Shichun Jiang

Nanostructured Hybrid Organic–Inorganic Lanthanide Complex Films Produced In Situ via a Sol‐Gel Approach

Communication: Nanostructural hybrid organic-inorganic lanthanide complex films were prepared in situ by use of a novel sol-gel precursor containing pendant triethoxy-silyl and carboxyl groups (see Figure). The resulting transparent and crack-free films gave rise to strong red or green emission, even at low lanthanide ion concentration. Phase separation and lanthanide ion aggregation were controlled at the nanoscale.

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

Amphiphilic hyperbranched copolymers bearing a hyperbranched core and a dendritic shell as novel stabilizers rendering gold nanoparticles with an unprecedentedly long lifetime in the catalytic reduction of 4-nitrophenol

A series of organo-soluble gold nanoparticles (AuNPs) were prepared through the reduction of HAuCl4 by NaBH4 in the presence of amphiphilic hyperbranched copolymers bearing a hydrophilic hyperbranched polyethylenimine (PEI) core and a hydrophobic dendritic shell. For comparison, the corresponding analogues with a PEI core and a linear shell were also used to prepare the organo-soluble AuNPs. All the obtained AuNPs were characterized by transmission electron microscopy. It was found that under a high feed ratio of polymer to HAuCl4, the average diameter of the obtained small AuNPs was similar, and was independent of the shell morphology of the hyperbranched polymeric stabilizers. Reducing the feed ratio of polymer to HAuCl4 led to the formation of larger AuNPs and irregularly shaped AuNP aggregates. The stability evaluation on the basis of two-month shelf-storage demonstrated that the obtained AuNPs were stable under shelf-storage regardless of whether the shell of the hyperbranched polymeric stabilizer was dendritic or linear. These organo-soluble AuNPs could be used as efficient catalysts for the biphasic catalytic reduction of 4-nitrophenol by NaBH4, and could also be conveniently recovered and reused. The stabilizers with a dendritic shell endowed the AuNP catalyst with a higher performance than the corresponding stabilizers with a linear shell, including: (1) a higher catalytic rate; (2) the ability to be recovered and reused more times; (3) a maximal turnover number of around 23 000, which is unprecedented in the catalytic reduction of 4-nitrophenol.

Crystallization behaviors of n-octadecane in confined space: crossover of rotator phase from transient to metastable induced by surface freezing.

In this paper, the confined crystallization and phase transition behaviors of n-octadecane in microcapsules with a diameter of about 3 microm were studied with the combination of differential scanning calorimetry (DSC), temperature dependent Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The main discovery is that the microencapsulated n-octadecane crystallizes into a stable triclinic phase via a mestastable rotator phase (R I), which emerges as a transient state for the bulk n-octadecane and is difficult to be detected by the commonly used characterization methods. As evident from the DSC measurement, a surface freezing monolayer, which is formed at the interface between the microcapsule inner wall and n-octadecane, induces the crossover of the R I from transient to metastable. We argue that the existence of the surface freezing monolayer decreases the nucleating potential barrier of the R I phase, and consequently the lower relative nucleation barrier in the confined geometry turns the transient R I phase into a metastable one.

Hyperbranched Polymers with Thermoresponsive Property Highly Sensitive to Ions

The salt effects on the water solubility of thermoresponsive hyperbranched polyethylenimine and polyamidoamine possessing large amounts of isobutyramide terminal groups (HPEI-IBAm and HPAMAM-IBAm) were studied systematically. Eight anions with sodium as the counterion and ten cations with chloride as the counterion were used to measure the anion and cation effects on the cloud point temperature (T(cp)) of these dendritic polymers in water. It was found that the T(cp) of these dendritic polymers was much more sensitive to the addition of salts than that of the traditional thermoresponsive linear polymers. At low anion concentration, the electrostatic interaction between anions and the positively charged groups of these polymers was dominant, resulting in the unusual anion effect on the T(cp) of these polymers in water, including (1) T(cp) of these dendritic polymers decreasing nonlinearly with the increase of kosmotropic anion concentration; (2) the chaotropic anions showing abnormal salting-out property at low salt concentration and the stronger chaotropes having much pronounced salting-out ability; (3) anti-Hofmeister ordering at low salt concentration. At moderate to high salt concentration, the specific ranking of these anions in reducing the T(cp) of HPEI-IBAm and HPAMAM-IBAm polymers was PO(4)(3-) > CO(3)(2-) > SO(4)(2-) > S(2)O(3)(2-) > F(-) > Cl(-) > Br(-) > I(-), in accordance with the well-known Hofmeister series. At moderate to high salt concentration, the specific ranking order of inorganic cations in reducing the T(cp) of HPEI-IBAm polymer was Sr(2+) ≈ Ba(2+) > Na(+) ≈ K(+) ≈ Rb(+) > Cs(+) > NH(4)(+) ≈ Ca(2+) > Li(+) ≈ Mg(2+). This sequence was only partially similar to the typical Hofmeister cation series, whereas at low salt concentration the cation effect on T(cp) of the dendritic polymer was insignificant and no obvious specific ranking order could be found.

Tuning and Erasing Surface Wrinkles by Reversible Visible-Light-Induced Photoisomerization.

