Superior mechanical properties of multilayer covalent-organic frameworks enabled by rationally tuning molecular interlayer interactions.

Two-dimensional (2D) covalent-organic frameworks (COFs) with a well-defined and tunable periodic porous skeleton are emerging candidates for lightweight and strong 2D polymeric materials. It remains challenging, however, to retain the superior mechanical properties of monolayer COFs in a multilayer stack. Here, we successfully demonstrated a precise layer control in synthesizing atomically thin COFs, enabling a systematic study of layer-dependent mechanical properties of 2D COFs with two different interlayer interactions. It was shown that the methoxy groups in COFTAPB-DMTP provided enhanced interlayer interactions, leading to layer-independent mechanical properties. In sharp contrast, mechanical properties of COFTAPB-PDA decreased significantly as the layer number increased. We attributed these results to higher energy barriers against interlayer sliding due to the presence of interlayer hydrogen bonds and possible mechanical interlocking in COFTAPB-DMTP, as revealed by density functional theory calculations.

Quality by design (QbD) approach to match tablet glossiness.

A quality by design (QbD) approach was used for a polyvinyl alcohol (PVA)-based coating to develop a 'look-alike' placebo tablet, which can match the glossiness (shine) of an innovator tablet. Critical coating parameters such as exhaust temperature, drying capacity, solid concentration in coating dispersion, and plasticizer concentration were studied using a full factorial design of experiment (DoE). Total of 20 experimental coating runs was executed on a pilot scale using a perforated pan coater. Coated tablets were evaluated visually against the innovator product by a panel of 13 volunteers using an individual questionnaire about the tablet appearance. The tablet appearance included factors such as tablet surface shine, surface roughness, and logo bridging. These data were analyzed using JMP software. Solid concentration in coating dispersion and drying capacity were found to be the key contributing parameters for tablet surface shine. Human observations were more discerning in spotting subtle differences in tablet appearance than Munsell evaluation. By the judicious selection of a solid concentration in coating dispersion and drying conditions, a look-alike placebo tablet was successfully developed. Change in tablet shape or size did not affect the tablet shine. However, replacement of PVA-based coating with hydroxypropyl methylcellulose (HPMC)-based coating resulted in reduced shine irrespective of tablet shape and size.