Hygroscopicity of Fumed Silica: 80-Day Actual Measurement Results Under Different Processing Technologies

The applications of fumed silica are extensive, ranging from high-end products such as silicone sealants, coatings, and inks to cosmetics, pharmaceutical carriers, and food additives. Its hygroscopicity significantly affects the storage stability, rheological properties, anti-caking effects, and flow-aiding properties of materials.

HIFULL expert conducted a systematic analysis of the hygroscopicity influence patterns of hydrophilic fumed silica HL-200 and hydrophobic fumed silica treated with different modifiers. They also revealed the intrinsic correlation between processing technology and hygroscopic performance based on experimental data, providing a scientific basis for the selection of HIFULL® fumed silica and process optimization in industrial applications.

Fumed silica, with its nano-scale particle size, high specific surface area, unique three-dimensional network structure, and excellent physical and chemical properties, provides outstanding thickening, thixotropic, and reinforcing performance. It has become an indispensable functional inorganic new material in modern industry. <Learn More>

  • Hydrophilic Fumed Silica
  • Hydrophobic Fumed Silica

First, technicians systematically monitored the loss on drying (LOD) of hydrophilic fumed silica HL-200 and fumed silica samples processed via different techniques over an 80-day period, all under the same constant temperature and humidity environment.

The experiment included four sample groups: the untreated hydrophilic HL-200 product served as the baseline reference, while the three control groups consisted of hydrophobic fumed silica treated with three different surface modifiers—hexamethyldisilazane (HMDS), dimethyldichlorosilane (DDS), and polydimethylsiloxane (PDMS).

Experimental data showed that as time increased from day 0 to day 80, the LOD of HL-200 rose continuously. Its initial LOD was 1.17% (factory specification), reaching 1.84% on day 10, 2.73% on day 20, and gradually increasing thereafter to 4.85% on day 80.

This phenomenon occurs because the surface of hydrophilic fumed silica is rich in silanol groups (Si-OH), which form strong hydrogen bonds with water molecules. As time elapses, water molecules are continuously adsorbed and permeate the material. Under the influence of ambient humidity, the amount of adsorbed moisture accumulates with contact time, demonstrating significant hydrophilicity. Long-term storage of such material is prone to moisture absorption, which impairs the stability of the material system—for instance, it may cause agglomeration and reduced fluidity in powder coatings.

For the hydrophobic fumed silica treated with HMDS, the LOD curve remained nearly flat, with LOD consistently maintained at a low level. Similarly, the DDS-treated hydrophobic fumed silica exhibited a flat LOD curve with low LOD values. The PDMS-treated hydrophobic fumed silica also kept its LOD within an extremely low range.

The hydrophilic HL-200, with a large number of silanol groups on its surface, showed increasing hygroscopicity over time, reflecting strong hydrophilicity. In contrast, the hydrophobic fumed silica modified with different small-molecule modifiers (HMDS, DDS, PDMS) had hydrophobic groups introduced onto its surface, which significantly inhibited moisture absorption and allowed LOD to remain stably low over the long term.

Hexamethyldisilazane (HMDS) is a chemical compound that is commonly used as a surface treatment for fumed silica to make it hydrophobic. The hydrophobic treatment involving HMDS enhances the dispersibility and compatibility of fumed silica in hydrophobic systems. The HMDS molecules attach to the surface of the silica particles, creating a water-repellent coating. This modification improves the performance of fumed silica in various applications.

Although different modifiers vary in chemical structure and reaction mechanism, any of these modifiers can effectively regulate the hygroscopicity of fumed silica, meeting the requirements of different application scenarios (such as sensitivity to moisture, rheological performance demands, electrical properties, and weather resistance).

The hygroscopicity of fumed silica is dominated by its surface chemical structure, including the number of silanol groups and the type of hydrophobic groups. Through precise experimental design and monitoring, the technicians clearly demonstrated the differences in hygroscopicity between various products over different time periods. In practical applications, the appropriate type of fumed silica must be selected based on specific scenarios, such as the need for long-term storage and moisture tolerance requirements.

In the future, Hubei Huifu Nanomaterial Co., Ltd. will further investigate changes in hygroscopicity under extreme environments (such as high humidity, high-low temperature cycles) and the synergistic effects of hygroscopicity—from both hydrophilic and hydrophobic fumed silica—on the overall performance of materials. The company will continue to expand the application potential of fumed silica under more complex working conditions, driving the development of precise and high-performance applications of fumed silica materials across various industries.

  • Hello, Customers

    My name is Van, I’m the business manager of HIFULL, I have been in Fumed Silica Industry for more than 10 years. Feel free to contact me. I’m happy to provide you the best service and products.
    Van
    Business Manager