Increasing Fiber Length Research Articles

Physical and mechanical properties of gypsum-based composites reinforced with basalt, glass, and PVA fibers

The purpose of this experiment is to investigate the influence of basalt fibers (BF), glass fibers (GF), and Polyvinyl alcohol (PVA) fibers on the properties of fiber-reinforced gypsum-based composites including setting time, extended diameter, water absorption, and flexural strength. In this study, the change of experimental results was obtained by selecting the fiber type, length, volume, and surface treatment as influencing factors; the mechanisms of change in the context of existing research was explained. Moreover, the scanning electron microscope was further analyzed, and analysis models of different factors on the fiber reinforced gypsum matrix were depicted. The results indicated that, with the increase in fiber length and volume, the setting time and fluidity will decrease and water absorption will increase. Compared with control group, the optimal ratios of three selected fibers were all 10 mm and 1.0%; in addition, the flexural strength can be increased by more than 50%. Moreover, the setting time, fluidity, and water absorption can increase by HCl, NaOH, and KH550 silane coupling agent treatments on the BF surface, with an improvement effect within 5%. The HCl and NaOH treatments can form pit etching on the fiber surface through an oxide reaction, while a hairy transmission stress interface layer between the BF and gypsum can be formed by the KH550 silane coupling agent treatment, where the strength lifting effect is better.

Enhancing the properties of starch-fiber foaming material by adjusting fiber length: The synergistic effect of macro-micro stress conduction

Starch-fiber based foaming materials are a promising alternative to petroleum-based plastics. The fiber length, as an important factor affecting the process of making foamed materials, was studied in this paper to investigate its influence on slurry rheology and the foaming process, and the mechanism of its influence on mechanical properties was analyzed from the perspective of macro-micro synergistic stress transfer. Different lengths [10 mm (L 10 ), 5 mm (L 5 ), 1 mm (L 1 ), 0.5 mm (L 0.5 ), 0.1 mm (L 0.1 )] of fibers were used to prepare different composites. The results showed that the increase in fiber length leads to higher slurry viscosity, a more uniform cell structure, and stronger mechanical properties. The L 10 composite achieved a tensile strength of 3.25 MPa, which was more than 4 times of the L 0.1 composite. Interestingly, the most hydrophobic microstructure was found on the surface of the L 0.5 composite, on which the water contact angle reached 130°. Finally, the effect of fiber length on the degradation rate of composites was explored. In summary, this study provides a new idea for the performance analysis of starch-fiber based foaming materials and is helpful in the selection of fiber length in their manufacturing process. • Starch-fiber composites were made using different lengths (0.1-10 mm) of sisal fibers. • The effect of macro-micro stress conduction on properties were investigated. • Composites with longer fibers can achieve better macro-micro stress conduction. • Longer fibers can build more stable supports, leading to better cell structures.

Development and Mechanical Characterization of Short Curauá Fiber-Reinforced PLA Composites Made via Fused Deposition Modeling.

The increase in the use of additive manufacturing (AM) has led to the need for filaments with specific and functional properties in face of requirements of structural parts production. The use of eco-friendly reinforcements (i.e., natural fibers) as an alternative to those more traditional synthetic counterparts is still scarce and requires further investigation. The main objective of this work was to develop short curauá fiber-reinforced polylactic acid (PLA) composites made via fused deposition modeling. Three different fiber lengths (3, 6, and 8 mm), and three concentrations in terms of weight percentage (2, 3.5, and 5 wt.%) were used to fabricate reinforced PLA filaments. Tensile and flexural tests in accordance with their respective American Society for Testing and Materials (ASTM) standards were performed. A thermal analysis was also carried out in order to investigate the thermal stability of the new materials. It was found that the main driving factor for the variation in mechanical properties was the fiber weight fraction. The increase in fiber length did not provide any significant benefit on the mechanical properties of the curauá fiber-reinforced PLA composite printed parts. The composites produced with PLA filaments reinforced by 3 mm 2% curauá fiber presented the overall best mechanical and thermal properties of all studied groups. The curauá fiber-reinforced PLA composites made via fused deposition modeling may be a promising innovation to improve the performance of these materials, which might enable them to serve for new applications.

