Browsing by Author "Nelson, A"

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    Adsorption at a solid-liquid interface
    (Saha Institue of Nuclear Physics, 2012-07-25) Gerth, S; Nelson, A; Klimczak, M; Steinrück, HG; Weißer, M; Magerl, A
    Surfactants from tri-block copolymers are well known for the reduction of surface tension or friction at an interface. We investigate the tri-block copolymer Pluronic® P123 consisting of a central part of 70 propylene oxide (PO) units terminated by two end groups of 20 ethylene oxide (EO) units (E020 - PO70 — E020). In concentrated solutions above 27 weight percent (wtp) and at intermediate temperatures the micelles self-assemble into crystalline structures. In addition we found a near surface crystallization for a diluted P123 system below the critical temperature and concentration for bulk crystallization. Different chemical surface treatments (hydrophilic or hydrophobic) influence this near-interface ordering. The initiation of crystal growth is preferred at an attractive interface, whereas no layering of micelles is observable for a hydrophobic coating. The build up of a Bragg peak at Q w 0.05 A1 observed in reflectometry provides evidence for a micellar layering at the surface. We note, that this dense surface structure is present under conditions where there is no bulk crystallization. To access the stability of the surface layer, we have studied the destruction and the kinematic recovery of this surface layer under shear. To this end we have built a cone-plate shear device suitable for in-situ neutron reflectometry. The recovery of the adsorbed micellar layer in dependence of a previously applied shear rate, temperature and polymer concentration yields a nucleation time for layer growth. In addition, the structural fidelity of the adsorbed layer system is elucidated by the integrated Bragg intensity.
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    Advancing the reflectometry cause at ANSTO - updates and upgrades to the time-of-flight Platypus Neutron Reflectometer.
    (International Conference on Neutron Scattering, 2017-07-12) Nelson, A; Holt, SA; Darmann, FA; Klose, F
    Since the first suite of neutron scattering instruments was commissioned in 2008 the Australian Nuclear Science and Technology Organisation (ANSTO) has invested in instrumentation for the analysis of thin interfacial films. The horizontal time-of-flight reflectometer, Platypus [1], has now been joined by an X-ray reflectometer and a variable angle spectroscopic imaging ellipsometer. The high quality science possible on these complementary instruments has lead to a large oversubscription rate on Platypus. Here, we outline the key developments and upgrades we have made to Platypus that have led to this success. These include the development of event mode acquisition for studying kinetic processes, new sample environments (confinement cell, vapour delivery systems), as well as projects to upgrade its performance by installing new collimation systems and detectors.
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    The application of neutron reflectometry and atomic force microscopy in the study of corrosion inhibitor films
    (Elsevier B. V., 2006-11-15) John, D; Blom, ACM; Bailey, S; Nelson, A; Schulz, JC; De Marco, R; Kinsella, B
    Corrosion inhibitor molecules function by adsorbing to a steel surface and thus prevent oxidation of the metal. The interfacial structures formed by a range of corrosion inhibitor molecules have been investigated by in situ measurements based on atomic force microscopy and neutron reflectometry. Inhibitors investigated include molecules cetyl pyridinium chloride (CPC), dodecyl pyridinium chloride (DPC), 1-hydroxyethyl-2-oleic imidazoline (OHEI) and cetyl dimethyl benzyl ammonium chloride (CDMBAC). This has shown that the inhibitor molecules adsorb onto a surface in micellar structures. Corrosion measurements confirmed that maximum inhibition efficiency coincides with the solution critical micelle concentration. Copyright © 2006 Elsevier B.V.
