35 research outputs found
Controlling Polymer Capture and Translocation by Electrostatic Polymer-Pore Interactions
Polymer translocation experiments typically involve anionic polyelectrolytes
such as DNA molecules driven through negatively charged nanopores. Quantitative
modelling of polymer capture to the nanopore followed by translocation
therefore necessitates the consideration of the electrostatic barrier resulting
from like-charge polymer-pore interactions. To this end, in this work we couple
mean-field level electrohydrodynamic equations with the Smoluchowski formalism
to characterize the interplay between the electrostatic barrier, the
electrophoretic drift, and the electro-osmotic liquid flow. In particular, we
find that due to distinct ion density regimes where the salt screening of the
drift and barrier effects occur, there exists a characteristic salt
concentration maximizing the probability of barrier-limited polymer capture
into the pore. We also show that in the barrier-dominated regime, the polymer
translocation time increases exponentially with the membrane charge and decays
exponentially fast with the pore radius and the salt concentration. These
results suggest that the alteration of these parameters in the barrier-driven
regime can be an efficient way to control the duration of the translocation
process and facilitate more accurate measurements of the ionic current signal
in the pore
Improvement of Temperature Distribution across Thick Thermoset Composites Using Carbon Nanotubes
The effect of adding carbon nanotubes (CNT) into epoxy on the temperature gradient in thick thermoset composites was studied and presented. Addition of CNT increases the thermal diffusivity of the resin and reduces the curing reaction speed. The latter slows down the rate of energy liberation, while the former helps to dissipate faster the released heat in the exothermic reaction. The results showed that the addition of up to 1 wt% CNT can reduce the difference between temperatures at the center and at the surface of 1.5-inch thick column of epoxy by 41%. Measured variations of heat capacity and thermal diffusivity by changes in both temperature and carbon nanotube contents as well as the empirically-evaluated cure kinetics of epoxy were used in a transient one-dimensional heat transfer finite difference model to determine the temperature distribution across thickness during the cure. Good agreement was obtained between calculated and experimental trends
Entropic force of polymers on a cone tip
We consider polymers attached to the tip of a cone, and the resulting force
due to entropy loss on approaching a plate (or another cone). At separations
shorter than the polymer radius of gyration R_g, the only relevant length scale
is the tip-plate (or tip-tip) separation h, and the entropic force is given by
F=A kT/h. The universal amplitude A can be related to (geometry dependent)
correlation exponents of long polymers. We compute A for phantom polymers, and
for self-avoiding (including star) polymers by epsilon-expansion, as well as by
numerical simulations in 3 dimensions
Fabrication of a single sub-micron pore spanning a single crystal (100) diamond membrane and impact on particle translocation
The fabrication of sub-micron pores in single crystal diamond membranes, which span the entirety of the membrane, is described for the first time, and the translocation properties of polymeric particles through the pore investigated. The pores are produced using a combination of laser micromachining to form the membrane and electron beam induced etching to form the pore. Single crystal diamond as the membrane material, has the advantages of chemical stability and durability, does not hydrate and swell, has outstanding electrical properties that facilitate fast, low noise current-time measurements and is optically transparent for combined optical-conductance sensing. The resulting pores are characterized individually using both conductance measurements, employing a microcapillary electrochemical setup, and electron microscopy. Proof-of-concept experiments to sense charged polystyrene particles as they are electrophoretically driven through a single diamond pore are performed, and the impact of this new pore material on particle translocation is explored. These findings reveal the potential of diamond as a platform for pore-based sensing technologies and pave the way for the fabrication of single nanopores which span the entirety of a diamond membrane
Controlling polymer capture and translocation by electrostatic polymer-pore interactions
In vivo quantification of spatially varying mechanical properties in developing tissues
The mechanical properties of the cellular microenvironment and their spatiotemporal variations are thought to play a central role in sculpting embryonic tissues, maintaining organ architecture and controlling cell behavior, including cell differentiation. However, no direct in vivo and in situ measurement of mechanical properties within developing 3D tissues and organs has yet been performed. Here we introduce a technique that employs biocompatible, magnetically responsive ferrofluid microdroplets as local mechanical actuators and allows quantitative spatiotemporal measurements of mechanical properties in vivo. Using this technique, we show that vertebrate body elongation entails spatially varying tissue mechanics along the anteroposterior axis. Specifically, we find that the zebrafish tailbud is viscoelastic (elastic below a few seconds and fluid after just 1 min) and displays decreasing stiffness and increasing fluidity toward its posterior elongating region. This method opens new avenues to study mechanobiology in vivo, both in embryogenesis and in disease processes, including cancer