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The 2010 Deepwater Horizon oil release posed the challenges of two types of spill: a familiar spill characterized by buoyant oil, fouling and killing organisms at the sea surface and eventually grounding on and damaging sensitive shoreline habitats, and a novel deepwater spill involving many unknowns. The subsurface retention of oil as finely dispersed droplets and emulsions, wellhead injection of dispersants, and deepwater retention of plumes of natural gas undergoing rapid microbial degradation were unprecedented and demanded the development of a new model for deepwater well blowouts that includes subsurface consequences. Existing governmental programs and policies had not anticipated this new theater of impacts, which thereby challenged decisionmaking on the spill response, on the assessment of natural resource damages, on the preparation for litigation to achieve compensation for public trust losses, and on restoration. Modification of laws and policies designed to protect and restore ocean resources is needed in order to accommodate oil drilling in the deep sea and other frontiers.

Flotation beneficiation of ores containing fibrous minerals is highly problematic due to transport of such gangue minerals from pulp to the froth phase. Earlier studies have attributed such transport to the entrainment of fibrous minerals. In this work, this problem is investigated for the case of flotation of ultramafic Ni ore with fibrous serpentines (Mg silicates) interfering with their separation. Serpentines are proposed to form large (~ 1–2 cm) networks in pulp and thus unlikely to be transported by entrainment. Various simulation based studies suggest that the networks are stable under the dynamic flotation conditions. Furthermore, the pores in the networks are relatively small (e.g.

Abiotic and biotic processes catalyzed by ferric (hydr)oxide nanoparticles (NPs) in aquatic media underlie many important nanotechnologies including chemical catalysis, biomedical engineering, remediation of contaminants, and clean renewable energy sources. These processes have been extensively addressed in the past and commonly interpreted within the so-called chemical paradigm neglecting semiconducting properties of the NPs. Using batch kinetic measurements coupled with X-ray photoelectron spectroscopy (XPS) as well as a new method that combines in situ FTIR spectroscopy and ex situ XPS, we study the effect of size on the catalytic oxygenation of Mn(II) in the presence of hematite (α-Fe2O3) and ferrihydrite NPs. We find that oxidative catalytic performance of these NPs degrades with decreasing their size. Using Density Functional Theory (DFT) modeling, we show that this unusual trend cannot be rationalized within the traditional chemical paradigm. Given the nanosize-induced changes in the electronic properties of ferric (hydr)oxides and the thermodynamic properties of the system, we demonstrate that the catalytic reaction proceeds through the electrochemical pathway. The new mechanistic insights suggest new interpretation of literature data, open up new possibilities for manipulating technological performance of metal oxides, and conceptually broaden our general understanding of (bio)chemical activity of NPs.

The interaction of iron (hydr)oxides with fatty acids is related to many industrial and natural processes. To resolve current controversies about the adsorption configurations of fatty acids and the conditions of the maximum hydrophobicity of the minerals, we perform a detailed study of the adsorption of sodium laurate (dodecanoate) on 150 nm hematite (α-Fe(2)O(3)) particles as a model system. The methods used include in situ FTIR spectroscopy, ex situ X-ray photoelectron spectroscopy (XPS), measurements of the adsorption isotherm and contact angle, as well as the density functional theory (DFT) calculations. We found that the laurate adlayer is present as a mixture of inner-sphere monodentate mononuclear (ISMM) and outer-sphere (OS) hydration shared complexes independent of the solution pH. Protonation of the OS complexes does not influence the conformational order of the surfactant tails. One monolayer, which is filled through the growth of domains and is reached at the micellization/precipitation edge of laurate, makes the particles superhydrophobic. These results contradict previous models of the fatty acid adsorption and suggest new interpretation of literature data. Finally, we discovered that the fractions of both the OS laurate and its molecular form increase in D(2)O, which can be used for interpreting complex spectra. We discuss shortcomings of vibrational spectroscopy in determining the interfacial coordination of carboxylate groups. This work advances the current understanding of the oxide-carboxylate interactions and the research toward improving performance of fatty acids as surfactants, dispersants, lubricants, and anticorrosion reagents.

Nanotechnology has influenced the direction of research across the sciences, medicine, and engineering. Carbon nanotubes (CNTs) and, more recently, protein nanotubes (PNTs) and protein-inorganic nanocomposites have received considerable attention due to their unique nanostructures that can be utilized as a scaffold to house proteins or create nanowires. A shift towards protein-inorganic interactions has numerous applications from biosensors to biofuel cells and bio-based nanodevices. We examine several systems where protein hot spots, the active domains on proteins and the interactive dynamics in them, play a critical role in the interactions at the interface of these unique systems.

Coadsorption of electrolyte ions can have a marked influence on the adsorption and hence interfacial reactivity of multicharged ions but has generally been overlooked in previous density functional...

The addition of a small amount of surfactants enhances hydrocarbon enclathration rates without any mechanical agitation, but the role of surfactants has yet to be clarified. This work presents the effect of sodium dodecyl sulfate (SDS) on the water structure around cyclopentane (CP), a sII hydrate former, at the hydrate−water interface. The arrangement of local water molecules was obtained using surface-enhanced Raman spectroscopy (SERS). The Raman spectra reveal that the water structure around CP at the water−hydrate interface is identical to the hexakaidecahedron (51264) cavity of sII hydrates at a SDS concentration higher than 0.087 mM. However, at the CP−water interface, with and without SDS, the water arrangement is clathrate-like. Additionally, we found that the microenvironment of CP in bulk aqueous solutions is close to that in hydrates at a SDS concentration higher than 0.35 mM.