Periodic wrinkling across different scales has received considerable attention because it not only represents structure failure but also finds wide applications. How to prevent wrinkling or create desired wrinkling patterns is non-trivial because the dynamic evolution of wrinkles is a highly nonlinear problem. Herein, we report a simple yet powerful method to dynamically tune and/or erase wrinkling patterns with visible light. The light-induced photoisomerization of azobenzene units in azopolymer films leads to stress release and consequently to the erasure of the wrinkles. The wrinkles in unexposed regions are also affected and oriented perpendicular to the exposed boundary during the stress reorganization. Theoretical models were developed to understand the dynamics of the reversible photoisomerization-induced wrinkle evolution. This method can be applied for designing functional materials/devices, for example, for the reversible optical writing/erasure of information as demonstrated here.

Well-defined orthogonal surface wrinkles directed by the wrinkled boundary

In this report, we systematically investigate the as-formed wrinkles to act as a novel boundary to direct the surface wrinkling for controllable fabrication of hierarchical wrinkling patterns. Here the wrinkled boundary is the highly aligned wrinkling patterns, formed in the O2 plasma-exposed region (denoted as D1) when a uniaxially strained polydimethylsiloxane (PDMS) is subjected to the first selective O2 plasma treatment (OPT) via a copper grid. Subsequently, a stiff crust with the tunable composition is fabricated on the whole PDMS including the O2 plasma-unexposed region (denoted as D2), by means of the second OPT and/or additional film deposition (e.g., polystyrene and Pt). The subsequent solvent swelling or heating induces wrinkles in the D2 region, which are highly oriented perpendicular to those in the D1 region. The physics underpinning the experimental phenomenon is elucidated by our theoretical analysis based on Koiters elastic stability theory and finite element simulations. Additionally, we demonstrate that the wavelengths of the well-organized orthogonal wrinkles can be independently tailored via the exposure duration and the additionally deposited film thickness.

Luminescent properties of organic-inorganic hybrid monoliths containing rare-earth complexes

Transparent organic-inorganic hybrid monoliths containing rare-earth complexes (Eu(TTA)(3)Phen, Tb(Sal)(3)) were prepared via the sol-gel technique. It could be observed by transmission electron microscopy that the fluorescent particles are distributed in the matrix at the microscopic level. The matrix is composed of organic-inorganic semiinterpenetrating networks, i.e., PHEMA-SiO2 system. The fluorescence emission spectra of samples are similar to those from corresponding powdered Eu(III) and Tb(III) complexes, and the half-widths of the strongest bands are less than 10 nm, which indicates that the monolith exhibits high fluorescence intensity and color purity. Furthermore, the fluorescence spectra exhibit no obvious change with decreasing nanoparticle size of the rare-earth complex. The fluorescence lifetimes of samples are longer than pure Eu(III), Tb(III) complexes, respectively. Samples irradiated with an UV lamp (365 nm) are still transparent but become bright red and green in color due to fluorescence of Eu(III) and Tb(III) complexes

In-situ synchrotron SAXS and WAXS investigations on deformation and α–β transformation of uniaxial stretched poly(vinylidene fluoride)

The crystalline structure evolution of poly(vinylidene fluoride) (PVDF) during tensile deformation at 60 °C, 140 °C and 160 °C, i.e. between the glass transition temperature (Tg) and the melting temperature (Tm), was investigated by in-situ synchrotron SAXS and WAXS techniques. The analysis of the obtained scattering results indicated either yielding or α–β transformation in PVDF occurred and initiated at almost the same strain level with different stretching temperatures. A deformation mechanism was proposed for PVDF to illustrate the structure evolution during uniaxial stretching at high temperature indicating that the initial crystallite and crystalline lamellae structures of stretched PVDF are destroyed and orientated not simultaneously, which is intimately related to the yield point and the initial of α–β transformation on a certain degree of orientation. The long period along tensile direction increases to a maximum and then drops into a lower but stable value during this stage of deformation.

Amphiphilic hyperbranched copolymers bearing a hyperbranched core and dendritic shell: synthesis, characterization and guest encapsulation performance

The 2,2-bis(hydroxymethyl)propionic acid (BHP)-based generation 1 dendron with two palmitate tails (D1-C16) and the generation 2 dendron with four palmitate tails (D2-C16) were synthesized. The coupling of D1-C16 or D2-C16 with hyperbranched polyethylenimine (PEI) through the amidation reaction resulted in amphiphilic hyperbranched copolymers bearing a hyperbranched PEI core and a dendritic D1-C16 shell or dendritic D2-C16 shell. The structure of the obtained copolymers was verified through Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) characterization. Differential scanning calorimetry (DSC) measurement demonstrated that the existence of the branching units in the shell pronouncedly reduced the crystallinity of the hyperbranched copolymers, and the copolymers with less branched shells had a higher melting temperature and melting enthalpy. These novel amphiphilic hyperbranched copolymers could be used as nanocarriers to efficiently accommodate the hydrophilic guests, including Methyl Orange (MO), Congo Red (CR) and Direct Blue 15 (DB), into the hydrophilic amidated PEI core. Each nanocarrier with a branched shell could accommodate a much higher number of guests than the corresponding nanocarriers with linear shells, which indicated that the dendritic structure of the shell played a key role in significantly enhancing the encapsulation capacity of the nanocarriers. As far as the weight ratio of the encapsulated guests to the nanocarriers was concerned, the nanocarriers with branched shells could be modulated to have a similar encapsulation capacity for the small MO with a mono-sulfonate group, but a much superior encapsulation capacity for the large CR and DB guests with multi-sulfonate groups to the nanocarriers with linear shells.