Effect of emulsifiers on surface properties of sucrose by inverse gas chromatography

Inverse gas chromatography (IGC) was employed to characterize the changes in surface properties of sucrose particles coated with either lecithin or polyglycerol polyricinoleate. IGC was performed using polar and non-polar adsorbates at infinite dilution with the sucrose particles as the solid stationary phase. Coating the sugar surface with emulsifiers induced an increase in the lipophilicity of the sugar particles, i.e. a sharp decrease in the acidity of the surface. Yet the two emulsifiers induced a slightly different increase in the surface basicity. It was hypothesized that this observation was due to a difference in the molecular structure of the emulsifiers.     

Inversion gas chromatography in studies of adsorption properties of the surface of carbon materials: Dispersion component of the surface free energy

Inversion gas chromatography was used to determine at exceedingly low surface coverages the dispersive component of the surface free energy γ_s^d for various types of carbon blacks and their graphitized analogs. A comparative analysis of the values obtained for γ_s^d with published data on γ_s^d for other carbon materials (graphite, activated carbons, carbon nanomaterials) was made.     

Inversion gas chromatography in studies of adsorption properties of carbon materials. Specific component of the surface free energy

Inversion gas chromatography was used to determine at extremely low surface coverages the specific component Isp of the surface free energy for various types of carbon blacks. It was demonstrated that the Rohrschneider-McReynolds model can be used to evaluate the capacity of carbon adsorbents for various kinds of intermolecular interactions.     

Property control of new forms of carbon materials by fluorination

Multiwall carbon nanotubes (MWNTs) based on the template carbonization technique were fluorinated in a temperature range 323-473 K by elemental fluorine. The fluorination of the carbon nanotubes results in functionalization and modification of pristine nanotubes with respect to adsorption and electrochemical properties. Selective fluorination of the inner surface of the carbon nanotubes, brings about a decrease in the surface free energy of the inner surface of the tubes and an increase in colombic efficiency of Li/nanotubes rechargeable cells in an aprotic medium. Electrochemical fluoride-ion doping of fullerene C₆₀ thin films (250-450 nm) was carried out in a fluoride-ion conductive solution, MeCN solution of 1 M Et₄NF·4HF. Galvanostatic oxidation yielded C₆₀F_ca.1-3 where fluorine exists as a semi-ionic species in the cavity surrounded by C₆₀ molecules without forming covalent CF bonds     

The surface properties of cellulose and lignocellulosic materials assessed by inverse gas chromatography: a review

The physicochemical surface properties of cellulose and lignocellulosic materials are of major importance in the context of the production of composites, in papermaking, and textile area. These properties can be evaluated by using inverse gas chromatography (IGC), a particularly suitable technique for the characterization of the surface properties of fibrous materials and powders. At infinite dilution conditions of appropriate gas probes, IGC may provide important parameters including the dispersive component of the surface energy of the material under analysis, thermodynamic data on the adsorption of specific probes, and Lewis acid–base interaction parameters between the matrix and the filler of composite materials. This paper critically reviews the most relevant results available in the literature concerning the characterization of cellulose and lignocellulosic materials using IGC. Emphasis will be put into the cellulose and nanocellulose surface properties, changes in the surface properties of cellulose and lignocellulosic materials after chemical and physical modifications, and in the compatibility of cellulose-based materials with polymeric matrices. The surface properties of non-woody fibers will also be considered. Before discussing the results available in the literature, the theoretical background and the main approaches used for the calculation of parameters accessed by IGC will be given. It is expected that this review can contribute to a better knowledge of the physicochemical surface properties of cellulosics.     

