Adhesion between oppositely charged polyelectrolytes

The adhesion between a grafted polyelectrolyte layer (brush) and a gel of an oppositely charged polyelectrolyte has been measured as a function of applied pressure, and the interface has been traced using neutron reflectometry. The interface (in aqueous medium at pH 6) between the (polycationic) brush and the (polyanionic) gel has a limited pressure dependence, with a small amount of deformation of the interface at the brush–gel contact. Brushes with a dry thickness of up to 13 nm exhibit weak adhesion (measured using a mechanical force tester) with an adhesive failure when the gel is detached. Thicker brushes result in the gel exhibiting cohesive failure. Reversing the geometry, whereby a polycationic brush is replaced with a polyanion and the polyanionic gel is replaced with a polycation, reveals that the pH dependence of the adhesion is moderately symmetric about pH 6, but that the maximum force required to separate the polycation gel from the polyanion brush over the range of pH is greater than that for the polycation brush and polyanion gel. The polyanion used is poly(methacrylic acid) (PMAA) and polycations of poly[2-(diethylamino)ethyl methacrylate] (PDEAEMA) and poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) were used.     

Enhanced gas migration through permeable bubble networks within consolidated soft sediments

Many consolidated sediments experience in situ gas generation from methanogenesis, corrosion, or radiolysis reactions and can retain bubbles for long periods. Particular interest is motivated by the retention and acute release of flammable hydrogen from nuclear legacy waste sludge. X‐ray computed tomography was employed to observe 0.07–10 mm bubble populations within 30–1112 Pa yield strength Mg(OH)₂ sediments. High rates of partial coalescence were observed among sub‐millimeter microvoids, forming extensive bubble networks which spanned the 32 mm field of view. Lattice Boltzmann and Monte Carlo modeling demonstrated these networks to be highly pervious to gas, with effective diffusivities for hydrogen of 3.7–12.5 × 10^?5 m² s^?1. Continuous vessel‐spanning bubble networks, dynamic connectivity between ganglia of coalesced bubbles, Haines jumps, and composite diffusion through the gas and aqueous phase can account for enhanced gas migration over length‐scales of several meters, thus enabling chronic gas release from low‐intermediate strength sediments ( kPa) too strong for buoyant bubble ebullition and too weak for vertical channel formation. © 2018 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers. AIChE J, 64: 4131–4147, 2018     

Identification of Sulfur‐Containing Impurities in Biodiesel Produced From Brown Grease

Fatty acid methyl esters (FAME) from waste grease usually contain higher concentrations of sulfur (S) than allowed to meet the specified quality standard for biodiesel (<15 ppm). Brown grease lipid‐derived FAME was produced and fractionated by two passes through a wiped‐film evaporator (WFE) to produce three fractions: (1) a 120 °C pass distillate, (2) a 170 °C pass distillate, and (3) a heavy residue. Solid phase extraction (SPE) was used to concentrate the S species from the distillate fractions so that they could be detected by a gas chromatography–pulsed flame photometric detector (GC–PFPD) and GC–mass spectrometry (MS). The ethyl acetate and methanol (MeOH) fractions obtained by SPE of the 120 °C WFE distillate and methyl tert‐butyl ether and acetone fractions obtained by SPE of the 170 °C WFE distillate had the highest concentration of S and were, therefore, the best candidates for GC–PFPD analysis. GC–PFPD methods were developed to separate the S species adequately enough for those peaks to be analyzed by GC–MS which matched fragmentation patterns identified by the MS chemical library as tetrahydrothiophenes, dithiolanes, and thiophenes. MS fragmentation patterns were used to identify other, larger, S‐bearing species as sulfides and disulfides cross‐linking between two FAME molecules. The results obtained from this study provide a foundation for developing effective purification methods to remove S‐containing impurities from waste grease‐derived biodiesel.     

