Characterization of natural resin materials using water adsorption and various advanced techniques

A physicochemical characterization of natural raw resin material was evaluated and reported. The studied material is a natural resin, a natural product from pinus halepensis trees which is collected from the forests of Chalkidiki region of North Greece. The plurality of this product combined with its special property of removing water from commercial liquid fuels commands the detailed physicochemical characterization of this material. In particular, various techniques, such as water adsorption at 22 °C, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy and X-ray diffraction, were used in order to evaluate the structural and surface properties of the material. The water adsorption isotherm was also measured and fitted using the Guggenheim, Anderson and De Boer model in order to correlate the water activity characteristics. In addition, the kinetics of the adsorption was also fitted with good accuracy using the exponential Chapman model. Furthermore, as the results show, the natural resin presents good thermal characteristics. Finally, the studied material presents efficient water adsorption properties, up to 246.8 mmol/g, and it can be proposed as a promising dehydration material.     

Stepwise aromatic nucleophilic substitution in continuous flow. Synthesis of an unsymmetrically substituted 3,5-diamino-benzonitrile library

Aromatic or heteroaromatic ring precursors with 2–3 identical functionalities are often used in sequential derivatization depending on the reactivity difference or the selective execution of the reaction such as nucleophilic aromatic substitution. Continuous flow chemistry offers an enhanced parameter space (pressure and temperature) with rapid parameter optimization that ensures selectivity in many cases. We developed a flow chemistry procedure to carry out a stepwise aromatic nucleophilic substitution of difluoro-benzenes having an activating group in meta position to the fluorines. The mono-aminated products were obtained in high yield and selectivity in an extremely short reaction time, while applying higher temperature, longer reaction zone (or time), and employing higher excess of another amine reactant, the subsequent introduction of the second amino group was also successfully achieved leading to an unsymmetrically substituted 3,5-diamino-benzonitrile library.     

Yield stress fluids and ageing

Many high-concentration multiphase materials that are industrially and academically important do not reach thermodynamic equilibrium because of kinetic constraints originating from the structurally arrested microstructure. However, owing to thermal or elastic energy of the constituents, their microstructure progressively reorganizes to form thermodynamically more stable states. In this physical ageing process, the whole spectrum of relaxation times evolves that makes relaxation dynamics increasingly sluggish. In a process of rejuvenation, deformation field increases mobility, but non-trivially alters the shape of relaxation time spectrum. Interestingly, this class of materials also demonstrates yield stress, whose origin could be closely related to physical aging, and as a result, it depends on time and deformation history. In this review, we present an overview of experimental behaviors and theoretical advances that indicate a complex coupling between ageing and rejuvenation for this class of materials having diverse microstructures.