Crystallization-Inspired Design and Modeling of Self-Assembly Lattice-Formation Swarm Robotics

Self-assembly formation is a key research topic for realizing practical applications in swarm robotics. Due to its inherent complexity, designing high-performance self-assembly formation strategies and proposing corresponding macroscopic models remain formidable challenges and present an open research frontier. Taking inspiration from crystallization, this paper introduces a distributed self-assembly formation strategy by defining free, moving, growing, and solid states for robots. Robots in these states can spontaneously organize into user-specified two-dimensional shape formations with lattice structures through local interactions and communications. To address the challenges posed by complex spatial structures in modeling a macroscopic model, this work introduces the structural features estimation method. Subsequently, a corresponding non-spatial macroscopic model is developed to predict and analyze the self-assembly behavior, employing the proposed estimation method and a stock and flow diagram. Real-robot experiments and simulations validate the flexibility, scalability, and high efficiency of the proposed self-assembly formation strategy. Moreover, extensive experimental and simulation results demonstrate the model's accuracy in predicting the self-assembly process under different conditions. Model-based analysis indicates that the proposed self-assembly formation strategy can fully utilize the performance of individual robots and exhibits strong self-stability.

Chiral Flipping in Viedma Deracemization

Understanding deracemization is crucial for progress in chiral chemistry, especially for improving separation techniques. Here, we first report the phenomenon of chiral flipping (or reverse deracemization) in a chiral material (i.e., sodium chlorate crystals) during Viedma deracemization, employing a small-volume reactor system for precise analysis. We observe considerable chiral flipping, influenced by the initial imbalance in the numbers of L- and D-form particles. We developed a simple probabilistic model to further elucidate this behavior. We find that the fluctuation in the populations of chiral crystal particles resulting from their random dissolution and regeneration is the key factor behind chiral flipping. This study not only brings to light this intriguing observation of chiral flipping but also contributes to the enhancement of deracemization techniques.

Role of Additives: Modified Hemihydrate Phosphogypsum Morphology and Enhanced Filtration Performance of Wet-Process Phosphoric Acid

The morphology of hemihydrate phosphogypsum crystals is of vital importance in the hemihydrate-dihydrate (HH-DH) wet-process phosphoric acid production for high filtration strength. The morphology of hemihydrate phosphogypsum is commonly needlelike due to the strong acidic crystallization environment, which is unfavorable to the following filtration process. In this study, the crystal habit of hemihydrate phosphogypsum with a large aspect ratio was skillfully modified by additives to achieve a higher filtration strength. d-Glucitol (DG) reduces the theoretical aspect ratio of hemihydrate phosphogypsum crystals from 2.076 to 1.583 by interacting with the (002) face of CaSO4·0.5H2O preferentially, and poly(vinyl alcohol) (PVA) facilitates the aggregation of small grains to gather into a clusterlike structure. The modified morphologies of hemihydrate phosphogypsum have a lower bulk density and a larger porosity of the formed filter cake, which increases the filtration strength up to 45.9% when DG is added. Our work provides an in-depth explanation of the evolution mechanism of hemihydrate phosphogypsum morphology with the additives and its influence on the filtration performance. The improved filtration strength would reduce the water content of hemihydrate phosphogypsum and relieve the storage pressure of the phosphogypsum slag dump, which is meaningful to the clean production and process emission reduction of the phosphorus chemical industry.

Templated Reactive Crystallization of Active Pharmaceutical Ingredient in Hydrogel Microparticles Enabling Robust Drug Product Processing

Commercialization of most promising active pharmaceutical ingredients (APIs) is impeded either by poor bioavailability or challenging physical properties leading to costly manufacture. Bioavailability of ionizable hydrophobic APIs can be enhanced by its conversion to salt form. While salt form of the API presents higher solution concentration than the non-ionized form, poor physical properties resulting from particle anisotropy or non-ideal morphology (needles) and particle size distribution not meeting dissolution rate targets can still inhibit its commercial translation. In this regard, API physical properties can be improved through addition of non-active components (excipients or carriers) during API manufacture. In this work, a facile method to perform reactive crystallization of an API salt in presence of the microporous environment of a hydrogel microparticle is presented. Specifically, the reaction between acidic antiretroviral API, raltegravir and base potassium hydroxide is performed in the presence of polyethylene glycol diacrylamide hydrogel microparticles. In this bottom-up approach, the spherical template hydrogel microparticles for the reaction lead to monodisperse composites loaded with inherently micronized raltegravir-potassium crystals, thus improving API physical properties without hampering bioavailability. Overall, this technique provides a novel approach to reactive crystallization while maintaining the API polymorph and crystallinity.

