ORIGINAL CONTRIBUTION Smart borax complexes starting from anionic surfactant in association with unlabeled or fluorescently labeled poly(acrylic acid)s Elena Livia Simion 1 & Gabriela Stîngă 1 & Adriana Băran 1 & Ludmila Aricov 1 & Ioana Cătălina Gîfu 1 & Dan Florin Anghel 1 Received: 11 December 2015 /Revised: 29 January 2016 /Accepted: 13 February 2016 /Published online: 10 March 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract In this study, we evaluated borax’ s effect upon so- dium dodecyl sulfate (SDS)–poly(acrylic acid) (PAA) com- plexes. Comparison was made by using both unmodified and fluorescently modified polymers. Also, the influence of sodium chloride on the polymer–surfactant association was followed. To this end, a poly(acrylic acid) with molecular weight of 25,000 was grafted with 2.4 % 1-naphthylmethylamine. Surface tension, conductivity, and steady-state and time- resolved fluorescence measurements were performed. By inves- tigation of the adsorption ability at water/air interface and by conductivity, it was revealed that both naphthyl tag and borax reinforce the interaction between SDS molecules and polymer. The photophysical data (polarity index, excimer formation, and lifetime of fluorophores) give more insight about stable nano- structures of surfactant–polyelectrolyte with the same charge. At low pH as well as sodium chloride and SDS contents, the heterogeneous microdomains of surfactant molecules with seg- ments of coiled polymer were formed. At high pH, H-bonding nanostructures between borax and both sulfate of surfactant and carboxyl groups of the macromolecular chain were revealed. Keywords Poly(acrylic acid) . Naphthalene labeled poly(acrylic acid) . Sodium dodecyl sulphate . Borax . Fluorescence . Self-assembly Introduction During the last decades, the association between polyelectro- lytes and surfactants has attracted a growing attention in both academic and industrial fields. Through the manipulation of pH, ionic strength, the hydrophilic/hydrophobic balance, and temperature, a huge variety of new surfactant–polymer mate- rials have been created [1]. The important forces, such as the electrostatic and hydrophobic interactions or H-bonding, con- trol the properties and structure of the surfactant–polymer su- pramolecular complexes that change at certain surfactant concentrations. Poly(acrylic acid) (PAA) is a weak polyelectrolyte that re- sponds to changes in environmental conditions (pH, ionic strength, surfactant, cyclodextrin, etc.). The response to stim- uli constitutes an attractive tool that enables the use of PAAs as smart biomedical [2–4] and wastewater treatment materials [5, 6], sensors [7, 8], supercapacitors [9], etc. The covalent attachment of aromatic compounds at polymer’ s backbone tunes its hydrophobic character. Moreover, the fluorescent signal of fluorophores offers a general view at molecular level about polymer conformation and its interactions with different external stimuli [10–13]. It is well known that common inorganic electrolytes (i.e., NaCl) can moderate the electrostatic effect influencing the surfactant–polymer association [14, 15]. Mya et al. [16] evi- denced that the salt stabilizes the binding of micelles on poly- mer. This is due to the inorganic electrolyte that diminishes the electrostatic repulsion between the charged groups of both surfactant and polyelectrolyte. Borax is the most important source of boron. Borax has applications in a diversity of fields including detergents, soaps, medicine, optoelectronics, ener- gy, hydraulic fluids for oil recovery, metallurgy, ceramics and glass, insecticides, etc. [17, 18]. Although borax is considered to act as a common inorganic salt or as a buffer in * Gabriela Stîngă gstinga@gmail.com * Dan Florin Anghel danflorin.anghel@gmail.com 1 Department of Colloids, BIlie Murgulescu^ Institute of Physical Chemistry, Romanian Academy, 202 Spl. Independentei, 060021 Bucharest, Romania Colloid Polym Sci (2016) 294:927–939 DOI 10.1007/s00396-016-3848-0