Scaling Behavior of Dendritic Nanoparticle Mobility in Semidilute Polymer Solutions

Abstract

In our studies on particle mobility in polymer solutions, we have investigated and determined self-diffusion coefficients of nanoparticles in semidilute solutions of poly(ethylene glycol) (PEG, M w = 6, 20, 35, and 100 kDa). Specially designed PEGylated dendrimers with well-defined sizes (d h = 3.4−11.0 nm) and with internal 19 F moieties allow for background-free 19 F NMR diffusion measurements. This way, we were able to assess the self-diffusion coefficients as a function of particle diameter and length scales (correlation length, tube diameter, polymer radius of gyration) with high resolution. Scaling arguments allowed us to visualize a clear crossover between particles probing a lower apparent viscosity to near macroviscosity when the nanoparticle size is comparable to the PEG polymer coil size. The same arguments are shown to correctly predict particle diffusion coefficients as a function of polymer concentration when the particles are smaller than the polymer coils.

Estimating microstructural length scales in κ-carrageenan hydrogels by PFG NMR nanoprobe diffusometry

“…Diffusion-ordered spectroscopy (DOSY) experiments were performed with a Bruker Avance II spectrometer at 300 MH frequency for 1 H, equipped with a Bruker diff25 gradient probe (maximum pulsed eld gradient (PFG) intensity 9.60 T/m was equipped with a 10-mm RF insert that could be tuned to the 1 H and 19 F NMR resonance frequencies. Experimen analysis were performed as outlined previously 3 . In short, DOSY experiments based on a spin echo were performed variation of the gradient pulse amplitude at an effective gradient pulse duration of 5 ms, whilst keeping the diffusion time at 200 ms. For 1 H NMR measurements, the minimum gradient amplitude was chosen to be high enough to atten NMR signal of water almost completely.…”

“…Particles larger than the structural features of the polymer network are completely immobilized. [2][3][4] The latter effect has been observed in polysaccharide hydrogels if the size of the particles exceeds a certain threshold, which likely corresponds to the size of the smallest interstitials between the polymer strands. 5 For the largest part, however, diffusion of nanoparticles remains hindered but unrestricted.…”

Dramatic change of the self-diffusions of colloidal ellipsoids by hydrodynamic interactions in narrow channels*

“…When α > 1, it corresponds to the super-diffusive motion, which is generally observed in the presence of an external field or the self-motile motion of cells [4][5][6] or Janus particles. [7] When α < 1, it corresponds to the sub-diffusive motion, which is suggested to be more ubiquitous in nature and generally occurs in confined diffusion, such as macromolecular crowding in biology, [8,9] polymer solutions, [10][11][12][13] hydrogels, [14,15] etc.…”

Nanoparticle diffusometry in hydrogels

“…Higher MF concentrations lead to an upward shift in viscosity of the whole flow curve, whereas the viscosity effect of CMC can only be seen at higher shear rates. Local measurements of the apparent viscosity of the continuous phase from the mobility of nanoparticles by diffusion NMR de Kort, Rombouts, Hoeben, Janssen, Van As, et al, 2015a;de Kort, van Duynhoven, Van As, & Mariette, 2015b), and an assessment of the molecular mobility of CMC by 1 H NMR spectroscopy show that at most 5% of CMC closely associates with the MFs, while the rest remains dissolved in solution (SI, section S7.1b). In the high shear rate regime, the dispersive effect of the addition of CMC leads to an increase of bulk viscosity significantly larger than only the contribution of the viscosity of the continuous phase (which is < 6 mPa).…”

“…The probe was equipped with a 10-mm rf insert tuned to the 19 F resonance frequency. The samples contained 0.1 wt% 19 F labeled, nonsticky dendritic nanoparticles with a hydrodynamic radius of 7.5 nm de Kort, Rombouts, Hoeben, Janssen, Van As, et al, 2015a). The overall sample volume was chosen as to not exceed the linear part of the magnetic field gradient.…”