Hydrogels with rapid and strong response to external stimuli and possessing high elasticity and strength have been considered as platform materials for numerous applications, e.g., in biomaterials engineering. Thermoresponsive hydrogels based on semi-interpenetrating polymer networks (semi-IPN) featuring N-isopropylacrylamide with copolymers of poly(N-isopropylacrylamide-co-hydroxyethyl methacrylate) p(NIPAM-HEMA) chains are prepared and described. The copolymer was characterized by FTIR, NMR, and GPC. The semi-IPN structured hydrogel and its responsive properties were evaluated by dynamic mechanical measurements, SEM, DSC, equilibrium swelling ratio, and dynamic deswelling tests. The results illustrate that the semi-IPN structured hydrogels possess rapid response and high elasticity compared to conventional pNIPAM hydrogels. By using a microfluidic device with double coaxial laminar flow, we succeeded in fabricating temperature responsive (“smart”) hydrogel microfibers with core–shell structures that exhibit typical diameters on the order of 100 μm. The diameter of the fibers can be tuned by changing the flow conditions. Such hydrogel fibers can be used to fabricate “smart” devices, and the core layer can be potentially loaded with cargos to incorporate biological function in the constructs. The platforms obtained by this approach hold promise as artificial “muscles”, and also “smart” hydrogel carriers providing a unique biophysical and bioactive environment for regenerative medicine and tissue engineering.Keywords: core−shell hydrogel microfibers; microfluidics; p(NIPAM-HEMA); thermoresponsive polymers;

Microfluidics appeared in the 1990s as a promising technology and has received considerable attention in developing stimuli-responsive hydrogel fibres in microscale for tissue engineering and actuation devices. In this work, thermo- and electro-responsive graphene oxide/poly(N-isopropylacrylamide)/sodium alginate (GO/PNIPAM/SA) hydrogel fibres were prepared via microfluidics and off-chip free radical polymerization. The composite hydrogel fibres were characterised using FTIR, SEM, and DSC. The thermo-triggered volume-phase transition and electrically triggered bending behaviours were also investigated. The results show that the hydrogel fibres have porous internal structures and the pore size becomes smaller with the increase of GO content due to the hydrogen bonding between the amide groups of PNIPAM chains and oxygen-containing groups on the GO nanosheets. Besides this, the incorporation of increased GO content enlarges the swelling ratio of the hydrogel fibre. The hydrogel fibres also exhibit bending behaviour under the non-contact direct current electric field.

•UHMWPE pre-stretched fibers were examined by in situ SAXS/WAXD during the ultra-high stretching process.•We reported the transition from shish-kebab to fibrillar morphology crystals of UHMWPE fibers.•There still exist chain conformation defects even in the majorly fibrillar morphology crystals.The ultra-high hot stretching was conducted on four-times pre-stretched ultra-high molecular weight polyethylene (UHMWPE) fibers to the ratio of about 508% to achieve the total ultra-high stretching ratio of about 2000%. In situ small and wide-angle X-ray scattering (SAXS/WAXS) measurements using synchrotron radiation and Raman spectroscopy were applied to study the structural evolutions of ultra-high stretched fibers. SAXS images revealed the transition from shish-kebab to fibrillar crystals, which is believed to involve with the increasing trans-configuration ratio of C–C backbone. WAXS results demonstrate the further stretching could still be applied to the fibers to acquire the complete extended-chain crystals.

•The SnF2–SnO–P2O5 glasses with low glass transition temperature (Tg) were prepared.•The composition and melting time play an important role on the properties of the glasses.•The relation between properties and structure of the glasses was studied.SnF2–SnO–P2O5 glasses with low glass transition temperature (Tg) were prepared in this paper. The effect of composition and melting time on the properties of these glasses was studied. X-ray diffraction (XRD) indicated that these prepared samples were glasses regardless of the composition and melting time. The properties of these glasses such as Tg, dilatometric softening temperature (Tf), thermal expansion coefficient (α) and density (ρ) were tested. The structure of these glasses was studied by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA). The glasses' structure and network dimension were supposed to play a critical role on the properties of the glasses. The fluorine and hydroxyl can decrease the network dimension of the glasses and thus decrease the Tg values. While, the oxidation of Sn2 + to form the Sn4 + could increase the network dimension of glasses and thus increase the Tg values.

