The ability to achieve simultaneous intrinsic deformation with fast response in commercially available materials that can safely contact skin continues to be an unresolved challenge for artificial actuating materials. Rather than using a microporous structure, here we show an ambient-driven actuator that takes advantage of inherent nanoscale molecular channels within a commercial perfluorosulfonic acid ionomer (PFSA) film, fabricated by simple solution processing to realize a rapid response, self-adaptive, and exceptionally stable actuation. Selective patterning of PFSA films on an inert soft substrate (polyethylene terephthalate film) facilitates the formation of a range of different geometries, including a 2D (two-dimensional) roll or 3D (three-dimensional) helical structure in response to vapor stimuli. Chemical modification of the surface allowed the development of a kirigami-inspired single-layer actuator for personal humidity and heat management through macroscale geometric design features, to afford a bilayer stimuli-responsive actuator with multicolor switching capability.
Both primary and secondary nucleation rates are considered in a model developed for unseeded batch crystallization. A carefully designed strategy was employed to minimize the effects of the stochastic nature of induction time; nucleation was induced at designed supersaturations on known temperature plateaus. Crystallization kinetics of paracetamol from ethanolic solutions were extracted from measurements of in situ solute concentrations and combined with sieve (ex situ) data on the final product. Parameters in models for primary and secondary nucleation and for crystal growth rate were estimated by fitting a full population balance model to the measurements, and the evolution of the crystal size distribution was compared against in situ estimation from focused-beam reflectance measurements using the technique that we previously developed. The resulting models suggest that primary nucleation produces fewer surviving crystals than had been expected and that most of the product crystals from the process involving a temperature plateau result from secondary nucleation.
Digital in-line holography (DIH) is broadly used to reconstruct 3D shapes of microscopic objects from their 2D holograms. One of the technical challenges in the reconstruction stage is eliminating the twin image originating from the phase-conjugate wavefront. The twin image removal is typically formulated as a non-linear inverse problem since the scattering process involved in generating the hologram is irreversible. Conventional phase recovery methods rely on multiple holographic imaging at different distances from the object plane along with iterative algorithms. Recently, end-to-end deep learning (DL) methods are utilized to reconstruct the object wavefront (as a surrogate for the 3D structure of the object) directly from the singleshot in-line digital hologram. However, massive data pairs are required to train the utilize DL model for an acceptable reconstruction precision. In contrast to typical image processing problems, well-curated datasets for in-line digital holography do not exist. The trained models are also highly influenced by the objects' morphological properties, hence can vary from one application to another. Therefore, data collection can be prohibitively laborious and time-consuming, as a critical drawback of using DL methods for DH. In this paper, we propose a novel DL method that takes advantages of the main characteristic of auto-encoders for blind single-shot hologram reconstruction solely based on the captured sample and without the need for a large dataset of samples with available ground truth to train the model. The simulation results demonstrate the superior performance of the proposed method compared to the state-of-the-art methods used for singleshot hologram reconstruction.
A high-resolution atomic force microscopy (AFM) study has shown that the molecular packing on the tetragonal lysozyme (110) face corresponds to only one of two possible packing arrangements, suggesting that growth layers on this face are of bimolecular height [Li et al. (1999). Acta Cryst. D55, 1023-1035]. Theoretical analyses of the packing also indicated that growth of this face should proceed by the addition of growth units of at least tetramer size, corresponding to the 43 helices in the crystal. In this study, an AFM linescan technique was used to measure the dimensions of individual growth units on protein crystal faces as they were being incorporated into the lattice. Images of individual growth events on the (110) face of tetragonal lysozyme crystals were observed, shown by jump discontinuities in the growth step in the linescan images. The growth-unit dimension in the scanned direction was obtained from these images. A large number of scans in two directions on the (110) face were performed and the distribution of lysozyme growth-unit sizes were obtained. A variety of unit sizes corresponding to 43 helices were shown to participate in the growth process, with the 43 tetramer being the minimum observed size. This technique represents a new application for AFM, allowing time-resolved studies of molecular processes to be carried out.
Crystallization from solution is a key unit operation utilized across the synthetic scheme to remove impurities. However, little is still known of the underlying impurity purge mechanisms that are responsible for controlling the final purity of the product. Reported herein is the solubility-limited impurity purge mechanism in which the impurity exists as a separate solid phase with its own solubility. A mathematical framework is presented that describes the separation of the impurity in the solid and liquid phases based on the relative solubilities of the product and impurity, and initial impurity level. Three theoretical solubility-limited impurity purge mechanisms are derived that are confirmed experimentally using salicylic acid, ibuprofen, and acetaminophen as model compounds. A practical experimental test is introduced that is used to identify if the impurity is rejected by solubility-limitation and its corresponding type. Finally, development strategies are presented to remove impurities that are purged based on their solubilities.
The mechanisms of purging structurally similar impurities in solution crystallization have been evaluated using the model compound salicylic acid. Of the 11 added impurities, 3 showed appreciable entrapment in the solid phase: viz., salicylamide, anthranilic acid, and benzoic acid. X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and the use of a previously reported solubility-limited impurity purge (SLIP) test have shown that the impurities are entrapped by a lattice incorporation mechanism. Impurities become integrated within the product crystals during the crystallization by forming terminal solid solutions. Most of the impurity entrapment was found to take place very early in the crystallization, immediately after seeding. The least entrapment occurred at the end of the crystallization, despite the mother liquor being enriched in impurities. These changes caused purity variations in the solids, which were not properly captured by the average value. A mathematic framework was developed to afford the material impurity distribution (MID), which represents the mass-based impurity profile across a material based on the SLIP test. It is shown that the level of impurities in the crystallized material is far from constant and in fact varies by orders of magnitude, in many cases by more than 20 times. These differences give rise to changes in the physical properties of salicylic acid, as exemplified by a reduction in crystallinity, a lower and broader melting event, and a doubling of solubility.
Monitoring crystal size distributions in situ is a challenge in crystallization engineering. Such a capability provides comprehensive information on the crystallization, which can be used to improve the quality of products. We developed an empirical focused-beam reflectance measurement (FBRM) model to provide such estimates. By experimentally fixing the CSD as a system input and the chord-length distribution (CLD) from the FBRM as the output, we constructed the model as a linear transformation from CSD to CLD. A regularized least-squares algorithm, which considers the mass balances on solid and liquid phases, was used to estimate the CSD. The results of batch cooling crystallization experiments show that estimates of the evolution of CSD are in accordance with the general understanding of crystallization kinetics, and the CSD estimates of final product agreed with the CSD obtained from sieving. The simplicity and practicality of the model make it a significant enhancement to the use of FBRM in monitoring, simulating, and controlling crystallization processes.
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