反相气相色谱法表征聚丁二烯橡胶的表面性质

采用反相气相色谱技术测定了聚丁二烯橡胶的表面性质。以正己烷、正庚烷、正辛烷、正壬烷作为非极性探针测定其表面色散自由能,以二氯甲烷、三氯甲烷、丙酮、乙酸乙酯、乙醚和四氢呋喃作为极性探针测定其路易斯酸碱常数。经计算得出聚丁二烯橡胶在303、313、323、333和343 K的表面色散自由能分别为47.07、46.46、45.85、45.60和45.09 mJ/m2。结果表明,聚丁二烯橡胶表面色散自由能随着温度的升高呈线性降低,路易斯酸常数Ka为0.34,碱常数Kb为1.77,总酸碱作用能力2.11,该聚合物为弱碱性Lewis两性聚合物材料。此外还计算出聚丁二烯橡胶的酸碱作用吸附自由能（~ΔGsa）和吸附焓（~ΔHsa）。     

Polybutadiene-coated zirconia packing materials in solvating gas chromatography using carbon dioxide as mobile phase

Summary In this paper, practical considerations of column efficiency, separation speed, thermal stability, and column polarity of capillary columns packed with polybutadiene-coated zirconia were investigated under solvating gas chromatography (SGC) conditions using carbon dioxide as mobile phase. When compared with results obtained from conventional porous octadecyl obtained from conventional porous octadecyl bonded silica (ODS) particles, PBD-zirconia particles produced greater change in mobile phase linear velocity with pressure than conventional ODS particles under the same conditions. The maximum plate number per second (N_t) obtained with a 30 cm PBD-zirconia column was approximately 1.5 times higher than that obtained with an ODS column at 100 °C. Therefore, the PBD-zirconia phase is more suitable for fast separations than conventional ODS particles in SGC. Maximum plate numbers per meter of 76,900 and 63,300 were obtained using a 57 cm×250 μm i.d. fused silica capillary column packed with 3 μm PBD-zirconia at 50 °C and 100 °C, respectively. The PBD-zirconia phase was stable at temperatures up to 320 °C under SGC conditions using carbon dioxide as mobile phase. Polarizable aromatic compounds and low molecular weight ketones and aldehydes were eluted with symmetrical peaks from a 10 cm column packed with 3 μm PBD-zirconia. Zirconia phases with greater inertness are required for the analysis of more polar compounds by SGC.     

A study of the surface properties of cotton fibers by inverse gas chromatography

In the present study, the potential relationships between the microstructure and the surface properties of different cotton fibers are analyzed by inverse gas chromatography (IGC) at infinite dilution. By measuring the retention time of polar and nonpolar gaseous probes into a column containing the fibers, surface characteristics of these fibers, in particular the dispersive component of their surface energy and their surface morphological index, were determined. It is clearly shown that the presence of natural waxes on cotton fibers plays a major role on their thermodynamic surface properties, affecting the surface energy and the acid-base character as well as the morphological aspects of such fibers. Finally, it appeared that IGC is a well appropriate method for the evaluation of the surface characteristics of cotton fibers.     

Influence of relative humidity on the properties of examined materials by means of inverse gas chromatography

Inverse gas chromatography (IGC) at infinite dilution was applied to evaluate the surface properties of sorbents and the effect of different carrier gas humidity. They were stored in different environmental humidity – 29%, 40%, and 80%. The dispersive components of the surface free energy of the zeolites and perlite were determined by Schulz-Lavielle method, whereas their tendency to undergo specific interactions was estimated basing on the electron donor–acceptor approach presented by Flour and Papirer. Surface parameters were used to monitor the changes of the properties caused by the humidity of the storage environment as well as of RH of carrier gas. The increase of humidity of storage environment caused a decrease of sorbents surface activity and increase the ability to specific interaction.     

Effect of surface fluorination on the electrochemical and photoelectrocatalytic properties of nanoporous titanium dioxide electrodes

Titanium dioxide is a widely used photocatalyst whose properties can be modified by fluoride adsorption. This work is focused on the effect of surface fluorination on the electrochemical and photoelectrocatalytic properties of TiO(2) nanoporous thin films. Surface fluorination was achieved by simple addition of HF to the working solution (pH 3.5). Open circuit potential as well as ex situ XPS measurements verify that surface modification takes place. Fluorination triggers a significant capacitance increase in the accumulation potential region, as revealed by dark voltammetric measurements for all the TiO(2) samples studied. The photoelectrocatalytic properties (measured as photocurrents under white light illumination) depend on the substrate being oxidized and, in some cases, on the nature of the TiO(2) sample. In particular, the results obtained for electrodes prepared with a mixed phase (rutile + anatase) commercial nanopowder (PI-KEM) indicate that the processes mediated by surface trapped holes, such as the photooxidation of water or methanol, are accelerated while those occurring by direct hole capture from the adsorbed state (formic acid) are retarded. The photooxidation of catechol and phenol is also enhanced upon fluorination. In such a case, the effect can be rationalized on the basis of a diminished recombination and a surface displacement of both the oxidizable organic substrates and the poisoning species formed as a result of the organics oxidation. Photoelectrochemical and in situ infrared spectroscopic measurements support these ideas. In a more general vein, the results pave the way toward a better understanding of the photocatalysis phenomena, unravelling the importance of the reactant adsorption processes.     

