Small Angle Neutron Scattering Study of Structural Aspects of Nonionic Surfactants (Tween 20 and Tween 80) in the Presence of Polyethylene Glycols and Triblock Polymers Rakesh Kumar Mahajan, 1 Jyoti Chawla, 1 Kulwinder Kumar Vohra, 1 Vinod Kumar Aswal 2 1 Department of Chemistry, Guru Nanak Dev University, Amritsar 143005, India 2 Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India Received 7 September 2009; accepted 13 December 2009 DOI 10.1002/app.32134 Published online 29 April 2010 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Small angle neutron scattering (SANS) technique has been used to study the micellar behavior of nonionic surfactants, Tween 20 and Tween 80 with additives like polyethylene glycols (PEG with molecular mass 400, 6000, and 15,000) and triblock polymers (TBPs) of varying composition. Surfactant-additive interactions have been explained on the basis of param- eters like aggregation number (N agg ), core radius (R c ), hard sphere radius (R hs ), volume fraction (/) and axial ratio (b/a). The SANS analysis indicate the reduction in values of N agg of Tween on addition of PEG additive. Shape of Tweens (3 wt %) micelles in the presence of PEG (10 wt %) is found to oblate ellipsoidal. Similarly, the shape of Tween (3 wt %) micelles is oblate ellipsoi- dal at low concentration of TBPs (1 wt %); however, they become spherical as the concentration of TBP increases to 10 wt %. The shape of micelles of pure TBPs also comes out to be spherical. Results reflects that at low concentration of TBP shape is controlled by surfactant (Tween 20 and Tween 80) while at high con- centration of TBP shape of mixed micelle is controlled by TBP. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3038–3046, 2010 Key words: Tweens; polyethylene glycols; triblock polymer; SANS studies; aggregation INTRODUCTION Mixing two or more surfactants has been a common and yet beneficial practice in industries to formulate products with desired properties that are not achiev- able from the individual surfactants by themselves. 1 To optimize the applications of surfactant mixtures, research enthusiasm has never ceased in probing the properties of surfactant mixtures. Polymer and sur- factants are very often used in combination in cos- metic, medicinal, and pharmaceutical preparations. These are also used in injecting fluid for the enhanced oil recovery process. The study of surfac- tant/polymer mixture is therefore also of potential importance in the applied surface-chemical field. Since different types of surfactants exist, various kinds of combinations are possible with different properties and application fields. Solution mixtures of some surfactant systems have been well studied while some are less explored. 2 It is well known 3,4 that polyethylene nonionic sur- factants interact attractively with both anionic and cationic surfactants such as sodium dodecyl sulfate (SDS) and dodecylammonium chloride, respectively, in adsorbed films and micelles. Interactions between nonionic surfactant and nonionic polymer are diffi- cult to explain as the critical micelle concentration (CMC) is smaller than those of the ionic counterparts and the micelle interface is not as clear as for ionic surfactant micelles. Nonionic surfactants are often considered to be indifferent to nonionic polymers and are considered not to interact or very weakly interact with the polymers. 5 Hydrophilic nonionic polymers do not interact with polyoxyethylenated surfactant. If, however, the polymer contains hydro- phobic segments in its molecule, nonionic surfactant can interact with such polymers due to hydrophobic interactions between surfactant and polymer hydro- phobic segments. However, relatively few investiga- tions related to these systems have been carried out. 6,7 The ethoxylated sorbitan esters (Tweens) are a large class of nonionic surfactants. The groups that are attached to the sorbitan include oleate, palmitate, Correspondence to: R. K. Mahajan (rakesh_chem@yahoo. com). Contract grant sponsors: IUC-DAE (BARC). Journal of Applied Polymer Science, Vol. 117, 3038–3046 (2010) V C 2010 Wiley Periodicals, Inc.