What do solar cells, printed circuit boards, microprocessors, and LED displays have in common? They are essential to 21stcentury life, and they are all limited to flat geometries by the use of spin coating during manufacturing. Here, we present a lubrication-based model for the flow of a thin film on a rotating sphere. This was used to model spin coating a polymer film, which cures over time, on a spherical substrate. We see that centrifugal force causes the accumulation of fluid in a distinct peak near the equator of the sphere. We investigate the effect of varied substrate kinematics and film thickness, as well as the impact of different fluid properties. Finally, we briefly consider the effect of rotation on the spreading of a fluid film from a nonuniform initial condition. Overall, the uniformity and smoothness of the coated film consistently worsened as a result of spin coating, compared to the effect of gravity only.

Increasing the temperature of a chemical system generally causes covalent bonds to lengthen and weaken, often the first step in initiating chemical reactions. However, for some hydrogen-bonded systems, infrared (IR) spectroscopy measurements reveal that covalent O–H bonds actually strengthen and therefore shorten when heated. In 1957, Finch and Lippincott proposed a simple one-dimensional (1D) model to explain this effect, in which thermal excitation of intermolecular stretching modes leads to lengthening and weakening of intermolecular O–H···O hydrogen bonds, thereby indirectly strengthening the associated covalent O–H bonds. Taking cellulose (an infinitely repeating polymer of d-glucose) as an example, we use molecular dynamics modeling to show that the same mechanism is responsible for temperature-dependent blue shifting of O–H stretching bands in IR spectra of carbohydrate biopolymers, except that interchain hydrogen bonds are weakened by thermal excitation of chain-separation modes, while intrachain hydrogen bonds are weakened by thermally induced changes in ring puckering and orientation of ring substituents but not reorientation of glucose units relative to one another or overall twisting of the cellulose chains.

Editor's Note: Written contributions relating to material published in the Bulletin will generally appear in the Discussion Section of the Bulletin. Occasionally individuals may be invited to offer discussion for printing with the original paper, article or note. In this instance, Mr. Shepherd, whose paper was referred to by Mr. McKenzie, was invited. His comment and Mr. McKenzie's response appear below. Others may contribute for publication in later issues.