Yongmei Ma

Rutile TiO2 particles exert size and surface coating dependent retention and lesions on the murine brain

The rising commercial use and large-scale production of engineered nanoparticles (NPs) may lead to unintended exposure to humans. The central nervous system (CNS) is a potential susceptible target of the inhaled NPs, but so far the amount of studies on this aspect is limited. Here, we focus on the potential neurological lesion in the brain induced by the intranasally instilled titanium dioxide (TiO₂) particles in rutile phase and of various sizes and surface coatings. Female mice were intranasally instilled with four different types of TiO₂ particles (i.e. two types of hydrophobic particles in micro- and nano-sized without coating and two types of water-soluble hydrophilic nano-sized particles with silica surface coating) every other day for 30 days. Inductively coupled plasma mass spectrometry (ICP-MS) were used to determine the titanium contents in the sub-brain regions. Then, the pathological examination of brain tissues and measurements of the monoamine neurotransmitter levels in the sub-brain regions were performed. We found significant up-regulation of Ti contents in the cerebral cortex and striatum after intranasal instillation of hydrophilic TiO₂ NPs. Moreover, TiO₂ NPs exposure, in particular the hydrophilic NPs, caused obvious morphological changes of neurons in the cerebral cortex and significant disturbance of the monoamine neurotransmitter levels in the sub-brain regions studied. Thus, our results indicate that the surface modification of the NPs plays an important role on their effects on the brain. In addition, the difference in neurotoxicity of the two types of hydrophilic NPs may be induced by the shape differences of the materials. The present results suggest that physicochemical properties like size, shape and surface modification of the nanomaterials should be considered when evaluating their neurological effects.

Non-ultraviolet photocatalytic kinetics of NaYF4:Yb,Tm@TiO2/Ag core@comby shell nanostructures

An effective near-infrared (NIR) active photocatalyst, NaYF4:Yb,Tm@TiO2/Ag (UC@TiO2/Ag) core@comby shell composite, was synthesized by a simple three-step hydrothermal process. Under the full-spectrum light of a Xe lamp in UV-Vis absorbance experiments, about 96% of R6G dyes in solution were degraded by UC@TiO2/Ag in 120 minutes, while only about 64% of the dyes were degraded by pure TiO2 under the same conditions. Under a UV-filtered Xe lamp, about 35% of the dyes were degraded by UC@TiO2/Ag in 120 minutes; interestingly, only about 8% of the dyes were degraded by pure TiO2. Under irradiation by a 785 nm laser in surface enhanced Raman scattering (SERS) experiments, the photodegradation rate constants were 0.02612 s−1 for UC@TiO2/Ag and 0.00046 s−1 for TiO2/Ag, indicating a nearly 58 fold improvement. After deducting the photobleaching effect, the photodegradation rate constants for UC@TiO2/Ag under 633 and 532 nm lasers were 0.00715 s−1 and 0.00565 s−1, respectively, revealing a sharp decrease under irradiation at shorter wavelengths. Electron spin resonance (ESR) analysis revealed that the presence of UC in this photocatalytic system certainly induced the increase of ˙OH free radicals with NIR irradiation, i.e. the UC core converts NIR light into ultraviolet (UV) light and initiates excellent photocatalytic activity of the TiO2/Ag comby shell. Furthermore, the decorating of Ag nanoparticles not only enhances the photocatalytic ability, but also provides a structural basis for monitoring the photocatalytic kinetics by the SERS technique. By virtue of monochrome laser lines, SERS analysis provides direct evidence to prove the capability of UC-initiated non-UV photocatalysis and the improvement of the utilization of non-UV lights on TiO2. The results revealed that this new photocatalytic platform can efficiently utilize different bands of the solar spectrum and also find new applications in SERS fields.

Electrospun shape memory film with reversible fibrous structure

A shape memory polymer film with a stable micro/nano-fibrous structure is prepared via electrospinning of a triethoxysilane end-capped precursor solution, followed by crosslinking. The fibrous structure is stable and reversible for at least three cycles of shape memory tests. The electrospun SMP film also exhibits consistently faster recovery than the bulk film.

Enhancing the Thermal Conductance of Polymer and Sapphire Interface via Self-Assembled Monolayer

Interfacial thermal conductance (ITC) receives enormous consideration because of its significance in determining thermal performance of hybrid materials, such as polymer based nanocomposites. In this study, the ITC between sapphire and polystyrene (PS) was systematically investigated by time domain thermoreflectance (TDTR) method. Silane based self-assembled monolayers (SAMs) with varying end groups, -NH2, -Cl, -SH and -H, were introduced into sapphire/PS interface, and their effects on ITC were investigated. The ITC was found to be enhanced up by a factor of 7 through functionalizing the sapphire surface with SAM, which ends with a chloride group (-Cl). The results show that the enhancement of the thermal transport across the SAM-functionalized interface comes from both strong covalent bonding between sapphire and silane-based SAM, and the high compatibility between the SAM and PS. Among the SAMs studied in this work, we found that the ITC almost linearly depends on solubility parameters, which could be the dominant factor influencing on the ITC compared with wettability and adhesion. The SAMs serve as an intermediate layer that bridges the sapphire and PS. Such a feature can be applied to ceramic-polymer immiscible interfaces by functionalizing the ceramic surface with molecules that are miscible with the polymer materials. This research provides guidance on the design of critical-heat transfer materials such as composites and nanofluids for thermal management.

