A new method for the investigation of porous structures using mercury porosimetry

The influence of wetting angle hysteresis on volume hysteresis and retention of mercury in porous solids was considered. Although different explanations are possible (as explained in the paper), the resulting effect for cylindrical pores in the examined sample of active carbon was that the advancing angle θ_A = 162°, and the effective value of the receding angle θ_R = 90°. The rise of the mercury volume (V_m) intruded in the second run after the preceding reduction of pressure (p) to zero corresponds with a formation of spherical caps at the orifice of pores. The dependence of V_m on p in such a case has been called local hysteresis and it has been used to evaluate the true θ_A, the number of pores with a radius corresponding to the pressure of intrusion and their mean length.     

WETTABILITY AND SURFACE ENERGETICS OF ROUGH FLUOROPOLYMER SURFACES

Hydrophobic solid surfaces with controlled roughness were prepared by coating glass slides with an amorphous fluoropolymer (Teflon® AF1600, DuPont) containing varying amounts of silica spheres (diameter 48?μm). Quasi-static advancing, θ_A, and receding, θ_R, contact angles were measured with the Wilhelmy technique. The contact angle hysteresis was significant but could be eliminated by subjecting the system to acoustic vibrations. Surface roughness affects all contact angles, but only the vibrated ones, θ_V, agree with the Wenzel equation. The contact angle obtained by averaging the cosines of θ_A and θ_R is a good approximation for θ_V, provided that roughness is not too large or the angles too small. Zisman's approach was employed to obtain the critical surface tension of wetting (CST) of the solid surfaces. The CST increases with roughness in accordance with Wenzel equation. Advancing, receding, and vibrated angles yield different results. The θ_A is known to be characteristic of the main hydrophobic component (the fluoropolymer). The θ_V is a better representation of the average wettability of the surface (including the presence of defects).     

Contact angle of surfactant solutions on precipitated surfactant surfaces. III. Effects of subsaturated anionic and nonionic surfactants and NaCl

The contact angles of saturated calcium dodecanoate (CaC₁₂) solutions containing a second subsaturated surfactant on a precipitated CaC₁₂ surface were measured by using the drop shape analysis technique. The subsaturated surfactants used were anionic sodium dodecylsulfate (NaDS), anionic sodium octanoate (NaC₈), and nonionic nonylphenol polyethoxylate (NPE). Comparing at the critical micelle concentration (CMC) for each surfactant, NaC₈ was the best wetting agent, followed by NaDS, with NPE as the poorest wetter (contact angles of 32⁰, 42⁰, and 62⁰, respectively). Surface tension at the CMC increased in the order NaC₈<NPE<NaDS, and subsaturated surfactant adsorption increased in the order NPE≪NaDS (1.4 vs. 84 μmole/g); adsorption of the NaC₈ was not measurable. Interfacial tension (IFT) reduction at the solid-liquid interface due to subsaturated surfactant adsorption is an important contribution to contact angle reduction, in addition to surface tension reduction at the air-water interface. Surfactant adsorption onto the soap scum solid is crucial to solid-liquid IFT reduction and to good wetting. The fatty acid was the best wetting agent of the three surfactants studied, probably because calcium bridging with the carboxylate group synergizes surfactant adsorption onto the solid of the higher molecular weight soap. NaCl added to NaDS surfactant results in depressed CMC, lower surface tension at the CMC, decreased NaDS adsorption onto the solid, and decreased reduction in solid-liquid IFT. The contact angle is not dependent on the NaCl concentration for NaDS. The NaCl causes an increased tendency to form monolayers, which decrease air-water surface tension, but a decreased tendency to form adsorbed aggregates on the solid; the two trends offset each other, so wettability is not affected by added salt. The Zisman equation does not describe the wetting data for these systems well except for NaDS, further emphasizing the danger of ignoring solid-liquid IFT reduction in interpreting wetting data in these systems.     

