Application of programmed thermodesorption of the liquid under quasi-isothermal conditions to investigate physicochemical properties of liquid layers and solid surfaces

This paper presents the results of measurements of the programmed thermodesorption of polar and nonpolar liquids from the surface of different types of solids. The course of thermodesoption was found to depend on the properties of the solid and the wetting liquid. Thermodesorption occurred not exponentially but in steps, which reflects the noncontinuous changes in the properties of the surface layer with the distance from the solid surface. This effect intensified with the increase in polarity of the wetting liquid and the heterogeneity of the solid surface. The earlier investigations showed that application of the method of differential thermal analysis allowed determination of the distribution of the adsorption potential of the liquid on the solid surface.The author is indebted to Prof. M. Jaroniec for very fruitful discussions and to Prof. J. Choma for the activated carbon samples.     

Effect of surface heterogeneity on adsorption on solid surfaces. Application of inverse gas chromatography in the studies of energetic heterogeneity of adsorbents

The paper presents a literature review of the chromatographic methods used for investigations of the heterogeneity of solid surfaces. Special attention is paid to inverse gas chromatography (IGC). Quantitative characteristics of heterogeneity of real solid surfaces including extreme models on adsorption centre topography of the "patch-wise" and "random" types are described. Analytical and numerical methods used for calculating the adsorption energy distribution function as a quantitative measure of surface heterogeneity are presented. Special attention is paid to the condensation approximation as well as to other approximations based on this assumption. IGC is presented as a quick, precise and effective method to characterise physicochemical properties of different kinds of adsorbents. Advantages of IGC over traditional methods of gas and vapour adsorption are shown.     

Controlled-rate thermal analysis

Controlled-rate thermal analysis (CRTA) and differential scanning calorimetry (DSC) were used to investigate the adsorbed water layers and the surface properties of different commercial activated carbons. A simple method is proposed to obtain information on the properties of the adsorbed water film and the surface heterogeneity of the materials studied. This method utilizes TG mass loss and the first derivative of the DTG mass loss curves with respect to temperature and time, obtained during programmed liquid thermodesorption. The obtained TG mass loss curves, which reflect the energetic heterogeneity, consisted of steps and inflections which were associated with the mechanism of wetting of the solid surfaces. The heights of these steps and inflections depend on the adsorption capacity, the adsorption potential and the nature and number of the active centers of the carbon samples studied. The values of the total porosity and the surface phase capacity obtained by this method are in good agreement with those estimated on the basis of independent methods. The behaviour of water/carbon samples was studied by means of DSC at subambient and elevated temperatures. The experimental results provided novel data on the structural heterogeneity, the thermal stability of the water/carbon interface and its phase and structural transitions.Support from the Research Council of Kent State University (Ohio, USA) is acknowledged. The author is pleased to thank Drs M. Jaroniec, R. K. Gilpin, J. Choma and R. Dobrowolski for fruitful discussions and the active carbon samples.     

Influence of analysis conditions on low pressure adsorption measurements and its consequences in characterization of energetic and structural heterogeneity of microporous carbons

Nitrogen adsorption isotherms on nonporous and microporous carbons were thoroughly studied at low relative pressures. For nonporous carbons low pressure measurements seem to be unaffected by analysis conditions. However, these measurements on microporous solids may be affected by analysis conditions at relative pressures below 10^–4. It was shown that selection of proper equilibration time is crucial for correct measurements of equilibrium pressures during adsorption on microporous carbons. The isotherm shift induced by insufficient equilibration of the system may affect the surface heterogeneity and microporosity analysis. A comparison of the adsorption energy and pore volume distribution functions calculated from low pressure nitrogen adsorption isotherms measured at different equilibration times on a microporous carbon shows that this effect is smaller than it was expected.     

Investigation of energetic heterogeneity of carbon black surfaces during adsorption of chromatographically low concentrations of n-pentane

Energetic heterogeneity of different types of industrial carbons was studied by gas-adsorption chromatography in regions of low surface coverages. The main thermodynamic characteristics of n-pentane adsorption on the carbon black surfaces were experimentally determined under the conditions close to the zero coverage of the surface (Henry region). These characteristics include the Henry constants, differential molar heats of adsorption, changes in the entropy of adsorption, and differences in molar heat capacities of the adsorbate in the adsorbed state and its vapors at a constant pressure. The specific features of the geometric structure and ratio of surface regions different in the adsorption energy make it possible to establish the presence of the Henry region in the adsorption isotherm. The gas-chromatographic criteria, which can be used to estimate the degree of energetic heterogeneity of the adsorbent surface, were considered.     

