Aerogels: Overview and Outlook for Future Space and Terrestrial Applications at NASA

National Aeronautics and Space Administration

NASA Glenn Research Center

Dr. Rocco Viggiano Materials Chemistry and Physics Branch

www.nasa.gov National Aeronautics and Space Administration NASA Glenn Research Center

www.nasa.gov 2 National Aeronautics and Space Administration

NASA GRC Core Competencies

Aerospace Propulsion In-Space Propulsion and Physical Sciences and Cryogenic Fluids Management Biomedical Technologies in Space

Communications Technology Power, Energy Storage and Materials and Structures and Development Conversion for Extreme Environments

www.nasa.gov 3 National Aeronautics and Space Administration Materials and Structures Division High Temperature Materials Lightweight Concepts Electric Propulsion Materials Ceramic Matrix Protective Materials for High Power Composite Coatings Hybrid Composite Nanotube Yarn Density Electric Motors Gear

Thermal Protection Lattice Block Flexible Aerogel Silicon Carbide Seal Hybrid Disk Lightweight Power Semiconductor Transmission Cable

Mechanisms and Drive Systems Computational Modeling Flight Structures Low Impact High Efficiency Shape Memory Alloy- Orion Fairing Jettison Docking Seal Gear Based Actuation

Superelastic Large Composite Bearing Vibration Testing Spring Tire Structures

4 www.nasa.gov 4 National Aeronautics and Space Administration What are Aerogels? Aerogels are a class of porous solids which exhibit many extreme properties which originate from a nanoporous skeletal architecture

• Highly porous solids made by drying a wet gel without shrinking • Pore sizes extremely small (typically 10-40 nm)—makes for very good insulation • 2-4 times better insulator than fiberglass under ambient pressure, 10-15 times better in light vacuum • Invented in 1930’s by Prof. Samuel Kistler

Silica Aerogel Monoliths

Sol Gel Aerogel

www.nasa.gov 5 National Aeronautics and Space Administration Aerogel Fabrication

= 𝟐𝟐𝜸𝜸 𝐜𝐜𝐜𝐜𝐜𝐜 𝜽𝜽 𝑷𝑷γ 𝒄𝒄𝒄𝒄𝒄𝒄= Interfacial Tension θ = Wetting Angle𝒓𝒓 r = Pore Radius

Aerogel Fabrication Steps: 1. Dissolve monomeric precursors into solution (sol) 2. Gel network forms incorporating monomers into skeleton 3. Removal of solvent occurs either by sublimation or supercritical extraction Supercritical Extraction 1. Avoids liquid/vapor boundary by solvent removal above critical point 2. No liquid-vapor interface exists thus no capillary stresses 3. Based on capillary pressure equation, a small diameter (r), leads to a huge force resulting in compaction

www.nasa.gov 6 National Aeronautics and Space Administration Monolithic silica aerogels provides superior insulation

Data provided by Institution of Civil Engineers

…but are extremely fragile …and limited to a few and moisture sensitive exotic applications

www.nasa.gov 7 National Aeronautics and Space Administration Potential applications for durable aerogels in aeronautics and space exploration

Cryotank Insulation Fan engine containment Antenna substrates (Ballistic protection)

Sandwich structures

Ultra-lightweight, multifunctional structures for habitats, rovers

Heat shielding Insulation for EVA suits Propellant tanks Inflatable aerodynamic and habitats decelerators

www.nasa.gov 8 National Aeronautics and Space Administration

Insulation for Future Mars Concepts Mars System Taxi

Initial Cis-Martian Habitat

Mars Surface Phobos Exploration Rover Vehicle (PEV)

Mars Crew Lander Mars Ascent Vehicle (MAV)

www.nasa.gov 9 National Aeronautics and Space Administration Hypersonic inflatable aerodynamic decelerator concept • Hard aeroshells used to land rovers on Mars limit size of payload • Inflatable structure overcomes this limitation • Concept is a series of stacked inflatable tori tied with a network of straps • Flexible thermal protection system on fore body • Baseline insulation was Aspen silica Aerogel composite blanket • Loses fragile silica aerogel on handling

www.nasa.gov 10 National Aeronautics and Space Administration Polyimide aerogels

Monomers Polyamic Polyimide Polyimide Acid Gel Gel Aerogel • Entire aerogel skeletal architecture synthesized from a polymer should be flexible as a thin film • Polyimides are known for their high temperature stability • Family of polymer aerogels made by cross-linking polyimide oligomers to form gel network • Supercritical fluid extraction to remove liquid from gels

