Use of poly(styrene)-block-poly(ethyleneoxide) as emulsifier in emulsion polymerization

Summary Poly(styrene)-block-poly(ethyleneoxide), abbreviated as (PS-b-PEO) were used as emulsifiers in emulsion polymerization of styrene and methyl methacrylate. The block copolymers had a poly(styrene) block with M_n=1000 g/mol and a poly(ethyleneoxide) block with M_n=1000, 3000 or 5000 g/mol, respectively. Stable dispersions were obtained when the PEO block molecular weight was higher than 1000 g/mol. Also the amphiphilic properties of the copolymers depended on the PEO chain length. Block copolymer micelles with hydrodynamic radii between 11 and 17nm were observed. Emulsion polymerization was performed at different block copolymer concentration at 60 and 80°C. Particle size varied between 50 and 300nm and decreased with increasing copolymer concentration. The particle size was larger at higher temperature, but the size distribution was narrower. Polymerization of methyl methacrylate gave smaller particles when compared to styrene. The dispersions were very stable towards high electrolyte concentration, but flocculation occurred at elevated temperatures. Both observations indicate that the dispersions are sterically stabilized.     

Mechanical properties of organosolv-lignin-filled thermoplastics

Summary Organosolv lignin was used as organic filler for polypropylene (PP) and poly(ethene-co-vinylacetate) (EVA) containing 13wt-% vinylacetate. As a function of the lignin content, which was varied between 0 and 30wt-%, mechanical properties such as Young's modulus, yield stress, fracture stress, and elongation at break of the thermoplastic lignin-based compounds were measured. Both lignin-filled thermoplastics exhibit pronounced matrix reinforcement with increasing lignin content. Due to better interfacial adhesion between lignin and EVA, 30wt-% lignin addition to EVA doubles Young's modulus without sacrificing high elongation at break.     

Characterization of Mg-doped InP grown by MOCVD using a bis(methylcyclopentadienyl)magnesium dopant source

The use of bis(methylcyclopentadienyl)magnesium (MCp₂Mg) as ap-dopant source for MOCVD-grown InP has been investigated. The Mg incorporation was nonlinear. The relationship between the H₂ flow through the MCp₂Mg bubbler and the Mg concentra-tion in the epilayers suggested that when [Mg] <20 ppb in the reactor it was mostly depleted from the gas mixture, probably by means of reaction with O₂ or H₂O, but at higher concentrations a large fraction of the Mg diffusing to the epilayers was incor-porated. For concentrations >10¹⁹ cm^s-3 the layer morphology deteriorated and stacking faults were observed by TEM, at a density greater than 10⁹ cm^s−2. Significant diffusion of Mg into the substrates during the growth was observed, with diffusion depths up to 0.1 μm at a concentration of 10¹⁹ cm^s−3 in S-doped, and up to 32 μm at 10¹⁷ cm^s-3 in Fe-doped substrates. These concentrations correspond to the S and Fe doping level in those substrates, and the results are explained in terms of the formation of a complex between the S or Fe dopants and the diffusing Mg, which immobilizes the latter species. At [Mg] >10¹⁸ cm^s−3, the net hole concentration, measured by means of electrochemical C-V pro-filing, decreases with increasing [Mg], indicating significant self compensation. Com-pensation at high [Mg] was also suggested by the effect of excitation power density on the peak shift of the donor to acceptor transition observed during photoluminescence measurements at 7 K.     

A current-mode biquadratic amplitude equalizer

A boost biquad transfer function with two symmetrical zeros on the real axis is derived; it provides a technique for amplitude equalization with a second-order continuous-timeg _m -C section using current injection. The synthesis procedure yields a differential boost biquad consisting of three double-input OTAs and a single-input high-g _m boost OTA. SPICE simulations show that for boost gain up to 20 dB the phase of the biquad is essentially unaffected. The presented technique is found suitable for amplitude equalization of disk-drive read channels operating in the range of 100 MHz.