Najam Sardar | Aligarh Muslim University (original) (raw)

Papers by Najam Sardar

The interaction of Polyethylene oxide (PEO) and cationic conventional surfactant (CTAB) in aqueou... more The interaction of Polyethylene oxide (PEO) and cationic conventional surfactant (CTAB) in aqueous solutions is investigated by conductivity and viscosity techniques. Electrostatic and hydrophobic interactions play a dominant role in such systems. The conductivity study reveals that the interaction takes place between PEO and CTAB and the addition of PEO induces aggregation and instead of one break point, two break points appears in the conductivity curve being represented as Critical aggregation concentration (CAC) and Critical micelle concentration (CMC). The CMC of CTAB was increased by the addition of polymer. Viscosity study shows that the relative viscosity increases with surfactant concentration as well as polymer concentration.

Journal of Chemical & Engineering Data, 2010

Nonionic cellulose ether-water systems have a characteristic feature of phase separation at certa... more Nonionic cellulose ether-water systems have a characteristic feature of phase separation at certain temperatures, also termed the cloud point. The effect of various surfactants as additives on the phase behavior of nonionic cellulose ether, hydroxypropylmethyl cellulose (HPMC), has been studied. It was found that in the presence of ionic surfactants the cloud point (T CP) of HPMC decreased when small amounts of surfactant were added, and at higher concentration it increased. In the case of alkyltrimethylammonium bromides, surfactants with a longer alkyl chain (cetyltrimethylammonium bromide, CTAB, and tetradecyltrimethylammonium bromide, TTAB) influenced the T CP much more than that with a shorter alkyl chain (dodecyltrimethylammonium bromide, DTAB). Cetylpyridinium chloride (CPC) and cetylpyridinium bromide (CPB) were utilized to see the counterion effect on the T CP of polymer. Anionic surfactant sodium dodecyl sulfate (SDS) was found to be more effective as compared to its cationic counterpart with the same alkyl chain (DTAB), whereas nonionic surfactants showed no influence. From these observations it was concluded that the driving force was the interaction between the charged head groups of the surfactants and polar sites present in the nonionic HPMC. Gemini surfactants (R,ω-bis(hexa/tetradecyldimethylammonium)alkane dibromides) showed more influence on the T CP as compared to their conventional counterparts. The energetic parameters of clouding in HPMC in the presence of all surfactants used in the study were also calculated. Conventional surfactants had shown the contrast behavior of enthalpy and entropy changes at lower and higher concentration regions; i.e., ∆H c 0 and T∆S c 0 were positive at low concentration of surfactants but negative at higher surfactant concentrations. In the presence of gemini surfactants, both the enthalpy and entropy changes were always negative.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012

Abstract The interaction of sodium carboxymethylcellulose (NaCMC) and cationic gemini surfactants... more Abstract The interaction of sodium carboxymethylcellulose (NaCMC) and cationic gemini surfactants (16- s -16, s = 5, 6)/conventional surfactant (CTAB) in aqueous solutions is investigated by conductivity, fluorescence and viscosity techniques. Electrostatic and hydrophobic interactions play a dominant role in such systems. The conductivity results showed that the geminis interact strongly with NaCMC as compared to CTAB. Fluorescence measurements were used to calculate aggregation number for the three combinations which were found about the same as those for the corresponding free micelles. Addition of surfactants leads to an increase in relative viscosity after certain concentration of the surfactants. Further increase in relative viscosity is significant in case of geminis and this increase is ascribed to the physical cross-linking of surfactant micelles with NaCMC chains.

Chemical Engineering Communications, 2013

The interactions of two gemini surfactants (16-s-16, s = 5, 6) and their conventional counterpart... more The interactions of two gemini surfactants (16-s-16, s = 5, 6) and their conventional counterpart cetyltrimethylammonium bromide (CTAB) with polyvinylpyrrolidones (PVP K15 and PVP K90) were investigated using conductivity, steady-state fluorescence, and viscosity techniques. The results indicate that there is no PVP/CTAB complex formation if molecular weight of PVP < 15,000. Both PVP K15 and PVP K90 interact with gemini surfactants. The critical aggregation concentration (cac) and critical micelle concentration (cmc) increase with polymer concentration and do not depend on the polymer molecular weight. Fluorescence study shows that the addition of PVP results in a decrease of the aggregation number in all the systems investigated due to the adsorption of the PVP chain in the micelle palisade layer and the ensuing increase of micelle ionization. The viscosity results suggest that the interactions between the surfactants and the polymer affect both inter-polymer-polymer association and chain expansion. [Supplementary materials are available for this article. Go to the publisher's online edition of Chemical Engineering Communications for the following free supplemental resources: additional data tables and figures.]

