Centrifugal Mixing Research Articles

Numerical investigation of centrifugal passive mixing in Omega shaped microchannel and comparison with fixed platform

The extraction of DNA from isolated cells is crucial for diagnosing and treating various diseases, including cancer, which has become a leading cause of death in recent years. Circulating tumor cells (CTCs) in the blood can be separated from other blood cells, allowing for DNA extraction and analysis for further research. Microfluidic methods are more cost-effective than conventional DNA extraction techniques and have significant potential for high-throughput mixing in lab-on-a-chip (LOC) and lab-on-a-disk (LOD) devices without damaging DNA. Chemical methods for cell lysis, where the mixing of reagents is essential, are particularly efficient on these platforms due to the generation of secondary flows. This is especially true in microchannels with a serpentine design, which enhances mixing quality—a critical parameter for cell lysis efficiency. This study presents and compares the mixing capabilities of the two microchannel platforms (LOC and LOD). Additionally, we introduce a new Omega-shaped serpentine microchannel that combines features of both straight and curved serpentine channels. The mixing quality across all geometries and both platforms has been investigated. Our findings indicate that the centrifugal platform is the most effective for mixing at low inlet velocities. Furthermore, we examine the number of stages in the Omega channel and conclude that 7 Ω stages are sufficient for achieving high mixing quality (∼100 %).

Efficient Synthesis of Metastable Cyclodextrin-Based Polyrotaxanes with Tunable Threading Ratios.

Cyclodextrin-based polyrotaxanes (CD-PRs) are gaining attention for their dynamic sliding rings along the polymer axis, enabling various applications in molecular shuttles, drug delivery, and durable polymers with slidable cross-links. However, the conventional synthesis of CD-PRs with tunable threading ratios is typically laborious, time-consuming, and complicated, which limits their scalability and cost-effectiveness. Herein, we highlight the great potential of planetary centrifugal mixing, a process that significantly accelerates and simplifies the initial synthesis of polypseudorotaxanes (PPRs), followed by a thiol-ene click reaction as an efficient end-capping reaction for the synthesis of PRs. Notably, PRs synthesized with glutathione (GSH) as the end-capping reagent are in a metastable state, where GSH act as a molecular bumper that significantly prevent de-threading of α-CD rings at room temperature. Moreover, the rate of ring de-threading can be precisely controlled by heating, enabling the preparation of metastable PRs with tunable threading ratios over a wide range. The developed strategy is of great significance to the efficient synthesis of CD-PRs, thus marking a significant step towards their practical application in advanced functional materials and devices.

Efficient Synthesis of Metastable Cyclodextrin‐Based Polyrotaxanes with Tunable Threading Ratios

AbstractCyclodextrin‐based polyrotaxanes (CD‐PRs) are gaining attention for their dynamic sliding rings along the polymer axis, enabling various applications in molecular shuttles, drug delivery, and durable polymers with slidable cross‐links. However, the conventional synthesis of CD‐PRs with tunable threading ratios is typically laborious, time‐consuming, and complicated, which limits their scalability and cost‐effectiveness. Herein, we highlight the great potential of planetary centrifugal mixing, a process that significantly accelerates and simplifies the initial synthesis of polypseudorotaxanes (PPRs), followed by a thiol‐ene click reaction as an efficient end‐capping reaction for the synthesis of PRs. Notably, PRs synthesized with glutathione (GSH) as the end‐capping reagent are in a metastable state, where GSH act as a molecular bumper that significantly prevent de‐threading of α‐CD rings at room temperature. Moreover, the rate of ring de‐threading can be precisely controlled by heating, enabling the preparation of metastable PRs with tunable threading ratios over a wide range. The developed strategy is of great significance to the efficient synthesis of CD‐PRs, thus marking a significant step towards their practical application in advanced functional materials and devices.

