Polypropylene/organoclay nanocomposites compatibilized with hydroxyl‐functional polypropylenes

The properties of polypropylene composites can be tailored through the use of nanoclay fillers. The effectiveness of a metallocene‐catalyzed hydroxyl‐functional polypropylene in the compatibilization of polypropylene layered nanosilicate composites was studied, and the results were compared with those for a commercial maleic anhydride functionalized polypropylene. Polypropylene/organoclay nanocomposites were prepared by melt blending, and two polypropylene/compatibilizer/organoclay ratios, 90/5/5 and 70/20/10, were characterized. The organomodification of the clay was carried out with octadecylamine and N‐methylundecenylamine. The structure of the layered silicate was studied by transmission electron microscopy, wide‐angle X‐ray scattering, and small‐angle X‐ray scattering. The fracture surfaces of the composites and thus the efficiency of the compatibilizers to penetrate the galleries of the organoclays were characterized by scanning electron microscopy, and the melt viscosity was studied by stress‐controlled rotational rheometry. The nanostructure was observed with both alkyl amines used for intercalation. The fillers facilitated the processability of all the composites, consisting of equal amounts of compatibilizer and organoclay filler and, in some of the composites, containing twice as much compatibilizer as organoclay filler. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1892–1903, 2005     

Identification of extracellular nanoparticle subsets by nuclear magnetic resonance

Exosomes are a subset of secreted lipid envelope-encapsulated extracellular vesicles (EVs) of 50–150 nm diameter that can transfer cargo from donor to acceptor cells. In the current purification protocols of exosomes, many smaller and larger nanoparticles such as lipoproteins, exomers and microvesicles are typically co-isolated as well. Particle size distribution is one important characteristics of EV samples, as it reflects the cellular origin of EVs and the purity of the isolation. However, most of the physicochemical analytical methods today cannot illustrate the smallest exosomes and other small particles like the exomers. Here, we demonstrate that diffusion ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR) method enables the determination of a very broad distribution of extracellular nanoparticles, ranging from 1 to 500 nm. The range covers sizes of all particles included in EV samples after isolation. The method is non-invasive, as it does not require any labelling or other chemical modification. We investigated EVs secreted from milk as well as embryonic kidney and renal carcinoma cells. Western blot analysis and immuno-electron microscopy confirmed expression of exosomal markers such as ALIX, TSG101, CD81, CD9, and CD63 in the EV samples. In addition to the larger particles observed by nanoparticle tracking analysis (NTA) in the range of 70–500 nm, the DOSY distributions include a significant number of smaller particles in the range of 10–70 nm, which are visible also in transmission electron microscopy images but invisible in NTA. Furthermore, we demonstrate that hyperpolarized chemical exchange saturation transfer (Hyper-CEST) with ¹²⁹Xe NMR indicates also the existence of smaller and larger nanoparticles in the EV samples, providing also additional support for DOSY results. The method implies also that the Xe exchange is significantly faster in the EV pool than in the lipoprotein/exomer pool.

Diffusion and xenon NMR based methods to determine a very broad range of sizes and sub-sets of extracellular vesicles.     

Cortical sensitivity to periodicity of speech sounds

Previous non-invasive brain research has reported auditory cortical sensitivity to periodicity as reflected by larger and more anterior responses to periodic than to aperiodic vowels. The current study investigated whether there is a lower fundamental frequency (F0) limit for this effect. Auditory evoked fields (AEFs) elicited by natural-sounding 400 ms periodic and aperiodic vowel stimuli were measured with magnetoencephalography. Vowel F0 ranged from normal male speech (113 Hz) to exceptionally low values (9 Hz). Both the auditory N1m and sustained fields were larger in amplitude for periodic than for aperiodic vowels. The AEF sources for periodic vowels were also anterior to those for the aperiodic vowels. Importantly, the AEF amplitudes and locations were unaffected by the F0 decrement of the periodic vowels. However, the N1m latency increased monotonically as F0 was decreased down to 19 Hz, below which this trend broke down. Also, a cascade of transient N1m-like responses was observed in the lowest F0 condition. Thus, the auditory system seems capable of extracting the periodicity even from very low F0 vowels. The behavior of the N1m latency and the emergence of a response cascade at very low F0 values may reflect the lower limit of pitch perception.     

A self-assembling protein template for constrained synthesis and patterning of nanoparticle arrays

Self-assembling biomolecules that form highly ordered structures have attracted interest as potential alternatives to conventional lithographic processes for patterning materials. Here, we introduce a general technique for patterning nanoparticle arrays using two-dimensional crystals of genetically modified hollow protein structures called chaperonins. Constrained chemical synthesis of transition metal nanoparticles is initiated using templates functionalized with polyhistidine sequences. These nanoparticles are ordered into arrays because the template-driven synthesis is constrained by the nanoscale structure of the crystallized protein. We anticipate that this system may be used to pattern different classes of nanoparticles based on the growing library of sequences shown to specifically bind or direct the growth of materials.     

