Extreme Treatments

Nonpolar and anisotropic molecules are also significantly perturbed near surfaces. Electron and x-ray diffraction studies of films of long chain molecules on metal surfaces indicated the presence of structure well above the melting point in layers 100 molecules thick. There have been many observations [93] that the melting points of relatively thick films may differ considerably from the corresponding bulk characteristics. An extreme example of the long-range structural perturbation in a liquid adjacent to an interface arises in liquid crystals where the anchoring mechanism and bulk orientation are extremely sensitive to simple surface treatments such as rubbing [94]. In addition to the influence of surface orientation on static forces, this perturbation can have a profound effect on layer dynamics discussed in the next section.  [c.245]

It is still the case that most m.o. (molecular orbital) treatments of aromatic reactivity use the Hiickel approximation. The energy difference which, within the limits already discussed, measures aromatic reactivity, can be divided into three parts one relating to change in Tt-electronic energy, another to changes in the energies of the [c.129]

Secondary Treatments and Uses. Because hardboard products are utilized in a myriad of different ways, the variety of secondary treatments used by customers are practically unlimited. Hardboards are used in furniture, cabinets, paneling, doors, toys, and a host of other uses. Post-treatments may include cutting-to-size, finishing treatments with roU-appHed patterns, melamine overlays, printed paper overlays, paints, and even some extremely durable and water-resistant coatings used in tub and shower linings or other uses where water contact is frequent and extreme.  [c.390]

In the paper conservation laboratory, washing is probably the most common treatment. Suction tables are often used to minimize exposure time to water or other solvents used in the treatments. The amount of care bestowed on single works of art on paper in museums would be impractical for individual documents or books in archival and Hbrary collections, where the number of items exceeds that in art museum collections by several orders of magnitude. Hence, ongoing development and testing of appropriate technologies for mass deacidification is especially of great importance for Hbraries and archives. These often contain very large amounts of books and documents on paper produced between the late eighteenth and early nineteenth century from chemically treated wood pulp. Such paper has become extremely britde as a result of acid hydrolysis, known as the brittle book phenomenon. Proposed mass deacidification processes involve the use of aqueous or nonaqueous solutions of various magnesium and calcium carbonates, or diethylzinc as a gas-phase reagent (163).  [c.428]

Wooden Objects. Wooden objects (150, 167) cause several special problems, particularly when recovered from underwater sites. Waterlogged wood (139, 168), if allowed to dry out, suffers irreparable damage through warping and cracking. It is, therefore, kept underwater until it arrives in the laboratory, where a few treatments are available. Freeze drying has proven to be extremely effective. Another well estabhshed treatment is the immersion of the object in a tank with water, in which poly(ethylene glycol) (PEG) is subsequentiy introduced in a slowly increasing concentration, until impregnation of the wood with PEG has been achieved. Yet another technique involves impregnation with a solution of rosin in acetone.  [c.428]

Whereas these preparations ate extremely useful for obtaining sufficient quantities of the D metabohtes and analogues for study and as possible therapeutic treatments, their cost is high compared to the cost of manufacture of vitamin D. For this reason, the metabohtes ate unlikely to be successful in replacing vitamin D as an ingredient in animal or human nutrition.  [c.136]

The antistatic protection provided by surface treatment is excellent while it lasts. However, surface treatments provide only temporary protection. The antistat layer is extremely vulnerable to mbbing and wiping, especially when wet (45). Loss of antistatic agent can also occur by diffusion from the surface into the bulk of the material on storage (77,78). Several attempts have been made to obtain more durable antistatic coatings with varying degrees of success using reactive resins and surface grafting (122,138—144).  [c.299]

Chlorinated paraffins with the general molecular formula x 2x-y+2) have been manufactured on a commercial basis for over 50 years. The early products were based on paraffin wax feedstocks and were used as fine retardants and plasticizers in surface coatings and textile treatments and as extreme pressure—antiwear additives in lubricants. The development of chlorinated paraffins into new and emerging technologies was constrained principally because of the limitations of grades based on paraffin wax and the lack of suitable alternative feedstocks to meet the demands of the new potential markets.  [c.41]