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    The application of neutron reflectometry and atomic force microscopy in the study of corrosion inhibitor films
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) John, D; Blom, ACM; Bailey, S; Nelson, A; Schulz, JC; De Marco, R; Kinsella, B
    In the search for new, superior and environmentally friendly corrosion inhibitor molecules, it is important to understand their mechanism of inhibition. Characterising the chemical and physical nature of the adsorbed inhibitor layer is a major part of understanding this mechanism. An accurate account of this character necessitates the use of surface analysis techniques that are capable of in-situ measurements. Ex-situ techniques are likely to cause changes either by oxidation of the metal and corrosion product film or rearrangement and loss of the inhibitor film during exposure to air and during the drying and analysis under vacuum. Neutron reflectometry in combination with atomic force microscopy provides the capability of in-situ surface analysis of thin interfacial layers. These complementary techniques make it possible to investigate the structure and orientation of molecules on a surface. which can ultimately assist in gaining an insight into the inhibitor mechanism. This paper will explore how these techniques can be used to determine the mechanism of corrosion inhibitors, with particular emphasis on surfactant molecules used to prevent carbon dioxide corrosion of steel during petroleum production. Results will be presented from experiments using the aforementioned in-situ surface analysis with generic corrosion inhibitor molecules cetyl pyridinium chloride (CPC), dodecyl pyridinium chloride (DPC), 1-hydroxyethyl-2-oleic imidazoline (OHEI) and cetyl dimethyl benzyl ammonium chloride (CDMBAC). These results will be further discussed with respect to the observed inhibition of carbon dioxide corrosion of carbon steel electrodes. © The Authors
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    Calcium mediated interaction of calf-thymus DNA with monolayers of distearoylphosphatidylcholine: a neutron and X-ray reflectivity study
    (Royal Society of Chemistry, 2013-01-01) Dabkowska, AP; Talbot, JP; Cavalcanti, L; Webster, JRP; Nelson, A; Barlow, DJ; Fragneto, G; Lawrence, MJ
    X-ray and neutron reflection studies, the latter in conjunction with contrast variation, have been combined to study the interaction of calf thymus DNA (ctDNA) with monolayers of distearoylphosphatidylcholine (DSPC) in the presence of 20 mM Ca2+ ions, at the air-liquid interface as a function of surface pressure (10, 20, 30 and 40 mN m-1). Analysis of the X-ray and neutron reflection data showed that, regardless of the surface pressure of the monolayer, a layer of ctDNA was present below the DSPC lipid head groups and that this ctDNA-containing layer (thickness [similar]12.5 to 15 A) was separated from the DSPC head groups by a layer of water of [similar]9 A thickness. The thickness of the ctDNA-containing layer was thinner than that reported for monolayers of cationic lipid at the air-water interface (18-25 A) although in these monolayers no water layer separating the lipid head groups from the layer containing ctDNA has been reported. At all surface pressures the amount of ctDNA present in the layer was in the range 30-40% by volume. As no significant re-arrangement of the DSPC film was required to accommodate the presence of the ctDNA, this suggests that the distribution of charges in the lipid film matches well the charge spacing of ctDNA. Brewster angle microscopy measurements of DSPC on water in the absence of Ca2+ showed the presence of a continuous film containing small, regular shaped domains at all four surface pressures examined. When Ca2+ ions were present in the sub-phase, although the film was still continuous, the domains comprising the film were more irregular in appearance while the presence of Ca2+ ions and ctDNA resulted in the domains becoming smaller and more regularly packed on the surface. © 2013, Royal Society of Chemistry.
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    Comparisons of alumina barrier films deposited by thermal and plasma atomic layer deposition
    (Elsevier, 2019-03) Jarvis, KL; Evans, PJ; Nelson, A; Triani, G
    Barrier films are commonly deposited onto flexible substrates by atomic layer deposition (ALD) to protect organic electronics from degradation due to the ingress of moisture. Both thermal ALD and plasma-enhanced ALD (PEALD) have been used for this purpose, but few comparisons have been made as to which technique produces superior barrier films. In this study, alumina (Al2O3) barrier films have been deposited by thermal ALD and PEALD to investigate the effect of the deposition technique on the water vapor transmission rate (WVTR). Al2O3 films with thicknesses of approximately 10 or 20 nm were deposited at 100 or 120°C. The chemistry, morphology, and density of the films were investigated with X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray reflectometry respectively. The WVTRs of the films were measured using tritiated water (HTO) permeation at 25°C and 95% relative humidity. Both the thermal and PEALD films had similar Al:O ratios, whereas the PEALD films were slightly smoother than the thermal ALD films. No significant difference in the film densities was observed. All PEALD films had lower WVTRs than their thermally deposited counterparts. The lowest WVTR measured was 4.2 × 10−2 g m−2/day for a 17-nm-thick PEALD Al2O3 film deposited at 120°C. These results indicate the importance of optimizing deposition parameters to enable production of the most effective barrier films, which are essential in applications such as organic electronics. © 2018 Elsevier Ltd.
