A Neutron Scattering Study of the Structure of Poly(dimethylsiloxane)-Stabilized Poly(methyl methacrylate) (PDMS–PMMA) Latexes in Dodecane

Hard-sphere particles in nonpolar solvents are an essential tool for colloid scientists. Sterically stabilized poly(methyl methacrylate) (PMMA) particles have long been used as the exemplary hard-sphere system. However, neither the particles themselves nor the poly(12-hydroxystearic acid) (PHSA) stabilizer necessary to prevent aggregation in nonpolar solvents are commercially available. To counter this, several alternatives have been proposed. In recent years, there has been an increased interest in poly(dimethylsiloxane) (PDMS) stabilizers as a commercially available alternative to PHSA, yet the structure of particles made in this way is not as well understood as those produced using PHSA. In this work, we employ small-angle neutron scattering to determine the internal structure of PDMS-stabilized PMMA particles, synthesized with and without an additional crosslinking agent. We report data consistent with a homogeneous PMMA core with a linearly decaying PDMS shell. The thickness of the shell was in excess of 50 nm, thicker than the PHSA layer typically used to stabilize PMMA but consistent with reports of the layer thickness for similar molecular weight PDMS at planar surfaces. We also show that the amount of the hydrogenous material in the particle core of the crosslinked particles notably exceeds the amount of added ethylene glycol dimethacrylate crosslinker, suggesting some entrapment of the PDMS stabilizer in the PMMA matrix

Probability Distribution Function of the Diquark Condensate in Two Colours QCD

We consider diquark condensation in finite density lattice SU(2). We first present an extension of Vafa-Witten result, on spontaneous breaking of vector-like global symmetries, that allows us to formulate a no-go theorem for diquark condensation in a region of the chemical potential-mass parameter space. We then describe a new technique to calculate diquark condensation at any number of flavours directly at zero external source without using any potentially dangerous extrapolation procedure. We apply it to the strong coupling limit and find compelling evidences for a second order phase transition, where a diquark condensate appears, as well as quantitative agreement between lattice results and low-energy effective Lagrangian calculations.Comment: 21 pages, 7 figure

Adsorption of the prototypical organic corrosion inhibitor benzotriazole on the Cu(100) surface

M.T. gratefully acknowledges financial support from Lubrizol Limited and thanks the Engineering and Physical Sciences Research Council (EPSRC) grant EP/L015307/1 for the Molecular Analytical Science Centre for Doctoral Training (MAS-CDT). C.G. acknowledges the use of the Euler cluster at ETH Zurich for the DFT calculations. F.G. acknowledges funding from the EPSRC (grant EP/S027270/1).The interaction of benzotriazole (BTAH) with Cu(100) has been studied as a function of BTAH exposure in a joint experimental and theoretical effort. Scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS) and density functional theory (DFT) calculations have been combined to elucidate the structural and chemical characteristics of this system. BTAH is found to deprotonate upon adsorption on the copper surface and to adopt an orientation that depends on the molecular coverage. Benzotriazolate (BTA) species initially lie with their planes parallel to the substrate but, at a higher molecular coverage, a transition occurs to an upright adsorption geometry. Upon increasing the BTAH exposure, different phases of vertically aligned BTAs are observed with increasing molecular densities until a final, self-limiting monolayer is developed. Both theory and experiment agree in identifying CuBTA and Cu(BTA)2 metal-organic complexes as the fundamental building blocks of this monolayer. This work shows several similarities with the results of previous studies on the interaction of benzotriazole with other low Miller index copper surfaces, thereby ideally completing and concluding them. The overall emerging picture constitutes an important starting point for understanding the mechanism for protection of copper from corrosion.Publisher PDFPeer reviewe

Understanding the passivation layer formed by tolyltriazole on copper, bronze, and brass surfaces

Funding: Lubrizol Ltd is acknowledged for funding and supplying TTAH. EPSRC is acknowledged (EP/L017008/1, EP/T019298/1, and EP/R023751/1) for electron microscopy.Tolyltriazole (TTAH) is used industrially as a corrosion inhibitor for copper alloys, particularly in organic media. In this study, the morphology and chemistry of the layer formed by TTAH on copper and copper alloys under realistic conditions is investigated, with focus on the effects due to the presence of tin or zinc in the substrates. A combination of X-ray photoelectron spectroscopy (XPS), medium energy ion scattering (MEIS), and scanning transmission electron microscopy (STEM) has been used. It was found that an inhomogeneous metal–organic layer forms on the surface of copper specimens, likely in the form of copper nanoparticles surrounded by CuxTTAy complexes. This layer increases in thickness for at least 30 days. Chemically, the copper species in the layer are initially in the +2 oxidation state, but after longer exposure to TTAH, mostly Cu(I) is observed. In bronze samples, tin does not appear to segregate to the surface layer. In brass samples, zinc is depleted from the bulk and forms a thicker ZnxTTAy layer.Peer reviewe

Understanding the interaction of organic corrosion inhibitors with copper at the molecular scale : benzotriazole on Cu(110)