High energy dyes are based on large molecules with polar groups. These dyes have excellent heat fastness resulting from extremely low rates of sublimation. Their main use is in dyeing fabrics that are to be given a subsequent high temperature heat treatment, eg, permanent pleating finish, or sewing threads whose future use and treatments are unknown and therefore every possibiHty must be considered. Although they have very high heat fastness these dyes do not necessarily have any better wetfastness than medium energy dyes because although they desorb slowly, dye that does desorb has a high affinity for hydrophobic adjacent fibers. Dyeing with these dyes requires either longer times or temperatures than with medium energy dyes to achieve hiU exhaustion, eg, 45—60 min at 125—135°C in exhaust dyeing. They are sensitive to the conditions of thermofixation needing 60—90 s at 210—220°C to give hiU yield.  [c.364]

There are a large number of life-threatening or chronically debilitating human diseases such as solid tumor cancers, AIDS, antibiotic-resistant microbial infections, asthma, and diabetes that urgently require improved medical treatments. Drug therapy represents one well-established and still attractive approach to treating these serious diseases. In order for the chemotherapeutic approach to be more effective, there is a pressing need to discover and develop new drugs that act against cancer cells, viruses, microbial pathogens, and other molecular disease targets by novel biochemical mechanisms and have diminished side effects. Secondary metabolites produced by the plants, animals, and microorganisms living in the world s oceans represent a vast and relatively unexplored resource of structurally diverse low molecular weight organic molecules that are ideal raw materials for the development of new drugs. Exploitation of this extremely valuable molecular resource is a complex and lengthy process that is shaped by many scientific, legal, business, and environmental issues. The goal of this chapter is to highlight the tremendous opportunities and the considerable challenges involved in developing new pharmaceuticals from the sea.  [c.55]

Extreme sensitivity to the outer surface is the most useful advantage of ISS. It is unexcelled in this respect and has the unique capability to detect only the outermost atomic layer without signal dilution from many additional underlying layers. No other technique, including static SIMS or angle-resolved XPS, can detect only the outermost atomic layer. ISS is also very fast and sensitive, so that even very low level impurities within the outer few A can be detected. Other very important advantages are the speed of depth profiling and the extreme detail one can obtain about the changes in chemical composition within the outer surface, especially the first 50-100 A (i.e., the high depth resolution owing to sensitivity to the first atomic layer). The indirect detection of hydrogen also has proven extremely applicable to studies of polymers and other materials containing surface hydrogen in any form. This has been especially valuable in applications involving plasmas and corona treatments of polymers. ISS is routinely applicable to the analysis of insulators and irregularly shaped samples. In some research and development applications its ability to detect certain isotopes, such as are especially important. Quantitative analysis is also advantageous, since ISS does not miss elements that are often overlooked in other spectroscopies due to poor sensitivity (such as H, the alkalis, and the noble metals), and quantitative calculations are not affected by the matrix. In addition these relative sensitivities do not vary as dramatically as in some other spectroscopies and they are uniformly increasing with the mass of the elements.  [c.522]

Surface treatments, while extremely effective for the current day short pulse tokamaks (pulses typically less than a few seconds), are of limited value for the next generation (quasi-steady state) machines because of the significant surface erosion expected. However, if the entire graphite PFM were altered, rather than a surface layer, the beneficial effects would be gained regardless of how much erosion occurs. Promising results have been obtained by doping graphite with boron, which is a substitutional element in the graphite lattice and at higher concentrations forms stable carbides, and thus traps migrating interstitials and alters  [c.416]

Different industries assign different roles to surface preparation. The aerospace industry, with relatively low throughput and extreme emphasis on safety, carefully prepares the surface prior to bonding during original manufacture and repair to assure the best practical bond strength and durability. This is done even when the bonding areas are very large as in the Space Shuttle where insulating tiles are adhesively bonded to virtually the entire surface area of the Orbiter and an insulating urethane foam is bonded to over 1/4 acre of the External Tank surface. On the other hand, the automotive industry, with high throughput, prefers almost no surface preparation and therefore uses contamination-tolerant adhesives and overdesign of joints. Likewise, the packaging industry, with very high throughput but relatively low requirements for stress and durability, also minimizes surface preparation. This chapter will focus on surface treatments used for high-performance bonds, primarily of the type used in the aerospace industry.  [c.948]

Scattering techniques using light, neutrons and x-rays are extremely usefiil to study the structure, size and shape of large molecules in solids, liquids and solutions. The principles of the scattering teclmiques, which involve the interaction of radiation with matter, are the same. However, the data treatment for scattermg from light, neutrons or x-rays can be quite different because the intrinsic property of each radiation and its interactions with matter are different. One major difference in the data treatment arises from the states of matter. Although the general equations describing the interaction between radiation and matter are valid for all classes of materials, unique analytical treatments have been made to suit the different states of matter.  [c.1384]

