Nanostructured Polymethylsiloxane/Fumed Silica Blends

Abstract

Polymethylsiloxane (PMS) and fumed silica, alone and in a blended form (1:1 w/w), differently pretreated, hydrated, and treated again, were studied using TEM and SEM, nitrogen adsorption–desorption, 1H MAS and 29Si CP/MAS NMR spectroscopy, infrared spectroscopy, and methods of quantum chemistry. Analysis of the effects of adding water (0–0.5 g of water per gram of solids) to the blends while they are undergoing different mechanical treatment (stirring with weak (~1–2 kg/cm2) and strong (~20 kg/cm2) loading) show that both dry and wetted PMS (as a soft material) can be grafted onto a silica surface, even with weak mechanical loading, and enhanced mechanical loading leads to enhanced homogenization of the blends. The main evidence of this effect is strong nonadditive changes in the textural characteristics, which are 2–3 times smaller than additive those expected. All PMS/nanosilica blends, demonstrating a good distribution of nanosilica nanoparticles and their small aggregates in the polymer matrix (according to TEM and SEM images), are rather meso/microporous, with the main pore-size distribution peaks at R > 10 nm in radius and average <RV> values of 18–25 nm. The contributions of nanopores (R < 1 nm), mesopores (1 nm < R < 25 nm), and macropores (25 nm < R < 100 nm), which are of importance for studied medical sorbents and drug carriers, depend strongly on the types of the materials and treatments, as well the amounts of water added. The developed technique (based on small additions of water and controlled mechanical loading) allows one to significantly change the morphological and textural characteristics of fumed silica (hydrocompaction), PMS (drying–wetting–drying), and PMS/A-300 blends (wetting–drying under mechanical loading), which is of importance from a practical point of view.

Textural characteristics and organization of composites with fumed silicas and high-molecular weight compounds

“…In contrast to other studied polymers, PMS is 3D polymer with nanoclews bonded by certain bridges into 3D porous structures, which can be decomposed during MCA treatment [36,37]. The SSA value of PMS is larger than that of A-300 with main contribution of mesopores (Table 10, Fig.…”

“…10, Table 10). This effect for the latter can be explained by the fact that for the PMS/A-300 blends, aggregates of nanoparticles of types remain in the composite [36,37]. 9 for four series of samples) Fig.…”

“…% of PMS and 93-92 wt. % of water (Enterosgel, Kreoma-Pharm, Ukraine) was used as an initial material (Table 10) [35][36][37]. After drying at room temperature for a week, the amount of water bound in PMS was small (0.7 wt.…”

“…This is a hydro-compacted sample labeled as cPMS/A-300. Hydro-compaction of a set of nanomaterials based on unmodified and modified nanooxides was described in detail elsewhere [35][36][37][57][58][59][60][61][62].…”

“…Clearly, features of the polymerpolymer, polymer-NPNP, and NPNP-NPNP interactions play not only an important role in the properties and characteristics of the composites but also determine the reorganization of the hierarchical structures under any external action. Therefore, changes in the textural organization of polymer (or protein)/nanosilica composites prepared using various routes are here analyzed for different polymers: linear polydimethylsiloxane (PDMS) [33,34], 3D polymethylsiloxane (PMS) [35][36][37], poly(vinyl pyrrolidone) (PVP) [38][39][40][41][42][43], poly(vinyl alcohol) (PVA) [43][44][45], poly(ethylene oxide) (PEO) [43,46], and poly(ethylene glycol) (PEG) [43], and proteins: egg albumin, gelatin, and ossein [47][48][49][50][51][52][53], which are characterized by different adsorbate-adsorbate and adsorbate-NPNP interactions. Several samples of nanosilicas with the S BET values from 232 to 378 m 2 /g (for the pristine powders) are used to prepare various composites (105 samples in total).…”