The production and stabilization of amorphous drugs by the nanoconfinement effect has recently become a research hotspot in pharmaceutical sciences. Herein, two guest/host systems, indomethacin (IMC) and griseofulvin (GSF) confined in anodic aluminum oxide (AAO) templates with different pore diameters (25–250 nm) are investigated by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The crystallization of the confined drugs is suppressed, and their glass transition temperatures show an evident pore-size dependency. Moreover, a combination of dielectric and calorimetric results demonstrates that the significant change in the temperature dependence of the structural relaxation time during the cooling process is attributed to the vitrification of the interfacial molecules and the local density heterogeneity under isochoric confinement. Interestingly, compared with the case of IMC/AAO, which can be described by a typical two-layer model, GSF/AAO presents an rare scenario of three glass transition temperatures under fast cooling (40–10 K/min), indicating that there exists a thermodynamic nonequilibrium interlayer between the bulk-like core and interfacial layer. In contrast, the slow cooling process (0.5 K/min) would lead confined GSF into the stable core–shell nanostructure. Using surface modification, the interfacial effect is confirmed to be an important reason for the different phenomena between these two guest/host systems, and intermolecular hydrogen bonding is also suggested to be emphasized considering the long-range effect of interfacial interactions. Our results not only provide insight into the glass transition behavior of geometrically confined supercooled liquids, but also offer a means of adjusting and stabilizing the nanostructure of amorphous drugs under two-dimensional confinement.

The glass transition behaviors of poly(methyl methacrylate) (PMMA) nanofibers confined in pristine and surface-modified AAO templates are investigated by differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). During an ultraslow cooling process (0.1 K/min) across the Tg, two glass transition temperatures (Tg,low and Tg,high) are clearly identified by DSC and BDS, which correspond to the core and shell, respectively. The Tg,high originates from the transition of the adsorbed layer and is mainly dominated by the geometric curvature radius of the nanopores rather than the chemical nature of the wall surface. A dramatic change in the glass transition behaviors is detected when the cooling rate is changed from 40 to 0.1 K/min, which reflects the inherent evolution between the shell and the core through a nonequilibrium interlayer. Furthermore, by studying the system before and after surface modification of the nanopores by silanization, we suggest that such evolution could be sped up through the benefit of the stronger interfacial interactions. Our findings provide insight into achieving stable glassy polymer structures confined in nanopores by balancing the geometric curvature, interfacial interactions, and cooling rate.

Twisted polymer microfiber/nanofiber yarns were manufactured by using a direct twisted electrospinning method. Compared with typical electrospinning setup, a significant difference in this method was that a high-speed motor was used to induce the spinneret tip with relatively short collecting distance at the electrospinning process. Two types of polymer self-bundling yarns were prepared successfully: poly(vinylpyrrolidone) and poly(ether sulfones). The collecting distance was a very important factor to achieve twisted polymer microfiber/nanofiber yarns from ejected fiber bundles by this self-bundling and rotating electrospinning method. In addition, the possible mechanism for the self-bundling formation of twisted microfiber/nanofiber yarn was proposed.

•The surfactant may be introduced to the surface of gold nanoparticles by synthesis methods.•Solid state NMR was efficient to characterize the residual surfactant.•The surfactant was found to cause decrease in the Tg of polystyrene on gold nanoparticles.The adsorbed species on nanofillers is one of the most important factors that may influence the performance of polymer nanocomposites. Herein, we performed a systematic investigation of the effects of the residual surfactant introduced by a synthetic method on the glass transition temperature (Tg) of polystyrene/gold nanoparticle nanocomposites. The surfactant was found to cause an obvious decrease in the Tg of polystyrene confined on gold. Furthermore, we used dipolar-filtered 1H solid-state nuclear magnetic resonance to characterize the mobility of the molecules confined on gold. It was impossible to completely remove the surfactant once it had been adsorbed on the gold nanoparticles; thus it is important to choose suitable methods of synthesis, and special attention should be paid to the adsorbed species on nanofillers.

