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Soluble starch polymers are shown to enhance the lubrication of ionic liquid-water solvent mixtures in low-pressure tribological contacts between hydrophobic substrates. A fraction of starch polymers become highly soluble in 1-ethyl-3-methylimidazolium acetate (EMIMAc)-water solvents with ionic liquid fraction ≥60 wt%. In 65 wt% EMIMAc, a small amount of soluble starch (0.33 wt%) reduces the boundary friction coefficient by up to a third in comparison to that of the solvent. This low-friction is associated with a nanometre thick film (ca. 2 nm) formed from the amylose fraction of the starch. In addition, under conditions where there is a mixture of insoluble starch particles and solubilised starch polymers, it is found that the presence of dissolved amylose enhances the lubrication of starch suspensions between roughened substrates. These findings open up the possibility of utilising starch biopolymers, as well as other hydrocolloids, for enhancing the performance of ionic liquid lubricants. Refereed/Peer-reviewed

Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to study the Cuactivation of the (110) surface of sphalerites with Fe content varying from 0 to 14.79 wt%. Time resolvedAFM images show the development of surface oxidation products at high-energy step edges. These smallprotrusions evolve into larger conglomerates and finally full surface coverage with time. Surface morphologychanges show an increase in the number of cleavage steps and the size of precipitates as a functionof Fe concentration. Both of these factors contribute to the increased rate of Cu activation of high Fesphalerite as compared to low Fe sphalerite. XPS analysis of the sphalerites Cu activated for 1 h at pH 5,indicates an increased Cu concentration and the formation of disulphide and polysulphide that correlateswith an increase in bulk Fe content. Refereed/Peer-reviewed

The co-sorption reaction products of arsenate (As(V)) and copper (Cu(II)) on goethite (alpha-FeOOH) and natro-jarosite (Na(3)Fe(3)(SO(4))(2)(OH)(6)) were investigated with extended X-ray absorption fine structure (EXAFS) spectroscopy to determine if Cu(II) and As(V) would form precipitates or compete with each other for surface sites. The reaction products were prepared by mixing 250 microM Cu(SO(4)) with 10, 25, or 50 microM Na(2)HAsO(4) at pH 5.65 and allowing the mixture to react in 10 m(2) L(-1) goethite or jarosite suspensions for 12 days. In addition, EXAFS data of Cu(SO(4)) and As(V) sorbed on goethite and jarosite were collected as control species. All reaction conditions were under-saturated with respect to common copper bearing minerals: tenorite (CuO), brochantite (Cu(4)(OH)(6)SO(4)), and hydrated clinoclase (Cu(3)(AsO(4))(2)2H(2)O). The extents of the As(V) and Cu(II) surface adsorption reactions showed a strong competitive effect from Cu(II) on As(V) adsorption for a nominal Cu:As mole-ratio of 25:1. With increasing nominal As(V) concentration, As(V) sorption on goethite and jarosite increased without diminishing the amount of Cu(II) sorption. In the absence of either co-sorbate, As(V) and Cu(II) formed the expected surface adsorption species, i.e., bidentate binuclear and edge-sharing surface complexes, consistent with previously published results. In each other's presence, the local bonding environments of As(V) and Cu(II) showed that the co-sorbates form a precipitate on the goethite and jarosite surface at nominal concentrations of 10:1 and 5:1. At nominal Cu:As mole-ratios of 25:1, Cu(II) did not form significantly different surface complexes on goethite or jarosite from those in the absence of As(V), however, As K-edge EXAFS results distinctly showed Cu(II) atoms in As(V)'s local bonding environment on the goethite surface. The structures of the two precipitates were different and depended on the anion-layer structure and possibly the presence of structural oxyanions in the case of jarosite. On goethite, the copper-arsenate precipitate was similar to hydrated clinoclase, while on jarosite, a euchroite-like precipitate (Cu(2)[AsO(4)](OH)3H(2)O, P 2(1)2(1)2(1)) had formed. Despite under-saturated solution conditions, the formation of these precipitates may have occurred due to a seed-formation effect from densely surface adsorbed Cu(II) and As(V) for which the "new" saturation index was significantly lower than homogeneous values would otherwise suggest. Synergistic reactions between two co-sorbates of fundamentally different surface adsorption behaviour can thus be achieved if the number of available sites for surface adsorption is limited.

