142 research outputs found
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
Influence of Solution pH on Stability of Fumed Silica–Polyacrylic Acid Systems
The influence of polyacrlic acid (PAA) adsorption on fumed silica (SiO2) surface on suspension stability has been studied. Сhanges in the suspension stability were monitored using a Turbiscan LabExpert with a TLAb Cooler cooling module at 25oC. PAA is an anionic polymer containing carboxyl groups; therefore all the measurements were carried out at different pH 3, 6 and 9. Analysis of obtained transmission and backscattering curves and Turbiscan Stability Indexes (TSI) allowed determination of the most probable mechanism of the system stability.Вивчено вплив адсорбції поліакрилової кислоти (ПAК) на поверхні високодисперсного кремнезему (SiO2) на стабільність суспензії. Зміни стабільності суспензії спостерігались за допомогою приладу Turbiscan LabExpert із охолоджуючим модулем TLAb Cooler при 25oC. ПAК є аніонним полімером, що містить карбоксильні групи, тому всі вимірювання проводились при різних рН (3, 6 та 9). Аналіз одержаних кривих перенесення та зворотнього розсіяння, а також індексів стабільності (Turbiscan Stability Indexes (TSI)) дозволив визначити найбільш вірогідний механізм стабілізації вивчених систем.Изучено влияние адсорбции полиакриловой кислоты (ПAA) на поверхности высокодисперсного кремнезема (SiO2) на стабильность суспензии. Изменения стабильности суспензии наблюдались с помощью прибора Turbiscan LabExpert с охлаждающим модулем TLAb Cooler при 25oC. PAA является анионным полимером, содержащим карбоксильные группы, поэтому все измерения проводились при различных рН (3, 6 и 9). Анализ полученных кривых переноса и обратного рассеяния, а также индексов стабильности (Turbiscan Stability Indexes (TSI)) позволил определить наиболее вероятный механизм стабилизации изученных систем
The Influence of Protonation on the Electroreduction of Bi (III) Ions in Chlorates (VII) Solutions of Different Water Activity
Investigation of the polyvinyl alcohol stabilization mechanism and adsorption properties on the surface of ternary mixed nanooxide AST 50 (Al2O3–SiO2–TiO2)
Determination of relevance between surface free energy and adsorption capacity of cement particles
ABSTRACT The compatibility between superplasticizer and cement was influenced by the adsorption capacity of cement particles. This study investigated the relevance between the adsorption capability and surface free energy. Adsorption capacity and surface free energy of both sulphoaluminate cement and portland cement were measured. The adsorption capacity of cement particles was measured by ultraviolet spectrophotometry. The test showed that particles of sulphoaluminate cement adsorbed more molecules of superplasticizer than portland cement particles. The weight of superplasticizer adsorbed by 2g of sulphoaluminate cement and portland cement were 0.28mg and 0.159mg respectively. Surface free energy of cement particles was calculated by contact angle and the contact angles were determined by the thin-layer wicking technique and washburn equation which is theoretical basis of thin-layer wiching technique presented by Chibowski E. The sulphoaluminate cement, portland cement's surface free energy were 51.46 mJ·m-2 and 49.36 mJ·m-2 respectively. The results showed that the higher adsorption capacity of particles was usual accompanied by higher surface free energy. The fluidity of cement paste was influenced by the adsorption capacity of cement particles because the more molecules of superplasticizer was adsorbed by cement particles there were lacking superplasticizer in the paste. The macro-behaviour of higher adsorption capacity is that the cement paste need more superplasticizer to reach the needed fluidity
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
Hysteresis of Contact Angle of Sessile Droplets on Smooth Homogeneous Solid Substrates via Disjoining/Conjoining Pressure
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.langmuir.5b01075A theory of contact angle hysteresis of liquid droplets on smooth, homogeneous solid substrates is developed in terms of the shape of the disjoining/conjoining pressure isotherm and quasi-equilibrium phenomena. It is shown that all contact angles, θ, in the range θr < θ < θa, which are different from the unique equilibrium contact angle θ ≠ θe, correspond to the state of slow “microscopic” advancing or receding motion of the liquid if θe < θ < θa or θr < θ < θe, respectively. This “microscopic” motion almost abruptly becomes fast “macroscopic” advancing or receding motion after the contact angle reaches the critical values θa or θr, correspondingly. The values of the static receding, θr, and static advancing, θa, contact angles in cylindrical capillaries were calculated earlier, based on the shape of disjoining/conjoining pressure isotherm. It is shown now that (i) both advancing and receding contact angles of a droplet on a on smooth, homogeneous solid substrate can be calculated based on shape of disjoining/conjoining pressure isotherm, and (ii) both advancing and receding contact angles depend on the drop volume and are not unique characteristics of the liquid–solid system. The latter is different from advancing/receding contact angles in thin capillaries. It is shown also that the receding contact angle is much closer to the equilibrium contact angle than the advancing contact angle. The latter conclusion is unexpected and is in a contradiction with the commonly accepted view that the advancing contact angle can be taken as the first approximation for the equilibrium contact angle. The dependency of hysteresis contact angles on the drop volume has a direct experimental confirmation
Early Staphylococcal Biofilm Formation on Solid Orthopaedic Implant Materials: In Vitro Study
Biofilms forming on the surface of biomaterials can cause intractable implant-related infections. Bacterial adherence and early biofilm formation are influenced by the type of biomaterial used and the physical characteristics of implant surface. In this in vitro research, we evaluated the ability of Staphylococcus epidermidis, the main pathogen in implant-related infections, to form biofilms on the surface of the solid orthopaedic biomaterials, oxidized zirconium-niobium alloy, cobalt-chromium-molybdenum alloy (Co-Cr-Mo), titanium alloy (Ti-6Al-4V), commercially pure titanium (cp-Ti) and stainless steel. A bacterial suspension of Staphylococcus epidermidis strain RP62A (ATCC35984) was added to the surface of specimens and incubated. The stained biofilms were imaged with a digital optical microscope and the biofilm coverage rate (BCR) was calculated. The total amount of biofilm was determined with the crystal violet assay and the number of viable cells in the biofilm was counted using the plate count method. The BCR of all the biomaterials rose in proportion to culture duration. After culturing for 2-4 hours, the BCR was similar for all materials. However, after culturing for 6 hours, the BCR for Co-Cr-Mo alloy was significantly lower than for Ti-6Al-4V, cp-Ti and stainless steel (P0.05). These results suggest that surface properties, such as hydrophobicity or the low surface free energy of Co-Cr-Mo, may have some influence in inhibiting or delaying the two-dimensional expansion of biofilm on surfaces with a similar degree of smoothness
- …