Dynamic rheology studies of in situ polymerization process of polyacrylamide–cellulose nanocrystal composite hydrogels

A series of dynamic small-amplitude oscillatory shear experiments for in situ polymerization process of polyacrylamide–cellulose nanocrystal (PAM–CNC) nanocomposite hydrogels were performed to investigate the relationship between rheological properties and synthesis parameters including chemical cross-linker concentration, polymerization temperature, initiator concentration, and CNC aspect ratios. The results showed that CNCs accelerated the onset of gelation (t _onset) and acted as a multifunctional cross-linker during the gelation reaction. The composite hydrogels exhibited enhanced steady-state elastic modulus ( G_￥￠ ) \left( {G_\infty^\prime } \right) and plateau loss factor (tanδ) compared to these of the pure PAM hydrogels, indicating that adding CNCs not only reinforced but also toughened PAM hydrogels. ( G_￥￠ ) \left( {G_\infty^\prime } \right) and the effective network junction density (N) increased with increased cross-linker concentration, polymerization temperature, and CNC aspect ratios, but decreased with increased initiator concentration. The changes of plateau tanδ were opposite to that of G_￥￠ G_\infty^\prime . The sol–gel transition kinetics of PAM–CNC hydrogels accelerated with increased cross-linker concentration and polymerization temperature and, however, reached optimization at 0.25 wt% of initiator concentration. CNCs with lower aspect ratios promoted t _onset and the sol–gel transition of PAM–CNC hydrogels, suggesting the fact that CNCs with lower aspect ratios further facilitated the formation of network of PAM–CNC nanocomposite hydrogels.     

Synthesis and characterization of chitosan–poly(acrylamide–co-acrylic acid) magnetic nanocomposite hydrogels for use in catalysis

A novel hydrogel based on chitosan–poly(acrylamide-co-acrylic acid) (CAA) with different formulations were synthesized by the effect of gamma radiation. The magnetic CAA hydrogels were also synthesized and characterized by using different techniques, e.g., TEM and XRD. The prepared hydrogels and magnetic hydrogel nanocomposite were utilized for in situ cobalt nanoparticle preparation and employed as a reaction media in catalytic reduction of 2-nitrophenol (2-NP), to 2-aminophenol (2-AP). The experimental parameters that affect the reduction rates such as temperature and amount of catalyst were also, investigated.     

Preparation and characterization of polyacrylamide–silver nanocomposites

Polyacrylamide–silver nanocomposites are successfully prepared by irradiating the aqueous solution of AgNO₃ and acrylamide monomer with ⁶⁰Co γ-ray. The composites are found to contain nanometer silver particles with a narrow size distribution and a homogeneous dispersion. The existing of isopropanol (as a hydroxyl radical scavenger and chain transfer agent) in system affects the properties of both the dispersed phase and matrix of the nanocomposites. The fast-formed polymer chains probably play a key role in preventing the aggregation of silver particles which are reduced later.     

Synthesis and characterization of cuprous selenide nanocrystals at room temperature

A simple method has been developed to prepare cuprous selenide nanocrystals by the reaction of copper nitrate trihydrate with selenium and sodium mercaptoacetate in aqueous ammonia system. Cu_2Se nanocrystals were characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), electron diffraction (ED), fluorescence spectrum and ultraviolet-visible absorption spectrum. Cu_2Se nanocrystals showed berzelianite structure with 20-40 nm in length and 10-20 nm in width. A possible mechanism is also discussed.     

