Local polymer dynamics under strong connectivity constraints: The dendrimer case

Abstract

The characteristics of local motion are explored by molecular dynamics simulations in a series of AB 2 -type dendrimer melts. Systems of generations 3-5 were simulated in a wide temperature range, allowing the assessment of effects associated with molecular size, proximity to the detected glasslike transitions, and the strong connectivity constraints imposed by the dendritic topology. Investigation of the mechanisms involved in local motion at short temporal and spatial scales revealed the connection between the non-Gaussian nature of monomer displacements to ␣-relaxation and the caging/decaging process under different degrees of confinement. In the latter mechanism, two characteristic localization lengths were identified: at the low temperature limit spatial localization was realized within approximately 10% of the nearest neighbor distance while at temperatures higher than the glass transition, the existence of an analogous length scale is ascribed to the geometric constraints due to the dense connectivity pattern. As the results from this study are discussed in comparison to the behavior observed in linear polymers and supercooled liquids, new insight is provided on the universal/specific mechanisms involved in local dynamics of different glass-forming systems.

Association of a Weakly Acidic Anti-Inflammatory Drug (Ibuprofen) with a Poly(Amidoamine) Dendrimer as Studied by Molecular Dynamics Simulations

“…Such deviations are most probably associated with the non-Gaussian character of the drug molecules' displacement at such short distances and to the more constricted environment. 60,61 To explore the collective motion of ibuprofen, we have examined the distinct Van Hove correlation function (eq 3), which probes density fluctuations due to the cooperative motion of the neighbors around each particle 59 (here a drug molecule).…”

Is the manifestation of the local dynamics in the spin–lattice NMR relaxation in dendrimers sensitive to excluded volume interactions?

“…In our case, every segment contains two bonds. A similar dendrimer model was simulated in the papers of Karatasos et al 18,19 This model allows monitoring the dendrimer dynamics not only on the segment scale but also on the scale of bonds.…”

Calculation of Conformational Properties and Rouse Relaxation Times of PAMAM‐EDA Dendrimers under Different pH Conditions

“…[ 31 ] Several schemes have been proposed to apply this notion to the dynamics of dendrimers, some of them including local rigidity or excluded volume effects. [33][34][35] Other theoretical and simulation studies have been devoted to the study of specifi c global and segmental relaxations [ 36 ] or relaxations related with the glass transition in the case of melts, [ 37 ] without specifi cally using the Rouse scheme.…”