A new approach for the attachment of vertically-aligned shortened carbon nanotube architectures to a silicon (100) substrate by chemical anchoring directly to the surface has been demonstrated for the first time. The ordered assembly of single-walled carbon nanotubes (SWCNTs) was accomplished by hydroxylating the silicon surface followed by a condensation reaction with carboxylic acid functionalised SWCNTs. This new nanostructure has been characterised by X-ray photoelectron, Raman and Fourier transform infrared (FTIR) spectroscopy as well as scanning electron and atomic force microscopy. The assembly behaviour of SWCNTs onto the silicon surface shows a fast initial step producing isolated functionalised carbon nanotubes or nanotube bundles anchored to the silicon surface followed by a slower step where the adsorbed nanotubes grow into larger aggregates via van der Waals interactions between adsorbed and solvated nanotubes. The electrochemical and optical properties of the SWCNTs directly attached to silicon have also been investigated. These new nanostructures are excellent electrochemical electrodes. They also fluoresce in the wavelength range 650-800 nm. The successful attachment of the SWCNTs directly to silicon provides a simple, new avenue for fabrication and development of silicon-based nanoelectronic, nano-optoelectronic and sensing devices. Compared to existing techniques, this new approach has several advantages including low operating temperature, low cost and the possibility of further modification.

We present the first attempt to characterise surfactant adsorption from solution onto a particle film using total internal reflection Raman spectroscopy. Three surfactant collectors of interest to the mineral processing industry were studied in their adsorption onto sphalerite: heptyl xanthate, 2-mercaptobenzothiazole (MBT), and O,O-dibutyldithiophosphate (DTP). All three surfactants adsorbed to the surface of the sphalerite. Adsorption of heptyl xanthate was monitored as a function of time and increasing concentration. The spectrum of heptyl xanthate indicated the presence of a small amount of dixanthogen on the surface of the sphalerite. MBT adsorption studies were complicated due to the fluorescence of the adsorbed layer. However, peaks due to the adsorbed MBT were observed on top of the fluorescent background, allowing the identification of the adsorbed species to be confirmed as the oxidised dimer species. Spectra obtained from MBT and DTP co-adsorption studies did not display the strong adsorbate layer fluorescence, indicating that the fluorescence spectrum of the adsorbed MBT is most likely affected by ring–ring interactions.

The adsorption and action of various polymers on talc has been investigated. Two families of polymers (starch-based polysaccharides and synthetic polyacrylamides) with specific molecular weights and functional group chemistry were studied. Adsorption isotherms, acoustophoresis, and contact angle studies enabled polymer adsorption behaviour, adsorbed layer thickness, and the hydrophilicity of the polymer-treated talc surface to be determined. Flotation testing on the treated talc revealed a hierarchy of effectiveness within the group of polymers studied. The observed trends in flotation performance are discussed with reference to the measured polymer layer properties. A 3D correlation plot of adsorbed layer thickness and contact angle against flotation recovery indicates that it may be feasible to predict an order of effectiveness for polymeric depressants based solely on measurements of the adsorbed layer properties, without recourse to flotation testing. This approach would be desirable when screening large numbers of potential depressants.

X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry have been used to determine the specific effect of sulphite ions on the surface chemistry of copper-activated pyrite pre-treated with isobutyl xanthate in flotation experiments with nitrogen and air purging at pH 7. The results from these spectroscopic techniques illustrate that sulphite ions affect the surface chemistry of pyrite similarly whether nitrogen or air purged. It was found that sulphite ions interact with adsorbed collector species, as well as with the pyrite surface itself. A reduction in the adsorbed collector concentration and a commensurate increase in surface hydrophilicity explain the low flotation recovery of pyrite in the presence of sulphite. As expected, this effect was more pronounced in the flotation experiments with air purging.

