Nature | Vol 584 | 20 August 2020 | 391smartphones and optical devices. To illustrate the utility of silica aero-
gel in thermal management, we show that heat can be isolated at the
source. A printed aerogel insulator cap, combined with a heat sink, miti-
gates the local hotspot on a circuit board, making the heat-generating
component safe to touch (Fig. 3e–l). We also show that heat-sensitive
components can be protected. The local temperature of a capacitor
exposed to contact heat is only 36 °C with printed aerogel cap, com-
pared to 75 °C without protection and 48 °C with a cap made from a
conventional insulator of the same thickness (Extended Data Fig. 7).
Another application involves using aerogel membranes as a thermal
transpiration gas pump. Thermal transpiration generates a gas flow
when a thermal gradient is applied to a capillary with a diameter that
approaches the mean free path length of the gas molecules (that is, with
a Knudsen number Kn that approaches 1; Fig. 4a)^32. Silica aerogels are
ideal membrane materials for Knudsen pumping, owing to their high
mesopore volume and low thermal conductivity, which ensures that
a steep thermal gradient can be maintained^33. We printed thin silica
aerogel membranes (Kn = 2.04; see Methods) with a top layer containing
(black) ramsdellite MnO 2 microspheres (Fig. 4b–e, Extended Data Fig. 8).
Upon light radiation (Extended Data Fig. 9), the black-MnO 2 -bearing
side of the membrane heats up, a thermal-transpiration-driven gas
flow is established across the membrane (Fig. 4f), and volatile organic
compounds (VOCs; such as toluene) that are part of the gas stream are
degraded photothermocatalytically by the MnO 2 particles (Fig. 4g).
In summary, our additive manufacturing protocol produces silica
aerogel objects with high precision and shape fidelity, the flexibility to
include additional functionality and excellent material properties, most
notably an ultralow thermal conductivity and high mesoporosity. The
3D-printing process avoids the issues of subtractive manufacturing and
opens up new applications for silica aerogels. For thermal insulation,
additive manufacturing will enable miniaturized applications (such as
portable devices and consumer electronics), adding to the existing silica–50050 100150 200 2503003504000510152025Flow rate (μl min–1mm–2)Exposuretime(min)Flowrate0306090120150180
TemperatureTemperature(°C)MnO 2 and SiO 2MnO 2 and SiO 2SiO 2SiO 210 μmacfdgeb05 0 100 1502 00 250 300 350400024681012141618Toluene concentration (ppm)Time(min)20 μm 100 nmCold chamber
Hot chamberFig. 4 | Light-driven thermal transpiration gas pump with simultaneous
VOC degradation. a, Thermal transpiration. A temperature gradient induces
the movement of gas molecules from the cold (blue) to the hot (red) side of a
mesoporous membrane. b, A bilayer silica aerogel membrane (inks SP1.2 and
SP1.3M0.9 (Extended Data Table 1), 410-μm conical nozzle, 6 min at 15 mm s−1).
c, SEM image of the interface between the two inks. d, Magnification of the
orange-boxed region in c, showing the MnO 2 distribution in the silica aerogel.
e, Magnification of the orange-boxed region in d, showing the MnO 2 particles.
f, Light-driven pumping performance. The initial spike in f low rate is due to
thermal expansion of gases in the sample chamber; the steady-state f low rate
of around 8 μl min−1 mm−2 is due to thermal transpiration. g, Photocatalytic
degradation of toluene during thermal transpiration.