Faculty Publications
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Item Contact Angle Measurements(Elsevier Inc., 2017) Hebbar, R.S.; Isloor, A.M.; A.F., A.F.Contact angle has been an important parameter to determine the wetting ability of the polymer membrane surface. Contact angle has gained interest in surface science in regards to its fundamental aspects and application point of view. This chapter will give an insight into fundamentals of contact angle including the theoretical backgrounds, brief history, and importance of contact angle. The various factors that affect the contact angle measurement will also be discussed. The chapter will also present contact angle hysteresis phenomena, comprising of advancing and receding contact angles along with the manifestations of contact angle hysteresis. The chapter will highlight the various methods and techniques available for the measurement of contact angle along with the comprehensive description of the methods. The chapter also covers the application contact angle on surface characterization, permeation, and antifouling nature of the membrane. © 2017 Elsevier B.V. All rights reserved.Item Wetting characteristics of sn-0.7cu lead-free solder alloy on copper substrates(Trans Tech Publications Ltd ttp@transtec.ch, 2012) Satyanarayan, S.; Prabhu, K.N.In the present work, the effect of surface texture on wetting characteristics of lead-free solder Sn-0.7Cu on copper substrates have been investigated at 298°C. The wetting tests were carried out using FTA 200 (First Ten Angstrom) dynamic contact angle analyzer. The surface texture of copper substrate significantly affected the wetting properties of Sn-0.7Cu solder alloy. Contact angles of about 30° were obtained on Cu substrate having smooth surface texture (Ra = 0.0155μm). On other hand contact angles on rough copper surface texture (Ra = 1.1194μm) were reduced to 20°. The contact angles decreased with increasing surface texture of Cu substrate. For rough Cu substrate, it seems that the solder atoms dissolve into the substrate in the time period of 200-600s. © (2012) Trans Tech Publications.Item Development of clay based nanofluids for quenching(2012) Ramesh, G.; Prabhu, K.N.In the present work the effect of addition of nanoclay particles having concentrations of 0.001, 0.01 and 0.1 vol% on cooling performance of water during immersion quenching was investigated. Cooling curve analyses were carried out by using standard ISO/DIS 9950 quench probe. Wetting behavior of nanoquenchant was studied using dynamic contact angle analyzer. The spreading behavior of droplets of quench media on INCONEL 600 substrate indicates improved wetting behavior of nanofluids. The peak cooling rate and cooling rate at 700°C for water decreased by addition of nanoparticles. Further, quenching in nanofluid shows longer vapour blanket stage as compared to water. The estimated flux transients and Grossmann H factor clearly show that decreased cooling performance of water by addition of nanoparticles. Copyright © 2012 ASM International® All rights reserved.Item Wetting behavior of lead-free solders on copper substrates(Institution of Engineering and Technology jbristow@theiet.org, 2013) Satyanarayan, S.; Prabhu, K.N.The effect of substrate surface roughness on the wetting behavior of Sn-0.7Cu and Sn-0.3Ag-0.7Cu solder alloys on copper (Cu) substrates was investigated. The contact angles of both solder alloys decreased with increase in substrate surface roughness. The exponential power law (EPL), φ = exp (-KÏ„n), was used to model the relaxation behaviour of solders. Solder spreading kinetics was successfully represented by the (EPL). EPL parameters (K and n) alloy decreased with an increase in surface roughness. Spreading of solder alloys on both substrates exhibited capillary, gravity and viscous regimes. High spreading rates in the capillary regime, moderate in gravity regime and almost constant rates in viscous regimes were observed.Item Effect of surface treatment on wetting behavior of copper(Elsevier Ltd, 2019) Kalgudi, S.; Pavithra, G.P.; Prabhu, N.K.; Koppad, P.G.; Venkate Gowda, C.; Satyanarayan, S.Super-hydrophobic surfaces are very useful in cleaning activities. Surfaces with water contact angles above 150° are regarded as superhydrophobic surfaces. In the present study an attempt has been made to achieve superhydrophobicity on copper substrate by electrochemical etching and electro-deposition of Co-Ni alloy and