The adsorption of carboxymethylcellulose polymers on molybdenite was studied using spectroscopic ellipsometry and atomic force microscopy imaging with two polymers of differing degrees of carboxyl group substitution and at three different electrolyte conditions: 1 × 10(-2) M KCl, 2.76 × 10(-2) M KCl, and simulated flotation process water of multicomponent electrolyte content, with an ionic strength close to 2.76 × 10(-2) M. A higher degree of carboxyl substitution in the adsorbing polymer resulted in adsorbed layers that were thinner and with more patchy coverage; increasing the ionic strength of the electrolyte resulted in increased polymer layer thickness and coverage. The use of simulated process water resulted in the largest layer thickness and coverage for both polymers. The effect of the adsorbed polymer layer on bubble-particle attachment was studied with single bubble-surface collision experiments recorded with high-speed video capture and image processing and also with single mineral molybdenite flotation tests. The carboxymethylcellulose polymer with a lower degree of substitution resulted in almost complete prevention of wetting film rupture at the molybdenite surface under all electrolyte conditions. The polymer with a higher degree of substitution prevented rupture only when adsorbed from simulated process water. Molecular kinetic theory was used to quantify the effect of the polymer on the dewetting dynamics for collisions that resulted in wetting film rupture. Flotation experiments confirmed that adsorbed polymer layer properties, through their effect on the dynamics of bubble-particle attachment, are critical to predicting the effectiveness of polymers used to prevent mineral recovery in flotation.

Ionic liquids (ILs) are a unique family of molecular liquids ('molten salts') that consist of a combination of bulky organic cations coupled to inorganic or organic anions. The net result of steric hindrance and strong hydrogen bonding between components results in a material that is liquid at room temperature. One can alter the properties of ionic liquids through chemical modification of anion and cation, thus tailoring the IL for a given application. One such property that can be controlled or selected is the wettability of an IL on a particular solid substrate. However, the study of wetting of ionic liquids is complicated by the care required for accurate and reproducible measurement, due to both the susceptibility of the IL properties to water content, as well as to the sensitivity of wettability measurements to the state of the solid surface. This review deals with wetting studies of ILs to date, including both static and dynamic wetting, as well as issues concerning line tension and the formation of precursor and wetting films. Refereed/Peer-reviewed

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The adsorption of two dextrin-based polymers, a regular wheat dextrin (TY) and a carboxymethyl-substituted (CM) dextrin, onto an anatase TiO2 particle film has been studied using in situ attenuated total reflection (ATR) FTIR spectroscopy. Infrared spectra of the polymer solutions and the polymer adsorbed at the anatase surface were acquired for two solution conditions: pH 3 and pH 9; below and above the isoelectric point (IEP) of anatase, respectively. Comparison of the polymer solution spectra and the adsorbed layer spectra highlighted a number of spectral differences that were attributed to involvement of the carboxyl group of CM Dextrin interacting with the anatase surface directly and the adsorption of oxidized dextrin chains in the case of regular dextrin (TY) at high pH. The adsorption/desorption kinetics were determined by monitoring spectral peaks of the pyranose ring of both polymers. Adsorption equilibrium was not established for Dextrin TY for many hours, whereas CM Dextrin reached equilibrium in its adsorption within 60 min. The extent of desorption of Dextrin TY (observed by flowing a background electrolyte dextrin-free solution) was extensive at both pH values, which reflects the poor affinity and binding of the polymer on anatase. In contrast, CM Dextrin underwent almost no desorption, indicating a high affinity between the carboxyl groups of the polymer and the anatase surface. Refereed/Peer-reviewed

Synchrotron FTIR microscopy has been used to probe the structure of model boundary lubricant layers confined at the solid−solid interface. The combination of high brightness of the IR source and a novel contact geometry that uses a hemispherical internal reflection element as the means for light delivery has enabled the detection of

