Percolation Concentration Research Articles

Design of interconnected graphene loaded thermoplastic elastomeric blend composite films for minimizing electromagnetic radiation and efficient heat management

AbstractIn this work, electrically conductive thermoplastic elastomeric blend composite films based on polystyrene (PS)/ethylene‐co‐methyl acrylate (EMA) filled with functionalized graphene were developed via the solution mixing technique. Morphological analysis revealed that selective localization of amine‐functionalized reduced graphene oxide (G‐ODA) sheets in the EMA phase of co‐continuous binary blend formed a well‐connected dense conductive pathway by graphene sheets ultimately facilitating the double percolation phenomenon. The electrical percolation threshold was achieved at ~2 wt% of G‐ODA loading which was much lower than that for both single polymer composites. An electrical conductivity of 0.9 S/cm was obtained for blend composite film with 10 wt% of graphene concentration whereas for the same filler loading, PS and EMA composites exhibited electrical conductivity of 1.9 × 10−1 and 2.3 × 10−1 S/cm, respectively. The obtained thermal conductivity of the blend composite with 10 wt% of G‐ODA loading was 0.95 W/m K with 400% enhancement compared to the neat blend system. The same composite exhibited increased real and imaginary permittivity of 92 and 83, respectively. The electrical percolation threshold is well‐correlated with the percolation concentration found from storage modulus and thermal conductivity data. The fabricated PS/EMA blend composite film exhibited absorption‐dominant electromagnetic interference SE of −25 and − 35 dB in X‐band frequency (8.2–12.4 GHz) for 10 wt% of graphene loading with a sample thickness of 0.5 and 1 mm, respectively.

A century of nitrogen dynamics in agricultural watersheds of Denmark

Intensive agriculture has been linked to increased nitrogen loads and adverse effects on downstream aquatic ecosystems. Sustained large net nitrogen surpluses have been shown in several contexts to form legacies in soil or waters, which delay the effects of reduction measures. In this study, detailed land use and agricultural statistics were used to reconstruct the annual nitrogen surpluses in three agriculture-dominated watersheds of Denmark (600–2700 km2) with well-drained loamy soils. These surpluses and long-term hydrological records were used as inputs to the process model ELEMeNT to quantify the nitrogen stores and fluxes for 1920–2020. A multi-objective calibration using timeseries of river nitrate loads, as well as other non-conventional data sources, allowed to explore the potential of these different data to constrain the nitrogen cycling model. We found the flux-weighted nitrate concentrations in the root zone percolate below croplands, a dataset not commonly used in calibrating watershed models, to be critical in reducing parameter uncertainty. Groundwater nitrate legacies built up in all three studied watersheds during 1950–1990 corresponding to ∼2% of the surplus (or ∼1 kg N ha yr−1) before they went down at a similar rate during 1990–2015. Over the same periods active soil nitrogen legacies first accumulated by approximately 10% of the surplus (∼5 kg N ha yr−1), before undergoing a commensurate reduction. Both legacies appear to have been the drivers of hysteresis in the diffuse load at the catchments’ outlet and hindrances to reaching water quality goals. Results indicate that the low cropland surpluses enforced during 2008–2015 had a larger impact on the diffuse river loads than the European Union’s untargeted grass set-aside policy of 1993–2008. Collectively, the measures of 1990–2015 are estimated to have reset the diffuse load regimes of the watersheds back to the situation prevailing in the 1960s.

Moisture and frequency dependent conductivity as an obstacle to determining electrical percolation thresholds of cementitious nanocomposites made with carbon nanotubes

Impedance spectroscopy was applied to Portland cement and its carbon nanotubes (CNT) composites to measure and describe the electrical conductance phenomena and their dependency on the moisture. Two series of composites were prepared, one with multi-walled, and the other with single-walled CNTs. The percolation concentration was reached only with the single-walled CNTs between 0.10 and 0.25 wt%; it was therefore possible to compare a percolative and a non-percolative system. The kinetic of the drying process was measured in the range of 24 h and described by a decay model with a stretched exponential to be correlated with the composite composition. The polarization phenomena occurring in the materials before and after the moisture removal were modelled with logistic sigmoid and explained by the morphology. In particular, the three found sigmoid were correlated to the polarization phenomena occurring at well-defined structural levels of the specimens. Their mathematical definition was shown to be fundamental for a correct interpretation of the Cole-plots of the real conductivity. Such phenomena presented a peak of intensity at a well define frequency but their effects spread across a broad range of Hertz. Moreover, over the AC frequency of 10 Hz, the conductive effect of the moisture overlapped the conductivity increase caused by the percolative network of the CNT. A dry sample is therefore necessary for accurately evaluating the source of the conductivity, a distinction which is crucially important for sensing applications.