Nanoparticles have been widely applied in many applications due to their specific physical or chemical properties that differ from the bulk counterparts. Because nanoparticles vary significantly in composition and geometry, the comparison of their interaction with another matter is difficult, although in many cases, to characterize and assort nanoparticles in a quantified way is highly desired. Among the many properties of nanoparticles, the surface energy is especially important in evaluating their potential affinity to the environment. Pretty elegant techniques have been developed to evaluate the surface energy of pure metal oxides. However, heating or acid treatment would destroy the real surface conditions, for example, organic coatings outside of the particles. An effective method has to be developed to determine the surface energy of the as-received natural particles, whether they are pure, contaminated, or prehydrated. We designed a technique to quantitatively evaluate the surface energy of the as-...

This work presents the adsorption of an anionic surfactant, sodium dodecyl sulfate (SDS), and a cationic one, dodecyl-trimethylammonium bromide (DTAB), on cyclopentane (CP) hydrates. Adsorption isotherms were obtained by liquid−liquid titrations. Also, the adsorption was qualitatively studied by zeta potential measurements. The isotherm of both SDS and DTAB exhibits a two-plateau (L-S) type. The saturated adsorption amount in the first step (Langmuir type) is 0.01 and 0.03 mmol g−1 for SDS and DTAB, respectively. The Langmuir equilibrium constant is 1.17 mM−1 for SDS and 0.32 mM−1 for DTAB. The maximum adsorption amount of SDS in the second step (S type) is 2.5 times higher than that in the Langmuir step. The similar trend is observed for DTAB. SDS adsorption shifts the zeta potential from −60 to −90 mV in the first step, followed by a further 30 mV decrease as the adsorption approaches the second plateau. For DTAB, the zeta potential increases from −60 to 50 mV in the Langmuir step and then it approaches...

Interactions of polymers with salts are of primary importance in industry as well as scientific research. In this paper, we focus on the system of poly(acrylic acid) (PAA) in concentrated sodium carbonate aqueous solutions. From the results obtained by density, static/dynamic light scattering, conductivity, and rheometry, the size/shape of single polymer chains, their effective hydrodynamic region, and the condensation of ionic species were evaluated as a function of salt and PAA concentrations. The formation of special morphological structures of PAA chains in solution and the resultant rheological behavior of the solutions were also examined.

Adsorption, contact angle and flotation of anionic Atrac and non-ionic ethaloxylated nonylphenol surfactant, and their mixture on apatite and magnetite were studied. The effect of calcium ions and sodium silicate on Atrac adsorp- tion was investigated. The effect of Atrac adsorption on the contact angle data of apatite and magnetite in the presence and absence of sodium silicate was also examined. Wettability of solids depends on solids surface free energy and the surface energies of apatite and magnetite powders were calculated from polar and non-polar liquid contact angle data. A decrease in particle size increased the polar contribution to surface free energy due to unsaturated broken bonds on the surface. Atrac is seen to adsorb equally on apatite and magnetite, and the adsorption increased in the presence of calcium ions. The presence of water glass decreased the Atrac contact angle data on magnetite and also the flotation response demonstrating its role as magnetite depressant in flotation. The presence of non-ionic surfactant enhanced the Atrac flota- tion of apatite with no flotation of magnetite. Bench-scale flotation tests showed that 50% of Atrac can be replaced with non-ionic collector without impairing the flotation results. Results also illustrate that the non-ionic adsorbs on apatite in equal amount of Atrac collector signifying 1:1 composition of anionic and non-ionic collector on apatite surface. Non- ionic head group sitting in between anionic head groups screens the electrostatic repulsion and forms compact adsorbed layer on apatite surface thereby increasing the hydrophobicity and flotation.

Comb polymers are commonly used as dispersants to stabilize highly concentrated cement suspensions. The effectiveness of such polymeric additives to stabilize these suspensions is determined to a large extent by the amount adsorbed. In this study we investigated the adsorption characteristics of various comb dispersant containing different graft densities on surfaces of cement particle. The effect of inorganic salts on their adsorption was also examined in order to elucidate their adsorption mechanism. The results show that the adsorption of comb polymer dispersants on cement surface conforms approximately to Langmuir's adsorption isotherm and the characteristic plateau A s and adsorption free energy ΔGads are largely dependent on the anionic group content of the comb polymers. The A s and ΔGads increase with increasing anionic group content. This information suggests that the adsorption of comb polymers on cement surfaces is dominated by electrostatic interaction between COO-groups on the comb polymers a...

The shape of deposits obtained from drying drops containing colloidal particles matters for technologies such as inkjet printing, microelectronics and bioassay manufacturing. In this work, the formation of deposits during the drying of nanoliter drops containing colloidal particles is investigated experimentally with microscopy and profilometry, and theoretically with an inhouse finite-element code. The system studied involves aqueous drops containing titania nanoparticles evaporating on a glass substrate. Deposit shapes from spotted drops at different pH values are measured using a laser profilometer. Our results show that the pH of the solution influences the dried deposit pattern, which can be ring-like or more uniform. The transition between these patterns is explained by considering how DLVO interactions such as the electrostatic and van der Waals forces modify the particle deposition process. Also a phase diagram is proposed to describe how the shape of a colloidal deposit results from the competition between three flow patterns: a radial flow driven by evaporation at the wetting line, a Marangoni recirculating flow driven by surface tension gradients, and the transport of particles towards the substrate driven by DLVO interactions. This phase diagram explains three types of deposits commonly observed experimentally, such as a peripheral ring, a small central bump, or a uniform layer. Simulations and experiments are found in very good agreement.

Surfactants find wide commercial use as foaming agents, emulsifiers, and dispersants. Currently, surfactants are produced from petroleum, or from seed oils such as palm or coconut oil. Due to concerns with CO(2) emissions and the need to protect rainforests, there is a growing necessity to manufacture these chemicals using sustainable resources In this report, we describe the engineering of a native nonribosomal peptide synthetase pathway (i.e., surfactin synthetase), to generate a Bacillus strain that synthesizes a highly water-soluble acyl amino acid surfactant, rather than the water insoluble lipopeptide surfactin. This novel product has a lower CMC and higher water solubility than myristoyl glutamate, a commercial surfactant. This surfactant is produced by fermentation of cellulosic carbohydrate as feedstock. This method of surfactant production provides an approach to sustainable manufacturing of new surfactants.