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    Competitive specific ion effects: a neutron reflectometry study of thermoresponsive
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Robertson, H; Johnson, EC; Gresham, IJ; Prescott, SW; Nelson, A; Wanless, EJ; Webber, GB
    Specific ion effects are phenomena that depend on the identity of ions present in a system, and not merely their valence or concentration. For example, the Hofmeister series orders ions on their ability to either stabilise (salting-in ions) or destabilise (salting-out ions) proteins and is vital in biochemistry.[1] In recent years, polymer brushes, which consist of end-tethered polymer chains to a substrate, have been used as exemplar systems to investigate specific ion effects. [2] The effective solvent quality influences the conformation of these brushes (collapsed or expanded), which is directly linked to application properties (e.g. switchable adhesion and self-cleaning). We have performed a significant body of work on brush conformation in single salt electrolytes.[2-4] However, our understanding of the influence that mixed electrolytes have on the behaviour of polymer brushes is currently limited, which is necessary for real-world applications. Here, we present the behaviour of poly(ethylene glycol) methyl ether methacrylate (POEGMA) brushes in a variety of both pure and mixed electrolytes, as studied with neutron reflectometry. Reflectometry allows for the extraction of volume fraction profiles, which can provide detailed information regarding the influence of ion specificity on polymer brush conformation. Consistent results were also obtained from other techniques, such as ellipsometry, which is used to track overall changes in brush thickness. In the presence of electrolytes composed of ions from the same end of the Hofmeister series (salting-in and salting-in or salting-out and salting-out), a non-monotonic concentration-dependent influence of the two ions was observed. The specific ion effects imparted by two salting-in ions were dependent on the influence of the ions with the polymer chains. In contrast, the impact of two salting-out ions was dependent on the available solvent molecules. In the presence of electrolytes composed of ions from opposite ends of the Hofmeister series (salting-in and salting-out), ion behaviour was observed to be temperature-dependent.[3] Much can be gained by improving our knowledge of ion specificity and understanding the subtle structural changes of a brush are essential in order to unravel the dominant drivers behind specific ion effects.
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    Competitive specific ion effects: a neutron reflectometry study of thermoresponsive polymer brushes in mixed electrolytes
    (Elsevier, 2020-10-26) Robertson, H; Johnson, EC; Gresham, IJ; Prescott, SW; Nelson, A; Wanless, EJ; Webber, GB
    Grafted poly(ethylene glycol) methyl ether methacrylate (POEGMA) copolymer brushes change conformation in response to temperature ('thermoresponse'). In the presence of different ions the thermoresponse of these coatings is dramatically altered. These effects are complex and poorly understood with no all-inclusive predictive theory of specific ion effects. As natural environments are composed of mixed electrolytes, it is imperative we understand the interplay of different ions for future applications. We hypothesise anion mixtures from the same end of the Hofmeister series (same-type anions) will exhibit non-additive and competitive behaviour. © 2023 Elsevier B.V.
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    Correlation of diffusion and performance in sequentially processed P3HT/PCBM heterojunction films by time-resolved neutron reflectometry
    (Royal Society of Chemistry, 2013-01-01) Lee, KH; Zhang, YL; Burn, PL; Gentle, IR; James, M; Nelson, A; Meredith, P
    Control over the structure of donor/acceptor blends is essential for the development of solution processable organic solar cells (OSCs). We have used time-resolved neutron reflectometry (NR) and in situ annealing to investigate the nanoscale structure and interdiffusion of sequentially spin-coated thin films of poly(3-n-hexylthiophene-2,5-diyl) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and correlated the evolving structure with the device performance. While the as-prepared film shows a clear two-layer structure it is evident that (19 wt%) PCBM has percolated throughout the lower P3HT layer. Upon heating, analysis of time-resolved NR data shows that the diffusion process is dependent on the annealing temperature. At temperatures up to 110 [degree]C, the two-layer structure is retained and only a small amount of PCBM diffuses from the interface into the lower layer, increasing the total PCBM content throughout the P3HT layer to 26 wt%. Significantly, this small change in acceptor content leads to a profound increase in device performance; with the power conversion efficiency (PCE) of the OSCs increasing from 0.47% (unannealed, 19 wt% PCBM) to 3.23% (annealed, 26 wt% PCBM) with the latter showing a similar efficiency to devices prepared from a blend containing 50 wt% PCBM. Further annealing at 120 and 130 [degree]C sees rapid interdiffusion between the two layers, along with an overall expansion in the thickness of the bilayer film. Despite the complete intermixing of the PCBM and P3HT to form a structure resembling a bulk heterojunction, essentially no improvement in device performance was observed for annealing at temperatures above 110 [degree]C. © 2013, Royal Society of Chemistry
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    Determination of fullerene scattering length density: a critical parameter for understanding the fullerene distribution in bulk heterojunction organic photovoltaic devices
    (American Chemical Society, 2014-01-27) Clulow, AJ; Armin, A; Lee, KH; Pandey, AK; Tao, C; Velusamy, M; James, M; Nelson, A; Burn, PL; Gentle, IR; Meredith, P
