What is the Difference Between Aerogel and Xerogel

The key difference between aerogel and xerogel is that aerogels form when the liquid from the gel is extracted at a supercritical state, whereas xerogel forms when the liquid from the gel is evaporated at room temperature.

Gel-based nano adsorbents can be broadly classified into aerogel, hydrogel, and xerogel. We can describe aerogels and xerogels as dried gels that can retain their porous texture after the drying process. This retaining can be either complete or partial. These porous gels have attractive properties that arise from the extraordinary flexibility of the sol-gel processing. We can combine this with various drying techniques, which can lead to aerogels or xerogels.

CONTENTS

1. Overview and Key Difference
2. What is Aerogel 
3. What is Xerogel
4. Aerogel vs Xerogel in Tabular Form
5. Summary – Aerogel vs Xerogel

What is Aerogel?

Aerogel can be defined as a solid that forms from a gel by drying at a supercritical state. The drying process in aerogels can be described as freeze-drying, supercritical drying, or ambient pressure drying. Aerogel is a lightweight material and exhibits a large surface area that ranges between 200 – 1000 m²/g. It has many important properties such as:

• A large amount of controlled pore size distribution
• A high conductivity
• Transparency
• A low density
• Flexibility
• Low dielectric constant
• High mechanical strength

These properties make aerogel a potent candidate for a wide range of applications, such as the adsorption of water contaminants. Comparatively, this type of gel exhibits a large surface area and porosity along with a large pore volume. There are different types of aerogels, including graphene-based aerogels, silica-based aerogels, zeolite-based aerogels, etc. These are the most common examples of aerogels. Moreover, these aerogels can be easily modified and functionalized in order to improve selective adsorption via electrostatic interaction.

What is Xerogel?

Xerogel is a solid form of a gel obtained by drying it with unhindered shrinkage. The drying process of xerogels involves solvent evaporation under standard conditions using conventional methods. Xerogels are mesoporous materials having high thermal stability. The most important properties of xerogel are as follows:

• Nontoxic
• Cost-effective
• Biocompatible
• High surface area
• High porosity
• Can easily be modified

The most common examples of xerogels are carbon-based xerogels and silica-based aerogels. These are mostly studies for water purification.

When considering the drying process, alcogel or hydrogel that is obtained from another process is converted into xerogel. In this process, the volume decreases by an amount that is equal to the volume of the liquid that is lost by evaporation. Moreover, the shrinkage of the gel occurs because of the capillary forces that are exerted by the pore-filling liquid to the pore wall. This is the stage where the greatest changes in volume, weight, density, and structure occurs. Thereafter, the shrinkage can cease because the dried gel network has reached some considerable stiffness.

What is the Difference Between Aerogel and Xerogel?

The key difference between aerogel and xerogel is that aerogels form when the liquid from the gel is extracted at a supercritical state, whereas xerogel forms when the liquid from the gel is evaporated at room temperature. Moreover, aerogel has a comparatively larger surface area than xerogel.

The below infographic presents the differences between aerogel and xerogel in tabular form for side-by-side comparison.

Summary – Aerogel vs Xerogel

Aerogel and xerogel are important types of solid gel materials. The key difference between aerogel and xerogel is that aerogels form when the liquid from the gel is extracted at a supercritical state, whereas xerogel forms when the liquid from the gel is evaporated at room temperature.

Reference:

1. “Xerogels.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Aerogel Vial” By Zach from Gamboa, Panama – Aerogel Vial (CC BY-SA 2.0) via Commons Wikimedia
2. “Porous xerogel for biomedical applications” By ZEISS Microscopy (CC BY-NC-ND 2.0)