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Title: Nanorod Mobility within Entangled Wormlike Micelle Solutions

Abstract

In the semi-dilute 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 semi-dilute solutions of entangled wormlike micelles formed by the surfactant cetylpyridinium chloride (CPyCl) and the counter-ion 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 recentmore » 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.« less

Authors:
 [1];  [2];  [1];  [3]
  1. Argonne National Lab. (ANL), Argonne, IL (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States); Federal Univ. of Parana, Curitiba (Brazil)
  3. Johns Hopkins Univ., Baltimore, MD (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1339282
Grant/Contract Number:
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Macromolecules
Additional Journal Information:
Journal Volume: 50; Journal Issue: 1; Journal ID: ISSN 0024-9297
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
77 NANOSCIENCE AND NANOTECHNOLOGY

Citation Formats

Lee, Jonghun, Grein-Iankovski, Aline, Narayanan, Suresh, and Leheny, Robert L. Nanorod Mobility within Entangled Wormlike Micelle Solutions. United States: N. p., 2016. Web. doi:10.1021/acs.macromol.6b02091.
Lee, Jonghun, Grein-Iankovski, Aline, Narayanan, Suresh, & Leheny, Robert L. Nanorod Mobility within Entangled Wormlike Micelle Solutions. United States. doi:10.1021/acs.macromol.6b02091.
Lee, Jonghun, Grein-Iankovski, Aline, Narayanan, Suresh, and Leheny, Robert L. 2016. "Nanorod Mobility within Entangled Wormlike Micelle Solutions". United States. doi:10.1021/acs.macromol.6b02091. https://www.osti.gov/servlets/purl/1339282.
@article{osti_1339282,
title = {Nanorod Mobility within Entangled Wormlike Micelle Solutions},
author = {Lee, Jonghun and Grein-Iankovski, Aline and Narayanan, Suresh and Leheny, Robert L.},
abstractNote = {In the semi-dilute 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 semi-dilute solutions of entangled wormlike micelles formed by the surfactant cetylpyridinium chloride (CPyCl) and the counter-ion 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.},
doi = {10.1021/acs.macromol.6b02091},
journal = {Macromolecules},
number = 1,
volume = 50,
place = {United States},
year = 2016,
month =
}