Supramolecular architecture-directed synthesis of a reactive and purely inorganic ladder polyhydrosilsesquioxane

A reactive and purely inorganic high Mw perfect ladder polyhydrosilsesquioxane (H-LPSQ) was first prepared under the direction of two imperative supramolecular architectures: ladder superstructure (H-LS) and donor-acceptor complex (DAC).

Tuning the Interfacial Thermal Conductance between Polystyrene and Sapphire by Controlling the Interfacial Adhesion

In polymer-based electric microdevices, thermal transport across polymer/ceramic interface is essential for heat dissipation, which limits the improvement of the device performance and lifetime. In this work, four sets of polystyrene (PS) thin films/sapphire samples were prepared with different interface adhesion values, which was achieved by changing the rotation speeds in the spin-coating process. The interfacial thermal conductance (ITC) between the PS films and the sapphire were measured by time domain thermoreflectance method, and the interfacial adhesion between the PS films and the sapphire, as measured by a scratch tester, was found to increase with the rotation speed from 2000 to 8000 rpm. The ITC shows a similar dependence on the rotation speed, increasing up to a 3-fold from 7.0 ± 1.4 to 21.0 ± 4.2 MW/(m(2) K). This study demonstrates the role of spin-coating rotation speed in thermal transport across the polymer/ceramic interfaces, evoking a much simpler mechanical method for tuning this type of ITC. The findings of enhancement of the ITC of polymer/ceramic interface can shed some light on the thermal management and reliability of macro- and microelectronics, where polymeric and hybrid organic-inorganic nano films are employed.

A novel method to improve the thermal stability of poly(propylene carbonate)

In the present work, a surfactant, the phosphoric ester of poly(ethylene oxide) (10) nonylphenyl (abbreviated as NP-10P throughout the paper), was incorporated into poly(propylene carbonate) (PPC) by melt-blending. Characterization data by TGA and Py-GC/MS have suggested that the obtained PPC/NP-10P complex displays excellent thermal stability compared to pure PPC. The thermal decomposition temperature, with a 5% loss in weight, increases by about 103 °C from 180 °C for PPC to 283 °C for PPC with 15 wt% NP-10P. Furthermore, with only 1 wt% of NP-10P incorporated into the PPC, an increase of about 74 °C in the decomposition temperature is found. The pyrolysis mechanism of PPC before and after modification with NP-10P varies from chain unzipping degradation to chain random scission followed by unzipping degradation. The results of 31P NMR, FTIR and intrinsic viscosity measurements have illustrated that the PPC is end-capped with NP-10P, which leads to the improvement of thermal stability and the change in pyrolysis mechanism of PPC. Moreover, this new finding will facilitate development and widespread applications of this biodegradable material.

Fabrication of superhydrophobic surfaces via poly(methyl methacrylate)-modified anodic aluminum oxide membrane

Superhydrophobic surfaces were prepared by poly(methyl methacrylate) (PMMA) or polystyrene (PS) modification on an optimized anodic aluminum oxide (AAO) honeycomb-like structure surface. The AAO membrane was initially etched in sodium hydroxide solution to get a hierarchical polygon-cavity structure in micro- and nano-scales, and then, it was coated with the polymer solution. The obtained polymer-modified AAO films show superhydrophobicity with water contact angles of larger than 150°. The intrinsic contact angles of the PMMA and PS are 68° and 94°, respectively. The morphology and components of the micro-/nano-structure were characterized by SEM and XPS, respectively, and the mechanism is discussed. This work provides a simple method to obtain superhydrophobic surfaces by common polymers without the need for low surface energy compounds.

The influence of rare earth ions on the rheological behavior of polyamide

The polyamide 66 (PA66)/lanthanum acetate blends with small amounts of salt loadings (≤ 1 wt% of PA) have been prepared in a twin-screw extruder. The rheology of PA66 and its blends has been investigated by a rotational rheometer. The results suggested that with the salt loading in excess of 0.2 wt% the typical Newtonian viscosity plateau disappeared and both the low-frequency complex viscosities η* and storage modulus G′ of blends were much higher than those of neat PA66, the storage modulus was higher than the loss modulus at low frequencies (tanδ < 1), i.e., the melt changed from a viscoelastic liquid for unfilled polymer to a viscoelastic solid (G′ > G″). While the viscosity followed a strong shear thinning with increasing frequency, the η* and G′ decreased significantly even lower than those of neat PA66 at high frequencies. The combination of dynamic mechanical analysis (DMA) and X-ray photoelectron spectroscopy (XPS) analysis has revealed that coordination effect occurred between lanthanum and carbonyl oxygen atoms in amide groups of the polymer to form pseudocrosslinked network structure, which makes the glass transition temperatures (Tg) and storage modulus (E′) of blends enhanced. The network structure formation-destruction and chains entanglement-disentanglement processes at different frequencies are responsible for the above rheological behaviors of blends.