Theoretical studies of the movement of mineral fertilizer granules in the mixing chamber of a centrifugal mixing plant

Relevance. The use of mineral fertilizers helps to improve soil fertility, stimulates the growth and development of plants, which is achieved due to the availability of necessary nutrients. In turn, it is important to observe the correct application of fertilizers, which allows you to control the level of nutrients in the soil, preventing both their excess and deficiency. Currently, the main application of fertilizers falls on complex mineral fertilizers, while one of their disadvantages is that they may contain nutrients that will not be in demand by the plant, which can lead to a violation of the ecological balance. One of the solutions to this problem is the use of flour mixtures. When using mixtures, the determining factor is the uniformity of mixing, which is largely determined by the equipment used. In this regard, the urgent task is to develop a mixing equipment that meets the necessary indicators.Methods. During the research, the processes occurring in the mixing chamber of the developed mixing plant were studied using methods of mathematical analysis, graphical and mathematical modeling.Results. As a result of the research, it was found that during the operation of the mixing plant, the mixing quality is determined by the rotation frequency of the conical rotor. At the same time, the granules of mineral fertilizers after leaving the conical rotor, pouring into the collecting funnel, continue their movement along a spiral trajectory. During the movement of the granules along the surface of the rotating cone, as well as when moving through the funnel, their trajectories will intersect with each other, which will lead to their active mixing.

Modelling the centrifugal mixing process of minced meat to optimise the production of chopped meat semi-finished products

One of the most important problems in ensuring the quality of mincemeat preparation in the production of sausages is the effective structuring of components and mixing of their ingredients. To solve this problem, researchers added a multifunctional admixture based on whey protein in the process of centrifugal mixing of the components, which determined the composition of the factor space of the investigated process. Based on the results of the research, the effective content of whey protein, sodium alginate, and soy fiber in the developed recipe was proven, which showed high characteristics in terms of fat-retaining and moisture-retaining ability, digestibility, pH level – activity, and other parameters. The developed formulation made it possible to improve the general indicator of the balance of amino acids in the product and increase the functional-technological and quality parameters of the developed products. The physical and mechanical characteristics of the obtained meat product were evaluated based on the results of physical and mathematical modelling. Modelling was carried out using Federman-on-Buckingham's second similarity theory and the "dimension theory" method, which allows the processing of the obtained experimental data in the form of a criterion equation, which was compiled using Froude, Euler, and Sherwood criteria. The purpose of this study was to obtain dependencies between such process factors as product density, the coefficient of dynamic viscosity of the technological medium, the ultimate shear stress, the change in the concentration of the main impurities of lactic acid in the raw material, the value of the diffusion coefficient and the coefficient of mass transfer in the loading mass, the weight of one load of products, the angular frequency of rotation of the screws of the minced meat mixer, the radius of the rotating working bodies, the characteristic size of the products after grinding. Using the complex criterion equation and the developed program, we find a recommended set of operating mode parameters for preparing minced meat under the conditions of centrifugal influence on the mixing process and the action of the specified factors.

Planetary centrifugal mixing for robust, ultrahighly sensitive sensors with positive piezoresistive effect across an exceptionally broad pressure range based on polyurethane/carbon black composite foam

The pursuit of high sensitivity across a broad measurement range has been a significant and intriguing subject in developing piezoresistive sensors. However, it is important to acknowledge that high sensitivity often comes at the cost of sacrificing the measurement (pressure or strain) range due to the negative piezoresistive coefficient. In this study, a robust piezoresistive sensor based on aqueous polyurethane (APU)/conductive carbon black (CCB) composite foam was fabricated through a planetary centrifugal mixing (PCM) strategy. Under the dual action of high centrifugal and tangential forces in PCM, nano-scaled dispersion of CCB particles and resulting conductive network were embedded within the foam skeleton, combined with a unique thick-wall pore structure through the high viscosity APU/CCB blending during the foaming process. This robust sensor exhibited a distinctive positive piezoresistive behavior. It demonstrated impressively high sensitivity (gauge factor up to 211 at strain over 35 %) across an exceptionally broad pressure range (0.5 kPa-2.84 MPa), far exceeding previously reported piezoresistive sensors. Good durability and reproducibility were also testified over 2000 compression cycles, even at high pressures of 500 kPa,1000 kPa and 1500 kPa after an initial stabilization process. The sensor can monitor diverse stimuli and give stable real-time feedback, ranging from low-pressure fingertip bending to extremely high-pressure vehicle rolling. Without the need for complex preparation processes or expensive materials, the developed strategy opens up an attractive pathway for designing advanced piezoresistive sensors with high sensitivity across a broad measurement range.