Meador, US Patent application filed 9-30-2009 Meador and Guo, US Patent application filed 2/4/2012

www.nasa.gov 11 National Aeronautics and Space Administration

Two approaches to cross-linked PI aerogels developed

H2N NH2 O O O O O NH Si Si 2 O NH2 X O O R Si O NH + H2N Si 2 O O H N NH O H N 2 2 O 2 NH2 O Si Si O O O H N Si O 2 Si O O O O O O O NH2 H2N H2N OH OH O H H O N N POSS TAB X R X O O O O n

NH2 O O O R = or NH2 • Made by cross-linking polyimide O

X = C=O or nil NH2 oligomers to form gel network O NH O O OH O • POSS decorated with eight O HN HN X O HO HO O O H aminophenyl groups or aromatic OH N O HN X HN R O n

triamine (TAB) O acetic anhydride, pyridine O • Supercritical fluid extraction same O X N R O as silica aerogels N N O O N O O

X O O n N N O

Meador, US Patent 9,309,369, April 12, 2016. O Meador and Guo, US Patent 9,109,088, August 18, 2015. Nguyen and Meador, US Patent 8,974,903, March 10, 2015.

www.nasa.gov 12 National Aeronautics and Space Administration Polyimide Aerogels much stronger than silica aerogels at similar density

0.4 BPDA BTDA 0.3 3

0.2 Density, g/cm Density, 0.1 Silica aerogel is easily broken by 0.0 ODA PPDA DMBZ light finger press Diamines while PI aerogel 100 BPDA easily supports BTDA

the weight 10 of a car Modulus,MPa 1

0.1 ODA PPDA DMBZ Diamines This formulation is actually stronger and lighter than one shown in picture

www.nasa.gov 13 National Aeronautics and Space Administration Cross-linked polyimide aerogels cast as thin film are flexible

• Density of film is similar to molded cylinder • Middle picture is 9” x 13” pan; film is folded multiple times • Currently can cast up to 18” inches wide, 33 feet long at a film casting line in the University of Akron • Surface area, porosity and thermal conductivity similar to monolithic silica aerogels

As-cast wet films Dry aerogel

www.nasa.gov 14 National Aeronautics and Space Administration

Baseline insulation for HIAD is Pyrogel-2250 • Composite insulation made up of silica aerogel particles in O-PAN batting • Flexible but sheds dust particles on handling • Begins to out gas at 380 oC • High heat flux testing at Large Core Arc Tunnel (LCAT) facility at Boeing • Time to 300 oC of bottom thermocouple measured • Related to weight of insulation

• Pyrogel layers lose 20-34 % weight during test

220 1500 TC3R Nextel BF-20 200 1200 TC3K TC4K Nextel BF-20 C 180 C o TC3R

TC5K o TC6K Pyrogel 2250 900 TC7K TC3K 160 Pyrogel 2250 TC4K 140 600 Pyrogel 2250

TC5K 300 to Time Temperature, Temperature, 120 Pyrogel 2250 300 TC6K 100 Kapton TC7K 0 80 0 100 200 300 400 500 5.5 6.0 6.5 7.0 7.5 8.0 8.5 Time, seconds Weight, g

www.nasa.gov 15 National Aeronautics and Space Administration LCAT test—Saffil in combination with PI aerogel

• Layer of Saffil backed by two equivalent thicknesses PI aerogel – 50% DMBZ \ 50% ODA • Test stopped after 247 s when the bottom RC reached 300 °C • Top of PI stack ~590 oC max • PI lost much less weight than Pyrogel

1500 Before test TC2R TC3R Nextel BF-20 1200 TC4K C o TC5K Nextel BF-20 TC6K 900 TC2R Saffil TC3R 600 Top, after test PI aerogel

Temperature, Temperature, TC4K 300 PI aerogel TC5K Kapton 0 TC6K 0 100 200 300 400 500 Bottom, after test Time, seconds

www.nasa.gov 16 National Aeronautics and Space Administration Multifunctional, Universal Thermal Insulation System

• Current multilayer insulation (MLI) only functions in vacuum – Layers of Mylar separated by scrim layers • Aerogel is best insulation in Baseline MLI (Mylar + scrim) gaseous environment Pi aerogel + Mylar • MLI incorporating aerogel in 0.030 0.028 Baseline MLI (Mylar with scrim) place of scrim reduces TC by PI aerogel + Mylar 0.026 23-37% 0.024 • Partnership with JSC and GRC 0.022 0.020 0.018

ThermalConductivity, W/m-K 0.016 0.014 -140 -120 -100 -80 -60 -40 -20 0 20 40 Temperature, oC MLI with and without aerogel tested under simulated Mars atmosphere (8 Torr Argon, -120 to 20 oC)

www.nasa.gov 17 National Aeronautics and Space Administration Mixtures of rigid and flexible diamines give better combination of properties • 100% DMBZ too stiff 100 % • 100% ODA moisture DMBZ sensitive • 50-50 formulation is flexible, strong, moisture resistant 100 % ODA

