Stefano Angioletti-Uberti

Re-entrant melting as a design principle for DNA-coated colloids

Colloids functionalized with DNA hold great promise as building blocks for complex self-assembling structures. However, the practical use of DNA-coated colloids (DNACCs) has been limited by the narrowness of the temperature window where the target structures are both thermodynamically stable and kinetically accessible. Here we propose a strategy to design DNACCs, whereby the colloidal suspensions crystallize on cooling and then melt on further cooling. In a phase diagram with such a re-entrant melting, kinetic trapping of the system in non-target structures should be strongly suppressed. We present model calculations and simulations that show that real DNA sequences exist that should bestow this unusual phase behaviour on suitably functionalized colloidal suspensions. We present our results for binary systems, but the concepts that we develop apply to multicomponent systems and should therefore open the way towards the design of truly complex self-assembling colloidal structures.

A general theory of DNA-mediated and other valence-limited colloidal interactions

We present a general theory for predicting the interaction potentials between DNA-coated colloids, and more broadly, any particles that interact via valence-limited ligand-receptor binding. Our theory correctly incorporates the configurational and combinatorial entropic factors that play a key role in valence-limited interactions. By rigorously enforcing self-consistency, it achieves near-quantitative accuracy with respect to detailed Monte Carlo calculations. With suitable approximations and in particular geometries, our theory reduces to previous successful treatments, which are now united in a common and extensible framework. We expect our tools to be useful to other researchers investigating ligand-mediated interactions. A complete and well-documented Python implementation is freely available at http://github.com/patvarilly/DNACC.

Solid-liquid interface free energy through metadynamics simulations

The solid-liquid interface free energy

Ab initio simulations of molten Ni alloys

{\ensuremath{\gamma}}_{sl}

Predicting DNA-mediated colloidal pair interactions

is a key parameter controlling nucleation and growth during solidification and other phenomena. There are intrinsic difficulties in obtaining accurate experimental values, and the previous approaches to compute

Theory and simulation of DNA-coated colloids: a guide for rational design

{\ensuremath{\gamma}}_{sl}

Thermosensitive Cu2O–PNIPAM core–shell nanoreactors with tunable photocatalytic activity

with atomistic simulations are computationally demanding. We present an approach which is to obtain

Theory of Solvation-Controlled Reactions in Stimuli-Responsive Nanoreactors

{\ensuremath{\gamma}}_{sl}

Competitive Protein Adsorption to Soft Polymeric Layers: Binary Mixtures and Comparison to Theory

from a free-energy map of the phase transition reconstructed by metadynamics. We apply this to the benchmark case of a Lennard-Jones potential, and the results confirm the most reliable data obtained previously. We demonstrate several advantages of our approach: it is simple to implement, robust and free of hysteresis problems, it allows a rigorous and unbiased estimate of the statistical uncertainty, and it returns a good estimate of the thermodynamic limit with system sizes of a just a few hundred atoms. It is therefore attractive for applications which require more realistic and specific models of interatomic forces.

Catalyzed Bimolecular Reactions in Responsive Nanoreactors

Convective instabilities responsible for misoriented grains in directionally solidified turbine airfoils are produced by variations in liquid–metal density with composition and temperature across the solidification zone. Here, fundamental properties of molten Ni-based alloys, required for modeling these instabilities, are calculated using ab initio molecular dynamics simulations. Equations of state are derived from constant number-volume-temperature ensembles at 1830 and 1750 K for elemental, binary (Ni–X, X=Al, W, Re, and Ta) and ternary (Ni–Al–X, X=W, Re, and Ta) Ni alloys. Calculated molar volumes agree to within 0.6%–1.8% of available measurements. Predictions are used to investigate the range of accuracy of a parameterization of molar volumes with composition and temperature based on measurements of binary alloys. Structural analysis reveals a pronounced tendency for icosahedral short-range order for Ni–W and Ni–Re alloys and the calculations provide estimates of diffusion rates and their dependence ...