Polypyrrole coated carbon fiber/ magnetite/ graphene oxide reinforced hybrid epoxy composites for high strength and electromagnetic interference shielding

Carbon fiber reinforced polymer composites (CFRPs) are in huge demand in the aviation industry for reducing fuel consumption despite their unfavorable electromagnetic interference (EMI) shielding properties. The present work aims to improve the mechanical properties and EMI shielding effectiveness (SE) of polypyrrole (PPy) coated carbon fibers/graphene oxide (GO)/magnetite nanoparticles (MP)/ epoxy hybrid composites. For this purpose, PPy was coated on desized woven carbon fibers (CFs) woven mats via electrophoretic deposition. Graphite oxide and magnetite nanoparticles were synthesized through improved Hummers’ method and modified Massart’s method, respectively. GO was synthesized via ultra-sonication of graphite oxide, with its average thickness determined to be ∼ 1.4 nm as verified by atomic force microscopy (AFM). Solution mixing method and vacuum centrifugal mixing were utilized to disperse GO in epoxy resin. Porosity-free composites were fabricated using the vacuum bag technique. PPy coating, graphite oxide, GO and MP were characterized by scanning electron microscopy (SEM), AFM and Fourier transform infrared spectroscopy (FTIR). The SEM images showed the globular morphology of the deposited PPy on CFs. Hybrid composites containing CFPPy-0.2 wt% GO-0.2 wt% MP showed ∼52%, ∼24%, ∼60% and ∼25% increase in tensile strength, Young’s modulus, toughness, and elongation, respectively, compared to neat CF-epoxy composite. All hybrid composites prepared in this work have SE > 30 dB and could be promising lightweight and high-strength materials for EMI shielding applications in the X-band frequency range.

Experimental investigations of epoxy/boron nitride nanotubes composites prepared by centrifugal mixing and oven curing

Boron nitride nanotubes are reinforced into epoxy to achieve enhanced mechanical properties. BNNTs have high Young’s modulus and tensile strength, thus reinforcing BNNTs uniformly in the epoxy matrix using a centrifugal mixing followed by curing in an oven has enhanced the mechanical properties remarkably. It has been observed that with 1 %, 2 % and 3 % volume fraction of BNNTs reinforcement enhances the mechanical properties like Young’s modulus, tensile stress and fracture toughness by more than 11 % compared to virgin epoxy. With addition of BNNTs to epoxy, Young’s modulus, tensile stress and fracture toughness has increased from 2400 MPa to 2675 MPa, 60 MPa to 67 MPa, and 0.9 MPa-m1/2 to 1.6 MPa-m1/2 respectively. It has also been observed that with addition to BNNTs more than or equal to 4 %, the problem of agglomeration arises. The manufacturing process parameters are optimized for only addition up to 3 % of BNNTs in epoxy.

Physical, Thermal Transport, and Compressive Properties of Epoxy Composite Filled with Graphitic- and Ceramic-Based Thermally Conductive Nanofillers.

Epoxy polymer composites embedded with thermally conductive nanofillers play an important role in the thermal management of polymer microelectronic packages, since they can provide thermal conduction properties with electrically insulating properties. An epoxy composite system filled with graphitic-based fillers; multi-walled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs) and ceramic-based filler; silicon carbide nanoparticles (SiCs) was investigated as a form of thermal-effective reinforcement for epoxy matrices. The epoxy composites were fabricated using a simple fabrication method, which included ultrasonication and planetary centrifugal mixing. The effect of graphite-based and ceramic-based fillers on the thermal conductivity was measured by the transient plane source method, while the glass transition temperature of the fully cured samples was studied by differential scanning calorimetry. Thermal gravimetric analysis was adopted to study the thermal stability of the samples, and the compressive properties of different filler loadings (1–5 vol.%) were also discussed. The glass temperatures and thermal stabilities of the epoxy system were increased when incorporated with the graphite- and ceramic-based fillers. These results can be correlated with the thermal conductivity of the samples, which was found to increase with the increase in the filler loadings, except for the epoxy/SiCs composites. The thermal conductivity of the composites increased to 0.4 W/mK with 5 vol.% of MWCNTs, which is a 100% improvement over pure epoxy. The GNPs, SiCs, and MWCNTs showed uniform dispersion in the epoxy matrix and well-established thermally conductive pathways.

