The structure and dynamics of polyelectrolytes differ from those of neutral polymers. How these differences affect the transport of anisotropic particles remains incompletely understood. Here, we investigate the transport of semiflexible M13 bacteriophage (phage) in aqueous semidilute solutions of sodium polystyrenesulfonate (PSS) with various ionic strengths using fluorescence microscopy. We tune the characteristic length scales of the PSS using two molecular weights of 68 and 2200 kDa and by varying the ionic strength of the solutions from 10–6 to 10–1 M. Phage exhibit diffusive dynamics across all polymer concentrations. For 2200 kDa PSS solutions, the phage dynamics monotonically deviate from the bulk prediction as polymer concentration increases and exhibit non-Gaussian distributions of displacements. Existing scaling theories can approximately collapse dynamics as a function of phage hydrodynamic radius to polymer size ratio Rh/ξ onto a master curve across polymer concentrations and ionic strengths. This partial collapse, however, does not follow the prediction for diffusion of isotropic particles in flexible Gaussian chains, suggesting the presence of multiple diffusive modes due to the anisotropic structure of the phage and the confining length scales set by the structure and dynamics of charged polymers.
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Influence of polymer flexibility on nanoparticle dynamics in semidilute solutions
The hierarchical structure and dynamics of polymer solutions control the transport of nanoparticles (NPs) through them. Here, we perform multi-particle collision dynamics simulations of solutions of semiflexible polymer chains with tunable persistence length l p to investigate the effect of chain stiffness on NP transport. The NPs exhibit two distinct dynamical regimes – subdiffusion on short time scales and diffusion on long time scales. The long-time NP diffusivities are compared with predictions from the Stokes–Einstein relation (SER), mode-coupling theory (MCT), and a recent polymer coupling theory (PCT). Increasing deviations from the SER as the polymer chains become more rigid ( i.e. as l p increases) indicate that the NP motions become decoupled from the bulk viscosity of the polymer solution. Likewise, polymer stiffness leads to deviations from PCT, which was developed for fully flexible chains. Independent of l p , however, the long-time diffusion behavior is well-described by MCT, particularly at high polymer concentration. We also observed that the short-time subdiffusive dynamics are strongly dependent on polymer flexibility. As l p is increased, the NP dynamics become more subdiffusive and decouple from the dynamics of the polymer chain center-of-mass. We posit that these effects are due to differences in the segmental mobility of the semiflexible chains.
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- Award ID(s):
- 1705968
- NSF-PAR ID:
- 10098535
- Date Published:
- Journal Name:
- Soft Matter
- Volume:
- 15
- Issue:
- 6
- ISSN:
- 1744-683X
- Page Range / eLocation ID:
- 1260 to 1268
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Polyelectrolyte complexes formed from nucleic acids and synthetic polycations are studied because of their potential in gene delivery. Coarse‐grained molecular dynamics simulations are performed to examine the impact of chain length and polyanion stiffness on polyplex formation and aggregation. Polyplexes containing single polyanion chain fall into three structural regimes depending on polyanion stiffness: flexible polyanions form collapsed complexes, semiflexible polyanions form various morphologies including toroids and hairpins, and stiff polyanions form rod‐like structures. Polyplex size generally decreases as polycation length increases. Polyelectrolyte complexes aggregate in some simulations containing multiple polyanions and an excess of short polycations. Aggregation is observed to only occur for semiflexible and stiff polyanions and is promoted by shorter polycation lengths. Simulations of short, stiff polyanions condensed by long polycations are used as a model for siRNA gene delivery complexes. These simulations show multiple polyanions are spaced out along the polycation with polyanion–polyanion interactions, usually limited to overlapping chain ends. These structures differ from aggregates of longer polyanions in which the polyanions are packed together in parallel, forming bundles.
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We study the collective elastic behavior of semiflexible polymer solutions in a nematic liquid-crystalline state using polymer field theory. Our polymer field-theoretic model of semiflexible polymer solutions is extended to include second-order fluctuation corrections to the free energy, permitting the evaluation of the Frank elastic constants based on orientational order fluctuations in the nematic state. Our exact treatment of wormlike chain statistics permits the evaluation of behavior from the nematic state, thus accurately capturing the impact of single-chain behavior on collective elastic response. Results for the Frank elastic constants are presented as a function of aligning field strength and chain length, and we explore the impact of conformation fluctuations and hairpin defects on the twist, splay, and bend moduli. Our results indicate that the twist elastic constant Ktwist is smaller than both bend and splay constants (Kbend and Ksplay, respectively) for the entire range of polymer rigidity. Splay and bend elastic constants exhibit regimes of dominance over the range of chain stiffness, where Ksplay > Kbend for flexible polymers (large-N limit) while the opposite is true for rigid polymers. Theoretical analysis also suggests the splay modulus tracks exactly to that of the end-to-end distance in the transverse direction for semiflexible polymers at intermediate to large-N. These results provide insight into the role of conformation fluctuations and hairpin defects on the collective response of polymer solutions.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C8SM01834K