In this paper, we present recent work from our group focussed on the fabrication of nanopore and nanotube arrays using self-ordered electrochemistry, and their application in several key areas including template synthesis, molecular separation, optical sensing, and drug delivery. We have fabricated nanoporous anodic aluminium oxide (AAO) with controlled pore dimensions (20-200 nm) and shapes, and used them as templates for the preparation of gold nanorod/nanotube arrays and gold nanotube membranes with characteristic properties such as surface enhanced Raman scattering and selective molecular transport. The application of AAO nanopores as a sensing platform for reflective interferometric detection is demonstrated. Finally, a drug release study on fabricated titania nanotubes confirms their potential for implantable drug delivery applications. Refereed/Peer-reviewed

Scanning photoemission microscopy (SPEM) has been applied to the investigation of homogeneous and heterogeneous metal sulfide mineral surfaces. Three mineral samples were investigated: homogeneous chalcopyrite, heterogeneous chalcopyrite with bornite, and heterogeneous chalcopyrite with pyrite. Sulfur, copper and iron SPEM images,i.e.surface-selective elemental maps with high spatial resolution acquired using the signal from the S 2pand Cu and Fe 3pphotoemission peaks, were obtained for the surfaces after exposure to different oxidation conditions (either exposed to air or oxidized in pH 9 solution), in addition to high-resolution photoemission spectra from individual pixel areas of the images. Investigation of the homogeneous chalcopyrite sample allowed for the identification of step edges using the topography SPEM image, and high-resolution S 2pspectra acquired from the different parts of the sample image revealed a similar rate of surface oxidation from solution exposure for both step edge and a nearby terrace site. SPEM was able to successfully distinguish between chalcopyrite and bornite on the heterogeneous sample containing both minerals, based upon sulfur imaging. The high-resolution S 2pspectra acquired from the two regions highlighted the faster air oxidation of the bornite relative to the chalcopyrite. Differentiation between chalcopyrite and pyrite based upon contrast in SPEM images was not successful, owing to either the poor photoionization cross section of the Cu and Fe 3pelectrons or issues with rough fracture of the composite surface. In spite of this, high-resolution S 2pspectra from each mineral phase were successfully obtained using a step-scan approach.

Synchrotron-based photoemission electron microscopy (PEEM; probing the surface region) and time-of-flight secondary ion mass spectrometry (ToF-SIMS; probing the uppermost surface layer) have been used to image naturally heterogeneous samples containing chalcopyrite (CuFeS2), pentlandite [(Ni,Fe)9S8] and monoclinic pyrrhotite (Fe7S8) both freshly polished and exposed to pH 9 KOH for 30 min. PEEM images constructed from the metal L3 absorption edges were acquired for the freshly prepared and solution-exposed mineral samples. These images were also used to produce near-edge X-ray absorption fine-structure spectra from regions of the images, allowing the chemistry of the surface of each mineral to be interrogated, and the effect of solution exposure on the mineral surface chemistry to be determined. The PEEM results indicate that the iron in the monoclinic pyrrhotite oxidized preferentially and extensively, while the iron in the chalcopyrite and pentlandite underwent only mild oxidation. The ToF-SIMS data gave a clearer picture of the changes happening in the uppermost surface layer, with oxidation products being observed on all three minerals, and significant polysulfide formation and copper activation being detected for pyrrhotite. Refereed/Peer-reviewed