An Experimentally Fitted and Simple Model for the Pores in Nuclepore Membranes

Abstract

The porosities (percentage of empty volume over the total volume) of several Nuclepore membranes are measured by means of a pycnometric method which is shown. If cylindrical pores are assumed, the porosities can be calculated from the surface pore densities and mean pore radii, both measured by microscopy. The disagreement between these two methods implies that the pores are not cylindrical in shape. A model is proposed that assumes an internal pore radius, r_r different from the external one, r_e (mean pore radius). When it is assumed that there is a mean angle, φ, between the pores and the membrane surface, this angle can be calculated if we assume that the experimental surface pore density is the maximum one compatible with the model. From a comparison of calculated and experimental φ, the maximization of the surface pore density can be tested.     

压汞法测定材料孔结构的误差分析

根据压汞法测量材料孔结构的基本原理分析了可能引起误差的来源。压汞法测定材料的孔径分布依据的是Washburn方程,基本的理论模型是圆柱孔模型,实际样品中的孔隙均存在异形孔,这给测量带来误差。汞的表面张力和汞与材料表面的接触角直接影响测量结果。     

Development of polymer derived carbon coated monolith for liquid adsorption application by response surface methodology

The preparation of polymer derived activated carbon coated monolith is reported. The response surface methodology based on Box–Behnken design is used to find the optimal condition for synthesis of mesoporous carbon. The dominant parameters identified are the carbonization temperature, concentration, and molecular weight of pore former agent. Typical values for BET surface area are 341 m²/g _carbon and 20 m²/g _{supported carbon} with pores size distribution in the range of 4–400 nm. The highest pore volume obtained is 182.77 mm³/g _{supported carbon}.     

Characterization of Pore Space of Cement-Based Materials by Combined Mercury and Wood's Metal Intrusion

Analysis of the pore space is crucial for a profound understanding of the transport and mechanical properties of porous materials. Mercury intrusion porosimetry (MIP) is an easy and widely applied method to determine the pore size distribution of mesoporous materials, but a principal problem makes data interpretation difficult. Large ink-bottle pores may be accessed by the intruding mercury through smaller, so-called neck pores only. This leads to significant under estimaion of pore sizes and to hysteresis effects between intrusion and extrusion in materials with a broad pore size distribution such as cement-based materials. More accurate pore space information is obtained when ink-bottle pores in the measurement are excluded from analysis. This may be achieved by repeated intrusion cycles or by impregnating the ink-bottle pore space with Wood's metal. The combination of Wood's metal impregnation (WMI) and mercury intrusion in mortars and cement pastes as presented allows a characterization of the pore space independent of accessibility considerations. Different special pore types are defined, analyzed, and quantified. In a cement paste, 50% of all pores are found to be ink-bottle type, of which 60% are accessible through neck entrances larger than 20 nm in diameter. A further 30% of all pores are nonink-bottle type but are connected to the surface through such ink-bottle pores only. Furthermore, hysteresis and contact angle alternation effects between intrusion and extrusion were studied. A contact angle shift of 26° between intrusion and extrusion is proposed.     

Critical Surface Tension of Non-crosslinking Linear Low Density Polyethylene-graft-acrylic Acid by the Contact Angle Method

Abstract

The contact angles θ of polar liquid on surface of non-crosslinking linear low density polyethylene-graft-acrylic acid (LLDPE-g-AA) were measured. The critical surface tension (γ_c) of LLDPE-g-AA films were evaluated by three different plots, the Zisman plot, the Young-Dupre-Good-Girifalco plot, and the log(1 + cos θ) versus log θ _L , plot. The θ _c of LLDPE-g-AA obtained by the 1 + cosθ versus θ _L ^?1/2 plot were higher than those obtained by other plots.     

