The short and intermediate range structures of a large series of bioactive borophosphosilicate (BPS) glasses were probed by solid-state nuclear magnetic resonance (NMR) spectroscopy and atomistic molecular dynamics (MD) simulations. Two BPS glass series were designed by gradually substituting SiO by BO in the respective phosphosilicate base compositions 24.1NaO-23.3CaO-48.6SiO-4.0PO ("S49") and 24.6NaO-26.7CaO-46.1SiO-2.6PO ("S46"), the latter constituting the "45S5 Bioglass" utilized for bone grafting applications. The BPS glass networks are built by interconnected SiO, BO, and BO moieties, whereas P exists mainly as orthophosphate anions, except for a minor network-associated portion involving P-O-Si and P-O-B motifs, whose populations were estimated by heteronuclear P{B} NMR experimentation. The high Na/Ca contents give fragmented glass networks with large amounts of nonbridging oxygen (NBO) anions. The MD-generated glass models reveal an increasing propensity for NBO accommodation among the network units according to BO < SiO < BO ≪ PO. The BO/BO intermixing was examined by double-quantum-single-quantum correlation B NMR experiments, which evidenced the presence of all three BO-BO, BO-BO, and BO-BO connectivities, with B-O-B bridges dominating. Notwithstanding that B-O-B linkages are disfavored, both NMR spectroscopy and MD simulations established their presence in these modifier-rich BPS glasses, along with non-negligible B-NBO contacts, at odds with the conventional structural view of borosilicate glasses. We discuss the relative propensities for intermixing of the Si/B/P network formers. Despite the absence of pronounced preferences for Si-O-Si bond formation, the glass models manifest subtle subnanometer-sized structural inhomogeneities, where SiO tetrahedra tend to self-associate into small chain/ring motifs embedded in BO/BO-dominated domains.

.66. Dk, 68.37.Lp Crystallization of hafnia and zirconia and their alloys with silica and lanthana was studied in bulk and thin film samples by thermal analysis, X-ray diffraction and electron microscopy. Crystallization temperatures of hafnia and zirconia increase by more than 300 °C with increase of surface/interface area of the amorphous phase. Crystallization temperatures of zirconia and hafnia alloys with silica and lanthana increase with dopant content and exceed 900 °C for 50 mol% SiO 2 and LaO 1.5 . Energies for tetragonal HfO 2 and ZrO 2 interfaces with amorphous silica were derived from their crystallization enthalpies from silicates as 0.25 ± 0.08 and 0.13 ± 0.07 J/m 2 , respectively. The crystallization pathways in bulk powders and films of zirconia and hafnia can be interpreted as resulting from thermodynamic stabilization by the surface energy term of tetragonal and amorphous phases over monoclinic.

By combining 11B, 29Si, and 31P nuclear magnetic resonance (NMR) experimental results, we present the first comprehensive structural investigation of 15 borophosphosilicate (BPS) glasses of the Na2O–CaO–B2O3–SiO2–P2O5 system.

By using double-quantum–single-quantum correlation 11B nuclear magnetic resonance (NMR) experiments and atomistic molecular dynamics (MD) simulations, we resolve the long-standing controversy of whether directly interlinked BO4–BO4 groups exist in the technologically ubiquitous class of alkali/alkaline-earth based borosilicate (BS) glasses. Most structural models of Na2O–B2O3–SiO2 glasses assume the absence of B[4]–O–B[4] linkages, whereas they have been suggested to exist in Ca-bearing BS analogs. Our results demonstrate that while B[4]–O–B[4] linkages are disfavored relative to their B[3]–O–B[3]/B[4] counterparts, they are nevertheless abundant motifs in Na2O–B2O3–SiO2 glasses over a large composition space, while the B[4]–O–B[4] contents are indeed elevated in Na2O–CaO–B2O3–SiO2 glasses. We discuss the compositional and structural parameters that control the degree of B[4]–O–B[4] bonding.

We present a comprehensive molecular dynamics (MD) simulation study of composition-structure trends in a set of 25 glasses of widely spanning compositions from the following four systems of increasing complexity: NaO-BO, NaO-BO-SiO, NaO-CaO-SiO-PO, and NaO-CaO-BO-SiO-PO. The simulations involved new B-O and P-O potential parameters developed within the polarizable shell-model framework, thereby combining the beneficial features of an overall high accuracy and excellent transferability among different glass systems and compositions: this was confirmed by the good accordance with experimental data on the relative BO/BO populations in borate and boro(phospho)silicate networks, as well as with the orthophosphate fractions in bioactive (boro)phosphosilicate glasses, which is believed to strongly influence their bone-bonding properties. The bearing of the simulated melt-cooling rate on the borate/phosphate speciations is discussed. Each local {BO, BO, SiO, PO} coordination environment remained independent of the precise set of co-existing network formers, while all trends observed in bond-lengths/angles mainly reflected the glass-network polymerization, i.e., the relative amounts of bridging oxygen (BO) and non-bridging oxygen (NBO) species. The structural roles of the Na/Ca cations were also probed, targeting their local coordination environments and their relative preferences to associate with the various borate, silicate, and phosphate moieties. We evaluate and discuss the common classification of alkali/alkaline-earth metal ions as charge-compensators of either BO tetrahedra or NBO anions in borosilicate glasses, also encompassing the less explored NBO-rich regime: the Na/Ca cations mainly associate with BO/NBO species of SiO/BO groups, with significant relative Na-BO contacts only observed in B-rich glass networks devoid of NBO species, whereas NBO-rich glass networks also reveal substantial amounts of NBO-bearing BO tetrahedra.