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  • Surfactant molecules found in soaps and detergents can self-assemble into a great variety of morphologies (e.g., spherical micelles, cylindrical micelles, and lamellar phases). The resulting morphology is highly affected by ionic strength, temperature, and flow conditions. In particular, cylindrical micelles in the presence of inorganic or organic salts can self-assemble into large flexible and elongated wormlike micelles. In equilibrium, the wormlike micelles transition from slightly entangled to branched and, finally, to multi-connected structures with increasing salt concentration. In our work, by introducing external flow conditions via microfluidics, these micellar structures can follow very different trajectories on the phase map andmore » new nanoporous structures can be created. This flow induced approach offers great potential to create novel materials and nanoporous scaffolds from wormlike micelles under ambient temperature and pressure, without any chemical and thermal means (1). As a result, this work provides attractive solutions for synthesizing new biocompatible materials under ambient conditions with biosensing, encapsulation, catalysis, photonics, and self-healing applications.« less
  • Recently proposed theories for shear banding in wormlike micellar solutions (WLMs) rely on a shear-induced isotropic-nematic (I-N) phase separation as the mechanism for banding. Critical tests of such theories require spatially-resolved measurements of flow-kinematics and local mesoscale microstructure within the shear bands. We have recently developed such capabilities using a short gap Couette cell for flow-small angle neutron scattering (flow-SANS) measurements in the 1-2 plane of shear with collaborators at the NIST Center for Neutron Research. This work combines flow-SANS measurements with rheology, rheo-optics and velocimetry measurements to present the first complete spatially-resolved study of WLMs through the shear bandingmore » transition for a model shear banding WLM solution near the I-N phase boundary. The shear rheology is well-modeled by the Giesekus constitutive equation, with incorporated stress diffusion to predict shear banding. By fitting the stress diffusivity at the onset of banding, the model enables prediction of velocity profiles in the shear banded state which are in quantitative agreement with measured flow-kinematics. Quantitative analysis of the flow-SANS measurements shows a critical segmental alignment for banding and validates the Giesekus model predictions, linking segmental orientation to shear banding and providing the first rigorous evidence for the shear-induced I-N transition mechanism for shear banding.« less
  • The origin of shear thickening in an equimolar semidilute wormlike micellar solution of cetylpyridinium chloride and sodium salicylate was investigated in this work by using Couette rheometry, flow visualization, and capillary Rheo-particle image velocimetry. The use of the combined methods allowed the discovery of gradient shear banding flow occurring from a critical shear stress and consisting of two main bands, one isotropic (transparent) of high viscosity and one structured (turbid) of low viscosity. Mechanical rheometry indicated macroscopic shear thinning behavior in the shear banding regime. However, local velocimetry showed that the turbid band increased its viscosity along with the shearmore » stress, even though barely reached the value of the viscosity of the isotropic phase. This shear band is the precursor of shear induced structures that subsequently give rise to the average increase in viscosity or apparent shear thickening of the solution. Further increase in the shear stress promoted the growing of the turbid band across the flow region and led to destabilization of the shear banding flow independently of the type of rheometer used, as well as to vorticity banding in Couette flow. At last, vorticity banding disappeared and the flow developed elastic turbulence with chaotic dynamics.« less
  • Wormlike micellar salt/surfactant solutions (X-salicylate, cetylpyridinium chloride) are studied with respect to the applied shear stress, concentration, temperature, and composition of the counterions (X = lithium, sodium, potassium, magnesium, and calcium) of the salicylate salt solute to determine vorticity and gradient shear bands. A combination of rheological measurements, laser technique, video analysis, and rheo-small-angle neutron scattering allow for a detailed exploration of number and types of shear bands. Typical flow curves of the solutions show Newtonian, shear-thinning, and shear-thickening flow behavior. In the shear-thickening regime, the solutions show vorticity and gradient shear bands simultaneously, in which vorticity shear bands dominate the visualmore » effect, while gradient shear bands always coexist and predominate the rheological response. It is shown that gradient shear bands change their phases (turbid, clear) with the same frequency as the shear rate oscillates, whereas vorticity shear bands change their phases with half the frequency of the shear rate. Furthermore, we show that with increasing molecular mass of the counterions the number of gradient shear bands increases, while the number of vorticity shear bands remains constant. The variation of temperature, shear stress, concentration, and counterions results in a predictable change in the rheological behavior and therefore allows adjustment of the number of vorticity shear bands in the shear band regime.« less
  • Electron spin resonance (ESR) and electron spin-echo studies of the photoionization of N,N,N',N'-tetramethylbenzidine (TBM) to give the cation radical have been carried out in anionic (sodium octyl sulfate (S8S), sodium decyl sulfate (S10S), sodium dodecyl sulfate (S12S), and sodium tetradecyl sulfate (S14S)), cationic (dodecyltrimethylammonium chloride (DTAC) and hexadecyltrimethylammonium chloride (HTAC)), and nonionic (Triton X-100) micellar solutions frozen to 77 K. Cation-water interactions have been detected by electron spin-echo modulation (ESEM) analysis and are found to increase with decreasing alkyl chain length in anionic micelles. This is interpreted as consistent with an asymmetric solubilization site for the cation near the micellarmore » surface and with little water penetration into the micelle. The photoionization efficiency in anionic micelles correlates with increased cation-water interactions. In cationic micelles the photoionization is about twofold more efficient than in anionic micelles of the same alkyl chain length, although the cation-water interaction is less. The overall photoionization efficiency of a micellized solute appears to depend on micellar surface charge as well as on solute location within the micelle.« less