Simultaneous Predictions of Chemical and Phase Equilibria in Systems with an Esterification Reaction Using PC-SAFT

The study of chemical reactions in multiple liquid phase systems is becoming more and more relevant in industry and academia. The ability to predict combined chemical and phase equilibria is interesting from a scientific point of view but is also crucial to design innovative separation processes. In this work, an algorithm to perform the combined chemical and liquid-liquid phase equilibrium calculation was implemented in the PC-SAFT framework in order to predict the thermodynamic equilibrium behavior of two multicomponent esterification systems. Esterification reactions involve hydrophobic reacting agents and water, which might cause liquid-liquid phase separation along the reaction coordinate, especially if long-chain alcoholic reactants are used. As test systems, the two quaternary esterification systems starting from the reactants acetic acid + 1-pentanol and from the reactants acetic acid + 1-hexanol were chosen. It is known that both quaternary systems exhibit composition regions of overlapped chemical and liquid-liquid equilibrium. To the best of our knowledge, this is the first time that PC-SAFT was used to calculate simultaneous chemical and liquid-liquid equilibria. All the binary subsystems were studied prior to evaluating the predictive capability of PC-SAFT toward the simultaneous chemical equilibria and phase equilibria. Overall, PC-SAFT proved its excellent capabilities toward predicting chemical equilibrium composition in the homogeneous composition range of the investigated systems as well as liquid-liquid phase behavior. This study highlights the potential of a physical sound model to perform thermodynamic-based modeling of chemical reacting systems undergoing liquid-liquid phase separation.

Monitoring and Visualization of Crystallization Processes Using Electrical Resistance Tomography: CaCO3 and Sucrose Crystallization Case Studies

In the current research work, electrical resistance tomography (ERT) was employed for monitoring and visualization of crystallization processes. A first-of-its-kind MATLAB-based interactive GUI application “ERT-Vis” is presented. Two case studies involving varied crystallization methods were undertaken. The experiments were designed and performed involving calcium carbonate reactive (precipitative) crystallization for the high conductivity solution-solute media, and the cooling crystallization of sucrose representing the lower conductivity solution–solute combination. The software successfully provided key insights regarding the process in both crystallization systems. It could detect and separate the solid concentration distributions in the low as well as high conductivity solutions using the visual analytics tools provided. The performance and utility of the software were studied using a software evaluation case study involving domain experts. Participant feedback indicated that ERT-Vis software helps by reconstructing images instantaneously, interactively visualizing, and evaluating the output of the crystallization process monitoring data.

K A. Enantioselective Separation of Amino Acids Using Chiral Polystyrene Microspheres Synthesized by a Post-Polymer Modification Approach

The enantioselective separation of a racemic mixture of amino acids was achieved by chiral amino acid-modified polystyrene (PS) that was developed by a post-polymer modification approach. Styrene was polymerized using the reversible addition-fragmentation chain-transfer (RAFT) polymerization technique and further post-polymer modification was applied by Friedel-Crafts acylation reaction with chiral N-phthaloyl-l-leucine acid chloride to obtain the protected PS-l-Leu. The chiral PS (protected PS-l-Leu) was assembled into microspheres using a surfactant and was used for carrying out the enantioselective separation of amino acid racemic mixtures by enantioselective adsorption followed by a simple filtration process. Compared to as-precipitated chiral PS (protected PS-l-Leu) powder, the protected PS-l-Leu microspheres exhibited a better enantioselective separation efficiency (ee %). Furthermore, the protected PS-l-Leu was deprotected to obtain the amine-functionalized deprotected PS-l-Leu chiral PS, which was also assembled into microspheres and used for carrying out enantioselective separation. Deprotected PS-l-Leu-functionalized chiral PS microspheres could achieve up to 81.6 ee % for the enantioselective separation of a racemic mixture of leucine. This is one of the first reports of the synthesis of amino acid-modified chiral PS microspheres and their application to the simple filtration-based enantioselective separation of native amino acids from their racemic mixtures.

Experimental and Quantum Chemical Studies of Nicotinamide-Oxalic Acid Salt: Hydrogen Bonding, AIM and NBO Analysis