Design and fabrication of integrated solid-phase extraction-zone electrophoresis microchip

Integrated solid-phase extraction-zone electrophoresis (SPE-ZE) device has been designed and fabricated on microchip. The structures were fabricated by using multiple layers of SU-8 polymer with a novel technique that enables easy alignment and high yield of the chips. SU-8 adhesive bonding has two major advantages: it enables bonding of high aspect ratio pillars and it results in fully SU-8 microchannels with uniform electrokinetic flow properties. The SPE-ZE device has a fluidic reservoir with 15:1 high aspect ratio pillars for bead filters that act as a SPE part in the chip structure. The separation unit is a 25 mm long electrophoresis channel starting from the outlet of SPE reservoir. Argon laser-induced fluorescence (LIF) detector was used to monitor simultaneously the SPE reservoir and the detection site at the end of the electrophoresis channel. Flow characteristics and electric field distributions were simulated with Femlab software. Fluorescein was used as the analyte for detecting the operational performance of the chip. Adsorption, bead rinsing, elution and detection were tested to verify functioning of the chip design.     

Predictable quantum efficient detector for low optical flux measurements

Optical Review - The predictable quantum efficient detector (PQED) is a primary standard of optical power, which utilizes two custom-made induced-junction photodiodes that are mounted in a wedged...     

Heterogenization of racemic ethylenebis(1-indenyl)zirconium dichloride on trimethylaluminum vapor modified silica surface

Heterogeneous metallocene catalysts were prepared by adsorbing rac-Et(Ind)₂ZrCl₂ on a modified silica surface in solution. The modification of silica was conducted in gas phase with atomic layer chemical vapor deposition (ALCVD) technique, where the silica, preheated at either 350 or 600°C, was allowed to react with vaporized trimethylaluminum (TMA) at 250°C. Modified carriers and heterogeneous catalysts were characterized with FTIR, ¹H MAS (magic-angle spinning) NMR, ¹³C, and ²⁹Si CP (cross-polarization) MAS NMR spectroscopies and elemental analyses. In the reaction of TMA with silica, a saturated surface was formed consisting of different (---O)_4−nSi(CH₃)_n (n=1, 2 or 3) and ---AlCH₃ groups. The ratio of ---SiMe to ---AlMe groups was approximately 1.5 in the TMA/SiO₂ carriers. When the metallocene was adsorbed onto the carrier it seemed to react with the surface ---AlCH₃ groups and possibly ---ZrCH₃ groups were formed. Heterogeneous catalysts were tested in the polymerization of ethylene and propylene in the presence of methylalumoxane (MAO). And they produced similar polymer as the homogeneous rac-Et(Ind)₂ZrCl₂ catalyst, but with lower activity. A catalyst with the best activity was achieved from silica that was preheated at 600°C. Moreover, leaching of catalyst was examined whereupon a part of zirconium was observed to desorb from the carrier.     

Analysis of plate in second strain gradient elasticity

The bending analysis of a thin rectangular plate is carried out in the framework of the second gradient elasticity. In contrast to the classical plate theory, the gradient elasticity can capture the size effects by introducing internal length. In second gradient elasticity model, two internal lengths are present, and the potential energy function is assumed to be quadratic function in terms of strain, first- and second-order gradient strain. Second gradient theory captures the size effects of a structure with high strain gradients more effectively rather than first strain gradient elasticity. Adopting the Kirchhoff’s theory of plate, the plane stress dimension reduction is applied to the stress field, and the governing equation and possible boundary conditions are derived in a variational approach. The governing partial differential equation can be simplified to the first gradient or classical elasticity by setting first or both internal lengths equal to zero, respectively. The clamped and simply supported boundary conditions are derived from the variational equations. As an example, static, stability and free vibration analyses of a simply supported rectangular plate are presented analytically.     

Fabrication of enclosed SU-8 tips for electrospray ionization-mass spectrometry

We describe a novel electrospray tip design for MS which is fabricated completely out of SU-8 photoepoxy. A three-layer SU-8 fabrication process provides fully enclosed channels and tips. The tip shape and alignment of all SU-8 layers is done lithographically and is therefore very accurate. Fabrication process enables easy integration of additional fluidic functions on the same chip. Separation channels can be made with exactly the same process. Fluidic inlets are made in SU-8 during the fabrication process and no drilling or other postprocessing is needed. Channels have been fabricated and tested in the size range of 10 microm x 10 microm-50 microm x 200 microm. Mass spectrometric performance of the tips has been demonstrated with both pressure-driven flow and EOF. SU-8 microtips have been shown to produce stable electrospray with EOF in a timescale of tens of minutes. With pressure driven flow stable spray is maintained for hours. Taylor cone was shown to be small in volume and well defined even with the largest channel cross section. The spray was also shown to be well directed with our tip design.