Arabian Journal for Science and Engineering

Petroleum industry has transformed by the introduction of the nanotechnology. Drilling mud used f... more Petroleum industry has transformed by the introduction of the nanotechnology. Drilling mud used for drilling oil and gas wells is an expensive blend of chemicals which is lost in the pores of rocks while drilling. According to study loss of drilling fluid costs approximately $800 million per year (2003 data). By introducing nanoparticles in the drilling fluid the performance of drilling fluid can be enhanced. In this study, the impact of carbon nanotubes on the properties of a water based drilling mud is investigated. The influence of nanoparticle on prevention of fluid loss is investigated by performing LPLT (low pressure low temperature) filter press test. There are several approaches for the preparation of the nano materials; namely chemical and mechanical methods. Of course there is a big difference in both of them and one can detect these variations by measuring its characterisation and properties. Characterisation of these nano materials can be done by SEM (scanning electron m...

Journal of Chemical and Engineering Data, 2010

Journal of Chemical & …, 2011

The aim of the present work is to investigate the effect of various salts such as NaCl, KCl, NaBr... more The aim of the present work is to investigate the effect of various salts such as NaCl, KCl, NaBr, KBr, NaNO3, Na2SO4, and Na3PO4 as additives on the phase behavior of nonionic polymer hydroxypropylmethyl cellulose, HPMC. The cloud point of HPMC has been found ...

Journal of Surfactants and Detergents

Industrial & Engineering Chemistry Research, 2012

The purpose of this study was to investigate the interaction between a nonionic polymer, (hydroxy... more The purpose of this study was to investigate the interaction between a nonionic polymer, (hydroxypropyl)methyl cellulose (HPMC), and cationic gemini surfactants, bis(hexadecyldimethylammonium)hexane dibromide (16-6-16), bis(hexadecyldimethylammonium)pentane dibromide (16-5-16), and their corresponding monomeric counterpart cetyltrimethylammonium bromide (CTAB), by using electrical conductometry, fluorescence, and viscometry methods. It was found that the gemini surfactants interact strongly with HPMC as compared to conventional surfactant CTAB. The free energies of aggregation, ΔG agg , micellization, ΔG mic , and transfer, ΔG t , associated with the binding interaction between surfactant and polymer, have also been evaluated. The negative values of ΔG t confirm the feasibility of interaction between the surfactant and polymer. The aggregation number (N agg) obtained from steady state fluorescence measurement with CTAB was found to be more than with the geminis. A significant viscosity increment was observed in the case of gemini surfactants as compared to CTAB. The rapid increase of the viscosity with surfactant concentration was, therefore, attributed to the considerable cross-links among micelles and polymers (transient network).

The interactions between dodecyltrimethylammonium bromide and anionic polymers such as neutralize... more The interactions between dodecyltrimethylammonium bromide and anionic polymers such as neutralized poly(acrylic acid) and methacrylic acid/ethyl acrylate copolymers were investigated using isothermal titration calorimetry (ITC). The ITC results suggest that in the initial stage of titration, the cationic headgroups of surfactant individually bind to the anionic carboxylate groups on the polymer chains due to electrostatic attraction. When the surfactant concentration reaches a critical value C′, the micellization of polymerbound surfactant occurs, resulting in the formation of insoluble polymer/surfactant complexes. The thermodynamic parameters derived from ITC measurements suggest that the electrostatic binding is an endothermic process driven by entropy. The positive entropy is attributed to the recovery of translational entropy of released counterions by the bound surfactant. The ITC curves for titrations performed in different salt conditions show that addition of salt screens the electrostatic repulsion between surfactant headgroups and attraction between oppositely charged polymer chains and surfactant molecules, which favors the formation of free micelles, and weakens the binding of surfactant onto the polymers.