Injection Molding of Soft Robots

AbstractTo date, injection molding has not been a practical manufacturing method for soft robots due to machine costs, large volumes of liquid silicones required, and the inability to change materials quickly between shots. Injection molds are typically machined from metals to allow for high pressure and clamping forces, which further limits the ability to rapidly prototype soft robots when molds could cost thousands of dollars. To circumvent these issues, a low‐cost injection molding system and process are pioneered. In this article, the apparatus, design process, economics, and workflow are described using standard stereolithography and polyjet 3D printers to rapidly iterate on soft robot designs. The mold design process is further detailed to allow for proper material flow, clamping, alignment, and rapid curing times. Static mixing nozzle efficacy is characterized with common silicone materials compared to manual mixing and centrifugal planetary mixing. Lastly, a number of applications that could only be achieved through injection molding due to geometry, embedded components, or cure times are presented.

Improving wear resistance of epoxy/SiC composite using a modified apparatus

A centrifugal mixing method was developed to disperse ceramic particles inside a thermosetting polymer. Horizontal centrifugal equipment was used to fabricate cylindrical rods from epoxy reinforced with silicon carbide particles. Silicon carbide particles (SiC) are used for the outer coating of epoxy to increase wear resistance. In the centrifugal mixing process, there are three important variables: rotational speed, ceramic percentage and, ceramic size which affect ceramic particle distribution. This paper aims to find the relationship between these variables and the distribution of ceramic particles then determine the optimum conditions to get maximum wear resistance and hardness. From the experiment and analysis, it can be concluded that when mixing speed was greater than 600 rpm, the possibility of air bubbles formation was increased especially for ultrafine particles. Otherwise, the maximum wear resistance and hardness values were found in ultrafine size SiC samples reinforced with 30 wt% which were mixed at a low speed of 300 rpm.

Characteristics and Mechanical Properties of Graphene Nanoplatelets-Reinforced Epoxy Nanocomposites: Comparison of Different Dispersal Mechanisms

The preparation of polymer-based nanocomposites requires considerable time (i.e., the dispersal of nanomaterials into a polymer matrix), resulting in difficulties associated with their commercial use. In this study, two simple and efficient dispersion methods, namely planetary centrifugal mixing and three-roll milling, were used to enable the graphene nanoplatelets to disperse uniformly throughout an epoxy solution (i.e., 0, 0.1, 0.25, 0.5, and 1.0 wt.%) and allow the subsequent preparation of graphene nanoplatelets/epoxy nanocomposites. Measurements of mechanical properties of these nanocomposites, including ultimate tensile strength, flexural strength, and flexural modulus, were used to evaluate these dispersal methods. Dispersing graphene nanoplatelets into the epoxy resin by planetary centrifugal mixing not only required a shorter process time but also resulted in a more uniform dispersion of graphene nanoplatelets than that by three-roll milling. In addition, compared with traditional dispersal methods, planetary centrifugal mixing was a more efficient dispersal method for the preparation of epoxy-based nanocomposites.

