Colloids and Surfaces A: Physicochem. Eng. Aspects 386 (2011) 54–64 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journa l h omepa g e: www.elsevier.com/locate/colsurfa Aqueous block copolymer–surfactant mixtures—Surface tension, DLS and viscosity measurements and their utility in solubilization of hydrophobic drug and its controlled release A.D. Thummar a , N.V. Sastry a,∗ , G. Verma b , P.A. Hassan b a Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388120, Gujarat, India b Chemistry Division, Bhabha Atomic Research Centre (BARC), Trombay, Mumbai 400085, India a r t i c l e i n f o Article history: Received 5 March 2011 Received in revised form 26 June 2011 Accepted 28 June 2011 Available online 2 July 2011 Keywords: Copolymer micelles Copolymer–surfactant systems Surface active properties Mixed micelles Regular solution theory Synergistic behavior Drug solubilization Hydrogel Drug release a b s t r a c t The effects of sodium dodecyl sulfate (SDS) and dodecyl trimethylammonium bromide (DTAB) and poly- oxyethylene (10) isooctyl phenyl ether (TX-100) as additives on the association characteristics of an amphiphilic tri-block copolymer P105 (E 37 P 56 E 37 ) were monitored by surface tension, dynamic light scattering and viscosity measurements at 303.15 and 313.15 K in water as well as in 200 mM sodium chlo- ride aqueous solutions. The successive addition of surfactants resulted not only in the increase of critical micelle concentration (CMC) of the copolymer and also in CMC/C 20 values indicating that the adsorption tendency of the copolymer–surfactant complexes at water/air interface is more than the association in the bulk. The experimental CMC data of binary mixtures were analyzed using regular solution theory to calculate the interaction parameter. The mixtures exhibited synergistic interaction behavior. The appar- ent hydrodynamic radius of copolymer micelles decreased drastically by the addition of surfactants and this destabilization effect has been attributed to the shift of copolymer micelle ↔ unimer equilibrium in favor of latter. Dexamethasone, a drug poorly soluble in aqueous media was solubilized into individual copolymer or copolymer–surfactants solutions followed by their loading onto agar agar hydrogels for its immobilization and dispersion. The drug release profiles were established and drug diffusion coefficients were calculated. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (EPE) based tri-block copolymers with variation in molec- ular characteristics such as E/P ratio and molar mass are available commercially under the trade names of pluronics or poloxamers [1,2]. The amphiphilic nature of these block copolymers lead to interesting adsorption features at air/water interface and self- association behavior in water. The aqueous solutions of these copolymers typically display a critical micellization concentration (CMC) and critical micellization temperature (CMT) in aqueous media and the critical features of self association and adsorption of these copolymers have been well reviewed [2,3]. The adsorption and micelle generating properties of EPE copolymers have been exploited for technology based applications such as detergency, dispersion, stabilization, foaming, emulsification, lubrication, controlled release of drugs, and product formulations in industries ranging from agriculture to pharmaceuticals [4–7], as templating ∗ Corresponding author. Tel.: +91 2692 226856; fax: +91 2692 236475. E-mail address: nvsastry 17@rediffmail.com (N.V. Sastry). agents in the preparation of mesoporous metal oxide thin films [8,9] and also for separation of DNA and proteins, etc. [10,11]. In most of these applications, block copolymers and low molar mass surfactants are commonly employed, as the mixture solutions are expected to possess not only improved colloidal characteristics but also help in fine tuning the viscosity of the media. There- fore the ternary block copolymers/anionic or cationic or nonionic surfactants/water systems either in the presence or absence of electrolytes as additives have received considerable attention and subject of many of the scientific investigations [12]. The nature of the type of species that are formed in copolymer–surfactant mixture solutions is found to be highly dependent on the surfactant concentration. At very low surfactant concentration, copolymer–surfactant charged complexes are formed and while at moderate concentrations, these complexes are broken into mixed micelles of smaller dimension and at higher concentrations, how- ever the micellization of copolymers is suppressed. Therefore it is essential to fix and work out the particular concentration regimes for a given copolymer–surfactant system to adjudge their maxi- mum performance in a given application. The CMCs for mixture solutions of F127 (E 97 P 69 E 97 )–nonionic hexaethylene glycol mono- n-dodecyl ether (C 12 EO 6 ) [13] and –SDS [14] were determined and 0927-7757/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2011.06.027