Porous electrospun nanocomposite mats based on chitosan–cellulose nanocrystals for wound dressing: effect of surface characteristics of nanocrystals

Randomly oriented fiber mats of chitosan–polyethylene oxide matrix reinforced with cellulose nanocrystals (CNCs) were prepared by electrospinning technique. The cellulose nanocrystals used were isolated using hydrochloric acid (CNC_HCl) or sulphuric acid (\({\text{CNC}}_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}\)) and the concentration of CNCs was 50 wt% in the electrospun mats. The surface characteristics of the nanocrystals were found to affect the dispersion, viscosity, conductivity and zeta-potential of the respective spinning solutions and resulted in better spinnability, homogeneity as well as crosslinking of CNC_HCl based nanocomposite fiber mats compared to \({\text{CNC}}_{{{\text{H}}_{ 2} {\text{SO}}_{ 4} }}\) ones. The microscopy studies showed that the diameter of the electrospun fibers decreased with the inclusion of both types of nanocrystals and that crosslinking decreased the porosity of the mats. The tensile strength and tensile modulus of the mats increased with the addition of nanocrystals and increased further for the CNC_HCl based mats (58 MPa, 3.1 GPa) after crosslinking. The as-spun CNC_HCl based mats had average pore diameters of 1.6 μm and porosity of 38 %. The water vapor permeability and the O₂/CO₂ transmission increased with the addition of CNC_HCl. The used nanocrystals as well as electrospun mats showed non-cytotoxic impact on adipose derived stem cells (ASCs), which was considered favorable for wound dressing.     

Synthesis and characterization of alkyl cellulose ω-carboxyesters for amorphous solid dispersion

Poor drug solubility and consequently poor bioavailability are major impediments to new drug innovation, and they limit the performance of many existing drugs. In recent years amorphous solid dispersion (ASD) has emerged as one of the most effective approaches for enhancing drug solution concentration, and thereby bioavailability, including in many marketed drug formulations. Recently efforts have been under way in several laboratories to design new ASD polymers, rather than relying on polymers that are already in FDA-approved formulations, but were not designed as ASD polymers. We describe here the design and synthesis of a new class of polymers, alkyl cellulose ω-carboxyesters, for ASD formulation. We synthesize these polymers by reaction of cellulose alkyl ethers with monoprotected (benzyl ester), monofunctional long chain acid chlorides, followed by protecting group removal using mild hydrogenolysis to form the target alkyl cellulose ω-carboxyalkanoate. These new amphiphilic polymers have high glass transition temperatures (T_g), tunable carboxyl content for controlling release pH and drug-polymer interactions, and certain members of this new group of amphiphilic cellulose ether esters are shown to be successful at forming ASDs with the important model drug ritonavir. These ASDs efficiently release ritonavir at small intestine pH, creating the maximum attainable amorphous solubility (20 μg/mL), and maintaining it for a time period substantially greater than the normal residence time in the absorptive region of the stomach and small intestine. Members of this new class of alkyl cellulose ω-carboxyester amphiphiles show significant potential as ASD polymers for enhancing oral bioavailability of otherwise poorly soluble drugs.     

Preparation and characterization of rigid polyurethane–polyglycerol nanocomposite foams

This work reports on the preparation of polyurethane–polyisocyanurate (PUR–PIR) foams containing different polyglycerols and layered silicate nanoclays. The rigid polyurethane foams were obtained in a laboratory scale, in a single step method, from a two-component system with a NCO to OH groups ratio equal to two. The reaction mixture consisted of the proper amounts of a commercial oligoetherpolyol, polyglycerol, catalysts, water, nanofiller, and polymeric diphenylmethane diisocyanate. The obtained foams containing 6% of one of three types of montmorillonite (MMT) (Cloisite 30B, Laponite RD, Bentonite) were characterized in terms of their structure, density, brittleness, compressive strength and thermal stability. The nanocomposite foams showed a higher number of cells with a smaller cell size in the presence of MMT, while the foams modified with nanofiller Cloisite 30B presented the best compressive strength and the best fire resistance.     

Synthesis and characterization of cobalt acrylate–melamine co-crystals

A new co-crystal of tetraaqua acrylato cobalt (II) complex and melamine, [Co(acr)₂(H₂O)₄]·4MA·2DMF (acr = acrylate, MA = melamine, DMF = dimethylformamide), has been synthesized and characterized using IR, UV-Vis, thermogravimetric analysis, and single-crystal X-ray diffraction. The complex contains discrete unities of [Co(acr)₂(H₂O)₄], melamine, and DMF linked by hydrogen bonds. Investigations evidenced that Co(II) has an octahedral stereochemistry and both acrylate ions present unidentate coordination mode. Thermal decomposition occurs in four steps and denotes that melamine is lost at high temperatures, and this indicates a greater stability that may be associated with the presence of hydrogen bonds network.