Multilayer thin-film flake dispersion gel for surface-enhanced Raman spectroscopy

Ag nanorod arrays/dielectrics/mirror-structured multilayer thin-film are well known, highly sensitive surface-enhanced Raman scattering (SERS) substrates that enhance the Raman scattering cross-section by the interference of light. However, extracting biomarkers directly from human skin using these solid substrates is difficult. To overcome this problem, we propose a multilayer thin-film flake dispersion gel by centrifugal mixing of the multilayer thin-film and hydroxyethyl cellulose (HEC) gel. The multilayer thin-film was prepared by serial bideposition using the dynamic oblique angle deposition technique. The mixing process was optimized to obtain flakes of ~10 {\mu}m so that the optical properties of the multilayer film can be preserved, and there is no risk of adverse effects on humans. The SERS features of the flakes dispersion gel were tested using 4, 4'-bipyridine (BPY). The BPY molecules diffused through the highly porous gel within a few seconds, generating significant SERS signals. The multilayer film flakes dispersion gel showed a SERS signal about 20 times better than the gel-dispersed Ag nanorod arrays without a multilayer film structure. These SERS active flakes dispersion gel can be used directly on the skin surface to collect body fluids from sweat, for biomarker sensing.

ВИБРО-ЦЕНТРОБЕЖНЫЕ АГРЕГАТЫ ДЛЯ КОМПЛЕКСНОЙ ПЕРЕРАБОТКИ ТЕХНОГЕННЫХ МАТЕРИАЛОВ

The article deals with the problem of complex processing of technogenic anisotropic materials. The direction of production activity, which requires the creation of special equipment for selective exposure at each stage of the technological process, is determined. A description of the devices of aggregates that have a basic crank-slide scheme of the mechanism for performing various technological functions is presented: grinding, classification, thin and ultrafine grinding, homogenization, agglomeration, etc. A brief description of patent-protected designs of vibro-centrifugal units is given: centrifugal grinding and mixing unit, centrifugal unit with parallel grinding blocks, vibration-centrifugal granulator, vibro-centrifugal unit of combined action. The design features of the vibro-centrifugal unit of combined action intended for complex processing of technogenic fibrous materials in two ways are considered. One of the developed technological options for the implementation of the vibration-centrifugal combined effect on the material is described in detail, in which, according to the single-branch variant, the processes of deagglomeration of technogenic fibrous materials in the first chamber, grinding and mixing of the components of the composite mixture in the second chamber and micro-granulation of the mixture with fiber fillers in the third the camera. The results of the analysis of the kinematic scheme of the basic crank-slide mechanism are presented and a system of equations for determining the position functions of the points of the mechanism links is obtained, the characteristics of speed and power parameters in individual units of the unit are defined. Taking into account the identified advantages of the vibro-centrifugal unit, the directions of its use for complex processing of technogenic materials are determined.

Novel synthesis of aluminum hydroxide gel-coated nano zero-valent iron and studies of its activity in flocculation-enhanced removal of tetracycline

A newly designed aluminum hydroxide gel-coated nanoscale zero-valent iron (AHG@NZVI) with enhanced activity and dispersibility of NZVI was successfully synthesized. The AHG@NZVI composite was synthesized via control of the surface AHG content. AHG@NZVI-1, AHG@NZVI-2 and AHG@NZVI-3 were prepared under centrifugal mixing speeds of 1000, 2000 and 4000 r/min, respectively. The activity of AHG@NZVI was evaluated by its tetracycline (TC) removal efficiency. The effects of AHG content, pH value, reaction temperature, and presence of competitive anions on TC removal were investigated. TC could be removed by both adsorption and chemical reduction on AHG@NZVI-2 (centrifugal speed 2000 r/min) in a short time with high removal efficiency (≥98.1%) at the optimal conditions. Such excellent performance can be attributed to a synergistic interaction between aluminum hydroxide gel and NZVI: (1) AHG could enhance the stability and dispersity of NZVI; (2) aluminum hydroxide gel could absorb a certain amount of TC and Fe2+/Fe3+, which facilitated the mass transfer of TC onto the NZVI surface, resulting in acceleration of the reduction rate of TC by the AHG@NZVI composite; and (3) AHG-Fe2+/Fe3+ could absorb a certain amount of TC by flocculation. The kinetics of TC removal by AHG@NZVI composite was found to follow a two-parameter pseudo-first-order model. The presence of competitive anions slightly inhibited the activity of AHG@NZVI systems for TC removal. Overall, this study provides a promising alternative material and environmental pollution management option for antibiotic wastewater treatment.

