Microscopic Viscoelasticity of Polymer Solutions and Gels Observed from Translation and Rotation of Anisotropic Colloid Probes

Phage probes couple to DNA relaxation dynamics to reveal universal behavior across scales and regimes

Microrheology has become an indispensable tool for measuring the dynamics of macromolecular systems. Yet, its ability to characterize polymer dynamics across spatiotemporal scales, which vary among polymers and concentration regimes, is limited by the selection of probe morphologies and sizes. Here, we introduce semiflexible M13 phage as a powerful microrheological probe able to circumvent these constraints to robustly capture the dynamics of polymeric solutions across decades of concentrations, sizes, and ionic conditions. We show that phage mobility directly couples to the relaxation dynamics of DNA solutions spanning from semidilute to entangled regimes with ionic strengths varying by four orders of magnitude. Phage mobility metrics across a broad range of timescales collapse onto universal master curves that are unexpectedly insensitive to ionic strength and exhibit robust crossovers from semidilute to entangled regime scaling, not captured by current theoretical models. Our results open the door to the use of phage probes to elucidate the complex dynamics of systems exhibiting a spectrum of thermal and active relaxation processes.

The coupling of rotational and translational dynamics for rapid diffusion of nanorods in macromolecular networks

The rod-like viruses show anomalously rapid diffusion in bio-tissue networks originated from the rotation-facilitated transportation; however, the experimental investigation of the correlation of the rotational and translational dynamics is still in blank. Herein, typical rod-like and spherical gold nanoparticles (NPs) are dispersed in the classical Tetra-PEG gels, respectively, as model systems for light scattering studies. The contributions from translational and rotational diffusive dynamics, and network fluctuation dynamics can be well-resolved and the stretch exponent of rotational dynamics at 0.25 is proven to be the fingerprint for the coupled rotational and translational dynamics of nanorods. The rotation facilitated re-orientation finally leads to the fast transportation of nanorods. The discoveries are confirmed to be valid for rod-like biomacromolecule systems by studying the diffusive dynamics of Tobacco mosaic virus in gels. The work can be inspiring for the development of protocols to prevent infection of microorganism and regulate the transportation of nano-medicines.

Electro-optical Study of the Anomalous Rotational Diffusion in Polymer Solutions

Brownian diffusion of spherical nanoparticles is usually exploited to ascertain the rheological properties of complex media. However, the behavior of the tracer particles is affected by a number of phenomena linked to the interplay between the dynamics of the particles and polymer coils. For this reason, the characteristic lengths of the dispersed entities, depletion phenomena, and the presence of sticking conditions have been observed to affect the translational diffusion of the probes. On the other hand, the retardation effect of the host fluid on the rotational diffusion of nonspherical particles is less understood. We explore the possibility of studying this phenomenon by analyzing the electro-orientation of the particles in different scenarios in which we vary the ratio between the particle and polymer characteristic size, and the geometry of the particles, including both elongated and oblate shapes. We find that the Stokes-Einstein relation only applies if the radius of gyration of the polymer is much shorter than the particle size and when some repulsive interaction between both is present.

Rotational and translational microrheology from shape-anisotropic particles

In this work, we report measurements of the mean squared angular and translational displacements of a colloidal dumbbell immersed in a viscoelastic fluid using digital microscopy. From the mean squared displacements, we obtain the mechanical properties of the media. Both angular and translational motions provide the same viscoelastic complex modulus and agree with that obtained from the translational motion of a spherical probe particle.