Percolation and phase behavior in cellulose nanocrystal suspensions from nonlinear rheological analysis

We examine the influence of surface charge on the percolation, gel-point and phase behavior of cellulose nanocrystal (CNC) suspensions in relation to their nonlinear rheological material response. Desulfation decreases CNC surface charge density which leads to an increase in attractive forces between CNCs. Therefore, by considering sulfated and desulfated CNC suspensions, we are comparing CNC systems that differ in their percolation and gel-point concentrations relative to their phase transition concentrations. The results show that independently of whether the gel-point (linear viscoelasticity, LVE) occurs at the biphasic - liquid crystalline transition (sulfated CNC) or at the isotropic - quasi-biphasic transition (desulfated CNC), the nonlinear behavior appears to mark the existence of a weakly percolated network at lower concentrations. Above this percolation threshold, nonlinear material parameters are sensitive to the phase and gelation behavior as determined in static (phase) and LVE conditions (gel-point). However, the change in material response in nonlinear conditions can occur at higher concentrations than identified through polarized optical microscopy, suggesting that the nonlinear deformations could distort the suspensions microstructure such that for example a liquid crystalline phase (static) suspension could show microstructural dynamics similar to a biphasic system.

Sustainable, bio-based conductive materials from peanut waste for flexible electronics and tunable piezoresistive strain sensors

Sustainable engineering applications are of great significance in materials science because of limited natural resources. This study presents a sustainable, bio-based approach for the fabrication of flexible electronics and sensors by using peanut shell and skin as the precursors for conductive carbon-based fillers. Carbonized samples showed differences in terms of morphological, structural, and electrical properties. While peanut shell-based carbon showed higher crystallinity and morphology with multiple channels; peanut skin-based carbon showed stacked, layered morphology with smaller particle size. Elastic modulus of the samples increased, tensile strength, and tensile strain values were decreased for both composite sets. The electrical conductivity of the samples prepared by carbon from peanut shell showed lower percolation concentration. Both composites showed piezoresistive response under cycling loading/unloading and tunable piezoresistive sensors were shown to be sensitive to human motions including horizontal and vertical elbow movement and back and forth knee bending and squatting.

Heterogeneous Percolation in Poly(methylvinylsiloxane)/Silica Nanocomposites: The Role of Polymer–Particle Interaction

Agglomeration and linking of nanoparticles or aggregates lead to the formation of percolated particle networks and alter the mechanical enhancement in polymer nanocomposites. Although critical behaviors have been widely studied, the solidlike behavior is only well described under the condition of the uniform dispersion of nanoparticles. In this work, we illustrate the role of particle–polymer interaction in the uniformity of particle dispersion and mechanical enhancement. Two types of silica with different interfacial adhesion energies with poly(methylvinylsiloxane) were adopted, resulting in different uniformities of particle dispersion. The critical percolation concentrations from the yield shear stress and yield first normal stress difference are identical. A lower interfacial adhesion energy leads to a higher critical concentration. The preshear stress only affects the critical concentration but does not change the critical exponents, which rely on the particle–polymer interaction. The mechanical enhancement, expressed as the power-law dependence of the yield stresses on the filler content, exhibits extraordinarily large power-law exponents for nanocomposites with lower interfacial adhesion energy, seriously deviating from the theoretical prediction in homogeneous dispersion systems. Based on the structural information from small-angle X-ray scattering (SAXS)/ultrasmall-angle X-ray scattering (USAXS) and transmission electron microscopy (TEM), we propose a model describing the heterogeneous percolation of loose aggregates in the presence of compact aggregates. This model shows that the heterogeneity of aggregates, including the fraction of compact aggregates and their fractal dimension, is the key factor in the scaling relationship between the yield stress and the particle volume fraction.

