The effect of polymer adsorption on the wetting properties of partially hydrophobized magnetite

Upon reverse flotation of iron ore, the surface of the iron ore concentrate may become partially hydrophobized due to adsorption of flotation collector, which is facilitated by the calcium ions present in the process water. Hydrophobic areas on the concentrate surface may introduce problems in subsequent pelletization of the concentrate. A possible way to restore the wettability of the surface could be by modifying the surface with a hydrophilic polymer. The effect of hydrophilic polymers of different types, viz. cationic, anionic, and non-ionic, on the wettability of the magnetite surface after adsorption of a surfactant was investigated. Although all the polymers could adsorb on magnetite at pH 8.5, the contact angle measurements revealed that only anionic ammonium polyacrylate could decrease the contact angle of synthetic magnetite after surfactant adsorption to a level close to that of as-synthesized magnetite. Such effect was probably achieved due to shielding of the hydrophobic surfactant chains from the aqueous phase by hydrophilic polyacrylate molecules. The fact that polyacrylate adsorption on magnetite occurred via calcium ions makes polyacrylate suitable for application in calcium-rich process water. The results presented in this work illustrate that ammonium polyacrylate could be successfully used to improve the wettability of magnetite after adsorption of surfactants.     

Polymer dynamics under nanoscopic constraints: the "corset effect" as revealed by NMR relaxometry and diffusometry.

A spinodal demixing technique was employed for the preparation of linear poly(ethylene oxide) (PEO) confined in nanoscopic strands, which in turn are embedded in a quasi-solid methacrylate matrix impenetrable to PEO. Both the molecular weight of the PEO and the mean diameter of the strands are variable to a certain degree. Chain dynamics of the PEO in the molten state were examined with the aid of field-gradient NMR diffusometry and field-cycling NMR relaxometry. The dominating mechanism for translational displacements in the nanoscopic strands is shown to be reptation. A formalism for the evaluation of NMR diffusometry is presented, which permits the estimation of the mean PEO strand diameter. Samples of different composition revealed diameters in the range 9-58 nm, in reasonable agreement with electron micrographs. The time scale of the diffusion measurements was 10-300 ms. On the much shorter time scale of field-cycling NMR relaxometry, 10(-9)-10(-4)s, a frequency dispersion of the spin-lattice relaxation time characteristic for reptation clearly showed up in all samples. An effective tube diameter of only 0.6 nm was found even when the strand diameter was larger than the radius of gyration of the PEO chain random coils. The finding that the tube diameter effective on the short time scale of field-cycling NMR relaxometry is much smaller than the diameter of the confining structure is termed the "corset effect", and is traced back to the lack of local free-volume fluctuation capacity under nanoscale confinements. The order of magnitude of the 'pore' diameter, at which the cross-over from confined to bulk chain dynamics is expected, is estimated.     

Determination of the location of coke in catalysts by a novel NMR-based, liquid-porosimetry approach

In this work, a new technique, suitable for chemically-heterogeneous materials, has been used to characterise the structural properties of porous heterogeneous catalysts. A liquid-liquid exchange (LLE) process within nanoporous catalysts has been followed using NMR relaxometry and NMR diffusometry. In order to validate the new technique, two model materials were used. First, a chemically-pure, sol-gel silica, with a simple, mono-disperse pore-space, was studied. The second model material was a bidisperse, eggshell Pt-alumina catalyst. The Pt-alumina catalyst was studied both fresh, and coked following chemical reaction. The degree of structural and chemical complexity added by coking was restricted by the localisation of the coke deposition to the Pt-eggshell layer. Under so-called 'metered' supply conditions, when a high affinity liquid (water) displaced a low affinity liquid (cyclohexane) from the sol-gel silica, entrapment of the low affinity liquid was observed which was similar to that observed in mercury porosimetry. In a similar experiment, comparing LLE in fresh and coked samples of the Pt-alumina catalyst pellets, it was found, for the fresh sample, that water initially displaced cyclohexane from a sub-set of the most accessible, smallest pores, as might expected under metered conditions, but this did not occur for coked catalysts. This finding suggested coking had removed some smaller pores located close to the surface of the pellet, in agreement with where the Pt-metal was preferentially located and coking was known to have occurred.     

