The impact of conditions was investigated on a model photoinduced electron/energy transfer reversible addition−fragmentation chain transfer (PET-RAFT) polymerization. Within the cylindrical geometries studied, with relatively small changes in path length, the impact of reaction vessel dimensions and dilution was relatively small on the polymerization kinetics and control of the polymerization. This suggests that PET-RAFT can be relatively insensitive to small changes in reactor geometry and reaction volume when cylindrical systems are used. The intensity of the photoreactor was a key factor in determining reaction rate, with an approximate 1/2 order scaling of the apparent rate with intensity. Reactant concentration ratios were also important, with an approximate 1/2 order of the apparent rate with the photocatalyst loading and an approximate −1/2 order scaling apparent polymerization rate coefficient with the RAFT agent concentration. However, there is a limit to rate increases with higher Ir catalyst loadings due to the optical density.

Dynamic covalent Diels-Alder chemistry was combined with multiwalled carbon nanotube (CNT) reinforcement to make strong, tough and conductive dynamic materials. Unlike other approaches to functionalizing CNTs, this approach uses Diels-Alder...

Organic chemistry students often struggle with reaction mechanisms, particularly in how they are proposed and justified. In this activity targeting second year organic undergraduates, students used infrared spectroscopy (IR) to track the reaction progress of two distinct aldol reactions and used polarimetry to analyze the stereoselectivity of aldol catalysts. Students worked in two pairs, with one focusing on the traditional hydroxide-catalyzed aldol reaction (two units of propionaldehyde combining via an enolate intermediate) and the other focusing on the enantioselective L-proline-catalyzed aldol reaction (propionaldehyde catalyzed by Lproline, showing an iminium intermediate). During the course of the lab period, students used IR spectra showing kinetic data and guided questions to propose and validate the reaction mechanisms. After the pairs of students analyzed their individual reactions, they formed groups of four to further analyze and compare the two mechanisms. This comparison of IR and polarimetry data allowed students to discuss both pathways and consider why chemists use different reaction conditions to reach the same product. The focus of this experiment is to improve the understanding of reaction mechanisms and the process by which scientists propose and justify mechanisms, while giving students practical experience with IR spectroscopy, polarimetry, and intermediate analysis.

Artificial and synthetic skins are widely used in the medical field; used in applications ranging from skin grafts to suture training pads. There is a growing need for artificial skins with tunable properties. However, current artificial skins do not take into account the variability of mechanical properties between individual humans as well as the age-dependent properties of human skin. Furthermore, there has been little development in artificial skins based on these properties. Thus, the primary purpose of this research is to develop variable stiffness artificial skin samples using magnetorheological elastomers (MREs) whose properties that can be controlled using external magnetic fields. In this study, multiple MRE skin samples were fabricated with varying filler particle volume contents. Using a precision dynamic mechanical analyzer, a series of indenting experiments were performed on the samples to characterize their mechanical properties. The samples were tested using a spherical indenter that indented a total depth of 1 mm with a speed of 0.01 mm/s and unloaded at the same rate. The results show that the modulus or stiffness increases significantly as the iron percent (w/w) in the sample increases. Additionally, the stiffness of the sample increases proportional to the intensity of the applied external magnetic field. To assess the MRE samples’ variability of properties, the testing results were compared with in vivo human skin testing data. The results show the MRE samples are feasible to represent the age-dependent stiffness demonstrated in in vivo human skin testing. The MRE materials studied will be further studied as a variable-stiffness skin model in medical devices, such as radial pulse simulators.

Current wearable technologies strive to incorporate more medical functionalities in wearable devices for tracking health conditions and providing information for timely medical treatments. Beyond tracking of a wearer’s physical activities and basic vital signs, the advancement of wearable healthcare devices aspires to continuously monitor health parameters, such as cardiovascular indicators. To properly monitor cardiovascular health, the wearables should accurately measure blood pressure in real-time. However, current devices on the market are not validated for continuous monitoring of blood pressure at a clinical level. To develop wearable healthcare devices such applications, they must be validated by considering various parameters, such as the effects of varying skin properties. Being located between the blood vessel and the wearable device, the skin can affect the sensor readings of the device. The primary goal of this study is to investigate the effect of skin property on the radial pulse measurements. To this end, a range of artificial vein-inserted skin samples with varying properties is fabricated using Magneto-Rheological Elastomers (MRE), materials whose mechanical properties can be altered by external magnetic fields. The samples include layers to simulate the structure of skin and a silicone vein for the pulse to pass through. Note that they are not intended to represent real human skin-vein properties but created to vary a range of stiffness properties to carry out the study. Experiments are performed using a cam system capable of generating realistic human pulse waveforms to pass through the samples. During the indentation testing, the sample is compressed using a dynamic mechanical analyzer (DMA) to record experienced surface pressure, allowing the pulse patterns to be studied. Various samples are used to probe the effects of base resin hardness, iron content, and magnetic field. A pressure sensor incorporated in the cam simulator is used to benchmark the internal pulse pressure of the vein while the DMA indents the sample in order to note the pulse pressures being passed through the sample. Test results show that the properties of the skin influence the resulting pulse behaviors, particularly the ratio of the recorded pulse pressures from the sensor and the DMA.