     

Synthesis,characterization and magnetic properties of supramolecular metal–organic complexes constructed from flexible–rigid mixed ligands

Two new supramolecular metal–organic complexes have been synthesized under hydrothermal conditions. Complex 1 exhibits a three-dimensional supramolecular network, constructed from [Co₂(H₃BPTC)₂(phen)₂] (H₄BPTC = 3,3′4,4′-benzophenone tetracarboxylate acid, phen = 1,10-phenanthroline) discrete units. Complex 2 similarly exhibits discrete [Cu₂(DPA)₂(bipy)₂(H₂O)₂] (DPA = 1,1′-biphenyl-2,2′-dicarboxylate acid, bipy = 2,2′-bipyridine) units, which are linked to form a three-dimensional supramolecular network through π–π interactions. It is interesting that during the synthesis of complex 1, the H₄BPTC ligands undergo partial decomposition to give 1,2,4-benzenetricarboxylate (H₃BTC) ligands, which react with Co to form [Co₃(BTC)₂]_n (3). Complex 3 shows a three-dimensional covalent network. The magnetic properties of complexes 1 and 2 have been studied.     

Synthesis and characterization of sol–gel alumina nanofibers

Abstract Alumina nanofibers of high aspect ratio with surface area of >300 m² g⁻¹ has been prepared successfully in bulk quantities by the sol–gel method. The synthesis parameters including the binary water–alcohol solvent system to aluminium isopropoxide ratio, pH, type of solvent and aging temperature affect the uniformity and formation of nanofibers. It is proposed that alumina nanofibers were formed by the curling of the nanosheets upon condensation after the hydrolysis. The phase evolution of alumina nanofibers from pseudoboehmite to α phase has been shown by XRD and FTIR. ²⁷Al NMR investigations show that the Al atoms are six and four coordinated. The morphology of the alumina nanofibers does not change much as the calcination temperature was increased. In addition, the average pore size increases and the BET surface area decreases as a function of calcination temperature. The thermal behavior of alumina nanofibers was investigated by TGA. Graphical Abstract      

Thermal characterization of bacterial cellulose–phosphate composite membranes

Cellulose–phosphate composite membranes have been prepared from bacterial cellulose membranes (BC) and sodium polyphosphate solution. The structure and thermal behavior of the new composites were evaluated by X-ray diffraction (XRD), ³¹P-nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetry (TG) and thermomechanical analysis (TMA). From XRD analyses the Iα and Iβ cellulose crystalline phases were identified together with crystalline sodium phosphate that covers the cellulose microfibrils as revealed by SEM. ³¹P NMR spectra show peaks assigned to Q⁰ and Q¹ phosphate structures to be compared to the Q² units that characterize the precursor polyphosphate. Glass transition temperature, T _g, obtained from TMA curves and thermal stability obtained from TG and DSC measurements, were observed to be dependent on the phosphate content.     

Thermo-sensitive chitosan–cellulose derivative hydrogels: swelling behaviour and morphologic studies

