Periodic Micro Research Articles

Comparative thermo-hydraulic analysis of periodic stepped open micro pin-fin heat sink

Comparative thermo-hydraulic analysis of periodic stepped open micro pin-fin heat sink

Investigation on acoustic performance of distributed periodic micro perforated panel

In this article, an equivalent “material,” called distributed periodic microperforated panel (DSPMPP), is proposed, which is formed by periodically arranging microperforated panels (MPPs). To determine a cubic DSPMPP, 4 parameters are needed, which are size of unit cell L, MPP thickness th, holediameterd and perforation ratio sigma. It is found that d, th, and sL are 3 independent parameters to determine its acoustic properties. Through a homogenization process, DSPMPP is treated as an equivalent material with equivalent density rhoc, speed of sound cc, characteristic impedance zc and bulk modulus kappac, whose frequency dependency is similar to porous material. Acoustic performance of DSPMPP is analyzed, and compared with porous material. It is found that, choosing parameters with the provided procedure, DSPMPP can generally reproduce acoustic performance of porous material.

Laser beam shaping using a photoinduced azopolymer droplet-based mask.

The dewetting of an azopolymer droplet, followed by the photostructuration of the evaporated droplet, is employed to create an amplitude mask. This straightforward process yields a large area featuring periodic micro- and nanostructures. The resulting pattern is utilized to generate a nondiffracting beam. Starting with a Gaussian beam illuminating the amplitude mask, the critical aspect is the production of a bright, ring-shaped beam with a high radius-to-width ratio and symmetric central laser spots, each with the same intensity. This alternative approach to shaping a laser beam is demonstrated as a rapid and cost-effective fabrication technique.

Nanosecond Laser Fabrication of Novel Micro-/Nanostructured Metal Surfaces: A Dual-Functional Supersurface Combining Antireflectivity and Superhydrophobic Properties.

The research and applications in the field of micro/nano surface manufacturing are progressively shifting their focus toward multifunctional surfaces. In practical applications, objects often need to operate under demanding environmental conditions, and single-function surfaces have inherent limitations in terms of performance, adaptability, and longevity. In this paper, a micro-/nanolayered structural strategy with dual functions of ultrahigh antireflective properties and superhydrophobicity was created on the surface of titanium alloy by using nanosecond pulsed laser processing, and two structural modes of periodic honeycomb and lattice with controllable shapes were designed. In addition, the morphology and formation mechanism of multilevel micro-/nanostructures were investigated in depth, combining laser texturization and silanization of substrate microstructures. The effects of the micro-/nanostructured morphology on the reflection and wettability properties were evaluated with different pulse widths and lateral overlap index. This study also demonstrated that water droplets exhibit excellent bouncing and rolling behavior on superhydrophobic surfaces, further verifying the excellent hydrophobic properties of the prepared samples. Furthermore, in addressing the challenges of susceptibility to dust contamination and performance degradation in extreme environments associated with antireflective surfaces, a series of durability and mechanical stability tests were conducted on controllability periodic micro-/nanostructured surfaces. Successfully meeting this challenge will open up great potential and opportunities for significant improvements in equipment performance and stable operation under extreme operating conditions.

Replicative Production of Multifunctional Microfluidic Polymer Films for Biomedical Disposables

Increasing demands on the reproducibility and accuracy of lab-on-a-chip systems in the life science sector require new tools for the molding of polymer films with spatially selectively functionalized surfaces. By applying local micro- and nanostructuring to the molding tools, the aim is to achieve multifunctionality of the polymer films, by setting certain wetting properties. This means that fluid-affecting properties (hydrophobic, hydrophilic) should be possible. To functionalize polymer films, the replication tools were specifically microstructured using laser-based surface functionalization. The periodic micro- and nanostructures were produced with the help of nanosecond pulsed and picosecond pulsed laser systems using Direct Laser Interference Patterning. For this purpose, complex functional microstructures in the range of 0.1 µm to 100 µm were developed based on a bionic approach. The functional properties were transferred in a one-step replicative process using UV-imprinting and were subsequently verified by determining the wetting behavior of the molded microfluidic films and the corresponding laser microstructured replication tools. This publication presents the successfully developed processes and the promising results of this series of experiments.

