Long-lived and unstable modes of Brownian suspensions in microchannels

We investigate the stability of the pressure-driven, low-Reynolds flow of Brownian suspensions with spherical particles in microchannels. We find two general families of stable/unstable modes: (i) degenerate modes with symmetric and anti-symmetric patterns; (ii) single modes that are either symmetric or anti-symmetric. The concentration profiles of degenerate modes have strong peaks near the channel walls, while single modes diminish there. Once excited, both families would be detectable through high-speed imaging. We find that unstable modes occur in concentrated suspensions whose velocity profiles are sufficiently flattened near the channel centreline. The patterns of growing unstable modes suggest that they are triggered due to Brownian migration of particles between the central bulk that moves with an almost constant velocity, and highly-sheared low-velocity region near the wall. Modes are amplified because shear-induced diffusion cannot efficiently disperse particles from the cavities of the perturbed velocity field.Comment: 11 pages, accepted for publication in Journal of Fluid Mechanic

Structure–Properties Relationship in Waterborne Poly(Urethane-Urea)s Synthesized with Dimethylolpropionic Acid (DMPA) Internal Emulsifier Added before, during and after Prepolymer Formation

Dimethylolpropionic acid (DMPA) internal emulsifier has been added before, during and after prepolymer formation in the synthesis of waterborne poly(urethane-urea)s (PUDs) and their structure–properties relationships have been assessed. PUDs were characterized by pH, viscosity and particle size measurements, and the structure of the poly(urethane-urea) (PU) films was assessed by infra-red spectroscopy, differential scanning calorimetry, X-ray diffraction, thermal gravimetric analysis, plate–plate rheology and dynamic mechanical thermal analysis. The adhesion properties of the PUDs were measured by cross-hatch adhesion and T-peel test. The lowest pH value and the highest mean particle size were found in the PUD made by adding DMPA after prepolymer formation, all PUDs showed relatively ample mono-modal particle size distributions. The highest viscosity and noticeable shear thinning were obtained in the PUD made by adding DMPA during prepolymer formation. Depending on the stage of addition of DMPA, the length of the prepolymer varied and the PU films showed different degree of micro-phase separation. Because the shortest prepolymer was formed in the PU made with DMPA added before prepolymer, this PU film showed the lowest storage moduli and early melting indicating higher degree of micro-phase separation. The highest storage modulus, later melting, higher temperature and lower modulus at the cross between the storage and loss moduli corresponded to the PU made by adding DMPA after prepolymer formation, because the longer prepolymer produced during synthesis. The lowest thermal stability corresponded to the PU made by adding DMPA during prepolymer formation and the structures of all PU films were dominated by the soft domains, the main structural differences derived from the hard domains. Whereas DMPA-isophorone diisocyanate (IPDI) urethane and urea hard domains were created in the PU film made by adding DMPA during prepolymer formation, the other PU films showed DMPA-IPDI, polyester-IPDI and two different DMPA-IPDI-polyester hard domains. Finally, the adhesion properties of the PUDs and PU coatings were excellent and they were not influenced by the structural differences caused by adding DMPA in different stages of the synthesis

Novel nano molten salt tetra-2,3-pyridiniumporphyrazinato-oxo-vanadium tricyanomethanide as a vanadium surface-free phthalocyanine catalyst: Application to Strecker synthesis of α-aminonitrile derivatives

Efficient and recyclable novel nano tetra-2,3-pyridiniumporphyrazinato-oxo-vanadium tricyanomethanide, {[VO(TPPA)][C(CN)3]4}, as a vanadium surface-free phthalocyanine-based molten salt catalyst was successfully designed, produced and used for the Strecker synthesis of α-aminonitrile derivatives through a one-pot three-component reaction between aromatic aldehydes, trimethylsilyl cyanide and aniline derivatives under neat conditions at 50 °C. This catalyst was well characterized using Fourier transform infrared, UV–visible, X-ray photoelectron and energy-dispersive X-ray spectroscopies, X-ray diffraction, scanning and high-resolution transmission electron microscopies, inductively coupled plasma mass spectrometry and thermogravimetric analysis. The catalyst can be simply recovered and reused several times without significant loss of catalytic activity.We thank Bu‐Ali Sina University, Nahavand University, the Iran National Science Foundation (INSF, grant no. 95820271), the National Elites Foundation, the University of Alicante (VIGROB‐173) and the Spanish Ministerio de Economíay Competitividad (CTQ2015‐66624‐P) for financial support to our research groups

1H-imidazol-3-ium tricyanomethanide {[HIM]C(CN)3} as a nanostructured molten salt catalyst: application to the synthesis of pyrano[4,3‐b]pyrans

In this work, we have synthesized a novel nanostructured molten salt, 1H-imidazol-3-ium tricyanomethanide {[HIMI]C(CN)3} (1), as an efficient and green protocol-compatible catalyst. This new molten salt has been fully characterized by different analytical techniques, such as FT-IR, 1HNMR, 13CNMR, thermal gravimetric analysis, derivative thermal gravimetric analysis, differential thermal analysis, X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. Additionally, the catalytic activity of {[HIMI]C(CN)3} (1, 2 mol%) has been tested in a three-component domino Knoevenagel condensation reaction. A range of structurally diverse aromatic aldehydes (2a–p), malononitrile (3), and 4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one (4) are tolerated for the synthesis of 2-amino-7-methyl-5-oxo-4-aryl-4,5-dihydropyrano[4,3-b]pyran-3-carbonitrile derivatives (5a–p) under neat conditions at 50 °C. The obtained results have demonstrated that catalyst 1 shows interesting catalytic properties, such as clean reaction profile, cost-effectiveness, and green conditions. Importantly, the aforementioned catalyst is thermally stable with a 171 °C melting point not showing any significant loss in catalytic activity after 7 reaction cycles.We thank Bu-Ali Sina University, Iran National Science Foundation (INSF) (Grant of Allameh Tabataba’i’s Award, Grant Number BN093), National Elites Foundation, University of Alicante (VIGROB-173), and the Spanish Ministerio de Economíay Competitividad (CTQ2015-66624-P) for financial support to our research groups

