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Traditional acoustic wave based sensing devices such as quartz crystal microbalance (QCM) rely on the thin films coated on the piezoelectric substrates as the sensing films for chemical and biological detection. This study demonstrates that significant sensitivity enhancement over traditional film based QCM (QCM-F) devices can be achieved by simply attaching a poly(methylmethacrylate) (PMMA) micropillar film onto a QCM substrate (QCM-P) by using a UV-curable glue. Humidity absorption measurements shows that the unique resonance occurred between the micropillars and the piezoelectric substrate improved the mass sensitivity of the QCM sensor by more than eight-fold. In addition, the newly developed QCM-P sensor and traditional QCM-F were utilized to detect bovine serum albumin (BSA) protein immobilization on PMMA surfaces. It was found that the glued QCM-P was capable of measuring BSA at a much lower concentration (200 nM) in comparison to QCM-F (1500 nM). The glue-based micropillar QCM device showed great potential for improving the sensitivity, simplifying the fabrication process, and reducing the cost of QCM sensors for various biosensing and chemical usages.

Magnetic assembly of micro/nano materials are of great interest due to their unique properties. These nano-scale materials can be ensemble with other matrixes to prepare for new functional micro/nano composites with enhanced specific properties such as, thermal conductivity. In this study, we demonstrated the distribution and magnetic alignment of nickel (Ni) nanoparticle/nanowires inside of a non-magnetic matrix, (e.g., water or a molten wax), experimentally and computationally. A two-dimensional Monte Carlo simulation model is employed to investigate the aggregate structures of Ni nanoparticle/nanowires subjected to a one-directional static magnetic field. It is anticipated that the applied magnetic strength will influence the attractive forces between nanoparticle/nanowires that will produce chain-like cluster structures parallel to magnetic direction where the aligned chains will be separated by a range of distances that are also function of magnetic field strength.

Enhancing the thermal conductivity of phase change materials (PCMs) is attracting attention for renewable energy applications such as solar, geothermal and wind energy. The use of energy storage can significantly improve the efficiency of renewable energy systems due to their intermittent nature. Latent heat thermal energy storage is a particularly attractive technique due to its high capacity can store energy at near constant temperature corresponding to the phase transition temperature of the PCMs. The present work aims to overcome this undesirable property of low thermal conductivity by manipulating metal fillers including nickel (Ni) nanoparticles/nanowires within the paraffin wax to improve its thermal property. In present work, a finite element method (FEM) was developed to obtain a fundamental understanding of the behavior of the Ni particles/wires under a uniform magnetic field by predefined magnetic pads. In the model, the Navier-Stokes equations were introduced as governing equations for the fluid field and the magnetic field was simulated by Maxwell’s equations. Then the motion of single Ni wire was modeled and the translation and rotational movements of the wire was studied in this paper.

We unexpectedly observed a large amplification of the dielectric properties associated with the photoswitching effect and the new unusual phenomenon of delayed photoinduced capacitor-like (i.e. electric polarization) behavior at the interface on samples of three-layered core-shell (γ-FeOx@AuNP)@[C60(DPAF-C9)](n)2 nanoparticles (NPs) in frequencies of 0.5-4.0 GHz. The detected relative dielectric constant amplification was initiated upon switching off the light followed by relaxation to give an excellent recyclability. These NPs having e(-)-polarizable fullerosomic structures located at the outer layer were fabricated from highly magnetic core-shell γ-FeOx@AuNPs. Surface-stabilized 2 in a core-shell structure was found to be capable of photoinducing the surface plasmonic resonance (SPR) effect by white LED light. The accumulated SPR energy was subsequently transferred to the partially bilayered C60(DPAF-C9) fullerosomic membrane layer in a near-field (∼1.5 nm) region without producing radiation heat. Since the monostatic SAR signal is dielectric property-dependent, we used these measurements to provide evidence of derived reflectivity changes on a surface coated with 2 at 0.5-4.0 GHz upon illumination of LED white light. We found that a high,99%, efficiency of response amplification in image amplitude can be achieved.

