On the use of catalysis to bias reaction pathways in out-of-equilibrium systems

We show, via simulations, how catalytic control over individual paths in a fuel-driven non-equilibrium chemical reaction network in batch or flow gives rise to responses in maximum conversion, lifetime and steady states.

Transient Colloid Assembly by Fuel-Driven Modulation of Depletion Interactions

In biology, energy stored in chemical fuels is used to drive processes energetically uphill, enabling the highly dynamic behavior of living organisms. The out-of-equilibrium behavior can propagate from molecular reaction networks to the micro- and macroscopic scale. These natural phenomena have sparked the design of man-made out of equilibrium chemical reaction networks (CRNs) and dissipative assembly systems with hydrogels, (supra)polymers, vesicles/micelles and colloids. In colloidal systems, the assembly process is typically controlled by balancing the interaction forces. Here, we use a polymeric depletant integrated in a fuel driven esterification CRN to induce transient colloidal assembly. The polymer undergoes a temporal coil-globule transition upon acetylation by the chemical fuel. In the random coil conformation it acts as depletant agent for the silica colloids, promoting colloidal aggregation. As compact globule, the polymer loses its<br>depletant characteristics. During the fuel cycle the polymer cyclically transitions from one form to the other, directly influencing colloidal aggregation and redispersion. Thus, a fuel-driven CRN on the molecular scale results in a microscopic response with a transient colloidal depletion cycle. Overall, the time-dependent propagation of out-of-equilibrium activity across length scales presented here, offers opportunities to design responsive materials with life like properties.

Transient Colloid Assembly by Fuel-Driven Modulation of Depletion Interactions

In biology, energy stored in chemical fuels is used to drive processes energetically uphill, enabling the highly dynamic behavior of living organisms. The out-of-equilibrium behavior can propagate from molecular reaction networks to the micro- and macroscopic scale. These natural phenomena have sparked the design of man-made out of equilibrium chemical reaction networks (CRNs) and dissipative assembly systems with hydrogels, (supra)polymers, vesicles/micelles and colloids. In colloidal systems, the assembly process is typically controlled by balancing the interaction forces. Here, we use a polymeric depletant integrated in a fuel driven esterification CRN to induce transient colloidal assembly. The polymer undergoes a temporal coil-globule transition upon acetylation by the chemical fuel. In the random coil conformation it acts as depletant agent for the silica colloids, promoting colloidal aggregation. As compact globule, the polymer loses its<br>depletant characteristics. During the fuel cycle the polymer cyclically transitions from one form to the other, directly influencing colloidal aggregation and redispersion. Thus, a fuel-driven CRN on the molecular scale results in a microscopic response with a transient colloidal depletion cycle. Overall, the time-dependent propagation of out-of-equilibrium activity across length scales presented here, offers opportunities to design responsive materials with life like properties.

Growth of Crystalline Silicon Carbide by CVD Using Chlorosilane Gases

The forefront of semiconductor silicon carbide technology now approaches commercialization for both materials and device technology. The commercialization of SiC epitaxy processes requires improvement in defect density, uniformity and repeatability. Especially problematic are graphite particles, gas phase nucleation of particles and the limitations placed on achieving growth rates that can positively impact process costs. When it approached the same historical point of development, silicon epitaxy technology shifted to the use of chlorosilane precursor gases to suppress gas phase nucleation and achieve targeted growth rates. Recent work on SiC epitaxy chemistry now investigates the use of HCl, halocarbons and most recently chlorosilane precursors. This paper will review the original work on gas phase nucleation and its control in silicon epitaxy processes using HCl additives and chlorosilanes. Using established dissociation pathways for chlorosilanes, equilibrium chemical reaction models are used to assess the impact of HCl, halocarbons and chlorosilane precursors on growth rates and particle formation SiC epitaxy. Experimental data is presented on the comparative performance of HCl additive and chlorosilane precursors in SiC epitaxy and film properties.

Re-Entrant Hexagons and Locked Turing–Hopf Fronts in the CIMA Reaction

Aspects of the mode-interaction and pattern-selection processes in far-from-equilibrium chemical reaction–diffusion systems are studied through numerical simulation of the Lengyel–Epstein model. By varying the feed concentrations, a transition is observed in which hexagons are replaced by stripes and these again by inverted hexagons. The competition between Hopf oscillations and Turing stripes is investigated by following the propagation of a front connecting the two modes. In certain parameter regimes, mode-locking is found to occur. The front then moves an integer number of Turing stripes during an integer number of Hopf oscillations. This phenomenon can be seen as arising from depinning of the Turing front under influence of the Hopf mode.