Influence of Abaca Fiber Inclusion on the Unconfined Compressive Strength of Reconstituted Sandy Silts

The present investigation determines the influence of abaca (Musa textilis) fiber inclusion on the simple compressive strength of reconstituted sandy silt specimens. For this purpose, fibers of different lengths (5, 10 and 15 mm) and quantities (0.5, 1.0, 1.5 and 2.0% of soil dry weight) are added to produce the reconstituted specimens. Subsequently, the physical and mechanical behavior of soil–fiber mixtures were evaluated through compaction and unconfined compression tests. The experimental results showed that increases in fiber content or length, or both, led to a 1235.1% increase in maximum compression stress (compared to the fiber-free soil). Compression failure occurred at a greater axial strain when 10 and 15 mm fibers were added at 1% dosage or in percentages equal to or greater than 1.5% regardless of fiber length. A series of linear mixed models identified statistically significant effects of fiber length and percentage on the level of effort and on the unitary deformation.

Effect of fiber properties and dispersion management on distortions associated with two subcarriers modulation of laser diode in radio over fiber systems

We present numerical modeling and simulation on the effects of standard single-mode fiber (SSMF) properties and different dispersion management approaches on the distortions of laser diode. These distortions are associated with the two-tone modulation of laser diode for use in radio over fiber systems. The fiber properties include attenuation and dispersion. The dispersion management approaches include the use of nonzero dispersion-shifted fiber (NZ-DSF), fiber Brag grating (FBG), and dispersion-compensating fiber (DCF). The laser is directly modulated with two analog frequencies of 25 and 25.1 GHz at different modulation depths (m). The modulated laser signals are then propagated through SSMF at different lengths (L). The investigated laser signal distortions include the 2nd harmonic distortion (HD2), and the 2nd and 3rd intermodulation distortions (IMD2 and IMD3, respectively). The results reveal that all laser distortions are exacerbated as the fiber length increases, which is mainly due to the chromatic dispersion, while fiber attenuation has no effect. The use of dispersion management approaches gives almost similar effects on the reduction of IMD3 when L = 1 km, regardless of the value of m. Up to m = 0.3, DCF is the most effective approach for reducing all distortions over the entire fiber length range, while NZ-DSF is the least. When L = 2 km, FBG is the most effective approach for reducing both IMD2 and HD2 when m ≥ 0.4, whereas when L is increased to 6 km, DCF is the most effective approach up to m = 0.5.Graphical abstractSimulation setup of RoF system for two-tone direct modulation of laser diode using different dispersion management approaches

Mix optimization of hybrid steel and polypropylene fiber-reinforced concrete for anti-thermal spalling

Concrete tends to spall explosively under fire due to the combined effect of thermal stress and pore pressure build-up. For an anti-spalling strategy in the concrete mix design, one can add steel fibers to improve the material strength and fine-polypropylene (PP) fibers to mitigate the pore pressure build-up. However, the addition of steel fibers causes noticeable increments in the spalling risk, while the addition of PP fibers causes slight decrements in the material strength capacity. Hence, the mix optimization of hybrid fiber reinforced concrete (HFRC) is studied in this research focusing on the individual and synergistic effects of steel and PP fibers on the mechanical degradations and pore pressure peaks at elevated temperatures. An apparent plateau in the pore pressure rises at 165 °C (PP melting point) is frequently observed in HFRC, which is the combined opposite effects of the two different fiber types. The increase of PP fiber length, rather than the dosage, is recommended to mitigate the pore pressure build-up, because of the better retention of residual strength and improvement in pore connection thanks to the observed fiber adhering effect (FAE) on aggregates. Based on a comprehensive experimental investigation, the cementitious mix with 1% of steel and 0.2% of 19-mm-length PP fiber in volume is recommended to obtain a high strength capacity and low pore pressure at elevated temperature. Finally, a new mathematical formula for prediction of the maximum pore pressure variation when steel, PP, or both fibers are employed in the concrete mix is here proposed for guiding the anti-spalling mix design of fiber-reinforced cementitious material.

