Amorphes Kalziumcarbonat (ACC) ist ein wichtiger Vorläufer in der Biomineralisierung und von zentraler Bedeutung für die geologische und industrielle Kalzifizierung. Einige kleine organische Moleküle haben die Fähigkeit, die Bildung, Zusammensetzung und Stabilität von ACC stark zu beeinflussen. In ihrem Forschungsartikel (e202208475) entschlüsseln Asher Schmidt, Dirk Zahn, Stephan E. Wolf et al. die zugrundeliegenden molekularen Mechanismen, die sowohl die Pränukleation als auch die Zusammensetzung der Lösung regulieren. Amorphes Kalziumcarbonat (ACC) ist ein wichtiger Vorläufer in der Biomineralisierung und von zentraler Bedeutung für die geologische und industrielle Kalzifizierung. Einige kleine organische Moleküle haben die Fähigkeit, die Bildung, Zusammensetzung und Stabilität von ACC stark zu beeinflussen. In ihrem Forschungsartikel (e202208475) entschlüsseln Asher Schmidt, Dirk Zahn, Stephan E. Wolf et al. die zugrundeliegenden molekularen Mechanismen, die sowohl die Pränukleation als auch die Zusammensetzung der Lösung regulieren. Organische Halbleiter Photokatalyse Polymere Heterogene Katalyse

Small-molecular-weight (MW) additives can strongly impact amorphous calcium carbonate (ACC), playing an elusive role in biogenic, geologic, and industrial calcification. Here, we present molecular mechanisms by which additives regulate stability and composition of both CaCO3 solutions and solid ACC. Potent antiscalants inhibit ACC precipitation by interacting with prenucleation clusters (PNC); they specifically trigger and integrate into PNCs or feed PNC growth. Only PNC-interacting additives are traceable in ACC, considerably stabilizing it against crystallization. The selective incorporation of potent additives in PNCs is a reliable chemical label that provides conclusive chemical evidence that ACC is a molecular precipitate derived PNCs. Our results reveal additive-cluster interactions beyond established mechanistic conceptions. They reassess the role of small-MW molecules in crystallization and biomineralization, while breaking grounds for new sustainable antiscalants.

We present novel data on the composition-, pH-, and salt-dependent zero shear viscosity of the commercially important mixture of anionic sodium dodecyl sulfate (SDS) and zwitterionic lauramidopropyl betaine (LAPB). We show via proton NMR experiments that the notionally zwitterionic LAPB exhibits a large pKa shift in the presence of SDS and can become partially cationic at formulation-relevant pH ranges of 4.5-6.0-that is, the binary system is effectively a ternary system. This has a pronounced effect on the viscosity of the system at low pH, especially if the fraction of LAPB is high. We use theoretical arguments to motivate a semiempirical but practical approach to model the viscosity of the mixtures using thermodynamic parameters such as the excess chemical potentials or activity coefficients of the surfactants. We demonstrate this using an augmented regular solution theory-based mixed micelle thermodynamic model and develop robust regression models using Bayesian approaches. We also show how the pKa shift from NMR experiments can be used to parameterize the thermodynamic model. This framework should be extensible to other arbitrary surfactant mixtures in the future and hence will be of broad interest for the development of surfactant formulations for household, personal care, and other applications.

A chain-revised Groot-Warren equation of state (crGW-EOS) was developed and tested to describe systems of homo-oligomeric chains in the framework of dissipative particle dynamics (DPD). First, thermodynamic perturbation theory is applied to introduce correction terms that account for the reduction in pressure with an increasing number of bonds at constant bead number density. Then, this EOS is modified by introducing a set of switching functions that yields an accurate second virial coefficient in the low-density limit. The crGW-EOS offers several improvements over the revised Groot-Warren equation of state and Groot-Warren equation of state for chain molecules. We tested the crGW-EOS by using it to predict the pressure of oligomeric systems and the B2 virial coefficient of chain DPD particles for a range of bond lengths. Additionally, a method is developed for determining the strength of cross-interaction parameters between chains of different compositions and sizes and for thermal and athermal mixtures. We explored how different levels of coarse-graining affect the upper-critical solution temperature.

Understanding solute uptake into soft microstructured materials, such as bilayers and worm-like and spherical micelles, is of interest in the pharmaceutical, agricultural, and personal care industries. To obtain molecular-level insight on the effects of solutes loading into a lamellar phase, we utilize the Shinoda-Devane-Klein (SDK) coarse-grained force field in conjunction with configurational-bias Monte Carlo simulations in the osmotic Gibbs ensemble. The lamellar phase is comprised of a bilayer formed by triethylene glycol mono- n-decyl ether (C10E3) surfactants surrounded by water with a 50:50 surfactant/water weight ratio. We study both the unary adsorption isotherm and the effects on bilayer structure and stability caused by n-nonane, 1-hexanol, and ethyl butyrate at several different reduced reservoir pressures. The nonpolar n-nonane molecules load near the center of the bilayer. In contrast, the polar 1-hexanol and ethyl butyrate molecules both load with their polar bead close to the surfactant head groups. Near the center of the bilayer, none of the solute molecules exhibits a significant orientational preference. Solute molecules adsorbed near the polar groups of the surfactant chains show a preference for orientations perpendicular to the interface, and this alignment with the long axis of the surfactant molecules is most pronounced for 1-hexanol. Loading of n-nonane leads to an increase of the bilayer thickness, but does not affect the surface area per surfactant. Loading of polar additives leads to both lateral and transverse swelling. The reduced Henry's law constants of adsorption (expressed as a molar ratio of additive to surfactant per reduced pressure) are 0.23, 1.4, and 14 for n-nonane, 1-hexanol, and ethyl butyrate, respectively, and it appears that the SDK force field significantly overestimates the ethyl butyrate-surfactant interactions.