The specificity exhibited by Acidithiobacillus ferrooxidans, a chemolithoautotrophic acidophile, in their attachment to different sulphide minerals has resulted in effective physical separation of these minerals. This can be explained in terms of surface forces of interaction between the cells and substrates using AFM. In the light of this, the present study reports interaction studies with A. ferrooxidans cells and an AFM silicon nitride tip. The aim of the present investigation is to probe the nanoscale interactions between A. ferrooxidans cells and silicon nitride tip of an AFM, model the approach and retraction forces, and elucidate the effects of pH, ionic strength and surface biopolymers on interfacial forces.

Settling tests are normally carried out for short durations to study dewatering characteristics of materials. Natural gravitational settling and associated consolidation processes continue for longer periods before a substantially stable structure is attained. For example, the structural stabilization of a tailing dam involving fine particulates continues for years. To simulate the conditions of gravitational stabilization of particulate materials in the presence of polymers, in this investigation batch settling trials were carried out for prolonged durations with the model colloidal alumina and polyacrylic acid (PAA) flocculants of different molecular weights. It is observed that a critical molecular weight exists where superior flocculation and consolidation performances are observed due to synergistic effects of charge neutralization and bridging. Based on the interesting findings, it is suggested that the design of an optimum dewatering reagent scheme need not be based on short duration sedimentation and/or filtration trials alone. The long-term gravitational stabilization behaviour is an important area of concern from environmental and safety points of view and should be appropriately addressed.

The relative arrangement and interaction of the cationic butane-1,4 bis(dodecyl dimethyl ammonium chloride) gemini (12–4–12) with nonionic sugar-based surfactant n-dodecyl-β- d -maltoside (DM) was studied by NMR techniques. It is shown that the methylene group next to the ammonium head in the gemini is close to the penultimate sugar ring of DM in their mixed micelles, and the hydrophobic chain of DM molecule and the two hydrophobic chains of 12–4–12 gemini are side by side in the interior of the micellar core. The size of the mixed micelles is largely dependent on the DM composition at fixed total surfactant concentrations. At fixed DM concentration, the interaction between DM and 12–4–12 gemini increases gradually with decrease in DM/12–4–12 ratio from 1:1 to 1:4. At higher 12–4–12 gemini ratios of 1:6 and 1:8.5, the intermolecular interaction starts to decrease gradually, implying the intramolecular interaction is more dominant than intermolecular interactions in the mixed micelles. NMR results suggest that relatively strongest intermolecular interactions in the mixed micelles of DM and 12–4–12 gemini exist at DM/12–4–12 mixing ratio of 1:4.

Characterisation of particle tribo-charging and electron transfer with reference to eloectrostatic dry coal cleaning

Adsorption behavior of cationic C 12 - C 4 - C 12 gemini surfactant on silica has been investigated, along with that of nonionic surfactant n-dodecyl-β- d -maltoside (DM). While DM alone shows meager adsorption on silica, because of the lack of any electrostatic adsorption, cationic gemini adsorbs significantly on the oppositely charged silica surface. Due to the electrostatic nature of cationic gemini adsorption on silica, solution pH affects adsorption of C 12 - C 4 - C 12 gemini dramatically. Meanwhile, C 12 - C 4 - C 12 gemini hemimicelle size at silica/water interface does not seem to change with solution pH. For the mixtures of DM and cationic C 12 - C 4 - C 12 gemini, there is a sharp increase of DM adsorption at silica/water interface, up to 100 times more than DM alone. After mixing with DM, saturation adsorption of cationic C 12 - C 4 - C 12 gemini decreases, due to competition for adsorption sites from DM. At the same time, in its mixture with DM, there is an increased adsorption of C 12 - C 4 - C 12 gemini in the rising part of the adsorption isotherm. Hydrophobic chain–chain interactions, especially with two hydrophobic chains in one C 12 - C 4 - C 12 gemini molecule, and adsorbed C 12 - C 4 - C 12 gemini molecule acting as an anchor or nucleation sites for forming mixed aggregates with DM on silica surface, are attributed to the marked adsorption synergy between DM and cationic C 12 - C 4 - C 12 gemini. The adsorption of surfactants and their mixtures has a marked effect on silica surface charge and silica's wettability.

The adsorption behavior of a series of nonionic polyoxyethylated nonyl phenol surfactants having same hydrocarbon chain length but varying oxyethylene chain has been studied spectrophotometrically at the silica−cyclohexane interface. The adsorption density is found to be independent of the number of oxyethylene units throughout the adsorption isotherms, except at higher surface coverage, where the adsorption density decreases with the increase in the number of oxyethylene units. The settling rate of the silica particles in cyclohexane decreases with the increase in adsorption density as well as oxyethylene chain length. On the other hand, the sediment volume decreases with the increase in the adsorption density, with a minimum for the surfactant having the least number of oxyethylene units. Surfactants with a longer oxyethylene chain partitions preferentially to the bulk solvent at higher concentrations, as a result of the change in the polarity of the medium. On the basis of adsorption density, settling ...

The effect of the solubilized model drug, carbamazepine, on the internal structure of fully dilutable nonionic microemulsions was examined for the first time using electron paramagnetic resonance (EPR). Systems containing different surfactant to oil ratios, at two different pH values (4.6 and 8.5), with continuous dilution implementing structural transformations (micellar solution-W/O-bicontinuous-O/W) were investigated. The internal order, micropolarity, and microviscosity were scrutinized utilizing pH-dependent amphiphilic probe 5-doxylstearic acid (5-DSA). In the basic environment, the probe explored the vicinity of the surfactant head region; the deeper hydrophobic region of the surfactant tails was investigated in the acidic milieu. The study demonstrated that the EPR technique enables efficient monitoring of structural changes and examination of drug influence on structure in surfactant-poor systems. Lower order and microviscosity values were obtained in surfactant-poor systems in comparison to surfactant-rich systems. The drug functioned as a spacer of the surfactant molecules or as a cosurfactant depending on the formed microemulsion structure and the surfactant to oil ratio. The structural changes, pH variation, and presence of the drug did not alter the polarity parameter, indicating that the probe most likely does not sense a water environment in any of the examined systems. Under the basic conditions, higher microviscosity and order values were obtained in comparison to those at low pH, suggesting a higher order packing of the surfactant chains near the surfactant heads. The structural changes initiated in the vicinity of the surfactant heads, therefore, are more apparent in the basic environment. The ability to control and monitor the intramicellar interactions within drug carrier systems may be of significant interest for understanding the kinetics of drug release.