    Fullerene derivatives are commonly used as electron acceptors in combination with (macro)molecular electron donors in bulk heterojunction (BHJ) organic photovoltaic (OPV) devices. Understanding the BHJ structure at different electron donor/acceptor ratios is critical to the continued improvement and development of OPVs. The high neutron scattering length densities (SLDs) of the fullerenes provide effective contrast for probing the distribution of the fullerene within the blend in a nondestructive way. However, recent neutron scattering studies on BHJ films have reported a wide range of SLDs ((3.6–4.4) × 10–6 Å–2) for the fullerenes 60-PCBM and 70-PCBM, leading to differing interpretations of their distribution in thin films. In this article, we describe an approach for determining more precisely the scattering length densities of the fullerenes within a polymer matrix in order to accurately quantify their distribution within the active layers of OPV devices by neutron scattering techniques.© 2014, American Chemical Society.
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    Developments on the platypus neutron reflectometer
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Nelson, A; Le Brun, AP; Huang, TY; Paul, O; Holt, SA
    PLATYPUS is the initial neutron reflectometer at the Australian Centre for Neutron Scattering with the capability to study surface and interface systems ranging from biomolecules, soft matter through to magnetic thin films [1-3]. There have been a number of significant improvements to both the instrument and data reduction and treatment software [4] over the last two years. On the hardware front the original detector has been replaced yielding higher count-rate capabilities, greater detection efficiency at shorter wavelengths and significantly lower background. The slits which define the neutron beam have been replaced with upgraded positioning mechanisms enabling greater flexibility in experimental setup. These changes have significantly enhanced the instrument performance with improved reproducibility. This presentation will highlight the enhancements and recent publications.
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    Direct measurement of van der waals and diffuse double-layer forces between titanium dioxide surfaces produced by atomic layer deposition
    (American Chemical Society, 2012-04-12) Walsh, RB; Nelson, A; Skinner, WM; Parsons, DF; Craig, VSJ
    The van der Waals forces between titanium dioxide surfaces produced by atomic layer deposition (ALD) at the isoelectric point have been measured and found to agree with the calculated interaction using Lifshitz theory. It is shown that under the right conditions very smooth ALD surfaces are produced. At pH values slightly below and above the isoelectric point, a repulsive diffuse double-layer repulsion was observed and is attributed to positive and negative charging of the surfaces, respectively. At high pH, it was found that the forces remained repulsive up until contact and no van der Waals attraction or adhesion was evident. The absence of an attraction cannot be explained by the presence of hydration forces.© 2012, American Chemical Society
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    Direct visualisation of mesh phases at the solid/solution interface by AFM and neutron reflectometry
    (The Bragg Institute, Australian Nuclear Science and Technology Organisation, 2005-11-27) Blom, ACM; Warr, GG; Nelson, A
    Using soft-contact AFM imaging, the adsorbed layer structure of mixed solutions of single-chained dodecyltrimethylammonium bromide (DTAB) and double-chained didodecyldimethylammonium bromide (DDAB) at varying compositions has been studied. On quartz, the observed morphologies as composition was varied from DDAB-rich mixtures to DTAB-rich mixtures changed from a bilayer -> mesh -> rods -> globules. This novel mesh structure is consistent with the average curvature progression from bilayer to rods, and consists of densely branched rods. There was a narrow solution composition over which this mesh structure was observed and a fractional change in solution composition resulted in a film transformation to rods. Neutron reflectometry experiments on multiple contrasts have been performed in ISIS and at ANSTO and confirm the curvature sequence observed using AFM. The composition of the mixed film was determined as were adsorbed amounts, film thicknesses and surface coverages. Despite there being an excess of DTAB in solution, the surface was very enriched in DDAB for the two mixed films. © 2005 The Authors
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    Effect of functionalized gold nanoparticles on floating lipid bilayers
    (American Chemical Society, 2013-06-04) Tatur, S; Maccarini, M; Barker, R; Nelson, A; Fragneto, G
    The development of novel nano-engineered materials poses important questions regarding the impact of these new materials on living systems. Possible adverse effects must be assessed in order to prevent risks for health and the environment. On the other hand, a thorough understanding of their interaction with biological systems might also result in the creation of novel biomedical applications. We present a study on the interaction of model lipid membranes with gold nanoparticles (AuNP) of different surface modifications. Neutron reflectometry experiments on zwitterionic lipid double bilayers were performed in the presence of AuNP functionalized with cationic and anionic head groups. Structural information was obtained that provided insight into the fate of the AuNPs with regard to the integrity of the model cell membranes. The AuNPs functionalized with cationic head groups penetrate into the hydrophobic moiety of the lipid bilayers and cause membrane disruption at an increased concentration. In contrast, the AuNPs functionalized with anionic head groups do not enter but seem to impede the destruction of the lipid bilayer at an alkaline pH. The information obtained might influence the strategy for a better nanoparticle risk assessment based on a surface charge evaluation and contribute to nano-safety considerations during their design. © 2013, American Chemical Society.
