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Montmorillonite was modified with different amounts of chitosan to obtain chitosan/montmorillonite bionanocomposites (CSMMT). The structural and surface characteristics of the raw materials and bionanocomposites were analyzed. XPS results showed that the obtained bionanocomposites had MMT-rich surfaces with chitosan essentially intercalated in the host clay galleries. IGC at infinite dilution confirmed that the increase of CS mass ratio in the bionanocomposites significantly affected the surface properties. IGC at finite concentration revealed a clear evolution in the surface heterogeneity in chitosan/montmorillonite bionanocomposites by the progressive disappearance of shoulders of high energy with the increase of CS mass ratio in MMT. [ABSTRACT FROM AUTHOR]

The description of the surface chemistry of reservoir rock is essential in understanding the physico-chemical interaction between the rock surface and its environment. In this study, inverse gas chromatography (IGC) is used to characterize the surface chemistry of rocks extracted from four petroleum reservoirs in Algeria. By means of IGC at infinite dilution (IGC-ID), the dispersive component of the surface energy (γ_s^d), the nanomorphological index I_M (χ_t) and the specific component of the surface energy were determined at 100 °C. IGC at finite concentration (IGC-FC) was implemented using n -octane and isopropanol probes, allowing the irreversibility indexes and the adsorption isotherms to be obtained. From the latter, the BET specific surface area and BET constant of the injected probes were determined. Energy distribution functions and indexes of heterogeneity were also computed for the n -octane and isopropanol probes. The results showed that the polar probe, isopropanol, interacts more strongly with the rock surface than the apolar probe. In the second part of this study, the influence of a surfactant used in drilling mud on the heterogeneity of the surface energy was investigated. Different surfactant impregnation ratios were examined by means of IGC-FC. The results indicated that the progressive covering of the solid surface by the surfactant hid chemical functions likely to interact with the injected probes and made the surface smooth by covering the roughness of the surface, which led to the decrease in all parameters obtained by IGC-CF. [ABSTRACT FROM AUTHOR]

The kinetic of the ageing process of 3 pyrogenic silica samples, exhibiting increasing surface areas (Wacker N20, T30 and T40), was followed through gravimetric measurements, during about 1000 h at 22.5 °C, under different relative humidities (RH) from 62% up to100%. Silanol chemical titration, and IR spectroscopy were also called on to evidence the change of the surface chemistry induced by the ageing process. This study evidenced that pyrogenic silicas are, at room temperature, sensitive to RH humidity over a threshold of about 50% of RH. Exposed to high RH, a strong change of the surface functionality occurs bound to an important chemisorption of water. At RH of 100%, the silanol density could increase up to quite 40%. It is more important for low specific area samples than for the higher ones. The limit value of 3.5–3.8 SiOH/nm 2 suggests that no polysilicic layer are formed. Moreover IR spectroscopy indicates that the new silanol groups appear in the vicinity of the pre-existing silanol groups at the border between hydrophilic and hydrophobic domains. It is hence evidenced that the patch like distribution of the silanol groups and the surface morphology, flat or rough play a main role on the ageing process. [ABSTRACT FROM AUTHOR]

In the present study, we have examined the influence of the aging process under controlled relative humidity on the surface properties of 3 silicas samples of increasing specific surface area. Both comparison of the specific surface areas, determined using either nitrogen (BET) or cetyltrimethylamonium bromide (CTAB), and the surface nanoroughness indexes, determined by size exclusion inverse gas chromatography, indicates that the ageing process has no significant influence on the surface morphology at the molecular level. On the contrary, IGC at finite concentration using isopropanol as probe evidences clearly an increase of the surface heterogeneity induced by the formation of new silanol groups into the preexisting hydrophilic domains by opening of siloxane bridges by water. [ABSTRACT FROM AUTHOR]