Topochemical Engineering of Cellulose—Carboxymethyl Cellulose Beads: A Low-Field NMR Relaxometry Study

The demand for more ecological, highly engineered hydrogel beads is driven by a multitude of applications such as enzyme immobilization, tissue engineering and superabsorbent materials. Despite great interest in hydrogel fabrication and utilization, the interaction of hydrogels with water is not fully understood. In this work, NMR relaxometry experiments were performed to study bead–water interactions, by probing the changes in bead morphology and surface energy resulting from the incorporation of carboxymethyl cellulose (CMC) into a cellulose matrix. The results show that CMC improves the swelling capacity of the beads, from 1.99 to 17.49, for pure cellulose beads and beads prepared with 30% CMC, respectively. Changes in water mobility and interaction energy were evaluated by NMR relaxometry. Our findings indicate a 2-fold effect arising from the CMC incorporation: bead/water interactions were enhanced by the addition of CMC, with minor additions having a greater effect on the surface energy parameter. At the same time, bead swelling was recorded, leading to a reduction in surface-bound water, enhancing water mobility inside the hydrogels. These findings suggest that topochemical engineering by adjusting the carboxymethyl cellulose content allows the tuning of water mobility and porosity in hybrid beads and potentially opens up new areas of application for this biomaterial.     

Physico-chemical characterization of biochars from vacuum pyrolysis of South African agricultural wastes for application as soil amendments

The physico-chemical properties of biochars from the vacuum pyrolysis of black wattle and vineyard annual prunings were investigated for their potential as soil amendments and compared to biochar from sugar cane bagasse. Biochar from sugar cane bagasse seems to be a promising sorbent and soil conditioner due to its high surface area, high surface acidity and microporous structure. This biochar can be applied to a wide pH range of soils for enhancing nutrient and water retention. On the other hand, the biochars from black wattle and vineyard possessing high concentrations of aromatic carbon, nutrients, and alkalinity are potential soil amendment agents. Black wattle biochar is more beneficial compared to biochar from vineyard due to its higher surface area, microporosity and cation exchange capacity. Therefore, this study recommends the utilization of biochars from black wattle as soil amendment agents especially in subtropical regions.     

Enclosed volume determination of concentrated dioctadecyldimethylammonium chloride (DODAC) vesicular dispersions by low-resolution proton NMR diffusometry and T2 relaxometry

The enclosed volume of concentrated dioctadecyldimethylammonium chloride (DODAC) dispersions has been determined by means of low-resolution NMR pfg-diffusometry and T(2) relaxometry. The pfg-NMR diffusometry method is based on the different diffusion behaviors of water in the external and internal phases and as such does not require the addition of a tracer. On the other hand, T(2) relaxometry is based on the different relaxation behaviors of water fractions upon addition of manganese chloride as external (paramagnetic) probe. It was noticed that reliable results are found only for temperatures below the phase transition temperature of DODAC, when the exchange between the two water compartments can be neglected. At 5 °C, these two independent methods resulted in similar enclosed volume values, meaning that the results are reliable and reflect the real enclosed volume. In addition, the T(2) relaxometry method has been proven to be useful in the investigation of the DODAC membrane permeability.     

Physicochemical characterization of chemical hydrogels based on PVA

In this paper, we report on the physicochemical characterization of hydrogels recently obtained by crosslinking poly (vinylalcohol), PVA, with telechelic PVA (telPVA, bearing terminal aldehydic groups) via acetalization in aqueous solution. These gels were studied by equilibrium swelling, compression modulus measurements, and proton relaxometry experiments. Swelling and compression modulus data allow to estimate the average molecular weight of PVA chain between crosslinks, the average mesh size of the networks, and the polymer–solvent interaction parameter χ₁. The average mesh size of PVA‐telPVA compares well with domain dimensions of diffusionally confined water as detected by NMR relaxometry. Proton relaxometry also showed different network domains in which water is compartmentalized, indicating a complex heterogeneity. The study of the temperature behavior of the nuclear spin–spin relaxation times of the confined water was also considered. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1225–1233, 1999     

Standardizing the use of fast-field cycling NMR relaxometry for measuring hydrological connectivity inside the soil

Hydrological connectivity inside the soil (HCS) is applied to study the effects of heterogeneities in complex environmental systems. It refers to both the spatial patterns inside the soil (i.e., structural connectivity [SC]) and the physical–chemical processes at a molecular level (i.e., functional connectivity [FC]). NMR relaxometry has been already applied to assess both SC and FC components of the HCS by defining SC and FC indexes. Here, fast-field cycling NMR relaxometry has been applied on a water suspended soil and a sediment to optimize the conditions to standardize the technique. Proton Larmor frequencies (ω_L) from 0.01 to 25 MHz were used on samples suspended in three different rates of Milli-Q grade water. The application of different magnetic fields revealed that the T₁ values of the sediment sample are always shorter than those measured for the soil sample. This difference was attributed to the soil erosion processes limiting FC by reducing the size of macropores. For the soil sample, analyses showed that both structural and functional connectivity indexes can be assumed ω_L independent. For the sediment sample, the connectivity indexes resulted ω_L independent only for ω_L ≥ 0.1 MHz. This could be due either to instrumental problems for ω_L < 0.1 MHz or to a real magnetic field effect when a finer textured sample is examined. Further research is required in this area. Finally, the experiments revealed that the optimal water amount to obtain reliable results was corresponding to the water holding capacity.     