Experimental study on the mechanical behaviour of short chopped basalt fibre reinforced concrete beams

The use of short chopped basalt fibres (CBFs) in concrete structures, as a promising alternative to conventional fibres, is of great importance to the sustainable development and plays a well-balanced role between strength improvement and workability in construction. Hence, this paper successively presents two series of test programs. Series Ⅰ as the preliminary material tests is conducted to understand the effects of short CBFs on concrete matrix, while Series Ⅱ as the beam tests is primarily to explore the flexural performance of concrete beams mixed with CBFs based on various three kinds of parameters. The results showed that in Series Ⅰ, the inclusion of CBFs can relieve the crack patterns from a sudden failure to a more ductile behaviour, and effectively upgrade the flexural strength of concrete. While in Series Ⅱ, concrete beams mixed with CBFs can help enhance the crack-resistance ability and greatly improve the flexural behaviour during the working stage. In addition, the improvement effects were enlarged with increasing fibre length, and that were reduced as the tensile reinforcement ratio increases. An FRL height ratio of 0.35 was suggested to ensure that the composite beams worked well and to avoid potential interface issues. Finally, the calculated methods of cracking moment and section stiffness during the service life, were proposed and verified by collecting other test data.

Mitigating Crosstalk of Vortex Beam Within an OAM-Mode Group Over an OAM Fiber by Reversing Transmission Matrix

For enhancing channel capacity and spectrum efficiency, vortex beam carrying orbital angular momentum (OAM) has been ardently investigated in optical communication. However, the crosstalk among OAM modes induced by mode coupling has seriously hindered the development of vortex beam communication (OBC). A novel concept of mitigating crosstalk within an OAM-mode group for a short-haul optical fiber communication (OFC) is proposed by reversing the transmission matrix. To support more OAM modes propagation, a step-index OAM fiber with ring-shaped profile is also designed and fabricated, which can support 6 vector/OAM modes propagation. A proof-of-concept experiment is performed for verifying the feasibility of the proposed concept, where a quadrature-phase-shift-keying (QPSK) signal is utilized as an excitation signal. Bit-error-ratio (BER) and constellation diagram (CD) are employed to evaluate the performance of the proposed system. The captured intensity profiles and interference diagrams demonstrate that the propagated four OAM beams within the 2rd OAM-mode group are successfully received. The measured BER and CD illustrate that the crosstalk within the mode group can be significantly mitigated. Further, although the data speed or fiber length is increased, the system performance using the proposed concept is still superior to the case without increasing fiber length or data speed when the proposed concept is missed. Therefore, the proposed concept is effective for mitigating the crosstalk and can be then used for a short-haul OAM-based OFC.

Cultivar, irrigation management, and mepiquat chloride strategy: Effects on cotton growth, maturity, yield, and fiber quality

Drought negatively affects cotton growth and yield, whereas excessive irrigation can limit yield through excessive vegetative growth and poor fruit retention. Mepiquat chloride (MC) application limits plant height, improves fruit retention and hastens maturity in responsive cultivars. Thus, the objective of this study was to address the effects of cultivar, irrigation, and MC strategy on cotton growth, maturity, yield, and fiber quality. Therefore, a field study was carried out using three cultivars, three different irrigation treatments, and three different MC treatments during the 2020 and 2021 growing seasons. In both years there was an interaction between irrigation and MC management for plant height. In 2020, MC treatments hastened cutout by two to three weeks in irrigated plots but did not affect cutout date in dryland plots. 2020 and 2021 differed substantially in rainfall (347 mm and 735 mm, respectively from planting to harvest). 2020 was a dry year in which yield responded positively to irrigation and 2021 was a wet year in which yield responded negatively to irrigation. There was no effect of MC treatments or interaction between MC and any other effect on lint yield. Fiber length was reduced, whereas strength and micronaire were increased by drought stress in 2020. Increased fiber length, strength, uniformity, and micronaire were observed by MC application in both years. Therefore, we can conclude that aggressive MC management reduces vegetative growth, promotes earlier physiological maturity under well-watered conditions, and affects fiber quality, but does not necessarily interact with irrigation management to affect lint yield. • Growth and maturity responses to mepiquat chloride depend on water availability. • Mepiquat chloride hastens maturity under water replete conditions, but not dryland. • Occasionally, fiber quality was positively impacted by mepiquat chloride application. • Mepiquat chloride did not alter cotton yield response to water excess or drought.

