Publications & Patents
1) Varade, S. R., Ghosh, P., Foaming in aqueous solutions of mixtures of a zwitterionic and a cationic surfactant in presence of an electrolyte. Journal of Dispersion Science & Technology. (10.1080/01932691.2019.1614944).
Abstract: This paper reports the foamability and the stability of foams of aqueous solutions of mixed systems of a zwitterionic surfactant (i.e. N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) and a cationic surfactant (i.e. cetyltrimethylammonium bromide) in the presence of NaCl. The synergism between the surfactants was examined by measuring the surface tension for various compositions of the surfactants and the salt. The interaction occurring between the surfactant molecules adsorbed at the air–water interface influenced the monolayer properties. The mixed surfactant system produced a significant decrease in surface tension as compared to the single surfactant systems. In the presence of salt, the surface tension reduction was larger. The interaction among the surfactant molecules at the air–water interface and the same in the mixed micelles was quantified by the respective interaction parameters. The foamability studies showed synergistic behavior inasmuch as higher foam volumes were generated in the mixed surfactant systems as compared to the single surfactant systems. It increased the stability of foams significantly. The synergism between the surfactant molecules had a notable influence on the zeta potential at the air–water interface.
2) Varade, S. R., Ghosh, P., Foaming in aqueous solutions of zwitterionic surfactant in presence of monovalent salts: the specific ion effect. Chemical Engineering Communication (10.1080/00986445.2019.1647178).
Abstract: The specific ion effect on foamability and foam stability was investigated. The foams were prepared from the aqueous solutions of a zwitterionic surfactant [i.e. N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS)] in the presence of three monovalent salts (i.e. LiCl, NaCl, and CsCl). Addition of salt to the DDAPS solution increased the adsorption of surfactant at the interface and decreased the CMC. The efficiency of these salts in decreasing the surface and interfacial tension followed the order: CsCl>NaCl>LiCl. Similarly, the efficiency of these salts in decreasing the foam stability followed the above-mentioned order. The zeta potential at the hexane–water interface was measured. The efficiency of the salts in making the zeta potential more negative followed the same order. The hydrated radii of the ions played a significant role in the foaming properties of the surfactant solutions.
3) Varade, S. R., Ghosh, P., Foaming in aqueous solutions of zwitterionic surfactant: Effects of oil and salts. (2017), 38, 1–15, Journal of Dispersion Science & Technology. (10.1080/01932691.2017.1283509)
Abstract: This paper reports a study on the stability of foams generated from the aqueous solutions of the zwitterionic surfactant, N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, in presence of NaCl, CaCl2 and AlCl3. The effect of oil (i.e. n-hexane) on foam was also studied. The surface and interfacial tensions were measured. These tensions and the CMC decreased upon salt addition, signifying an increased adsorption of the surfactant molecules at the interface. The quantity of salt required for reducing the surface tension and CMC was in the sequence: NaCl > CaCl2 > AlCl3. The salts had a pronounced effect on the foaming characteristics, i.e. they reduced the initial foam volume. The effectiveness of salts in reducing the foam stability followed the sequence: AlCl3 > CaCl2 > NaCl. However, the foam collapse rate was reduced in the presence of salt. The presence of oil decreased the foam volume and reduced its stability. The entering, bridging, and spreading coefficients were calculated, which explained the stability of foams in presence of oil.
4) Behera, M. R., Varade, S. R., Ghosh, P., Paul, P., Negi, A. S. Foaming in micellar solutions: Effects of surfactant, salt, and oil concentrations. (2014), 53(48), 18497–18507, Industrial Engineering & Chemistry Research. (10.1021/ie503591v )
Abstract: Foaming in products based on micellar solutions has considerable importance in various consumer applications, such as washing and cleaning. In this work, the effects of surfactant concentration, oil content, and salts containing mono-, di-, and trivalent counterions on foam formation and stability were studied. The foams were generated by employing the Blender Test. The presence of salts caused a significant reduction in foam volume. Effectiveness of the salts followed the sequence Al3+ > Ca2+ > Na+. However, the foam collapse rate was slower in the presence of salt. The rate of adsorption of surfactant molecules at the air−water interface was augmented by salt. Oil reduced the foam volume and its stability. The entering, spreading, and bridging coefficients were calculated. These coefficients qualitatively explained the stability of foam in the presence of oil.
5) Tatiana Marques Pessanha, Shailesh Varade, Anniina Salonen, and Dominique Langevin, Coalescence Frequency in O/W Emulsions: Comparisons of Experiments with Models, Langmuir 2024 40 (45), 23695-23705; DOI: 10.1021/acs.langmuir.4c02573
We have studied the coalescence of oil in water emulsions under the influence of gravity. The emulsions were made with alkane oils and surfactants with varying physical chemistry. We chose cationic alkyl trimethylammonium bromides of different chain lengths and nonionic surfactants of ethylene oxide and sugar head groups, including polymeric surfactants. We observed phase separation in two steps. Creaming of the oil drops is followed by their rapid coalescence, increasing the average drop size and resulting in complete surfactant surface coverage of the interfaces. Full phase separation occurs after much longer times Tc when the emulsion drops coalesce dramatically. We have used a model by Dinh et al. to relate Tc to the coalescence frequency and hence to the activation energy for the rupture of the films between two neighboring drops. Our results support the view that the coalescence of stable emulsions (stable at least for a few hours) is a thermally activated process and is controlled by the surface compression elastic modulus. This modulus was determined using surface tension measurements and calculations using the Gibbs adsorption equation. The observed differences between ionic and nonionic systems are attributed to a two-step film rupture process in the case of ionic surfactants, which is not found in nonionic systems.