•Pglass is an inorganic polymer with low Tg and mutable viscosity.•Kinetics models and activation energy can be used to analyze the process.•Pglass can play different effect on the crystallization process of PET.The physical state of phosphate glass (Pglass) has an influence on the non-isothermal crystallization behaviors of PET matrix in the PET/Pglass blends, which has been investigated via heating the glassy state and cooling the melt state of the blends at various scanning rates, respectively, by means of differential scanning calorimetry (DSC) technique. The kinetics models based on the Avrami and Mo equations were used to analyze the non-isothermal crystallization process. Furthermore, the activation energy of non-isothermal crystallization, according to Kissinger theory for heating process and Friedman theory for cooling process, has been evaluated. The results showed that the Pglass accelerated the non-isothermal cold crystallization rate of PET matrix due to its nucleation effect. In contrast, for the non-isothermal melt crystallization, the Pglass hindered the crystallization process due to its large melt viscosity.

Polyvinylpyrrolidone (PVPON)-boehmite hybrid thin film was deposited onto glass by sol–gel dip-coating method. The Fabry-Pérot fringe in visible spectra was applied to monitor the multilayer film thickness growth. Field-emission scanning electron microscope and Atomic force microscope were used to characterize the film’s microstructure. The film was composed of uniform boehmite nanoparticles about 20 nm. Addition of PVPON in the boehmite sol was effective in increasing the critical thickness of the films. When the as-deposited films were sintered at 500 °C, the boehmite was transformed to γ-alumina with the decreased film thickness.

A new approach for the fabrication of γ-AlOOH nanoflake films has been developed. The nanoflakes were successfully formed on a glass substrate via a simple, low temperature, and seed-assisted hydrothermal technique. A large amount of γ-AlOOH nanoflakes with various thicknesses interlaced together, resulting in a nest-like layer of film with their sharp edges preferentially vertical to glass substrates. The effects of hydrothermal temperature, time and concentration on the morphology and phase of the γ-AlOOH nanoflake films are investigated. X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Raman microscopy were used to characterize the structures and morphologies of the films. The growth mechanism of the γ-AlOOH nanoflake films was also discussed. Moreover, the nanostructural films of γ-AlOOH showed a transition from hydrophilic to super-hydrophobic with the chemical vapor deposition of PFOS.

A super-hydrophobic 2024 aluminum alloy surface with multi-scale hierarchical flower-like boehmite (γ-AlOOH) structure has been fabricated via a facile hydrothermal approach. The different morphologies of the γ-AlOOH films were totally controlled by the preparation conditions for crystal growth, such as reaction solution and time. The morphology and structure of the films were characterized using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The super-hydrophobicity can be attributed to both the rough multi-scale structural boehmite coating and surface enrichment of low surface energy with the chemical vapor deposition of 1H,1H,2H,2H-perfluorodecyltriethoxysilane (POTS). The resulting super-hydrophobic surface exhibits a water contact angle of 155° and a sliding angle of about 5°. The corrosion behavior was investigated with potentiodynamic polarization measurements and it was found that the super-hydrophobic coating considerably improved the corrosion resistant performance of aluminum alloy.

Nanosheet AlOOH and silica spheres composite thin film was deposited onto glass by sol–gel dip-coating method through hydrolysis of boiling water immersion. A silica sol and an alumina sol are employed in dipping process for the preparation of hierarchical nanostructures thin film. The morphology and structure of the films were characterized using field emission scanning electron microscopy and X-ray diffraction. The super-hydrophobicity with high adhesion forces can be attributed to both the rough multi-scale structural coating and surface enrichment of low surface energy with the chemical vapor deposition of 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

•Aluminum nitrate and polyacrylonitrile form spinning solution in DMF.•Transparent spinning solution is stable.•The alumina nanofibers possess porous surfaces and hollow cross sections.•The “Kirkendall effect” mechanism is proposed to explain the formation process.Porous alumina nanofibers with hollow structure were fabricated by single capillary electrospinning of aluminum nitrate (Al(NO3)3)/polyacrylonitrile (PAN) precursor solution, followed by sintering treatment. The Al(NO3)3/PAN composite nanofibers and sintered nanofibers were characterized by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). It is found that the obtained alumina nanofibers show porous external surfaces and hollow sections. Upon sintering the composite nanofibers at 1300 °C, the nanofibers are consisted of α-phased crystalline grains. Sintering temperature plays an important role in controlling the morphology and crystal structure of the nanofibers. A mechanism based on “Kirkendall effect” was proposed to explain the formation process of the hollow structure.Porous alumina nanofibers with hollow structure were fabricated by single-spinneret electrospinning of aluminum nitrate (Al(NO3)3)/polyacrylonitrile (PAN) precursor solution, followed by sintering treatment. A mechanism based on “Kirkendall effect” was proposed to explain the formation process of the hollow structure.