Experimental Study on Frost Heave Behavior of Steel Fiber Improved Soil

The incorporation of steel fibers into the natural soil is generally considered to be a novel and effective way to reduce the amount of frost heave induced by an artificial freezing process in underground engineering. In order to analyze the frost heave behavior of the steel fiber improved soil, a one-dimensional frost heave test under the open recharge system was conducted in this paper, focusing on the influence of steel fiber content, size, and soil properties. The results show that small amounts of steel fibers in the soil will not significantly affect the freezing process and temperature distribution, while the water-conducting properties of the steel fibers and the effect of limiting the ice lens growth can reduce the frost heave rate of the samples incorporated with 0.5% steel fibers by 26.93%. At the same time, the reduction effect of the frost heave rate increases linearly with the increase of steel fiber content and length but weakens with the increase of steel fiber diameter. In terms of soil property influence, the frost heave rate of the clay samples was reduced by 14.31% compared to the silt samples, while the water migration was reduced by 11.99%. In addition, the cementation of the steel fibers with the soil will also inhibit the growth of the ice lens and reduce the external water migration, thus significantly lowering the frost heave rate. The results can provide a reference for the research of the frost deformation of similar modified soils.

Evolutionary divergence of duplicated genomes in newly described allotetraploid cottons

Allotetraploid cotton (Gossypium) species represents a model system for the study of plant polyploidy, molecular evolution, and domestication. Here, chromosome-scale genome sequences were obtained and assembled for two recently described wild species of tetraploid cotton, Gossypium ekmanianum [(AD)6, Ge] and Gossypium stephensii [(AD)7, Gs], and one early form of domesticated Gossypium hirsutum, race punctatum [(AD)1, Ghp]. Based on phylogenomic analysis, we provide a dated whole-genome level perspective for the evolution of the tetraploid Gossypium clade and resolved the evolutionary relationships of Gs, Ge, and domesticated G. hirsutum. We describe genomic structural variation that arose during Gossypium evolution and describe its correlates-including phenotypic differentiation, genetic isolation, and genetic convergence-that contributed to cotton biodiversity and cotton domestication. Presence/absence variation is prominent in causing cotton genomic structural variations. A presence/absence variation-derived gene encoding a phosphopeptide-binding protein is implicated in increasing fiber length during cotton domestication. The relatively unimproved Ghp offers the potential for gene discovery related to adaptation to environmental challenges. Expanded gene families enoyl-CoA δ isomerase 3 and RAP2-7 may have contributed to abiotic stress tolerance, possibly by targeting plant hormone-associated biochemical pathways. Our results generate a genomic context for a better understanding of cotton evolution and for agriculture.

Macroscopic Mechanical Properties and Microscopic Bonding Mechanisms of Glass Fiber-Modified Loess

Focusing on the performance improvement of glass fiber-modified loess, a series of laboratory tests were carried out, and the macroscopic mechanical properties of glass fiber-modified loess were studied by conventional triaxial shear tests. With the help of scanning electron microscopy (SEM), the pores and cracks image analysis system (PCAS) and nuclear magnetic resonance (NMR) tests, the microscopic properties of the improved loess were studied qualitatively and quantitatively from three aspects: mode of structural contact, pore morphological characteristics and pore structure arrangement characteristics. Finally, the interface zone bond-slip model was used to analyze the internal mechanism of glass fiber and loess interface zone slip. The macroscopic test results show with the same glass fiber length, the shear strength, cohesion and internal friction angle of the modified loess all increased first and then decreased with increasing incorporation of glass fibers. And the optimal ratio of glass fibers is 0.6%. Under the same fiber ratio, the shear strength and cohesion of the improved loess continued to increase with increasing fiber length. The optimal fiber length used in the project was 9 mm. Qualitative analysis of the SEM images show that with the increase in the glass fiber incorporation ratio, the fiber increasingly sutures the cracks in the soil and tightens the soil at both ends of the cracks. Quantitative analysis shows that the proportion of pore area is the largest at the 0.8% mixing ratio, followed by the 0% mixing ratio, and the smallest at the 0.6% mixing ratio. It can be seen from the NMR test results that the T2 spectral distribution curve under the fiber ratios of 0.2%–0.6% is shifted to the left compared with the ratios of 0% and 0.8%. The peak-top signal intensity of the main spectrum peak when the fiber ratio is 0.6% is the weakest.

Effect of Carbon Fibres on Electromagnetic-Interference-Shielding Properties of Geopolymer Composites.