50 % ODA 50% DMBZ

Guo et al, ACS Applied Materials and Interfaces, 2012, ASAP

www.nasa.gov 18 National Aeronautics and Space Administration Alternative lower cost, commercially available cross-linkers

• Much commercial interest in PI Cl O

aerogel for insulation O Cl = – Refrigeration, clothing, sporting goods, Cl O consumer electronics, building and construction, etc. • Two cross-linkers either not commercially available (TAB) or expensive (OAPS) • Some alternatives: – Benzenetricarbonyl chloride (BTC)— amide cross-links – Polymaleic anhydride (PMA)—aliphatic cross-links – Tri-isocyanates—urea cross-links

www.nasa.gov 19 National Aeronautics and Space Administration Polyimide aerogels with alternate commercially available cross-linker—BTC

• Used ODA or DMBZ in backbone to compare to other cross-linkers • Modulus, morphology depend on backbone, not cross-linker

• Surface areas about DMBZ ODA 2 DMBZ/ODA 100 m /g higher with 600

/g 550 2 BTC 500

450 400

40 Surface area, m area, Surface 350 30 300 20 n 9 8 Polymer conc., wt% 10 7

Meador et al, ACS Appl. Mater. Interfaces 2015, 7 1240-1249

www.nasa.gov 20 National Aeronautics and Space Administration Shrinkage of the aerogel is limiting factor for higher temperature use • High onset of decomposition

600 C temperature o • Varies based on diamine used 575 550

• Shrinkage is lowest for 525 40 500 DMBZ/ODA aerogels 30

Onset of decomposition, decomposition, of Onset 475 20 n • Preconditioning at use 9 8 DMBZ Polymer conc., % 10 temperature stabilizes shrinkage 7 DMBZ/ODA ODA

60 0.8 Initial Initial o 50 After 150 C After 150oC o After 200 C 0.6 After 200oC 40 3

30 0.4 Shrinkage,%

20 Density,g/cm 0.2 10

0 0.0 DMBZ/ODA DMBZ ODA DMBZ/ODA DMBZ ODA Diamine Diamine Meador et al, ACS Appl. Mater. Interfaces 2015, 7 1240-1249

www.nasa.gov 21 National Aeronautics and Space Administration Use of bulky substituents in polymer chain reduces shrinkage after 500 hours aging • Replacing 50 mol % of ODA with BAPF reduces shrinkage by up to half • Surface area still above 300 m2/g after aging

600 100 As Fabricated 500 150 °C 200 °C /g) 2 400

300 10

200 Modulus,MPa 0% BAPF Surface(m Area 25% BAPF 100 50% BAPF

0 1 0.08 0.09 0.1 0.2 Density, g/cm3 7%/n=30 10%/n=30 10%/n=20 10%/n=40

Viggiano et al, ACS Appl. Mater. Interfaces 2017, 9, 8287−8296

www.nasa.gov 22

National Aeronautics and Space Administration

Multifunctional Energy Storage to Improve Efficiency Enable hybrid electric propulsion for commercial aircraft by coupling load- bearing structure with energy storage

Challenges • Producing a structure capable of bearing weight and resisting forces associated with flight Risks • Current Li-Ion battery technology utilizes flammable components Goals • Develop a separator/electrolyte system which possesses sufficient ionic conductivity with non- flammability

Hybrid electric aircraft with multifunctional storage could reduce emissions by 80% and fuel consumption by 60%

www.nasa.gov 23 National Aeronautics and Space Administration Polyolefin Separators used in Li-Ion Batteries

Separator/Properties Celgard 2730 Celgard 2400 Celgard 2325 Asahi Hipore Tonen Setela Structure Single Layer Single Layer Trilayer Single Layer Single Layer Composition PE PP PP/PE/PP PE PE Thickness (μm) 20 25 25 25 25 Porosity (%) 43 40 42 40 41 Melt Temp. (°C) 135 165 135/165 138 137 • Polyethylene and polypropylene are among the most flammable polymers • Limited number of electrolytes wet the polyolefins www.nasa.gov National Aeronautics and Space Administration

Down Selection to ODA-BPDA-N3300A

O O O + O O NMP H2N NH2 O

O 500 nm O N O H HO N NH2 H O O N O O OH O O O N N O n N N N N H H O O C N O O n

O O N O O O O O N O C N N C N O O N N Acetic Anhydride H O TEA HO N N N N N H H H O OH O

