Segmental Dynamics in Dendrimers with Perfluorinated End Groups:  A Study Using Quasielastic Neutron Scattering

Abstract

A series of carbosilane dendrimer generations, GxRF6 (x = 1−3) with perfluorohexyl (−C6F13) groups on the surface and one dendrimer G3 without these end groups, have been studied using X-ray scattering and quasielastic neutron scattering. The GxRF6 form generation dependent superstructures as a result of the microphase separation between the end groups and the carbosilane core. The helical end groups tend to arrange in layers between the carbosilane domains. The dynamic structure factor was measured with two backscattering spectrometers (IN10, IN16). For GxRF6 it was composed of two separable contributions referring to the segmental diffusion in the dendrimer core and the rotational diffusion of the end groups. G3 shows only one component. The segmental diffusion in the G3RF6 is reduced by a factor of 7.4 compared to G3, demonstrating the influence of the end groups on the segmental diffusion. A universal length controls the segmental diffusion of the four dendrimers. It gives rise to a characteristic scattering vector dependence of the quasielastic line width. Increasing generation number slows down the segmental diffusion and extends the lifetime of a local dynamical process. The rotational diffusion of the end groups is not strongly affected by x. It is less strongly dependent on temperature than the segmental diffusion.

Hyperbranched Fluoropolymers and their Hybridization into Complex Amphiphilic Crosslinked Copolymer Networks

“…For instance, Percec et al reported the observation of unexpected columnar supramolecular morphologies for perfluorocarbon-functionalized dendrimers, produced by assembly processes that were driven by a fluorophobic effect, in contrast to spherical dendrimer assemblies that were characterized for perhydrogenated analogs. [1,2] The inclusion of fluorocarbons within the structures of phenylene, [3] carbosilane, [4,5] benzyl ether, [6] and phosphorus-containing dendrimers [7] has also been utilized to modify their respective physical properties. [8] Many examples of fluorocarbon-containing hyperbranched polymers have been reported, for which the fluorocarbon content is either the intentional or unintentional result of the chemistry employed for polymerization [9][10][11][12][13][14][15][16][17][18] or is introduced through subsequent chemical modification.…”

Molecular characteristics of poly(propylene imine) dendrimers as studied with translational diffusion and viscometry

“…Keywords Dendrimers AE Hydrodynamic properties AE Volume of end groups X-ray scattering [10,19,20], light scattering [21,22], and by size-exclusion chromatography [21,[23][24][25][26]. In several works the hydrodynamic properties of dendrimer molecules were measured by different techniques [9,16,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39].…”

“…Reports studying the molecular properties of dendrimers by different physical techniques are not numerous enough. In general, dendrimer molecules were studied by neutron scattering [9][10][11][12][13][14][15][16][17][18],…”

Internal Dynamics of Dendritic Molecules Probed by Pyrene Excimer Formation

“…NMR [46,51,59,60], neutron scattering [61][62][63], dielectric relaxation spectroscopy [64,65], rheology [66], fluorescence anisotropy [67], and molecular and Brownian dynamics computation [68][69][70][71] have provided some information about the mobility of the different segments constituting a dendrimer, generally via the rotational correlation time (τ C ) of the segments. The overall conclusion of these studies is that the chain ends are more mobile than the internal segments, and that their rotational correlation time is not much affected by increasing G values.…”