In this study, the links between interfacial chemistry, polyethylene oxide (PEO) flocculant adsorption behaviour, orthokinetic flocculation and dewatering behaviour of talc mineral dispersion have been investigated. The effect of Mg(II) ions, suspension conditioning time, solid loading, PEO dosage and shear was probed. Unflocculated dispersion of weakly charged, polydispersed talc particles at pH 7.5 displayed very poor settling rate but good sediment consolidation (∼47 wt.% solid). PEO polymer adsorption rate and density were greater at higher than lower Mg(II) ion concentration. The adsorption propensity also decreased with increasing suspension conditioning time. An inverse correlation was observed between PEO adsorption rate/affinity and settling rate where slower adsorption kinetics led to larger and faster settling flocs. At equivalent PEO dosages (e.g., 200 g polymer t−1 solid), 8 wt.% solid dispersion solid produced both superior supernatant clarity and greater sediment consolidation than the markedly faster settling, dilute (2 and 4 wt.% solid) suspensions. The influence of Mg(II) ions and conditioning time on settling rate was PEO dosage dependent, however, these factors had no noticeable effect on sediment consolidation. Dramatic enhancement of flocculated sediment compaction (from 38 to 52 ± 2 wt.% solid)was achieved in secondary dewatering under moderate shear. The results provide useful fundamental knowledge of polymer adsorption rate, adsorption affinity and interparticle bridging behaviour whichunderpin the flocculation and dewatering of talcaceous clay suspensions for significant improvement. Refereed/Peer-reviewed

The influence of adsorbed dextrin-based polymers on the attachment of a rising air bubble to a talc surface has been investigated. Liquid film rupture and dynamic contact angle studies have highlighted the major role that adsorbed polymers can play in bubble-particle attachment. No direct link was established between the equilibrium contact angle of polymer-treated talc surfaces and talc flotation recovery. However, clear correlations were observed between the flotation recovery of polymer-treated talc and the measured wetting film rupture time and rate of dewetting for a bubble attaching to a talc basal plane surface treated with the polymers. The retardation of the three-phase contact line expansion caused by the adsorbed polymers was found to have the largest influence on the bubble-particle attachment. The effect of the morphology (coverage, distribution, and shape) of the adsorbed layer on the wetting film rupture and the motion of the receding water front is discussed. Refereed/Peer-reviewed

Carboxymethyl cellulose (CMC), in solution and adsorbed on the surface of talc, has been studied with ATR FTIR spectroscopy as a function of the solution pH. The solution spectra enable the calculation of the extent of ionization of the polymer (due to protonation and deprotonation of the carboxyl group) at various pH values, yielding a value of 3.50 for the pKapp1/2 (pH at which half of all carboxyl groups are ionized) in a simple electrolyte solution and a value of 3.37 for the pKapp1/2 in solutions containing magnesium ions (3.33 × 10−4 M). The spectra of the adsorbed layer reveal that CMC interacts with the talc surface through a chemical complexation mechanism, via the carboxyl groups substituted on the polymer backbone. The binding mechanism is active at all pH values down to pH 2 and up to pH 11. The adsorbed layer spectra reveal that protonation and deprotonation of the polymer are affected by adsorption, with an increase in the pKapp1/2 to a value of 4.80. Spectra of the adsorbed polymer were also acquired as a function of the adsorption time. Adsorption kinetic data reveal that the polymer most likely has two different interactions with the talc surface, with a stronger interaction with the talc edge through chemical complexation and a weaker interaction with the talc basal plane presumably through the hydrophobic interaction. Refereed/Peer-reviewed

The adsorption of three modified dextrins on the basal plane of talc has been studied using in situ tapping mode atomic force microscopy (TMAFM). The images have been used to determine the layer thickness and coverage of the adsorbed polymers. Adsorption isotherms of the polymers on talc particles were also determined using the depletion technique. Values of the adsorbed amount at equilibrium were compared with the volume of adsorbed material as determined using in situ TMAFM, revealing the presence of significant amounts of hydration water in the adsorbed layer structure. This deduction was confirmed by comparing in and ex situ TMAFM images of the adsorbed dextrins. The effect of layer thickness, coverage, and hydration water content on the contact angle of talc particles treated with polymer was investigated using the Washburn method and the equilibrium capillary pressure (ECP) method. Distinct correlations were observed between adsorbed layer properties and the measured contact angles, with the ECP measurements especially highlighting the effect of the adsorbed polymer layer hydration water. The implications for the performance of the modified dextrins in flotation are discussed. Refereed/Peer-reviewed