The Woodward-Hoffmann rules state what the outcome of a pericyclic reaction will be, but they do not define the mechanism by which the reaction occurs. Many theoretical techniques have been applied to the study of these problems over the years [Houk et al. 1992] and a passionate debate has ensued on the nature of the transition structures involved in these reactions. The debate has been fuelled by fhe fact that different theoretical treatments (especially semi-empirical methods) give different results. For example, at one extreme the Diels-Alder reaction between butadiene and ethene would proceed via a two-step mechanism involving a brradial transition structure. At the other extreme the reaction would involve a symmetrical transition state formed in a concerted, synchronous reaction. Ab initio calculations at various levels of theory suggest the concerted transition structure. The geometry obtained for the prototypical Diels-Alder reaction between butadiene/ ethene using a CASSCF calculation and a 6-31G basis set is shown in Figure 5.35 [Houk et al. 1995]. The alternative biradial structure is also shown in Figure 5.35 this is predicted to be 6kcal/mol higher in energy than the symmetrical transition structure.  [c.309]

Beating ndRefining. Virtually all pulps are subjected to certain mechanical actions before being formed into a paper sheet. Such treatments are used to improve the strength and other physical properties of the finished sheet and influence the behavior of the system during the sheet-forming and drying steps. During refining, the cellulose fibers are swollen, cut, macerated, and fibnllated. The most desirable action is the development of internal fibrillation, which makes the wet fiber more compliant or flexible. This flexibiUty enhances the number of interfiber contacts during formation of the paper, and bonding during subsequent pressing and drying operations. Although refining markedly alters the physical properties, no significant chemical changes occur. A sheet formed from an unbeaten pulp has low density and is rather soft and weak. If the same pulp is well beaten, however, the resultant paper is much more dense, hard, and strong. If taken to the extreme, beating produces very dense, translucent, glassine-type sheets. Refining greatly increases the wet specific surface of pulp fibers, swollen specific volume, and fiber flexibiUty. Although hydration in the chemical sense does not occur, the affinity for water is enhanced. Because of the unique cellulose—water relationship, these changes significantly increase the abiUty of the fibers to bond when dried from a water suspension and, therefore, enhance the strength of the sheet. Optical micrographs of a softwood kraft pulp before and after several periods of extensive beating are given in Figure 2. In Figure 3, the tensile strength, bursting strength, and tearing resistance are shown as functions of beating time for a softwood kraft pulp. It generally is tme that, within the commercial range, beating increases tensile strength, bursting strength, folding endurance, and sheet density, whereas it reduces tearing resistance.  [c.3]

The neat resin preparation for PPS is quite compHcated, despite the fact that the overall polymerization reaction appears to be simple. Several commercial PPS polymerization processes that feature some steps in common have been described (1,2). At least three different mechanisms have been pubUshed in an attempt to describe the basic reaction of a sodium sulfide equivalent and -dichlorobenzene these are S Ar (13,16,19), radical cation (20,21), and Buimett s (22) Sj l radical anion (23—25) mechanisms. The benzyne mechanism was ruled out (16) based on the observation that the para-substitution pattern of the monomer, -dichlorobenzene, is retained in the repeating unit of the polymer. Demonstration that the step-growth polymerization of sodium sulfide and /)-dichlorohenzene proceeds via the S Ar mechanism is fairly recent (1991) (26). Eurther complexity in the polymerization is the incorporation of comonomers that alter the polymer stmcture, thereby modifying the properties of the polymer. Additionally, post-polymerization treatments can be utilized, which modify the properties of the polymer. Preparation of the neat resin is an area of significant latitude and extreme importance for the end user.  [c.442]

Supercritial boilers use all-volatile treatments, generally consisting of ammonia and hydrazine. Because of the extreme potential for deposit formation and steam contamination, no soHds can be tolerated in supercritical once-through boiler water, including treatment soHds.  [c.264]

As the side effect during the experiments, there found a better plants growth in the group treated with WPA in comparison with the control group, especially the plants treated with magnesium WPA salt. That effect could not be explained by the phosphorus doping, due to extremely low concentration of phosphoms in WPA solutions using for spraying during the experiments. So, the effects of WPA and its compounds (its magnesium salt and compounds with Gly and Ala) on element profile of tobacco plants, tried to be connected. For such purpose, after the appropriate procedure of collecting, separating and storage, the EDXRF spectrometry of the leaves, tmnks and summitas was performed. Radioisotope excitation source Cd was used, the tablets weighted 100 mg of dried plant material and the measurement time was 2000 s. The contents of K, Ca, Fe, Cu, Zn, Na and Sr were determined in the control plant group, as well as in the tobacco plants groups after the once, twice and thrice spraying with ten days between the two treatments. A special attention was paid on the element profile of summitas (the top of the plant) witch was not directly spraying during the experiments, and its content of Zn, important element for the plant growth.  [c.239]

