A conceptual thermal actuation system driven by interface tension of nanofluids

Xu, Baoxing,Qiao, Yu,Park, Taehyo,Tak, Moonho,Zhou, Qulan,Chen, Xi Royal Society of Chemistry 2011 Energy & environmental science Vol.4 No.9

<P>In a system containing nanoporous materials and liquids, the well-known thermo-capillary effect can be amplified by the ultralarge specific surface area of the nanopores. With appropriate temperature change, the relative wetting–dewetting transition can cause the liquid to flow in or out of the nanopores, and part of the thermal energy is converted to significant mechanical output. A conceptual design of such a thermal actuation/energy conversion/storage system is investigated in this paper, whose working mechanism, <I>i.e.</I> the thermally dependent infiltration behaviors of liquids into nanopores, is analyzed using molecular dynamics simulations. The fundamental molecular characteristics, including the density profile, contact angle, and surface tension of the confined liquid molecules, are examined in considerable detail. The influences of pore size, solid phase and liquid species are elucidated, which couple with the thermal effect. The energy density, power density, and efficiency of the thermal actuation system are evaluated. An infiltration experiment on a zeolite/water system is performed to qualitatively validate these findings.</P> <P>Graphic Abstract</P><P>We design a thermally actuated system using nanofluids with high energy and power densities. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1ee01405f'> </P>

Effect of Electric Field on Liquid Infiltration into Hydrophobic Nanopores

Xu, Baoxing,Qiao, Yu,Zhou, Qulan,Chen, Xi American Chemical Society 2011 Langmuir Vol.27 No.10

<P>Understanding the variation of nanofluidic behavior in the presence of an external electric field is critical for controlling and designing nanofluidic devices. By studying the critical infiltration pressure of liquids into hydrophobic nanopores using molecular dynamics (MD) simulations and experiments, important insights can be gained on the variation of the effective liquid–solid interfacial tension with the magnitude and sign of electric field, as well as its coupling with the pore size and the solid and liquid species. It is found that the effective hydrophobicity reduces with the increase of electric intensity and/or pore size, and the behavior is asymmetric with respect to the direction of the electric field. The underlying molecular mechanisms are revealed via the study of the density profile, contact angle, and surface tension of confined liquid molecules.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2011/langd5.2011.27.issue-10/la200477y/production/images/medium/la-2011-00477y_0014.gif'></P>

Liquid flow-induced energy harvesting in carbon nanotubes: a molecular dynamics study

Xu, Baoxing,Chen, Xi The Royal Society of Chemistry 2013 Physical chemistry chemical physics Vol.15 No.4

<P>Energy harvesting by the flow of a hydrochloric acid–water solution through a carbon nanotube (CNT) is explored using atomistic simulations. Through ion configurations near the CNT wall, the ion drifting velocity is obtained, and the induced voltage along the axial direction is obtained as a function of key material and system parameters, including the applied flow rate, ambient temperature, solution concentration and nanotube diameter. The molecular mechanism of ion hopping and motion is elucidated and related to the variation of material and system parameters.</P> <P>Graphic Abstract</P><P>The molecular mechanism of flow-induced voltage inside a nanopore is elucidated for exploring the potential of harvesting mechanical and thermal energy simultaneously. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2cp42204b'> </P>

Characterization of strain rate sensitivity and activation volume using the indentation relaxation test

Xu, Baoxing,Yue, Zhufeng,Chen, Xi Institute of Physics [etc.] 2010 Journal of Physics. D, Applied Physics Vol.43 No.24

<P>We present the possibility of extracting the strain rate sensitivity, activation volume and Helmholtz free energy (for dislocation activation) using just one indentation stress relaxation test, and the approach is demonstrated with polycrystalline copper. The Helmholtz free energy measured from indentation relaxation agrees well with that from the conventional compression relaxation test, which validates the proposed approach. From the indentation relaxation test, the measured indentation strain rate sensitivity exponent is found to be slightly larger, and the indentation activation volume much smaller, than their counterparts from the compression test. The results indicate the involvement of multiple dislocation mechanisms in the indentation test.</P>