We present a scheme to calculate wormlike micelle scission free energies from a potential of mean force (PMF) derived from a weighted histogram analysis method (WHAM) applied to coarse grained dissipative particle dynamics (DPD) simulations. In contrast to previous related work, we use a specially chosen external potential based on a reaction coordinate that reversibly drives surfactants out of the nascent scission location. For the application to a model body wash formulation, we predict how addition of NaCl and small molecules such as perfume raw materials (PRMs) affect scission energies. The results show qualitative agreement and correct trends compared to recently determined scission energies for the same system; however, a more rigorous parametrization of the underlying DPD potential is required for quantitative agreement.

In this work, the vapor–liquid equilibria of binary and multinary systems comprise perfume raw materials and ionic liquids have been computed using two different models: COSMO-RS, a solvation model, and UNIFAC, a group contribution method. For systems already well-known in the literature, a comparison with experimental data was performed, and good agreement was observed with both models. Although UNIFAC was not applicable to nonparametrized ionic liquids, COSMO-RS proved very reliable in predicting the vapor–liquid equilibria of solutions of perfume raw materials in new-to-the-world ionic liquids. This opens the door for the prediction and modeling of new formulations for novel consumer products, prior to embarking on detailed experimental investigations.

We link micellar structures to their rheological properties for two surfactant body-wash formulations at various concentrations of salts and perfume raw materials (PRMs) using molecular simulations and micellar-scale modeling, as well as traditional surfactant packing arguments. The two body washes, namely, BW-1EO and BW-3EO, are composed of sodium lauryl ethylene glycol ether sulfate (SLEnS, where n is the average number of ethylene glycol repeat units), cocamidopropyl betaine (CAPB), ACCORD (which is a mixture of six PRMs), and NaCl salt. BW-3EO is an SLE3S-based body wash, whereas BW-1EO is an SLE1S-based body wash. Additional PRMs are also added into the body washes. The effects of temperature, salt, and added PRMs on micellar lengths, breakage times, end-cap free energies, and other properties are obtained from fits of the rheological data to predictions of the "Pointer Algorithm" [ Zou , W. ; Larson , R.G. J. Rheol. 2014 , 58 , 1 - 41 ], which is a simulation method based on the Cates model of micellar dynamics. Changes in these micellar properties are interpreted using the Israelachvili surfactant packing argument. From coarse-grained molecular simulations, we infer how salt modifies the micellar properties by changing the packing between the surfactant head groups, with the micellar radius remaining nearly constant. PRMs do so by partitioning to different locations within the micelles according to their octanol/water partition coefficient POW and chemical structures, adjusting the packing of the head and/or tail groups, and by changing the micelle radius, in the case of a large hydrophobic PRM. We find that relatively hydrophilic PRMs with log POW < 2 partition primarily to the head group region and shrink micellar length, decreasing viscosity substantially, whereas more hydrophobic PRMs, with log POW between 2 and 4, mix with the hydrophobic surfactant tails within the micellar core and slightly enhance the viscosity and micelle length, which is consistent with the packing argument. Large and very hydrophobic PRMs, with log POW > 4, are isolated deep inside the micelle, separating from the tails and swelling the radius of the micelle, leading to shorter micelles and much lower viscosities, leading eventually to swollen-droplet micelles.

Wormlike Micelles (WLMs) provide the basis for structure and rheology of many consumer products. This includes laundry detergents, shampoos, body washes, dish detergents. Rheology determines key “touchpoints” of the consumer in handling of products, including the dispensing, pooling, spreading and dissolution of products in use, as well as process transformations such as mixing and bottle filling during manufacturing. This project developed molecular simulation tools to describe the structure and dynamics of WLMs for elucidating the mechanisms leading to different rheological behavior. The computational chemistry teams at P&G and U. Michigan collaborated with experimentally focused teams at U. Cincinnati and P&G to provide characterization (neutron scattering, light scattering, rheometry) of the systems studied using simulations. Contributions from XSEDE’s extended collaborative support services (ECSS) provided help with computing needs, including benchmarking, generation and optimization of work flows and code optimization. The ECSS team is working on making some of the code developments available to the scientific community. The industrial and academic teams intend to continue to use the learning from those developments beyond the lifetime of this project. XSEDE’s resources contributed to the development of simulation tools for both atomistic and coarse grained (dissipative particle dynamics) simulation tools to assess key properties of WLM’s that are relevant to rheological properties, including: cross-section, stiffness (persistence length) and average length (assessed through scission energy). This novel toolbox allows for the first time the connection of formula composition to properties from simulations. Resources

This comment addresses a few issues of concern regarding the use of Dissipative Particle Dynamics (DPD) to characterize molecular phase diagrams and identify phase morphologies in the recent paper by Son et al. (J. Chem. Eng. Data 2014, 59, 3036-3040). While useful solubility modeling and self-assembly can be aided by various coarse graining strategies including DPD, one should employ as well complementary techniques and ensure consistency of conclusions through experiments or readily available tools. We believe the approach and parametrization scheme is inappropriate to the system of study resulting in unrealistic results and interpretations.