The colloid stability of thymine-coated gold nanoparticles under light irradiation as a function of particle size, surface charge, and exposure time was investigated in alkaline, aqueous solutions as well as in a 0.5 vol % of DMF in H2O mixture. With increasing exposure to light irradiation at 280 nm, more and more particles coagulated. Light-induced aggregation of colloidal gold nanoparticles was attributed to reorientation of thymine terminal groups tethered on gold particle surfaces. A smaller particle size and negatively charged surface reduced the rate of photodimerization or even inhibited the photoreaction. UV−vis and FTIR spectroscopy confirmed the photodimerization of terminal thymine molecules under 280 nm light irradiation. The reaction kinetics of thymine photodimerization appears to be a combination of first-order reactions, each having different rates, reflecting the inhomogeneity and high curvature of the gold nanoparticle surfaces. Refereed/Peer-reviewed

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The adsorption of carboxymethyl cellulose (CMC) onto talc has been studied using particle film ATR FTIR. This approach allows for the in situ acquisition of vibrational spectra, i.e., acquired as the polymer is adsorbing from solution, enabling adsorption to be studied as a function of varying solution conditions. In this work, adsorption has been studied in the absence and presence of calcium ions, as well as under conditions of increased ionic strength of a simple electrolyte. Calcium ions have been implicated in the enhancement of adsorption of CMC on talc and an increase in the effectiveness of CMC as a talc depressant. The in situ spectra of the adsorbed polymer indicate clearly that CMC interacts chemically with the talc surface. In addition, the effects of ionic strength and the presence of Ca ions on the adsorption of the polymer were seen to be similar: they increased the adsorbed amount and altered the polymer conformation at the surface. Refereed/Peer-reviewed

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Thymine-functionalized SAM-protected gold nanoparticles with diameters of 2.2 +/- 0.3 nm and 7.0 +/- 1.0 nm were prepared via a modified two-phase transfer method. UV-vis spectra showed that particle size and solvent type, as well as surface charge, influenced the gold surface plasmon band absorption, along with the interaction between thymine terminal groups in the solution. Although the bulky thymine end groups interacted strongly on the particle surface, a well-ordered monolayer of thyminethiol derivatives with a long hydrocarbon chain was formed on the particle surface, exhibiting an ordered, all-trans conformation of the methylene backbone, similar to those of corresponding self-assembled monolayers (SAMs) generated from normal alkanethiols. A larger particle size and a longer reaction time facilitated the formation of more ordered thymine-terminated thiol SAMs. Thermal analysis indicated that reorientation of the SAMs during heat treatment occurred by two processes, caused possibly by the separate recrystallization of the hydrocarbon long chains and thymine units. More ordered SAMs with a higher thermal stability were formed on the larger particle surfaces when compared with those on the smaller ones. A greater density of molecular packing was found on the smaller particle surfaces. However, SAMs formed on the larger gold particles resembled 2D SAMs on the smooth, flat gold surfaces. XPS results confirmed the thymine structure as well as the chemical bond between gold and sulfur. One type of adsorbed sulfur species was observed for the smaller particles and two for the larger ones, but a slightly higher binding energy of thiolate was found for the smaller ones.

Raman spectroscopy has been used to study the confinement of octamethylcyclotetrasiloxane (OMCTS) and n-hexadecane between a prism and a lens at contact pressures of 40 MPa. Both lens and prism surfaces were optically smooth but not atomically flat. A total internal reflection geometry was employed to provide the sensitivity needed to detect liquid films of sub-nanometre thickness. For both liquids, the thickness of the residual film under load corresponded to less than a monolayer of liquid. The Raman spectra of the confined liquids were identical or very similar to that of the bulk liquid. Similar results were obtained for hexadecane confined between two surfaces coated with a Langmuir-Blodgett monolayer of a fatty acid. We infer that the liquids do not form a boundary layer under these conditions but rather they are squeezed out of the contact under the modest pressure applied. We ascribe the residual signal to liquid trapped in scratches or other defects on the surfaces.

