Modeling Lower Critical Solution Temperature Behavior of Associating Dendrimers Using Density Functional Theory

Abstract

We study the phase behavior of associating dendrimers in explicit solvents using classical density functional theory. The existence of association enables uptake of solvent inside the dendrimer even for unfavorable Lennard-Jones interaction between the solvent and dendrimer. Depending on the distributions of associating sites, the dendrimer conformation can be either dense-core or dense-shell. The conformation of the associating dendrimer is greatly affected by the temperature. Due to the interplay between association interaction and Lennard-Jones attractions, we find the lower critical solution temperature (LCST) behavior of dendrimer conformation and study how it changes as the dendrimer size or solvent size changes. The dendrimer in our study displays no LCST behavior at low generations, and it has a maximum LCST at G4. Moreover, increasing the solvent chain length decreases the LCST. For solvents with self-association, the competition between solvent-solvent association and solvent-dendrimer association also tends to reduce the LCST. Qualitatively consistent with experiments, our results provide insight into the molecular mechanism of the LCST behavior of associating dendrimers.

Formation of a Hollow Core in Dendrimers in Solvents

“…The density of the outer shell is higher than the density of the inner volume of the dendrimer (dense‐shell structure), i.e., a hollow is formed inside the dendrimer. A similar structure has been observed using DFT method [ 177 ] (e.g., see Figure 14b). We emphasize that the average density of dendrimer in such conformation is significantly higher than for classical dendrimer (i.e., homodendrimer) in a good solvent, therefore a free space inside dendrimer is reduced as well as its efficiency as nanocontainer is negated.…”

“…Reproduced with permission. [ 177 ] Copyright 2019, American Chemical Society. Both cases represent pseudocavity, since the minimum density in the inner volume of copolymer dendrimer in selective solvent is higher than the density of copolymer dendrimer in nonselective solvent, i.e., when “pseudocavity” is absent.…”

Photocycloaddition as a Tool for Modulation of the Lower Critical Solution Temperature in a Molecular π‐System to Control Transmission of Solar Radiation

“…Noticeably, the photocycloaddition in 9‐PA‐1 is severely retarded in water. The LCST phase transition and the retarded photoreaction of 9‐PA‐1 is ascribed to the self‐assembly of the molecule to supramolecular rods below LCST and spheres above LCST due to the hydrated and dehydrated states respectively wherein the chromophores are hidden in the core of the structures [49,50] . While providing one of the first reports on small‐molecule based stable LCST systems, the smart window prototypes unambiguously corroborate its practical application in regulating solar transmission.…”

“…The transparent phase of 9‐PA‐1 and 9‐PA‐2 is believed to be due to the better dispersion of the initially formed smaller aggregates in which the hydrophobic core is hidden from aqueous environment through π–π stacking at temperatures below their LCST ( T cloud ). When the temperature is above LCST, the opaqueness arises due to the thermal disturbance of the H‐bonds between water molecules and glycol chains, facilitating the hydrophobic part of the molecules coming closer along with the crumbling of the oxyethylene chains leading to the formation of larger spherical structures that scatter light [12,48,49] …”

“…When the temperature is above LCST, the opaqueness arises due to the thermal disturbance of the H-bonds between water molecules and glycol chains, facilitating the hydrophobic part of the molecules coming closer along with the crumbling of the oxyethylene chains leading to the formation of larger spherical structures that scatter light. [12,48,49] In other words, below the T cloud , non-covalent interaction between glycol chains of the molecules with water dominates, whereas, above the T cloud , dehydration of glycol chains takes place which results in hydrophobic pocket, leading to the formation of larger spherical aggregates. The size and shape of the supramolecular aggregates formed below and above the LCST phase are corroborated by DLS data.…”