Correlations between pore structure parameters and gas permeability of corundum porous materials

Corundum porous materials with different contents of calcium hexaluminate formed in situ were prepared using pure calcium aluminate cement as the calcium source. The surface fractal dimensions of the porous materials were calculated based on the experimental data of mercury intrusion. Correlations between pore structural parameters and the permeability coefficients k₁ and k₂ of the porous materials were then studied based on the grey system theory. The results showed that pores in the corundum porous materials have great fractal characteristics. The surface fractal dimension was a significant pore structural parameter that reflected the complexity of pore shape, pore surface, and pore-size distribution, which had the maximum correlation coefficient with the permeability of this type of porous materials. The apparent porosity and pore-size distribution had relatively high correlation coefficients to the permeability as well. Increasing the apparent porosity and the volume percentage of larger pores, and decreasing the volume percentage of smaller pores all benefited the permeability of the porous materials. In addition, the mean pore size and median pore size showed lower correlation coefficients to the permeability—especially for porous materials with a wide pore-size distribution.     

Pore size distribution in Separon using mercury contact angles in pores and hysteresis in porosimetry

The porous co-polymer Separon HEMA 1000 for HPLC column packing was examined by using a special method of mercury porosimetry evaluation. The advancing and receding contact angles of mercury in pores were determined and the method used is described in detail. The pore distribution curves obtained from mercury porosimetry and from the nitrogen desorption isotherms are in good agreement. The dependence of the hysteresis of the porosimetry curves and mercury retention in the pores on the intrusion volume was investiaged to characterize the porous structure of the sample. The influence of the pore potential on the hysteresis was evaluated.     

Critical Surface Tension of Wetting and Flotation Separation of Hydrophobic Solids

Abstract

Wetting characteristics of a number of minerals including layer-type hydrophobic minerals as well as common sulfides were investigated. For the majority of the minerals, the critical surface tension of wetting, γ_c determined using Zisman's technique was in the range of 40 to 45 mN/m. Surface pressures of water, II_e, on molybdenite and coal samples were determined from adsorption isotherms. The dispersion component of the surface-free energy, γ_s ^d, for molybdenite was estimated to be 113 ± 3 mJ/m² as compared to the γ_s ^d value for graphite, 109 mJ/m². The wettability data of aqueous methanol solutions, presented in the form of adhesion tension diagrams, yielded significantly lower γ_c values. Flotation behavior of common sulfides, which was similar to that of inherently hydrophobic polymers and minerals, was attributed to elemental sulfur formation. The relevance of critical surface tension of wetting to selective flotation and separation of hydrophobic solids is discussed.     

Studies on synthetic polymer plates with high surface energy. III. Diethylene glycol bis(allyl carbonate)–unsaturated sulfonic acid system

Synthetic polymer plates (GPs) with high surface energy were prepared by the two-step copolymerization process previously reported, using diethylene glycol bis(allyl carbonate) (CR-39) as M₁ monomer and unsaturated sulfonates [sodium vinyl sulfonate (VS^?Na⁺), potassium styrene sulfonate (StS^?K⁺), and sodium 2-sulfoethyl methacrylate (SEM^?Na⁺)] as M₂ monomer. The contact angle (θ_H) of water for the acid-treated (immersed in an aqueous 0.1 N HCl solution for 2 h) GPs decreased in the order StS^?K⁺, VS^?Na⁺, and SEM^?Na⁺. In the case of M₂ = SEM^?Na⁺, the θ_H value was about 20°. By adding NaCl in the immersion solution and changing the pH of the immersion solution, the θ_H values for the CR-39–SEM^?Na⁺ GPs were lowered to 18.9 and 13.1°, respectively. The θ_H values for the above GPs were smaller than those for the CR-39–acrylic acid or the CR-39–methacrylic acid GPs in the previous report, whereas the contact angle (θ_Na) of water for the former after alkali treatment (immersed in an aqueous 0.1 N NaOH solution for 2h) was larger than those for the latter. The former had durability of water wettability superior to the latter because of the difference in dissociation characteristic of the respective functional group.     