Remendable polymers via reversible Diels–Alder cycloaddition of anthracene‐containing copolymers with fullerenes

Poly(lauryl methacrylate)s with anthracene moieties in the side chain were converted with C₆₀‐fullerene and phenyl‐C₆₁‐butyric acid methyl ester (PCBM), resulting in new remendable (self‐healing) polymeric materials. The utilization of differently substituted anthracene monomers enabled the tuning of the reactivity and the resulting mechanical properties. Copolymers with different contents of the anthracene moieties were synthesized and characterized using size exclusion chromatography, ¹H nuclear magnetic resonance (NMR) spectroscopy as well as differential scanning calorimetry (DSC). ¹H NMR spectroscopic studies were utilized in order to investigate the reversibility of the Diels–Alder reaction between copolymers with C₆₀‐fullerene and PCBM, respectively, in solution. In order to investigate the conversion of the polymers with C₆₀‐fullerene and PCBM in bulk, additionally, DSC, nanoindentation, rheology, atomic force microscopy (AFM), 3D microscopy, simultaneous thermal analysis (STA) and FT‐Raman investigations were performed. The fullerene‐containing copolymers could be healed in a temperature range of 40–80 °C. Consequently, a new generation of low temperature remendable polymers could be established. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45916.     

Tetraacylgermanes as highly efficient photoinitiators for visible light cured dimethacrylate resins and dental composites

Tetrabenzoylgermane 1 and various substituted tetrabenzoylgermanes 2 – 7 were investigated as visible light (VL) photoinitiators (PIs) for dental dimethacrylate resins and dimethacrylate‐based composites. The tetrabenzoylgermanes 1 – 7 show a very strong VL absorption between 400 and 450 nm. Substituents on the benzoyl chromophore strongly influence their properties such as melting point, solubility, absorption behavior, or PI reactivity. A good photobleaching behavior and a very high reactivity as VL PI was found in photo‐differential scanning calorimeter experiments for selected tetrabenzoylgermanes. Composite pastes containing only ～0.1 wt % of Ge‐PI exhibited a sufficient photocuring due to the high PI‐reactivity of the tetraacylgermanes. Among the investigated germane PIs, tetrakis(2‐methylbenzoyl)germane 2 shows the best performance as VL PI for restorative composites and enables the composites to be photocured using an LED with an emission maximum of 500 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46115.     

Unravelling the Carbohydrate‐Binding Preferences of the Carbohydrate‐Binding Modules of AMP‐Activated Protein Kinase

The β subunit of adenosine monophosphate (AMP)‐activated protein kinase (AMPK), which exists as two isoforms (β1 and β2) in humans, has a carbohydrate‐binding module (CBM) that interacts with glycogen. Although the β1‐ and β2‐CBMs are structurally similar, with strictly conserved ligand‐contact residues, they show different carbohydrate affinities. β2‐CBM shows the strongest affinity for both branched and unbranched oligosaccharides and it has recently been shown that a Thr insertion into β2‐CBM (Thr101) forms a pocket to accommodate branches. This insertion does not explain why β2‐CBM binds all carbohydrates with stronger affinity. Herein, it is shown that residue 134 (Val for β2 and Thr for β1), which does not come into contact with a carbohydrate, appears to account for the affinity difference. Characterisation by NMR spectroscopy, however, suggests that mutant β2‐Thr101Δ/Val134Thr differs from that of β1‐CBM, and mutant β1‐Thr101ins/Thr134Val differs from that of β2‐CBM. Furthermore, these mutants are less stable to chemical denaturation, relative to that of wild‐type β‐CBMs, which confounds the affinity analyses. To support the importance of Thr101 and Val134, the ancestral CBM has been constructed. This CBM retains Thr101 and Val134, which suggests that the extant β1‐CBM has a modest loss of function in carbohydrate binding. Because the ancestor bound carbohydrate with equal affinity to that of β2‐CBM, it is concluded that residue 134 plays an indirect role in carbohydrate binding.     

