Exploring the role of telechelic polymers and temperature variations on the behavior of diluted microemulsions: A molecular dynamics study

R Elhajjam and M Khatouri and R Ahfir and L Talha and A Arbia and S El Khaoui and Z Basbassi and M Naji and M Filali, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 709, 136148 (2025).

DOI: 10.1016/j.colsurfa.2025.136148

Microemulsions are widely employed as drug delivery systems due to their unique solubilization capacity and ability to enhance drug permeability across biological membranes. In this study, we utilize molecular dynamics simulations to investigate the structural and dynamic properties of a decane/water microemulsion system at a low volume fraction phi=2.8%, stabilized by cetylpyridinium chloride (CpCl) as the surfactant and octanol as the co-surfactant. To further enhance stability, we graft a telechelic steric polymer, polyethylene oxide PEO - C12H25, onto the surface of the microemulsion particle. This polymer has been shown to prevent aggregation, increase solubilization, and reduce toxicity. The number of polymers grafted onto each microemulsion particle is denoted as n(PEO - C12H25), where n varies from 0 to 32. The potential of this system includes Van der Waals interactions, electrostatic interactions, and steric interactions. The structural properties of the microemulsion particle are analyzed using the pair correlation function g(r), structure factor S(q), interaction potential U(r) between particles, and osmotic compressibility chi(T). Results indicate that the addition of PEO - C12H25 increases the inter-particle distance between microemulsion particles due to the steric repulsive interactions introduced by the polymer, while an increase in temperature brings the microemulsion particles closer together due to thermal energy. Dynamic properties are examined using the mean square displacement MSD, intermediate scattering function F(q,t), and viscosity eta. From the MSD curves, two diffusion regimes are identified: the ballistic regime (=3k(B)T/m t(2)) and the Fickian regime (=6Dt). The intermediate scattering function F(q, t) decreases exponentially according to the law F(q, t) approximate to e(-t/tau), indicating that diffusion remains normal. We also calculate the diffusion coefficient D from the MSD, relaxation time tau from F(q, t), and activation energy Ea from the Arrhenius equation (eta = eta(infinity)xexp(E-a/RT)). Results show that the diffusion coefficient decreases with the addition of the polymer, while the relaxation time tau, viscosity eta, and activation energy E-a increase, indicating that PEO - C12H25 inhibits microemulsion particle diffusion. Conversely, increasing the temperature T enhances particle diffusion by increasing the diffusion coefficient and decreasing both the relaxation time tau and viscosity eta, indicating a temperature-dependent increase in particle mobility.

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