Thermoresponsive poly(N-isopropylacrylamide) copolymers: contact angles and surface energies of polymer films

Surface properties of poly(N-isopropylacrylamide) (PNIPAM) copolymer films were studied by contact angle measurements and optical and atomic force microscopy. We prepared a series of copolymers of N-isopropylacrylamide with N-tert-butylacrylamide (NtBA) in order of increasing hydrophobicity. The measurements of the advancing contact angle of water at 37 degrees C were hampered by the observation of a distinct stick/slip pattern on all polymers in the series with the exception of poly(NtBA) (PNtBA). We attributed this behavior to the film deformation by the vertical component of liquid surface tension leading to the pinning of the moving contact line. This was confirmed by the observation of a ridge formed at the pinned contact line by optical microscopy. However, meaningful contact (without the stick/slip pattern and with a time-independent advancing contact angle) angles for this thermoresponsive polymer series could be obtained with carefully selected organic liquids. We used the Li and Neumann equation of state to calculate the surface energy and contact angles of water for all polymers in the series of copolymers and van Oss, Chaudhury, and Good (vOCG) acid-base theory for PNtBA. The surface energies of the thermoresponsive polymers were in the range of 38.9 mJ/m2 (PNIPAM) to 31 mJ/m2 (PNtBA) from the equation of state approach. The surface energy of PNtBA calculated using vOCG theory was 29.0 mJ/m2. The calculated contact angle for PNIPAM (74.5 +/- 0.2 degrees ) is compared with previously reported contact angles obtained for PNIPAM-modified surfaces.     

2D framework materials for energy applications

In recent years a massive increase in publications on conventional 2D materials (graphene, h-BN, MoS₂) is documented, accompanied by the transfer of the 2D concept to porous (crystalline) materials, such as ordered 2D layered polymers, covalent-organic frameworks, and metal–organic frameworks. Over the years, the 3D frameworks have gained a lot of attention for use in applications, ranging from electronic devices to catalysis, and from information to separation technologies, mostly due to the modular construction concept and exceptionally high porosity. A key challenge lies in the implementation of these materials into devices arising from the deliberate manipulation of properties upon delamination of their layered counterparts, including an increase in surface area, higher diffusivity, better access to surface sites and a change in the band structure. Within this minireview, we would like to highlight recent achievements in the synthesis of 2D framework materials and their advantages for certain applications, and give some future perspectives.

In recent years the 2D concept has been transferred from conventional 2D materials to porous 2D framework materials. This minireview takes a closer look onto the preparation of 2D framework materials and their merits for energy applications.     

Convergence of Numerical Algorithms for the Approximations to Riccati Equations Arising in Smart Material Acoustic Structure Interactions

An optimal control problem governed by a coupled hyperbolic-paraboliclike dynamics arising in structural acoustic problems isconsidered. The control operator is assumed to be unbounded on thespace of finite energy (for the so-called boundary or pointcontrol problems). A numerical algorithm (based on FEM methods) forcomputations of discrete solutions to Algebraic Riccati Equations(ARE) is formulated.It is shown that the proposed algorithm provides strongly convergentsolutions of the ARE. As the result, the convergence of optimal solutions as well as the associatedperformance index is established.     

Crystal and molecular structure of 2-cyano-2-phenyl-sparteinium perchlorate

The structure of the title compound has been solved and found to comprise two ionic components. The cation skeleton is built of two quinolizidine moieties with transAIE andcis C/D conformation. The phenyl-substituent is in an equatorial orientation, with the cyano-substituent axial. Owing to N(16) protonation, an intramolecular hydrogen bond has been formed with an N(1)N⁺(16) distance of 2.763(5) Å. The protonation and subsequent hydrogen-bond formation are the main factors that cause an inversion of the N(16) configuration. The cyano-substituent at C(2) has weakened the intramolecular hydrogen bond in comparison with that of 2-phenylsparteinium cation.     

Carbamoylphosphonates part 7. An efficient method for the synthesis of hindered carbamoylphosphonates using 4-nitrophenoxycarbonylphosphonate diesters

Hindered primary amines that resist other reagents can be converted to carbamoylphosphonates by means of 4-nitrophenoxycarbonylphosphonate diesters in high yields and under mild conditions.     

The synthesis and conformational analysis of optical isomers of 4-phenyl-perhydropyrido[1,2-a]pyrazine-1,3-dione: an example of ‘solid state–frozen’ dynamics in nitrogen-bridged bicyclic 2,6-diketopiperazines

The synthesis, chemical properties, and conformational analysis of enantiopure (4R,9aS)-, (4S,9aR)-, (4S,9aS)-, and (4R,9aR)-4-phenyl-perhydropyrido[1,2-a]pyrazine-1,3-diones having potential biological activity are described. An interesting example of the coexistence of two invertomers of the (4R,9aR)-diastereomer in a single crystal unit cell is reported. The invertomers differ in the cis/trans-relationship between the fused rings and in the absolute configuration at the chiral nitrogen atom. The structure and equilibrium distributions of the respective conformers have been determined by NMR spectroscopy in both polar and non-polar solvents at various temperatures. The NMR spectra show that dynamic processes in the imide parts of the interconverting species are restrained by self-aggregation. The (4S,9aR)-diastereomer exists in a single conformation with insignificant dynamic effects.     

High concentration of hematite nanoparticles in a silica matrix: Structural and magnetic properties

The α-Fe₂O₃/SiO₂ nanocomposite containing 45 wt% of hematite was prepared by the sol-gel method followed by heating in air at 200 °C. The so-obtained composite of iron(III) nanoparticles dissolved in glassy silica matrix was investigated by X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. XRPD confirms the formation of a single-phase hematite sample, whereas TEM reveals spherical particles in a silica matrix with an average diameter of 10 nm. DC magnetization shows bifurcation of the zero-field-cooled (ZFC) and field-cooled (FC) branches up to the room temperature with a blocking temperature T_B=65 K. Isothermal M(H) dependence displays significant hysteretic behaviour below T_B, whereas the room temperature data were successfully fitted to a weighted Langevin function. The average particle size obtained from this fit is in agreement with the TEM findings. The small shift of the T_B value with the magnetic field strength, narrowing of the hysteresis loop at low applied field, and the frequency dependence of the AC susceptibility data point to the presence of inter-particle interactions. The analysis of the results suggests that the system consists of single-domain nanoparticles with intermediate strength interactions.     

Modeling spatio-temporal field evolution

Prediction of spatio-temporal field evolution is based on the extraction of a physical law from joint experimental data. This extraction is usually described by a set of differential equations. If the only source of information is a field record, a method of field generators based on nonparametric modeling by conditional average can successfully replace differential equations. In this article we apply the method of field generators to a two-dimensional chaotic field record that describes the asynchronous motion of high-amplitude striations. We show how to choose the model structure in order to optimize the quality of the prediction process.