The segmental dynamics of rigid, intermediate, and mobile molecular components in carboxyl terminated polybutadiene (CTPB)/organo–clay (C18–clay) systems was characterized by fully refocused 1H NMR FID. In addition, 1H DQ NMR experiments allowed semiquantitative monitoring of changes in segmental dynamics near the interface. Both methods suggest a critical concentration of 60 wt % CTPB, indicating a saturation effect for the surface-adsorbed polymer. While the critical concentration value of a polymer/clay system can be measured in several ways, this is its first direct evidence at the molecular scale. The polymer–clay interaction is found to profoundly change with the removal of the CTPB end group or the organic modifier on the clay surface thus impacting the polymer segmental dynamics near the clay surface. In C18–clay by itself, with increasing temperature, the dynamic behavior of surface modifier changes from homogeneous to heterogeneous, on the basis of which the nonreversible exfoliation process of CTPB/clay nanocomposites could be explained at the molecular level. Based on the 1H NMR results, a tentative model was proposed to illustrate the evolution of the structure and segmental dynamics in CTPB/organo–clay nanocomposites.

In this article, we characterized the polymeric gold(I) thiolates that precipitated from the intermediate solutions during the synthesis process of gold nanoparticles (GNPs) by the Brust–Schiffrin two-phase method and investigated the formation mechanism of the polymeric gold(I) thiolates. The solution 1H NMR confirmed the complete reduction from Au(III) to Au(I) with the addition of the first two equivalents of thiols, while only the third and fourth equivalents of thiols were found to participate in forming gold(I) thiolates. Gold(I) thiolates, [Au(I)SR]n, precipitated from these solutions were further characterized by 1H solid-state NMR spectroscopy under fast magic angle spinning (MAS), Raman spectroscopy, and thermogravimetric analysis. Further quantitative studies revealed that the composition of [Au(I)SR]n could be controlled by changing the order of addition of the third and fourth equivalents of thiols. This work has great significance to better understand the mechanism of gold nanoparticle formation and thus to tailor the properties of the final products.

Hydrogenation has been proved to be an efficient way to remove the toxicity of phthalate plasticizer. However, other influences of this hydrogenation are still unknown. Here we chose di-2-ethylhexyl phthalate (DOP) and di(2-ethylhexyl) cyclohexane-1,2-dicarboxylate (DEHHP) to study the influence on interaction with poly(vinyl chloride) (PVC). By combining experiment and calculation, we found the interaction was stronger in PVC/DEHHP than in PVC/DOP. Low-Field 1H NMR results showed that PVC chains could restrict much more DEHHP molecules than DOP. FTIR results showed that the interaction exists in form of hydrogen bonding complex, and it was stronger in PVC/DEHHP than in PVC/DOP system. Combined with FTIR results, theoretical calculation results revealed the three-center hydrogen bonded structure of the complex. Both the proportion and the binding energy of pre-complex in DEHHP are much larger than in DOP. Here, the hydrogenation-induced change of interaction was elucidated systematically and could be generalized to other phthalate plasticizers.

Understanding interfacial water behavior is essential to improving our understanding of the surface chemistry and interfacial properties of nanomaterials. Here using 1H solid-state nuclear magnetic resonance (1H SSNMR), we successfully monitored ligand exchange reaction between oleylamine (OLA) and adsorbed water on titanium dioxide nanoparticles (TiO2 NPs). Three different types of interfacial waters with different reactivities were distinguished. The mobility of the adsorbed water molecules was characterized by dipolar filtered 1H SSNMR. Our experimental results demonstrate that the adsorbed water can be categorized into three different layers: (i) rigid water species with restricted mobility closest to the surface of TiO2 NPs, (ii) less mobile water species weakly confined on TiO2 NPs, and (iii) water molecules with high mobility. Water in the third layer could be replaced by OLA, while water in the first and second layers remained intact. The finding that the interfacial water with the highest mobility has the strongest reactivity has guiding significance for tailoring the hydrophilic and hydrophobic properties of TiO2 NPs.Keywords: 1H solid-state NMR; interfacial water; TiO2 nanoparticles;