The effect of sodium bisulphite on the xanthate-induced flotation of copper-activated sphalerite has been studied using batch flotation testing, surface analysis techniques (XPS and ToF-SIMS), and FTIR. The various techniques have been used to identify the mechanisms of interaction of sulphite ions with both collector and the sphalerite surface. The results indicate that sodium bisulphite depressed the flotation of sphalerite particles pre-treated with copper and xanthate at pH 9 with nitrogen and air purging. It was found that sodium bisulphite interacts with the sphalerite surface, as well as with xanthate in its adsorbed state. Based on the evidence obtained in the present study, and in conjunction with previous work, the mechanisms involved in the depression of the xanthate-induced flotation of copper-activated sphalerite by sulphite are proposed. It is suggested that copper xanthate decomposition on the surface of the activated sphalerite and the decomposition of the hydrophobic copper-sulphide-like species on the sphalerite surface are the active mechanisms for sphalerite depression by sodium bisulphite.

The rheological properties of dewatered tailings and cemented paste backfill have been measured and subsequently altered using polymeric dispersants. Polyphosphate and naphthalene sulfonate formaldehyde condensate (NSF) were selected as potential candidates to reduce the yield stress (τB) of the two slurries. Adsorption isotherms, acoustophoresis, and rheology measurements indicate that the polymers adsorb onto the dewatered tailings, causing an increase in the particle zeta potential, accompanied by comparably low values of τB for both polymers. The reduction in τB was due to electrostatic repulsion (polyphosphates and NSF) and steric repulsion (NSF). However, the efficacy of the polymers in reducing the yield stress of the cemented paste is complicated by hydration reactions in the cement phase. Polyphosphate was found to be less effective in lowering the τB of the cemented paste than NSF. Rheology measurements performed on the cement phase alone in the presence of the dispersants indicate that cement plays a major role in the adsorption of both NSF and polyphosphate in the cemented paste backfill. This is in spite of the fact that cement makes up only a small fraction of the total solids content of the paste. Adsorption isotherms determined for the cement phase alone indicate that NSF adsorbs strongly, whereas polyphosphate was seen to form a precipitate with calcium ions, released due to cement hydration. Acoustophoresis measurements mirrored this result, with NSF alone causing charge reversal and subsequently increasing the negative charge present on the surface of the cement phase.

The adsorption of a low molecular weight unmodified polyacrylamide (Polymer-N) and a hydroxyl-substituted polyacrylamide (Polymer-H) onto talc was studied using in situ particle film ATR-FTIR spectroscopy in the multiple internal reflection mode. Spectra of the adsorbed polymer were collected as a function of increasing concentration and as a function of time. Measurement of the peak intensities of the adsorbed polymer allowed adsorption isotherms and adsorption kinetics to be determined for both polymers. Langmuir adsorption isotherm analysis of in situ data yielded Gibbs free energies of adsorption (deltaG0(ads)) for Polymer-N and Polymer-H of -44.5 and -45.7 kJ/mol, respectively, which correlate well with similar values determined from ex situ adsorption isotherms. Kinetic analysis indicated that the adsorption of both polymers was a pseudo-first-order process. The apparent rate constants for Polymer-N and Polymer-H were 0.10 and 0.15 min(-1), respectively. Absence of spectral shifts in the spectra of adsorbed polymer is indicative of a hydrophobic interaction between the polyacrylamides and the talc surface.

