Chain dynamics in microgels: poly(N-vinylcaprolactam-co-N-vinylpyrrolidone) microgels as examples

Microgels are highly swollen colloids built up of flexible cross-linked chains. We studied the static and dynamic light scattering (LS) behavior of thermosensitive microgels based on N-vinylcaprolactam and N-vinylpyrrolidone prepared by precipitation copolymerization in H2O (CP-1) and D2O (CP-2). Striking differences in behavior were observed in the two solvents. In both cases the angular dependence of static LS could reasonably well be described by a soft sphere model (J. Polym. Sci., Polym. Phys. Ed. 1982, 20, 157) with small deviations at large qRg. At temperatures larger than the collapse temperatures, the CP-1 sample in water started to aggregate whereas the CP-2 sample in D2O showed no association and developed the expected change toward hard sphere behavior. Dynamic LS permitted the determination of internal or segmental mobility. A remarkable shift toward large qRg was found for CP-1 compared to the behavior of linear chains. The dynamic behavior is clearly displayed in a plot of Gamma*(q) = (Gamma1(q)/q3)(eta0/kT), with Gamma1(q) the first cumulant of the field time correlation function and the common meaning of the other parameters. A long range of hard sphere behavior indicated the suppression of internal modes, but at large qRg the swollen microgel CP-1 in water displayed internal motions with a spectrum similar to that of Zimm relaxations. No internal mobility could be detected with the CP-2 sample in D2O. The behavior is in agreement with observations in the literature. The differences in the two similar solvents were attributed to the poorer solvent quality of D2O.     

Binukleare Nickel(II)‐Komplexe mit Oxalamidinaten als Brückenliganden: Synthese und Strukturen von Verbindungen mit planarer,tetraedrischer, tetragonal‐pyramidaler und oktaedrischer Koordination

Binuclear Nickel(II) Complexes with Oxalamidinates as Bridging Ligands: Synthesis and Struktures of Compounds with Planar, Tetrahedral, Tetragonal‐pyramidal, and Octahedral Coordination Oxalamidines R¹–NH–C(=NR²–C(=NR²)–NH–R¹ react selectively with Ni(acac)₂ under formation of the planar complexes [(acac)Ni(oxalamidinate)Ni(acac)]. Two crystal structures of the binuclear complexes with R = R′ = Ph ( 1 ) or p‐tolyl ( 2 ) show that the bridging oxalamidinates bind as bidendate ligands at each Nickel(II) atom. In contrast, the more sterically demanding fragment (Ph₃P)NiBr can only coordinate at sterically less demanding oxalamidinates to form complexes of the type [(Ph₃P)NiBr]₂(oxalamidinate) with tetrahedral coordination of Ni^II found by X‐ray analyses. Oxalamidines containing additional donor atoms in the side arms react very different, but in each case under formation of binuclear complexes, such as [(acac)₂Ni]₂( H₂E ) ( 8 ) (with R¹: –(CH₂)₃PPh₂, R²: p‐tolyl) in which the oxalamidine acts as bidentate neutral P,N‐ligand and the Ni^II atom has an octahedral environment. H₂F (with R¹: –(CH₂)₃PPh₂, R²: Mesityl), however, yields the planar complex [(acac)Ni]₂( F ) ( 9 ) with dianionic oxalamidinate under elimination of acetylacetone. There is no coordination of the donor groups of the side arms in the solid state of complex 9 , in contrast to the analogous binuclear complex [(acac)Ni]₂( H ) 10 (R¹: –CH₂–CH₂‐2‐pyridyl, R²: Mesityl). In this complex a distorted tetragonal‐pyramidal coordination of Ni^II is achieved. 2 reacts with an excess of LiCH₃ under elimination of the oxalamidinate to form the cluster compound Li₄(THF)₄Ni₂Me₈ in very good yields, while 9 yields the THF poorer cluster Li₂(THF)₂Li₂Ni₂Me₈ under similar conditions.     

ADOL‐C: Automatic Differentiation Using Operator Overloading in C++

In this paper, we present two strategies for the implementation of Automatic Differentiation (AD) based on the operator overloading facility in C++. Subsequently, we describe the capabilities of the AD‐tool ADOL‐C that applies operator overloading to differentiate C‐ and C++‐code. Finally, we discuss some applications of ADOL‐C.     

Synthesis by ATRP of poly(ethylene‐co‐butylene)‐block‐polystyrene,poly(ethylene‐co‐butylene)‐block‐poly(4‐acetoxystyrene) and its hydrolysis product poly(ethylene‐co‐butylene)‐block‐poly(hydroxystyrene)

Diblock copolymers of poly(ethylene‐co‐butylene) and polystyrene or poly(4‐acetoxystyrene) are synthesized by atom transfer radical polymerization (ATRP) using a 2‐bromopropionic ester macroinitiator prepared from commercial monohydroxyl functional narrow dispersity hydrogenated polybutadiene (Kraton Liquid Polymer, L‐1203). ATRP carried out in bulk and in xylene solution with cuprous bromide and two different complexing agents 2,2′‐bipyridine (bipy) and 1,1,4,7,10,10‐hexamethyltriethylenetetraamine (HMTETA) yielded well‐defined diblock copolymers with polydispersities around 1,3. The diblock copolymer with poly(4‐acetoxystyrene) was hydrolyzed to the corresponding poly(4‐hydroxystyrene) sequence.     

InAs/GaSb superlattices for advanced infrared focal plane arrays

We report on the development of high performance focal plane arrays for the mid-wavelength infrared spectral range from 3–5 μm (MWIR) on the basis of InAs/GaSb superlattice photodiodes. An investigation on the minority electron diffusion length with a set of six sample ranging from 190 to 1000 superlattice periods confirms that InAs/GaSb superlattice focal plane arrays achieve very high external quantum efficiency. This enabled the fabrication of a range of monospectral MWIR imagers with high spatial and excellent thermal resolution at short integration times. Furthermore, novel dual-color imagers have been developed, which offer advanced functionality due to a simultaneous, pixel-registered detection of two separate spectral channels in the MWIR.