Controlled confined space effects on clustered water bound to hydrophobic nanosilica with nonpolar and polar co-adsorbates

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 644; p. 128919
• Main Authors: Turov, Volodymyr V., Krupska, Tetyana V., Guzenko, Nataliia V., Borysenko, Mykola V., Nychiporuk, Yury M., Gun’ko, Volodymyr M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.07.2022
• Subjects: Bound water; Chloroform; Confined space effects; DMSO; Hydrophobic nanosilica; Trifluoroacetic acid; Chloroform; Trifluoroacetic acid; DMSO; Confined space effects; Hydrophobic nanosilica; Bound water
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2022.128919

It has been assumed that hierarchical nanoparticle/aggregate/agglomerate structure, texture, and surface characteristics of hydrophobic nanosilica AM1 stirred with a small amount of water may lead to different interfacial and temperature behaviors of bound weakly (WAW, δH = 0.5–1.5 ppm) and strongly (SAW, δH = 4–6 ppm) associated waters, depending on the amounts of weakly polar (chloroform), polar (dimethyl sulfoxide, DMSO), and ionic (trifluoroacetic acid, TFAA) co-adsorbates. Initial and hydro-compacted nanosilicas are characterized using adsorption, desorption, microscopic, spectroscopic, XRD, SAXS, and quantum chemistry methods. The 1H NMR spectroscopy (at 210–280 K) and cryoporometry (T < 273 K) results show significant re-organization of the interfacial water forming clusters and domains differently affected by chloroform, TFAA, and DMSO. Changes in the free surface energy (γS) due to interaction of unfrozen (T < 273 K) water with silica nanoparticles depend on the hydration degree and type and amounts of co-adsorbates. The γS value is maximal for SAW affected by chloroform + TFAA, and it is six times greater than that without TFAA, but a similar effect of TFAA is absent for WAW. Chloroform enhances WAW contribution, but DMSO similarly affects SAW. Thus, the use of a small amount of water bound to treated AM1 allows one to perform quantitative analysis of WAW and SAW, as well as weakly (frozen at 265–273 K) and strongly (unfrozen at T < 265 K) bound waters affected by various co-adsorbates. A fraction of water (its volume per gram of AM1 h/ρw >Vp pore volume) added to AM1 without strong stirring remains unbound due to hydrophobic properties of AM1, but another fraction of water (<Vp) is bound. The behavior of water bound to treated hydrophobic nanosilica depends strongly on the amounts of water, polar or nonpolar co-adsorbates and temperature, especially at T < 273 K [Display omitted] •The characteristics of wetted hydrophobic nanosilica depend on treatment conditions and temperature.•Weakly polar chloroform enhances contribution of weakly associated water.•Polar dimethyl sulfoxide enhance contribution of strongly associated water.•Trifluoroacetic acid is dissolved only in strongly associated water causing down-field shift in 1H NMR spectra.