title: Interfacial phenomena at a surface of partially silylated nanosilica.
abstract: Unmodified pyrogenic silica PS300 and partially silylated nanosilica samples at a degree of substitution of surface silanols by trimethylsilyl (TMS) groups Θ(TMS)=27.2% and 37.2% were studied to elucidate features of the interfacial behavior of water adsorbed alone, or co-adsorbed with methane, hydrogen, or trifluoroacetic acid (TFAA). In the aqueous suspension modified PS300 at Θ(TMS)=37.2% forms aggregates of 50-200 nm in size and can bind significant amounts of water (up to ∼5 g/g). Only 0.5 g/g of this water is strongly bound, while the major fraction of water is weakly bound. The presence of surface TMS groups causes the appearance of weakly associated water (WAW) at the interfaces. The adsorption of methane and hydrogen onto TMS-nanosilica with pre-adsorbed water (hydration degree h=0.05 or 0.005 g/g) increases with increasing temperature. In weakly polar CDCl3 medium, interfacial water exists in strongly (SAW, chemical shift δ(H)=4-5 ppm) and weakly (δ(H)=1-2 ppm) associated states, as well as strongly (changes in the Gibbs free energy -ΔG>0.5-0.8 kJ/mol) and weakly (-ΔG<0.5-0.8 kJ/mol) bound states. WAW does not dissolve TFAA but some fraction of SAW bound to TMS-nanosilica surface can dissolve TFAA.
authors.affiliation: Chuiko Institute of Surface Chemistry, 17 General Naumov Street, 03164 Kyiv, Ukraine. Electronic address: vlad_gunko@ukr.net.
authors.forename: V M
authors.initials: VM
authors.lastname: Gun'ko
authors.affiliation: Chuiko Institute of Surface Chemistry, 17 General Naumov Street, 03164 Kyiv, Ukraine.
authors.forename: V V
authors.initials: VV
authors.lastname: Turov
authors.affiliation: Vasyl Stefanyk Precarpathian National University, 57 Shevchenko Street, 76018 Ivano-Frankovsk, Ukraine.
authors.forename: I F
authors.initials: IF
authors.lastname: Myronyuk
authors.affiliation: Chuiko Institute of Surface Chemistry, 17 General Naumov Street, 03164 Kyiv, Ukraine.
authors.forename: O V
authors.initials: OV
authors.lastname: Goncharuk
authors.affiliation: Chuiko Institute of Surface Chemistry, 17 General Naumov Street, 03164 Kyiv, Ukraine.
authors.forename: E M
authors.initials: EM
authors.lastname: Pakhlov
authors.affiliation: Vasyl Stefanyk Precarpathian National University, 57 Shevchenko Street, 76018 Ivano-Frankovsk, Ukraine.
authors.forename: N A
authors.initials: NA
authors.lastname: Bezruka
authors.affiliation: Faculty of Chemistry, Maria Curie-Skłodowska University, 20-031 Lublin, Poland.
authors.forename: E
authors.initials: E
authors.lastname: Skwarek
authors.affiliation: Faculty of Chemistry, Maria Curie-Skłodowska University, 20-031 Lublin, Poland.
authors.forename: W
authors.initials: W
authors.lastname: Janusz
authors.affiliation: Eastern Illinois University, Department of Chemistry, Charleston, IL 61920, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Blitz
keywords: Dispersion medium effects; Partially silylated nanosilica; Water–hydrogen co-adsorption; Water–methane co-adsorption