Co-Ni-Graphene composite. A contact angle of about 105° was obtained on Cu surface with electro-deposited Co-Ni alloy and on electro-deposited Co-Ni-G alloy contact angle was found to be 106°. The contact angle was significantly higher at about 142° with electro etched surface. Corrosion test was carried out with electrochemically etched Cu. Electrochemical etching time was varied from 30 to 240 min. The electro-etched Cu substrate etched for 60 min. showed better corrosion resistance with a corrosion rate of 0.197 mm/year. The surface topography of both etched and electrodeposited samples was studied by atomic force microscopy (AFM) and the results were correlated with the wettability data. © 2019 Elsevier Ltd.Item Wetting behaviour of a Green cutting fluid (GCF); influence of surface roughness and surface energy of AA5052, Ti6Al4V and EN31(Elsevier Ltd, 2022) Edachery, V.; Ravi, S.; Badiuddin, A.F.; Tomy, A.; Kailas, S.V.; Suvin, P.S.Green Cutting fluids (GCFs) are biodegradable and eco-friendly alternatives that can be employed in metalworking processes. They facilitate better tool service life and surface quality by removing the heat built, reducing coefficients of friction at tool-chip, and tool-work interfaces, flushing away the chip and preventing the formation of Built-up edges (BUEs). Conventionally, mineral oil (MO) based CFs are used, which can cause serious health hazards in humans as well as negatively impact the environment. Sustainable Green-cutting fluids (GCF) were found to be the solution for reducing the issues raised by the MO-based cutting fluids. The GCF used in the present study was synthesized using coconut oil (Cocos Nucifera) as the base, which is a clean, bio-degradable and eco-friendly substitute for petroleum-based mineral oils. This work is focused on experimentally determining the effectiveness of green cutting fluids on surfaces of (Aluminium)AA5052, (Titanium alloy)Ti6AL4V and Steel(EN31) with various surface topographies. In order to do so, the wetting properties were measured by a stable contact angle θ between the solid–liquid surface and the vapour-liquid interface. Wettability responses from the roughened surfaces in the range of 0.06–2.1 µm was evaluated using a profilometer and contact angle goniometer. Results show that the wetting characteristics of GCF are comparable to that of the MO-based CFs and can be a viable alternative, thus reducing the adverse effects on the environment. In conclusion, this study shows the potential of GCFas an alternative to MO-based cutting fluids used in machining operations in the manufacturing industries. © 2022Item Compositionally modulated multilayer Cu-Zn alloy coatings fabricated using eco-friendly non-cyanide pulse electrochemical deposition(Elsevier Ltd, 2023) Bharadishettar, N.; Kumar, K.; Udaya Bhat, K.Pulse electrodeposition of Cu-Zn compositional modulated multilayer alloy (CMA) coatings was carried out onto AISI 304 stainless steel substrate using an environmentally friendly alkaline non-cyanide electrolytic bath. Cu-Zn alloy multilayer coating was co-electrodeposited using a trapezoidal pulse current. Multilayer coatings can have two different metals in layers or two-phase mixtures. Different sets of multilayers of 10, 20, 50, and 100 were done using a trapezoidal pulse current. In the trapezoidal pulse current module, during the higher current stage (0.1 A) Zn was deposited as compared to the lower current module (0.02 A) where Cu was deposited. Microstructural and structural analysis of the coatings confirmed nanocrystalline morphology with peaks corresponding to crystallographic planes of (002), (111), (020), and (022). Deposited coatings are hydrophilic in nature. The microhardness of the coatings is decreased with an increase in the number of layers deposited. © © 2023 Elsevier Ltd. All rights reserved.Item Reactive wetting, evolution of interfacial and bulk IMCs and their effect on mechanical properties of eutectic Sn-Cu solder alloy(2011) Satyanarayan, S.; Prabhu, K.N.Lead free solders are increasingly being used in electronic applications. Eutectic Sn-Cu solder alloy is one of the most favored lead free alloys used for soldering in electronic applications. It is inexpensive and principally used in wave soldering. Wetting of liquid solder on a substrate is a case of reactive wetting and is accompanied by the formation of intermetallic compounds (IMCs) at the interface. Wettability of Sn-0.7Cu solder on