Hydrogels are three-dimensional, hydrophilic, polymer networks that are able to imbibe large amounts of water or biological fluids, while maintaining their dimensional stability. The polymer binding might be achieved by chemical or physical interactions. Physical crosslinking of a polymer to form its hydrogel, might be accomplished either by casting-solvent evaporation (SC) method or by freeze–thaw (FT) technique. The physical hydrogels, especially the ones based on natural biopolymers, like polysaccharides, are being widely used in industry and medicine due to their favourable properties: biocompatibility; biodegradability; low toxicity and eco-friendly characteristics. Polysaccharides, like chitosan (CH) and (hydroxypropyl)methyl cellulose (HPMC) have gained great attention due to its stimuli sensitive properties: pH and temperature responsiveness, respectively. Thus, within this work we have developed physically crosslinked CH:HPMC hydrogel films, using both SC and FT techniques. The attained CH:HPMC membranes were evaluated in terms of their swelling, thermal (low critical solution temperature—LCST), structural (attenuated total reflectance Fourier transform infrared spectroscopy) and morphological (scanning electron microscopy and atomic force microscopy) properties. According to these results, the developed membranes exhibit a good miscibility between the two component biopolymers. Moreover, the CH:HPMC membranes exhibit a high swelling capacity (SW_FT = 1,172 and SW_SC = 7,323), a low surface roughness (Sq = 5.6–9.5 nm) and an elevated LCST (LCST = 85.2–87.5 °C). The stimuli sensitive behaviour makes hydrogels appealing for the design of smart devices applicable in a variety of technological fields. In our particular case, we envisage the application of such materials as active substances (moisturisers, antiperspirants and scents) delivers, into textile substrates in a controlled manner.     

Development of flexible zinc–air battery with nanocomposite electrodes and a novel separator

In this paper, we present the development of flexible zinc–air battery. Multiwalled carbon nanotubes(MWCNTs) were added into electrodes to improve their performance. It was found that MWCNTs were effective conductive additive in anode as they bridged the zinc particles. Poly(3,4-ethylenedioxythiophene)polystyrene sulfonate(PEDOT:PSS) was applied as a co-binder to enhance both the conductivity and flexibility. A poly(acrylic acid)(PAA) and polyvinyl alcohol(PVA) coated paper separator was used to enhance the battery performance where the PVP–PAA layer facilitated electrolyte storage. The batteries remained functional under bending conditions and after bending. Multiple design optimizations were also carried out for storage and performance purposes.     

Synthesis and characterization of magnetic nanoparticles

Magnetic nanoparticles with average diameter in the range of 6.4-8.3 nni have been synthesized by a chemical co-precipitation of Fe(Ⅱ)and Fe(Ⅲ)salts in 1.5 M NH4OH solution.The size of the magnetic particles is dependent on both temperature and the ionic strength of the iron ion solutions.The magnetic particles formed at higher temperature or lower ionic strength were slightly larger than those formed at lower temperature or higher ionic strength respectively.In spite of the different reaction conditions,all the resultant nanoparticles are nearly spherical and have a similar crystalline structure.At 300 K,such prepared nanoparticles are superparam-agnetic.The saturation magnetizations for 7.8 and 6.4 nm particles are 71 and 63 emu/g respectively,which are only ~ 20-30% less than the saturation magnetization(90 emu/g)of bulk Fe3O4 Our results indicated that a control of the reaction conditions could be used to tailor the size of magnetic nanoparticles in free precipitation.     

Synthesis and characterization of new hybrid inorganic–organic polymer nanocomposite as efficient catalyst for oxidative desulfurization of real fuel

Sulfur-containing compounds are responsible for much air pollution, and therefore eliminating these compounds is of importance. Herein, a hybrid organic–inorganic recyclable nanocatalyst (TBA-PW₁₁Ni@PANI) was synthesized successfully to investigate its effects on the catalytic oxidative desulfurization (CODS) process of real gasoline/model fuel. To this end, the Keggin-based mono-lacunary polyoxometalate [PW₁₁NiO₃₉] was prepared and modified with quaternary cation tetrabutylammonium (TBA). Then, this was further immobilized on polyaniline (PANI) via the sol–gel method. The synthesized nanocomposite was characterized using various techniques. The high dispersion of polyoxometalate on PANI was confirmed. Also, it was found that the crystalline structure remained unaltered after immobilization. In addition, the effects of various parameters such as dosage and temperature on the CODS of model fuel in the presence of H₂O₂–acetic acid (1:2 v/v) were studied in detail. Moreover, the kinetics of the CODS process was also studied and a mechanism proposed. According to the results, TBA-PW₁₁Ni@PANI showed an efficiency of up to 97% with 0.1 g at 35°C (optimum values) which implies its good catalytic functionality in the CODS process. Finally, the TBA-PW₁₁Ni@PANI catalyst displayed long-term stability and good reusability after five runs.     