This study used laser multiphoton absorption (MPA) to crosslink and immobilize protein in 3D microfluidics. MPA can be used to crosslink proteins to form smaller crosslinked-protein structures than those formed through single-photon absorption. However, studies on MPA protein crosslinking in 3D microfluidics are lacking. In this study, the MPA was implemented using pulse laser to induce bovine serum albumin (BSA) crosslinking. We also applied (3-glycidyloxypropyl)trimethoxysilane to increase the adhesion of crosslinked BSA. Also, the width of crosslinked-BSA structure was measured, and then curve-fitting and optical equation were used to predict heights of the crosslinked-BSA structures formed under various laser powers. At last, BSA structures were effectively crosslinked in the three-layered glass or polydimethylsiloxane microchannels. In contrast to studies on single-photon absorption in 3D microfluidics or MPA protein crosslinking in 2D microfluidics, we obtained relatively small crosslinked-BSA structures through MPA and immobilize BSA in 3D microfluidics. In the future, this method can be applied in monolithic 3D microfluidics for protein crosslinking to avoid misalignment and leakage in layer-by-layer 3D microchannels and form more compact 3D microfluidics. These features are conducive to enhance the diversity and convenience of microfluidics in biomedical testing.

The spontaneously jumping motion of condensed droplets by coalescence on superhydrophobic surfaces has been an active area of research due to its great potential for enhancing the condensation efficiency. Despite a considerable amount of microscopic observations, the interfacial wetting characterization during jumping-droplet condensation is still notably lacking. This work focuses on applying a novel acoustic sensor - quartz crystal microbalance (QCM), to characterize the interfacial wetting on nanostructured surfaces during jumping-droplet condensation. Copper oxide nanostructures were generated on the surface of QCM with a chemical etching method. Based on the geometry of the nanostructures, we modified a theoretical model to reveal the relationship between the frequency shift of the QCM and the wetting states of the surfaces. It was found that the QCM is extremely sensitive to the penetrated liquid in the structured surfaces. Then, the QCM with nanostructured surface was tested on a customed flow condensation setup. The dynamic interfacial wetting characteristics were quantified by the normalized frequency shift of the QCM. Combined with microscopic observation of the corresponding drop motion, we demonstrated that partial wetting (PW) droplets with an about 25% penetrated area underwent spontaneously jumping by coalescence. However, the PW droplets no longer jumped when the penetrated area exceeds 50% due to the stronger adhesion between liquid and the surface. It shows that the characterization of the penetrated liquid in micro/nanostructures, which is very challenging for microscopic observation, can be easily carried out by this acoustic technique.

The high conductive nickel (Ni) nanoparticles mixed with paraffin wax at two different volume ratios were prepared to investigate thermal conductivity enhancement of Phase Change Material (PCM) under random and aligned particle distribution. For each particle concentration, two samples were prepared. After mixing of the particles into the melted paraffin through sonication, one sample was placed in a static magnetic field to align the nanoparticles while the PCM was allowed to solidify; whereas, the second sample was solidified immediately after sonication to obtain a randomly distributed nanoparticles in the solid PCM. The thermal conductivity of both nanoPCM samples along with a pure paraffin sample were measured experimentally. The conductivity of both nanoPCM samples were substantially higher than the pure wax and the sample with magnetically aligned nanoparticle exhibited significantly higher thermal conductivity in comparison to the randomly distributed nanoPCM sample. It was anticipated that the configuration of the metallic fillers that are parallelly aligned with the applied heat flux direction does enhance the heat dissipation through the particle chains. However, the magnitude of thermal enhancement and sample fabrication in larger scales require further research efforts.

Naonofluidics is increasingly attracting more attention for their wide range of potential applications such as water desalination and purification, biosensing, osmotic energy conversion, drug delivery and DNA analysis. It is critical to understand the behavior of the water fluid in nanochannels in order to better design nanofluidic-based systems for these applications. Most applications use Carbon Nanotubes (CNT), boron nitride nanotubes, graphene and graphene oxide. CNTs are good pore models for studying the transport of gases and liquids through nanoporous materials to design ultrafiltration devices and energy efficient water filters. It should be mentioned that fluids confined in nanoscale tubes exhibit significantly different behaviors compare to fluids in the macroscale and microscale. As experimental study in nanoscales is still a challenging task facing scientific society, different numerical technologies such as Molecular Dynamics (MD) method are becoming powerful tools for understanding the fluid behaviors at molecular level in nanofluidics. In the present study, MD simulation method, which is based on Newton’s second law, is employed to study the water flow through smooth CNT. The effect of CNT diameter on density and velocity profiles are investigated. Our results show that by increasing the diameter of CNT, the results are approaching to the continuum condition.

Fluid flow in nanochannels is attracting increasing attention for a wide range of potential applications such as drug delivery, desalination, and DNA analysis. As experimental study in nanoscales is still a challenging task facing scientific society, different numerical technologies such as Molecular Dynamics (MD) method are becoming powerful tools for understanding the fluid behaviors at molecular level in nanofluidics. In the present study, MD simulation method, which is based on Newton’s second law, is employed to study the liquid argon flows through smooth and rough nanochannels. The effects of various parameters including moving-wall speed, nanochannel height, pair coefficients of fluid/wall interaction, and surface roughness on velocity profiles and slip velocity were investigated. Preliminary results show that these parameters have a significant impact on the flows in nanoscales.