Physicochemical characterisation of graphene-ammonium lactate ionic liquid nanofluid

A new series of nanofluids based on graphene dispersed in 2-hydroxyethylammonium lactate (ML) ionic liquid was developed. Concentrations of 0.1, 0.5 and 1 wt% of graphene were studied and these dispersions were stable after 2 months. Raman spectra showed a strong interaction between ML and graphene. The effect of the concentration of graphene and temperature on the viscoelastic behaviour and conductivity of the nanofluids was studied. An unexpected decrease in the viscosity was found with a low concentration of graphene due to the suppression of hydrogen bonding of the ionic liquid. Shear thinning effects appeared with higher concentrations of graphene and Ostwald and Herschel-Bulkley equations were used to describe the steady-state viscosity results. Creep-recovery tests were also performed, and the data were fitted to a complex Burgers model for the nanofluid with 1 wt% of graphene, with a 47 % of elastic response. The complexity of the model was related to the presence of different molecular arrangements in the nanofluid. An enhancement of the conductivity was observed with increasing values of the graphene concentration. The effect of temperature on viscosity and electrical conductivity was successfully modelled by using both Vogel-Fulcher-Tammann and Power Law equations. Electrochemical characterisation at room temperature was also carried out, finding an irreversible oxidation at 1 V only for the highest concentration (1 wt%). The concentration of percolation was estimated in the range of 0.5 to 1 wt% of graphene.

The Processing and Electrical Properties of Isotactic Polypropylene/Copper Nanowire Composites.

Polypropylene (PP), a promising engineering thermoplastic, possesses the advantages of light weight, chemical resistance, and flexible processability, yet preserving insulative properties. For the rising demand for cost-effective electronic devices and system hardware protections, these applications require the proper conductive properties of PP, which can be easily modified. This study investigates the thermal and electrical properties of isotactic polypropylene/copper nanowires (i-PP/CuNWs). The CuNWs were harvested by chemical reduction of CuCl2 using a reducing agent of glucose, capping agent of hexadecylamine (HDA), and surfactant of PEG-7 glyceryl cocoate. Their morphology, light absorbance, and solution homogeneity were investigated by SEM, UV-visible spectrophotometry, and optical microscopy. The averaged diameters and the length of the CuNWs were 66.4 ± 16.1 nm and 32.4 ± 11.8 µm, respectively. The estimated aspect ratio (L/D, length-to-diameter) was 488 ± 215 which can be recognized as 1-D nanomaterials. Conductive i-PP/CuNWs composites were prepared by solution blending using p-xylene, then melt blending. The thermal analysis and morphology of CuNWs were characterized by DSC, polarized optical microscopy (POM), and SEM, respectively. The melting temperature decreased, but the crystallization temperature increasing of i-PP/CuNWs composites were observed when increasing the content of CuNWs by the melt blending process. The WAXD data reveal the coexistence of Cu2O and Cu in melt-blended i-PP/CuNWs composites. The fit of the electrical volume resistivity (ρ) with the modified power law equation: ρ = ρo (V − Vc)−t based on the percolation theory was used to find the percolation concentration. A low percolation threshold value of 0.237 vol% and high critical exponent t of 2.96 for i-PP/CuNWs composites were obtained. The volume resistivity for i-PP/CuNWs composite was 1.57 × 107 Ω-cm at 1 vol% of CuNWs as a potential candidate for future conductive materials.