Electrospun nanofibrous film doped with a fluorescent conjugated polymer P was developed as a sensory device for detection of the explosive 2,4-dinitrotoluene (DNT). Polymer P obtained through a Sonogashira cross-coupling polymerization showed high affinity and excellent fluorescence quenching property toward electro-deficient compound DNT in solution. A versatile and effective electrospinning technique, which effectively reduced aggregation and fluorescence self-quenching of the conjugated polymers in thin film by the traditional spin-casting, was successfully employed to develop explosive-sensing nanofibrous devices. By doping with polystyrene as supporting matrix and subsequent electrospinning, the obtained fluorescent nanofibrous film exhibited remarkable sensitivity to trace DNT vapor due to a large surface area-to-volume ratio and unique porous structure. The sensitivity of the device was further improved by introducing secondary pores into the nanofibers through addition of a surfactant, sodium dodecyl sulfate, as a porogen agent. This strategy can provide a platform for other conjugated polymers using electrospinning technology to construct new optical chemo-and biosensors.

Carbon nanotube (CNT)-encapsulated metal sulfides/oxides are promising candidates for application as anode materials in lithium ion battery (LIB), while their electrochemical behavior and mechanism still remain unclear. A comprehensive understanding of the lithiation mechanism at nanoscale of this type of composites will benefit the design and development of high-performance LIB materials. Here, we use Co9S8/Co nanowire-filled CNTs as a model material to investigate the lithium storage mechanism by in situ transmission electron microscopy. For a Co9S8/Co nanowire-filled closed CNT, the reaction front propagates progressively during lithiation, causing an axial elongation of 4.5% and a radial expansion of 32.4%, while the lithiated nanowire core is still confined inside the CNT. Contrastingly, for an open CNT, the lithiated Co9S8 nanowire shows an axial elongation of 94.2% and is extruded out from the open CNT. In particular, a thin graphite shell is drawn out from the CNT wall by the extruded lithiated Co9S8. The thin graphite shell confines the extruded filler and protects the filler from pulverization in the following lithiation–delithiation cycles. During multiple cycles, the Co segment remains intact while the Co9S8 exhibits a reversible transformation between Co9S8 and Co nanograins. Our observations provide direct electrochemical behavior and mechanism that govern the CNT-based anode performance in LIBs.

When exposed to body fluids, mesoporous bioactive glasses (MBGs) of the CaO–SiO2–P2O5 system develop a bone-bonding surface layer that initially consists of amorphous calcium phosphate (ACP), which transforms into hydroxy-carbonate apatite (HCA) with a very similar composition as bone/dentin mineral. Information from various 1H-based solid-state nuclear magnetic resonance (NMR) experiments was combined to elucidate the evolution of the proton speciations both at the MBG surface and within each ACP/HCA constituent of the biomimetic phosphate layer formed when each of three MBGs with distinct Ca, Si, and P contents was immersed in a simulated body fluid (SBF) for variable periods between 15 min and 30 days. Directly excited magic-angle-spinning (MAS) 1H NMR spectra mainly reflect the MBG component, whose surface is rich in water and silanol (SiOH) moieties. Double-quantum–single-quantum correlation 1H NMR experimentation at fast MAS revealed their interatomic proximities. The comparatively minor H species of each ACP and HCA component were probed selectively by heteronuclear 1H–31P NMR experimentation. The initially prevailing ACP phase comprises H2O and “nonapatitic” HPO42–/PO43– groups, whereas for prolonged MBG soaking over days, a well-progressed ACP → HCA transformation was evidenced by a dominating O1H resonance from HCA. We show that 1H-detected 1H → 31P cross-polarization NMR is markedly more sensitive than utilizing powder X-ray diffraction or 31P NMR for detecting the onset of HCA formation, notably so for P-bearing (M)BGs. In relation to the long-standing controversy as to whether bone mineral comprises ACP and/or forms via an ACP precursor, we discuss a recently accepted structural core–shell picture of both synthetic and biological HCA, highlighting the close relationship between the disordered surface layer and ACP.