The interaction between surfactants and hydrates provides insight into the role of surfactants in promoting hydrate formation. This work aims at understanding the adsorption behavior of sodium dodecyl sulfate (SDS) on cyclopentane (CP) hydrates and its derivative surfactant on tetrabutylammonium bromide (TBAB) hydrates. Cyclopentane (CP) is a hydrophobic former whereas tetrabutylammonium bromide (TBAB) is a salt that forms semiclathrate hydrates. The adsorption on these two hydrates was studied by zeta potential and pyrene fluorescence measurements. CP hydrates have a negative surface charge in the absence of SDS, and it decreases to a minimum as the SDS concentration increases from 0 to 0.17 mM. Then, it increases with further increased SDS concentration. The adsorption density of DS (-) on CP hydrates reaches a saturated value at 1.73 mM SDS. The micropolarity parameter of the TBAB hydrate/water interface starts to increase rapidly at 0.17 mM SDS and levels off at 1.73 mM SDS. The presence of Br (-) in TBAB hydrate suspensions could compete with TBADS (from association of DS (-) and TBA (+)) and DS (-) for the adsorption on the hydrate surface, but they have a much stronger affinity for the hydrates than does Br (-). From the fluorescence measurements, it was found that the micropolarity of the hydrate/water interface is mainly dependent on the polarity of hydrate formers.

Understanding the interaction between sodium dodecyl sulfate (SDS) and gas hydrates provides insight into the role of SDS in promoting gas hydrate formation. The aim of this study was to investigate the relationship between tetrahydrofuran (THF) hydrate induction and SDS adsorption at the hydrate/liquid interface. The adsorption behavior was studied by ζ-potential and pyrene fluorescence measurements. The negative charge of the hydrate particles remains constant at SDS concentrations of 0 to 0.17 mM. The ζ-potential becomes more negative as the SDS concentration increases from 0.17 to 3.4 mM. The micropolarity of the THF hydrate/liquid interface decreases with increasing SDS concentrations, and then it remains almost unchanged at SDS concentrations above 0.17 mM. A monolayer of DS− is completed at a SDS concentration of 0.17 mM. The reduction of induction time in the presence of SDS levels off at a SDS concentration of 0.17 mM. This provides strong evidence that the short induction is due to the adsorptio...

Adsorption of surfactants on solids is affected by the intermolecular packing in the adsorbed layer besides the driving forces. The adsorption behavior of a double-chain surfactant on silica is studied here along with that of the single-chain one. Comparison of adsorption of these two surfactants is warranted since while the single-chain surfactants form spherical micelles, the double-chain ones form bilayered vesicles in solution. While the adsorption of the single-chain surfactant reaches the plateau in a wide concentration range, the adsorption of the double-chain one increases sharply in a concentration range 10 −5 mol/L up to the plateau. The single chain is found to form ∼1.5 monolayers under saturation coverage suggesting adsorption with reverse orientation at high concentration. In contrast, the adsorption of the double-chain surfactant under saturation coverage is equivalent to a ∼0.9 monolayer. Fluorescence tests revealed the hydrophobicity change of the surface with increase in adsorption. However, the hydrophobicity tests show the solid surface to be hydrophilic in this range; the double-chain surfactant is proposed to form a partial bilayer.

Microstructures of the micelles of cationic surfactants, dodecyltrimethyl ammonium chloride (DTAC), alkane-bis(dodecyl dimethyl ammonium chloride) (12-4-12 and 12-8-12 geminis) in aqueous solutions, as well as the mixed micelles of their mixtures respectively with nonionic sugar-based surfactant n-dodecyl-β- d -maltoside (DM) were studied using NMR by 1H chemical shift, self-diffusion coefficient, spin–spin and spin–lattice relaxation time, and two-dimensional nuclear Overhauser enhancement (2D NOESY). In individual aqueous solution, 12-8-12 gemini molecules seem to be tighter packed in the micelles than 12-4-12 gemini, and DTAC molecules are looser packed than both gemini surfactants in the micelles. Calculated hydration dynamics radii indicate that DTAC is the largest in size, while 12-8-12 gemini is the smallest. It is suggested that in the mixed micelles of DM and cationic surfactant, all three cationic surfactants studied give similar relative molecular arrangement to DM, with the methylene group next to the ammonium head in the near vicinity of penultimate sugar ring. The short intermolecular distance between the two headgroups of surfactants in their mixed micelles, evidenced by the existence of intermolecular cross-peaks in 2D NOESY spectrum, implies attractive interactions between DM and these cationic surfactants. The interactions between DM and 12-4-12, and 12-8-12 geminis are stronger than that of DM and DTAC, and increase in spacer length of cationic gemini from 12-4-12 to 12-8-12 results in increased interactions with DM in their mixed micelles.

Nature exhibits a variety of remarkable phenomena that are useful but difficult to imitate in real life. Examples are the “touch me not” plant (Mimosa pudica), which folds up upon being attacked, or microbes that deposit on ocean vessels even under hostile conditions. Understanding the mechanisms governing these phenomena can prove powerful for developing new classes of cosmetic products. This article examines the development of novel materials with functional properties such as controlled delivery and the deposition of sensory attributes (fragrances, flavors, etc.) desirable in cosmetic products. Particularly, systems based on polymer/surfactant chemistry are explored for achieving transport and release of cosmetic and pharmaceutical molecules at desired rates. The hybrid polymers and nanogel particle systems discussed here represent new classes of materials with nanodomains that can be tuned to extract and deliver cosmetic attributes by means of changes in natural parameters such as temperature and pH. While the safety of existing nanomaterials marketed for decades has not been an issue, methods are urgently needed to validate the toxicological safety of future nanomaterials.