Spin-wave theory in a randomly disordered lattice: A Heisenberg ferromagnet

Starting from the hamiltonian for the Heisenberg ferromagnet which comprise randomly distributed nonmagnetic ions as impurities in a Bravais lattice, we express the spin operators by means of the Dyson–Maleev transformation in terms of the Bose operators of the second quantization. Then by using methods of quantum statistical field theory, we derive the partition function and the free energy for the system. We adopt the Matsubara thermal perturbation method to a portion of the hamiltonian which describes the interaction between magnons and the stationary field of nonmagnetic ions. Upon averaging over all possible distributions of impurities, we express the free energy of the system as a function of the mean impurity concentration. Subsequently, we set up the double-time single particle Green function at temperature T in the momentum space in terms of magnon operators and derive the equation of motion for the Green function through the Heisenberg equation of motion and then solve the resulting equation. From this, we calculate the self-energy and then the spectral density function for the system. We apply the formalism to the case of the simple cubic lattice and compute the density of states, the spectral density function and the lifetime of the magnons as a function of energy for several values of the mean concentration of nonmagnetic ions in the ferromagnetic lattice. We calculate the magnon energy spectrum as a function of the average impurity concentration fraction c, which shows that for low lying states, the excitation energy increases continuously with c in the studied range 0.1≤c≤0.7. We also use the spectral density function to compute some thermodynamical quantities through the magnon occupation number. We have obtained closed form expressions for the configurationally averaged physical quantities of interest in a unified fashion as functions of the mean concentration of nonmagnetic impurities c to any order of c applicable below a critical percolation concentration cp. The quantities of interest comprise the thermodynamic potential (free energy), the spin-wave self-energy and the spectral density function from which other quantities can be derived.

Structural and electronic transitions in thulium-substituted manganese selenide

The structural, transport, optical, and acoustic properties of a new TmXMn1‒XSe (0 ≤ Х ≤ 0.2) chalcogenide system have been studied in the temperature range of 80–500 K. The morphology and microstructure of the polycrystalline samples have been studied by scanning electron microscopy. Temperatures of maxima of the thermal expansion and sound attenuation coefficients related to the lattice strain and electronic transitions have been determined. The variation in the energy of activation of carriers near the percolation concentration caused by a change in the thulium valence has been revealed. The type of majority carriers has been established from the thermopower data. The temperature range of the anomalous compressibility associated with delocalization of electrons has been found from the temperature dependence of the thermal expansion coefficient. Jahn‒Teller polarons have been found above the percolation concentration using the infrared spectroscopy data.

Modeling of Bentazone Leaching in Soils with Low Organic Matter Content.

The aim of this study was to estimate bentazone’s potential to leach to groundwater in the Arenosols developed from sand, Luvisols developed from loamy sand or sandy loam, and Luvisols or Cambisols developed from loess, and to identify the major factors influencing bentazone’s fate in the soils. Potato and maize cultivations were simulated using the FOCUS PELMO 5.5.3 pesticide leaching model. The amount of bentazone reaching groundwater was highly sensitive to degradation parameters, water-holding capacity, evapotranspiration, organic carbon content, and pH. The highest bentazone concentrations in percolate were noted in Arenosols. The risk of bentazone concentration exceeding 0.1 μg/L was low only in Arenosols with high organic carbon content (3.0% for topsoil or higher). In Luvisols developed from loamy sand or sandy loam, the estimated bentazone concentrations in percolate were highly dependent on the climate. In Luvisols or Cambisols developed from loess, concentrations of >0.1 μg/L were the least likely due to the high water-holding capacity and high organic carbon content of these soils. The study also revealed that the FOCUS Hamburg scenario, representing the coarsest soils in the European Union with relatively low organic carbon content, does not reflect the leaching potential of Arenosols and Luvisols.

Rheological behaviors of plasticized polyvinyl chloride thermally conductive composites with oriented flaky fillers: A case study on graphite and mica

AbstractIn this study, two oriented flaky fillers in plasticized polyvinyl chloride (P‐PVC) matrix were respectively compared on some rheological behaviors such as dynamic rheological behavior, melt flow rate, and Barus effect. By comparing and analyzing the rheological behaviors and thermal conductivity of P‐PVC/graphite and P‐PVC/mica composites with oriented fillers, it is found that the P‐PVC/graphite composites have obvious percolation thresholds of viscosity, modulus and thermal conductivity at 23.6 vol%. However, P‐PVC/mica composites did not show similar phenomenon. Moreover, the variable parameter K′ in the modified Kerner–Nielson equation was used to relate the rheological behavior, percolation concentration and thermal conductivity of the composites, and the formation of the filler network was analyzed through the rheological behavior to explain the influence of the percolation threshold in the composites caused by the change of internal structure on the thermal conductivity. It has important guiding significance for the mechanism research and comprehensive performance improvement of the filled composites.

