Tablet ejection: A systematic comparison between force, static friction, and kinetic friction.

The magnitude of the frictional forces during the ejection of porous pharmaceutical tablets plays an important role in determining the occurrence of tabletting defects. Here, we perform a systematic comparison between the maximum ejection force, static friction coefficient, and kinetic friction coefficient. All of these metrics have different physical meanings, corresponding to different stages of ejection. However, experimental limitations have previously complicated comparisons, as static and kinetic friction could not be measured simultaneously. This study presents a method for simultaneously measuring the maximum ejection force, static friction coefficient, and kinetic friction coefficient in situ during tablet ejection in routine compaction simulator experiments. Using this method, we performed a systematic comparison, including variations of (1) ejection speed, (2) compaction pressure, (3) material, and (4) lubrication method. The relative importance of each variable is discussed in detail, including how ejection speed alone can be a decisive factor in tablet chipping. The reliability of the newly developed method is supported by excellent agreement with previous studies and finite element method (FEM) simulations. Finally, we discuss the suitability of friction coefficients derived from Janssen-Walker theory and explanations for the phenomenon of die-wall static friction coefficients with apparent values far above unity.

Parameterless detection of liquid-liquid interfaces with sub-micron resolution in single-molecule localization microscopy.

HYPOTHESIS: Knowing the exact location of soft interfaces, such as between water and oil, is essential to the study of nanoscale wetting phenomena. Recently, iPAINT was used to visualize soft interfaces in situ with minimal invasiveness, but computing the exact location of the interface remains challenging. We propose a new method to determine the interface with high accuracy. By modelling the localizations as points generated by two homogeneous Poisson processes, the exact location of the interface can be determined using a maximum likelihood estimator (MLE). EXPERIMENTS: An MLE was constructed to estimate the location of the interface based on the discontinuity in localization density at the interface. To test the MLE, we collected experimental data through iPAINT experiments of oil-water interfaces and generated simulated data using the Monte Carlo method. FINDINGS: Simulations show that the interface given by the MLE rapidly converges to the true interface location. The error of the MLE drops below the experimental localization precision. Furthermore, we show that the MLE remains accurate even if the field-of-view is reduced or when one or more particles are on the interface within the field-of-view. This work provides a key step towards the in situ, sub-micron characterization of (nanoparticle-laden) interfaces with minimal invasiveness.

Closed-Form Coexistence Equation for Phase Separation of Polymeric Mixtures in Dissipative Particle Dynamics.

To date, no extensive study of the phase diagram for binary fluid mixtures in dissipative particle dynamics (DPD) has been published. This is especially pertinent for newer parameterization schemes where the self-self interaction, or the effective volume, of different particle types is varied. This work presents an exhaustive study of the parameter space concerning DPD particles with soft interaction potentials. Moreover, we propose a closed-form coexistence equation or binodal curve that is inspired by the Flory-Huggins model. This equation describes the phase diagram of all binary mixtures made up out of monomers, homopolymers, and the mixtures thereof when self-self interactions are varied. The mean absolute percentage error (MAPE) of the equation on simulated data, including validation simulations, is 1.02%. The equation can a priori predict the phase separation of mixtures using only DPD interaction parameters. The proposed coexistence equation can therefore be used to directly validate interaction parameters resulting from novel parameterization schemes, including coarse graining and equations of state, without the need for additional simulations. Finally, it is shown that the choice of bond potential markedly influences phase behavior.