Strong effect of minor impurities in a gas on the rate of evaporation of solid surfaces

Evaporation of surfaces of quartz, corundum, and germanium monoxide precipitates in a flow of nitrogen and air was studied by the method of molecular nuclei of condensation, which makes it possible to determine extremely low concentrations of molecules from 10² to 10⁸ per I cm³ of a gas. The appreciable effect of low concentrations of gas impurities on the rate of evaporation of solid surfaces was found and studied in the region of low evaporation rates. Equations describing the dissimilar effects of the retention of molecules of impurities on the surface on the rates of evaporation and reverse condensation were proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 808–813, April, 1996.     

Prediction of densities for solid energetic molecules with molecular surface electrostatic potentials

The densities of high energetic molecules in the solid state were calculated with a simplified scheme based on molecular surface electrostatic potentials (MSEP). The MSEP scheme for density estimation, originally developed by Politzer et al., was further modified to calculate electrostatic potential on a simpler van der Waals surface. Forty-one energetic molecules containing at least one nitro group were selected from among a variety of molecular types and density values, and were used to test the suitability of the MSEP scheme for predicting the densities of solid energetic molecules. For comparison purposes, we utilized the group additivity method (GAM) incorporating the parameter sets developed by Stine (Stine-81) and by Ammon (Ammon-98 and -00). The absolute average error in densities from our MSEP scheme was 0.039 g/cc. The results based on our MSEP scheme were slightly better than the GAM results. In addition, the errors in densities generated by the MSEP scheme were almost the same for various molecule types, while those predicted by GAM were somewhat dependent upon the molecule types.     

Application of programmable liquid thermodesorption under quasi-isothermal conditions to study physicochemical properties of liquid films and solid surfaces

The paper presents possible applications of differential thermal analysis for study of the physicochemical properties of liquid/solid systems, mainly through programmable liquid thermodesorption from the sample under quasi-isothermal conditions. The results prove its applicability in the determination of solid physicochemical properties, and particularly in calculations of adsorption potential distribution, the activation energy of molecules adsorbed on the surface and the surface heterogeneity by means of computer techniques.The authors are indebted to Dr. Ryszard Dobrowolski for very fruitful discussions, and to Prof. Jerzy Choma for the activated carbon samples.     

Application of fractal geometry for studies of heterogeneity properties of nanomaterials

Calculations based on the fractal geometry in the estimation of surface heterogeneity are superior compared with conventional calculation methods (e.g. from the data of gas adsorption or X-ray radiation scattering) as they can be applied without limitation as far as the range of surface sizes of the studied structures is concerned. This paper presents structural characteristics of carbon and carbon- free nanomaterials based on the determined surface and volumetric fractal coefficients. Fractal coefficients were determined from the data obtained by means of two independent methods: sorptometry and atomic force microscopy (AFM). Correlation between porosity parameters and fractal coefficients is presented.     

微流控技术在循环肿瘤细胞异质性分析领域的应用

循环肿瘤细胞(circulating tumor cells,CTCs)的检测是液体活检的重要组成部分,可以通过低损伤甚至无创的方法达到检测体液中肿瘤细胞的目的 .肿瘤细胞在增殖、转移过程中极易产生多种类型的变异,如基因突变、蛋白质组学和表观遗传学改变等,这导致肿瘤细胞个体间发生差异,给临床诊疗带来巨大挑战.通过CTC...     

Characterization of surface energetic heterogeneity of pure and poly (acrylic acid)‐adsorbed carbon nanotubes by deconvoluting the nitrogen adsorption isotherm

The surface energetic heterogeneity of pure and poly (acrylic acid) (PAA)‐adsorbed carbon nanotubes (CNTs) were studied by a nitrogen probe adsorption technique in a wide range of pressures. The adsorption energy distributions (AEDs) were calculated from the low‐pressure data of isotherms by deconvoluting the low‐pressure experimental nitrogen adsorption isotherms. The surface of pure CNTs is heterogeneous as its AED presents four peaks at 42, 52, 57 and 78 K. It is observed that the AED of CNTs can be evidently modified by PAA adsorption. While the PAA adsorption amount increases, the high‐energy peaks at 52, 57 and 78 K gradually weaken and diminish at last, whereas the low ones such as at 42 K strengthen and new peaks arise at 27 and 32 K. It is proposed that PAA molecules prefer interacting with and screening the higher energetic sites to the lower ones. It will facilitate the understanding of the polymer adsorption on energetic heterogeneity surfaces. Copyright © 2006 John Wiley & Sons, Ltd.     

Application of thermal analysis in solid industrial wastes treatment

The choice of an appropriate and safe disposal alternative should be based on the wide range of physicochemical examination thermal analysis in conjunction with other data enables identification of wastes, allows determination of weight losses at any stage of thermal decomposition and characterization of the combustible properties of wastes. In this paper the physicochemical composition of some industrial wastes, which create serious hazards to the natural environment is presented. The following waste materials were investigated:

tar wastes from several departments of the coking plant

paint-shop wastes from a metallurgical factory.