Nuclear magnetic resonance (NMR) spectroscopy is a versatile technique at a molecular level for the study of surfactants. Mixed micellization of nonionic sugar-based surfactant n-dodecyl-β-d-maltoside (DM) and cationic surfactant octane-1,8 bis(dodecyl dimethyl ammonium chloride) gemini (12-8-12) was studied using NMR by self-diffusion coefficient, spin–spin and spin–lattice relaxation time, and two-dimensional nuclear Overhauser enhancement (2D NOESY). NMR results reveal the relative arrangement of the surfactant molecules in the mixed micelles. It is shown that the methylene group next to the ammonium head is in the near vicinity of penultimate sugar ring, and the hydrophobic chain of DM molecule and the two hydrophobic chains of 12-8-12 gemini are side by side in the interior of the micellar core. At fixed total surfactant concentrations of DM and 12-8-12 gemini, calculated self-diffusion coefficient suggests that the size of the mixed micelles is largely dependent on the DM concentration, higher the DM concentration, larger the mixed micelles in size. From 2D NOESY maps of mixed micelles, it is found that at fixed DM concentration, surfactant interaction between DM and 12-8-12 gemini in their mixed solutions increases gradually with increase of 12-8-12 gemini concentration from DM/12-8-12 ratio of 1:1–1:3. Interestingly, with further increase of 12-8-12 gemini concentration from DM/12-8-12 ratio of 1:4–1:8, the inter-molecular interaction starts to decrease, which is attributed to the more and more dominant intra-molecular proton–proton dipolar coupling of two surfactant molecules.

Surfactants have been used to enhance the removal of phenol from aqueous system; therefore, the interaction between surfactants and phenol is important for selection of the surfactant and understanding the process. In this work, sugar based surfactant, n-dodecyl-beta-D-maltoside (DM), was utilized to separate phenol from aqueous solution using ultrafiltration. 2-D NMR and Cryo-TEM techniques were employed to obtain information on the orientation of phenol molecules in the micellar phase and the shape transition of the micelles. The flux was found to decrease linearly with the solute concentration and the equilibrium constant was found to be constant. 2-D NMR spectra have shown that phenol molecules reside in the palisade layer of the DM micelles with the benzene ring interacting with the hydrocarbon chain of DM molecules, especially the first methylene group. Cryo-TEM results have shown the shape transition from spherical to worm-like due to the presence of phenol. The results will help understand the interaction between surfactants and phenol and the select the optimum surfactant reagents and operational conditions for micellar enhanced ultrafiltration process.

Knowledge of the shape and size of surfactant micelles in the presence of small organic molecules is important for understanding the solubilization properties of micellar phases. In this work, structural information on micelles of mixed n-dodecyl-beta-d-maltoside (DM) and phenol, including the aggregation number, diffusion coefficient, and effective radius, was obtained using an analytical ultracentrifugation technique. The micelles were found to increase in size and undergo shape transition from quasispherical to cylindrical with an increase in the surfactant and phenol concentrations in the micellar phase. Importantly, the coexistence of different micellar species was observed in certain cases with the larger species double the size of the smaller one. Based on the results obtained, a two-step micellar growth model is proposed to describe the micelles shape transition in the system. In the first step, the micelles expand continuously, whereas in the second step, it undergoes a sudden shift from the existing micellar species to a larger species causing the coexistence of two micellar species. This micellar growth is attributed to molecular packing and intermicellar interaction energy parameters. The mechanism proposed can be applied to other mixed systems and utilized for devising chemicals for the efficient removal of pollutants.

The interaction of a hydrophobically modified anionic polymer (PMAOVE) with a cationic surfactant (DTAB) was studied using a multi-technique approach: turbidity, surface tension, and viscosity measurements, as well as EPR (5-doxyl stearic acid) and fluorescence (pyrene) probe techniques were used. In the investigated pH range (4-10), the cationic surfactant headgroups interact with the anionic carboxylic groups of the polymer backbone. In addition, nonpolar interactions of the surfactant chains with the n-octyl chains of PMAOVE stabilize the PMAOVE-DTAB complexes. Charge neutralization of the anionic polymer by the cationic surfactant leads to precipitation of the PMAOVE-DTAB complex at a certain DTAB concentration range. Further addition of DTAB causes a charge reversal of the complex and, subsequently, resolubilization of the precipitate. At an acidic pH (pH = 4), a second precipitation was observed, which is probably caused by conformational changes in the PMAOVE-DTAB complex. This second precipitate can be resolubilized by further addition of surfactant. At a neutral and basic pH, this second precipitation is absent. EPR analysis indicates that the surfactants form an ordered structure at the extended polymer chain at a neutral and basic pH, whereas at an acidic pH, a less ordered surfactant layer is formed on the coiled polymer with more hydrophobic microdomains.