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    The effects of acid hydrolysis on protein biosurfactant molecular, interfacial, and foam properties: pH responsive protein hydrolysates
    (Royal Society of Chemistry, 2012-03-23) Dimitrijev-Dwyer, M; He, LZ; James, M; Nelson, A; Wang, LG; Middelberg, APJ
    The success of hydrolysis in improving the functional foaming properties of surface-active proteins is usually attributed to three factors: decreased molecular size; increased hydrophobicity; and microchemical changes, specifically deamidation of glutamine and asparagine. Studying these individual factors is difficult using naturally-occurring proteins, as hydrolysate products are complex mixed systems, and the mechanisms of foam stabilization are likewise complex. To address this complexity we report studies of a recombinant protein (DAMP4) which comprises four peptide surfactant (DAMP1) molecules connected by acid-labile amino acid (Asp-Pro) linkers. Hydrolysis of DAMP4 under conditions of low pH and high temperature produced h-DAMP1, a mixture of deamidated variants of the chemically-synthesized DAMP1 peptide surfactant. By examining foaming performance of these molecules, we are able to isolate the effects of molecule size (DAMP1 vs. DAMP4) and deamidation (h-DAMP1 vs. DAMP1). Molecule size had little effect on foaming for the conditions studied. However, deamidation completely changed foaming behaviour, most likely due to alteration of interfacial charge structure (through deamidation of glutamine to glutamic acid) and consequent effects on thin-film stability. Good foaming was observed only at pH values away from the isoelectric points (pI) of the biomolecules where an electrostatic barrier to film rupture can occur. The addition of Zn2+ to DAMP4, h-DAMP1 and DAMP1 caused visible aggregation under all conditions, which assisted in stabilising foams only in situations where a net charge would be expected. © 2012, Royal Society of Chemistry
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    Electrical double-layer capacitance in room temperature ionic liquids: ion-size and specific adsorption effects
    (American Chemical Society, 2010-09-02) Lauw, Y; Horne, MD; Rodopoulos, T; Nelson, A; Leermakers, FAM
    The electrical double-layer structure and capacitance in room temperature ionic liquids at electrified interfaces were systematically studied with use of the self-consistent mean-field theory. The capacitance curve departs from symmetry with respect to the point of zero charge when unequal ion-size is implemented or when specific adsorption of ions is introduced. For the case of unequal ion-size, the shape of the capacitance curve is strongly determined by the size of the counterion and only weakly influenced by the co-ion size. When present, specifically adsorbed ions would change the capacitance within a limited range of applied potential from the point of zero charge, which itself varies with the strength of specific adsorption. © 2010, American Chemical Society
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    Electrochemical cell for neutron reflectometry studies of the structure of ionic liquids at electrified interface
    (American Institute of Physics, 2010-07) Lauw, Y; Rodopoulos, T; Gross, M; Nelson, A; Gardner, R; Horne, MD
    We describe the design and use of a closed three-electrode electrochemical cell for neutron reflectometry studies of the structure of the electrical double-layer in ionic liquids. A transparent glass counter electrode was incorporated to allow easy monitoring of any gas bubbles trapped in the cell. A 100 mm diameter silicon wafer polished to 0.1 nm rms roughness coated with gold over a chromium adhesion layer was used as the working electrode. The utility of the cell was demonstrated during neutron reflectometry measurements of the ultrahigh purity ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][NTf2]) at two different applied potentials. © 2010, American Institute of Physics
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    Elimination of undesirable water layers in solid-contact polymeric ion-selective electrodes
    (American Chemical Society, 2008-09-01) Veder, JP; De Marco, R; Clarke, G; Chester, R; Nelson, A; Prince, KE; Pretsch, E; Bakker, E
