Xiangling Ji

Crystallization behavior of PCL in hybrid confined environment

Poly(epsilon -caprolactone) (PCL) and silica (SiO2) organic-inorganic hybrid materials have been synthesized by the sol-gel method. The crystallization behavior of PCL in silica networks has been investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The degree of PCL crystallinity in PCL/SiO2 hybrid networks reduces with increase of SiO2. PCL is in an amorphous state when the concentration of PCL is lower than 40wt% in the hybrid system. The melting point of PCL in the networks is lower than, but close to that of pure PCL. WAXD and SEM results show that the crystalline behavior of PCL in PCL/SiO2 hybrid system is strictly confined

Evaluation of Hydrophobic Polyvinyl-Alcohol Formaldehyde Sponges As Absorbents for Oil Spill

Macroporous materials are a class of absorbents used for oil spill cleanup. In this article, novel macroporous and hydrophobic polyvinyl formaldehyde (PVF-H) sponges were prepared by the reaction of stearoyl chloride with hydroxyl groups of hydrophilic PVF sponge at different temperatures. Attenuated total reflectance-infrared (ATR-IR) spectroscopy confirmed the successfully anchoring of hydrophobic stearoyl groups on the PVF networks. Scanning electron microscopy (SEM) images demonstrated that the as-prepared PVF-H had interconnected open-cell structures, and mercury intrusion porosimetry indicated that the average pore size ranged from 60 to 90 μm and porosity was greater than 94.8%. Such PVF-H sponges can absorb oil products effectively, such as toluene, n-hexane, kerosene, soybean oil, hydraulic oil, and crude oil up to 13.7 g·g(-1) to 56.6 g·g(-1), and this level of absorption was approximately 2-4 times higher than that absorbed by commercial polypropylene nonwoven mat. In low-viscosity oils, the samples can reach the saturated absorption amount only in 1 min, but in higher-viscosity oils, absorption equilibrium can be reached in 10 min. In a simulated oil slick system, these macroporous and hydrophobic sponges can still maintain high oil absorption capacities within the range of 14.4 g·g(-1) to 57.6 g·g(-1), whereas a relatively low absorption rate (approximately 20 min) indicated high absorption performance and excellent selectivity in the oil-water mixture. In addition, the absorbed oils were collected effectively only through a simple squeeze. The PVF-H sponges were subjected to 35 absorption-squeeze cycles and exhibited good reusability and 90% recovery for oils. The samples prepared at different temperatures differed in their absorption capacities to some extent. However, this new kind of macroporous and PVF-H sponges had excellent absorption performance on oil products.

Shape- and Size-Controlled Synthesis and Dependent Magnetic Properties of Nearly Monodisperse Mn3O4 Nanocrystals†

Manganese oxides have attracted considerable interest related to their potential for use in a wide range of applications, for example, high-density magnetic storage, catalysis, ion exchange, molecular adsorption, electrochemical materials, varistors, and solar-energy transformation. Understanding structural and magnetic properties of manganese oxides, and the correlation between these properties, provides a fundamental platform for extending their use in the above areas. From the manganese oxide series, Mn3O4 is well known to be an active catalyst in a variety of oxidation and reduction reactions, such as the decomposition of waste gases NOx, selective reduction of nitrobenzene, and so on. [3]

Phase Behavior of Poly(sulfobetaine methacrylate)-Grafted Silica Nanoparticles and Their Stability in Protein Solutions

Biocompatible and zwitterionic poly(sulfobetaine methacrylate) (PSBMA) was grafted onto the surface of initiator-modified silica nanoparticles via surface-initiated atom transfer radical polymerization. The resultant samples were characterized via nuclear magnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Their molecular weights and molecular weight distributions were determined via gel permeation chromatography after the removal of silica by etching. Moreover, the phase behavior of these polyzwitterionic-grafted silica nanoparticles in aqueous solutions and stability in protein/PBS solutions were systematically investigated. Dynamic light scattering and UV-visible spectroscopy results indicate that the silica-g-PSBMA nanoparticles exhibit an upper critical solution temperature (UCST) in aqueous solutions, which can be controlled by varying the PSBMA molecular weight, ionic strength, silica-g-PSBMA nanoparticle concentration, and solvent polarity. The UCSTs shift toward high temperatures with increasing PSBMA molecular weight and silica-g-PSBMA nanoparticle concentration. However, increasing the ionic strength and solvent polarity leads to a lowering of the UCSTs. The silica-g-PSBMA nanoparticles are stable for at least 72 h in both negative and positive protein/PBS solutions at 37 °C. The current study is crucial for the translation of polyzwitterionic solution behavior to surfaces to exploit their diverse properties in the development of new, smart, and responsive coatings.