Guar gum (GG) and locust bean gum (LBG) are two galactomannose polysaccharides with different mannose/galactose ratio which is widely used in many industrial sectors including food, textiles, paper, adhesive, paint, pharmaceuticals, cosmetics and mineral processing. They are natural nonionic polymers that are non-toxic and biodegradable. These properties make them ideal for industrial applications. However, a general lack of understanding of the interactions between the polysaccharides and solid surfaces has hindered wider application of these polymers. In this work, adsorption of locust bean gum and guar gum at the solid-liquid interface was investigated using adsorption tests, electrophoretic mobility measurements, FTIR, fluorescence spectroscopy, AFM and molecular modeling. Electrokinetic studies showed that the adsorption of GG and LBG on talc do not change its isoelectric point. In addition, GG and LBG adsorption on talc was found not to be affected by changes in solution conditions such as pH and ionic strength, which suggests a minor role of electrostatic force in adsorption. On the other hand, fluorescence spectroscopy studies conducted to investigate the role of hydrophobic bonding using pyrene probe showed no evidence of the formation of hydrophobic domains at talc-aqueous interface. Moreover, urea, a hydrogen bond breaker, markedly reduced the adsorption of LBG and GG on talc, supporting hydrogen bonding as an important role. In FTIR study, the changes in the infrared bands, associated with the CO stretch coupled to the CC stretch and OH deformation, were significant and therefore also supporting hydrogen bonding of GG and LBG to the solid surface. In addition, Langmuir modeling of adsorption isotherm further suggested that hydrogen bonding is the dominant force for polysaccharide adsorption since the adsorption free energy of these polymers is close to that for hydrogen bond formation. From molecular modeling, different helical structures are observed for LBG and GG because of their different galactose/mannose ratio and these polymers were found to adsorb flat on solid to let more of its OH groups in contact with the surface. All of the above results suggest that the main driving force for adsorption both of GG and LBG on talc is hydrogen bonding rather than hydrophobic force even though there is difference in G/M ratio between them.

It has been suggested that redissolution of sulfonate/multivalent precipitates occurs by micellar solubilization. The molecular mechanism governing the redissolution process has not been identified. In this study, the solubilization constant, which is an indicator of the capacity of the micelles to solubilize the precipitate, is determined with the aim of elucidating the molecular mechanism involved in the redissolution process. The effects of ionic strength, alkyl chain length, temperature, n-propanol and n-dodecane on the solubilization constant are examined under a variety of conditions. In addition, counter-ion binding to micelles and conductivity of micelles are determined for different sulfonates. Based on all these data, a mechanism involving the adsorption of Ca2+ on the micelle and the subsequent dissolution of calcium disulfonate to replenish the system is proposed to account for the precipitate redissolution.

Heterogeneous electroreduction of CO

The floatability of silica has been determined by adsorbing various concentrations of a series of polyoxyethylated nonyl and octyl alkyl phenols of varying oxyethylene units (10–40 units) to investigate the role of adsorbed layer. It is seen that the floatability of silica increases with increase in concentration till a maximum of ∼ 90% in premicellar region and then decrease to minimum of 40–45% in all cases in spite of the significant differences in adsorption densities. Zeta potential measurement reveals that a thin oxyethylene layer is formed at silica–water interface masking silica surface (Pramila K. Misra, P. Somasundaran, J. Surf. Deterg., Vol. 7, 2004, 373). This layer with oxyethylene units lying on silica surface and alkyl chain dangling to the bulk solution provides the same extent of hydrophobicity. The decrease in flotation recovery has been attributed to increase in the solvent hydrophobicity due to formation of premicellar aggregates and micelles.

A transport theory and supporting experiments are detailed for the adsorption of surfactant from micelle solutions onto a clean air/water interface. The study focuses on adsorption from very dilute solutions consisting of globular aggregates. In the usual mechanism conceived for the adsorption process, when a clean interface is created in the solution of monomer and globular aggregates, monomer initially kinetically adsorbs from the sublayer onto the surface, depleting the sublayer concentration of monomer. This depletion, as it perturbs the micelle/monomer equilibrium, is followed by the disassembly of aggregates in the sublayer (to replenish monomer). Co-currently, aggregates and monomer diffuse from the bulk to the depleted sublayer. Thus in this classical picture, while the micelles provide a reservoir for monomer adsorption by their disassembly – and thereby enhance the adsorption rate – they provide no direct route for adsorption. 14 15 16 17 18 19 20 Using this picture as a starting point, in this study an asymptotic transport theory is constructed for the case in which the time scale for the diffusion of the monomer is much slower than the time scale for the kinetic breakdown of the aggregates. With this separation of time scales, disassembly of micelles takes place only along a boundary separating regions without micelles (micelle-free zones) from regions containing micelles. In the regions containing micelles, the larger rate of disassembly relative to the rate of diffusion of monomer maintains the monomer concentration at the critical aggregate concentration (CCAC). Two regimes arise: in the first, at low aggregate concentrations, micelle diffusion cannot keep up with the kinetic surface adsorption of monomer, and a micelle-free zone emerges from the surface and moves into the bulk. Micelles diffuse from the bulk to the boundary of the zone, break-up and monomer diffuses through the micelle-free zone and kinetically adsorbs onto the surface. In the second regime, at higher aggregate concentrations, the micelle diffusive flux is commensurate with the kinetic rate of monomer surface adsorption, and a micelle-free zone does not form. Micelles diffuse directly to the surface, and break-up in the sublayer; monomer then kinetically adsorbs onto the surface. The adsorption rate is limited only by the kinetics of monomer adsorption since the monomer sublayer concentration is equal to the CCAC, and represents the fastest rate that surfactant can adsorb onto the surface in the absence of diffusion barriers. Numerical solutions are obtained for a polyethoxylated surfactant C14E6 whose micelle disassembly time scale satisfies the requirement that it be faster than the diffusion time scale of the monomer. For C14E6 the monomer adsorption parameters and diffusion coefficient of monomer are obtained from separate dynamic tension measurements below the CCAC; the micelle diffusion coefficient is estimated from the literature. A critical total surfactant concentration of 4.25CCAC is computed, below which a micelle-free zone forms and above which the zone does not form, and surface concentrations and tension reductions as a function of time are simulated for both regimes. 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