Design and preparation of centrifugal microfluidic chip integrated with SERS detection for rapid diagnostics

A microfluidic SERS chip integrated with blood separation and in-situ detection was designed and fabricated for the rapid detection of clinical blood samples. Each functional unit in the microfluidic SERS chip consist of separation-decantation cavity based on centrifugal separation principle, mixing channels and SERS detection chamber built with integrated nano-Au on Ag film microstructure. The serum creatinine was selected as a typical sample to demonstrate the capability of microfluidic SERS chip. It was found that the creatinine SERS characteristic peaks at 678 cm−1 can be effectively identified and the detection limit could be as low as 4.42 × 10−3 μmol mL−1 in water. The blood samples were also tested in microfluidic SERS chip. The whole separation and test process could be completed within 2 min, which is a significant improvement in the field of creatinine detection. The whole blood of six cases clinical blood samples were also tested, and the results were consistent with the enzymatic results. The developed microfluidic SERS chip has advantages including reduction of the required quantity of blood sample, reusable and easy to operate. It is expected to provide a new method for rapid diagnostics.

Optical and biological properties of polymer-based nanocomposites with improved dispersion of ceramic nanoparticles.

This article reports a new process for creating polymer-based nanocomposites with enhanced dispersion of ceramic nanoparticles without using any surfactants, and the resulted changes in their optical and biological properties. Specifically, dispersion of two different ceramic nanoparticles, that is, hydroxyapatite (nHA) and magnesium oxide (nMgO) nanoparticles, in a model biodegradable polymer, namely poly(lactic-co-glycolic acid) (PLGA), was studied. High-power sonication was integrated with dual asymmetric centrifugal (DAC) mixing to improve dispersion of nanoparticles during solvent casting. The polymer/solvent ratio was optimized to improve nanoparticle dispersion in the multistep processing, including enhancing the efficacy of sonication and DAC mixing and reducing nanoparticle sedimentation during solvent-casting. Microstructural characterization confirmed that this new process improved nanoparticle dispersion in nMgO/PLGA and nHA/PLGA nanocomposites. Improved nanoparticle dispersion increased the optical transparency visually and optical transmission quantitatively for both nHA/PLGA and nMgO/PLGA nanocomposites. Improved dispersion of nanoparticles improved the adhesion of bone marrow derived mesenchymal stem cells (BMSCs) on nHA/PLGA but decreased BMSC viability on nMgO/PLGA. This difference is likely because the chemistry of nHA and nMgO had different effects on BMSCs. This study provided a new process for enhancing dispersion of ceramic nanoparticles in a polymer matrix and revealed the effects of dispersion on optical properties and cell responses, which are valuable for engineering optimal ceramic/polymer nanocomposites for different biomedical applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2692-2707, 2018.

Electrical Performance of Epoxy Resin Filled with Micro Particles and Nanoparticles

Abstract Composite insulators are widely used in the overhead transmission system. Compared with porcelain products, composite has many advantages such as light in weight, hydrophobicity characteristic and superior mechanical property. However, composite products are also suffering from issues such as low tracking resistance and early failures. The use of nano or micro fillers is considered to be one of the methods that can further improve the properties of the composite product. This study is aimed to study the electrical properties of nano and micro filled epoxy resin. SiO 2 and Al 2 O 3 nano and micro fillers are used in this research for comparison purposes. The host matrix, which is epoxy resin, is filled with nano particles, micro particles or both nano and micro particles. Micro particles and nano particles are dispersed into epoxy resin using planetary centrifugal mixing technique and degassed in vacuum. In total, seven types of materials are prepared in this study. These materials are (1) neat epoxy, (2) nanocomposite filled with 1 wt% nano SiO 2 fillers, (3) micro-composite filled with 20 wt% micro SiO 2 fillers, (4) micro-nano composite filled with 1 wt% nano SiO 2 and 20 wt% micro SiO 2 fillers, (5) nanocomposite filled with 1 wt% nano Al 2 O 3 fillers, (6) micro-composite filled with 20 wt% micro Al 2 O 3 fillers, (7) micro-nano composite filled with 1 wt% nano Al 2 O 3 and 20 wt% micro Al 2 O 3 fillers. In this study, AC electrical breakdown strength test are performed using a sphere-to-sphere setup. The thickness of all the samples is 1 mm ± 0.1 mm in accordance to the IEC standard. Surface partial discharge measurement is also performed to evaluate the surface property.

