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Silica aerogels are 97 percent porous, meaning light moves through the material but the interconnecting nanolayers of silicon dioxide trap infrared radiation and greatly slow the conduction of heat. A thin translucent layer of low-thermal-conductivity material also blocks UV, directly replicating the radiative effects of Earth’s atmosphere.

The researchers behind this new study used models and experiments to show that a thin, 2 to 3 cm (.8 to 1.2 inch) layer of aerogel could allow sunlight to penetrate, but would trap heat.

My question is, what is the reason that UV light gets blocked, but infrared light doesn't? Is there a reason for this? And why/how does infrared get trapped? I assume silica aerogel is able to heat a surface, because infrared gets trapped and can't escape because of the low thermal conductivity, but why doesn't the infrared get blocked in the first place, like UV? Why would it block longer wavelengths but not shorter ones?

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    $\begingroup$ Isn't it just a matter of the optical properties of silica? Or are you saying that optical absorption characteristics of low-density silica aerogel are different from full density silica? $\endgroup$ – user93237 Sep 23 '19 at 18:27
  • $\begingroup$ What properties would cause UV light to be blocked and infrared to be trapped, which causes heating of a surface. So I am specifically interested in the type which could be used to heat a surface, for example on the moon Titan. $\endgroup$ – Stallmp Sep 23 '19 at 18:32
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    $\begingroup$ @Stallmp From what i read on Wiki, infrared radiation, like the visible wavelengths passes just through the silica gel. The low thermal conductivity is because of the bad conduction and bad convection. $\endgroup$ – Conelisinspace Oct 29 '19 at 17:46
  • $\begingroup$ @Conelisinspace I've read that silica gel can be made to block infrared radiation. Also, what explains the bad conduction in the first place? I'd suppose it has to do with the colloidal structure $\endgroup$ – Stallmp Oct 29 '19 at 17:49
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    $\begingroup$ @Stallmp The bad conduction is because of the bad conduction of the trapped air in the gel. Where did you read that silica gel blocks infrared radiation ? Do you have a link ? $\endgroup$ – Conelisinspace Oct 29 '19 at 18:04

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