arXiv subjects

Zhichun Liu

Publications and source records attributed to Zhichun Liu.

8 recordsLinked to original sources

arXiv2024

Programmable Jumping-Droplet Condensation

Self-propelled droplet jumping during condensation has attractive prospects for energy harvesting, water collection and thermal management, but its real-life applications are greatly limited to the challenge of enabling a sustainable control on the entire droplet lifecycle. Herein, we propose a programmable jumping-droplet condensation that evolves along an artificially designed pathway without external stimulations, where the droplets can uniformly form at specific sites, spontaneously migrate and coalesce with their neighboring droplets, and jump off effectively to continuously refresh surface, significantly enhancing the heat transfer performance and durability of condensation. The programmable jumping-droplet condensation is achieved using a wedge-walled rhombus lattice structure surface inspired from the structures and functions of Namib desert beetle skin, shorebird beak and setaria viridis leaf vein. This surface integrates wetting contrast patterns with dual-gradient hierarchical structures, providing persistent and multidimensional droplet rectifications and thus realizing a sustainable control on the entire droplet lifecycle. Furthermore, we systematically investigate the morphology and behavior evolutions of droplets throughout their entire lifecycle, and fully elucidate the programmable control mechanisms of the lattice structure determined by its topology and wettability features. This work not only serves as theoretical foundations and reference framework to realize a durable jumping-droplet condensation and achieve its performance ceiling in a controlled manner, but also promotes the design and fabrication of functional structured surfaces for droplet manipulation and delivery, self-cleaning and anti-fogging/icing.

physics.flu-dyn↗

arXiv2022

Sequential Self-Propelled Morphology Transitions of Nanoscale Condensates Diversify the Jumping-Droplet Condensation

The jumping-droplet condensation, namely the out-of-plane jumping of condensed droplets upon coalescence, has been a promising technical innovation in the fields of energy harvesting, droplet manipulation, thermal management, etc., yet is limited owing to the challenge of enabling a sustainable and programmable control. Here, we characterized the morphological evolutions and dynamic behaviors of nanoscale condensates on different nanopillar surfaces, and found that there exists an unrevealed domino effect throughout the entire droplet lifecycle and the coalescence is not the only mechanism to access the droplet jumping. The vapor nucleation preferentially occurs in structure intervals, thus the formed liquid embryos incubate and grow in a spatially confined mode, which stores an excess surface energy and simultaneously provides a asymmetric Laplace pressure, stimulating the trapped droplets to undergo a dewetting transition or even a self-jumping, which can be facilitated by the tall and dense nanostructures. Subsequently, the adjacent droplets merge mutually and further trigger more multifarious self-propelled behaviors that are affected by underlying surface nanostructure, including dewetting transition, coalescence-induced jumping and jumping relay. Moreover, an improved energy-based model was developed by considering the nano-physical effects, the theoretical prediction not only extends the coalescence-induced jumping to the nanometer-sized droplets but also correlates the surface nanostructure topology to the jumping velocity. Such a cumulative effect of nucleation-growth-coalescence on the ultimate morphology of droplet may offer a new strategy for designing functional nanostructured surfaces that serve to orientationally manipulate, transport and collect droplets, and motivate surface engineers to achieve the performance ceiling of the jumping-droplet condensation.

physics.flu-dyn↗

arXiv2019

Fluctuation and Inertia

In this work, using Jacobson's idea: '$δ$Q=TdS hold for all the local Rindler causal horizons through each spacetime point', we found that the transitions between the excited and ground state of a particle in a linear acceleration satisfy the fluctuation theorem. The up transition from the ground state to the excited state is an entropy-decreasing process, which requires an external force to contribute equal entropy increase to satisfy the second law of thermodynamics.

gr-qc↗

arXiv2019

Surface tension of the horizon

The idea of treating the horizon of a black hole as a stretched membrane with surface tension has a long history. In this work, we discuss the microscopic origin of the surface tension of the horizon in quantum pictures of spaces, which are Bose-Einstein condensates of gravitons. The horizon is a phase interface of gravitons, the surface tension of which is found to be a result of the difference in the strength of the interaction between the gravitons on its two sides. The gravitational source, such as a Schwarzschild black hole, creates a transitional zone by changing the energy and distribution of its surrounding gravitons. Archimedes' principle for gravity can be expressed as follows: "the gravity on an object is equal to the weight of the gravitons that it displaces."

gr-qc↗

arXiv2018

Black hole as fireplace: limited communications across the horizon

An insightful viewpoint was proposed by Susskind about AMPS firewall: the region behind the firewall does not exist and the firewall is an extension of the singularity. In this work, we provided a possible picture of this idea by combining Newman's complex metric and Dvali-Gomez BEC black holes, which are Bose-Einstein condensates of N gravitons. The inner space behind the horizon is a realized imaginary space encrusted by the real space outside the horizon. In this way, the singularity extents to the horizon to make a firewall for the infalling observer. Some gravitons escape during the fluctuation of the BEC black hole, resulting in a micro-transparent horizon which makes the firewall exposes slightly to an observer outside the horizon. This picture allows limited communications across the horizon.

hep-th↗

arXiv2016

Tailoring Thermal Conductivity of Single-stranded Carbon-chain Polymers through Atomic Mass Modification

Tailoring the thermal conductivity of polymers is central to enlarge their applications in the thermal management of flexible integrated circuits. Progress has been made over the past decade by fabricating materials with various nanostructures, but a clear relationship between various functional groups and thermal properties of polymers remains to be established. Here, we numerically study the thermal conductivity of single-stranded carbon-chain polymers with multiple substituents of hydrogen atoms through atomic mass modification. We find that their thermal conductivity can be tuned by atomic mass modifications as revealed through molecular dynamics simulations. The simulation results suggest that heavy homogeneous substituents do not assist heat transport and trace amounts of heavy substituents can in fact hinder heat transport substantially. Our analysis indicates that carbon chain has the biggest contribution (over 80%) to the thermal conduction in single-stranded carbon-chain polymers. We further demonstrate that atomic mass modifications influence the phonon bands of bonding carbon atoms, and the discrepancies of phonon bands between carbon atoms are responsible for the remarkable drops in thermal conductivity and large thermal resistances in carbon chains. Our study provides fundamental insight into how to tailor the thermal conductivity of polymers through variable substituents.

physics.chem-ph↗

arXiv2015

A Revisit to High Thermoelectric Performance of Single-layer MoS2

Both electron and phonon transport properties of single layer MoS2 (SLMoS2) are studied. Based on first-principles calculations, the electrical conductivity of SLMoS2 is calculated by Boltzmann equations. The thermal conductivity of SLMoS2 is calculated to be as high as 116.8 Wm-1K-1 by molecular dynamics (MD) simulations. The predicted value of ZT is as high as 0.26 at 500K. As the thermal conductivity could be reduced largely by phonon engineering, there should be a high possibility to enhance ZT in the SLMoS2-based materials.

cond-mat.mes-hall↗

arXiv2015

Extremely High Thermal Conductivity of Aligned Bulk Carbon Nanotube-Polyethylene Composites

The poor thermal conductivity of bulk polymers may be enhanced by combining them with high thermal conductivity materials such as carbon nanotubes. Different from random doping, we find that the aligned carbon nanotube-polyethylene composites (ACPCs) has a high thermal conductivity by non-equilibrium molecular dynamics simulations. The analyses indicate that the aligned structure can not only take advantage of the high thermal conduction of carbon nanotubes, but enhance thermal conduction of polyethylene (PE) chains. Our predictions may inspire manufacturing aligned polymer-based composites for a wide variety of applications.

cond-mat.mtrl-sci↗