Thermoanalytic measurements were carried out in the dynamic atmosphere of air. Enthalpic values were calculated from the peak areas of the DTA curves. Thermoanalytic data were compared with calorimetric results obtained from an oxygen bomb. The disposal methods for above-mentioned wastes are proposed.     

An analysis of the thermal aging behaviour in high-performance energetic composites through the glass transition temperature

Differential scanning calorimetry (DSC) was used to analyze the thermal aging behaviour in energetic composite materials where a hydroxyl-terminated polybutadiene (HTPB)/isophorone diisocyanate elastomer is the polymeric matrix. Different parameters from the analysis of the glass transition, such as the glass transition temperature (T_g), were used in order to monitor this isothermal aging at 65 °C during a total time of 3000 h, finding an increasing and broadening T_g. In addition, the accelerated aging behaviour of these materials was also studied by a classical method, based on the change of mechanical properties such as those of Young's modulus or strain at break. The correlation between both methodologies was examined, demonstrating that an analytical technique such as DSC allows the evaluation of the actual state of composite solid propellants with a small sample and a straightforward measurement.     

Dynamic adhesion behavior of micrometer-scale particles flowing over patchy surfaces with nanoscale electrostatic heterogeneity

The dynamic adhesion behavior of micrometer-scale silica particles is investigated numerically for a low Reynolds number shear flow over a planar collecting wall with randomly distributed electrostatic heterogeneity at the 10-nanometer scale. The hydrodynamic forces and torques on a particle are coupled to spatially varying colloidal interactions between the particle and wall. Contact and frictional forces are included in the force and torque balances to capture particle skipping, rolling, and arrest. These dynamic adhesion signatures are consistent with experimental results and are reminiscent of motion signatures observed in cell adhesion under flowing conditions, although for the synthetic system the particle–wall interactions are controlled by colloidal forces rather than physical bonds between cells and a functionalized surface. As the fraction of the surface (Θ) covered by the cationic patches is increased from zero, particle behavior sequentially transitions from no contact with the surface to skipping, rolling, and arrest, with the threshold patch density for adhesion (Θ_crit) always greater than zero and in quantitative agreement with experimental results. The ionic strength of the flowing solution determines the extent of the electrostatic interactions and can be used to tune selectively the dynamic adhesion behavior by modulating two competing effects. The extent of electrostatic interactions in the plane of the wall, or electrostatic zone of influence, governs the importance of spatial fluctuations in the cationic patch density and thus determines if flowing particles contact the wall. The distance these interactions extend into solution normal to the wall determines the strength of the particle–wall attraction, which governs the transition from skipping and rolling to arrest. The influence of Θ, particle size, Debye length, and shear rate is quantified through the construction of adhesion regime diagrams, which delineate the regions in parameter space that give rise to different dynamic adhesion signatures and illustrate selective adhesion based on particle size or curvature. The results of this study are suggestive of novel ways to control particle–wall interactions using randomly distributed surface heterogeneity.     

Non-isothermal kinetic studies on thermal decomposition of energetic materials

Thermal stability and decomposition kinetics for two energetic materials, potassium nitroform (KNF) and 5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO), were investigated to obtain information on their safety for handling, storage, and use. Differential scanning calorimetry (DSC) and simultaneous thermogravimetry-differential thermal analysis (TG-DTA) techniques have been used to study thermal behavior of these energetic compounds. The results of TG analysis revealed that the main thermal degradation for the KNF occurs during two temperature ranges of 270?C330 and 360?C430?°C. Meanwhile, NTO decomposes completely in temperature range of 250?C300 °C. TG-DTA analysis of KNF indicates that this energetic compound dehydrated (at about 108?°C) before its decomposition. However, NTO is thermally stable until its decomposition. The decomposition kinetic of energetic materials was studied by non-isothermal DSC under various heating rates. Kinetic parameters such as activation energy and frequency factor for thermal decomposition of energetic compounds were obtained via the methods proposed by ASTM E696 and Starink. Also, thermodynamic parameters correspond to the activation of thermal decomposition and critical ignition temperatures of the compounds were obtained.     

