Try reading, "Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing" by C. Jeffrey Brinker (Author), George W. Scherer (Author), you may get your answers.

Dear Srujan,

An aerogel is obtained when the liquid phase of a gel* is replaced by a gas in such a way that its solid network is retained, with only a slight or no shrinkage in the gel. It was firstly achieved under supercritical conditions but it is now possible under ambient drying conditions as well.

Shrinkage < 15%

A Xerogel (not to be confused by X-Aerogel) is obtained when the liquid phase of a gel* is removed by evaporation. It may retain its original shape, but often cracks due to the extreme shrinkage that is experienced while being dried.

Shrinkage >90%

Therefore the method of drying will dictate whether an aerogel or xerogel will be formed.

* The gel is usually an alcogel, that is, an alcohol-based gel. Nevertheless, there have been studies which uses hydrogel, that is, a water-based gel, as well.

Cryrogel is a commercialized-name for a product developed by Aspen Aerogels. It is flexible aerogel composite blanket designed for insulating cold temperature environments ranging from cryogenic to ambient.

Hope it helps.

Nadiir Bheekhun good explanation

I hope the sol and gel colloidal systems are well known. Gel is two component system in which liquid is dispersed in solid medium.  

As per my opinion, the aerogel, xerogel, hydrogel and cryogel are basically categorized as per preparation methods depending upon the method used for extraction of liquid from the solid network of gel system.

Hydrogel and alcogel terms are used when the liquid (solvent) in the gel network is water and alcohol, respectively.

When the liquid from the gel is evaporated at room temperature, the solid gels left behind are called xerogels. Whereas when the liquid from the gel is extracted at supercritical state of liquid, these materials are called aerogels. Aerogels are generally monolithic and have low density than xerogels. Xerogels on the other hand are generally cracked, shrinken or sometimes powdered. Cryogels term is used for those materails in which liquid from the gel is extracted at much lower temperature using vaccum (sublimation phase of solvent).     

Very useful. thank you

Thanks for sharing your explainations.

 xerogel:  is a solid formed from a gel by drying with unhindered shrinkage. Xerogels usually retain high porosity (15–50%) and enormous surface area (150–900 m2/g), along with very small pore size (1–10 nm). When solvent removal occurs under supercritical conditions, the network does not shrink and a highly porous, low-density material known as an aerogel is produced.

Aerogel: Aerogel is a translucent, synthetic solid-state substance with extremely low density and excellent thermal insulating properties. Also known as "frozen smoke," aerogel in its solid form has a texture similar to that of foamed polystyrene. Simply, the  aerogel refers to the fact that aerogels are derived from gels–effectively the solid structure of a wet gel, only with a gas or vacuum in its pores instead of liquid

Hydrogel:  is a network of polymer chains that are water-insoluble, sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels are superabsorbent (they can contain over 99% water) natural or

synthetic polymers. Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their significant water

content.

Cryogel: It is a form of a gel that is formed by freeze-drying a sol. This enables the solvent to convert to gas phase directly from solid phase. In freeze-drying, the pressure around the material is reduced and large amounts of heat is added which converts the solid phase to gas phase. 

What is then a Zerogel?

Nadir, good explanation, useful knowledge.

aerogel vs xerogel:

physical structure: the aerogel retains the shape of an expanded network observed in the hydrogel, but no water. While the three-dimensional network xerogel shrinks when water is evaporated.

preparation methods: Although both materials are obtained from a hydrogel there are differences in the methods used: the aerogel is obtained by water displacement using a gas at supercritical conditions, whereas the xerogel water is evaporated.

properties: the aerogel has a greater porosity and lower density than the xerogel.

aerogel vs xerogel:

physical structure: the aerogel retains the shape of an expanded network observed in the hydrogel, but no water. While the three-dimensional network xerogel shrinks when water is evaporated.

preparation methods: Although both materials are obtained from a hydrogel there are differences in the methods used: the aerogel is obtained by water displacement using a gas at supercritical conditions, whereas the xerogel water is evaporated.

properties: the aerogel has a greater porosity and lower density than the xerogel.

 Really good explanation. However, I would be glad if you can highlight the difference between aerogel materials  and foam materials? 

Thank you so much.

thanks a lot for your complete explanations

can some references be provided in support of all the answers you all have provided.

Refer to : Ind. Eng. Chem. Res., 2002, 41 (13), pp 3151–3162 for the above topic

Thanks for nice and useful explanation

xerogel is When the liquid from the gel is evaporated at room temperature

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Can any one suggest me which one (Aerogel/hydrogel/cryogel/xerogel)is more promising for wound care and hemostasis activity. Please mentioned the reason

Hello . When the drying process of gel by evaporation without certain conditions , the network of structure will collapse , that is called the xerogel . But when the drying process be under a supercritical conditions ,the network of structure will retained and the structure will be with low density.

Thank you everyone

Very nice answers are here. As in aerogel, the solvents are replaced by gas or air under supercritical conditions respect to xerogels. Xerogels are collapsed network removing the solvents. Can any one mention about the exact procedure for preparing exact aerogel for hydrogel. Most often hydrogel are lyophilized on that occasions. Is there any other method?

Thanks in advance.

what is the difference between aerogel and hydrogel

Tripti Rimza Hydrogel is a system with at least two components (solid and water) that no longer flows and can support its own weight exhibiting solid-like behaviour. Aerogel may be produced through liquid (water) extraction, keeping original solid structure, using supercritical drying conditions.

Tripti Rimza Srujan Singh

See the answer to a similar question

https://www.researchgate.net/post/Whats-the-basic-difference-between-Aerogel-Xerogel-Cryogel-and-Hydrogels