Nanostructured Amorphous Silicas Hydrophobized by Various Pathways

Abstract

Various nanostructured amorphous silicas [fumed silicas such as crude (A-300), hydro-compacted (cA-300, TS 100), and precipitated silica Syloid 244] were modified by different polydimethylsiloxanes such as PDMS5, PDMS100, PDMS200, PDMS1000, and PDMS12500 (the label numbers show the viscosity (η) values) using dimethyl carbonate (DMC) as a siloxane-bond-breaking reagent. In addition, hexamethyldisilazane was used to modify fumed silica cA-300. The nanocomposites were characterized using microscopy, infrared spectroscopy, thermodesorption, nitrogen adsorption–desorption, solid-state NMR spectroscopy, small-angle X-ray scattering, and zeta-potential methods. It was found that the morphological, textural, and structural characteristics of silicas grafted with PDMS depend strongly not only on the type and content of the polymers used but also on the organization of nonporous nanoparticles (NPNP) in secondary structures (aggregates of NPNP and agglomerated aggregates, ANPNP), as well on the reaction temperature ( T r ). Specifically, we determined that ANPNP with a macro/mesoporous character are favorable for the effective modification of the silicas studied with short polymers and no DMC addition but at higher temperatures or for a longer silicone polymer with the presence of DMC and at lower temperatures. In particular, the PDMS/DMC-modified silicas are of great interest from a practical point of view because they remain in a dispersed state with no strong compaction of the secondary structures after modification, and this corresponds to a better distribution of the modified nanoparticles in polymeric or other matrices.

Development of a Hydrophobicity-Controlled Delivery System Containing Levodopa Methyl Ester Hydrochloride Loaded into a Mesoporous Silica

“…Among MPSs, only a limited number of studies can be found on hydrophobized Syloid-based drug delivery systems [30,31], even though these materials have highly developed mesoporous networks and a large surface area. Moreover, these systems are ideal to adsorb a remarkable amount of API.…”

Surface Chemistry of Nanohybrids with Fumed Silica Functionalized by Polydimethylsiloxane/Dimethyl Carbonate Studied Using 1H, 13C, and 29Si Solid-State NMR Spectroscopy

“…Linear organosiloxanes are generally not considered to be reactive with inorganic oxide surfaces, and enormous efforts have been made over the last 50 years to develop silicon-containing reagents with reactive functional groups [ 42 ]. Previously, it was found that dimethyl carbonate (DMC) [ 43 ], which is an environmentally friendly reagent [ 44 , 45 , 46 ], can promote partial depolymerization of organosiloxanes (e.g., polydimethylsiloxane, PDMS) and breakage of the siloxane bonds in a surface layer of silica nanoparticles. These reactions allow the silica surface hydrophobization by PDMS fragments under relatively mild conditions.…”

Textural characteristics of composite adsorbents analyzed with density functional theory and self-consistent regularization procedure

“…This approach was based on a blend of Kelvin and modified BET equations [46][47][48] (MND method) that was used in the SCV/SCR method with models of slit-shaped and cylindrical pores and voids between spherical nanoparticles (SCV model) [43][44][45]. Note that the SCR procedure was also successfully applied to analyze the SAXS data to compute the particle size distributions with models of spherical, lamellar, and cylindrical particles [49][50][51]. However, the MND method has some disadvantages.…”