metallic substrates is significantly affected by the temperature and the type of flux. The wettability and microstructural evolution of IMCs at the Sn-0.7Cu solder/substrate interfaces are reviewed in the present paper. The reliability of solder joints in electronic packaging is controlled by the type and morphology of interfacial IMCs formed between Sn-0.7Cu solder and substrates. The formation and growth mechanisms of interfacial IMCs are highlighted. Mechanical behavior of bulk solder alloy and solder joint interfaces are analyzed. The characteristics of the IMCs which have marked effect on the mechanical properties and fracture behavior as well as reliability of solder joints of the alloy are discussed. An attempt has also been made to discuss the effect of cooling rate and strain rate on shear strength, tensile properties and creep resistance of the solder alloy. It is recommended that future work should focus on evolving a standard procedure involving sequential assessment of wetting behavior, evolution of IMCs and mechanical properties. © 2011 Elsevier B.V.Item Review of non-reactive and reactive wetting of liquids on surfaces(2007) Kumar, G.; Prabhu, K.N.Wettability is a tendency for a liquid to spread on a solid substrate and is generally measured in terms of the angle (contact angle) between the tangent drawn at the triple point between the three phases (solid, liquid and vapour) and the substrate surface. A liquid spreading on a substrate with no reaction/absorption of the liquid by substrate material is known as non-reactive or inert wetting whereas the wetting process influenced by reaction between the spreading liquid and substrate material is known as reactive wetting. Young's equation gives the equilibrium contact angle in terms of interfacial tensions existing at the three-phase interface. The derivation of Young's equation is made under the assumptions of spreading of non-reactive liquid on an ideal (physically and chemically inert, smooth, homogeneous and rigid) solid, a condition that is rarely met in practical situations. Nevertheless Young's equation is the most fundamental starting point for understanding of the complex field of wetting. Reliable and reproducible measurements of contact angle from the experiments are important in order to analyze the wetting behaviour. Various methods have been developed over the years to evaluate wettability of a solid by a liquid. Among these, sessile drop and wetting balance techniques are versatile, popular and provide reliable data. Wetting is affected by large number of factors including liquid properties, substrate properties and system conditions. The effect of these factors on wettability is discussed. Thermodynamic treatment of wetting in inert systems is simple and based on free energy minimization where as that in reactive systems is quite complex. Surface energetics has to be considered while determining the driving force for spreading. Similar is the case of spreading kinetics. Inert systems follow definite flow pattern and in most cases a single function is sufficient to describe the whole kinetics. Theoretical models successfully describe the spreading in inert systems. However, it is difficult to determine the exact mechanism that controls the kinetics since reactive wetting is affected by a number of factors like interfacial reactions, diffusion of constituents, dissolution of the substrate, etc. The quantification of the effect of these interrelated factors on wettability would be useful to build a predictive model of wetting kinetics for reactive systems. © 2007 Elsevier B.V. All rights reserved.Item Comparative study of heat transfer and wetting behaviour of conventional and bioquenchants for industrial heat treatment(2008) Fernandes, P.; Prabhu, K.N.An investigation was conducted to study the suitability of vegetable oils as bioquenchants for industrial heat treatment. The study involved the assessment of the severity of quenching and wetting behaviour of conventional and vegetable oil quench media. Quench severities of sunflower, coconut and palm oils were found to be greater than mineral oil. The quench severity of aqueous media is greater than oil media although their wettability is poor as indicated by their higher contact angles. A dimensionless contact angle parameter defined in this work is found to be a better parameter to compare the wetting behaviour with heat transfer. © 2007 Elsevier Ltd. All rights reserved.