D. Neil Furlong
Commonwealth Scientific and Industrial Research Organisation
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Journal of the Chemical Society, Faraday Transactions | 1984
D. Neil Furlong; Anton Launikonis; W. H. F. Sasse; John V. Sanders
Stable aqueous colloidal platinum sols have been prepared by the citrate reduction of chloroplatinic acid. Particle size at the completion of the reaction was found to increase with increased heat input during reduction. The u.v.–visible spectrum of the platinum sols depends upon particle size up to 4 nm. A stirring–centrifugation procedure was used to identify the extent of coagulation induced by added electrolytes. It was found that the smaller platinum particles required higher concentrations of added electrolyte before being destabilized. A survey was made of the coagulation of the platinum sols induced by mono-, di- and tri-valent cations.Hydrogen treatment of platinum sols leads to growth of particles up to a maximum size of ca. 5 nm and substantial linkage of primary particles to form extensive aggregates. Such growth and aggregation lead to significant changes in the u.v.–visible spectra and reduced resistance to electrolyte-induced coagulation.
Journal of the Chemical Society, Faraday Transactions | 1982
Robert N. Lamb; D. Neil Furlong
The wettability of flat quartz-crystal surfaces has been assessed by measurement at 25 °C of contact angle at the water-vapour/water-drop/quartz-plate three-phase line. Plates pretreated by heating in vacuum gave angles, measured through the drop 1 min after removal from vacuum, of 0–44 ° as pretreatment temperature was increased from 200 to 1000 °C. Fully hydroxylated, therefore hydrophilic, quartz surfaces are progressively rendered hydrophobic by mutual condensation of surface hydroxyls to form siloxane bridges. Hysteresis was at a maximum after heating at 700–800 °C, indicating that maximum surface chemical heterogeneity was produced by heating in this temperature range. Plates methylated subsequent to heat treatment gave angles that were constant at ca. 80° up to treatment at 600 °C and that decreased from 80 to ca. 47 ° as the pretreatment temperature was further increased to 1000 °C. This variation with temperature is consistent with a mechanism for methylation in which only non-hydrogen-bonded surface hydroxyl groups on quartz are reactive towards the methylating reagent. Contact angles on both heat-treated and methylated plates were observed to decrease following extended exposure to water vapour.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | 1995
Ingrid Söderberg; Calum J. Drummond; D. Neil Furlong; Simon Godkin; Barry Matthews
Abstract The air/water interfacial activity and self-assembly of the mono-dodecyl esters of glucose, sucrose, raffinose and stachyose have been investigated. These four non-ionic surfactants provide a series where the hydrocarbon chain length is invariant while the surfactant headgroup sequentially increases in size. The minimum area per surfactant molecule at the air/water interface increases smoothly with the sequential addition of galactose structural units, sucrose β followed by an L α phase as the temperature is increased. At a low weight percentage of surfactant, the other three surfactants form isotropic micellar phases. At relatively higher weight percentages of surfactant, the sucrose surfactant forms hexagonal and L β phases, the raffinose surfactant forms discrete cubic micellar and hexagonal phases, and the stachyose surfactant begins to crystallize. At a very high weight percentage of surfactant, the sucrose, raffinose and stachyose surfactants exist as hydrated crystals. Most of the self-assembly behaviour in water can be readily explained in terms of the geometric packing constraints.
Journal of the Chemical Society, Faraday Transactions | 1995
Herman S. Mansur; Franz Grieser; Mark S. Marychurch; Simon Biggs; Robert S. Urquhart; D. Neil Furlong
The photoelectrochemical (PEC) characteristics of thin films of ‘Q-state’ CdS semiconductor particles in arachidic acid Langmuir–Blodgett (LB) layers have been examined. Initially, ‘Q-state’ size CdS particles of ca. 2 nm were formed in the film and then progressively grown to ca. 10 nm by a cyclic sequence, which involves exposing the film to H2S(g) following its immersion in a CdCl2(aq) solution. A PEC cell was constructed using a layered glass/ITO–CdS/LB plate as the photoanode and a standard calomel electrode (SCE) as the reference electrode. The photoelectrical response of electrodes coated with LB films containing CdS particles of various sizes was investigated using white light. The reproducibility of current–voltage polarisation curves indicated the relatively good stability of the film to PEC degradation processes over several scanning cycles in the range 0 to –1000 mV vs. SCE. Values for the open-circuit (Voc) and the short-circuit current for the PEC cells were obtained and fill factors in the range 20 to 70–75% were calculated. Voc decreased from ca. –200 to ca. –800 mV vs. SCE with increasing particle size. This effect was attributed to the dielectric properties of the arachidic acid LB film matrix.