6) Alice Requier, Shailesh Varade, Nicolò Galvani, Marina Pasquet, Sylvie Cohen Addad, Cécile Gehin-Delval, Reinhard Höhler, Olivier Pitois, Emmanuelle Rio, Anniina Salonen, Dominique Langevin, Wet foam coarsening: more than film permeability, Journal of Colloid Interface Science (Just Accepted).
Foams with high liquid fractions, wet foams, are frequent in industrial applications. Understanding their stability is key to achieving control over foamy material design. Wet foams are difficult to study on ground as they rapidly destabilise through gravity-driven drainage. Experiments in micro-gravity avoid this drainage and allow to isolate the foam coarsening process, where bubble size grows as gas transfers from smaller to larger bubbles. We have studied the impact of stabiliser chemistry on coarsening with various surfactants and a protein, and over a range of liquid fractions. We measure coarsening rates that vary by almost a factor ten depending on the stabiliser. For moderately wet foams, we can rationalise the changing rates with surface tension and film permeability measured in independent experiments on ground. Once the foams become wetter and approach the volume fraction of random close packing, other stabiliser effects become evident. Molecules which exhibit strong adhesion between bubbles modify foam structure with larger films, resulting in faster than predicted coarsening rates. If the surface permeability is very low, coarsening is also faster than predicted, as some of the gas transfers outside of foam films. These results allow us to rationalise the multiple impacts of stabiliser chemistry on foam coarsening.
Patent
A Nano-emulsion Composition for Skin Care Application. (EP 3981379A2)
Ion Specific Effect in Stability of Foams and Emulsions: Role of Adsorption and Interfacial Charge (ISDN: 3659579858)
Shailesh Ravi Varade, Dominique Langevin, Anniina Salonen, Fredric Restagno, presented poster Investigating the Settling of Beads and Rising Bubbles in Viscoelastic Fluid at European Colloid and Interface Science (ECIS) Sept' 2023 at Naples, Italy.
Tatiana Marques Pessanha, Shailesh Ravi Varade, Anniina Salonen, François Lequeux, Dominique Langevin presented poster on Investigating the Surfactant Role in Coalescence of O/W Emulsion at European Colloid and Interface Science (ECIS) Sept' 2023 at Naples, Italy.
Shailesh Ravi Varade, Anniina Salonen, Dominique Langevin presented poster on Studying the Coarsening of Wet Foams in Microgravity at International Space Station at Journees CNES Jeunes Chercheurs (JC2) at 22nd edition at Cite de l'Espace, Tolouse, France.
Shailesh Ravi Varade, Completed Japanese Language and Culture Course - A1 - Upper Introductory held for eleven weeks at Indian Institute of Technology Guwahati between January to April, 2018.
Shailesh Ravi Varade, and Pallab Ghosh, presented Poster in Research Conclave '18 at Indian Institute of Technology Guwahati held between 8 - 11 March, 2018.
Shailesh Ravi Varade, 4th National Workshop on NEMS/MEMS and Theranostic Devices. NWNTD - 2018 organized by Centre of Excellence in Research and Development of Nanoelectronic Theranostic Devices in Indian Institute of Technology Guwahati, Assam, India.
Shailesh Ravi Varade, Participated in One-day Industry Academia Meet on State-of-the-Art Refinery Operations held at Indian Institute of Technology Guwahati organized by Indian Institute of Chemical Engineers held on 4 April, 2018.
Shailesh Ravi Varade, and Pallab Ghosh, presented poster at International Conference on 'Sophisticated Instruments in Modern Research' held at Indian Institute of Technology Guwahati between 30 June - 1 July, 2017.
Shailesh Ravi Varade, and Pallab Ghosh, Presented Poster in 7th Asian Conference in Colloid and Interface Science held at Kuala Lumpur between 8 - 11 August, 2017 organized by Asian Society for Colloid and Interface Science.
Shailesh Ravi Varade, and Pallab Ghosh, Presented Poster at International conference CompFlu@Hyd 2016 held at International Institute of Information Technology, Hyderabad between 12 - 14 December, 2016.
Shailesh Ravi Varade, Participated in International Workshop on Advances in Disinfection Technologies held at National Environmental Engineering Research Institute, Nagpur, India on 9 February, 2011.
Shailesh Ravi Varade, Presented paper at Poly-Era '05 at College of Engineering Technology, Akola organized by Department of Polymer Technology and Indian Plastics Institute on 24 September, 2005.