Biodegradable Polymer Microcapsules Fabrication through a Template-Free Approach

A detailed study on the direct synthesis of biocompatible polyesters (e.g., PLA, PLGA or PCL) microcapsules and multifunctional microcapsules, which does not require any template and core removal, is presented. The technique is based on the modified self-emulsification process within the emulsion droplets by simply adding sodium dioctyl sulfosuccinate (Aerosol OT or AOT) as a cosurfactant to the initial polymer solution, followed by double emulsion formation due to the coalescence of the internal water droplets. Microcapsules with tunable sizes (ranging from hundreds of nanometers to tens of micrometers) and morphologies were then obtained through solidification of droplet shell of the double emulsion via solvent removal. In this report, we have systematically investigated the effect of experimental parameters, such as polymer and AOT concentration, polymer molecular weight on the double emulsion formation process, and the final morphologies of the microcapsules. We demonstrate that the capsules can encapsulate either hydrophobic or hydrophilic dyes during solvent evaporation. Dye-release studies show a correlation between shell thickness, capsules size, and diffusive release rate, providing insights into the shell formation and shell thickness processing. Moreover, hydrophobic nanoparticles, such as oleic-acid coated Fe(3)O(4) nanoparticles and quantum dots, can also be incorporated into the walls of the microcapsules. Such functional microcapsules might find applications in the fields of controlled release, bioimaging, diagnostics, and targeting.

A General Synthesis of High-Quality Inorganic Nanocrystals via a Two-Phase Method

A two-phase method is exploited to prepare many kinds of nearly monodisperse, highly crystalline, size- and shape-controlled, surface-property-tunable inorganic nanocrystals, such as metal, semiconducting, magnetic, dielectric, and rare earth nanocrystals. The reaction of the two-phase system happens at the interface between the oil (nonpolar) and water (polar) phases and the interface is an exclusive site for both nucleation and growth. Interestingly, many solvent pairs with a clear interface can be applied to synthesize inorganic nanocrystals successfully. Generally, as-prepared nanocrystals with organic ligands are soluble in nonpolar solvents. Furthermore, exchange of ligands can also be realized readily and the final nanocrystals can be soluble in polar solvents. This two-phase method is a simple, reproducible, and general route and is becoming as powerful an approach as other solution-based synthetic approaches to high-quality inorganic nanocrystals.

Novel hydrophobic polyvinyl alcohol-formaldehyde foams for organic solvents absorption and effective separation

A novel macroporous and hydrophobic polyvinyl alcohol–formaldehyde foam (PVF-GA-H) with open-cell structure and good mechanical property was successfully prepared by the two-step substitution of the hydroxyl groups in polyvinyl alcohol–formaldehyde with glutaraldehyde and stearoyl chloride at ambient temperature. The as-prepared PVF-GA-H possessed fast absorption kinetics in a few seconds to organic solvents and can absorb organic solvents up to 89.3 g g−1 even in the presence of water. These hydrophobic foams also exhibited highly effective reusability and recovery of organic solvents through a simple absorption–squeezing cycle. Meanwhile, the separation experiment confirmed that the PVF-GA-H foams can absorb and separate organic solvents from a water–organic solvent mixture. Therefore, this kind of foam is a highly suitable candidate for organic chemical pollution and industry leakage.