    This study aimed to develop a novel approach for the production of analytically robust and miniaturized polymeric ion sensors that are vitally important in modem analytical chemistry (e.g., clinical chemistry using single blood droplets, modem biosensors measuring clouds of ions released from nanoparticle-tagged biomolecules, laboratory-on-a-chip applications, etc.). This research has shown that the use of a water-repellent poly(methyl methacrylate)/poly(decyl methacrylate) (PMMA/PDMA) copolymer as the ion-sensing membrane, along with a hydrophobic poly(3-octylthiophene 2,5-diyl) (POT) solid contact as the ion-to-electron transducer, is an excellent strategy for avoiding the detrimental water layer formed at the buried interface of solid-contact ion-selective electrodes (ISEs). Accordingly, it has been necessary to implement a rigorous surface analysis scheme employing electrochemical impedance spectroscopy (EIS), in situ neutron reflectometry/EIS (NR/EIS), secondary ion mass spectrometry (SIMS), and small-angle neutron scattering (SANS) to probe structurally the solid-contact/membrane interface, so as to identify the conditions that eliminate the undesirable water layer in all solid-state polymeric ion sensors. In this work, we provide the first experimental evidence that the PMMA/PDMA copolymer system is susceptible to water "pooling" at the interface in areas surrounding physical imperfections in the solid contact, with the exposure time for such an event in a PMMA/PDMA copolymer ISE taking nearly 20 times longer than that for a plasticized poly(vinyl chloride) (PVC) ISE, and the simultaneous use of a hydrophobic POT solid contact with a PMMA/PDMA membrane can eliminate totally this water layer problem. © 2008, American Chemical Society
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    Evidence of a water layer in solid-contact polymeric ion sensors
    (Royal Society of Chemistry, 2008-01-01) De Marco, R; Veder, JP; Clarke, G; Nelson, A; Prince, KE; Pretsch, E; Bakker, E
    This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 angstrom water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs). © 2008, Royal Society of Chemistry
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    Examining the structural and mechanical implications of surfactants on neutral polymer brushes through neutron reflectometry
    (Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Gresham, IJ; Willott, JD; de Vos, WM; Johnson, EC; Humphreys, BA; Murdoch, TJ; Wanless, EJ; Webber, GB; Nelson, A; Prescott, SW
    Layers of densely-tethered polymers (polymer brushes) are of interest due to their potential applications as nano-actuators, biocompatible coatings, and switchable lubricating or antifouling surfaces. These applicable properties are dependant on the structure of the polymer interface, so it is important that the structural effects of common compounds and relevant environmental variables be understood. Neutron Reflectometry (NR) is the only technique capable of providing detailed structural resolution of solvated multi-component polymer brush systems due to its penetrating power and the possibility of isotopic substitution. Here we present a Neutron Reflectometry study on the effects of surface-active molecules (surfactants) on two neutral polymer brushes, poly(ethylene oxide) (PEO) and Poly(N-isopropylacrylamide) (PNIPAM), focusing on small, single tail surfactants. PEO is a widely used biocompatible polymer with a range of medical and commercial applications, whilst PNIPAM is a well known thermoresponsive polymer, undergoing a swollen to collapsed transition over its critical solution temperature (CST) of 32˚C. We show that these two polymers exhibit similar yet distinct interactions with surfactants, with the observed differences having implications for the mechanism of brush-surfactant interaction. The presence of surfactants was found to raise the CST of PNIPAM; we show that this effect is dependent strongly on surfactant identity and concentration. As part of this work we have developed new modelling techniques for the analysis of NR data from polymer brush interfaces. These advancements will be explained in the context of the data at hand, and their applicability to other soft diffuse interfaces will be briefly discussed. © The Authors.