Effect of annealing treatment on optical properties of structural color films

Structural color materials based on periodic micro and nano structures present unique color rendering mechanism and optical properties, and have a wide range of applications in display, packaging, sensing and other fields. However, it is still facing the problems of constructing large area, good consistency and low cost periodic structures. In this paper, the structural color film was prepared by annealing treatment on a periodic template. The effects of coating time, annealing time and annealing process on the optical properties of the sample such as hue and saturation were analyzed. It was confirmed that the sample with 300 nm polystyrene microsphere template presented orange yellow with incident angle of 30° before annealing, then turned to be light pink under 800 °C for 120 min annealing process and orange red under 800 °C for 180 min in air. Additionally, the sample with 420 nm polystyrene microsphere template showed cyan before annealing, and yellow-green under 800 °C for 120 min annealing treatment and orange-yellow under 800 °C for 180 min. The periodicity of the annealed gold microspheres was still limited by the template period with different diameters. Morever, when the coating and annealing time were the same, the higher the annealing temperature was, the higher the saturation get. Under the same coating time and annealing temperature, the saturation was higher with short annealing time, and the hue blue-shifted as the incident angle increased from 15° to 45°. While fixing the annealing time and temperature, the saturation increased gradually as the coating time increasing from 10S to 40S, and the color of the sample red-shifted.

Fabrication of periodic hierarchical structures with anti-icing performance by direct laser interference lithography and hydrothermal treatment

Ice accumulation could result in a massive economic burden as well as major life safety issues. Because of their immense potential to ease icing problems, superhydrophobic structures have captured the curiosity of many researchers. Herein, the periodic hierarchical porous structures that have outstanding anti-icing performance were created using two-beam direct laser interference lithography and hydrothermal treatment. The periodic hierarchical porous structures were composed of periodic micro ridge arrays covered with interlaced grown standing nanoflakes. The high-water repellency of the periodic hierarchical porous structures was characterized by the high contact angle and the low rolling angle of 163.7° ± 1.5° and 3.4° ± 0.8°, respectively. The high-water repellency of the periodic hierarchical porous structures exhibits a long-term stability in air and durability in contact with water. The experimental results indicated that the anti-icing performance of the periodic hierarchical porous structures was achieved through the long-term inhibition of ice nucleation and low ice adhesion strength. The ice nucleation inhibition time could reach up to 378 s, which was more than 11.8 times longer than the untreated surface. The ice adhesion strength could be reduced to 48.3 kPa, which was more than 6.3 times lower than the untreated surface. The proposed manufacturing strategy and designed structures could be useful for designing anti-icing structures.

Real‐Time 3D Visualization of the Formation of Micrograting Structures Upon Direct Laser Interference Patterning of Ge

AbstractDirect Laser Interference Patterning (DLIP) is a versatile technique that enables the fabrication of periodic micro‐ to nanometric scale structures over large areas in a variety of materials. The periodically modulated excitation pattern can be exploited to trigger a range of complex processes, including heating, melting, ablation, and matter reorganization.In this work, a novel strategy is developed to combine deep‐ultraviolet (UV) DLIP (λ = 193 nm, τ = 23 ns) and real‐time optical reflectivity and diffraction techniques to unravel the formation dynamics of grating structures with periods down to Λ = 740 nm. Applied to crystalline Ge wafers, single‐pulse topography modulation profiles with amplitudes up to 85 nm can be imprinted. Moreover, the dynamics of the melting and solidification processes, as well as the surface topography deformation, can be followed in real‐time. Combined with a model, changes in topography over time with ns resolution can be obtained. The results unambiguously reveal that the formation process of the 3D structures can only be understood when taking both Marangoni convection and thermocapillary waves into account. The technique presented here has the potential to unravel the formation dynamics of a wide range of periodic structures in other materials.