Urine Advancing Contact Angle on Several Surfaces

Urine wetting properties may influence the design and performance of catheters, urinalysis instruments, and lab-on-a-chip technologies. In this study the advancing contact angle _adv of urine on several materials is characterized. Material type and surface tension have a significant effect on _adv, while pretreatment and aging do not. Mean urine _adv are between ≈78° and ≈89° on hydrophilic surfaces, and up to over ≈105° on hydrophobic surfaces. Expected urine contact angles will decrease from the DI water contact angles by on average 10°, and up to 20°, while urine surface tension will be lower than DI water by 12.12 mN/m and 18.53 mN/m. A unit change (mN/m) in surface tension results in a 0.75° change in _adv. These results indicate that systems attempting to exploit urine wetting must account for highly variable conditions.     

Synthesis,Physico-Chemical Properties and Enhanced Oil Recovery Flooding Evaluation of Novel Zwitterionic Gemini Surfactants

In this work, a novel series of zwitterionic gemini surfactants with different hydrophobic tails were synthesized and characterized. The physico‐chemical properties of these products (such as surface tension, oil/water interfacial tension, foaming ability, and the wetting ability of paraffin‐coated sandstone) were fully studied. The CMC of the synthesized surfactants ranged from 2.17 × 10^?4 mol L^?1 to 5.36 × 10^?4 mol L^?1 and corresponding surface tension (γ_CMC) ranged from 26.49 mN m^?1 to 29.06 mN m^?1, which showed excellent efficiency among the comparison surfactants. All the products can reduce the interfacial tension to a relatively low level of about 0.1–1.0 mN m^?1. Additionally, results from applying different hydrocarbons suggested that the synergy will be clearer and oil/water interfacial tension will be lower if the oil components are similar to the surfactants. Contact angle and foaming measurements indicated that the surfactants exhibited good wetting and foaming abilities. The results of oil flooding experiments using an authentic sandstone microscopic model showed that C‐12 and CA‐12 could effectively improve the displacement efficiency by 21–29 %.     

Assessment of the Wettability of Porous Electrodes for Lithium-Ion Batteries

The wettability of lithium cobalt oxide (LiCoO₂) and mesocarbon microbead electrodes in nonaqueous electrolyte is analyzed by a mathematical model of capillary liquid movement. Results show that wetting in the LiCoO₂ electrodes is difficult as compared with the MCMB electrodes at the same electrolyte composition. Wetting in the porous electrodes is controlled mainly by electrolyte penetration and spreading in pores. Electrolyte penetration is determined by viscosity. On the other hand, electrolyte spreading is controlled by surface tension. Organic solvent composition and lithium salt concentration may influence the wettability of porous electrodes due to changes in the viscosity and surface tension of the electrolyte. Increasing the amount of EC and/or lithium salts can cause poorer electrolyte spreading and penetration. Furthermore, careful pressure control has a positive effect on increasing the surface area of the solid–liquid interface. AC impedance data show that batteries with vacuuming prior to electrolyte filling may reach a maximum wetting in a few hours. If no vacuuming is applied, a few days are required to obtain sufficient wetting.     

The effect of washing process on the cracking of ZrO2 microspheres by internal gelation

ZrO₂ microspheres are widely used as a simulant of UO₂ in the development of nuclear fuel. However, the cracking of ZrO₂ microspheres prepared by internal gelation is still a challenge during drying and sintering processes. To address this issue, we designed and optimized the washing process for obtaining crack-free ZrO₂ microspheres. Through thermogravimetric, infrared, Raman, BET, and SEM analysis, it is shown that the cracking of the microspheres is mainly related to the pores in microspheres. The washing solvent with low surface tension is used to reduce the effect of capillary force on pore shrinkage. Therefore, the optimal washing process was designed as trichloroethylene (TCE)—0.5 M NH₃.H₂O—Propylene glycol methyl ether (PM) and gel microspheres with a high specific surface area of 315.3 m²/g and pore volume of 0.4125 cm³/g were obtained. The characterizations also further showed that when the microspheres were dried and sintered, the water vapor and the decomposition gas of organic matter were completely released from the pores in the microspheres. Our new washing process could be directly extended for preparing crack-free ceramic microspheres by internal gelation.     