Charge heterogeneity of surfaces: mapping and effects on surface forces

The DLVO theory treats the total interaction force between two surfaces in a liquid medium as an arithmetic sum of two components: Lifshitz–van der Waals and electric double layer forces. Despite the success of the DLVO model developed for homogeneous surfaces, a vast majority of surfaces of particles and materials in technological systems are of a heterogeneous nature with a mosaic structure composed of microscopic and sub-microscopic domains of different surface characteristics. In such systems, the heterogeneity of the surface can be more important than the average surface character. Attractions can be stronger, by orders of magnitude, than would be expected from the classical mean-field DLVO model when area-averaged surface charge or potential is employed. Heterogeneity also introduces anisotropy of interactions into colloidal systems, vastly ignored in the past. To detect surface heterogeneities, analytical tools which provide accurate and spatially resolved information about material surface chemistry and potential — particularly at microscopic and sub-microscopic resolutions — are needed.Atomic force microscopy (AFM) offers the opportunity to locally probe not only changes in material surface characteristic but also charges of heterogeneous surfaces through measurements of force–distance curves in electrolyte solutions. Both diffuse-layer charge densities and potentials can be calculated by fitting the experimental data with a DLVO theoretical model. The surface charge characteristics of the heterogeneous substrate as recorded by AFM allow the charge variation to be mapped. Based on the obtained information, computer modeling and simulation can be performed to study the interactions among an ensemble of heterogeneous particles and their collective motions. In this paper, the diffuse-layer charge mapping by the AFM technique is briefly reviewed, and a new Diffuse Interface Field Approach to colloid modeling and simulation is briefly discussed.     

Spectral force analysis using atomic force microscopy reveals the importance of surface heterogeneity in bacterial and colloid adhesion to engineered surfaces

Coatings developed to reduce biofouling of engineered surfaces do not always perform as expected based on their native properties. One reason is that a relatively small number of highly adhesive sites, or the heterogeneity of the coated surface, may control the overall response of the system to initial bacterial deposition. It is shown here using an approach we call spectral force analysis (SFA), based on force volume imaging of the surface with atomic force microscopy, that the behavior of surfaces and coatings can be better understood relative to bacterial adhesion. The application of vapor deposited TiO₂ metal oxide increased bacterial and colloid adhesion, but coating the surface with silica oxide reduced adhesion in a manner consistent with SFA based on analysis of the “stickiest” sites. Application of a TiO₂-based paint to a surface produced a relatively non-fouling surface. Addition of a hydrophilic layer coating to this surface should have decreased fouling. However, it was observed that this coating actually increased fouling. Using SFA it was shown that the reason for the increased adhesion of bacteria and particles to the hydrophilic layer was that the surface produced by this coating was highly heterogeneous, resulting in a small number of sites that created a stickier surface. These results show that while it is important to manufacture surfaces with coatings that are relatively non-adhesive to bacteria, it is also essential that these coatings have a highly uniform surface chemistry.     

Conversion of methane into C1 oxygenates by deep-UV photolysis on solid surfaces: influence of the nature of the solid and optimization of photolysis conditions

Deep-UV photolysis (either 165 or 185 nm) of surface hydroxy groups leads to homolytic O-H bond-cleavage with the generation of oxyl radicals that can initiate the room-temperature radical-chain methane activation. Whilst in the absence of oxygen, radical coupling reactions to give low-molecular-weight alkanes are observed in the gas phase, the presence of some oxygen quenches these radicals and increases the selectivity towards C1 oxygenates (methanol, formaldehyde, and formic acid species). The nature of the solid influences the efficiency of the photochemical process and the distribution between products in the gas and solid phases. Using Beta-, delaminated ITQ2 and ITQ6, and medium-pore ZSM5 zeolites, mesoporous MCM41 silicates, and non-porous TiO(2), we observed that confinement and porosity increased the proportion of C1 oxygenates adsorbed onto the solid and reduced the contribution of the gas-phase products. In addition, the presence of aluminum in the zeolite framework, which is responsible for the generation of acid sites, increased overoxidation of methanol and methoxy groups into formaldehyde and formic acids. For a given amount of methane and unchanged photolysis conditions, the conversion increased with the amount of the solid used as photocatalyst. In this way, methane conversions of up to 7% were achieved for the 185 nm photolysis of methane for 1 h with a 76 MJ mol(-1) energy consumption.     

Pharmaceutical formulation analysis of thalidomide by solid surface room temperature phosphorimetry

A rapid and simple method of analysis for thalidomide formulations has been reported based on solid surface room temperature phosphorimetry. Thalidomide phosphorescence was enhanced by Hg(II) ions deposited on paper substrates previously treated for background reduction. A calibration curve with a linear dynamic range of three orders of magnitude was obtained (1.37 × 10^–6 M – 10^–3 M) and a 1.8 ng absolute limit of detection was estimated. The recovery of the method was tested in pharmaceutical formulations containing thalidomide as the only active ingredient. The values obtained were 96.3 ± 6.6% (employing the calibration curve procedure) and 98.0 ± 5.3% (employing the standard addition procedure), which show the potential of the technique for the analysis of thalidomide in dosage forms.