How to Compare the Hydrophobicity of Hydrophobic Fumed Silica
Fumed silica is a crucial inorganic nanomaterial that is extensively utilized across fields such as coatings, rubber, plastics, cosmetics, and electronic packaging due to its high specific surface area, excellent dispersibility, and outstanding surface activity. Controlling the hydrophobicity of fumed silica is a key factor in improving the overall performance of materials. Hydrophobic fumed silica treated with different modifiers exhibits stronger moisture resistance, weather resistance, and stability.
HIFULL experts used contact angle measurement to systematically evaluate the hydrophobic properties of three hydrophobic fumed silicas treated with different modification processes: HB-132 (modifier hexamethyldisilazane, HMDS), HB-139 (modifier polydimethylsiloxane, PMDS), and HB-151 (modifier dimethyldichlorosilane, DDS).
The technicians adopted the tablet pressing method to quantitatively press the three types of fumed silica into uniform thin sheets, and then dropped liquid droplets onto the sample surfaces using a contact angle goniometer. The experimental results showed that HB-139 (126.5°) > HB-132 (122.3°) > HB-151 (120.7°).
A larger contact angle indicates stronger surface hydrophobicity of the material:
The core reason for this difference in hydrophobicity lies in the essential distinctions in the modification effects of different modifiers on the surface of fumed silica.
Firstly, the modifier used for HB-139 has a longer alkyl chain or higher reactivity, enabling it to more completely replace the hydroxyl groups on the silica surface, forming a dense hydrophobic layer that significantly reduces the surface energy, making it difficult for liquid droplets to spread on the surface.
Secondly, the modifier for HB-132 has slightly weaker reactivity or a shorter molecular chain, resulting in a slightly lower substitution rate of surface hydroxyl groups compared to HB-139, leading to insufficient compactness of the hydrophobic layer and a subsequent decrease in the contact angle.
As for HB-151, the modifier used may have issues such as low reaction efficiency and weak hydrophobic activity of functional groups, only partially covering the surface hydroxyl groups. The residual hydroxyl groups still possess a certain degree of hydrophilicity, ultimately resulting in the smallest contact angle.
From the contact angle data in the laboratory to the practical application in industrial scenarios, the hydrophobicity of materials directly affects the final performance of products. In fields such as sealants, coatings, and lithium battery separators, differences in the performance of hydrophobic fumed silica can lead to significant variations in the water resistance, dispersibility, and service life of products.
This experiment not only clarified the hydrophobicity ranking of the three materials through quantitative data but also revealed the root causes of performance differences from the perspective of modification mechanisms, providing a scientific basis for downstream enterprises in material selection.
Further Reading:
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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.
