Interplay of Molecular Hydrogelators and SDS Aﬀords Responsive Soft Matter Systems with Tunable Properties Vicent J. Nebot, †,§ Beatriu Escuder, † Juan F. Miravet,* ,† Johan Smets, ‡ and Susana Ferna ́ ndez-Prieto ‡ † Departament de Química Inorga ̀ nica i Orga ̀ nica, Universitat Jaume I, 12071 Castelló , Spain ‡ Procter & Gamble, Teemselaan 100, 1853 Strombeek-Bever, Belgium * S Supporting Information ABSTRACT: The gelation eﬃciency of low molecular weight bolaamphiphilic hydrogelators 1 and 2 is inﬂuenced by the presence of SDS micelles. Similarly, the critical micellar concentration value of SDS is reduced in the presence of the studied molecular hydrogelators. Rheological measurements indicate that the strength of the hydrogels can be modulated with SDS, the gels becoming weaker in the presence of micelles. This behavior has been rationalized with the help of NMR studies using diﬀusion measurements and NOE correlations. The results obtained clearly point to the formation of mixed micelles composed of SDS and the hydrogelators. In the case of 1, the gelator:SDS ratio in the mixed micelles has been estimated from solubility studies to be ca. 1:2.5. Electron microscopy reveals that when SDS is present, the morphology of the xerogels is modiﬁed in its appearance at the micrometer scale but ﬁbers with diameter in the nanometer range are observed in all the cases. The interplay between the surfactant and the gelators provides with new possibilities for the modulation of both gel and micelle formation. Examples are shown to highlight the potential usefulness of this type of interconnected system. In one case the release of a gel entrapped dye is modulated by the presence of SDS and sodium chloride. In another example, an intricate system that responds to a temperature excursion by irreversible micelle disassembly is shown. ■ INTRODUCTION The interest in molecular (hydro)gels has grown exponentially in recent years, and applications have been developed in a wide range of areas such as regenerative medicine, controlled drug release, optoelectronic materials, or catalysis among others. 1-5 The formation of molecular gels represents an intriguing case of self-assembly of low molecular weight species. Commonly the aggregation produces nano(micro)ﬁbrillar networks that percolate the solvent and transform it into a viscoelastic material. These materials are formed by weak noncovalent interactions that may be conveniently reversed by external physicochemical stimuli leading to environment responsive systems. 6 Besides, the study of complex supramolecular systems is gaining increased attention in the past years after the blossoming of the ﬁeld of systems chemistrythe chemistry of mixtures of interrelated components. 7-11 In this context, the development of complex and multiresponsive gels is of great interest considering that many of the real-world applications of those materials will face with complex dynamic mixtures, i.e., biological ﬂuids, cells, contaminated water, etc., where spatiotemporal combination of stimuli may be determinant for the reliability of the response. One of such complex systems is obtained when mixing two diﬀerent kinds of soft matter building blocks: molecular gelators and surfactants. These components may assemble orthogonally, 12-14 self-sorting into separated phases, or mutually interact leading to interconnected complex systems. The interplay between molecular hydro- gelators and surfactants has been scarcely addressed. In one case SDS and a zwitterionic amphiphile were shown to form a two-component gel which was heat- and pH-responsive. 15 Within the study of orthogonal self-assembly of surfactants and hydrogelators, it was reported that the critical micellar concentration (cmc) values of SDS and other surfactants were not signiﬁcantly altered in the presence of hydrogels formed from 1,3,5-triamide-cis,cis-cyclohexane-based hydro- gelators. 12-14 On the contrary, in the same work an important process of gelator solubilization was observed in the presence of cationic micelles. Recently, a system composed of an enzyme- sensitive hydrogelator and a liposome containing the appropriate enzyme was used for controlled release. 16 Addi- tionally, it has been shown that the addition of ionic surfactants to a tripodal urea is key for the formation of hydrogels, 17 and a supramolecular gelator and SDS have been used in protein separation by electrophoresis. 18 Received: May 2, 2013 Revised: June 21, 2013 Published: June 27, 2013 Article pubs.acs.org/Langmuir © 2013 American Chemical Society 9544 dx.doi.org/10.1021/la401653b | Langmuir 2013, 29, 9544-9550