Critical Surface Tension of Acrylamide-Grafted Polypropylene Copolymer by the Contact Angle Method

The contact angles θ of polar liquids on PP-g-AM copolymer (AM content 0.19, 0.26, and 0.37 wt%) were measured. The critical surface tension γ_C of PP-g-AM films were evaluated by the Zisman plot (cos θ versus-γl), the Young-Dupre-Good-Girifalco plot (1 + cos θ) versus 1/γ^0.5 l, and the log(1 + cos θ) versus log-γl plot. The-γl values estimated by the plot log(1 + cos θ) versus log-γl were smaller than those obtained by the other plots.     

Correlation of Flocculation and Agglomeration of Dolomite with its Wettability

Wettability is an important parameter which affects the shear flocculation and oil agglomeration behaviors of minerals. The critical surface tension of wetting (γ_c) as a wettability parameter describes wetting characteristics of any mineral. In this study, the correlation of shear flocculation and oil agglomeration processes of dolomite with its wettability parameter is investigated. The experimental studies have indicated that these processes improved with decreasing wettability depending on the increase of oleate adsorption despite a simultaneous increase in the zeta potential of dolomite. On the other hand, the flocculation and agglomeration of dolomite decreased with decreasing surface tension and did not occur below a particular value of surface tension, corresponding to the critical surface tension of wetting (γ_c) and the critical solution surface tension (γ_c-a) values, respectively. Also, the γ_c-a values are slightly higher than the γ_c values, indicating that the agglomeration of the particles requires a lower wettability.     

Synthesis of Mesoporous Silica Materials via Nonsurfactant Urea-Templated Sol-Gel Reactions

Mesoporous silica materials with pore diameters of 2 to 6 nm have been prepared using urea as a nonsurfactant template or pore-forming agent in HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate, followed by removing the urea molecules by extraction with methanol or water. Characterization results from nitrogen sorption isotherm, powder X-ray diffraction, and transmission electron microscopy indicate that the materials have large specific surface areas (e.g., 600 m²/g) and pore volumes (e.g., 0.8 cm³/g) as well as narrow pore size distributions. The mesoporosity is arisen from interconnecting wormlike channels and pores of regular diameters. As the urea concentration is increased, the nitrogen sorption isotherms of the silica matrices transform from the reversible type I to the type IV form with type H2 hysteresis, along with increases in the diameter and volume of the pores.     

The use of small angle neutron scattering with contrast matching and variable adsorbate partial pressures in the study of porosity in activated carbons

The porosity of a typical activated carbon is investigated with small angle neutron scattering (SANS), using the contrast matching technique, by changing the hydrogen/deuterium content of the absorbed liquid (toluene) to extract the carbon density at different scattering vector (Q) values and by measuring the p/p₀ dependence of the SANS, using fully deuterated toluene. The contrast matching data shows that the apparent density is Q-dependent, either because of pores opening near the carbon surface during the activation processor or changes in D-toluene density in nanoscale pores. For each p/p₀ value, evaluation of the Porod Invariant yields the fraction of empty pores. Hence, comparison with the adsorption isotherm, shows that the fully dry powder undergoes densification when liquid is added. An algebraic function is developed to fit the SANS signal at each p/p₀ value hence yielding the effective Kelvin radii of the liquid surfaces as a function of p/p₀. These values, when compared with the Kelvin equation, show that the resultant surface tension value is accurate for the larger pores but tends to increase for small (nanoscale) pores. The resultant pore size distribution is less model-dependent than for the traditional methods of analyzing the adsorption isotherms.