Interfacial interactions between nitrifying bacteria and mineral carriers in aqueous media determined by contact angle measurements and thin layer wicking

Contact angle measurements enable the determination of the surface free energy on flat and smooth solid surfaces. The thin layer wicking technique permits this determination for powdered materials. Both techniques were assayed on limestone and basalt which were the materials used as supports for bacterial adhesion. The resulting surface free energy components were compared. The free energy of interaction between nitrifying bacteria and support materials in aqueous medium (∆G132) was calculated and correlated with bacterial adhesion observed in a previous study. Although the values of the polar and apolar components were not exactly the same, both techniques lead to the same conclusions in terms of the ability for bacterial adhesion.Project 01:REGII:6:96.Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI - BD:9121:96

Adsorption of polyelectrolytes from semi-dilute solutions on an oppositely charged surface

We propose a detailed description of the structure of the layer formed by polyelectrolyte chains adsorbed onto an oppositely charged surface in the semi-dilute regime. We combine the mean-field Poisson-Boltzmann-Edwards theory and the scaling functional theory to describe the variations of the monomer concentration, the electrostatic potential, and the local grafting density with the distance to the surface. For long polymers, we find that the effective charge of the decorated surface (surface plus adsorbed polyelectrolytes) can be much larger than the bare charge of the surface at low salt concentration, thus providing an experimental route to a "supercharging" type of effect.Comment: 14 pages, 6 figure

Effect of the Molecular Weight of Polyvinyl Alcohol on Some Adsorption Parameters in the Titania-Polymer Solution System

Fractions of polyvinyl alcohol (PVA) obtained by separation of the PVA samples of the mean molecular weight of 72000 and 125000 have been studied. The effect of the molecular weight of PVA, pH value and concentration of the solution on the adsorbed amount and the thickness of the adsorption layer of PVA (<5) were measured. The value of d was determined from the viscosity change of titania suspensions with adsorbed PVA in relation to the same suspensions without PVA. The volume occupied by a polyvinyl alcohol molecule at the interface region was evaluated from the adsorbed amount and the value of d. Thus calculated volume was then compared with the volume occupied by a PVA molecule in the bulk solution

Ag:TiN-Coated Polyurethane for Dry Biopotential Electrodes: From Polymer Plasma Interface Activation to the First EEG Measurements

Several plasma treatments using argon, oxygen, and nitrogen are studied in order to increase the interfacial adhesion of the polyurethane/Ag:TiN system to be used as biopotential electrodes. The optimized plasma treatments conditions (100 W, 15 min, regardless of the gas) promote a steep decrease of the water contact angle values. The observed chemical and topographic alterations translate into excellent polyurethane/Ag:TiN interfacial adhesion of the plasma treated samples. The in-service validation of the proposed Ag:TiN-coated PU multipin electrodes is performed by acquiring EEG signals in parallel with the standard wet Ag/AgCl electrodes. No considerable differences are found in terms of shape, amplitude, and spectral characteristics of the signals when comparing reference wet and dry electrodes.This research is partially sponsored by FEDER funds through the program COMPETE – Programa Operacional Factores de Competitividade and by national funds through FCT – Fundação para a Ciência e a Tecnologia, under the projects PEst-C/EME/UI0285/2011, PTDC/SAU-ENB/116850/2010, PTDC/CTM-NAN/112574/2009 and Programa Pessoa 2012/2013 Cooperação Portugal/França, Project no. 27306UA Porous architectures in GRAded CERamic thin films for biosensors - GRACER. The authors would also like to acknowledge CEMUP for SEM analysis and Yantai Wanhua Polyurethanes Co., Ltd for providing the thermoplastic polyurethane pellets. P. Pedrosa acknowledges FCT for the Ph.D. grant SFRH/BD/70035/2010. P. Fiedler acknowledges the German Federal Ministry of Education and Research project – 03IPT605A. P. Pedrosa and P. Fiedler both acknowledge FP7-People Marie Curie IAPP project 610950 (ANDREA) and German Academic Exchange Services for the Germany/Portugal bi-lateral project – D/57036536

Electrostatic Potentials at Solid/Liquid Interfaces

This review deals with electrostatic potentials within solid/electrolyte interfaces. The electrostatic potentials of several planes are defined and discussed: the inner surface potential affecting the state of charged surface species due to interactions with potential determining ions (Ψ0), the potential affecting the state of associated counterions (Ψβ), the potential at the onset of diffuse layer (Ψd) and the electrokinetic potential (ζ). The relevance of zero values of these potentials is also discussed and the corresponding points of zero charge are defined. Experimental methods for the measurement of the interfacial potentials are presented. The relations between potentials and surface charges are given on the basis of the Surface Complexation model. Some experimental findings are provided

Electrostatic Potentials at Solid/Liquid Interfaces

This review deals with electrostatic potentials within solid/electrolyte interfaces. The electrostatic potentials of several planes are defined and discussed: the inner surface potential affecting the state of charged surface species due to interactions with potential determining ions (Ψ0), the potential affecting the state of associated counterions (Ψβ), the potential at the onset of diffuse layer (Ψd) and the electrokinetic potential (ζ). The relevance of zero values of these potentials is also discussed and the corresponding points of zero charge are defined. Experimental methods for the measurement of the interfacial potentials are presented. The relations between potentials and surface charges are given on the basis of the Surface Complexation model. Some experimental findings are provided

Methods to study microbial adhesion on abiotic surfaces

Microbial biofilms are a matrix of cells and exopolymeric substances attached to a wet and solid surface and are commonly associated to several problems, such as biofouling and corrosion in industries and infectious diseases in urinary catheters and prosthesis. However, these cells may have several benefits in distinct applications, such as wastewater treatment processes, microbial fuel cells for energy production and biosensors. As microbial adhesion is a key step on biofilm formation, it is very important to understand and characterize microbial adhesion to a surface. This study presents an overview of predictive and experimental methods used for the study of bacterial adhesion. Evaluation of surface physicochemical properties have a limited capacity in describing the complex adhesion process. Regarding the experimental methods, there is no standard method or platform available for the study of microbial adhesion and a wide variety of methods, such as colony forming units counting and microscopy techniques, can be applied for quantification and characterization of the adhesion process.This work was financially supported by: Project UID/EQU/00511/2013-LEPABE, by the FCT/MEC with national funds and co-funded by FEDER in the scope of the P2020 Partnership Agreement; Project NORTE-07-0124-FEDER-000025 - RL2_Environment&Health, by FEDER funds through Programa Operacional Factores de Competitividade-COMPETE, by the Programa Operacional do Norte (ON2) program and by national funds through FCT - Fundacao para a Ciencia e a Tecnologia; European Research Project SusClean (Contract number FP7-KBBE-2011-5, project number: 287514), Scholarships SFRH/BD/52624/2014, SFRH/BD/88799/2012 and SFRH/BD/103810/2014