Nanorod Mobility within Entangled Wormlike Micelle Solutions

Abstract

In the semidilute regime, wormlike micelles form an isotropic entangled microstructure that is similar to that of an entangled polymer solution with a characteristic, nanometer-scale entanglement mesh size. We report a combined X-ray photon correlation spectroscopy (XPCS) and rheology study to investigate the translational dynamics of gold nanorods in semidilute solutions of entangled wormlike micelles formed by the surfactant cetylpyridinium chloride (CPyCl) and the counterion sodium salicylate (NaSal). The CPyCl concentration is varied to tune the entanglement mesh size over a range that spans from approximately equal to the nanorod diameter to larger than the nanorod length. The NaSal concentration is varied along with the CPyCl concentration so that the solutions have the maximum viscosity for given CPyCl concentration. On short time scales the nanorods are localized on a length scale matching that expected from the high-frequency elastic modulus of the solutions as long as the mesh size is smaller than the rod length. On longer time scales, the nanorods undergo free diffusion. At the highest CPyCl concentrations, the nanorod diffusivity approaches the value expected based on the macroscopic viscosity of the solutions, but it increases with decreasing CPyCl concentration more rapidly than expected from the macroscopic viscosity. A recent model by Cai et al. [Cai, L.-H.; Panyukov, S.; Rubinstein, M. Macromolecules 2015, 48, 847−862] for nanoparticle "hopping" diffusion in entangled polymer solutions accounts quantitatively for this enhanced diffusivity.

Study of active Brownian particle diffusion in polymer solutions

“…In the past decades, diffusion of NPs in polymer solutions has received a lot of attention both experimentally [16][17][18][19][20] and theoretically [21][22][23][24][25][26][27]. In experiments, fluctuation correlation spectroscopy (FCS) [28][29][30][31], dynamic light scattering (DLS) [29,32], and capillary viscosimetry are general tools to investigate the diffusion of a NP in complex fluids.…”

Diffusion of rod-like nanoparticles in non-adhesive and adhesive porous polymeric gels

“…The shape of NPs is known to strongly affect their intravenous circulation time ( Geng et al, 2007 ), translocation across cell membrane ( Li et al, 2013;Shi et al, 2011;Wang et al, 2014;Yang and Ma, 2010 ), and intracellular transport route ( Hinde et al, 2017 ). So far, relatively few studies have focused on the effect of the shape of NPs on their transport in porous media ( Choi et al, 2015;Fakhri et al, 2010;Han et al, 2006;Lee et al, 2017;Peng et al, 2016 ). Recently, it has been shown that the diffusivity in mucus of nanorods with diameter × length of 80 × 240 nm is more than 3 times higher than that of nanospheres with diameter of 80 nm ( Yu et al, 2016 ).…”

Transport of a self-propelled tracer through a hairy cylindrical channel: interplay of stickiness and activity

“…The crowding associated with the environment greatly influences the mechanism of in vivo and in vitro molecular diffusions, for example nanoparticle diffusion in the cytoplasmic fluid of living cells, 5 intracellular transport, and proteins diffusing through the mucus membrane 6 or nuclear pore complex (NPC), which serves as a gateway connecting the nucleoplasm and cytoplasm of cells. [7][8][9][10][11] Over the past decades, the diffusion of probe particles in crowded media has been widely studied both experimentally 4,[12][13][14][15][16][17][18][19] and theoretically. [20][21][22][23][24][25][26][27][28][29] However, most of these studies focus on the passive diffusion of particles in crowded heterogeneous environments, but in the context of cellular biology, there are plenty of examples of diffusion of active particles such as molecular motors, [30][31][32] active filaments, 33 microtubules 34 etc.…”