Characterization of surface thermodynamic properties of p-toluene sulfonate-doped polypyrrole by inverse gas chromatography

Summary p-Toluene sulfonate-doped polypyrrole (PPyTos) powder has been characterized by inverse gas chromatography at various temperatures. We have used apolar n-alkanes and polar probes of differing acidity and basicity to interrogate the London dispersive and Lewis acid-base properties of PPyTos, respectively. We have found that the London component of the surface energy (γs^d) is about 90 mJ · m⁻² at 25°C and the acid-base contribution to the free energy of adsorption (ΔG_a ^AB) for Lewis bases is higher than 8 kJ · mol⁻¹. These results show that PPyTos is a high energy material and is capable of very strong specific acid-base interactions. Lewis acidity is, however, dominant and is shown to increase with temperature. The determination of the heats of adsorption for tetrahydrofuran and ethyl acetate enabled us to determine Drago’s E_A, C_A, E_B and C_B parameters. Whilst E_A and C_A are similar to those published for chloride-doped polypyrrole and rank PPyTos as a hard acidic species, the E_B and C_B values suggest that PPyTos is a very soft Lewis base.     

Characterization of the surface properties of heavy residues of oil distillation by inverse gas chromatography

Summary Heavy residues from the distillation of oils (SAFANYA) have been analyzed by inverse gas chromatography (IGC). The dispersive components of the surface energies of the residues could readily be determined. Acid/base characteristics could be appreciated using an original method developed in this Laboratory.     

Determination of the surface properties of untreated and chemically treated kaolinites by inverse gas chromatography

Inverse gas chromatography is used to study the surface properties of the untreated and chemically treated kaolinite samples. Changes in the enthalpy of adsorption for a variety of probes and in the surface energy of clays are measured and the effect of modification of the natural clay after chemical treatment with Na₂CO₃ is determined. The surface energy of the natural clay increased by the modification due to an increase in the surface area. It can be concluded that the dispersive component of surface free energy, γ _s ^d , decreases with temperature in the 200–275°C temperature range for both samples. Temperature coefficients of γ _s ^d for untreated and modified kaolinites are −0.1185 and −0.3966 mJ/(m² °C) with the correlation coefficients (R ²) of 0.8479 and 0.965, respectively. From the retention data for polar probes at infinite dilution, information on the accessibility of surface sites to the probes and on the acid-base character of the surface is obtained. The specific free energy of adsorption, the specific enthalpy of adsorption (ΔH ^sp), and the specific entropy of adsorption of polar probes on initial and modified kaolinites are determined. The ΔH ^sp values correlated with the donor numbers and modified acceptor numbers of the probes to quantify the acidity (K _A) and basicity (K _D) parameters of clay surfaces. The values of K _A and K _D for initial and modified kaolinites are determined to be 0.1202 and 0.2803; 0.0130 and 0.0408 with the correlation coefficients of −0.9805 and −0.9782, respectively. The unmodified clay sample indicated a more acidic character, while the modified clay sample conferred a largely basic character. Consequently, the predominant surface basicity of the modified kaolinite agrees with expectation, bearing in mind the treatment with Na₂CO₃, taking into consideration that such a modification contributes to a decrease in the hydrophilicity of the surface and also results in the surface showing only weak Lewis acidity. The text was submitted by the authors in English.     

A study of the adsorption and surface properties of KSKG silica gel by gas chromatography

The adsorption properties of commercial wide-pore KSKG silica gel with respect to n-alkanes and their derivatives, the molecules of which possess different electron-donor and electron-acceptor properties, were studied by gas chromatography. The adsorption isotherms were used to determine the heats of adsorption, differential molar Helmholtz energies, and contributions of dispersion and specific (acid-base or donor-acceptor) interactions to these energies. The electron-donor and electron-acceptor characteristics of extremely hydroxylated silica gel surface were estimated. The electron-acceptor properties of the surface of KSKG were found to be much stronger than its electron-donor properties.     