Chemical-flooding schemes for recovering residual oil have been in general less than satisfactory due to loss of chemicals by adsorption on reservoir rocks, precipitation, and resultant changes in rock wettability. Adsorption and wettability changes are determined mainly by the chemical structure and mix of the surfactants, surface properties of the rock, composition of the oil and reservoir fluids, nature of the polymers added and solution conditions such as salinity, pH and temperature. The mineralogical composition of reservoir rocks plays an important role in determining interactions between reservoir minerals and externally added reagents (surfactants/polymers) and their effects on solid–liquid interfacial properties such as surface charge and wettability. Some of the reservoir minerals can be sparingly soluble causing precipitation and changes in wettabilty as well as drastic depletion of surfactants/polymers. Most importantly, the effect of surfactants on wettability depends not only how much is adsorbed but also on how they adsorb. A water wetted rock surface that is beneficial for displacement of oil can be obtained by manipulating the orientation of the adsorbed layers. New surfactants capable of tolerating harsh conditions created by extremes of pH, temperature or inorganics and capable of interacting favorably with inorganics and polymers are promising for enhanced oil recovery. In this regard, such surfactants as sugar based ones and pyrrolidones are attracting attention, as they are also biodegradable. In many cases, mixed surfactants perform much better than single surfactants due to synergetic effects and ability to alleviate precipitation. Also, addition of inorganics such as silicates, phosphates and carbonates and polymers such as lignins can be used to control the adsorption and the wettability. In this paper, use of specialty surfactants and their mixtures is discussed along with the mechanisms involved.

Poly(acrylic acid) brushes were prepared on polystyrene-coated glass substrates via physisorption, and a number of techniques (Langmuir–Blodgett technique, X-ray photoelectron spectroscopy, water contact angle measurement, atomic force microscopy) were used to prepare and characterize the brushes. Contact angle measurements showed the polystyrene-coated glass surface to become more hydrophilic after poly(acrylic acid) grafting on it. XPS results confirmed the presence of PAA on the topmost surface of the substrate. From the results of AFM topographic imaging of the surface of PAA brush on PS-coated glass substrate, PAA brushes was found to form bigger and less densely distributed aggregates on the surface with a decrease in the grafting density. Also, PAA brush aggregates were found to undergo marked reversible conformational changes from coiled to stretched and vice versa with changes in pH, ionic strength and contact time.

A detailed population balance model for flocculation of colloidal suspensions by polymer bridging under quiescent flow conditions is presented. The collision efficiency factor is estimated as a function of interaction forces between polymer coated particles. The total interaction energy is computed as a sum of van der Waals attraction, electrical double layer repulsion and bridging attraction or steric repulsion due to adsorbed polymer. The scaling theory is used to compute the forces due to adsorbed polymer and the van der Waals attraction is modified to account for presence of polymer layer around a particle. The irregular structure of flocs is taken into account by incorporating the mass fractal dimension of flocs. When tested with experimental floc size distribution data published in the literature, the model predicts the experimental behavior adequately. This is the first attempt towards incorporating theories of polymer-induced surface forces into a flocculation model, and as such the model presented here is more general than those proposed previously.

Structural changes of pyrene-labeled and unlabeled poly(maleic acid/octyl vinyl ether) (PMAOVE) and poly(maleic acid/methyl vinyl ether) (PMAMVE) with changes in pH have been investigated in this study. The changes in the photophysical properties of pyrene are interpreted to investigate uncoiling or swelling of the polymeric chains with pH. The vibrational fine structure of the pyrene fluorescence (I(3)/I(1)) and the ratio between excimer and monomer fluorescence (I(e)/I(m)) of both pyrene-labeled and unlabeled PMAMVE and PMAOVE suggest that, at pH 4, the polymers are in the coiled form and PMAOVE forms hydrophobic nanodomains. An increase in pH ionizes a number of COOH groups on both PMAMVE and PMAOVE, which leads to the stretching or swelling of the polymers.

Measurement of forces between two individual particles in the millimeter and micrometer size range is difficult to accomplish and yet these are the particles that are normally encountered in many commercial systems. A cohesive force apparatus (CFA) first used by one of the authors [E.D. Shchukin, R.K. Yusupov, E.A. Amelina, P.A. Rebinder, Kolloidn. Zh. 31 (1969) 913] was modified here for studying cohesive force down to 1 nN between particles of various size, shape and chemical nature under different conditions. In this work, the interaction between fused glass surfaces in solutions containing surfactants, polymers and salts was investigated by measuring the detachment force using the cohesive force apparatus. The cohesive force between glass surfaces was found to gradually decrease with increase in pH due to a corresponding increase in their negative zeta potential. Addition of salt can increase the cohesive force significantly. Interestingly, the cohesive force was observed to increase significantly with the increase of DTAB concentration because of the hydrophobic interactions between monolayers of DTAB on glass. However, the force decreased with further increase in DTAB concentration due to electrostatic repulsion between surfaces and decrease of hydrophobic interactions when DTAB bi-layers are formed. In the case of the hydrophobically modified polymer, polyvinylcaprolactam (PVCAP), the cohesive force was shown to be directly proportional to the molecular weight of the polymer and the loading force. The cohesive interactions between PEO adsorbed glass also showed the force to increase as a function of the PEO concentration, reach a maximum, and then decrease gradually, the increase being due to the reduction in the zeta potential of the glass and the decrease due to steric effect between the fully covered layers. Interaction of anionic surfactant with the pre-adsorbed PEO layer can reduce the cohesive force between the surfaces.

The stability of colloidal suspensions is determined primarily by the interactions among suspended particles, which in turn depends on pH, electrolyte concentration, temperature and so on. In most practical systems, flocculation or stabilization is controlled by adsorbing polymers, surfactants or their mixtures. In this paper, the role of adsorbed layer microstructural properties, particularly polymer conformation at solid–liquid interface, in controlling stability and efficiency of flocculation is examined. When polymers are used, their conformation can be manipulated by changing solution conditions such as pH and/or by the addition of a secondary polymer or surfactant. A multi-pronged approach involving the use of fluorescence, ESR, Raman and NMR spectroscopic techniques along with measurements of surface charge and hydrophobicity was employed to explore the structure of the adsorbed layer. A detailed population balance model for coagulation and flocculation of colloidal suspensions by inorganic salts and polymers is then presented incorporating the modern theories of surface forces. In particular, the classical DLVO theory is modified for flocculation by polymers and integrated in a population balance framework for the kinetics of flocculation. The open and irregular structure of flocs is accounted for by embedding the mass fractal dimension of flocs in the model. For demonstration, the evolution of mean floc size with time is simulated for flocculation of hematite and polystyrene latex suspensions. The model predictions are in reasonable agreement with experimental data. As it is computationally less intensive, the proposed model can be utilized for online optimization and control of solid–liquid separation processes that are widely encountered in water treatment, mineral processing, waste management, and so on.