Journal of the Chemical Society, Faraday Transactions | 1992
Franz Grieser; D. Neil Furlong; David J. Scoberg; Itzumi Ichinose; Nubuo Kimizuka; Toyoki Kunitake
The generation of quantised-state (Q-state) particles of CdS, CdSe, CdTe, CdSxSe1–x, CdSxTe1–x and CdSexTe1–x in polymerized nonacosa-10, 12-diynoic acid Langmuir–Blodgett (LB) films is described. The use of mixed surfactants and mixed counterions Cd2+ and Ca2+ in the LB films is shown to influence the size of the particles formed. The possible factors controlling the particles formed. The possible factors controlling the particle size obtained in LB films are discussed.
Sensors and Actuators B-chemical | 1997
Frank Caruso; Elke Rodda; D. Neil Furlong; Volker Haring
The binding of various single- and double-stranded DNAs onto gold and derivatized gold surfaces, and their hybridization with complementary DNA species, have been investigated using a quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). The DNA species employed were a 21-mer oligonucleotide (Mbo21), several double-stranded plasmid DNAs (7.2 kilobases) modified by incorporation of α-phosphothio-nucleotides into the ends of the linearized plasmid DNA (pPS-Sx, where x represents the number of α-phosphothio-nucleotides), and a 30-mer oligonucleotide having a mercaptohexyl group at the 5′-phosphate end (BS1-SH). Both QCM and SPR data reveal that unmodified DNA does not spontaneously adsorb onto underivatized gold surfaces from aqueous solutions. Modification of the gold surface through the attachment of an ionizable thiol compound, 2-dimethylaminoethanethiol hydrochloride (DMAET), allows DNA to adsorb through electrostatic interactions. SPR measurements confirm the presence of Mbo21 DNA on the DMAET-modified gold surface. Immobilized Mbo21, however, does not undergo hybridization. QCM and SPR data suggest that pPS-S4, pPS-S50 and BS1-SH DNA all assume a flat orientation on gold. No hybridization of single-stranded DNA to gold-immobilized pPS-S4 and pPS-S50 could be detected. In contrast 30-mer DNA binding from solution to the complement BS1-SH immobilized on gold reveals hybridization of the DNA strands.
Colloids and Surfaces | 1992
Calum J. Drummond; Stefani Albers; D. Neil Furlong
Abstract The influence of ionic and non-ionic surfactants on the cloud point and viscosity under shear behaviour of an aqueous 1 wt.% (hydroxypropyl)cellulose (HPC) solution has been investigated. The surfactants used were hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, sodium dodecylsulphate, octaethyleneglycol mono n-dodecyl ether and dodecyl-β- d -maltoside (designated CTAC, CTAB, DTAC, DTAB, SDS, C12E8 and DM, respectively). Both the cloud point and rheological behaviour in HPC/charged surfactant systems have been interpreted in terms of the surfactant first adsorbing on the HPC molecules in a cooperative manner and then forming bulk micelles in solution. The cloud points in the HPC/DTAB, HPC/DTAC and HPC/SDS systems initially decrease with increasing surfactant concentration. Conversely, the cloud points in the HPC/CTAB and HPC/CTAC systems initially increase. This behaviour has been explained in terms of the relative contributions of the hydrophobic and electrostatic components to the total interaction force. It has been found that modifying HPC through surfactant adsorption, by either increasing the degree of hydrophobic chain substitution or the charge density, can result in an increase in both the relative viscosity and the shear-thinning. The formation of bulk micelles in the HPC/charged surfactant systems negates the initial surfactant adsorption effects. At relatively high surfactant concentrations ( ≫ CMC), the HPC/DTAC and HPC/DTAB systems have been found to exhibit different cloud point and rheological behaviour to the HPC/SDS, HPC/CTAB and HPC/CTAC systems. This has been attributed tentatively to aggregate size effects. Upon normalisation of the results to the CMC, SDS has been found to display a much stronger affinity for HPC than the cationic surfactants. These affinity differences can account for the differences in the values of the rheological parameters obtained. At the surfactant concentrations studied (i.e. up to at least 10−2 mol dm−3), both the C12E8 and DM molecules and micelles exhibit no significant interaction.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | 1999