Chemical origins of permanent set in a peroxide cured filled silicone elastomer - tensile and H NMR analysis

The aging of a commercial filled siloxane polymeric composite in states of high stress and Co-60 γ-radiation exposure has been studied. DC-745 is a commercially available silicone elastomer consisting of dimethyl, methyl-phenyl, and vinyl-methyl siloxane monomers crosslinked with a peroxide vinyl specific curing agent. It is filled with ∼ 30 wt.% mixture of high and low surface area silicas. This filled material is shown to be subject to permanent set if exposed to radiation while under tensile stress. Tensile modulus measurements show that the material becomes marginally softer with combined radiation exposure and tensile strain as compared to material exposed to radiation without tensile strain. In addition, the segmental dynamics as measured by both uniaxial NMR relaxometry and Multiple Quantum NMR methods indicate that the material undergoes radiatively-induced crosslinking in the absence of tensile strain. In the presence of tensile strain, relaxometry and MQ NMR studies show a strain dependent change in the dynamic order parameter and in the number of polymer chains associated with the filler surface. Solvent swelling measurements indicated no dependence on network crosslink density on strain ratio. Variable tau CPMG echo experiments indicate that a fraction of the polymer chains diffuses through areas of strong magnetic field gradients both at the filler-polymer interface and adjacent to micro-voids within the network. The population of the polymer chains influenced by the field gradients was observed to be dependent on the cumulative dose and degree of tensile strain applied during exposure. The relative change in crosslink density from the NMR and solvent swelling data deviates from that predicted from the Tobolsky model, particularly at higher doses. The likely reasons for this deviation are changes in the filler-polymer interface, increasing deviation from Gaussian chain statistics, and/or the formation of increased numbers of elastically ineffective network chains.     

129Xe NMR Studies of Pecan Shell-Based Biochar and Structure-Process Correlations

Pecan shell-based biochar is utilized as a filtration medium, sequestrant for metallic ions, soil conditioner, and other applications. One process for creating the biochar involves the use of phosphoric acid at high temperature in a partial oxygen atmosphere to produce a highly porous carbonaceous material. In this work, we found ¹²⁹Xe NMR to be an excellent technique to study micropores in biochar. Thus, the ¹²⁹Xe chemical shift in biochar was found to vary linearly with the xenon pressure; from the data an estimate of about 8–9 Å could be proposed for the average pore diameter in pecan shell-based biochar. Through saturation recovery and 2-D NMR exchange experiments, information on the exchange between free versus bound xenon was obtained. Furthermore, correlations of ¹²⁹Xe NMR data with the carbonization process conditions were made.     

Wettability and surface composition of partly and fully regenerated cellulose thin films from trimethylsilyl cellulose

The wettability and surface free energy (SFE) of partly and fully regenerated cellulose model surfaces from spin coated trimethylsilyl cellulose were determined by static contact angle (SCA) measurements. In order to gain detailed insight into the desilylation reaction of the surfaces the results from SCA measurements were compared with data from other surface analytical methods, namely thickness measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). Additionally, the influence of ultra high vacuum treatment (UHV) during XPS measurements on the water wettability and surface morphology of regenerated cellulose thin films was investigated. The wetting of polar and non-polar liquids increased with prolonged regeneration time, which is reflected in the higher SFE values and polarities of the films. After UHV treatment the water SCA of partly regenerated films decreases, whereas fully regenerated cellulose shows a higher water SCA. Therefore it is assumed that volatile desilylation products tend to adsorb on partly regenerated films, which strongly influences their wettability.     

Effect of biochar particle size on water retention and availability in a sandy loam soil

