Connections to Materials

Since 1997 different scientific institutions at Uppsala University have joined in a center for education and research within fields connected to materials science. The laboratory is named after Anders Johan Angstrom (Figures 10.9 and 10.10) whose achievements were described above, and also after his son Knut Angstrom, also professor in Uppsala. The son Knut devoted a great part of his research to the radiation from the sun [10.10]. 

A summary is a brief statement of main ideas or important concepts. Making a summary of what you have read provides you with a way to review what you have learned, see what information needs further clarification, and make connections to material previously studied. Paired summarizing helps strengthen your ability to read, listen, and understand. It is especially useful when a section of text has several subdivisions, each dealing with different concepts. 

A set-up for distillation under reduced pressure is shown in Fig. 11,60,3 it is generally more convenient to use a Kon receiver or a Perkin triangle (Fig. 11, 56, 31). The vessel at the side, connected to the assembly by rubber pressure tubing, may be immersed in a Dry Ice-acetone bath and serves as a trap for volatile materials. 

The following exercises and experiments help connect the material in this chapter to the analytical laboratory. 

Liquids. Liquids usually are moved through pipelines (qv) by pumps. Special alloys, plastic pipe and liners, glass, and ceramics are widely employed in the chemical industry for transport of corrosive hquids. Care is required in making the connections, to prevent exposure of unprotected metal such as flanges and bolts to the corrosive material inside the piping. 

A rotational viscometer connected to a recorder is used. After the sample is loaded and allowed to come to mechanical and thermal equiUbtium, the viscometer is turned on and the rotational speed is increased in steps, starting from the lowest speed. The resultant shear stress is recorded with time. On each speed change the shear stress reaches a maximum value and then decreases exponentially toward an equiUbrium level. The peak shear stress, which is obtained by extrapolating the curve to zero time, and the equiUbrium shear stress are indicative of the viscosity—shear behavior of unsheared and sheared material, respectively. The stress-decay curves are indicative of the time-dependent behavior. A rate constant for the relaxation process can be deterrnined at each shear rate. In addition, zero-time and equiUbrium shear stress values can be used to constmct a hysteresis loop that is similar to that shown in Figure 5, but unlike that plot, is independent of acceleration and time of shear. 

Piston Cylinder (Extrusion). Pressure-driven piston cylinder capillary viscometers, ie, extmsion rheometers (Fig. 25), are used primarily to measure the melt viscosity of polymers and other viscous materials (21,47,49,50). A reservoir is connected to a capillary tube, and molten polymer or another material is extmded through the capillary by means of a piston to which a constant force is appHed. Viscosity can be determined from the volumetric flow rate and the pressure drop along the capillary. The basic method and test conditions for a number of thermoplastics are described in ASTM D1238. Melt viscoelasticity can influence the results (160). 

Monolayers of alkyl chains on siUcon are a significant addition to the family of SAMs. An abiUty to directly connect organic materials to siUcon allows a direct coupling between organic materials and semiconductors. The fine control of supedattice stmctures provided by the self-assembly technique offers a route for building organic thin films with, for example, electrooptic properties on siUcon. 

Vacuum is applied to the chamber and vapor is removed through a large pipe which is connected to the chamber in a manner such that, if the vacuum is broken suddenly, the inrushing air will not greatly disturb the bed of material being dried. This line leads to a condenser where moisture or solvent that has been vaporized is condensed. The noncondensable exhaust gas goes to the vacuum source, which may be a wet or diy vacuum pump or a steam-jet ejector. 

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