Characterization of a sucrose/starch matrix through positron annihilation lifetime spectroscopy: unravelling the decomposition and glass transition processes

Interfacial-interaction induced modifications in segmental dynamics and free volume of the poly(ethyleneimine) canopy in nanoparticle-organic hybrid materials: an investigation by temperature dependent broadband dielectric and positron annihilation spectroscopy

Broadband dielectric spectroscopy, positron annihilation lifetime spectroscopy and differential scanning calorimetry are used to investigate the molecular dynamics, free volume and thermal behaviour of a poly(ethyleneimine), PEI, canopy in liquid-like nanoparticle-organic hybrid materials (NOHMs) consisting of alumina nanoparticles and nanorods as inorganic nanocores. It is confirmed that the highly branched PEI canopy in liquid-like NOHMs possesses an ordered structure having less entanglements of the side chains as compared to neat PEI. The size of the free volumes associated with the PEI canopy for nanoparticle- and nanorod-based NOHMs is larger and smaller, respectively, as compared to neat PEI. The time scales characterizing the segmental dynamics and side chain relaxations of the canopy in the nanorod-based NOHM are slowed down drastically as compared to the nanoparticle-based NOHM and neat PEI. These results confirm that the shape of the inorganic cores plays a deterministic role toward the structural arrangement (free volume) and segmental dynamics of the canopy polymer in liquid-like NOHMs.

Nanohole-boosted electron transport between nanomaterials and bacteria as a concept for nano-bio interactions

Biofilms contribute to bacterial infection and drug resistance and are a serious threat to global human health. Antibacterial nanomaterials have attracted considerable attention, but the inhibition of biofilms remains a major challenge. Herein, we propose a nanohole-boosted electron transport (NBET) antibiofilm concept. Unlike known antibacterial mechanisms (e.g., reactive oxygen species production and cell membrane damage), nanoholes with atomic vacancies and biofilms serve as electronic donors and receptors, respectively, and thus boost the high electron transport capacity between nanomaterials and biofilms. Electron transport effectively destroys the critical components (proteins, intercellularly adhered polysaccharides and extracellular DNA) of biofilms, and the nanoholes also significantly downregulate the expression of genes related to biofilm formation. The anti-infection capacity is thoroughly verified both in vitro (human cells) and in vivo (rat ocular and mouse intestinal infection models), and the nanohole-enabled nanomaterials are found to be highly biocompatible. Importantly, compared with typical antibiotics, nanomaterials are nonresistant and thereby exhibit high potential for use in various applications. As a proof-of-principle demonstration, these findings hold promise for the use of NBET in treatments for pathogenic bacterial infection and antibiotic drug resistance.

Effect of water on glass transition in starch/sucrose matrices investigated through positron annihilation lifetime spectroscopy: a new approach

Glass transition is studied through positron annihilation lifetime spectroscopy (PALS) in maize starch matrices containing 10 (batch STS10) and 20 (STS20) w/w% sucrose, as a function of temperature (T) and water content (c(w)). To circumvent important losses of water upon heating while recording the PALS spectra, a new method is developed: instead of a series of measurements of τ(3), the triplet positronium lifetime, at different T, the latter is kept constant and the series relates to c(w), which is left to decrease at a constant rate. Similarly to the changes in τ(3) with T, the τ(3)vs. c(w) plots obtained show a smooth linear increase until a break, denoting the occurrence of glass transition, followed by a sharper increase. The gradients appear to be independent of T. The variation of the glass transition temperature, T(g), with c(w) shows a broad sigmoid with a large linear central part; as expected from the plasticising effect of sucrose, the plot for STS20 lies some 10 K below that for STS10. Results from differential scanning calorimetry for STS20 yield T(g) values some 15 K higher than from PALS. On the basis of the general shape of the τ(3)vs. T variations, a general equation is set for τ(3)(T, c(w)), leading one to expect a similar shape for τ(3)vs. c(w), as experimentally observed.