The computational modeling supported with experimental results can explain the overall structural packing by predicting the hydrogen bond interactions present in any cocrystals (active pharmaceutical ingredients + coformer) as well as salts. In this context, the hydrogen bonding synthons, physiochemical properties (chemical reactivity and stability), and drug-likeliness behavior of proposed nicotinamide–oxalic acid (NIC–OXA) salt have been reported by using vibrational spectroscopic signatures (IR and Raman spectra) and quantum chemical calculations. The NIC–OXA salt was prepared by reactive crystallization method. X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) techniques were used for the characterization and validation of NIC–OXA salt. The spectroscopic signatures revealed that (N7–H8)/(N23–H24) of the pyridine ring of NIC, (C═O), and (C–O) groups of OXA were forming the intermolecular hydrogen bonding (N–H⋯O–C), (C–H⋯O═C), and (N–H⋯O═C), respectively, in NIC–OXA salt. Additionally, the quantum theory of atoms in molecules (QTAIM) showed that (C10–H22⋯O1) and (C26–H38⋯O4) are two unconventional hydrogen bonds present in NIC–OXA salt. Also, the natural bond orbital analysis was performed to find the charge transfer interactions and revealed the strongest hydrogen bonds (N7–H8⋯O5)/(N23–H24⋯O2) in NIC–OXA salt. The frontier molecular orbital (FMO) analysis suggested more reactivity and less stability of NIC–OXA salt in comparison to NIC–CA cocrystal and NIC. The global and local reactivity descriptors calculated and predicted that NIC–OXA salt is softer than NIC–CA cocrystal and NIC. From MESP of NIC–OXA salt, it is clear that electrophilic (N7–H8)/(N23–H24), (C6═O4)/(C3═O1) and nucleophilic (C10–H22)/(C26–H38), (C6–O5)/(C3–O2) reactive groups in NIC and OXA, respectively, neutralize after the formation of NIC–OXA salt, confirming the presence of hydrogen bonding interactions (N7–H8⋯O5–C6) and (N23–H24⋯O2–C3). Lipinski’s rule was applied to check the activeness of salt as an orally active form. The results shed light on several features of NIC–OXA salt that can further lead to the improvement in the physicochemical properties of NIC.

Nucleation kinetics of lithium phosphate precipitation

Fourth-order kinetics arises from the consecutive complexation leading to precipitation.

Hybrid scanning electrochemical cell microscopy-interference reflection microscopy (SECCM-IRM): tracking phase formation on surfaces in small volumes

We describe the combination of scanning electrochemical cell microscopy (SECCM) and interference reflection microscopy (IRM) to produce a compelling technique for the study of interfacial processes and to track the SECCM meniscus status in real-time. SECCM allows reactions to be confined to well defined nm-to-μm-sized regions of a surface, and for experiments to be repeated quickly and easily at multiple locations. IRM is a highly surface-sensitive technique which reveals processes happening (very) close to a substrate with temporal and spatial resolution commensurate with typical electrochemical techniques. By using thin transparent conductive layers on glass as substrates, IRM can be coupled to SECCM, to allow real-time in situ optical monitoring of the SECCM meniscus and of processes that occur within it at the electrode/electrolyte interface. We first use the technique to assess the stability of the SECCM meniscus during voltammetry at an indium tin oxide (ITO) electrode at close to neutral pH, demonstrating that the meniscus contact area is rather stable over a large potential window and reproducible, varying by only ca. 5% over different SECCM approaches. At high cathodic potentials, subtle electrowetting is easily detected and quantified. We also look inside the meniscus to reveal surface changes at extreme cathodic potentials, assigned to the possible formation of indium nanoparticles. Finally, we examine the effect of meniscus size and driving potential on CaCO₃ precipitation at the ITO electrode as a result of electrochemically-generated pH swings. We are able to track the number, spatial distribution and morphology of material with high spatiotemporal resolution and rationalise some of the observed deposition patterns with finite element method modelling of reactive-transport. Growth of solid phases on surfaces from solution is an important pathway to functional materials and SECCM-IRM provides a means for in situ or in operando visualisation and tracking of these processes with improved fidelity. We anticipate that this technique will be particularly powerful for the study of phase formation processes, especially as the high throughput nature of SECCM-IRM (where each spot is a separate experiment) will allow for the creation of large datasets, exploring a wide experimental parameter landscape.

Real-Time Fault Detection and Diagnosis of CaCO3 Reactive Crystallization Process by Electrical Resistance Tomography Measurements

In the present research work, an electrical resistance tomography (ERT) system is utilized as a means for real-time fault detection and diagnosis (FDD) during a reactive crystallization process. The calcium carbonate crystallization is part of the carbon capture and utilization scheme where process monitoring and malfunction diagnostics strategies are presented. The graphical logic representation of the fault tree analysis methodology is used to develop the system failure states. The measurement consistency due to the use of a single electrode from a set of ERT electrodes for malfunction identification is experimentally and quantitatively investigated based on the sensor sensitivity and standard deviation criteria. Electrical current measurements are employed to develop a LabVIEW-based process automation program by using the process-specific knowledge and historical process data. Averaged electrical current is correlated to the mechanical failure of the stirrer through standard deviation evaluation, and slopes of the measured data are used to monitor the pump and concentrations status. The performance of the implemented methodology for detecting the induced faults and abnormalities is tested at different operating conditions, and a basic signal-based alarming technique is developed.