Determining engineering stress-strain curve directly from the load-depth curve of spherical indentation test

Xu, Baoxing,Chen, Xi Cambridge University Press (Materials Research Soc 2010 Journal of materials research Vol.25 No.12

<P>The engineering stress-strain curve is one of the most convenient characterizations of the constitutive behavior of materials that can be obtained directly from uniaxial experiments. We propose that the engineering stress-strain curve may also be directly converted from the load-depth curve of a deep spherical indentation test via new phenomenological formulations of the effective indentation strain and stress. From extensive forward analyses, explicit relationships are established between the indentation constraint factors and material elastoplastic parameters, and verified numerically by a large set of engineering materials as well as experimentally by parallel laboratory tests and data available in the literature. An iterative reverse analysis procedure is proposed such that the uniaxial engineering stress-strain curve of an unknown material (assuming that its elastic modulus is obtained in advance via a separate shallow spherical indentation test or other established methods) can be deduced phenomenologically and approximately from the load-displacement curve of a deep spherical indentation test.</P>

Craze density based fatigue-damage analysis in polyethylene methacrylate

Zongzhan Gao,Wei Liu,Qinghai Li,Shiling Liu,Zhufeng Yue,Baoxing Xu 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1

The S-N curve, also known as the Wöhler curve, is well acknowledged and widely used in the prediction of fatigue life of engineering materials. In this study, we present a craze density model, as an alternative approach, to predict the fatigue life of polymer materialpolyethylene methacrylate (PMMA). Our experiments show that craze grows rapidly with the increase of fatigue loadings after their initiation on the surface of PMMA till to the failure of specimens. Dynamic measurements indicate that the growth rate of craze density reaches a stable stage after a rapid accumulation at the beginning, and dominates the fatigue life of PMMA. Both initiation time of crazing and deformation energy of PMMA are probed through the recorded fatigue stress-strain curves and the optical microscope (OM) observations on crazing evolutions. The critical growth rate of the craze density is correlated with the yield stress and strain of PMMA at quasi-static loadings. On the basis of the craze density, an experimental model is established to predict the fatigue damage and life of PMMA. The predication shows good agreement with that from both experiments and traditional S-N curves in a broad range of fatigue loadings.

Deterministic Nanoassembly of Quasi-Three-Dimensional Plasmonic Nanoarrays with Arbitrary Substrate Materials and Structures

Kim, Bongjoong,Jeon, Jiyeon,Zhang, Yue,Wie, Dae Seung,Hwang, Jehwan,Lee, Sang Jun,Walker, Dennis E.,Abeysinghe, Don C.,Urbas, Augustine,Xu, Baoxing,Ku, Zahyun,Lee, Chi Hwan American Chemical Society 2019 Nano letters Vol.19 No.8

<P>Guided manipulation of light through periodic nanoarrays of three-dimensional (3D) metal-dielectric patterns provides remarkable opportunities to harness light in a way that cannot be obtained with conventional optics yet its practical implementation remains hindered by a lack of effective methodology. Here we report a novel 3D nanoassembly method that enables deterministic integration of quasi-3D plasmonic nanoarrays with a foreign substrate composed of arbitrary materials and structures. This method is versatile to arrange a variety of types of metal-dielectric composite nanoarrays in lateral and vertical configurations, providing a route to generate heterogeneous material compositions, complex device layouts, and tailored functionalities. Experimental, computational, and theoretical studies reveal the essential design features of this approach and, taken together with implementation of automated equipment, provide a technical guidance for large-scale manufacturability. Pilot assembly of specifically engineered quasi-3D plasmonic nanoarrays with a model hybrid pixel detector for deterministic enhancement of the detection performances demonstrates the utility of this method.</P> [FIG OMISSION]</BR>