Many of the construction materials available are known to cause a drastic level of damage to the environment during their manufacturing stages. Hence, many researchers have attempted to formulate construction materials that are more environmentally friendly. Additionally, the rise in wireless communications in recent decades has seen a rapid increase in electromagnetic pollution and interference, which affects the functionality of sensitive electronic devices. This research is focused on fabricating a more sustainable construction material that could prevent electromagnetic interference for electronic devices housed inside. Carbon fibres of three different lengths were added in four variations to a geopolymer control mix to study their effect on electromagnetic interference shielding. The results showed that the amount of shielding produced by these composites increases with carbon fibre length and quantity. Morphological analyses showed that the interconnectivity of the fibres plays a crucial role in having a high level of shielding. While the flexural strength showed an improvement with the addition of carbon fibre, the compressive strength showed a slight reduction with the increase in carbon fibre length. The optimal level of shielding was produced by the specimen containing 0.7% of 12 mm carbon fibre, which was the maximum amount of fibre of any length used in this study; the optimal level of shielding generated was 43.43 dB within the frequency range of 30 MHz to 1.5 GHz.

Effect of fiber orientation on the fatigue crack initiation and propagation of glass fiber reinforced plastics

AbstractIn recent years, glass‐fiber‐reinforced plastic (GFRP) applications have expanded. This study elucidates the fatigue fracture mechanism of GFRP with different fiber orientations and experimentally clarifies the relationship between fiber orientation and fracture mechanism by using specimens with unidirectional simple fiber orientations. First, Static tensile and fatigue tests are performed on two types of specimens with fibers oriented in a single direction (parallel to the load axis and orthogonal to the load axis), and it is found that specimens with a single fiber orientation parallel to the load axis shows higher strength in both tests. Next, In the case of GFRP with fibers oriented parallel to the load axis, it is found that fatigue loading causes fatigue crack initiation at the fiber ends, followed by fiber localized debonding due to crack propagation at the fiber‐matrix interface and that the crack propagation rate gradually decreases and stops. Therefore, this suggests that the increase in fiber length of fibers oriented parallel to the load axis in GFRP leads to an increase in the crack propagation life at the fiber‐matrix interface, which leads to an increase in fatigue life.

Effects of agricultural by-product on mechanical properties of cemented waste soil

Waste soil produced from construction sites currently emerges as a big problem to environment. These soils cannot be reused directly cause of its weakness in strength properties. Hence, this study focuses on improving mechanical properties of waste soil by using cement and corn husk fiber . The environment has also benefited from using corn husk fiber since corn husk is agricultural by-product. In order to evaluate the impact of corn husk fiber and cement on mechanical characteristics of waste soil, a series of laboratory experiments containing tension and compression test is carried out. In addition, scanning electron microscopy (SEM) test is conducted to investigate interaction between fibers and soil-cement matrix. Fiber content from 0 to 1% by dry soil mass and corn husk lengths of 10 and 30 mm are used in this research. The results present that strength properties of cemented soil are enhanced when fiber is added. The most improvements corresponding to compressive strength , splitting tensile strength , and direct tensile strength are 30.6%, 206.1%, and 27.9%, respectively. A strong interaction between fibers and soil-cement matrix observed from SEM results in the improvement of strength properties of cemented soil. Fiber inclusion contributes to the more ductile and durable behavior under loading. Fiber length and fiber content have a remarkable effect on the cemented soil behavior. The increase in fiber length and content leads to the increase in residual stress and the decrease in loss of post-peak stress. • Corn husk is utilized in waste soil reinforcement. • Effect of corn husk fiber on cemented soil is investigated. • The addition of fiber delays failure process of cemented soil. • Fiber inclusion improves failure strength up to 206%. • Presence of fibers at crack contributes to the appearance of residual direct tensile stress.

Triaxial mechanical properties and microscopic characterization of fiber-reinforced cement stabilized aeolian sand–coal gangue blends

To understand the mechanical properties of fiber-reinforced cement stabilized aeolian sand–coal gangue blend materials and reveal their failure mechanism, polypropylene fiber was uniformly incorporated into cement stabilized aeolian sand–coal gangue blend materials. Triaxial compression tests were carried out to study the coupling effect of different fiber contents and fiber lengths on the shear strength of the blend materials. The internal physical and chemical mechanisms of structural performance evolution were clearly revealed by scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray diffraction (XRD) at the micro level. The results show that adding 2 ‰ 12 mm fiber can effectively improve the shear properties of the sample. When the fiber length is 12 mm, the elastic strain energy first increases and then decreases with the increase in fiber content. When the fiber content is 2 ‰, the total energy and elastic strain energy increases steadily with the increase in fiber length. SEM results revealed that the fiber was gradually wrapped with the formation of cement hydration products, which provided both induction and bridging properties. The interface between fiber and granular particles was composed mainly of single fiber grip and fiber network formed by the random distribution of fiber. In the shear process, the fibers in the sample exhibited two failure modes: interface slip and tensile break.

