The focus of this research was on the thermal conductivity and rheological properties of poly(ethylene glycol) with a molecular mass of 200 g mol
−1
(i.e., PEG200) loaded with four different types of ...multi-walled carbon nanotubes (MWCNTs) in a wide concentration range up to 10 mass%. MWCNTs used differ in size (both diameter and length) and the content of COOH (oxidized) functional groups on their surface. It was found that the use of oxidized, shorter and wider MWCNTs in PEG200 results in highest enhancement in thermal conductivity by 133% for 10 mass% MWCNTs-PEG200 nanofluids. Investigation of the shear rate dependence of dynamic viscosity (
η
) showed that the use of MWCNTs in concentrations greater than 0.1 mass% changes the Newtonian behavior of PEG200 and results in the shear-thinning behavior. This behavior is strongly influenced by the MWCNT concentration in the nanofluid. When comparing the same nanofluid concentration, the highest degree of MWCNT agglomeration in PEG200 nanofluids was observed when long, thin and pristine MWCNTs were used. The thermal conductivity results were correlated with the most commonly used theoretical models: Maxwell, Hamilton-Crosser, Xue, and Murshed. Dynamic viscosity results were correlated with Einstein, Brinkman, and Brenner-Condiff theoretical models. The best agreement with the experimental results was obtained by the Maxwell and Einstein models, indicating the formation of sphere-like MWCNT agglomerates in each PEG200 nanofluid studied.
This paper describes the synthesis of methacrylate-based terpolymer additives for diesel and biodiesel fuel that improve its properties at low temperatures. The synthesized additives contained ...different amounts of short-chain (methyl and benzyl) and long-chain (dodecyl and octadecyl) methacrylate comonomers. The crystallization behaviour of the additives and the formulations with diesel and biodiesel was observed by differential scanning calorimetry (DSC) and optical microscopy with polarization. DSC showed that the additives had a different effect on the crystallization temperature of the formulations. Microscopic images showed that the presence of additives influenced the size and number of wax crystals at low temperatures. Standard ASTM D5950 tests for pour point (PP) showed a large improvement in formulations with additives. In formulations with diesel, the addition of additives improved the PP value of diesel from − 18 °C to − 45 °C and in B10 diesel/biodiesel formulations from − 18 °C to − 54 °C.
Biodiesel has established itself as a renewable fuel that is used in transportation worldwide and is partially or in some cases completely replacing conventional fuels. Chemically, biodiesel is a ...fatty acid monoalkyl ester (FAAE). Generally, the term biodiesel refers to the fatty acid methyl or ethyl esters (FAME or FAEE). Herein, an overview of the research on the synthesis of FAAE in which the alkyl moiety is a C3+ alkyl chain (branched/unbranched) is given. In addition, a comparison of the properties of the aforementioned FAAE with each other, with FAME and FAEE, and with fuel standards is given. The length of the alkyl chain has a major influence on viscosity, while pour point temperatures are generally lower when branched alcohols are used, but the fatty acid part of the molecule also has a major influence. The development of new pathways for the synthesis of higher alcohols from biomass opens a future perspective for the production of long chain FAAE as biofuels, fuel additives, or biolubricants. Due to their properties, FAAEs produced from C3–C5 alcohols have the potential to be used as fuels, while all C3+ FAAEs can be used as valuable bioadditives, and C8+ FAAEs can be used as biolubricants and viscosity improvers.
Chitosan-based scaffolds offer significant potential in tissue engineering and regenerative medicine. Whilst exhibiting great bio-regenerative and biocompatible properties, their mechanical ...properties remain quite poor. The presented research is focused on the modification of macroporous chitosan scaffolds with various amounts of bioactive ceramics (hydroxyapatite) and its influence on the physical and rheological properties of the composite scaffold. Chitosan/hydroxyapatite composite scaffolds with a highly porous microstructure have been prepared by suspending hydroxyapatite (HAp) particles into the chitosan matrix. According to SEM imaging, homogeneous dispersion of the inorganic phase in a chemically-crosslinked chitosan matrix had been achieved. The obtained composite scaffolds exhibited lower swelling capacity with respect to pure chitosan after 24 h of incubation in Hanks’ balanced salt solution. Rheological measurements show an increase in storage and loss modulus indicating an improvement in mechanical properties under shear stress. Furthermore, no significant change in loss factor (tanδ) was observed indicating no change in composite viscoelastic properties with an increase in HAp content.
MoS2 monolayer samples were synthesized on a SiO2/Si wafer and transferred to Ir(111) for nano-scale characterization. The samples were extensively characterized during every step of the transfer ...process, and MoS2 on the final substrate was examined down to the atomic level by scanning tunneling microscopy (STM). The procedures conducted yielded high-quality monolayer MoS2 of milimeter-scale size with an average defect density of 2 × 1013 cm-2. The lift-off from the growth substrate was followed by a release of the tensile strain, visible in a widening of the optical band gap measured by photoluminescence. Subsequent transfer to the Ir(111) surface led to a strong drop of this optical signal but without further shifts of characteristic peaks. The electronic band gap was measured by scanning tunneling spectroscopy (STS), revealing n-doping and lateral nano-scale variations. The combined use of STM imaging and density functional theory (DFT) calculations allows us to identify the most recurring point-like defects as S vacancies.
