Nature - USA (2020-08-20)

390 | Nature | Vol 584 | 20 August 2020

Article

network of linked secondary silica particles and high mesoporosity
(Fig. 2i). The nitrogen sorption isotherms of the silica aerogel powder
starting material and the printed objects are similar; the specific surface
area and average pore sizes increase from 697 m^2  g−1  to 751 m^2  g−1 and
from 11.8 nm to 12.6 nm, respectively (Fig. 2m, n). The relatively high
bulk density (0.18 ± 0.02 g cm−3) is related to the growth of a low-density
silica aerogel phase throughout the entire object—not only in between,
but also inside the mesopores of the aerogel powder starting material,
owing to the infiltration of the 1-pentanol sol (Extended Data Fig. 1).
The high mesopore volume (3.13 cm^3  g−1) limits gas-phase conduction
(Knudsen effect). The printed aerogel has a thermal conductivity of
15.9 mW m−1 K−1 at 25 °C, well below that of standing air (26 mW m−1 K−1)
or conventional insulation materials (>30 mW m−1 K−1). This value is typi-
cal for silica aerogel thermal superinsulators, but far lower than that
for any 3D-printed object reported so far. Silica aerogel has no lower
temperature limit for cryogenic applications. At higher temperatures,
radiative conduction increases; the thermal conductivity is expected^30
to increase to around 30 mW m−1 K−1 at 200 °C and 70 mW m−1 K−1 at
500 °C. Surprisingly, the printed aerogel has a higher thermal stability
than the silica aerogel powder starting material (Fig. 2o). Substantial
loss of hydrophobic groups occurs only above 400 °C. The printed

samples have similar compressive and tensile strengths as standard

silica aerogels, but a better machinability (Extended Data Fig. 6), pos-

sibly because the structure with high-density aerogel particles inside

a lower-density matrix limits crack propagation. If higher mechani-

cal strength is required, polymer reinforcement has been shown^31 to

increase the Young’s modulus by a factor of nine and the maximum

compressive strength by a factor of seven (Extended Data Fig. 6).

The ability to precisely and reproducibly print superinsulating silica

aerogel objects in different sizes and geometries enables new insula-

tion applications. As a demonstration, we printed aerogel features

of variable size and thickness onto a substrate (Fig. 3a, b). Thermal

imaging when placed onto a hotplate (150 °C) or iceblock (−20 °C)

reveals temperature variations that relate directly to the thickness of

the printed aerogel insulator (Fig. 3c, d). Combined with appropriately

placed heat conductors and sinks, the ultralow thermal conductivity

of silica aerogel and the ease with which complex geometries can be

produced provide new opportunities for thermal management. Key

opportunities could include situations where space is limited, where

local hotspots may influence sensitive components or cause damage,

and where local temperature gradients need to be restricted, such

as in implants, wearable devices, micro-electromechanical systems,

10 mm

2mm

y 10 mm

x

z

y

x

1.2 2.0 3.6

1.2 2.0 3.6

1.2 2.0 3.6

50 °C

25 °C

a

i j k l

bc d

e f g h

3.6

1.2

2.0

Voltage

controller

Al strip

Aerogel

6.37 mm

7.11 mm

2.45 mm

5mm

110 °C

55 °C

15 °C

–15 °C

Fig. 3 | Thermal management. a, Design and 3D printing of the gel array (ink
SP1.6, 210-μm conic nozzle, 3.5 min at 15 mm s−1; Supplementary Video 4). The
thickness of each object is labelled (in millimetres). b, Optical image. c, Infrared
image when placed on a hotplate after more than 0.5 h of equilibration.
d, Infrared image when placed on an ice block after more than 0.5 h of
equilibration. The thickness (in millimetres) of the objects is also labelled in

b–d. e, i, Sketch (e) and photograph (i) of a printed aerogel component (410-μm

conic nozzle, 2 min at 12 mm s−1). f–h, j–l, Photographs (f–h) and infrared images

(j–l) of a circuit board with neither a sink nor an insulator on the voltage

regulator (RG2; f, j), with an aluminium strip as heat sink (g, k), and with both a

sink and an insulator (h, l).