O n

• Many polyimide backbone chemistries were synthesized and characterized • Several factors were considered in down selection: film forming, mechanical strength, porosity • ODA-BPDA-N3300A formed thin, mechanically robust films, with porosities of 93%

www.nasa.gov 25 National Aeronautics and Space Administration

Comparison of Commercial Separator and PI Aerogel

2.00 μm 2.00 μm

www.nasa.gov 26 National Aeronautics and Space Administration PI/EMIM Gel Separator is Nonflammable Under Direct Contact with Flame

www.nasa.gov 27 National Aeronautics and Space Administration Polyimide Aerogel Development • Over fifty different combinations of Clear to backbone chemistry studied opaque • Multiple cross-linkers evaluated • Properties more dependent on backbone Pore structure • Formulations identified with

– Best moisture resistance

– Best mechanical properties/density Nextel BF-20 1500

Nextel BF-20 TC2R TC2R – Low thermal conductivity 1200 TC3R Saffil TC4K C TC3R o TC5K TC6K – More optical clarity PI aerogel 900 TC4K PI aerogel TC5K Moisture 600 1000 Kapton

TC6K Temperature, resistant 300 High heat 100 0 0 100 200 300 400 500 flux testing Time, seconds 40

Modulus,MPa 10 35 PMDA/DMBZ Low thermal 6FDA/PMDA/DMBZ 30 BPDA/DMBZ BPDA/ODA 25 conductivity 1 20 0.07 0.08 0.09 0.1 0.2 15 Density, g/cm3 BAX 760 torr 10 BAX 0.01 torr ODA 760 torr Mechanical properties 5 ThermalConductivity, mW/m-K ODA 0.01 torr 0 related to density 20 60 100 140 180 220 Test temperature, oC

www.nasa.gov 28 National Aeronautics and Space Administration Polyamide aerogels

Cl H2N H H NH2 • Lower cost monomers and NH2 O N N + cross-linkers H2N O O O n Cl Amine capped oligomer mPDA IPC or TPC • No catalyst needed n +1 n O Cl BTC • Slightly less thermally stable crosslinker Cl O

O NH O Cl

O H H H N N H H N H H N HN N N O N n O O n O O

Crosslinked PA aerogel

Williams et al, Chem. Mater., 2014, 26(14), 4163-4171

www.nasa.gov 29 National Aeronautics and Space Administration

Polyamide aerogels—Kevlar based

O Cl + • Low cost monomers H2N NH2 CaCl O 2 Cl NMP • All para substitution kept in solution by n + 1 n O H H2N N use of CaCl N NH 2 2 H O • Salt also gets rid of distortion problem n of PA gels during solvent exchange

Supercritical CO2 • Different morphology, but still high Extraction Kevlar aerogel surface area, strong Kevlar gel

Model 100 400 Data

/g 350 2 300 10

250 Modulus, MPa Modulus, 200 40 1 20 wt% CaCl2

Surface area, m area, Surface 30 wt% CaCl2 150 35 40 wt% CaCl2 100 30 9 25 conc., % 0.1 8 2 7 0.09 0.1 0.2 0.3 Polymer conc., wt%6 20 5 CaCl Density, g/cm3

www.nasa.gov 30 National Aeronautics and Space Administration

PI aerogels are stronger than silica aerogels but PA aerogels stronger yet on a density basis

1000

100

10 PA aerogels PI aerogels/OAPS

1 PI aerogels/TAB

Modulus, MPa MPa Modulus, Silica aerogel PI aerogels/BTC 0.1 PU foam Polymer reinforced silica

0.01 0.04 0.05 0.06 0.07 0.080.090.1 0.2 0.3 0.4 Density, g/cm3

www.nasa.gov 31 National Aeronautics and Space Administration Summary • PI aerogels were originally produced for use as thin flexible films for use as insulation for inflatable decelerators or space suits • Same aerogels as thicker parts are stiff and strong • Development of lower cost options: new cross-linkers and other polymer chemistries (polyamide) have led to commercialization

• Commercially available from Aerogel Technologies, LLC (molded shapes) and Blueshift (roll-to-roll films) • Due to their porous architecture and flexibility, PI aerogels can be used as non-flammable battery separators

Aerogel Blueshift Technologies AeroZero Airloy

www.nasa.gov 32 National Aeronautics and Space Administration NASA Opportunities • Pathways Program o Prepares students for careers by providing related work experience o Rotates scheduled work sessions with school

• Pathways Intern and Recent Graduate Positions: o www.usajobs.gov o Example-Search “glenn pathways” o For PMF-STEM visit www.pmf.gov

• Regular Full-Time Positions: o www.usajobs.gov o Search “glenn research center”

• Other Student Opportunities: o https://intern.nasa.gov o Search Opportunities o Limited opportunities for international students

09/9/2004 www.nasa.gov 33 National Aeronautics and Space Administration NASA Glenn Research Center, Cleveland, OH

www.nasa.gov 34 National Aeronautics and Space Administration