The ability of biochar to enhance the physical and hydrological properties of light textured soils is highly dependent on the characteristics of biochar including its particle size. To investigate the effect of biochar particle size on water characteristics and soil structure of a sandy loam soil, date palm biochar prepared at a pyrolysis temperature of 450–500 °C was fractioned by dry sieving into four sizes: 2–1, 1–0.5, 0.5–0.1, and <0.1 mm, and mixed in soil pots with a sandy loam soil at an application rate of 4%. The soil pots were incubated in a greenhouse for 120 days, and water content was kept at field capacity throughout the experiment. Water retention, hydraulic conductivity, and soil structure parameters were measured. Results showed that the largest increase in both water content at field capacity and available water content was observed with the smallest biochar particle size due to increased microporosity as a result to the larger internal surfaces and the porous structure of the biochar particles. Condense particle packing and increased tortuosity due to increased microporosity resulted in a reduction in saturated hydraulic conductivity and bulk density of the soil and biochar mixtures. Soil structure was improved in the soil and biochar mixtures at all biochar particle sizes, nevertheless, no significant increase in soil structures was observed among biochar particle sizes < 1 mm. The application of biochar with particle sizes < 1 mm can enhance the physical and hydrological properties of light textured soils and increase water conservation in the soil, which will help to reduce the amount of water required for irrigation. However, assessment under field conditions is required to assess the long-term effect of biochar on water characteristics and soil structure.     

Effect of biochar on the mobility and photodegradation of metribuzin and metabolites in soil‒biochar thin-layer chromatography plates

Biochars obtained by biomass pyrolysis have been proposed as a soil amendment to improve soil properties and fertility as well as to retain pesticides and other environmental contaminants. The present study investigates the degradation of metribuzin herbicide and its metabolites deamino- (DA), deaminodiketo- (DADK) and diketo- (DK) metribuzin under simulated solar light and dark conditions as well as their mobility using TLC plates coated with soil and soil?biochar mixtures at 1% and 5% w/w ratio. Biochar was characterised by X-Ray diffraction, porosimetry, scanning electron microscopy and Fourier transform infrared spectroscopy. Degradation under light conditions followed biphasic kinetics, with bi-exponential model fitted better for the soil substrate, while the Gustafson–Holden model was found more appropriate to describe degradation kinetics in 1% soil/biochar mixture. In soil, DA presented the lowest degradation rate (DT₅₀:440.9 h), followed by metribuzin (DT₅₀:208.0 h), DADK (DT₅₀:110.8 h) and DK (DT₅₀:106.5 h). The addition of biochar reduced drastically the degradation or even inhibited the photolytic process for the studied reaction period. The mobility retention factor (Rf) in soil ranged from 0.49 for metribuzin to 0.63 for DADK. The addition of biochar practically immobilises the compounds in the surface layer as Rf ranged from 0.14 to 0.10 for metribuzin and from 0.23 to 0.16 for DADK in soil/biochar mixtures 1% and 5%, respectively. In conclusion, the addition of biochar reduced dramatically the photodegradation rates as well as the mobility of metribuzin and its metabolites due to increased adsorption.     

Pore morphology of porous polymer particles probed by NMR relaxometry and NMR cryoporometry

The pore size distribution (PSD) and pore connectivity (PC) within porous polymer particles are probed by combining NMR cryoporometry and NMR relaxometry (spin-spin relaxation). With water as a probe molecule, the constant K in the so-called Gibbs-Thompson equation and the surface relaxivity (rho2) were determined to be K = (420 +/- 50) KA and rho2 = (0.44 +/- 0.01) x 10(-6) ms(-1), respectively. Also, the thickness of the interface layer was estimated to be of the order of one monolayer of water molecules. A detailed analysis of the complete set of NMR data enabled the morphology or pore structure to be probed, and is thoroughly discussed in the text.     

NMR study of the nanomorphology in thin films of polymer blends used in organic PV devices: MDMO‐PPV/PCBM

The disclosure of the nanomorphology of thin films in organic solar cells, prepared from blends of conjugated polymers and PCBM, is of key importance for a better understanding of the occurring photovoltaic (PV) mechanisms. Hereto solid‐state NMR relaxometry has been evaluated as a complementary technique to traditional microscopic techniques like atomic force microscopy and transmission electron microscopy. It is demonstrated that proton wide‐line solid‐state NMR relaxometry is a useful and innovative tool to study the phase morphology of blends used in semi‐conducting polymer based PV devices. Attention is focused on the influence of the blend composition and casting conditions on the resulting phase morphology. Two different casting techniques, i.e. spincoating and Doctor Blading, were compared. To demonstrate the applicability of NMR relaxometry in this field, MDMO‐PPV/PCBM blends where used, since these are known for their significant phase separation behavior in combination with toluene as solvent. In films prepared from blends in toluene with a PCBM content ≥70 wt %, a fraction of the PCBM is phase separated into crystalline domains, whereas the remaining part remains homogeneously mixed with the MDMO‐PPV. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 138–145, 2008     

Multi-scale approach continuously relating the microstructure and the macroscopic mechanical properties of plaster pastes during their settings

A new multi-scale experimental approach is proposed to continuously relate the microstructure and the macroscopic mechanical properties of plaster pastes during their settings. (1)H NMR relaxometry is used to follow continuously and not destructively, the degree of hydration and the microstructure evolution during the setting and hardening of plaster paste. Transmission of shear and compressional ultrasonic velocities enable the determination of macroscopic mechanical properties of the material during the setting. On the basis of similar behaviors of Young's modulus and NMR-population of confined water as function of the degree of hydration, we conclude that NMR gives a better understanding of the evolution of the microstructure at the origin of a better control of the macroscopic mechanical properties.     

