Assembly, characterization of Ag nanoparticles in P(AAm-co-NVP)/CS semi-IPN, and swelling of the resulting composite hydrogels

Silver nanoparticles (AgNPs) with controlled size and size distribution were prepared by an in situ chemical reduction route based on a microreactor template composed of poly(acrylamide-co-N-vinylpyrrolidone)/chitosan semi-interpenetrating network hydrogels, P(AAm-co-NVP)/CS semi-IPN, in the presence of sodium hypophosphite. The characterization of structures and morphologies of the as-fabricated P(AAm-co-NVP)/CS–Ag nanocomposite hydrogels was conducted on a Fourier transformation infrared spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), and UV–vis spectrometer. The effect of various component proportions of the reactants on formation of AgNPs and swelling of the resulting P(AAm-co-NVP)/CS–Ag nanocomposite hydrogels was investigated. The experimental results indicated that the Ag grains were uniformly dispersed within P(AAm-co-NVP)/CS hydrogel networks in a spherical shape, and were stabilized by the semi-IPN structure and a complexation and/or electrostatic interaction between Ag⁺ cations and chemical functional groups, such as –OH, –CONH₂, –NH₂ or –C=O based on the semi-IPN structure reactor templates. The size of the majority of AgNPs ranges from 12 to 25 nm, depending on the three-network templates, the presence of functional groups as well as feed ratios of N-vinylpyrrolidone, acrylamide, and chitosan. Thermogravimetric analysis (TGA) provides the stability of the resulting nanocomposite hydrogels. The nanocomposite hydrogels demonstrate reduced swelling in comparison with the P(AAm-co-NVP)/CS ones. The kinetics modeling confirms that transport mechanism of the samples follows anomalous diffusion mode, and the kinetic parameters vary with the component ratios, and the maximal theoretical water volume S _∞ is well in agreement with the experimental values.     

Assembly, characterization and swelling kinetics of Ag nanoparticles in PDMAA-g-PVA hydrogel networks

A series of poly(N,N-dimethylacrylamide)-g-poly(vinyl alcohol) (PDMAA-g-PVA) graft hydrogel networks were designed and prepared via a free radical polymerization route initiated by a PVA-(NH₄)₂Ce(NO₃)₆ redox reaction. Silver nanoparticles with high stability and good distribution behavior have been self-assembled by using these hydrogel networks as a nanoreactor and in situ reducing system. Meanwhile the PDMAA or PVA chains can efficiently act as stabilizing agents for the Ag nanoparticles in that Ag⁺ would form complex via oxygen atom and nitrogen atom, and form weak coordination bonds, thus astricting Ag⁺. The structure of the PDMAA-g-PVA/Ag was characterized by a Fourier transform infrared spectroscope (FTIR). The morphologies of pure PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones were observed by a scanning electron microscopy (SEM) and transmission electron microscope (TEM). TEM micrographs revealed the presence of nearly spherical and well-separated Ag nanoparticles with diameters ranging from 10 to 20 nm, depending on their reduction routes. XRD results showed all relevant Bragg's reflection for crystal structure of Ag nanoparticles. UV–vis studies apparently showed the characteristic surface plasmon band at 410–440 nm for the existence of Ag nanoparticles within the hydrogel matrix. The swelling kinetics demonstrated that the transport mechanism belongs to non-Fickian mode for the PDMAA-g-PVA hydrogels and PDMAA-g-PVA/Ag nanocomposite ones. With increasing the DMAA proportion, the r₀ and S_∞ are enhanced for each system. The assembly of Ag nanoparticles and the swelling behavior may be controlled and modulated by means of the compositional ratios of PVA to DMAA and reduction systems.     

长庆油田三层分采工艺技术探索与实践

长庆油田纵向含油层系多,部分层系局部叠合,为有效解决多层系开发过程中笼统合采油井层间干扰矛盾,最大程度发挥各产层产能,研究形成了防气式分采泵两层分采主体工艺技术,现场试验78口井,平均单井产量提高0.58t/d,但对于油井三层分采,该技术却无能为力。在油井两层分采技术原理基础上,文章创新提出了“产层单向过流（进入油管）、油管内层间产液桥式多级过流、 封隔器层间封隔、普通抽油泵举升”三层分采技术思路,研发成功桥式分采器关键装置,设计了“桥式分采器+Y211封隔器+Y111封隔器N普通管式抽油泵”三层分采工艺技术管柱结构,并在长庆油田首次成功开展了,口井三层分采试验,效果明显,为长庆油田多层系开发区块油井多层分采提供了新的技术手段。     

