Modeling lower critical solution temperature behavior of associating polymer brushes with classical density functional theory

Abstract

We study the lower critical solution temperature (LCST) behavior of associating polymer brushes (i.e., poly(N-isopropylacrylamide)) using classical density functional theory. Without using any empirical or temperature-dependent parameters, we find the phase transition of polymer brushes from extended to collapsed structure with increasing temperature, indicating the LCST behavior of polymer brushes. The LCST behavior of associating polymer brushes is attributed to the interplay of hydrogen bonding interactions and Lennard-Jones attractions in the system. The effect of grafting density and molecular weight on the phase behavior of associating polymer brushes has been also investigated. We find no LCST behavior at low grafting density or molecular weight. Moreover, increasing grafting density decreases the LCST and swelling ratio of polymer brushes. Similarly, increasing molecular weight decreases the LCST but increases the swelling ratio. At very high grafting density, a partial collapsed structure appears near the LCST. Qualitatively consistent with experiments, our results provide insight into the molecular mechanism of LCST behavior of associating polymer brushes.

Density functional study of dendrimer molecules in solvents of varying quality

“…A modified DFT is developed to satisfy stoichiometry and got its name as iSAFT by Jain et al 32 and is further extended to study branched molecules, 45 demonstrating the versatility to apply to molecules of different architecture. With appropriate adaptation, iSAFT has been successfully applied to investigate block copolymers in confinement, 32 tethered polymers, [46][47][48][49] polymer-colloid mixtures, 50 and micelle formation. 51 One can also turn to the paper by Emborsky et al 37 for a good review.…”

Visual and in situ Raman spectroscopic observations of the liquid–liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420°C

“…Considering liquid-liquid immiscibility is common in organic-bearing solutions, the uranyl-sulfate ion association was suggested to create an organic-like aqueous solution favoring the separation of a new liquid phase at elevated temperatures [12]. In fact, it has been accepted that the LCST phenomenon characterizes polymer solution [30][31].…”

An EQT-based cDFT approach for thermodynamic properties of confined fluid mixtures

“…10,59,60 There are approaches that provide functional forms for F ex based on the fundamental-measure theory (FMT), 61,62 modified FMT (MFMT), 63,64 first-order mean-spherical approximation (FMSA), 65 accurate empirical equation of state, 41 and statistical associating fluid theory (SAFT). 54,[66][67][68][69] In this study, similar to our previous work, 31,32 we use the EQT fluid-fluid potential (Eq. (2)) to construct the excess part of the Helmholtz free energy,…”