Rui Huang

Water vapor transmission rate (WVTR) is widely used to assess breathability in skin‐interfaced electronics. In gravimetric wet‐cup tests, however, the measured flux depends on transport through both the membrane and the apparatus. Apparatus resistance can dominate measurements of highly permeable membranes. Evaporation, headspace transport, membrane permeation, and external vapor spreading are modeled as resistances in series under a common chemical‐potential driving force. The apparatus coefficients are calibrated using open‐cup measurements in the same setup, independently of the reference permeability. For poly(dimethylsiloxane) membranes, where membrane resistance dominates, both a literature air‐gap correction and the calibrated model reduce deviations from the reference. For a highly permeable anion‐exchange membrane (AEM), the air‐gap correction becomes unstable. Relative to a dynamic sweep‐cell reference, the calibrated model reduces mean absolute relative deviation from 49.8% for classical conversion to 6.2%. It also provides model‐based criteria for geometry selection and measurement duration, together with a procedure for converting WVTR to water vapor permeability (WVP).

Polymer chain scission is a key mechanism for fracture of soft materials such as elastomers and hydrogels. It is well known from single-molecule force spectroscopy experiments that the critical condition for chain scission depends on the loading rate and other environmental effects (e.g., temperature and solvent). Common approaches to describing the kinetics of chain scission often assume force-controlled conditions, that is, when a polymer chain is stretched by a prescribed force. As a result of this assumption, chain scission is irreversible, excluding the possibility of healing. In many soft materials, however, self-healing has been observed after fracture, suggesting possibly reversible chain scission. Here, we show that reversible chain scission with healing is possible under displacement-controlled conditions, that is, when a polymer chain is stretched with a prescribed end-to-end distance. We present a breakable freely-jointed chain model, assuming that a polymer chain breaks when one of its links breaks while the other links remain nearly rigid. At a prescribed end-to-end distance, the free energy of the chain has two local minima and a local maximum (the transition state), giving rise to energy barriers for chain scission and healing. As the prescribed displacement increases, the energy barrier decreases for scission but increases for healing, depending on the chain length (number of links) and the potential energy of the link. With the energy barriers, we adopt a kinetic approach to predict the statistics and kinetics of a single polymer chain under tension, first by integrating the rate equation for the survival probability of the chain and then by kinetic Monte Carlo simulations. Notably, the present model predicts rate-dependent chain scission, with a lower bound for the rupture force that could be several orders of magnitude lower than the upper bound (which is close to the theoretical strength of the covalent bonds in the backbone).

A 56-year-old man underwent a prospective study (ChiCTR2300070081), which is a head-to-head comparison of ¹⁸F-FDG and ⁶⁸Ga-DOTATATE PET/MR in EB-positive nonkeratinizing nasopharyngeal carcinoma after chemotherapy. Bilateral cervical abnormal lymph nodes were both detected by ¹⁸F-FDG and ⁶⁸Ga-DOTATATE PET/MRI, whereas 2 hepatic lesions only were shown on ⁶⁸Ga-DOTATATE, which subsequent pathologically proved to be primary hepatocellular carcinoma.