Novel temperature and pH dual-sensitive PNIPAM/CMCS/MWCNT semi-IPN nanohybrid hydrogels: Synthesis,characterization, and DOX drug release

Novel poly(N-isopropylacrylamide)/carboxymethyl chitosan/multiwalled carbon nanotube semi-interpenetrating nanohybrid hydrogels were prepared, and the chemical structure and morphology were characterized. The prepared hydrogels showed temperature and pH dual-responsiveness, and the one containing multiwalled carbon nanotubes (MWCNTs)–COOH possessed high maximal swelling ratios. The phase transition produced at pH of 6.8–7.4 and temperature of 35–40°C, hinging on the system compositions and charge ratios. The hydrogels were used to load hydrophilic anticancer drug, with high entrapped efficiency of about 44%. The drug release changed with temperature, pH, and MWCNTs–COOH contents. The designed hydrogels can be used for site-specific target delivery of protein or hydrophilic anticancer drug.     

Assembly of Cu nanoparticles in a polyacrylamide grafted poly(vinyl alcohol) copolymer matrix and vapor-induced response

A vapor-sensitive electroconductive film was designed and assembled by inserting Cu²⁺ particles into a polyacrylamide grafted poly(vinyl alcohol) (PAM-g-PVA) in virtue of a complexation between Cu²⁺ and PVA even PAM, as well as the establishment of inter- and intramolecular attractions between polymer matrices, which were in turn reduced into Cu nanoparticles by sodium hypophosphite as a reducing agent. The PAM-g-PVA graft copolymer was prepared via a simple free radical polymerization reaction initiated by a redox reaction. The resistance responsiveness of the film samples to various organic vapor surroundings was investigated. The responsive magnitude, response time and recovery properties depend on the molecular weight of the graft polymer or the PAM chain length and initial resistances of the film samples or Cu particle contents upon exposed to ether and petroleum ether vapor, etc. The structure and morphologies of the PAM-g-PVA/Cu were characterized by a Fourier transform infrared spectroscope and a transmission electron microscope. The response mechanism of the PAM-g-PVA/Cu films to solvent vapors was accounted for by a swelling theory and an interaction between solvent vapor molecules and nanocomposites as well as the type and strength of interaction that each solvent vapor exhibits on the material.     

Fabrication, characterization and vapor-induced electroresponsive behavior of P(St-alt-MA)/MWCNT conductive nanocomposite films

Novel electroconductive nanocomposites were prepared by an in situ polymerization avenue based on poly(styrene-alt-maleic anhydride) (P(St-alt-MA)), multi-walled carbon nanotubes (MWCNT) or hydroxyl-functionalized MWCNT (MWCNT–OH). Vapor sensing films with intensive response to polar solvent vapors were assembled through an covalent or non-covalent interaction between MWCNT or MWCNT–OH and P(St-alt-MA), as demonstrated by a Raman, infrared spectroscopy, scanning and transmission electron microscopes. The films gave an expeditious response, favorable reversibility and reproducibility, which were predominately controlled by an expansion effect and an interaction among carbon nanotubes, copolymers and solvent molecules.     

pH-Sensitive biodegradable PMAA2-b-PLA-b-PMAA2 H-type multiblock copolymer micelles: synthesis,characterization, and drug release applications

pH-Sensitive biodegradable polymethacrylic acid-block-polylactic acid-block-polymethacrylic acid (PMAA₂-b-PLA-b-PMAA₂) H-type multiblock copolymers were synthesized by atom transfer radical polymerization. The copolymer structure and molecular weight were characterized by FT-IR, ¹H NMR, and gel permeation chromatography. The physicochemical characterization revealed that the copolymers could spontaneously form spherical core–shell micelles in aqueous solution, with critical aggregation concentration of about 19.7–32.5 mg L^?1 and the hydrodynamic diameters below 200 nm. Zeta potentials measurements disclosed that the copolymer micelles were negatively charged due to ionized carboxyl groups in various PBS solutions. The H-type block copolymer micelles exhibited pH- sensitivity, as expected; and the hydrophobic anticancer drugs, 10-hydroxycamptothecin, and paclitaxel, had faster release rate in PBS solution of pH 5.6–7.4 than in PBS of pH 1.4, which was important for applications in the therapy of small intestine cancers. The copolymer micelle aggregates were proved to be biodegradable, and the degradation rates changed with copolymer compositions and environmental media. The micelle drug formulation indicated pH-dependent cytotoxicity and was thus capable of effectively killing the intestinal cells while avoiding doing harm to stomach. The biodegradable pH-sensitive PMAA₂-b-PLA-b-PMAA₂ H-type copolymer micelles can be used as water-insoluble drug targeting release carriers for targeted treatment of intestine cancers.