A Workability Characterization of Innovative Rubber Concrete as a Grouting Material.

The aim of this study is to assess the workability of an innovative rubber concrete to fill in the gaps in a shield tunnel construction. This grouting material includes porous sand, PVA (polyvinyl alcohol) fiber, cement, and rubber. One advantage of the material is its high toughness, which is good for the postfailure stage of an earthquake event. Evaluations were carried out on the physical properties in terms of the slurry density, consistency, fluidity, bleeding rate, consolidation shrinkage rate, setting time, and unconfined compressive strength (UCS) (i.e., 3 and 28 days). The toughness index was also introduced to evaluate the performance at the postfailure stage. The results demonstrate that the toughness index will increase as the rubber content increases. It increases from 1.0 at 0% to 1.7 at 80% rubber content (28 days’ curing) and from 1.2 at 0% to 2.2 at 80% rubber content (3 days’ curing). The increase in fiber content and fiber length will also increase the toughness index as the fiber will enhance the tensile strength of the matrix. The results show that when the fiber content increases from 0% to 1%, the toughness index increases from 1 to 7 (28 days’ curing) and from 1.1 to 10 (3 days’ curing). Similarly, if the fiber content or fiber length is above the optimum level, the UCS of the material will be compromised. The optimum fiber content is 0.8%, and the optimum fiber length is 6 mm to 9 mm. This study suggests that the balance of physical properties should be considered in designing a satisfactory grouting material based on the specific purpose of the engineering practice.

Effects of Fiber Volume Fraction and Length on the Mechanical Properties of Milled Glass Fiber/Polyurea Composites.

Composites of polyurea (PU) reinforced with milled glass fiber (MGf) were fabricated. The volume fraction and length of the milled glass fiber were varied to study their effects on the morphological and mechanical properties of the MGf/PU composites. The morphological attributes were characterized with scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The SEM investigations revealed a uniform distribution and arbitrary orientation of milled glass fiber in the polyurea matrix. Moreover, it seems that the composites with longer fiber exhibit better interfacial bonding. It was found from the FTIR studies that the incorporation of milled glass fiber into polyurea leads to more phase mixing and decreases the hydrogen bonding of the polyurea matrix, while having a negligible effect on the H-bond strength. The compression tests at different strain rates (0.001, 0.01, 0.1, 1, 2000 and 3000 s−1) and dynamic mechanical properties over the temperature range from −30 to 100 °C at 1 Hz were performed. Experimental results show that the compressive behavior of MGf/PU composites is nonlinear and strain-rate-dependent. Both elastic modulus and flow stress at any given strain increased with strain rate. The composites with higher fiber volume fraction and longer fiber length are more sensitive to strain rate. Furthermore, the elastic modulus, stress at 65% strain and energy absorption capability were studied, taking into account both the effect of fiber volume fraction and mean fiber length. It is noted that an increase in fiber volume fraction and fiber length leads to an increase in elastic modulus, stress at 65% strain and absorbed energy up to ~103%, 83.0% and 137.5%, respectively. The storage and loss moduli of the composites also increase with fiber volume fraction and fiber length. It can be concluded that the addition of milled glass fiber into polyurea not only improves the stiffness of the composites but also increases their energy dissipative capability.

(Digital Presentation) Effect of the Length of Carbon Nanofibers on Selective Dopamine Sensing

