polymers Article Investigation of Solution Behavior of Antidepressant Imipramine Hydrochloride Drug and Non-Ionic Surfactant Mixture: Experimental and Theoretical Study Malik Abdul Rub 1,2, * , Naved Azum 1,2 , Dileep Kumar 3,4, * , Muhammad Nadeem Arshad 1,2 , Anish Khan 1,2 , Maha Moteb Alotaibi 2 and Abdullah M. Asiri 1,2   Citation: Rub, M.A.; Azum, N.; Kumar, D.; Nadeem Arshad, M.; Khan, A.; Alotaibi, M.M.; Asiri, A.M. Investigation of Solution Behavior of Antidepressant Imipramine Hydrochloride Drug and Non-Ionic Surfactant Mixture: Experimental and Theoretical Study. Polymers 2021, 13, 4025. https://doi.org/10.3390/ polym13224025 Academic Editor: Michal Sedlaˇ cík Received: 25 October 2021 Accepted: 18 November 2021 Published: 21 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21589, Saudi Arabia; nhassan2@kau.edu.sa (N.A.); mnarshad@kau.edu.sa (M.N.A.); anishkhan97@gmail.com (A.K.); aasiri2@kau.edu.sa (A.M.A.) 2 Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia; mmsalotaibi@kau.edu.sa 3 Division of Computational Physics, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam 4 Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam * Correspondence: aabdalrab@kau.edu.sa (M.A.R.); dileepkumar@tdtu.edu.vn (D.K.); Tel.: +966-563671946 (M.A.R.) Abstract: In this paper, the interaction of imipramine hydrochloride (IMP, antidepressant drug) and a non-ionic surfactant Triton X-100 (TX-100) mixture in five different ratios through the tensiometric method in different solvents (aqueous/0.050 mol·kg −1 aqueous NaCl/0.250 mol·kg −1 aqueous urea (U)) were examined thoroughly at a temperature of 298 K. UV–Visible studies in an aqueous system of IMP + TX-100 mixtures were also investigated and discussed in detail. The pure (IMP and TX-100) along with the mixtures’ critical micelle concentration (cmc) were assessed by a tensiometric technique. The obtained deviation of the mixtures’ cmc values from their ideal values revealed the nonideal behavior of IMP + TX-100 mixtures amongst IMP and TX-100. Compared to aqueous systems, in the presence of aqueous NaCl, several changes in micelles/mixed micelles occurred, and hence a synergism/attractive interaction amongst components was found increased while in the existence of U, the synergism/attractive interaction between them decreased. The evaluated interaction parameter ( β Rb ) value of mixed micelles showed the attractive or synergism between the IMP and TX-100. Various evaluated thermodynamic parameters in an aqueous system showed that the mixed micellization of the IMP + TX-100 mixture was an entropically spontaneous phenomenon, although the existence of salt in all studied systems can somewhat increase the spontaneity of the micellization process and in the aqueous U system, the spontaneity of the micellization process decreased. In an aqueous system, the interaction between IMP and TX-100 was also confirmed by UV–Visible study. Keywords: imipramine hydrochloride; tensiometry; mixed micelles; interaction parameter; micellar composition 1. Introduction Usually, amphiphilic compounds undergo self-association into certain solvents to a rich diversity of phases liable upon their concentration as well as the solution environments, for instance, pH, temperature, and additive concentration, and so on [1–5]. The assembly of amphiphiles is called micelles and they have many applications in various fields such as materials synthesis, detergency, solubilization, pharmaceutical formulations, and so on [1,6–8]. The efficiency of surfactant implication for a certain utilization depends on their interfacial activity as well as solution mechanical/physical parameters of the associates’ structure, for example, size, shape, micellar inter-molecular interactions, and so on [9,10]. Polymers 2021, 13, 4025. https://doi.org/10.3390/polym13224025 https://www.mdpi.com/journal/polymers