Spreading of sessile water droplets on a solid graphite surface has been studied using atomistic molecular dynamics techniques. The system is in the partial wetting regime and a straightforward scheme is applied to extract the contact angle from the atomistic simulations. Even for droplets containing a thousand molecules, the calculated contact angle for water is 83°, which is close to the experimental macroscopic value. On addition of ethanol, the contact angle decreases to 30°and we approach complete wetting. Time-averaged structural analyses show that the ethanol molecules form a monolayer on top of the solid surface. A few Å above the solid surface, the ethanol molecules are preferentially located at the liquid/vapor interface rather than in the bulk of the droplet.

We present results of molecular dynamics simulations of water droplets at pillar surfaces comprised of sheets of carbon atoms. We examine variations in the contact angle with the height of the pillars. A crossover is observed between the Wenzel and Cassie−Baxter regimes when the height of the pillar is changed.

The experimental observation that certain crystal faces do not grow, despite being in contact with supersaturated solution, is a widely reported phenomenon. This concept of a growth 'dead zone' has been known for many years but its origin remains an unresolved problem in crystal growth. Sometimes it seems to be an inherent feature of the solution growth process while at others it appears that an impurity is an essential element for its appearance. Here we review existing data and provide new experimental evidence to confirm the widespread existence of the dead zone across a range of molecular materials. Available crystal growth kinetics are confronted with mechanistic models. Examination of the packing arrangements of appropriate crystal faces suggests that this behavior is linked to molecular scale surface roughness.Supporting information for this article is given via a link at the end of the document. Entry for the Table of Contents FULL PAPERThe 'general' existence of the dead zone has been confirmed and it appears to be related to surface rugosity.

A workflow for tailor-made additive screening and crystallisation control using a combination of molecular modelling and experimental techniques is presented. The impact of seven structurally analogous additives, the majority of which containing a carboxylic acid group, on the nucleation of alpha-para-aminobenzoic acid is assessed. Intermolecular grid-search modelling is used to determine dimer interaction energies. Of these, three tailor-made additives are found to form stronger carboxylic group dimer interactions with the compound. Solvation energy calculations demonstrate the stability of these dimers in solution. Subsequent intermolecular interaction assessment demonstrates an ability of one of the tailor-made additives to interfere with the molecular preassembly route to nucleation, with molecular charge distributions providing an insight into this effect. Polythermal crystallisation experimental screening confirms the effectiveness of these tailor-made additives to inhibit nucleation. Interestingly, the nucleation mechanism is found to change from instantaneous to progressive nucleation in the absence and presence of the tailor-made additives in solution, respectively, together with an increase in the effective interfacial tension.It includes: pABA crystallisation background science, grid optimization, intermolecular interaction energies and contributions, dimer interaction geometries, dimer solvation and pABA interaction energies, TMAs within pABA crystal structure, statistical T-test, TMA screen MSZWs, pABA optical micrographs, crystallisation and dissolution temperatures, crystallisability and van't Hoff analysis and nucleation kinetic analysis.

The molecular mechanisms underpinning the effects of impurities (reaction byproduct) on the crystallization of N-phosphonomethyl glycine (PMG), a common herbicide, are presented. The impurities, iminobismethylene phosphonic acid (IMPA) and amino methyl phosphonic acid (AMPA), were incorporated into PMG crystals by selectively adsorbing onto the (100) face, and subsequently, caused major reduction in the growth rate of this face of the crystal. In contrast, the impurity N-phosphonomethyl imino diacetic acid (PIDA), with a lower binding affinity to PMG crystals, did not affect the crystal habit significantly. These experimental results are rationalized based on stereospecific interaction of the impurities with the PMG crystal and binding energy calculations. Interestingly, when PIDA is present along with IMPA or AMPA in the crystallizing solution, it produced a beneficial effect by counteracting the habit-modifying effects of the other two impurities. In situ monitoring of crystal growth from pure and impure supersaturated aqueous solution using an atomic force microscope revealed that IMPA slowed down the propagation of steps on the (100) surface of PMG crystal and, in contrast, PIDA accelerated the propagation of steps on the crystal surface. On the basis of these observations, it is surmised that interaction of PIDA at the kink sites on the crystal surface reduced the step free energy and, in turn, led to resurrection of crystal growth from the inhibitory effect of IMPA.