We present data from the surface analysis of a mineral mixture of chalcopyrite, pyrite, and sphalerite, elucidating surface reactions occurring during grinding and flotation. Flotation tests are also performed on the mixture, carried out in the presence of collector (SIBX) and also in the absence and presence of sodium bisulphite (NaHSO 3 ), a gangue sulphide mineral depressant. X-ray photoelectron spectroscopy (XPS) studies on the ground mineral sample prior to flotation indicate that the mineral feed is heavily oxidised, especially the sphalerite in the mixture. Flotation recovery data clearly shows the effect of this oxidation, with the mineral recoveries of all three phases being lower than those observed in single mineral studies. In addition, the flotation recoveries show the effect of the inadvertent copper activation of pyrite and sphalerite, and the effect of bisulphite in reducing the flotation of sphalerite and pyrite in the mixture. Time of flight secondary ion mass spectrometry(ToF-SIMS) data indicates that the depressing effect of bisulphite is due to the removal of copper and sulphur-like species from the surface of pyrite and sphalerite and a consequent increase in the oxidation of these minerals. ToF-SIMS data also indicates that the low recovery of pyrite and chalcopyrite in the absence of collector is most likely due to precipitation of zinc hydroxide on the surfaces of these minerals, formed in solution due to copper activation of sphalerite.

The effect of sodium bisulphite on the collectorless flotation of copper-activated sphalerite has been studied at pH 9 with nitrogen purging. X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF-SIMS) and ion chromatography (IC) have been used to identify a mechanism of interaction of sulphite ions with sphalerite particles. The results indicate that sodium bisulphite acts as an effective depressant for the collectorless flotation of copper-activated sphalerite and has a specific effect on the surface chemistry of sphalerite particles under the experimental conditions studied. It is suggested that sulphite ions react with the surface of copper-activated sphalerite and subsequently decompose the hydrophobic sulphur-like species responsible for flotation. Most likely, sulphite ions specifically interact with the reduced coordination sulphur atoms associated with copper activation and report into solution as a thiosulphate, which is then oxidised to sulphate. At the same time, zinc hydroxide is formed at the sphalerite surface. The consequent reduction in surface hydrophobicity explains the depression of copper-activated sphalerite in the presence of sulphite.

Dipole-allowed transitions from vibrationally selected members of the lowest nd Rydberg state cluster in I2 (n = 5) and Br2 (n = 4) to autoionizing Rydberg series based on vibrationally excited states of the core are investigated. The photoelectron production spectrum is recorded using delayed field extraction to detect free electrons released by autoionization with up to a few hundred cm−1 of energy that are subsequently trapped for ∼1μs in the plasma formed at the laser focus. The final state principal quantum numbers typically range from n ∼ 20–35 and both p and f series can be identified. When one of these core-excited Rydberg state energies coincides with the ionization threshold of a lower vibrational state to within a few cm−1, a marked increase in the ZEKE-PFI signal is observed, leading to non-Franck–Condon behaviour. Probing the same Rydberg states based on the spin–orbit excited core reveals preferential autoionization by electron exchange rather than by vibronic coupling in the p series.

The vacuum ultraviolet absorption spectra of I2, Br2 and ICl have been re-analysed using new data from the zero kinetic energy-pulsed field ionization (ZEKE-PFI) photoelectron spectra of all three molecules, and the (2 + 1) resonance enhanced multiphoton ionization (REMPI) spectrum of ICl. A common pattern of absorption intensities emerges in which all transitions to states which have appreciable singlet character are strong. Thus, in all three molecules, strong transitions are observed to four np and six nf Rydberg series based on the X[2Π3/2]g and X[2Π1/2]g states of the molecular ions, to two ns and six nd states in ICl and to two ns states based on the A[2Π3/2]u and A[2Π1/2]u states of the ion in Br2. The Ω values of some of the Rydberg series have been determined directly from the (2 + 1) REMPI spectrum of ICl.

The importance of buried interfaces in our everyday lives and in current scientific research is highlighted, along with experimental difficulty associated with studying such systems. We present an overview of the application of second harmonic generation and sum-frequency spectroscopy to the study of buried interfaces. Several examples from the current literature are presented, ranging from chemical and biological, to electrical and magnetic interfaces. The importance of this work in the context of ongoing research in these areas is discussed. Finally, we provide a snapshot of the state of the art in non-linear optical spectroscopy by mentioning several new directions that are likely to have a large impact on future research into the physics and chemistry of buried interfaces.