Synthesis of cellulose–metal nanoparticle composites: development and comparison of different protocols

Deposition of nanoparticles on the surface of a variety of materials is a subject of great interest due to their potential applications in electronic devices, sensing, catalysis and bio-medical sciences. In this context, we have explored and compared various methodologies to generate gold and silver nanoparticles on the surface of cellulose fibers. It was found that boiling of the cellulose fibers in alkaline solution of gold and silver salts led to the formation and immobilization of gold and silver nanoparticles. However, in case of lecithin treated and thiol-modified cellulose fibers, high temperature was not essentially required for the formation and deposition of nanoparticles on cellulose substrate. In both these cases, fairly uniform metal nanoparticles were obtained in good yields (~43 wt% gold loading in case of thiol modified cellulose fibers) at room temperature. Borohydride-reduction method resulted in relatively lower loading (~22 wt%) with a wide size distribution of gold and silver nanoparticles on cellulose fibers. All these nanoparticle–cellulose composites were thoroughly characterized using scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy, UV–visible spectroscopy, and elemental analyzer. Thiol modified cellulose–gold nanoparticle composites served as active catalysts in the reduction of 4-nitrophenol into 4-aminophenol.     

Synthesis and characterization of mesoporous Mn–Ni oxides for supercapacitors

Mesoporous Mn–Ni oxides with the chemical compositions of Mn_1-x Ni _x O _δ (x = 0, 0.2, and 0.4) were prepared by a solid-state reaction route, using manganese sulfate, nickel chloride, and potassium hydroxide as starting materials. The obtained Mn–Ni oxides, mainly consisting of the phases of α- and γ-MnO₂, presented irregular mesoporous agglomerates built from ultra-fine particles. Specific surface area of Mn_1–x Ni _x O _δ was 42.8, 59.6, and 84.5 m² g⁻¹ for x = 0, 0.2, and 0.4, respectively. Electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge/discharge in 6 mol L⁻¹ KOH electrolyte. Specific capacitances of Mn_1-x Ni _x O _δ were 343, 528, and 411 F g⁻¹ at a scan rate of 2 mV s⁻¹ for x = 0, 0.2, and 0.4, respectively, and decreased to 157, 183, and 130 F g⁻¹ with increasing scan rate to 100 mV s⁻¹, respectively. After 500 cycles at a current density of 1.24 A g⁻¹, the symmetrical Mn_1–x Ni _x O _δ capacitors delivered specific capacitances of 160, 250, and 132 F g⁻¹ for x = 0, 0.2, and 0.4, respectively, retaining about 82%, 89%, and 75% of their respective initial capacitances. The Mn_0.8Ni_0.2O _δ material showed better supercapacitive performance, which was promising for supercapacitor applications.     

Synthesis,characterization and spectroscopic study of riboflavin–molybdenum complex

A riboflavin–molybdenum [(RF)–Mo(V)] complex in powder form was synthesized and characterized by elemental analysis, UV–Vis, IR, NMR spectroscopy and X-ray diffraction. During the synthesis of this metal complex, another metal complex [Mo₂O₄(H₂O)₆]²⁺ was also synthesized and characterized. The results of X-ray diffraction study have revealed an orthorhombic cubic system for the RF–Mo complex. The steady state absorption and emission studies of RF and RF–Mo in hydrochloric acid (HCl) of varying pH were investigated. The steady state absorption with RF–Mo showed distinct changes in the absorption spectra of RF after complexation. The steady state emission results, consistent with prior reports showed fluorescence quenching in the aqueous solution of both RF and RF–Mo in HCl with the proton acting as a quencher. The Stern–Volmer constant observed was 108.79 and 98.68 for RF and RF–Mo, respectively. The binding constant for RF–Mo complex was found to be 1.201 × 10³ M⁻¹ at 298 K.