Exploiting the Catalytic Diversity of Short‐Chain Dehydrogenases/Reductases: Versatile Enzymes from Plants with Extended Imine Substrate Scope

Numerous short‐chain dehydrogenases/reductases (SDRs) have found biocatalytic applications in C=O and C=C (enone) reduction. For NADPH‐dependent C=N reduction, imine reductases (IREDs) have primarily been investigated for extension of the substrate range. Here, we show that SDRs are also suitable for a broad range of imine reductions. The SDR noroxomaritidine reductase (NR) is involved in Amaryllidaceae alkaloid biosynthesis, serving as an enone reductase. We have characterized NR by using a set of typical imine substrates and established that the enzyme is active with all four tested imine compounds (up to 99 % conversion, up to 92 % ee). Remarkably, NR reduced two keto compounds as well, thus highlighting this enzyme family's versatility. Using NR as a template, we have identified an as yet unexplored SDR from the Amaryllidacea Zephyranthes treatiae with imine‐reducing activity (≤95 % ee). Our results encourage the future characterization of SDR family members as a means of discovering new imine‐reducing enzymes.     

Morphology- and ion size-induced actuation of carbon nanotube architectures

ABSTRACT

Future adaptive applications require lightweight and stiff materials with high active strain but low energy consumption. A suitable combination of these properties is offered by carbon nanotube-based actuators. Papers made of carbon nanotubes (CNTs) are charged within an electrolyte, which results in an electrical field forming a double-layer of ions at their surfaces and a deflection of the papers can be detected. Until now, there is no generally accepted theory for the actuation mechanism. This study focuses on the actuation mechanism of CNT papers, which represent architectures of randomly oriented CNTs. The samples are tested electrochemically in an in-plane set-up to detect the free strain. The elastic modulus of the CNT papers is analyzed in a tensile test facility. The influence of various ion sizes of water-based electrolytes is investigated.

During the tests, four parameters that have a significant influence on the mechanical performance of CNT papers were identified: the test conditions, the electrical charging, the microstructure and the ion size. All of these influencing factors point to the mechanically weak inter-tube linking at which the actuation seems to take place. Quadratic voltage-strain correlation suggests a combination of electrostatic and volumetric effects as the possible reason for CNT paper actuation.

Abbreviations: CNT: carbon nanotubes; CV: cyclic voltammetry; CVD: chemical vapor deposition; HiPCO: high pressure carbon monoxide; IL: ionic liquid; MWCNT: multi-walled carbon nanotube; MW: multi-walled; NHE: normal hydrogen electrode; PDMS: polydimethylsiloxane; PMMA: polymethylmethacrylate; PPy: polypyrrole; PVDF: polyvinylidenefluoride; SCE: saturated calomel electrode; SWCNT: single-walled carbon nanotube; SW: single-walled; 1M: one molar concentration     

Evaluation of high temperature polymers in nanolayered films and gradient refractive index (GRIN) lenses

A new polymer nanolayer gradient refractive index (GRIN) system with more robust thermal stability because of incorporation of a high glass transition temperature polyester, OKP4HT, was demonstrated. A combination of extruded nanolayered GRIN film systems, comprised of five unique polymer materials, were combined to produce laminate optics comprised of a large internal refractive index gradient distribution, n = 1.445 – 1.630, without degradation of optical transmissive properties. The optical performance of a series of varied magnitude GRIN lenses, ranging from Δn = 0 to 0.185, was evaluated. Increasing the lens refractive index range resulted in decreased optic sphericalaberrations that followed analytical predictions. An analytical approach was reported to correlate the polymer material upper service temperature (UST) to the onset of polymer material loss modulus as measured by DMTA. Thermo‐optical interferometry measurements of irreversible lens deformation confirmed the lenses UST at 125°C for the OKP4HT/PC system as compared to 75°C for a PMM/SAN17 system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42741.     

Revisiting analysis of phthalate plasticizers concentration in poly(vinyl chloride)

The method of the efficient analysis of di(2‐diethylhexyl) phthalate, tri(2‐ethylhexyl) trimellitate, di(2‐ethylhexyl) terephthalate, and other phthalate plasticizers concentrations in plasticized poly(vinyl chloride) (PVC) was developed. The method is based on quantitative dissolution of the PVC sample in methyl ethyl ketone with the consequent precipitation of PVC with hexane and concentration of phthalate in an organic layer. A capillary column‐based gas chromatographic technique for phthalates separation and quantification was developed and used in conjunction with the PVC and phthalates dissolution technique. The developed method of phthalate plasticizers analysis proved to be relatively fast, reproducible, and straightforward. J. VINYL ADDIT. TECHNOL., 21:197–204, 2015. © 2014 Society of Plastics Engineers