The first aim of this paper is to study the influence of four parameters of the transesterification reaction—reaction temperature (40–80 °C), time (1–3 h), the molar ratio of 1-octanol to sunflower ...oil (4:1–10:1) and mass fraction of the catalyst (1–3 wt%)—on the conversion of oil to biodiesel (octyl esters of fatty acids), with potassium hydroxide as a catalyst. The highest conversion, of 99.2%, was obtained at 60 °C, a molar ratio of 1-octanol to sunflower oil of 10:1, and with 2 wt% of the catalyst after an hour. The optimal conditions determined with response surface methodology (RSM) when aiming for the lowest possible parameter values and a conversion of 95% or higher were a temperature of 40 °C, time of 1 h, 1-octanol to oil molar ratio at 8.11:1 and mass fraction of catalyst of 2.01%. Furthermore, post-synthesis and purification (>99%), the application properties of pure fatty acid octyl esters (FAOCE) and their blends with mineral diesel and 1-octanol were evaluated. Standardized tests were conducted to measure the fuel’s density, viscosity, cold filter plugging point (CFPP), and lubricity. The addition of FAOCE in mineral diesel increases its density, viscosity, and lubricity. When added up to 20 vol%, FAOCE did not have an influence on the blend’s CFPP value. Still, all the blend property values fell within the limits required by standard EN 590.
Provedenim istraživanjem priređeni su kompozitni materijali na osnovi poli(metil-metakrilata) i poli(metil-metakrilat-ko-dimetilaminoetil-metakrilata) s nanocelulozom u udjelu 1, 2,5 i 5 mas. %. ...Metodom ex situ iz otopine dobivena je homogena raspodjela nanopunila u polimernoj matrici. Kromatografijom isključenja po veličini ustanovljeno je da jaka smična sila primijenjena pri homogenizaciji uzrokuje pucanje najvećih molekula polimera i time blago smanjenje prosjeka molekulskih masa polimerne matrice. Veća staklišta kompozita u odnosu na čiste polimerne matrice i porast staklišta s povećanjem udjela punila potvrđuju homogenost raspodjele i kompatiblnost nanoceluloze s istraživanim metakrilatnim matricama. Dodavanjem nanoceluloze povećava se hidrofilnost materijala, što olakšava tisak i može pogodovati njihovoj primjeni kao ambalažnih materijala.
Nanofluidi kao medij za prijenos topline Blažic, Roko; Faraguna, Fabio; Vidović, Elvira ...
Kemija u industriji,
10/2019, Letnik:
68, Številka:
9-10
Journal Article
Recenzirano
Odprti dostop
U posljednjih 20 godina nanofluidi su privukli pažnju znanstvene zajednice te se broj radova na temu nanofluida tijekom godina znatno povećao. Povećana toplinska vodljivost fluida uslijed dodatka ...nanočestica osnovno je svojstvo koje je potaknulo intenzivno istraživanje nanofluida. S obzirom na to da u industriji uvijek postoji težnja poboljšanju učinkovitosti proizvodnih procesa, pa tako i procesa hlađenja procesnih struja, povećana toplinska vodljivost rashladnih fluida otvara mogućnosti za postizanje navedenog cilja. U ovom radu dan je pregled metoda priprave nanofluida te opis parametara koji utječu na njihovu toplinsku vodljivost. Dan je i osvrt na modele kojima se opisuje toplinska vodljivost nanofluida te pregled mogućih mehanizama koji doprinose povećanju njihove toplinske vodljivosti.
Nanofluids have attracted the attention of the scientific community during last twenty years and the number of papers on nanofluids has increased significantly as a result. The increased thermal conductivity of the fluid due to the addition of nanoparticles is a basic feature that has raised intensive research on nanofluids. Considering a permanent urge in the industry to improve efficiency of production processes, including the cooling streams of processes, the increased thermal conductivity of cooling fluids opens the possibility of achieving that goal.
This paper provides an overview of nanofluid preparation methods and a description of parameters that affect the thermal conductivity of nanofluids. Also, the overviews of few models that describe the thermal conductivity of nanofluids as well as of possible mechanisms that contribute to the increase in thermal conductivity of nanofluids are given.
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Miscibility and rheological properties like kinematic viscosity at 40°C and 100°C, viscosity index, shear stability and pour point for solutions of polyolefin copolymer (OCP) and ...terpolymer poly(styrene-co-dodecyl methacrylate-co-octadecyl methacrylate) (PSAMA) in lubricating mineral oil are examined. Additives show complementary effect in which OCP increases solution viscosity while PSAMA increases viscosity index and lowers pour point. Repulsive interactions of OCP/PSAMA in oil solutions were determined by Krigbaum–Wall and Catsiff–Hewett models. Calculations employing the group contribution approach of Coleman, Graf and Painter confirmed immiscibility (Λ12>0, ΔGM>0) of OCP/PSAMA blends. The obtained results give the prospects for lubricant formulations with mixed polymeric additives as well as for lubricant handling in order to avoid separation of copolymers in solution.
A new synthetic approach is presented for the synthesis of naphthoxazoles and fused heterobenzoxazoles. The starting 5-(aryl/furyl/thienyl/pyridyl ethenyl)oxazoles are prepared from the corresponding ...α,β-unsaturated aldehydes using Van Leusen reagent in very good yields and are transformed into naphthoxazoles and fused heterobenzoxazoles on irradiation under aerobic conditions and in the presence of iodine.
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