Evolution of Microstructure and Viscoelasticity during Flow Alignment of a Lamellar Diblock Copolymer

The effects of flow alignment on the relaxation dynamics of a lamellar diblock copolymer melt and the dynamics of flow alignment itself are investigated using simultaneous measurements of shear stress and birefringence in both the flow plane and the sample plane. The primary advantage of this rheo-optical approach in the context of flow alignment is that it provides quantitative measurements of the evolution of the macroscopic mechanical properties and the state of the microstructure in real time, in situ as alignment occurs. Further, it provides information on the molecular and microstructural dynamics that give rise to flow alignment. An entangled, nearly symmetric poly(ethylene-propylene)-poly(ethylethylene) of 50 kg/mol (PEP-PEE-2) is studied during flow alignment under two different conditions, one that enhances alignment of the lamellae parallel to the sample plane and another that induces alignment perpendicular to the sample plane (lamellar normal along the vorticity axis). The results suggest that the flow process leading to parallel alignment in PEP-PEE-2 is associated with inhomogeneous deformation such that the orientation of domains in the material undergoes irreversible "rocking", while the process that produces perpendicular alignment occurs under conditions in which the deformation is nearly homogeneous throughout the material

Evolution of Microstructure and Viscoelasticity during Flow Alignment of a Lamellar Diblock Copolymer

The effects of flow alignment on the relaxation dynamics of a lamellar diblock copolymer melt and the dynamics of flow alignment itself are investigated using simultaneous measurements of shear stress and birefringence in both the flow plane and the sample plane. The primary advantage of this rheo-optical approach in the context of flow alignment is that it provides quantitative measurements of the evolution of the macroscopic mechanical properties and the state of the microstructure in real time, in situ as alignment occurs. Further, it provides information on the molecular and microstructural dynamics that give rise to flow alignment. An entangled, nearly symmetric poly(ethylene-propylene)-poly(ethylethylene) of 50 kg/mol (PEP-PEE-2) is studied during flow alignment under two different conditions, one that enhances alignment of the lamellae parallel to the sample plane and another that induces alignment perpendicular to the sample plane (lamellar normal along the vorticity axis). The results suggest that the flow process leading to parallel alignment in PEP-PEE-2 is associated with inhomogeneous deformation such that the orientation of domains in the material undergoes irreversible "rocking", while the process that produces perpendicular alignment occurs under conditions in which the deformation is nearly homogeneous throughout the material

Preferential and Increased Uptake of Hydroxyl-Terminated PAMAM Dendrimers by Activated Microglia in Rabbit Brain Mixed Glial Culture

Polyamidoamine (PAMAM) dendrimers are multifunctional nanoparticles with tunable physicochemical features, making them promising candidates for targeted drug delivery in the central nervous system (CNS). Systemically administered dendrimers have been shown to localize in activated glial cells, which mediate neuroinflammation in the CNS. These dendrimers delivered drugs specifically to activated microglia, producing significant neurological improvements in multiple brain injury models, including in a neonatal rabbit model of cerebral palsy. To gain further insight into the mechanism of dendrimer cell uptake, we utilized an in vitro model of primary glial cells isolated from newborn rabbits to assess the differences in hydroxyl-terminated generation 4 PAMAM dendrimer (D4-OH) uptake by activated and non-activated glial cells. We used fluorescently-labelled D4-OH (D-Cy5) as a tool for investigating the mechanism of dendrimer uptake. D4-OH PAMAM dendrimer uptake was determined by fluorescence quantification using confocal microscopy and flow cytometry. Our results indicate that although microglial cells in the mixed cell population demonstrate early uptake of dendrimers in this in vitro system, activated microglia take up more dendrimer compared to resting microglia. Astrocytes showed delayed and limited uptake. We also illustrated the differences in mechanism of uptake between resting and activated microglia using different pathway inhibitors. Both resting and activated microglia primarily employed endocytotic pathways, which are enhanced in activated microglial cells. Additionally, we demonstrated that hydroxyl terminated dendrimers are taken up by primary microglia using other mechanisms including pinocytosis, caveolae, and aquaporin channels for dendrimer uptake

Deformation-Induced Morphology Changes and Orientation Behavior in Syndiotactic Polypropylene

Syndiotactic polypropylene (sPP) exhibits a complex crystalline morphology, characterized by unique annealing- and deformation-induced changes. Rheooptical FTIR spectroscopy, wide-angle X-ray diffraction (WAXD), and Raman spectroscopy are used to characterize morphology and orientation responses of highly syndiotactic sPP to tensile drawing. Solid-state thin films of different initial morphology, either quenched or slowly cooled from the melt, are studied. Results suggest that a gradual transition in macromolecular chain conformation, from gauche−gauche−trans−trans helical to all-trans planar, is observed at room temperature for quenched samples that are drawn up to 400% strain. This transition is marked initially by the gradual disappearance of helical chains (disordered form I) and the subsequent emergence of a mesophase, which may transform into form III crystals at even greater strains. Our primary investigational tool, the rheo-FTIR spectrometer, allows us to monitor the presence and orientation of amorphous, mesomorphic, and crystalline domains directly, simultaneously, and sensitively. Results from all of the techniques used are correlated in an effort both to assign IR peaks to characteristic sPP moieties and to generate a plausible physical model of the deformation dynamics in melt-quenched sPP