초정밀 레이저를 이용한 연꽃잎 표면 자연 모사 연구

In a pilot natural super-hydrophobic surfaces study, a super-hydrophobic surface was made by coating, etching, laser ablation, chemical vapor deposition and lithography. In this study, cone-shaped periodic micro and nano-structures were constructed on a silica surface with femtosecond and picosecond laser, and the period of micro-structures between cone shape patterns was increased with 10 μm intervals. The contact angle and image of the super-hydrophobic surface were analysed and the cone (Aspect-ratio 1.27) shape model with micro-protrusion structure similar to the surface of the lotus leaf was made to measure the contact angle. To analyse the differences in the contact angles between the cone shapes and heights of the micro-protrusion, different samples with cone (Aspect-ratio 1.27), sphere (Aspect-ratio 1.00) shapes were made through laser micro-machining technology. To mimick the natural lotus leaves, the optimum condition was a cone shape. Samples of PDMS with different shapes and mixed micro/nano-structures were fabricated with a PDMS mold insert. The largest contact angle was measured at 170.42° which is similar to the contact angle of the lotus leaf. This mold insert could be used repeatedly. The molding process is advantageous for large areas and mass production.

A spiral microfluidic chip endows high efficiency single cell alignment at extremely low flow for ICP-MS analysis

A spiral microfluidic chip integrating periodic micro pillars was designed to achieve focusing and sorting of cells at ultra-low flow rate. It enables high efficiency single cell analysis by combining with time resolved inductively coupled plasma mass spectrometry (TRA-ICP-MS). The spiral chip facilitates focusing of particles or cells through the action of secondary flow and inertial induced lift force. The simulation illustrated that the periodic micro-pillars enhanced the influence of secondary flow and resulted in a superb focusing of cells. The focusing capability of the chip was demonstrated by using fluorescent particles of 9.77 μm in diameter and MCF-7 cells stained with DiI, wherein excellent focusing/alignment was achieved at flow rates of as low as 5 μL min−1 for fluorescent particles and 10 μL min−1 for MCF-7 cells, respectively. Furthermore, the spiral microfluidic chip was used for focusing/alignment of MCF-7 and LoVo cells after incubating with anticancer metal prodrug (cobalt curcumin complex [Co(tpa)(cur)](ClO4)2). The uptake of this prodrug in individual MCF-7 and LoVo cell was investigated with detection by TRA-ICP-MS in single cell resolution. The two types of cancer cells exhibit different uptake behaviors of the complex, and differences among individual cells of each type were also identified. A single cell detection efficiency of 67.5 ± 4.6% was obtained at the flow rate of 50 μL min−1.

Programmable droplet transport on multi-bioinspired slippery surface with tridirectionally anisotropic wettability

• Multi-bioinspired tridirectionally anisotropic slippery surfaces were prepared. • The pinning effect of step edge was critical to the tridirectional anisotropy. • Vertical vibration assisted programmable droplet transports were realized. • In-plane manipulation of droplet motion in more than two directions was realized. • Droplet-based chemical micro-reactors were designed. Directional droplet transport on functional surfaces with anisotropic wettability has shown great potential applications in various fields such as water harvesting, chemical micro-reaction, and biomedical analysis. However, the in-plane manipulation of the anisotropic droplet motion in more than two directions is still a challenge. Herein, through the fusion of inspirations from rice leaves, butterfly wings and Pitcher plants, we report a tridirectionally anisotropic slippery surface (TASS) with periodic step-like micro grooves for programmable droplet transport. TASS possesses a tridirectional droplet sliding behavior, i.e. , the ultra-slipperiness along the grooves with a sliding angle of ∼2°, and the bidirectionally anisotropic sliding perpendicular to the grooves with sliding angle difference up to ∼50°, which is caused by the pinning effect of the step edge. Under the assistance of periodic vertical vibration, groove-features and droplet-volume dependent unidirectional droplets transports are realized on horizontally placed TASS, based on which two micro-reactors are designed to control the sequence of droplets merging and subsequent chemical reactions. Additionally, by utilizing the slipperiness ( i.e. , ultra-low sliding angle for liquid droplet) along the grooves simultaneously, programmable droplet transport under vertical vibration is further demonstrated on a tilted TASS. This work will provide a new avenue for the understanding of anisotropic wettability on asymmetric slippery surface, and thus offer a great opportunity to develop advanced interface for multidirectional droplet transport, chemical micro-reactor, etc .