Three developments are presented that significantly expand the applicability of dissipative particle dynamics (DPD) simulations for symmetric and non-symmetric mixtures, where the former contain particles with equal repulsive parameter for self-interactions but a different repulsive parameter for cross-interactions, and the latter contain particles with different repulsive parameters also for the self-interactions. Monte Carlo and molecular dynamics simulations for unary phases covering a wide range of repulsive parameters and of densities for single-bead DPD particles point to deficiencies of the Groot and Warren equation of state (GW-EOS) [J. Chem. Phys. 107, 4423 (1997)]. A revised version, called rGW-EOS, is proposed here that is significantly more accurate over a wider range of parameters/densities. The second development is the generalization of the relationship between the Flory-Huggins χ parameter and the repulsive cross-interaction parameter when the two particles involved have different molecular volumes. The third aspect is an investigation of Gibbs ensemble Monte Carlo simulation protocols, which demonstrates the importance of volume fluctuations and excess volumes of mixing even for equimolar symmetric mixtures of DPD particles. As an illustrative example, the novel DPD methodology is applied to the prediction of the liquid-liquid equilibria for acetic anhydride/(n-hexane or n-octane) binary mixtures.

Molecular dynamics (MD) simulation is a useful tool for simulating formulations of surfactant mixtures from first-principles, which can be used to predict surfactant morphology and other industrially relevant thermodynamic properties. However, the surfactant structure is sensitive to the parameters used in MD simulations, and in the absence of extensive validation against experimental data, it is often not obvious a priori which range of parameter sets to choose. In this work, we compare the performance of ion parameters implemented in nonpolarizable classical MD simulations, and its effect on simulations of an idealized solution of sodium dodecyl sulfate (SDS). We find that previous artifacts reported in simulations of larger SDS constructs are a direct consequence of using parameters that poorly model ionic interactions at high concentration. Using osmotic pressure and/or other thermodynamic properties measured at finite concentration, such as Kirkwood-Buff integrals, is shown to be the most cost-effective means to validate and parametrize existing force fields. Our findings highlight the importance of optimizing intermolecular parameters for simulations of systems with a high local concentration, which may be applicable in other contexts, such as in molecular crowding, hotspot mapping, protein folding, and modeling pH effects.

Knowledge of the protonation behavior of pH-sensitive molecules in micelles and bilayers has significant implications in consumer product development and biomedical applications. However, the calculation of pKa’s in such environments proves challenging using traditional structure-based calculations. Here we apply all-atom constant pH molecular dynamics with explicit ions and titratable water to calculate the pKa of a fatty acid molecule in a micelle of dodecyl trimethylammonium chloride and liquid as well as gel-phase bilayers of diethyl ester dimethylammonium chloride. Interestingly, the pKa of the fatty acid in the gel bilayer is 5.4, 0.4 units lower than that in the analogous liquid bilayer or micelle, despite the fact that the protonated carboxylic group is significantly more desolvated in the gel bilayer. This work illustrates the capability of all-atom constant pH molecular dynamics in capturing the delicate balance in the free energies of desolvation and Coulombic interactions. It also shows the importance of the explicit treatment of ions in sampling the protonation states. The ability to model dynamics of pH-responsive substrates in a bilayer environment is useful for improving fabric care products as well as our understanding of the side effects of anti-inflammatory drugs.

Molecular dynamics simulations have been widely applied to study surfactant systems. However, traditional methods do not capture the effect of changing pH, as all molecules have a fixed protonation state. Continuous constant pH molecular dynamics (CpHMD), however, allows for atomistic study of pH-coupled phenomena, and has been successfully applied to study proteins. In this work we use CpHMD with pH-based replica exchange to study pH-sensitive surfactants in aqueous solution. Lauric acid, a twelve-carbon fatty acid, self-assembles in a pH-dependent manner, with a bilayer to micelle transition seen near the aggregate's pKa. The calculated pKa of a 0.5 M lauric acid solution is 7.0, in good agreement with the experimental value of 7.5. Decreasing the tail length by four carbons decreases the pKa by ∼0.5 units, in qualitative agreement with experiment. The effect of aggregate size and concentration was also examined. We have also simulated the titration of fatty acids in fully-solvated detergent bilayers, which sets the stage for exploring proton-coupled biological processes in cellular environments.

This chapter contains sections titled: Introduction Performance Properties of Complex Liquid Formulations Stability Assessment of Multiphase Formulations Process Factors: Metastable States of Multiphase Mixtures Summary