No abstract

We performed molecular dynamics simulations with a coarse-grained model to investigate the capillary filling dynamics of polymer chains in nanopores. Short chains fill slower than predicted by the Lucas−Washburn equation, but long chains fill faster. The analysis shows that the combination of the confinement effect on the free energy of chains and the reduction of the effective radius due to the "dead zone" slows down the imbibition. Reduction of the entanglements is the main factor behind the reversing dynamics because of the lower effective viscosity, which leads to a faster filling. This effect is enhanced in the smaller capillary and more profound for longer chains. The observed increase in the mean-square radius of gyration during capillary filling provides a clear evidence of chain orientation, which leads to the decrease in the number of entanglements. For the scaling relation between the effective viscosity and the degree of polymerization, we find the exponent will increase in the larger nanopore.

Improving the axial resolution for multiparticle three-dimensional (3D) holographic tracking is crucial but challenging. Here we study the impacts of incident light power, uniformity of the illumination as well as image pixel size on the axial tracking resolution for digital holographic microscopy (DHM). We demonstrate that the resolution highly depends on the image pixel size and the uniformity of the illumination. A 3D localization algorithm based on local-intensity-maxima searching and a Gaussian fit to the integrated intensity of the reconstructed lateral images along the axial direction proves a robust strategy to enhance the axial resolution for colloids and bacteria within a wide depth of field over several tens of micrometers.