A simple model is put forward which accounts for the occurrence of certain generic dewetting morphologies in thin liquid coatings. It demonstrates that by taking into account the elastic properties ...of the coating, a morphological phase diagram may be derived which describes the observed structures of dewetting fronts. It is demonstrated that dewetting morphologies may also serve to determine nanoscale rheological properties of liquids.
This unit of study is designed to teach the science of wild animals to students in the primary grades. Included are a list of materials for the unit, a discussion of the use of process skills, a list ...of unit objectives, vocabulary, teacher background information, 13 lessons, 3 quizzes, and a unit test. Lessons are oriented toward hands-on process learning. An appendix includes "Tracks, Stamps, and Stories"; "At Home Thermometer"; and "Food Tasting Part." (CW)
It is shown that the intrinsic stress in solvent cast polymer coatings plays
a key role in the nucleation of holes in the film. Nucleation is important
because it is meanwhile clear that ...heterogeneous nucleation is the only
relevant rupture mechanism for the technologically relevant thickness regime
well above 100 nm. The most striking feature is that in contrast to what has
been widely believed, the number density of holes scales not algebraically, but
exponentially with the film thickness.
This unit contains 15 lessons on dinosaurs for kindergarten children. It provides a materials list, supplementary materials list, use of process skill terminology, unit objectives, vocabulary, six ...major dinosaurs, and background information. Lessons are: (1) "Webbing"; (2) "Introduction to the Big Six"; (3) "Paleontology and Fossils"; (4) "How Big Is Big?"; (5) "How Big Is a Dinosaur Bone?"; (6) "Dinosaur Habitat"; (7) "Dinosaur Stories"; (8) "Tell Dinosaur Tales"; (9) "Dinosaurs in Motion"; (10) "A Dinosaur Song"; (11) "Alike But Different"; (12) "Who Ate What"; (13) "Gone Forever"; (14) "Be a Dinosaur Poet"; and (15) "Group Drawing." (YP)
It is shown that experimentally obtained isotherms of adsorption on solid substrates may be completely reconciled with Lifshitz theory when thermal fluctuations are taken into account. This is ...achieved within the framework of a solid-on-solid model which is solved numerically. Analysis of the fluctuation contributions observed for hydrogen adsorption onto gold substrates allows to determine the surface tension of the free hydrogen film as a function of film thickness. It is found to decrease sharply for film thicknesses below seven atomic layers.
A surface instability is reported in thin nematic films of 5CB and 8CB, occurring near the nematic--isotropic phase transition. Although this instability leads to patterns reminiscent of spinodal ...dewetting, we show that it is actually based on a nucleation mechanism. Its characteristic wavelength does not depend markedly on film thickness, but strongly on the heating rate.
We examine the profile of a liquid front of a film that is dewetting a solid substrate. Since volume is conserved, the material that once covered the substrate is accumulated in a rim close to the ...three phase contact line. Theoretically, such a profile of a Newtonian liquid resembles an exponentially decaying harmonic oscillation that relaxes into the prepared film thickness. For the first time, we were able to observe this behavior experimentally. A non-Newtonian liquid - a polymer melt - however, behaves differently. Here, viscoelastic properties come into play. We will demonstrate that by analyzing the shape of the rim profile. On a nm scale, we gain access to the rheology of a non-Newtonian liquid.
A simple and predictive model is put forward explaining the experimentally observed substantial shift of the glass transition temperature, Tg, of sufficiently thin polymer films. It focuses on the ...limit of small molecular weight, where geometrical `finite size' effects on the chain conformation can be ruled out. The model is based on the idea that the polymer freezes due to memory effects in the viscoelastic eigenmodes of the film, which are affected by the proximity of the boundaries. The elastic modulus of the polymer at the glass transition turns out to be the only fitting parameter. Quantitative agreement is obtained with our experimental results on short chain polystyrene (Mw = 2 kg/mol), as well as with earlier results obtained with larger molecules. Furthermore, the model naturally accounts for the weak dependence of the shift of Tg upon the molecular weight. It furthermore explains why supported films must be thinner than free standing ones to yield the same shift, and why the latter depends upon the chemical properties of the substrate. Generalizations for arbitrary experimental geometries are straightforward.
A transient surface instability is reported in thin nematic films of 5CB and 8CB, occurring near the nematic-isotropic phase transition. Although this instability leads to patterns reminiscent of ...spinodal dewetting, we show that it is actually based on a nucleation mechanism. Its characteristic wavelength does not depend markedly on film thickness, but strongly on the heating rate.
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