We propose a novel strategy for the synthesis of materials with a hierarchical structure. This strategy is based on in situ combination of two processes, namely, capping agent-mediated oriented growth and stirring-induced aggregation, and the growth of Cu crystals in the presence of linear alkyl diamines of short carbon chain length under vigorous stirring is shown to demonstrate its feasibility. Our experimental results have shown that the oriented growth of Cu nanowires can be significantly disturbed by vigorous stirring, resulting in large-scale growth of hierarchical dendritic Cu crystals. The morphology of grown dendritic Cu crystals has been found to vary with the stirring rate, type of diamine, and diamine concentration, which makes it possible to prepare hierarchical Cu structures of various morphologies. The growth mechanism of these hierarchical Cu structures is proposed based on the experimental observations. The present unique strategy offers a fresh way to fabricate materials with a hierarchical structure.
In industrial crystallization, spherical crystals have gained increasing interest due to their excellent physicochemical properties, such as high bulk density, flowability, stability, etc. However, their formation mechanism is still not well understood and is often oversimplified. In this work, spherical amoxicillin sodium crystals were obtained via a spherulitic growth strategy. It was found that agitation immediately after the addition of crystal seeds was critical for inducing radial noncrystallographic branching and spherulite formation of amoxicillin sodium. Without agitation during the aging period after seed addition, only discrete rod-shaped crystals were obtained. The formation mechanism of amoxicillin sodium spherulites was studied using process analytical technology (PAT) tools, including focused beam reflectance measurement (FBRM) and particle video microscope (PVM). The result was indicative of a three-step morphological evolution process: formation of polycrystalline agglomerates, noncrystallographic branching, and spherulite growth. During this process, agitation immediately after seed addition could help to solute diffusion and induce the agglomeration of small crystals that result from secondary nucleation. The polycrystalline agglomerates serve as the cores for further noncrystallographic branching and growth. On this basis, a new spherulitic growth strategy was proposed by the large addition of crystal seeds as the growth substrates of new branching and spherulite growth. High agitation rates during the aging period can increase the mass ratio of spherulites, and high initial supersaturation can promote branching. Compared with the discrete rod-shaped crystals, spherulites self-regulate the final size greatly up to three times and have a higher bulk density as well as much lower hygroscopicity.
Two novel cholesteryl derivatives of calix[4]arene with L- or D-phenylalanine residues in the linkers (1 and 2, respectively) were designed and synthesized. The gelation behaviors of the compounds in 30 organic solvents were tested. It was demonstrated that 1 gels n-butanol and n-pentanol at room temperature, but 2 gels isopropanol only under the treatment of heating–cooling cycling or energy supplementing via sonication, vortex or agitation at room temperature. AFM and SEM measurements revealed that the structures of the gel networks are greatly affected by the spatial configurations of the linkers contained in the calix[4]arene derivatives. Furthermore, mechanical treatment not only promotes the gelation of the system of 2–isopropanol, but also enhances the strength of the gel. Specifically, 18 min of agitation at room temperature makes the storage modulus and the yield stress of the gel (3.5%, w/v) exceed 1 × 106 Pa and 6 × 103 Pa, respectively, which are second only to the mechanically strongest low molecular mass gelator-based molecular gel reported until now. XRD analysis revealed the hexagonal packing structure of 1 in its n-pentanol gel.
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