Hybrid mullite sol was synthesized from an aqueous solution of aluminum nitrate (AN), aluminum isopropoxide (AIP) and tetraethylorthosilicate (TEOS), doped with boehmite sol with different ratios. Pressureless sintering of the xerogel was carried out at different temperatures in the presence of boehmite doping. The xerogel and sintered powder were characterized by FTIR, TG–DSC, XRD, SEM and bulk density. The addition of boehmite caused the formation of metaphase spinel (6Al2O3·SiO2) crystal before the appearance of mullite phase, which could lead to the formation of amorphous phase and suppress the premature formation of mullite. Both of these effects improve the densification of mullite. A maximum density about 98% of the theoretical density (TD, 3.01 g/cm3) of mullite could be obtained for 5 wt% boehmite addition at 1200 °C pressureless sintering.

Poly(vinylpyrrolidone) (PVPON) and poly(acrylic acid) (PAA) were layer-by-layer (LBL) assembled to prepare the thin films based on hydrogen-bonding complexation. The hydrogen-bonded PVPON/PAA films were incubated in acidic, neutral and basic vapors separately. To study the morphologies after incubation, the films were stained by pH-sensitive fluorescent dyes using chemical and physical ways, and investigated with confocal laser scanning microscope (CLSM). The chemical way (labeling) was covalently linking fluoresceinamine (FAM) to some monomer units of PAA while the physical way was adsorbing rhodamine B (RB) molecules from dilute solution. Atomic force microscope (AFM) was combined with CLSM to find that after incubation in neutral or basic vapor the hydrogen-bonded PVPON/PAA films form porous structure and the pores are through the whole film.Graphical abstractHighlights► Hydrogen-bonded films were stained both by chemical and physical methods. ► The stained films were incubated in different vapor environments. ► The films’ morphologies were studied with confocal laser scan microscopy (CLSM). ► CLSM and AFM were combined together to unveil the film's structure after incubation.

A novel pH- and temperature-sensitive nanocomposite microgel based on linear Poly(acrylic acid) (PAAc) and Poly(N-isopropylacrylamide) (PNIPA) crosslinked by inorganic clay was synthesized by a two-step method. First, PNIPA microgel was prepared via surfactant-free emulsion polymerization by using inorganic clay as a crosslinker, and then AAc monomer was polymerized within the PNIPA microgel. The structure and morphology of the microgel were confirmed by FTIR, WXRD and TEM. The results indicated that the exfoliated clay platelets were dispersed homogeneously in the PNIPA microgels and acted as a multifunctional crosslinker, while the linear PAAc polymer chains incorporated in the PNIPA microgel network to form a semi-interpenetrating polymer network (semi-IPN) structure. The hydrodynamic diameters of the semi-IPN microgels ranged from 360 to 400 nm, which was much smaller than that of the conventional microgel prepared by using N,N′-methylenebis(acrylamide) (MBA) as a chemical crosslinker, the later was about 740 nm. The semi-IPN microgels exhibited good pH- and temperature-sensitivity, which could respond independently to both pH and temperature changes.The PNIPA/PAAc semi-IPN microgels prepared via surfactant-free emulsion polymerization by using inorganic clay as a crosslinker have small particle size and exhibit good pH- and temperature-sensitivity.

A novel porous PNIPA/Clay nanocomposite hydrogel (NC hydrogel) was prepared by in situ free-radical polymerization using inorganic clay as a crosslinker and calcium carbonate (CaCO3) particle as a pore-forming agent and subsequent extraction of CaCO3 with acid. The structure and morphology of the hydrogels were characterized by means of FTIR, TEM and SEM. The temperature responsive behaviors, the deswelling behaviors and the mechanical properties of the NC hydrogels were investigated in detail. The results showed that the swelling ratios below VPTT and the deswelling rates of the NC hydrogels were significantly improved as compared with the hydrogels without introduction of CaCO3. Moreover, the NC hydrogels thus prepared also exhibited good mechanical properties.