The engineering of carbon nanofibers (CNFs) has recently received extensive attention in the field of biosensors due to their high surface area, rich nanoscale geometries, ability to selectively detect the analyte of interest (e.g., dopamine) in the presence of interfering molecules that exist in biological environment and inherent resistance to biofouling1 - 3. CNFs with the individual fiber length/size adjusted to the diffusion layer thickness can confine the analyte molecules within the nanostructures and result in the formation of a thin liquid layer, increasing their sensitivity 4. This points towards the potential of altering the aspect ratios and growth densities of CNFs to tune their biosensing properties. Thus, here we aim to evaluate the effect of the length, distribution, and microstructure of fibers on their electrochemistry and how this affects the sensitivity and selectivity for dopamine (DA) detection.Herein, CNFs of varying lengths have been grown on a silicon substrate using the thin layers of Ni and Cr as catalysts. Samples with different length and distribution of CNFs have been synthesized by controlling the duration of the growth phase. The length and the detailed structure of the CNFs have been investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The lengths of CNFs were found to be in the range of 900 nm-1µM, 500-600 nM, 200-300 nM, and <150 nM for 30 mins, 10 mins, 5 mins and 1 min growth times, respectively. Cyclic voltammetry measurements showed that the double-layer capacitance (Cdl) and oxidation current (Ipa) of dopamine increase continuously with the increase in the length of fibers indicating the increase in the surface area (Figure 1A). DA reaction kinetics tend to be reversible for the longest fibers and becomes slightly more sluggish with the decrease in the fiber length. However, it should be noted that carbon nanofiber length (hundreds of nM to 1µm) may match the diffusion layer thickness at certain scan rates, causing the thin liquid layer electrochemical behavior to contribute to the total kinetics. This implies that the variations in the peak separation (ΔEp) can be due to the combined changes in reaction kinetics and geometry. CNFs grown for 30 mins, 10 mins, 5 mins, and 1 min exhibited log Ipa vs v slope of 0.72, 0.63, 0.62 and 0.51, indicating that contribution of adsorption/thin layer formation is coming into effect with the increase in fiber length (Table 1). Washout experiments will be performed to distinguish further between thin layer and adsorption behavior affecting the electrochemistry of DA. It appears that DA reaction kinetics is fully under semi-infinite linear diffusion-control only at 1 min grown CNFs due to the relatively smooth surface of the electrode material. The selectivity of dopamine in the presence of physiological concentrations of ascorbic acid (AA) and uric acid (UA) greatly improves with the increase in the length of the fibers (Figure 1B). Electrodes with 1 min grown CNFs possessing metal particles and exhibiting little CNF growth did not show selectivity towards DA. Interestingly, with the increase in the growth time and consequently the length of the fiber, well-defined oxidation peaks of AA and DA and UA are observed. Moreover, the position of the oxidation potential appears to be affected both by the fiber length and presence/absence of other molecules, and often in the opposite directions (Table 1, Figure 1). The results discussed above point towards the significance of matching the CNF length with the scan rate used for in vivo detection of DA for optimized sensitivity and selectivity. References 1 S. Sainio, T. Palomäki, N. Tujunen, V. Protopopova, J. Koehne, K. Kordas, J. Koskinen, M. Meyyappan and T. Laurila, Mol. Neurobiol., 2015, 52, 859–866.2 S. Sainio, E. Leppänen, E. Mynttinen, T. Palomäki, N. Wester, J. Etula, N. Isoaho, E. Peltola, J. Koehne, M. Meyyappan and others, Mol. Neurobiol., 2020, 57, 179–190.3 A. Kousar, E. Peltola and T. Laurila, ACS omega, 2021, 6, 26391–26403.4 Q. Cao, Z. Shao, D. K. Hensley, N. V Lavrik and B. J. Venton, Langmuir, 2021, 37, 2667–2676. Figure 1

Numerical modeling and parametric study of a hollow fiber dialyzer using double porous media approach

Mathematical modeling is one of the efficient methods to improve the design of hemodialyzer and study affecting parameters on dialyzer performance.In this paper, mathematical modeling of hollow fiber dialyzer is done to investigate the effect of various parameters on the clearance of urea and creatinine. The computational domain is considered two-dimensional axisymmetry. The hollow fibers bundle is defined as a double porous media. The Darcy-Brinkman-Forchheimer equation is employed to determine flows in porous media. Modified Kedem–Katchalsky equations are used to calculate the transmembrane flow. Continuity, Navier–Stokes and concentration equations are solved by finite element method.The numerical results showed a change in the thickness of hollow fibers from 100 to 25 µm and a decrease in their inner diameter from 240 to 150 µm, could improve clearance of urea by 66.7 and 20.7 percent respectively. The increase in blood flow (40 to 120 mL.min−1), dialysate flow (80 to 200 mL.min−1), dialyzer diameter (28 to 38 mm) and length of hollow fibers (15 to 30 cm) increase the clearance of urea by 88.2, 20.4, 35 and 26.2 percent, respectively.The model has been validated and shows good agreement with experimental results. Such studies advance our understanding of the parameters affect the performance of the dialyzer.