Study of Mechanical and Thermal Performances of Epoxy Resin Filled with Micro Particles and Nanoparticles

Abstract Composite insulators which are widely used in outdoor insulating systems are considered to have superior mechanical properties than conventional porcelain insulators. The hydrophobic surface of composite inhibits the water on the surface to form a water filament which may create a continuous conductive path. The lower weight of the insulators also lowers the installation and maintenance cost. Superior mechanical strength allows the insulator to support heavy conductors in transmission system. The use of additives is a very common method to enhance the properties of composite. In this study, epoxy resin is used as basic polymer matrix and SiO 2 and Al 2 O 3 particles are used as additives to improve the mechanical and thermal performances of epoxy resin. The samples are prepared by planetary centrifugal mixing technique and degassed in vacuum to remove air bubbles before molding. The nanocomposite samples are prepared with 1 wt% loading of either SiO 2 fillers or Al 2 O 3 fillers. The micro-composite samples are prepared with 20 wt% loading of either SiO 2 fillers or Al 2 O 3 fillers. Nano-micro composite samples (either use SiO 2 or Al 2 O 3 fillers) are prepared by dispersing 1 wt% nano fillers and 20 wt% micro fillers in the epoxy resin. Dynamic Mechanical Analysis (DMA) is performed on Perkin-Elmer DMA7e instrument using the tensile mode. Thermal gravimetric analysis (TGA) is also used to evaluate thermal stability property of the samples. The results show that both nano and micro composites have a superior mechanical property. The glass transition temperature of nanocomposite has improved compared with the neat epoxy. Our results show that Al 2 O 3 filled nano-micro composite samples have better mechanical and thermal properties than SiO 2 filled samples.

Rigorous buoyancy driven bubble mixing for centrifugal microfluidics.

We present batch-mode mixing for centrifugal microfluidics operated at fixed rotational frequency. Gas is generated by the disk integrated decomposition of hydrogen peroxide (H2O2) to liquid water (H2O) and gaseous oxygen (O2) and inserted into a mixing chamber. There, bubbles are formed that ascent through the liquid in the artificial gravity field and lead to drag flow. Additionaly, strong buoyancy causes deformation and rupture of the gas bubbles and induces strong mixing flows in the liquids. Buoyancy driven bubble mixing is quantitatively compared to shake mode mixing, mixing by reciprocation and vortex mixing. To determine mixing efficiencies in a meaningful way, the different mixers are employed for mixing of a lysis reagent and human whole blood. Subsequently, DNA is extracted from the lysate and the amount of DNA recovered is taken as a measure for mixing efficiency. Relative to standard vortex mixing, DNA extraction based on buoyancy driven bubble mixing resulted in yields of 92 ± 8% (100 s mixing time) and 100 ± 8% (600 s) at 130g centrifugal acceleration. Shake mode mixing yields 96 ± 11% and is thus equal to buoyancy driven bubble mixing. An advantage of buoyancy driven bubble mixing is that it can be operated at fixed rotational frequency, however. The additional costs of implementing buoyancy driven bubble mixing are low since both the activation liquid and the catalyst are very low cost and no external means are required in the processing device. Furthermore, buoyancy driven bubble mixing can easily be integrated in a monolithic manner and is compatible to scalable manufacturing technologies such as injection moulding or thermoforming. We consider buoyancy driven bubble mixing an excellent alternative to shake mode mixing, in particular if the processing device is not capable of providing fast changes of rotational frequency or if the low average rotational frequency is challenging for the other integrated fluidic operations.