Due to the aging global civil infrastructure (e.g. bridges), there is a critical need for monitoring and assessing structural integrity of large scale structures. According to the ASCE, in 2008, the average bridge in the U.S.A. was 43 years old and 161,892 bridges were structurally deficient or obsolete. Currently, bridge health is assessed primarily using qualitative visual inspection, which is not always reliable because some damage is difficult to detect, quantify visually, or is subject to human interpretation. Traditional sensors such as strain gages, and displacement sensors, have been recently used to monitor bridges. These sensors only measure at discrete points or along a line, making it difficult to detect damage that is not in the immediate vicinity of the sensor or is difficult to interpret. To address these issues, this paper investigates the use of three-dimensional (3D) digital image correlation (DIC) as a sensing approach for improved bridge structural health monitoring. 3D DIC is a non-contact, full field, optical measuring technique that uses digital cameras to measure surface geometry, displacement, and strain. It is proposed that DIC can be used for monitoring by imaging a bridge periodically and computing strain and displacement from images recorded at different dates or operating conditions. In this paper, DIC is shown to locate non-visible cracks in concrete, quantify spalling, and measure bridge deformation. These techniques are first demonstrated in the laboratory. Field measurements are also made on three full-scale bridges. This paper discusses challenges and solutions to implementing DIC on large structures in the field. The results reveal that DIC is an effective approach to monitor the integrity of large scale civil infrastructure.

The nondestructive evaluation (NDE) inspection for building and bridge structures has attracted a lot of attentions for the fundamental research and the sensor system development. In this paper, development of a distant subsurface imaging radar is reported. Theoretical background of subsurface radar imaging is first provided. Experimental laboratory measurements using radar signals in the frequency range of 1-18 GHz were conducted. From the theoretical analysis and the initial experimental results on a laboratory reinforced concrete specimens, it is proved that the proposed subsurface imaging radar system can detect the location of steel reinforcement inside a concrete cylinder and identify the material property of panel specimens. Range-dependent attenuation of radar signals is experimentally studied using different materials. Findings are reported in the summary.

Nanoimprint Lithography (NIL) is becoming a powerful tool for nanolithography, nanofabrication and nanomanufacturing for nanotechnology applications. However, there is still a lack of systematic study of key processing parameters, which determine the imprinted pattern quality in terms of uniformity and replication fidelity.This research focuses on identifying the most important parameters in a nanoimprint process, in which microscale patterns were imprinted into polymethyl-methacrylate (PMMA) polymer with polydimethylsiloxane (PDMS) mold. The effects of several parameters such as pre-imprint temperature, pre-imprint pressure, imprint temperature, imprint pressure, imprint time, venting temperature and venting time, were varied in a certain range during the imprinting process. The imprinting results were analyzed with a three-level design of experiments (DOE) analysis. It was found that the pre-imprint pressure and imprint temperature are the key parameters. In addition, the DOE analysis is a powerful tool for NIL process optimization.As a practice, a vacuum assisted and selective coating (VASC) method based on a commerical nanoimprinting tool was developed to fabricate micro-hole arrays on a PbSe nanocrystal film to study its spectral response to IR radiation for applications such as IR detection and photovoltaic. The process optimization significantly improves imprinting quality.© 2012 ASME

A unique sensing device, which couples microscale pillars with quartz crystal microbalance (QCM) substrate to form a resonant system, is developed to achieve several orders of magnitude enhancement in sensitivity compared to conventional QCM sensors. In this research, Polymethyl Methacrylate (PMMA) micropillars are fabricated on a QCM substrate using nanoimprinting lithography. The effects of pillar geometry and physical properties, tuned by molecular weight (MW) of PMMA, on the resonant characteristics of QCM-micropillars device are systematically investigated. It is found that the resonant frequency shift increases with increasing MW. The coupled QCM-micropillars device displays nonlinear frequency response, which is opposite to the linear response of conventional QCM devices. In addition, a positive resonant frequency shift is captured near the resonant point of the coupled QCM-micropillars system. Humidity detection experiments show that compared to current nanoscale feature based QCM sensors, QCM-micropillars devices offer higher sensitivity and moderate response time. This research points to a novel way of improving sensitivity of acoustic wave sensors without the need for fabricating surface nanostructures.