Influence of hydrophobic nanosilica and hydrophobic medium on water bound in hydrophilic components of complex systems

The aim of this study was to analyze various theoretical models (clusters, systems with periodic boundary conditions) and methods, which could be applied to investigate the adsorption phenomena and for better interpretation of the experimental data. The density functional theory (DFT) and semiempirical (PM7) methods were used to model the adsorption phenomena at a surface of fumed nanooxides, silica gels, activated carbons, etc. The main idea is that appropriate theoretical analysis allows a deeper insight into interfacial phenomena related to the structure & properties of the adsorption layers vs. the textural and other characteristics of adsorbents. Comparison of the theoretically calculated characteristics with experimental ones can allow more accurate interpretation of the effects observed in various experiments on the adsorption phenomena. It was established that polarization of nonpolar and polar molecules adsorbed onto a polar surface and charge (& proton) transfer play an important role, as well as confined space effects. It enhances the interaction energy of adsorbed molecules bound to a solid surface and affects the surface orientation of adsorbed molecules, as well the behavior of the adsorption layer vs. temperature, pressure or concentration, as well other conditions. Surface hydrophobization reduces the interaction energy for both polar and nonpolar adsorbates. Adsorbates clusterization reduces the average energy of interaction of the adsorption layer with a surface per a molecule. The charge transfer is observed for both polar and nonpolar molecules interacting with polar surface functionalities. The mostly strong interfacial effects changing the behavior of the adsorption layer are observed upon proton transfer to the adsorbed molecules or vice versa. Variation in orientation of adsorbed molecules results in overestimation of the specific surface area estimated using a fixed value of surface area occupied by a probe molecule (e.g. 0.162 nm 2 for N 2).

Section: Resultsmentioning

confidence: 99%

Theoretical analysis of adsorption of various compounds onto hydrophilic and hydrophobic silicas compared to activated carbons

Gun’ko¹

2019

“…%), as well the PMS/A-300 11 and cPMS/A-300 11 blends ( = 1:1 g/g) (prepared using dried components stirred with water at h = 1 g/g) located in different dispersion media (air, CDCl 3 , and CDCl 3 with addition of deuterated trifluoroacetic acid CF 3 COOD, TFAA). Hydro-compaction of a set of nanomaterials based on unmodified and modified (hydrophobized) nanooxides was described in detail elsewhere [22,[43][44][45][46].…”

Section: Methodsmentioning

confidence: 99%

Structural and adsorption features of amorphous nanosilica modified by various addition of polymethylsiloxane

Туров¹,

Gun’ko²,

Krupska³

et al. 2019

alone and in the blends were characterized using microscopy, nitrogen adsorption, infrared spectroscopy, thermogravimetry, and quantum chemistry. It was shown that the properties of the blends depend not only on the components content but also on mechanical treatment causing stronger compaction of the secondary structures of nanoparticles (aggregates of nanoparticles and agglomerates of aggregates) with increasing mechanical loading. Note that a similar behavior of various blends with hydrophobic and hydrophilic nanostructured materials was observed after hydro-compaction under different mechanical loadings. Theoretical modelling shows that the structure of bound water located at a surface of hydrophilic and hydrophobic nanoparticles changes with compaction of aggregates because of changes in the confined space effects and polarity of bound water molecules. These results reflect a general regularity appearing at appropriate amount of added water and certain mechanical loading onto the blends of hydrophilic and hydrophobic nanostructured materials, which become hydrophilic but renew the hydrophobic properties after subsequent drying.

“…The particle size distributions (PaSD) for nanosilica A-300 samples were calculated using PAN analytical Easy SAXS V. 2.0.0.405 program. The SAXS based approach was successfully applied to carbon, silica, and polymeric materials in comparison with the results of different methods used to analyze the nitrogen adsorption data [14,27,28].…”

Section: Saxsmentioning

confidence: 99%

“…nanosilica A-300 [28,44] Upon the analysis, one should remember that SAXS gives information on both accessible and inaccessible (closed) pores. This is clear visible from comparison of PSD calculated using SAXS, NLDFT and SCV/SCR methods for initial and wetted-dried nanosilica [44], especially in the range of nanopores.…”

Section: Fig 15 Saxs Pasd Of Initial and Wetted-driedmentioning

confidence: 99%

Various methods to describe the morphological and textural characteristics of various materials

Gun’ko¹

2018

The aim of this study was to compare a variety of methods to describe the textural characteristics of various materials. Several ways could be used to describe the morphological and textural characteristics of various materials in detail such as: (i) adsorption-desorption of low-molecular weight probe compounds (N 2 , CO 2 , Ar, C 6 H 6 , H 2 O, etc.) in the gaseous (vapor) phase with increasing-decreasing pressure; (ii) adsorption of low-or highmolecular weight compounds from liquid solutions with increasing concentration of a solute; (iii) small angle X-ray scattering (SAXS) or small angle neutron scattering (SANS); (iv) quantitative analysis of images recorded using TEM, SEM, AFM, CLSM, etc.; (v) thermoporometry based on DSC or TG measurements with decreasing-increasing temperature; (vi) cryoporometry based on NMR spectroscopy measurements vs. temperature; and (vii) relaxometry based on NMR spectroscopy and thermally stimulated depolarization current measurements. There are several reasons of the use of mentioned above methods in parallel. For example, a material, which is strongly hydrated in native state, can strongly change the texture upon drying; thus, it should be studied in both states. Various adsorbates can penetrate into different pores or differently fill pores of different sizes that should be taken into account upon the analyses of various data. There are accessible and inaccessible pores (such as closed or too narrow for used adsorbate molecules), but SAXS can give information on all pores in contrast to the adsorption methods. Thus, the larger the number of applied methods, the more comprehensive the morphological and textural characterization of the adsorbents, and this is clearly shown below.