Strength molecular level

What causes the phenomenon of stress and strain reduction and why is the reduction in impact and work properties so visible at small or negligible changes in elastic modulus and ultimate strengths As discussed previously, mechanical properties deal with stress and strain relationships that are simply functions of chemical bond strength. At the molecular level, strength is related to both covalent and hydrogen intrapolymer bonds. At the microscopic level, strength... 

Nylon-6. Nylon-6—clay nanometer composites using montmorillonite clay intercalated with 12-aminolauric acid have been produced (37,38). When mixed with S-caprolactam and polymerized at 100°C for 30 min, a nylon clay—hybrid (NCH) was produced. Transmission electron microscopy (tern) and x-ray diffraction of the NCH confirm both the intercalation and molecular level of mixing between the two phases. The benefits of such materials over ordinary nylon-6 or nonmolecularly mixed, clay-reinforced nylon-6 include increased heat distortion temperature, elastic modulus, tensile strength, and dynamic elastic modulus throughout the —150 to 250°C temperature range. 

An important chemical finishing process for cotton fabrics is that of mercerization, which improves strength, luster, and dye receptivity. Mercerization iavolves brief exposure of the fabric under tension to concentrated (20—25 wt %) NaOH solution (14). In this treatment, the cotton fibers become more circular ia cross-section and smoother ia surface appearance, which iacreases their luster. At the molecular level, mercerization causes a decrease ia the degree of crystallinity and a transformation of the cellulose crystal form. These fine stmctural changes iacrease the moisture and dye absorption properties of the fiber. Biopolishing is a relatively new treatment of cotton fabrics, involving ceUulase enzymes, to produce special surface effects (15). 

Johnstone (2000) emphasises the importance of beginning with the macro and symbolic levels (Fig. 8.3) because both comers of the triangle are vistrahsable and can be made concrete with models (p. 12). The strb-micro level, by far the most difficult (Nelson, 2002), is described by the atomic theory of matter, in terms of particles such as electrorrs, atoms and molecules. It is commorrly referred to as the molecular level. Johnstone (2000) describes this level simirltaneorrsly as the strength and weakness of the subject of cherrristry it provides strength through the intellectual basis for chemical explanatiorrs, but it also presents a weakness when novice students try to learn and rmderstand it. 

Even though both ligands form Ni — N bonds of similar strength, ethylenediamine binds to Ni many orders of magnitude more strongly than does NH3. Why is this Think about complexation at the molecular level. One of the Ni — N bonds in either complex can be broken fairly easily. When this happens to [Ni (NH3)g, the ammonia molecule drifts away and is replaced by another ligand, t q)ically a water molecule from the solvent ... 

As a consequence, the development paths of surface Raman and infrared techniques will, given their different strengths and weaknesses, probably continue to proceed along divergent avenues of chemical application. Nevertheless, it seems inevitable that both will contribute in an increasingly important fashion to the detailed molecular-level elucidation of reactive as well as stable electrochemical systems. 

The benzofuran-naphthyridine linked dye compound (ABAN, see Fig. 1) has been successfully converted to fluorescent organic nanoparticles [34], for which their photophysical properties such as spectral features and emission intensity are remarkably different from those at the molecular level (solution). The results are rationalized by coplanarization of the benzofuran-naphthyridine molecule in the nanoparticle to extend its effective conjugation length and hence increase the oscillator strength, as is similar to the cases described above. 

Strength, brittleness, and solvent permeability properties are limited because of lack of control of the ceramic composition on a macro- and microlevel. Even small particle sizes are large compared with the molecular level. There have been a number of attempts to produce uniform ceramic powders including the sol-gel synthesis in which processing involves a stable liquid medium, coprecipitation in which two or more ions are precipitated simultaneously. More recently, Carraher and Xu have used the thermal degradation of metal containing polymers to deposit metal atoms and oxides on a molecular level. 

The extruded fiber is then often uniaxially stretched by take-up rollers rotating at different speeds. The fiber stretching encourages the polymer chains to align on a molecular level producing increased strength in the direction of the pull. 

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