Tumor Hypoxia Heterogeneity Affects Radiotherapy: Inverse-Percolation Shell-Model Monte Carlo Simulations.

Tumor hypoxia was discovered a century ago, and the interference of hypoxia with all radiotherapies is well known. Here, we demonstrate the potentially extreme effects of hypoxia heterogeneity on radiotherapy and combination radiochemotherapy. We observe that there is a decrease in hypoxia from tumor periphery to tumor center, due to oxygen diffusion, resulting in a gradient of radiative cell-kill probability, mathematically expressed as a probability gradient of occupied space removal. The radiotherapy-induced break-up of the tumor/TME network is modeled by the physics model of inverse percolation in a shell-like medium, using Monte Carlo simulations. The different shells now have different probabilities of space removal, spanning from higher probability in the periphery to lower probability in the center of the tumor. Mathematical results regarding the variability of the critical percolation concentration show an increase in the critical threshold with the applied increase in the probability of space removal. Such an observation will have an important medical implication: a much larger than expected radiation dose is needed for a tumor breakup enabling successful follow-up chemotherapy. Information on the TME’s hypoxia heterogeneity, as shown here with the numerical percolation model, may enable personalized precision radiation oncology therapy.

Attaining Toughness and Reduced Electrical Percolation Thresholds in Bio-Based PA410 by Combined Addition of Bio-Based Thermoplastic Elastomers and CNTs.

Multi-walled carbon nanotubes (CNTs) were added to provide electrical conductivity to bio-based polymer blends with improved toughness (based on commercially available Pebax thermoplastic elastomers and bio-based polyamide 4,10). A preliminary study including three different Pebax grades was carried out to select the grade and the composition that would best improve the impact properties of PA410. Thus, tough multiphasic PA/Pebax/CNT nanocomposites (NCs) with enhanced electrical conductivity were obtained. The CNTs were added either: (1) in the form of pristine nanotubes or (2) in the form of a PA6-based masterbatch. Hence, PA410/Pebax/CNT ternary NCs and PA410/PA6/Pebax/CNT quaternary NCs were obtained, respectively, up to a CNT content of 1 wt%. The ternary and quaternary NCs both showed similar mechanical and electrical properties. The electrical percolation threshold decreased with respect to previously studied corresponding NCs without Pebax, i.e., PA410/CNT and PA410/PA6/CNT, due to the partial volume exclusion effect of Pebax over the CNTs that were dispersed mainly in the PA matrix; materials with percolation concentrations as low as 0.38 wt% were obtained. With respect to mechanical properties, contrary to the NCs without Pebax, all the PA/Pebax/CNT NCs showed a ductile behavior and impact strength values that were from three to five-fold higher than that of the pure PA410.

Foaming characteristics of sugar- and polyvinylpyrrolidone-alcohol solutions during vacuum foam drying: A rheological approach

Vacuum foam drying offers great perspectives to formulate solid-state encapsulated active drugs. Taking into account the specific need of pharmaceutical formulations to keep drug molecules active and dispersed, we show in this paper that vacuum drying of pharmaceutical formulations can be substantially improved by using original rheological approaches. Typically, our formulations totally dried-up in less than 5 min, a delay much shorter than the long hours of the traditional vacuum drying process. Steady-shear rheology was used to evaluate the solution’s specific viscosity against the solutions’ concentrations, in order to correlate the dilution regime to the foamabiltiy. This rheological approach indicated that in miscible solutions, spontaneous foaming occurred in the semi-dilute entangled regime, near the transition to the concentrated regime; for partially miscible solutions, it occurred in solutions at a concentration near to the percolation concentration. The proposed methodology is versatile, and should provide a simple way to assess the foamability of pharmaceutical formulations.

