No abstract

The effects of various Cloisite nanoparticulate clays with different hydrophobicities on (80/20) polypropylene/polystyrene (PP/PS) blends were investigated using their linear and nonlinear rheological properties. In descending order of hydrophobicity the four Cloisite clays examined were C20A > C10A > C30B > CNa+. Clays with a wetting coefficient ω a of between 1 and −1, that is C20A and C10A, located at PP/PS polymer interfaces and suppressed coalescence, while clays with a ω a of >1, that is C30B and CNa+, accumulated inside the PS droplets and increased viscosity ratios. As a result, C20A and C10A caused PS droplet size reductions while C30B and CNa+ did not change morphology of the PP/PS blend. Linear rheological properties as determined by SAOS (small amplitude oscillatory shear) test and nonlinear rheological properties determined by LAOS (large amplitude oscillatory shear) test revealed C20A and C10A increased mechanical properties of PP/PS blends. Rheological properties from SAOS and LAOS tests decreased in the same order as clay hydrophobicities at same concentration. The nonlinear–linear viscoelastic ratio (NLR is defined as normalized nonlinear viscoelastic properties/normalized linear viscoelastic properties) was used to quantify degrees of PS droplet dispersion and to determine the compatibilizing effects of the four clays on PP/PS blends. PP/PS blends filled with hydrophilic clays (C30B and CNa+) exhibited constant NLR values (NLR ≅ 1) with increasing clay concentration. However, NLR values of PP/PS blends containing C20A and C10A were much larger than 1 (NLR > 1) and increased with clay concentration, which concurred with reductions in droplet sizes. Interestingly, NLR values and droplet size changes exhibited inverse relationships with clay hydrophobicity. In addition, PS droplet sizes in PP/PS/C20A blends in the medium amplitude oscillatory shear (MAOS) flow region (Q 0 zone) were observed to check NLR validation. It was found that droplet sizes did not change in the MAOS region where NLR values are calculated and that thus NLR values corresponded with droplet sizes. Finally, inverse composition (20/80) PP/PS/C20A blends were studied, and a good correlation was obtained between PP droplet sizes and NLR values.

Characterizing dispersion quality of polymer nanocomposite (PNC) is as important as dispersing nanosized fillers in the polymer matrix. In this study, to quantify the dispersion quality of PNCs, we used rheological properties, that is, linear viscoelasticities determined by small-amplitude oscillatory shear tests and nonlinear viscoelasticities determined by large-amplitude oscillatory shear tests. Nonlinear viscoelasticities were analyzed with Fourier transform (FT)-rheology. Two different disperse-controlled PNCs were investigated. One is a polypropylene (PP)/clay nanocomposite system compatibilized using maleic anhydride-grafted polypropylene (MAPP), and the other is a PP/silica nanocomposite system containing four different types of silica (two hydrophilic and two hydrophobic silicas). Rheological measurements and transmission electron microscopy (TEM) findings for both PNCs, and X-ray diffraction (XRD) findings for PP/MAPP/clay were used to investigate morphological evolutions. In the case of PP/MAPP/clay nanocomposites, dispersion qualities, as characterized by linear and nonlinear rheological properties, were consistent with each other and well matched TEM and XRD observations. In contrast, in the case of PP/silica nanocomposites, dispersion qualities as characterized by linear and nonlinear rheological properties were inconsistent with each other. In this study, dispersion states of PNCs predicted by nonlinear rheological properties corresponded with TEM observations, whereas linear rheological properties did not. Especially, NLR (nonlinear–linear viscoelastic ratio ≡ normalized nonlinear viscoelasticity as determined by FT-rheology/normalized linear viscoelasticity) parameter well predicted dispersion degrees of PP/MAPP/clay nanocomposites and PP/silica nanocomposites.

As a central feature of neuroinflammation, microglial dysfunction has been increasingly considered a causative factor of neurodegeneration implicating an intertwined pathology with amyloidogenic proteins. Herein, we report the smallest synthetic molecule (N,N′-diacetyl-p-phenylenediamine [DAPPD]), simply composed of a benzene ring with 2 acetamide groups at the para position, known to date as a chemical reagent that is able to promote the phagocytic aptitude of microglia and subsequently ameliorate cognitive defects. Based on our mechanistic investigations in vitro and in vivo, 1) the capability of DAPPD to restore microglial phagocytosis is responsible for diminishing the accumulation of amyloid-β (Aβ) species and significantly improving cognitive function in the brains of 2 types of Alzheimer’s disease (AD) transgenic mice, and 2) the rectification of microglial function by DAPPD is a result of its ability to suppress the expression of NLRP3 inflammasome-associated proteins through its impact on the NF-κB pathway. Overall, our in vitro and in vivo investigations on efficacies and molecular-level mechanisms demonstrate the ability of DAPPD to regulate microglial function, suppress neuroinflammation, foster cerebral Aβ clearance, and attenuate cognitive deficits in AD transgenic mouse models. Discovery of such antineuroinflammatory compounds signifies the potential in discovering effective therapeutic molecules against AD-associated neurodegeneration.

Multiple pathogenic elements, including reactive oxygen species, amyloidogenic proteins, and metal ions, are associated with the development of neurodegenerative disorders. We report minimalistic redox-based principles for preparing compact aromatic compounds by derivatizing the phenylene moiety with various functional groups. These molecular agents display enhanced reactivities against multiple targets such as free radicals, metal-free amyloid-β (Aβ), and metal-bound Aβ that are implicated in the most common form of dementia, Alzheimer's disease (AD). Mechanistic studies reveal that the redox properties of these reagents are essential for their function. Specifically, they engage in oxidative reactions with metal-free and metal-bound Aβ, leading to chemical modifications of the Aβ peptides to form covalent adducts that alter the aggregation of Aβ. Moreover, the administration of the most promising candidate significantly attenuates the amyloid pathology in the brains of AD transgenic mice and improves their cognitive defects. Our studies demonstrate an efficient and effective redox-based strategy for incorporating multiple functions into simple molecular reagents.