Nonlinear dynamic model for linear guideway with crowning subjected to external load in five directions

The motion accuracy of linear guideway is adversely affected by ball passage vibration (BPV) when rolling balls within carriage move in a loop. Reduced vibration amplitude can be realized by a carriage with crowning design by now. However, few dynamic models are availability for the BPV analysis when linear guideway is subjected to actual external load in five directions. In this paper, a nonlinear dynamic model is proposed to investigate the periodic micro fluctuation of linear guideway with crowning subjected to load in five directions. The idea of coordinate transformation is adopted for the easier derivations of time-dependent and piecewise restoring force function. The different contact states of each ball are described in detail due to load distribution. The numerical simulation is employed to deal with equation of motion and discuss the effects of ball grouping, external load, preload and carriage speed. Experiment is also conducted for the verification of proposed model. The analytical model developed here is promising to clarify the mechanism of BPV from a dynamic perspective and serve the walking parallelism accuracy monitoring of linear guideway.

Gold Nanoparticle-Functionalized Diatom Biosilica as Label-Free Biosensor for Biomolecule Detection.

Diatom biosilica (DBs) is the cell wall of natural diatom called frustule, which is made of porous hydrogenated amorphous silica possessing periodic micro- to nanoscale features. In this study, a simple, sensitive, and label-free photoluminescence (PL) immune-detection platform based on functionalized diatom frustules was developed. Gold nanoparticles (AuNPs) deposited on poly-dopamine-coated diatom frustules via in situ deposition which considerably decreased the intrinsic blue PL intensity of diatom biosilica. Then, goat anti-rabbit immunoglobulin G (IgG) was added to functionalize diatom biosilica-poly-dopamine-AuNPs (DBs-PDA-AuNPs). PL studies revealed that the specific binding with antigen rabbit IgG increased the peak intensity of PL in comparison with the non-complimentary antigen (human IgG). The enhancement in PL intensity of DBs-PDA had a linear correlation with antigen (rabbit IgG) concentration, whose limit of detection (LOD) reached 8 × 10-6 mg/ml. Furthermore, PL detection based on DBs-PDA-AuNPs showed a high detection sensitivity with the LOD as low as 8 × 10-9 mg/ml and spread over almost eight orders of magnitude, making it suitable for the sensitive quantitative analysis of immune complex compared with traditional fluorescence immunoassay. Hence, the study proves that the AuNP-functionalized diatom frustules can serve as an effective biosensor platform for label-free PL-based immunoassay.

A non-classical couple stress based Mindlin plate finite element framework for tuning band gaps of periodic composite micro plates

Composite micro plates with periodic microstructure at very small length scale have been a focus of intensive research. When length scale of the microstructure descends below millimetre level, size effects may emerge. To account for microstructure effect on the elastic wave band gap of microscopic composite plates, we propose a numerical framework based on the modified couple stress theory of elasto-dynamics associated with a non-classical 3-node triangular (T3) Mindlin plate finite element. Since couple stress elasto-dynamics incorporates dependence on the material scale length, the proposed approach is sensitive to size effects with microscopic problems while remaining compatible with macroscopic problems. In terms of the finite element implementation, we implemented a T3 plate finite element with 9 nodal degrees of freedom under the Mindlin kinematics assumptions. The approach presents enhanced flexibility to discretize complex microstructures owing to the triangular element topology, and offers sensitivity to account for size effects of microscopic problems. Therefore, it represents a good option for the design of band gap periodic composite micro plates. Validation of the framework is performed through comparison with both analytical and numerical models.