Palladium supported on bis(indolyl)methane functionalized magnetite nanoparticles as an efficient catalyst for copper-free Sonogashira-Hagihara reaction

A novel heterogeneous catalyst based on palladium nanoparticles supported on 3,3′-bisindolyl(4-hydroxyphenyl)methane functionalized magnetite (Fe3O4) nanoparticles was synthesized, characterized and used as catalyst for Sonogashira-Hagihara reaction. The alkynylation of a variety of aryl iodides and aryl bromides with terminal alkynes was carried out at 60 °C under copper and phosphane-free conditions using N,N-dimethyl acetamide as solvent, DABCO as base and low Pd loadings (0.18 mol%) under air. In the case of aryl chlorides, the reaction was carried out at 120 °C in the presence of tetra-n-butylammonium bromide (TBAB) and 0.36 mol% of Pd catalyst. The heterogeneous palladium catalyst introduced in this study is recoverable by an external magnet and it can be used for seven consecutive runs without a significant loss in catalytic activity.The authors thank Institute for Advanced Studies in Basic Sciences (IASBS) Research Council and Iran National Science Foundation (INSF-Grant number: 94010666) for financial support of this work. C. Nájera is also thankful to The Spanish Ministerio de Economia y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC), FEDER, the Generalitat Valenciana (PROMETEOII/2014/017) and the University of Alicante for financial support

Synthesis and application of chitosan supported vanadium oxo in the synthesis of 1,4-dihydropyridines and 2,4,6-triarylpyridines via anomeric based oxidation

Chitosan, as a biopolymer, exhibits a strong affinity for complexation with suitable metal ions. Thus, it has received increased attention for the preparation of stable bioorganic–inorganic hybrid heterogeneous catalysts. Herein, a novel chitosan based vanadium oxo (ChVO) catalyst was prepared and fully characterized by several techniques such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), derivative thermal gravimetric (DTG), differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). The synthesized catalyst has been successfully used as a reusable catalyst in the synthesis of dihydropyridines and triarylpyridines.We thank Bu-Ali Sina University, Nahavand University, the Iran National Science Foundation (INSF) (Grant No: 95831207) and the National Elites Foundation for financial support of our research group

Novel magnetic nanoparticles with ionic liquid tags as a reusable catalyst in the synthesis of polyhydroquinolines

In this study, we have introduced {Fe3O4@SiO2@(CH2)3Im}C(NO2)3 as a novel and heterogeneous reusable catalyst for the four component preparation of polyhydroquinoline derivatives under mild and eco-friendly reaction conditions. The structural confirmation of the novel heterogeneous reusable promoter was fully made using FT-IR, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS) elemental mapping analysis, high resolution transmission electron microscopy (HRTEM), thermogravimetry (TG), derivative thermal gravimetric (DTG), differential thermal (DTA) and vibrating sample magnetometer (VSM) analyses. The nanomagnetic heterogeneous catalyst was successfully applied for the synthesis of polyhydroquinoline derivatives via a four component condensation of a good range of aryl aldehydes, dimedone, ethyl acetoacetate or methyl acetoacetate as a β-ketoester, and ammonium acetate as a nitrogen source under solvent free conditions. Moreover, experimental evidence has demonstrated that {Fe3O4@SiO2@(CH2)3Im}C(NO2)3 could act as a recoverable nanomagnetic and reusable catalyst without any considerable drop in the yield and the reaction time for at least eight times.We thank the Bu-Ali Sina University, the Iran National Science Foundation (INSF) (Allameh Tabataba'i's Award, Grant Number BN093), the University of Alicante (VIGROB-173), and the Spanish Ministerio de Economía y Competitividad (CTQ2015-66624-P) for financial support to our research groups

An efficient catalytic method for the synthesis of pyrido[2,3-d]pyrimidines as biologically drug candidates by using novel magnetic nanoparticles as a reusable catalyst

A convenient method for the synthesis of pyrido[2,3-d]pyrimidines by using the novel nano-magnetic silica-bonded S-sulfonic acid[Fe3O4@SiO2@(CH2)3S–SO3H] as an efficient and recyclable catalyst under neat conditions is described. The major advantages of the present methodology are high yield, short reaction time, and reusability of the catalyst. Furthermore, the nano-magnetic silica-bonded S-sulfonic acid was fully characterized by using various techniques such as FT-IR, TG/DTG, DTA, EDX, μXRF, XRD, HRTEM, SEM, SEM elemental mapping, XPS, and N2 physisorption. The results obtained from this research support the idea of rational design, synthesis, and applications of task-specific and reusable catalysts for the preparation of various polynitrogenated heterocyclic compounds containing 1,4-dihydropyridine moieties.We thank Bu‐Ali Sina University, Iran National Science Foundation (INSF) (Grant Number: 940124), National Elites Foundation, University of Alicante (VIGROB‐173, UAUSTI16‐03), and the Spanish Ministerio de Economía y Competitividad (CTQ2015‐66624‐P) for financial support to our research groups