Nanosilica modified by polydimethylsiloxane depolymerized and chemically bound to nanoparticles or physically bound...

Area of Science:

• Materials Science
• Surface Chemistry
• Nanotechnology

Background:

• Polydimethylsiloxane (PDMS) is widely used for surface modification.
• Nanosilica (A-300) is a common material requiring surface functionalization for specific applications.
• Understanding the interaction between PDMS and silica surfaces is key to controlling material properties.

Purpose of the Study:

• To investigate the adsorption behavior of different molecular weight PDMS onto nanosilica.
• To analyze the impact of PDMS bonding type, molecular weight, and content on surface properties.
• To determine the optimal conditions for effective hydrophobization of nanosilica using PDMS.

Main Methods:

• Adsorption of three PDMS variants (PDMS200, PDMS1000, PDMS12500) onto nanosilica.
• Surface modification using dimethyl carbonate (DMC) as a siloxane bond breaking reagent.
• Characterization via microscopy, spectroscopy, thermodesorption, calorimetry, evaporation studies, nitrogen adsorption-desorption, and quantum chemical calculations.

Main Results:

• Shorter PDMS (PDMS200) forms denser silica surface coverage with minimal free silanols after chemical bonding.
• Thermal decomposition of PDMS layers involves both oxidation/depolymerization and pure depolymerization, with depolymerization increasing with layer thickness.
• Adsorption, desorption, and evaporation of probes are strongly influenced by PDMS bonding type and content.

Conclusions:

• The interfacial and temperature behavior of PDMS on silica is highly dependent on PDMS molecular weight and bonding characteristics.
• Effective hydrophobization of nanosilica is achieved using shorter PDMS chains and DMC, leading to smaller PDMS fragments.
• This finding has significant practical implications for tailoring nanosilica properties for various applications.