Solid surface mapping by inverse gas chromatography

Inverse gas chromatography (IGC) at infinite dilution, is a technique for characterising solid surfaces. Current practice is the injection of n-alkane homologous series to obtain the free energy of adsorption of the CH2 group, from which the London component of the solid surface free energy, gamma(d)s, is calculated. A value around 40 mJ/m2 is obtained for poly(ethylene), and 30 mJ/m2 for a clean glass fibre, while the potential surface interactivity of a glass fibre is far greater than that of poly(ethylene). A specific component of the surface, in mJ/m2, should be calculated in order to obtain significant parameters. As applied up to date, when calculating the specific component of the surface energy, the fact that W(sp)a energy values are in a totally different scale than AN or DN values is a major drawback. Consequently, Ka and Kb values obtained are in arbitrary energy units, different from those of the London component measured by injecting the n-alkane series. This paper proposes a method to obtain Ka and Kb values of the surface in the same energetic scale than the London component. The method enables us to correct the traditional London component of a solid, obtaining a new value, where the amount of WaCH2 accounting for Debye interactions with polar sites, is excluded. As a result, an approach to surface mapping is performed in several different substrate materials. We show results obtained on different solid surfaces: poly(ethylene), clean glass fibre, glass beads, chemically modified glass beads and carbon fibre.     

Effect of fluorination on the stability of carbon nanofibres in organic solvents

Beneficial effects of fluorination on the stability of carbon nanofibre (CNF) dispersion in organic solvents as a function of time are evidenced. Because of their excellent friction properties, fluorinated CNFs (CF_0.85) can be used as nanoparticles of tribo-active phase in lubrication; however, they have to be added into a matrix. We have shown that mixtures of CF_0.85 are more stable than CNF solutions. Investigations by ultraviolet–visible spectroscopy have been carried out 2 h after sonication and after an ageing of 4 months. Hansen solubility theory was used, and after ageing, tribological and Raman spectroscopy experiments showed no significant modification of physicochemical properties of the CF_0.85.     

Effect of acid treatment on surface properties evolution of attapulgite clay: An application of inverse gas chromatography

In this paper, the evolution of structural, textural and surface properties of attapulgite after treatment with increasing concentrations of hydrochloric acid (0.5, 1, 3 and 5 M) is reported. The solids obtained were characterized by SEM, XRD, FTIR and BET analysis. The surface properties were also evaluated using inverse gas chromatography at infinite dilution (IGC-ID) and finite concentration (IGC-FC). The IGC analysis permitted us to reach several parameters such as: specific surface area, BET constant with organic probes and the distribution functions of the adsorption energy sites on the solid surface. At dilute concentrations of acid, carbonates are eliminated and the specific surface area increases. However, the morphology and crystal structure of attapulgite are preserved. At higher concentrations of acid, dissolution of octahedral sheets and at the same time formation of an amorphous silica from the tetrahedral sheets occur. However, the fibrous morphology is still preserved. The calculation of distribution functions reveals a clear evolution in the heterogeneity of the surface during the acid treatment, the appearance of shoulders is attributed to the development of strong specific interactions between the injected polar probe and silanol groups on the surface of amorphous silica formed during the acid treatment.     

炭化温度对模板法合成介孔炭性能的影响

以蔗糖为炭源和硅酸钠为硅源,采用原位共聚法制备了炭/氧化硅复合体,除去氧化硅得到介孔炭材料.采用N2吸附-脱附、透射电子显微镜和红外光谱对不同炭化温度获得的样品进行表征.结果表明,随着炭化温度升高,所得的介孔炭比表面积和孔容均下降,650℃ ～ 950℃的炭化温度下获得的样品BET比表面积在586m2/g ～728 m2/g之间,孔容在0.549cm3/g～0.696cm3/g之间,孔径分布5-15nm之间.经红外光谱检测所得的介孔炭样品均含有氢和氧的功能团.