Temperature-Dependent Supramolecular Assemblies in Surfactant–Biopolymer Systems: Thermodynamic, Acoustic, and Computational Insights

We report a systematic investigation of temperature-dependent supramolecular assemblies and micellar behavior in aqueous sodium dodecyl sulfate (SDS) solutions in the presence of Aloe vera gel (AVG; 1%, 2%, and 5% w/v) as a biopolymeric modulator. Acoustic, thermodynamic, and physicochemical measurements, including conductivity, density, and viscosity, were performed at 303.15, 313.15, and 323.15 K to elucidate the molecular basis of surfactant-biopolymer interactions. Derived parameters partial molar volume (Φv), adiabatic compressibility (β), apparent molar compressibility (Φk), sound velocity (U), acoustic impedance (Z), free path length (Lf), Rao's constant (Ra), relaxation time (τ), and Gibbs free energy (ΔG) collectively reveal progressive supramolecular reorganization under thermal modulation. Density and viscosity trends indicate cooperative micellar growth, driven by enhanced hydrophobic packing and structured SDS-AVG interactions. Temperature-dependent shifts in the critical micelle concentration (CMC) confirm entropy-dominated micellization with a strengthened counterion association. A decrease in activation energy (Ea) with increasing AVG concentration further demonstrates reduced energetic barriers for micellar assembly. Associated increases in sound velocity and acoustic impedance, alongside reduced compressibility, substantiate enhanced structural ordering. Complementary density functional theory (DFT) analyses, including optimized geometries, frontier molecular orbitals, and molecular electrostatic potential mapping, support favorable interaction energetics and supramolecular stability. Collectively, these findings establish thermodynamic and acoustic foundations for temperature-dependent surfactant-biopolymer interactions, offering insights into the rational development of eco-compatible soft-matter formulations.