Highly Tunable Piezoresistive Behavior of Carbon Nanotube-Containing Conductive Polymer Blend Composites Prepared from Two Polymers Exhibiting Crystallization-Induced Phase Separation

Conductive polymer composites (CPCs) are suitable as piezoresistive-sensing materials. When using CPCs for strain sensing, it is still a big challenge to simultaneously improve the piezoresistive sensitivity and linearity along with the electrical conductivity and mechanical properties. Here, highly tunable piezoresistive behavior is reported for multiwalled carbon nanotube (CNT)-filled CPCs based on blends of two semicrystalline polymers poly(vinylidene fluoride) (PVDF) and poly(butylene succinate) (PBS), which are miscible in the melt. When cooling the homogeneous mixture of the blend components, successive crystallization of PVDF and PBS occurs, creating complex crystalline structures in a mixed amorphous phase. The morphology of the blend matrix, the crystallinity of the blend components, and the dispersion and location of the CNTs in the blend depend on the CNT content and the blend composition. Compared with PVDF/CNT composites, the substitution of 10 to 50 wt % PVDF by PBS in the composites shifts the electrical percolation concentration Φc from 0.79 wt % to filler contents as low as 0.50 wt % while improving the stretchability. The piezoresistive behavior is highly tunable by changing the PVDF/PBS ratio. The ternary composites with matrix compositions of PVDF (90 wt %)/PBS (10 wt %) and PVDF (50 wt %)/PBS (50 wt %) show either higher piezoresistive sensitivity or linearity, respectively, caused by the differences in the microstructure of the CPCs. For example, the crystallinity of PBS in the ternary composites increased from 19.8% to 52.0% as the PBS content increased from 10 wt % to 50 wt %, which is connected with altered CNT distribution and conductive network structure and substantial improvement of the linearity of the electrical response to strains up to >20%. Our findings highly contribute to the understanding of the piezoresistive properties of CPCs based on two semicrystalline polymers and are important for future studies to tune the piezoresistive behavior to achieve simultaneously improved sensitivity and linearity.

Shear-induced breakdown and agglomeration in nanoparticles filled polymer: The shift of phase boundary and kinetics

For the nanoparticle-filled polymers, weak attractive interactions between nanoparticles lead to agglomeration and even formation of a network of nanoparticles in the polymer matrix. Both the agglomeration and the deagglomeration (breakdown) of the particle network are affected by the shear flow, resulting in shear-induced liquid-solid (L-S) transition and shear-induced solid-liquid (S-L) transition, respectively. In this study, we quantify the percolation threshold of both transitions under shear-induced agglomeration and shear-induced breakdown processes. Both the present shear condition and the preshear condition affect the percolation threshold, which turns to only shear rate dependence under steady shear condition, indicating no shear hysteresis. A scaling relation is suggested to describe the percolation threshold at low shear rate. The critical strains at both S-L and L-S transitions are inversely proportional to the distance of the particle concentration to the percolation concentration under steady shear. The apparent phase boundary under shear, represented by the shear rate and shear history-dependent percolation threshold, is further conceptually converted to the space of structural parameter, from which the possible transitions pathway under steady shear are discussed.

Percolation Threshold of the Thermal, Electrical and Optical Properties of Carbonyl-Iron Microcomposites

Composites made up of microparticles embedded in a polymeric matrix have attracted increasing attention due to the possibility of tailoring their physical properties by adding the adequate quantity of fillers. As the concentration of these fillers increases, their connectivity changes drastically at a given threshold and therefore the electrical, thermal and optical properties of these composites are expected to exhibit a percolation effect. In this work, the thermal and electrical conductivities along with the emissivity of composites composed of carbonyl-iron microparticles randomly distributed in a polyester resin matrix are measured, for volume fractions ranging from 0 to 0.55. It is shown that both the thermal and electrical conductivities increase with the particles’ concentration, such that their percolation threshold appears at volume fractions of 0.46 and 0.38, respectively. The emissivity, on the other hand, decreases as the fillers’ concentration increases, such that it exhibits a substantial decay at a volume fraction of 0.41. The percolation threshold of the emissivity is thus higher than that of the thermal conductivity, but lower than the electrical conductivity one. This dispersion on the percolation concentration is justified by the different physical mechanisms required to activate the electrical, thermal, and optical responses of the considered composites. The obtained results thus show that the percolation phenomenon can efficiently be used to enhance or reduce the physical properties of particulate composites.

