The crystalline state of methylene blue: a zoo of hydrates

A re-investigation of the crystalline state of methylene blue has led to the identification of five different hydrates with clearly distinct structures. These include the already known pentahydrate, a hydrate with 2.2-2.3 equivalents of water, two dihydrates, and a monohydrate. Contrary to older reports, no trihydrate was found. The preparation and characterization of the hydrates as well as the transformations between them are reported. The applied analytical methods include X-ray powder diffraction (XRPD), infrared spectroscopy (ATR-IR), thermogravimetry (TGA), differential scanning calorimetry (DSC), dynamic water vapor sorption (DVS) and solution calorimetry (SolCal). A phase diagram of temperature vs. composition has been established, and the stability domains of the different hydrates as a function of water activity and temperature have been determined based on data from DSC, SolCal and suspension equilibration experiments. Four out of the five hydrates are thermodynamically stable within a certain range of temperature and humidity.     

Microwave-plasma interactions studied via mode diagnostics in ALPHA

The goal of the ALPHA experiment is the production, trapping and spectroscopy of antihydrogen. A direct comparison of the ground state hyperfine spectra in hydrogen and antihydrogen has the potential to be a high-precision test of CPT symmetry. We present a novel method for measuring the strength of a microwave field for hyperfine spectroscopy in a Penning trap. This method incorporates a non-destructive plasma diagnostic system based on electrostatic modes within an electron plasma. We also show how this technique can be used to measure the cyclotron resonance of the electron plasma, which can potentially serve as a non-destructive measurement of plasma temperature.     

Compression of antiproton clouds for antihydrogen trapping

Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report the first detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as ten, by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile and its relation to that of the electron plasma.     

Poly(styrene‐b‐isobutylene) multiarm star‐block copolymers

Multiarm star‐branched polymers based on poly(styrene‐b‐isobutylene) (PS‐PIB) block copolymer arms were synthesized under controlled/living cationic polymerization conditions using the 2‐chloro‐2‐propylbenzene (CCl)/TiCl₄/pyridine (Py) initiating system and divinylbenzene (DVB) as gel‐core‐forming comonomer. To optimize the timing of isobutylene (IB) addition to living PS⊕, the kinetics of styrene (St) polymerization at −80°C were measured in both 60 : 40 (v : v) methyl cyclohexane (MCHx) : MeCl and 60 : 40 hexane : MeCl cosolvents. For either cosolvent system, it was found that the polymerizations followed first‐order kinetics with respect to the monomer and the number of actively growing chains remained invariant. The rate of polymerization was slower in MCHx : MeCl (k_app = 2.5 × 10⁻³ s⁻¹) compared with hexane : MeCl (k_app = 5.6 × 10⁻³ s⁻¹) ([CCl]_o = [TiCl₄]/15 = 3.64 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M). Intermolecular alkylation reactions were observed at [St]_o = 0.93M but could be suppressed by avoiding very high St conversion and by setting [St]_o ≤ 0.35M. For St polymerization, k_app = 1.1 × 10⁻³ s⁻¹ ([CCl]_o = [TiCl₄]/15 = 1.82 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M); this was significantly higher than that observed for IB polymerization (k_app = 3.0 × 10⁻⁴ s⁻¹; [CCl]_o = [Py] = [TiCl₄]/15 = 1.86 × 10⁻³M; [IB]_o = 1.0M). Blocking efficiencies were higher in hexane : MeCl compared with MCHx : MeCl cosolvent system. Star formation was faster with PS‐PIB arms compared with PIB homopolymer arms under similar conditions. Using [DVB] = 5.6 × 10⁻²M = 10 times chain end concentration, 92% of PS‐PIB arms (M_n,PS = 2600 and M_n,PIB = 13,400 g/mol) were linked within 1 h at −80°C with negligible star–star coupling. It was difficult to achieve complete linking of all the arms prior to the onset of star–star coupling. Apparently, the presence of the St block allows the PS‐PIB block copolymer arms to be incorporated into growing star polymers by an additional mechanism, namely, electrophilic aromatic substitution (EAS), which leads to increased rates of star formation and greater tendency toward star–star coupling. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1629–1641, 1999     

Micellization and Adsorption to Carbon Black of Polyisobutylene-Based Ionic Liquids

Ionic liquid-terminated polyisobutylene (PIB-IL) dispersants suitable for stabilization of carbonaceous deposits found in automotive lubricating oils were derived by the quaternization of tertiary amines (1-methyl-imidazole, pyridine, and isoquinoline) with primary bromide-terminated PIB. Characterization of PIB intermediate and PIB-IL dispersants was carried out by nuclear magnetic resonance, gel-permeation chromatography, thermogravimetric analysis (TGA), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and differential scanning calorimetry. PIB-IL micellization in dodecane and characteristics thereof (hydrodynamic radius, aggregation number, and critical micelle concentration) were investigated by static (SLS) and dynamic light scattering; whereupon, the self-association of PIB-IL was found to be highly sensitive to anion hydrophobicity. Qualitative adsorption of PIB-IL onto carbon black was confirmed by Fourier transform infrared and TGA measurements. Using Langmuir adsorption studies, the affinity for and adsorption to carbon black of PIB-IL were characterized. PIB-IL adsorption onto carbon black occurred via cation–π interactions and was identified to be highly dependent on the molar volume of the cation and independent of the anion. From the parameters obtained by the Langmuir adsorption isotherms, the spatial arrangement of PIB-IL on the carbon black surface was elucidated, in which all adsorbed PIB-IL were determined to exist in the elongated brush regime. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 280–299     

Supersymmetric quantization of linearized supergravity

We give a manifestly supersymmetric quantization scheme for linearized supergravity, motivated by the desire to develop a background field method for the full non-linear theory. Supersymmetric gauge-fixing constraints are constructed and the corresponding ghost action is discussed. It is found that the Faddeev-Popov action itself possesses invariances, requiring “secondary” gauge fixing, which in turn leads to “secondary” ghost fields, the latter having normal statistics. The gauge-fixing constraints are used to construct gauge-fixing terms in the action, with a total of four gauge-fixing parameters. The superpropagators are found and may be greatly simplified by certain choices of these parameters.     

A study of 28Si(α, γ)32S resonances below Eα = 3.83 MeV

The γ-decays of eleven resonances in the ²⁸Si(α,γ)³²S reaction below E_α = 3.83 MeV have been studied using a large Ge(Li) detector. Results for branching ratios differ considerably from previous NaI work. The previous discrepancy in radiative strengths for the 2.61 MeV resonance is explained by this data. The strengths of the first five resonances at E_α = 1.77, 1.99, 2.19, 2.37 and 2.42 MeV appear to be (39 ± 13)% lower than previously reported. Spin-parities of l^?, 2⁺ and 2⁺ have been assigned to the levels at 8.50, 8.69 and 8.86 MeV respectively. The radiative width of the E_p = 1.467 MeV, J^π = 3^? resonance in the ³¹P(p,γ)³²S reaction has also been measured.     

Reactions of acyl nitroso compounds with amines: Production of nitroxyl (HNO) with the preparation of amides

Oxidation of hydroxamic acids in the presence of amines generates nitrous oxide (N₂O) and the corresponding amide. The identification of N₂O suggests the intermediacy of nitroxyl (HNO). Retro-Diels Alder dissociation of cyclopentadiene-acyl nitroso compound cycloadducts releases N₂O with amide formation.