Adsorption of surfactant mixtures on hydrophilic solid surfaces is of considerable theoretical and practical importance. Cooperative adsorption of nonionic surfactant mixtures of nonyl phenol ethoxylated decyl ether (NP-10) and n-dodecyl-beta-d-maltoside (DM) on silica and alumina was investigated in this study with a view to elucidate the nanostructures of their aggregates. In the mixed system, DM is identified to be the "active" component and NP-10 is the "passive" one for the process of adsorption on alumina, while their roles are reversed for silica. The difference in the adsorptive interactions of the surfactants with the above minerals is attributed to the differences in the molecular structures of the surfactants. To better understand the interaction between surfactants at solid/solution interface from a molecular structure point of view, the nanostructures of mixed surface aggregates have been quantitatively predicted for the first time using a modified packing parameter: the structures are spherical or cylindrical on silica and those on alumina undergo a spherical-to-cylindrical-to-bilayer transition with the addition of the active component. This work offers a new way for developing of structure-performance relationships.

Pitting corrosion in many important industrial materials such as stainless steels (SS) and aluminum alloys causes significant damage in terms of material loss or resulting accidents. Organ...

Interactions of surfactants with hydrophobically modified polyelectrolytes in aqueous solutions are important in several applications such as detergency, cosmetics, food, and paints. Complexes formed in these systems raise some fundamental questions about the polymer-surfactant interactions that control their behavior. In this work, the interactions of a nonionic surfactant, penta-ethyleneglycol mono n-dodecyl ether (C(12)EO(5)), with a hydrophobically modified anionic polymer, poly(maleic acid/octyl vinyl ether) (PMAOVE), in aqueous solutions were studied using surface tension, viscosity, electron paramagnetic resonance (EPR) spectroscopy, light scattering, and fluorescence spectroscopic techniques. When the nonionic surfactant C(12)EO(5) was added to aqueous solutions of the anionic polymer PMAOVE, it was incorporated into the hydrophobic nanodomains of PMAOVE far below the the critical micelle concentration (cmc) of the surfactant. Two inflection points were observed corresponding to the critical complexation concentration (formation of mixed micelles composed of C(12)EO(5) and the octyl chains of PMAOVE) and the saturation concentration (saturation of the polymer with C(12)EO(5) molecules). Above the saturation concentration, the coexistence of pure C(12)EO(5) micelles and mixed micelles of PMAOVE and C(12)EO(5) was observed. Such a coexistence of complexes has major implications in their performance in colloidal processes.

The formation of biofilms on solid surfaces is a universal bacterial strategy for survival and optimum positioning with respect to available nutrients. Bacterial adhesion is an important initial step in biofilm formation, which is controlled by the production of variable amounts of biopolymers. The formation of these extracellular polymers solely depends on the growth condition and the substrate type. In this paper, the mechanisms of bacterial adhesion on different minerals are discussed on the basis of results obtained using a multipronged approach involving zeta potential, contact angle, FTIR and TEM measurements. Paenibacillus polymyxa has been used as a model bacterium, and quartz and calcite have been used as model minerals. Bacterial interaction was found to make the calcite surface more negative, while the same bacterial treatment makes the quartz surface more positive. Furthermore, it was seen from the contact angle measurements that the bacterial treatments make quartz surfaces more hydrophobic and calcite surface more hydrophilic. Interestingly, the bacteria showed different cell-surface composition depending on the minerais in their vicinity. FTIR results revealed that Paenibacillus polymyxa grown in the presence of quartz produced more surface proteins, while the same bacterium grown in the presence of calcite produced more surface polysaccharides. From the TEM study it was found that a slime layer surrounded the Bromfield-grown cells, whereas the calcite-grown cells were surrounded by well-structured capsule consisting of polysaccharides. The quartz-grown cells, on the other hand exhibited neither a capsule nor a slime layer on their surfaces. From the flotation and flocculation studies it was found that both bacterial cells and their metabolites enhanced the flocculation of calcite, whereas similar biotreatments promoted the dispersion of quartz. Studies with Thiobacillus ferroxidans have also shown marked differences in their effect on flotation of sulfide minerals such as sphalerite and galena. These selective effects of bacterial treatments on different mineral substrates are potentially useful in the development of environmentally benign and efficient bioprocessing technologies to extract low-grade valuable minerals in a cost-effective way.

Ceramics that are composed of nanosized granules show enhanced properties in various applications. A layer-by-layer deposition process is developed in this study to prepare core-shell nanocomposite particles, using controlled polymer adsorption. Submicrometer-sized alumina particles that have been chosen as the starting core particles are first dispersed by pH control and then modified by adsorption of anionic poly(acrylic acid) to facilitate the subsequent deposition of nanoparticles on them. A key step in the processing involves the removal of excess polymer in the supernatant after the adsorption by controlled washing, so that the added nanoparticles do not self-flocculate among themselves. A coating of nanosized particles is indicated by the charge reversal of the micrometer-sized composite particles. The isoelectric point of the composite particle is similar to that of nanosized particles under both low and high coverage conditions. Scanning electron microscopic observation of coated particles shows full monolayer coverage of the nanoparticles on core particles, which confirms the efficiency of the coating scheme that is discussed here. The present study reveals the feasibility of coating nanoparticles onto micrometer-sized core particles, using controlled polymer bridging, for the preparation of the multilayer nanocomposite powders.