A field scale facility to evaluate the effect of soil organic matter content of sod‐established St. Augustinegrass lawns on nitrate‐nitrogen leaching

AbstractA field scale facility was constructed to investigate the impact of a wide range of potential management parameters on nitrate (NO3‐N) leaching from St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] turf. The facility was built to identify and quantify background NO3‐N sources and concentrations before turf cultural management factors were applied, and to examine how establishment of sod with two contrasting soil organic matter (SOM) contents influence NO3‐N concentrations in percolate and leachate. The performance of the facility's irrigation and vadose zone percolate sampling units were evaluated and found acceptable. St. Augustinegrass sod with a 2.5 cm rootzone containing either 4% or 10% SOM was installed and maintained at this facility. The NO3‐N amounts in percolate and leachate were nearly proportional to the amount of SOM associated with the sod rootzones at 4% and 10%, respectively. Based on this investigation, SOM content in the rootzone attached to sod and within the soil which sod is placed influences NO3‐N concentration in the rootzone and leachate. Therefore, SOM should be considered in best management practices for lawncare. This facility will allow for future investigations on cultural management strategies aimed at decreasing the potential for NO3‐N leaching from St. Augustinegrass lawns.

68 Comparison of two Percoll gradients for selection of frozen semen for invitro production of ovine embryos

Sperm selection methods are routinely applied to prepare semen for IVF in animal species. These procedures are used to improve sperm quality characteristics as well as to remove other background material and debris. Percoll gradient is widely used in animal IVF laboratories. Different Percoll gradient concentrations and volumes can be used to improve the sperm sample motility percentage. The objective of this research was to evaluate the effect of 2 different Percoll concentrations for ovine IVF sperm selection and effects, if any, on invitro embryo production (IVP). Specifically, Percoll gradients consisted of Group 1 (G1) 40–80% and Group 2 (G2) 45–90%, 400µL each. The research was carried out in the reproduction laboratory at Palominos Ranch (Jalisco, México). The IVP was performed with a continuous invitro culture system. Ovaries (n=157) were collected from a slaughterhouse (León, México) and transported to the laboratory within 2h in physiological saline solution (0.9% NaCl) supplemented with penicillin G (100IU mL−1) and streptomycin sulphate (100µg mL−1). For IVP, IVF Bioscience™ media were used for IVM, IVF, and invitro culture (IVC). For IVM, the cumulus–oocyte complexes (COCs) were selected (only grades 1 and 2) and matured for 24h at 38.5°C in 5% CO2 in air and 100% humidity. Matured oocytes (n=800, divided equally into 4 replicates) were divided into 2 groups, G1 and G2. The IVF process was conducted with semen selected through a mini-Percoll technique with gradients at a concentration of 45% (top layer) and 90% (bottom layer) or 40% (top layer) and 80% (bottom layer) for G1 and G2, respectively, using frozen–thawed semen from the same ram, at a concentration of 2×106 sperm mL−1, for 18h in 38.5°C, 5% CO2 in air, and 100% humidity. The presumptive zygotes were denuded by pipetting and set in IVC until Day 7 at 38.5°C, 5% CO2, 5% O2, and 90% N2 at 100% humidity. The percentages of cleavage, embryos with more than 6 cells, and blastocysts on Day 7 of culture were evaluated, based on the initial number of oocytes entering into IVM. The statistical analyses were carried out with the GLM procedure of SAS software (version 9.3; SAS Institute Inc.) to evaluate the results of G1 versus G2 (α level=0.05). Cleavage rate was 47.8%±2.5 and 55.9%±2.5, respectively, in G1 and G2. The percentages of embryos with more than 6 cells were 38.1%±2.2 and 43.5%±2.2, respectively, in G1 and G2. The percentage of blastocysts on Day 7 was 27.4%±1.1 and 37.3%±1.1, respectively, in G1 and G2. There were no significant differences between groups (P>0.05) for percentage of cleavage and embryos with more than 6 cells, although the percentage of cleavage tended to be greater for G2 (P=0.06). Additionally, G2 had a larger percentage of blastocysts on Day 7 compared with G1 (P<0.05). In conclusion, under the conditions of this research, the use of a Percoll gradient at a concentration of 40–80% increased the percentage of blastocysts for ovine IVP.