Characterization of Lipid Membrane Properties for Tunable Electroporation

Lipid bilayers form nanopores on the application of an electric field. This process of electroporation can be utilized in different applications ranging from targeted drug delivery in cells to nano-gating membrane for engineering applications. However, the ease of electroporation is dependent on the surface energy of the lipid layers and thus directly related to the packing structure of the lipid molecules. 1,2- dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid monolayers were deposited on a mica substrate using the Langmuir-Blodgett (LB) technique at different packing densities and analyzed using atomic force microscopy (AFM). The wetting behavior of these monolayers was investigated by contact angle measurement and molecular dynamics simulations. It was found that an equilibrium packing density of liquid-condensed (LC) phase DPPC likely exists and that water molecules can penetrate the monolayer displacing the lipid molecules. The surface tension of the monolayer in air and water was obtained along with its breakthrough force. Topics: Membranes, ElectroporationNational Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program

Parametric Study on the Effect of Partial Charge on Water Infiltration Behavior in MFI Zeolites

This work analyzes the infiltration behavior of water into sub-nanometer MFI zeolite pores using molecular dynamics simulations. Infiltration simulations are run for a range of partial charge values on the zeolite atoms. Infiltration behavior is compared to partial charges to verify dependence and determine critical charge above which infiltration becomes severely inhibited even at high pressures. Attraction energy is calculated and correlated to the observed infiltration behavior. The critical partial charge of Si~1.8 occurs when the waterzeolite interaction energy becomes stronger than water-water attraction due to which water molecules get stuck and infiltration is significantly reduced. Topics: Wate

Negative pressure characteristics of an evaporating meniscus at nanoscale

This study aims at understanding the characteristics of negative liquid pressures at the nanoscale using molecular dynamics simulation. A nano-meniscus is formed by placing liquid argon on a platinum wall between two nano-channels filled with the same liquid. Evaporation is simulated in the meniscus by increasing the temperature of the platinum wall for two different cases. Non-evaporating films are obtained at the center of the meniscus. The liquid film in the non-evaporating and adjacent regions is found to be under high absolute negative pressures. Cavitation cannot occur in these regions as the capillary height is smaller than the critical cavitation radius. Factors which determine the critical film thickness for rupture are discussed. Thus, high negative liquid pressures can be stable at the nanoscale, and utilized to create passive pumping devices as well as significantly enhance heat transfer rates

Device‐Scale Nanochannel Evaporator for High Heat Flux Dissipation

Abstract High heat flux values in thin film evaporation experiments are typically attained based on short wicking distance, ranging from tens to hundreds of micrometers between the meniscus and the liquid reservoir, thus making such devices vulnerable to quick drying out while also limiting their real‐world applicability. Here, the performance of a nanochannel (122 nm depth and 10 µm width) based evaporator with FC72 is demonstrated as working fluid. FC72 is an ideal fluid for electronics cooling as it is nonpolar and dielectric with a low boiling point. The 1 mm thick evaporator consists of more than 1000 nanochannels connecting two micro‐reservoirs 4.8 cm apart. Thin film evaporation experiments are conducted for four different power inputs, and the steady‐state wicking distance varied from 21 to 8 mm depending on the evaporator's working temperature. Direct weight measurement of evaporated FC72 is used to estimate the interfacial evaporative heat flux. Such a technique mitigates the need for contact angle measurement in micro/nano confined space, a methodology commonly used in literature studies that is prone to error and uncertainties. The maximum evaporative heat flux is 0.93 kW cm−2 at ≈65 °C hot spot temperature. Interestingly, the product of wicking distance and evaporative heat flux remain constant for all power inputs. Numerical simulations are performed to quantify heat loss and effectiveness of the evaporator

Origin of Surface-Driven Passive Liquid Flows

Passive liquid flow occurs in nature in the transport of water up tall trees and is desired for high-heat flux removal in thermal management devices. Typically, liquid–vapor surface tension is used to generate passive flows (e.g., capillary and Marangoni flows). In this work, we perform a fundamental molecular study on passive liquid flow driven by the solid–liquid surface tension force. Such surface tension values are first estimated by placing a liquid film over the surface and simulating various surface temperatures, followed by which simulations are performed by differential heating of the liquid film over the surface. Very strong passive liquid flows are obtained that lead to steady-state, continuous, and high-heat flux removal close to the maximum theoretical limit, as predicted by the kinetic theory of evaporation. Nondimensional empirical relations are developed for surface tension gradient, flow velocity, and evaporation rate