Treatment of MCS is difficult for physicians to define and diagnose. There is no single set of symptoms which fit together as a syndrome, nor a single diagnostic test for MCS. Instead, physicians should take a complete patient history which includes environmental and occupational exposures, and act as detectives in diagnosing this problematic condition. After the onset of MCS, a person s health generally continues to deteriorate. It may only begin to improve once the chemical sensitivity condition is uncovered. While a number of treatments may help improve the baseline health status for some patients, at the present time, there is no single "cure except avoidance. Avoiding the chemicals which may trigger reactions is an essential part of treating MCS. Those with MCS who are able to strictly avoid exposures often experience dramatic improvement in their health over the period of a year or more. Yet the profusion of new and untested synthetic chemicals makes this extremely difficult. Individuals affected by MCS often create a "sanctuary" relatively free from chemical emissions in their home, where they spend as much time as possible. Because of the serious impact of even an accidental unavoidable exposure, MCS sufferers often spend as much time at home as possible and often must choose not to participate in society.  [c.45]

Another application is uranium hexafluoride for enriching uranium in the fissile tsoione Lsraniurn-235 by diffusion. Fluorine is known for being difficult to handle because of its intense chemical reactivity. The solution required the development and use of fluorine-resistant materials so that fluorine manufacture is now routine. Other uses developed as a component in some rocket propellants, for the preparation of the extremely reactive interhalogen compounds such as chlorine trifluoride (ClFj), used for cutting steel, and for the preparation of sulfur hexafluoride, an extremely stable gas that has been employed as an insulator in electrical applications. Other u.ses arc teflon,, 1 fluorocarbon resin such as poly-tetrafluoroethylene for coating frying pans to prevent food from sticking. There are several other fluorocarbon and fluorinated hydrocarbon resins some htive highly specialized applications in the aerospace industry. Fluorinated compounds are also useti in textile treatments some are soil-release agents that make fabric easy to wash. The salt sodium fluoroacetate is an extremely powerful rodenticide. Sodium bifluoride is used to remove iron stains without weakening fabric. A minor but important use of fluorine in some countries is the fluoridation of drinking water for dental health.  [c.268]

If the protein of interest is a heteromultimer (composed of more than one type of polypeptide chain), then the protein must be dissociated and its component polypeptide subunits must be separated from one another and sequenced individually. Subunit associations in multimeric proteins are typically maintained solely by noncovalent forces, and therefore most multimeric proteins can usually be dissociated by exposure to pEI extremes, 8 M urea, 6 M guanidinium hydrochloride, or high salt concentrations. (All of these treatments disrupt polar interactions such as hydrogen bonds both within the protein molecule and between the protein and the aqueous solvent.) Once dissociated, the individual polypeptides can be isolated from one another on the basis of differences in size and/or charge. Occasionally, heteromultimers are linked together by interchain S—S bridges. In such instances, these cross-links must be cleaved prior to dissociation and isolation of the individual chains. The methods described under step 2 are applicable for this purpose.  [c.131]

It is still the case that most m.o. (molecular orbital) treatments of aromatic reactivity use the Hfickel approximation. The energy difference which, within the limits already discussed, measures aromatic reactivity, can be divided into three parts one relating to change in TT-electronic energy, another to changes in the energies of the cr-bonded structures, and another to electrostatic effects. Changes in cr-bonds are neglected since they are likely to be similar for similar compounds undergoing the same reaction. The problem of calculating the reactivity of an aromatic compound is thus reduced to that of calculating for it the change between ground and transition states of TT-electron and electrostatic energies, as compared with that for benzene. As implied above, two extreme models of the transition state can be considered in the isolated molecule treatment the transition state is taken to resemble the ground states of the reactants, whilst at the other extreme the Wheland intermediate (see below) is used to represent the transition state.  [c.129]

See pages that mention the term Extreme Treatments : [c.391]    [c.393]    [c.12]    [c.74]    [c.471]   
See chapters in:

The coming of materials science  -> Extreme Treatments