Configurational characteristics and scaling behavior of starburst molecules: a computational study

Lescanec, Robert L.; Muthukumar, Murugappan

doi:10.1021/ma00210a026

Cited by 407 publications

(457 citation statements)

References 4 publications

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“…This may indicate that the building up of the HBPL structure is changing with molecular weight regime. [44][45][46] As expected, the radius of gyration of the HBPLs increases upon complexation for high molecular weight polymer samples. For the polymer sample with M n ) 4400 g/mol; moreover, the R g remains unchanged within the experimental error.…”

Section: Resultssupporting

confidence: 73%

Thermotropic Ionic Liquid Crystals via Self-Assembly of Cationic Hyperbranched Polypeptides and Anionic Surfactants

et al. 2007

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This work describes the dilute solution and solid-state structure of polyelectrolyte complexes generated from hyperbranched polylysine (HBPL) and various anionic, sodium alkyl sulfate surfactants. In dilute solution, the radius of gyration (R g ) of the HBPL and HBPL-surfactant complexes was determined in the Guinier regime in good solvent conditions by means of small-angle X-ray scattering (SAXS). With increasing molecular weight of the HBPL, an increase in R g up to a maximum of 3.7 and 4.2 nm was observed for the HBPLs and HBPL-surfactant complexes, respectively. In the solid state, HBPL-surfactant complexes were found to form liquid crystalline (LC) phases, whose thermal stability and structure depended both on the molecular weight of the HBPL as well as on the nature of the anionic surfactant. Depending on the surfactant alkyl chain length, liquid crystalline phases with short range liquid-like order, columnar hexagonal packing or lamellar ordering were observed. By combination of small-angle X-ray scattering, differential scanning calorimetry (DSC), and cross-polarized light optical microscopy (CPOM), the exact structure of the LC phases, as well as their region of thermal stability, could be identified. HBPL-sodium dodecyl sulfate LC phases showed thermotropic behavior and underwent two transitions with increasing temperature. First, at lower temperatures, an order-nematic transition was observed. Upon further temperature increase, a second transition from a nematic to an isotropic phase was observed. Structural models for these different LC phases are proposed.

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Section: Resultssupporting

confidence: 73%

Thermotropic Ionic Liquid Crystals via Self-Assembly of Cationic Hyperbranched Polypeptides and Anionic Surfactants

et al. 2007

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“…Electronic mail: s.rathgeber@fz-juelich.de evaluated by Murat and Grest 2 using molecular dynamics simulations as well as by Mansfield 3,4 5 and poly͑propyleneimine͒ dendrimers 6 seem to support the M ϳR g 3 scaling behavior. Most computer simulations seem to agree that the endgroups of a dendrimer are distributed throughout the molecule 2,3,[7][8][9] and are not located predominantly on the outside of the dendrimer, as was postulated by the theory of de Gennes and Hervet. 10 Topp et al 11 however, concluded from SANS experiments on partially labeled dendrimers and the fact that the radius of gyration of the terminal groups R g,T was larger than R g of the entire gϭ7 dendrimer that the endgroups were concentrated near the periphery of the dendrimer.…”

Section: Introductionmentioning

confidence: 75%

Dynamics of star-burst dendrimers in solution in relation to their structural properties

Rathgeber

Monkenbusch

Kreitschmann³

et al. 2002

The Journal of Chemical Physics

134

160

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We have measured both the static and dynamic structure factors of a single dendrimer with small-angle x-ray scattering ͑SAXS͒ and neutron spin-echo spectroscopy under good solvent conditions with the aim of finding a consistent correlation between the structural properties of dendrimers and their dynamic behavior. The samples under investigation were star-burst polyamidoamine dendrimers with generations gϭ0 to 8 in dilute methanol solutions. A model independent approach employing inverse Fourier transformation and square root deconvolution methods has been used to analyze the SAXS data to obtain the pair distance distribution function p(r) and the radial excess electron density profile ⌬ (r). In addition, we formulated a model that takes both the colloidal ͑globular, compact shape with form polydispersity or fuzzy surface͒ as well as the loose, polymeric ͑self-avoiding random walk͒ character of dendrimers into account. With this model we were able to describe the spectra of all dendrimer generations consistently. Parameters discussed as a function of the dendrimer generation are, among others, the correlation length of the density fluctuations ͑blob radius͒ , the radius of gyration R g , the sphere radius R s , the form polydispersity s or analogously, the width of the fuzzy surface region 2 f . Both the model-independent approach and the model fits reveal that at least down to the third generation the dendrimers exhibit a rather compact, globular shape. These findings are in agreement with the dynamic results obtained by NSE spectroscopy which probes length scales both larger and much smaller than the dimension of a single dendrimer. The method reveals that the dynamics throughout is dominated by the center-of-mass diffusion-the internal dynamics is suppressed. The diffusion coefficients obtained are close to the values calculated from the Stokes-Einstein relation using the sphere radius R s determined from the SAXS spectra. Dynamically, the dendrimers behave like ''hard'', solid spheres.

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“…This study, albeit generally interesting, could cover a timescale of hundreds of picoseconds only. Later Lescanec and Muthukumar 23 have proposed a kinetic growth model in a 3-d off-lattice MC. They have reported the highest density at the core and have also found that the terminal monomers can traverse the dendrimer.…”

Section: Introductionmentioning

confidence: 99%

Conformations of dendrimers in dilute solution

Timoshenko

Kuznetsov

Connolly

2002

The Journal of Chemical Physics

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Conformations of isolated homo-dendrimers of G = 1 − 7 generations with D = 1 − 6 spacers have been studied in the good and poor solvents, as well as across the coil-to-globule transition, by means of a version of the Gaussian self-consistent (GSC) method and Monte Carlo (MC) simulation in continuous space based on the same coarse-grained model. The latter includes harmonic springs between connected monomers and the pair-wise Lennard-Jones potential with a hard core repulsion. The scaling law for the dendrimer size, the degrees of bond stretching and steric congestion, as well as the radial density, static structure factor, and asphericity have been analysed. It is also confirmed that while smaller dendrimers have a dense core, larger ones develop a hollow domain at some separation from the centre.PACS numbers: 36.20.Ey, 61.25.Hq

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Configurational characteristics and scaling behavior of starburst molecules: a computational study

Cited by 407 publications

References 4 publications

Thermotropic Ionic Liquid Crystals via Self-Assembly of Cationic Hyperbranched Polypeptides and Anionic Surfactants

Thermotropic Ionic Liquid Crystals via Self-Assembly of Cationic Hyperbranched Polypeptides and Anionic Surfactants

Dynamics of star-burst dendrimers in solution in relation to their structural properties

Conformations of dendrimers in dilute solution

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