David J. Elliot; D. Neil Furlong; Franz Grieser
Abstract Langmuir–Blodgett (LB) films were constructed on hydrophobic quartz substrates from monolayers of behenic acid on subphases containing only Cd 2+ or Hg 2+ and containing a mixture of Cd 2+ and Hg 2+ ions. The reaction of these films with H 2 S to form metal sulphide particles was investigated using UV/visible spectroscopy and X-ray photoelectron spectroscopy (XPS). For the mixed metal ion system it was concluded that reaction with H 2 S results in individual CdS and HgS particles forming rather than a mixed cadmium mercury sulphide. In order to investigate the kinetics of the H 2 S reaction, the frequencies of MBe (M=Cd or Hg) coated quartz crystal microbalances were followed as a function of H 2 S exposure time. Immersion of CdS particles into a Hg 2+ solution resulted in a change in the UV–visible absorbance spectrum attributed to the exchange of Cd 2+ ions in the particles for Hg 2+ ions most likely resulting in a HgS layer around the CdS core.
Journal of the Chemical Society, Faraday Transactions | 1990
Calum J. Drummond; D. Neil Furlong
The photochemical and physicochemical properties of 1′-hexadecyl-3′,3′-dimethyl-6-nitrospiro [2H-1-benzopyran-2,2′-indoline](SP-16) in micellar self-assembled surfactant aggregates have been investigated. For comparison the properties of 1′,3′,3′-trimethyl-6-nitrospiro [2H-1-benzopyran-2,2′-indoline](SP-1) in 1,4-dioxane–water mixtures and, to a lesser extent, some neat organic solvents have also been examined. In all the media studied, both SP-16 and SP-1 undergo heterolytic cleavage when irradiated with UV light. This process may be reversed thermally or by irradiation with visible light. The spirobenzopyran open form, which is generated by the UV irradiation, is solvatochromic. A complex interplay of open-form stereoisomer contributions complicates the analysis of the solvatochromism, especially for micellar systems. In all the media, the thermal decoloration of the open forms of SP-16 and SP-1 follows single first-order kinetics. In the micellar systems, the first-order rate constants are interpreted in terms of interfacial solvent and charge stabilization effects and steric restrictions. pH induced UV–VIS spectral changes of the open forms of SP-16 and SP-1, in the low to medium region of the pH scale, are ascribed to the phenoxide moiety functioning as an acid–base group. The apparent pKa of SP-16 in non-ionic micellar systems reflects solely a solvent effect whilst the apparent pKa of SP-16 in ionic micellar systems reflects solvent and electrostatic effects as well as either a complexation of anionic species to the indolenium nitrogen or a ‘Debye–Huckel’ screening effect. Light-induced UV–VIS spectral modifications of the protonated open forms of SP-16 and SP-1 are explained in terms of a cis–trans photoisomerization process. pH (adjusted with NaOH) induced UV–VIS spectral changes are indicative of a partially reversible hydroxide degradation of the open forms of SP-16 and SP-1. A photochemical and physicochemical scheme is presented which summarizes the behaviour of 1′-alkyl-3′,3′-dimethyl-6-nitrospiro [2H-1-benzopyran-2,2′-indoline] derivatives in environments that have an aqueous component.
Journal of the Chemical Society, Faraday Transactions | 1993
D. Neil Furlong; Robert S. Urquhart; Franz Grieser; Kentaro Tanaka; Yoshio Okahata
The fabrication of particles in Langmuir–Blodgett films of cadmium icosanoate and nonacosa-10,12-diynoate is followed using a quartz crystal microbalance. The mass changes accompanying the exposure of the film to hydrogen sulfide are consistent with a chemical reaction in the film which also produces the acid form of the surfactant. Film thermal stability is greatly reduced after the particles are formed, a result also consistent with formation of the more volatile acid form. The extent of film removal by heating/outgassing suggests that particles are capped by adsorbed icosano or diynoic acid. It is likely that this capping plays a role in particle growth control.
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