M.T. gratefully acknowledges financial support from Lubrizol Limited and, together with J.E., thank the Engineering and Physical Sciences Research Council (EPSRC) grant EP/L015307/1 for the Molecular Analytical Science Centre for Doctoral Training (MAS-CDT). C.G acknowledges the Euler cluster managed by the HPC team at ETH Zurich for computational resources and is grateful for computational support from the UK national high performance computing service, ARCHER, for which access was obtained via the UKCP consortium and funded by EPSRC grant EP/P022561/1.Benzotriazole (BTAH) has been used for several industrial applications, but most commonly as a corrosion inhibitor for copper, since the 1950s. However, the mechanism of its interaction with copper surfaces at the atomistic scale is still a matter of debate. Here, the adsorption of BTAH onto a clean Cu(110) surface has been investigated by a combination of scanning tunnelling microscopy, X-ray photoelectron spectroscopy, high resolution electron energy loss spectroscopy and density functional theory calculations. Different supramolecular structures have been observed depending on molecular coverage and annealing. In the low coverage regime, flat lying deprotonated species are formed which give way to benzotriazolate molecules in an upright configuration by increasing the BTAH exposure. The ensuing monolayer is self-limiting but, upon annealing above 150 °C, transforms into a highly ordered nano-ridge structure resulting from a significant in-plane and out-of-plane reconstruction of the surface. All structures are characterised by a strong molecule-substrate interaction and the high coverage phases are dominated by the formation of metal-organic complexes between copper adatoms and benzotriazolate species. These findings shed light on the nature and strength of the interaction occurring between BTAH and copper which lies at the basis of the effectiveness of this prototypical corrosion inhibitor.PostprintPeer reviewe

The African Global Mental Health Institute: Increasing capacity, inclusivity and translation of psychiatric research and care

The largest treatment gap for mental, neurological and substance use (MNS) disorders to date exists in Sub-Saharan Africa (e.g., South Africa, Malawi, Nigeria).  While efforts have been made to reduce the global burden of MNS disorders, there remain significant barriers to delivery of equitable mental health care in Africa and the diaspora. These barriers are deeply rooted in a lack of research structures to inform care delivery, few outlets to train in-country mental health professionals, and limited involvement of policymakers in translation of research findings. Given the demonstrated need across domains of research, education, service delivery and policy in Africa, it is in the purview of global leaders and mental health professionals to build the infrastructure necessary to make systematic, targeted strides to develop each of these areas. With this conceptual framework in mind, over fifty global leaders, psychiatrists, mental health professionals and advocates with expertise in cultural psychiatry convened at a global conference in Cape Town, South Africa in 2016 to establish the African Global Mental Health Institute (AGMHI). The AGMHI is an organizational effort that aims to reduce the global burden of mental illness through research, education and training, service delivery, and policy. Aligned with mental health initiatives posited by the World Health Organization (WHO) and the World Bank, the AGMHI represents an opportunity to explore and understand cultural nuance among populations in Africa and the diaspora. This article focuses on the AGMHI’s targeted strategies in the following actions: 1) bolstering training and education programs for clinicians and/or researchers in Africa and the diaspora to increase human capacity for mental health; 2) conducting and disseminating inclusive, culturally-relevant research (e.g., research that involves community stakeholders in its design and conduct) to meet the urgent need for a culturally-relevant evidence base;  3) identifying key stakeholders to promote sustainable mental health care and inform policy; and 4) fostering local and global collaborations (e.g., engaging local and national governments, non-governmental organizations (NGO), academic institutions, etc.) to share methods of improving access to mental health services. In concert with empirical data, these strategies were devised by members of the AGMHI, which is comprised of international leaders with decades of expertise in global psychiatry. While the MNS disorder treatment gap remains at large, the AGMHI believes these specific strategies are a step toward reducing the treatment gap and enhancing mental health care access globally

Undergraduate Research Participation in Electrical Engineering

During the 1990-2003 summers the Electrical Engineering Department at the University of Maine will offer ten undergraduate students the opportunity to actively participate in research. Students will receive financial awards plus a subsistence allowance. The available research projects include (1) Environmental Sensors; (2) Intelligent Systems for Automation; (3) Communications Devices and Applications; (4) Motion Control; (5) Microprocessor/Instrumentation Applications; (6) Growth and Characterization of Thin Film Materials; and (7) Power Systems Applications. At least five students will come from institutions where research opportunities are limited and at least four students will be women, minorities or students with disabilities. Students chosen for the program will have displayed a high degree of initiative and independence of thought in both laboratories and course work. Student research projects are chosen to match the student\u27s interest and educational level. In addition to extensive University facilities, students will also have access to facilities at various nearby industries such as Sensor Research and Development Corporation, BIODE Corporation, Bangor Hydro Electric and Central Maine Power Companies, James River, Champion, and Scott Paper Companies, Digital Equipment Corporation, Fairchild and National Semiconductor. At the program culmination a written report and an oral seminar are required from the student. Three academic credits are awarded to the student upon satisfactory completion of the program

The effect of solvent and counterion variation on inverse micelle CMCs in hydrocarbon solvents

Critical micelle concentrations (CMCs) for the formation of inverse micelles have been determined for anionic surfactants in nonpolar, hydrocarbon solvents. Sodium dioctylsulfosuccinate (Aerosol OT or AOT) was chosen as the model surfactant, with systematic variations in both the solvent (benzene, cyclohexane, and dodecane) and the surfactant counterion (sodium and tetrapropylammonium). Recent work (Langmuir 29 (2013) 3352–3258) has shown that high-resolution small-angle neutron scattering (SANS) measurements can be used to directly determine the presence or absence of aggregates in solution. No variation in the value of the CMC was found within the resolution of the measurements for changing either solvent or counterion; some effects on the structure of inverse micelles were observed. This lack of a significant difference in the onset of inverse micellization with changes to the molecular species is surprising, and the implications on the solvophobic effect in nonpolar solvents are discussed