OO
O
SiO
O
O
Si O
O
Post-gelation curing (“vulcanization”) for improvement in mechanical properties.
VulcanizedPVSQ gel
29Si MAS NMR
New peak appears around −65 ppm and increases with increasing [AIBN].
This can be assigned to T3 Si bonded with elongated alkyl chains.
Structural changes by vulcanization
SiO
OO
SiO
OO
n
[AIBN]= 48.7 mM24.4 mM12.2 mM6.09 mM
Pristine PVSQ
Chemical shift, δ/ppm
Ambient pressure drying
[AIBN]/mM0.1457
0.1459
Bulk density/g cm−3
Transmittance/%
6.090.1458
12.2 24.4 36.50.1558
48.70.1651
Stress and resilience increase with increasing [AIBN].
Nearly perfect spring-back in aerogels treated with AIBN with high concentration.
No obvious changes in bulk density and transparency.
0.1664
0
Uniaxial compression
Changes in compressive behavior
PVSQ Vulcanized(highest [AIBN])
Aerogel
Xerogel
Successful ambient pressure drying
0.14 g cm−3
0.81 g cm−3
0.16 g cm−3
0.17 g cm−3
T550nm = 60 %/10-mmλ = 15.3 mW m−1 K−1
or or
Radical polymerization
Vinylalkoxysilane orAllylalkoxysilane Alkoxysilane polymer
Doubly crosslinked network
or
R1,R2,R3 = OCH3, OCH3, OCH3
= OCH3, OCH3, CH3
= OCH3, CH3, CH3
Polysiloxane
Vinyl polymer
HydrolysisPolycondensation
Aerogels Xerogel
Zu, Kanamori, Nakanishi et al. ACS Nano 12, 521 (2018)Zu, Kanamori, Nakanishi et al., Chem. Mater. 30, 2759 (2018)
JP Patent 2017-162308
Doubly crosslinked system: 3rd generation
A detailed example in PVPMS
Polyvinyl-polymethylsiloxane(PVPMS) network
APD without any solvent-exchange
Di-tert-butyl peroxide
(1-5 mol%)
120 ºC, 48 h
BzOH or IPA,H2O, Catalyst (TMAOH)
Polyvinyl-methyldimethoxysilane
PVMDMS(n ~ 40-70)
Vinylmethyl-dimethoxysilane
100 ºC, 4 d
200 nm
Transparent to translucent
Homogeneous pores High BET surface area Scalable High hydrophobicity Compressive flexibility Bending flexibility Low-cost processBut lower thermal durability(~ 200 ºC)
Xerogel
80 % uniaxial compression and perfect recovery
Immersed in n-
hexane
APD againNot damaged!
Bending flexibility of a thick film
Unusual properties in PVPMS xerogels
Durability against solvents
Outstanding machinability
Zu, Kanamori, Nakanishi, et al. ACS Nano 2018, 12, 521.
DCエアロゲルの低熱伝導性と物性比較Thermal conductivity and other properties
DCエアロゲルの低熱伝導性と物性比較Aerogels based on decreased siloxane density
µm
Morphology
Particle size: 1.5-3.0 μm
Pore size: 2.0-20.0 μm
a
b
PA1-1
PA1-2
c PA2-1
d PA2-2
Particle size: 200-400 nm
Pore size: 200 nm-6 μm
PA1
PA2
Superhydrophobic
Superhydrophobic
低架橋DCエアロゲルの多孔構造Coarse pore structures of PA1,2 (less D units)
PA1-1
Mechanical properties High compression flexibility
High bending flexibility
PA1-1
PA2-1
PA1-1
1 cmshaping
PA2-2
ρ = 25 mg cm-3
Excellent machinability
低架橋DCエアロゲルの機械的物性Mechanical properties of PA1,2
Adsorption performance: efficient oil-water separation
PA1-1
Absorption capacity of PA1and PA2 for various organic solvents and oils
n-hexane/water
Absorption/drying cycle performance of PA1-1 for n-hexane (it is dried via evaporation at 60 ℃)
n-hexane
water
aerogel
低架橋DCエアロゲルの油吸収特性Oil absorption performanc of PA1
Porous structure
200 nm
PA3
SBET=438 m2 g-1
SBET=605 m2 g-1
200 nm
PA4
PA3 PA4
With the molar ratio of VDMMS to VMDMS decreasing to 1:1 and 1:2, the macroscopic phase separation is further suppressed by the network with lower hydrophobicity and higher cross-linking density, leading to a microstructure with smaller particle and pore sizes
Particle size: 35-100 nm
Pore size: 30-180 nm
Particle size: 20-80 nm
Pore size: 20-100 nm
the hydrophobicity of PA3 and PA4 becomes lower. In spite of this, the contact angles of water of PA3 and PA4 are still above 140°
Hydrophobicity
D単位の比較的多い系における微細な多孔構造の形成Fine pore structures of PA3,4 (more D units)
High compression flexibility
PA4
PA3
5.1 MPa4.2 MPa
PA4
bend release
shaping
PA4
High bending flexibility
Excellent machinability
air PA3 PA4
17.6 16.2
~26
Thermal superinsulation performance
微細な多孔構造をもつDCエアロゲルの機械的物性と低熱伝導性Mechanical/thermal properties of PA3,4
A simple hybridizing method
PA2-G
Graphene
PVPDMS/PVPMS network
The graphene nanopaltes with 2–10 nm thickness and 5–15 μm width are well distributed in the highly porous aerogel matrix
It is also superhydrophobic with a contact angle of water of ~157°
Morphology and superhydrophobicity
導電性物質 (グラフェン) の導入Introduction of graphene
PA2-GLEDreleasecompress
High compression flexibility Strain-sensitive conductivity
brightness fluctuates with compression and decompression of the aerogels
A strain sensor of PA2-G adhered to a finger
PA2-G
More contactsamong
graphene
less contactsamong
graphene
PA2-G
Normalized electrical resistance versus compressive strain
Zu, Kanamori, Nakanishi, et al. Angew. Chem. Int. Ed. 2018, 57, 9722.
Possibility as strain sensors
Conclusions
H2O, H+/OH−
−H2O, −ROH
Hydrolysispolycondensation
Aerogel-like
XEROGELS!
APD
n-Hexane
Wet Drying Low-densityTransparent
RSi(OR’)3
Si RR’OOR’
CH3
Si OR’OR’
CH3
Si RR’OOR’
OR’Si OR’OR’
OR’R1R2Si(OR’)2
Marshmallow gel
Other flexible aerogels/xerogels Macro-mesoporous RF
Chem. Mater. 29, 2122 (2017)Angew. Chem. Int. Ed. 52, 1986 (2013), etc
Resiliencefor Bendable, Stretchable, Machinable Aerogels
EnthalpyHardBrittle
EntropySoft
Large deformation
Organic-Inorganic Double Crosslink is the best current solution !!
Elasticity
Funds
Excellent Co-workers
Acknowledgements
Dr. Guoqing ZU (Kyoto Univ.)
Dr. Kazuyoshi KANAMORI(Kyoto Univ.)
Dr. Mamoru AIZAWA (tiem factory, Inc)
Dr. Taiyo SHIMIZU(AIST)
Incubation Program of Kyoto University