4 research outputs found
Microstructures of negative and positive azeotropes
Azeotropes famously impose fundamental restrictions on distillation processes, yet their special thermodynamic properties make them highly desirable for a diverse range of industrial and technological applications. Using neutron diffraction, we investigate the structures of two prototypical azeotropes, the negative acetone–chloroform and the positive benzene–methanol azeotrope. C–H⋯O hydrogen bonding is the dominating interaction in the negative azeotrope but C–Cl⋯O halogen bonding contributes as well. Hydrogen-bonded chains of methanol molecules, which are on average longer than in pure methanol, are the defining structural feature of the positive azeotrope illustrating the fundamentally different local mixing in the two kinds of azeotropes. The emerging trend for both azeotropes is that the more volatile components experience the more pronounced structural changes in their local environments as the azeotropes form. The mixing of the acetone–chloroform azeotrope is essentially random above 20 Å, where the running Kirkwood–Buff integrals of our structural model converge closely to the ones expected from thermodynamic data. The benzene–methanol azeotrope on the other hand displays extended methanol-rich regions and consequently the running Kirkwood–Buff integrals oscillate up to at least 60 Å. Our study provides the first experimental insights into the microstructures of azeotropes and a direct link with their thermodynamic properties. Ultimately, this will provide a route for creating tailored molecular environments in azeotropes to improve and fine-tune their performances
Polar stacking of molecules in liquid chloroform
Using neutron diffraction and the isotopic substitution technique we have investigated the local structure of liquid chloroform. A strong tendency for polar stacking of molecules with collinear alignment of dipole moments is found. We speculate that these polar stacks contribute to the performance of chloroform as a solvent
How the Surface Structure Determines the Properties of CuH
CuH
is a material that appears in a wide diversity of circumstances ranging
from catalysis to electrochemistry to organic synthesis. There are
both aqueous and nonaqueous synthetic routes to CuH, each of which
apparently leads to a different product. We developed synthetic methodologies
that enable multigram quantities of CuH to be produced by both routes
and characterized each product by a combination of spectroscopic,
diffraction and computational methods. The results show that, while
all methods for the synthesis of CuH result in the same bulk product,
the synthetic path taken engenders differing surface properties. The
different behaviors of CuH obtained by aqueous and nonaqueous routes
can be ascribed to a combination of very different particle size and
dissimilar surface termination, namely, bonded hydroxyls for the aqueous
routes and a coordinated donor for the nonaqueous routes. This work
provides a particularly clear example of how the nature of an adsorbed
layer on a nanoparticle surface determines the properties