超疏水性表面在冷凝条件下的润湿特性

采用测量接触角和观测偏光显微镜对超疏水表面在冷凝条件下的疏水特性进行了研究, 发现冷凝蒸汽进入超疏水表面的微凸起内冷凝, 表面的疏水特性被破坏, 表面的润湿特性变得不均匀, 部分区域甚至呈现亲水状态. 根据实验结果提出了冷凝条件下粗糙表面表观接触角的计算模型, 并使用冷凝条件下表面接触角的测量结果进行了验证.     

Mechanisms of Enhanced Oil Recovery by Surfactant-Induced Wettability Alteration

Different measurements were conducted to study the mechanisms of enhanced oil recovery (EOR) by surfactant-induced wettability alteration. The adhesion work could be reduced by the surfactant-induced wettability alteration from oil-wet conditions to water-wet conditions. Surfactant-induced wettability alteration has a great effect on the relative permeabilities of oil and water. The relative permeability of the oil phase increases with the increase of the water-wetness of the solid surface. Seepage laws of oil and water are greatly affected by surfactant-induced wettability alteration. Water flows forward along the pore wall in the water-wet rocks and moves forward along the center of the pores in the oil-wet rocks during the surfactant flooding. For the intermediate-wet system, water uniformly moves forward and the contact angle between the oil–water interface and the pore surface is close to 90°. The direction of capillary force is consistent with the direction of water flooding for the water-wet surface. While for the oil-wet surface, the capillary force direction is opposite to the water-flooding direction. The highest oil recovery by water flooding is obtained at close to neutral wetting conditions and the minimal oil recovery occurs under oil-wet conditions.     

Experimental investigation on wetting mechanism for coal dust with different metamorphic degree based on infrared spectrum and 13C-NMR

Respirable coal dust accounts for heart and respiratory diseases of coal miners such as asthma, pneumoconiosis, and black lung disease. What is more, coal dust explosion seriously affects coal mine safety production and coal miners' life safety. Generally, dust suppressants are commonly applied in coal mines. However, current dust suppressants are not working effectively. To develop a better dust suppressant, we attempt to explore the factors affecting the wettability of coal dust under different metamorphic levels from the essence of coal dust wetting mechanism in this paper. Specifically, we use Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) to reveal the microstructure of coal from two aspects of functional group and carbon skeleton structure and obtain the micro information of the surface functional group types, quantity, and carbon structure of coal with different degrees of metamorphism, as well as the change rule of functional group of coal sample with coal rank and the law of carbon increase and deoxidization of coal metamorphism. After that, we acquired the structural parameters of coal by the NMR experiments and fitted the quantitative mathematical relationship between the microstructure parameters and wettability of coal through SPSS and ORIGIN software. Finally, this paper constructs an evaluation model for the influencing factors of coal dust wettability, explains the influence degree of different coal dust structure on coal dust wettability, improves the coal dust wettability mechanism, and provides more quantitative research ideas and methods for the control of coal dust.     

Dynamics of hyaluronan aqueous solutions as assessed by fast field cycling NMR relaxometry

Fast field cycling (FFC) NMR relaxometry has been used to study the conformational properties of aqueous solutions of hyaluronan (HYA) at three concentrations in the range 10 to 25 mg mL^–1. Results revealed that, irrespective of the solution concentration, three different hydration layers surround hyaluronan. The inner layer consists of water molecules strongly retained in the proximity of the HYA surface. Because of their strong interactions with HYA, water molecules in this inner hydration layer are subject to very slow dynamics and have the largest correlation times. The other two hydration layers are made of water molecules which are located progressively further from the HYA surface. As a result, decreasing correlation times caused by faster molecular motion were measured. The NMRD profiles obtained by FFC-NMR relaxometry also showed peaks attributable to ¹H–¹⁴N quadrupole interactions. Changes in intensity and position of the quadrupolar peaks in the NMRD profiles suggested that with increasing concentration the amido group is progressively involved in the formation of weak and transient intramolecular water bridging adjacent hyaluronan chains. In this work, FFC-NMR was used for the first time to obtain deeper insight into HYA–water interactions and proved itself a powerful and promising tool in hyaluronan chemistry.