Solvent gradient fractionation and chain microstructure of complex branched polyethylene resin

AbstractA complex branched polyethylene resin with excellent processing and film-forming properties is fractionated through solvent gradient fractionation (SGF) technique. Here, the good solvent is 1,2,4-trimethylbenzene (TMB) and poor solvent is ethyl cellosolve (ECS). The fractions are further analyzed using high-temperature gel permeation chromatography (GPC) coupled with triple detectors (refractive index (RI)-light scattering (LS)-viscometer (VIS)), and 13C-nuclear magnetic resonance spectroscopy (13C-NMR). The molecular weight distribution of SGF fractions is very narrow, most of them are less than 1.1. The molecular weights of SGF fractions gradually increase as the content of good solvent increases in the mixture. The fractions with different molecular weights all have branching structure, the short chain branching is major in all fractions and along with certain content of long chain branching. Branching distribution across the molecular weight distribution is discussed in detail, and branching distribution within a SGF fraction is also researched. Graphical abstractA complex branched polyethylene resin is fractionated through solvent gradient fractionation (SGF) according to molecular weight. It is elaborated how to select appropriate experimental condition in order to obtain fractions with narrow molecular weight distribution. And the branching distribution in each molecular weight region of the whole resin is clearly understood.

pH/Temperature-Responsive Behavior of Amphiphilic Block Copolymer Micelles Prepared Using Two Different Methods

The pH- and temperature-responsive behavior of amphiphilic block copolymer poly(L-lactide)-b-poly(2-(dimethylamino)ethyl methacrylate) (PLLA-b-PDMAEMA) in aqueous solutions is investigated using static and dynamic light scattering. Electrostatic force, hydrophobic interaction, and hydrogen bonding coexist in the system. Micelles with different structures are prepared using water addition (WA) and direct dissolution (DD) methods. The aggregation from loose micelles into large micellar clusters is observed above the transition temperature under basic conditions. Only micellar clusters from the DD method could disaggregate when temperature was decreased to 24.3 °C after heating. The behavior of the micelles prepared with the DD method indicates that only the outer parts of the PLLA-b-PDMAEMA chains in the corona are solvated.

Highly efficient macroporous adsorbents for toxic metal ions in water systems based on polyvinyl alcohol–formaldehyde sponges

A series of macroporous adsorbents based on polyvinyl alcohol–formaldehyde (PVF) sponges was prepared using redox-initiated grafting polymerization of acrylamide (AM) followed by hydrolysis under alkaline conditions. The as-prepared sponges display average pore sizes in the range of 60–90 μm and interconnected pores with a porosity of approximately 90%. Elementary analysis confirmed that the amide groups in AM grafted PVF (PVF-g-GAM) have been rapidly converted into sodium carboxylate and the hydrolysis degree (HD) reaches approximately 65.5% within 6 h. The PVF-g-GAA (hydrolyzed PVF-g-GAM) sponges possess excellent water absorption performance with the ability to reach water absorption equilibrium within a few seconds and a saturated absorption capacity more than 300 g g−1. Importantly, the PVF-g-GAA can be used as adsorbents to remove toxic metal ions, such as Cu2+, Pb2+ and Cd2+, in wastewater efficiently due to the existence of abundant carboxylate groups in the abovementioned network. In single metal ion systems, the sponges could reach adsorption equilibrium within 10 min and the adsorption kinetics fit well with a pseudo-second order kinetic equation. The influence of pH and types of metal ions on the adsorption capacities have also been investigated extensively. PVF-g-GAA-20 displays high adsorption performances with maximum adsorption capacities for Cu2+, Pb2+ and Cd2+ up to 2.50, 3.20 and 3.15 mmol g−1 at pH 5.11, respectively. The equilibrium adsorption isotherm demonstrated that the adsorption equilibrium of the PVF-g-GAA-20 for Cu2+, Pb2+ and Cd2+ ions follows the Langmuir isotherm model very well with maximum adsorption capacities approximately 4.00, 3.97 and 3.34 mmol g−1, respectively. In the binary metal ion coexistence systems, including Cu2+/Pb2+, Cu2+/Cd2+ and Pb2+/Cd2+ mixtures, PVF-g-GAA-20 displayed excellent absorption selectivity for Cu2+ and Pb2+ and the values of and were 13.4 and 7.14, respectively. It can be noted that the adsorption capacities for the abovementioned three metal ions slightly decreased with the variation of ionic strength in the range of 0.01–0.08 M. The sample also exhibited a quick desorption procedure of less than 10 min and excellent reusability of atleast six re-cycles. The adsorption mechanism was also discussed. The PVF-g-GAA sponges are definitely ideal adsorbents for removing/separating toxic metal ions in waste/polluted water bodies.