b S Supporting Information P olymer-related content is increasingly being added to the undergraduate chemistry program curriculum in many departments. An experiment has successfully been incorporated into the undergraduate physical chemistry lab in which the phase transition of linear chain polymers from the disordered melt to the ordered, semicrystalline solid is examined. Low molecular weight poly(ethylene glycol) (PEG) crystallizes at room temperature forming spherical crystals called spherulites. The spherulites can grow large enough under the right conditions to be visible with the naked eye if a thin film of melted polymer is left to solidify on a glass surface. Sandwiching a film of melted polymer between standard, glass microscope slides, however, forces the solid into disc-shaped spherulites. The radii of the spherulites increase linearly with time if the sample is kept isothermal.This polymer crystallization experiment can be performed successfully using a polarized-light optical microscope equipped with a digital or video camera. (This is a standard piece of teaching equipment in most undergraduate geology departments and it may be feasible to borrow the equipment for the lab period.) Students measure the radial growth rates of disc-like crystals of polyethylene glycol and the results can be interpreted in terms of existing models of polymer crystallization kinetics. The experiment can be performed with or without the use of a temperature-controlled microscope hot stage, and both options are described with students' results. The experiment provides an opportunity to demonstrate and discuss the concepts of (i) nonequilibrium, kinetically controlled phase transitions; (ii) crystal growth; (iii) molecular weight effects on polymer crystallization; (iv) general polymer materials properties and applications; and (v) polarized light and birefringence. The experiment might also be adapted for use in a graduate-level course.At least two articles in this Journal describe polymer crystallization from the melt state and both contain an in-depth treatment of the background theory including the origin of the birefringence in the polymer spherulites. 1,2 Those articles are recommended reading for the instructor. A brief background theory describing the structural hierarchy within the spherulite crystals and the equations used to describe their kinetics of crystallization, with references, is contained in the Supporting Information. This material is presented to students in the form of a reading assignment prior to the lab and a discussion is held on the subject as part of a prelab lecture and demonstration. ' EXPERIMENTAL PROCEDURE EquipmentStandard microscope glass slides and glass coverslips are used to prepare the sample. A hot plate with surface temperature of 65°C is used to melt the PEG samples. As the temperature is relatively low, a simple beverage warmer plate (Radio Shack, Coffee/Beverage Warmer, model #61À8371) is used. A polarized-light microscope (Nikon Optiphot) is used to view the crystallization even...

Mass spectrometry is frequently introduced to undergraduate students as an instrument for both qualitative and quantitative chemical analysis. One of the most common uses of mass spectrometry (MS) is to deduce or confirm a compound's chemical formula, by relying on high-resolution accurate-mass measurements. However, like all forms of instrumental analysis, qualitative characterization of an unknown entails a degree of measurement uncertainty. By extension, the conclusions of any analysis may not be definitive. Here, we describe a form of inquiry-based learning wherein students acquire scientific evidence to probe a question ("Is the person guilty?"). A laboratory-based experiment involves the use of accurate-mass analysis to characterize a trace unknown, extracted from "simulated" forensic evidence. Together with the accurate mass, the isotopic distribution, some chemical intuition, and an online molecular-formula tool (available through ChemCalc), students arrive at the suspected chemical identity of the unknown. The analysis of cocaine on circulating currency is used in this report to illustrate the lab exercise. At the conclusion of the exercise, students should realize that the evidence they generate is insufficient to support a definitive identification. The strategies employed to deduce a molecular formula may also be adopted to a classroom setting.

The damping behavior of bent fiber near-field scanning optical microscopy ͑NSOM͒ probes operating in tapping mode oscillation is investigated in air and water. We show that the significant drop in probe quality factor Q, which occurs at the air-water interface, is due to meniscus damping. As the probe is immersed in water viscous damping adds to the meniscus damping. Damping effects which lead to a progressive drop in the peak tapping mode resonance frequency are accounted for by additional torsional modes of probe vibration. Understanding the damping processes should lead to the design of high sensitivity NSOM probes for scanning soft biological samples under liquid.

In this letter, we demonstrate a substantial improvement in the ease of attaching and recognizing chemical libraries on cantilevers for use with combinatorial atomic force microscopy. These experiments exploit chemically modified nanoparticles as a means of encoding various chemistries onto the cantilevers with structures that can be readily distinguished. For the first time, 16 combinations of interactions were measured in a single experiment and in the same solution. Furthermore, these experiments have not begun to push the limits of the technique; it is plausible that in the very near future hundreds of interactions could be rapidly measured, helping to transform AFM into a truly high throughput technique.

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