Periodic Relief Fabrication and Reversible Phase Transitions in Amorphous Ge2Sb2Te5 Thin Films upon Multi-Pulse Femtosecond Irradiation

Ge2Sb2Te5 based devices attract the attention of researchers due to wide opportunities in designing phase change memory. Herein, we studied a possibility to fabricate periodic micro- and nanorelief at surfaces of Ge2Sb2Te5 thin films on silicon oxide/silicon substrates under multi-pulse femtosecond laser irradiation with the wavelength of 1250 nm. One-dimensional lattices with periods of 1250 ± 90 and 130 ± 30 nm were obtained depending on the number of acted laser pulses. Emergence of these structures can be explained by plasmon-polariton generation and laser-induced hydrodynamic instabilities, respectively. Additionally, formation of the lattices whose spatial period is close to the impacted laser wavelength can be modelled by considering the free carrier contribution under intensive photoexcitation. Raman spectroscopy revealed both crystallization and re-amorphization of the irradiated films. The obtained results show a possibility to fabricate rewritable all-dielectric data-storage devices based on Ge2Sb2Te5 with the periodic relief.

Effects of sub-picosecond direct laser interference patterning on the optoelectronic properties of fluorine-doped tin oxide thin films

An increase in the angular spread of incident light was obtained in FTO thin films after the generation of periodic micro- and nano-structures with infrared sub-picosecond Direct Laser Interference Patterning.

Hybrid nanofluids: Significance of gravity modulation, heat source/ sink, and magnetohydrodynamic on dynamics of micropolar fluid over an inclined surface via finite element simulation

An exploration is sought for improved thermal transportation across an extending inclined sheet in the upper space to be influenced by periodic micro gravity g*(τ)=g0(1+acos(πωt)) and magnetic field B0. The mixed convection induced by g-jitter effects is studied for the flow of two colloidal liquids; the alone micropolar nano fluid (copper/ water) and micropolar hybrid nano fluid (alumenia-copper/ water). The leading formulation in its transformed form as ordinary differential format is manipulated via finite-element discretization. A computational code is coded in Matlab script to assess the impacts of involved parameters on dynamic of fluid. The differentiated enhanced performance of hybrid naofluids is observed in this upper space g-jitter influenced flow. The fluid velocity is slowed against growing strength of Hartmann number, but it becomes faster against micropolar material quantity. Both velocity and temperature distribution for hybrid nanofluid flow attains higher values in comparison with those of alone mono-nanofluid. The fluctuation of skin-friction factor and heat flux gradient improves with larger inputs of amplitude of modulation.

Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface.

A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis during sub-millisecond wrinkle formation and decay, after abruptly increasing or reducing the voltage, respectively. The decay time constant closely followed the film thickness dependence expected for surface tension driven viscous levelling. Modelling of the system using numerical solution of the Stokes flow equations with electrostatic forcing predicted that wrinkle formation was faster than decay, in accord with observations.

Suppression of serration of Al-Mg sheet by periodic indentation

Al-Mg alloy sheets often exhibit surface defects, e.g., stretcher strain, after sheet metal forming. The surface defects are formed by nonuniform deformation due to the dynamic strain aging where serrations appear on stress-strain curves in tensile test. In order to suppress the nonuniform deformation, the authors propose periodic micro indentation on sheet surface in this study. Four Al-Mg alloy sheets were subjected to the tensile test after the indentation. Strain gauges on specimen surface were used to investigate the evolution of local strain. It is concluded that the periodic indentation can suppress nonuniform deformation.

A time-dependent dynamic model for ball passage vibration analysis of recirculation ball screw mechanism

Ball passage vibration arising during recirculation of rolling elements is a limitation of high-precision performance associated with ball screw. A relatively deep understanding of this phenomenon when rolling balls leave load area and enter circulation channel has been achieved by now. However, few mechanical models are established for calculation of rolling ball contact deformation and force inside nut while moving by taking into account transient phase at import and export of circulation channel. In this work, we present a general time-dependent dynamic model for description of ball motion and axial periodic micro fluctuation within ball screw subjected to external load. The numerical simulation is employed to deal with equation of motion including segmented restoring force function. Effects of applied load, preload and screw rotational speed on dynamic response are discussed theoretically. Reduced vibration amplitude may be realized by small ball diameter and phase difference between ball groupings. Proposed model is experimentally illustrated.