Non-polymeric materials

Most polymers are applied either as elastomers or as solids. Here, their mechanical properties are the predominant characteristics quantities like the elasticity modulus (Young modulus) E, the shear modulus G, and the temperature-and frequency dependences thereof are of special interest when a material is selected for an application. The mechanical properties of polymers sometimes follow rules which are quite different from those of non-polymeric materials. For example, most polymers do not follow a sudden mechanical load immediately but rather yield slowly, i.e., the deformation increases with time ( retardation ). If the shape of a polymeric item is changed suddenly, the initially high internal stress decreases slowly ( relaxation ). Finally, when an external force (an enforced deformation) is applied to a polymeric material which changes over time with constant (sinus-like) frequency, a phase shift is observed between the force (deformation) and the deformation (internal stress). Therefore, mechanic modules of polymers have to be expressed as complex quantities (see Sect. 2.3.5). 

In non-polymeric materials the entropy change on deformation is minimal so that the intrinsic and stored elastic energies are the same at least for rapidly occurring events - but in polymers not only may the entropy contribution predominate but for large strains in rubbers the internal energy term is nearly negligible (but not at small strains where it may amount to 20% of the free energy). 

Non-Polymeric Materials. Waxes, soaps, greases, asphalts, oils. Complex mixtures of hydrocarbons of different molecular weight when treated to a common thermal history (such as slow program-cooling from above the melt) give complex but highly repeatable characteristic DSC melting profiles (16,17). In the absence of any other forensic evidence, these thermal profiles should be sufficiently specific and repeat-able to be definitive evidence. 

Williams DJ (1984) Organic polymeric and non-polymeric materials with large optical nonlinearities. Angew. Chem. Int. Ed. Engl. 23 690-703... 

Cast fihns Blends with polymeric and non-polymeric materials Batteries (sometimes heated)... 

For non-polymeric materials it is possible to get very good X-ray diffraction patterns and the intensities can be determined for many well-defined spots. The determination of the contents of the unit cell is then essentially a mechanical process using modern computational techniques. Because of the often rather poor quality of the fibre diffraction patterns obtained for polymers, the number of spots observed may be rather small and the spots are often quite broad and overlapping. It is thus difficult or impossible to determine the individual intensities accurately. Fortunately, the nature of polymer molecules themselves leads to some simple methods for deducing the likely contents of the unit cell, as discussed in the next section. 

In general, polymer dissolution differs from dissolution of a non-polymeric material in two aspects. Polymers require an induction time before starting to dissolve, while non-polymeric materials dissolve instantaneously. Also, polymer dissolution can be controlled either by the disentanglement of the polymer chains or by the diffusion of the chains through a boundary layer adjacent to the solvent-polymer interface. However, the dissolution of non-polymeric materials is generally controlled by the external mass transfer resistance through a liquid layer adjacent to the solid-liquid interface. 

In dissolution of non-polymeric materials in solvents, the resistance offered by the him adjacent to the material assumes significance. It is hence intuitive to examine the role of such an external mass transfer resistance in polymer dissolution. 

A number of polysaccharides activate the interferon system 18, 63) a natural body defense against virus attack. These include a (1 - 6)-a-D-mannopyranan to which are attached (l- 2)-a-D-mannopyranan side chains 64-66). The backbone of this polysaccharide has now been duplicated synthetically (67) A number of polyanions and oxidized polysaccharides are also effective 68,69), but have been considered less attractive clinical possibilities than the synthetic polynucleotide poly (I C) 63, 72). The activity of poly (I C) can also be enhanced by the use of DEAE dextran 73, 74). Recently a small molecule Tilorone hydrochloride has also been found effective and a variety of related non-polymeric materials are now being investigated (75) for interferon activation,... 

BCPs [117-121], The concepts discussed above may help to understand the crystallization behavior of bulk polymers as well as that of non-polymeric materials such as pharmaceuticals [122] and inorganic semiconductors [123] confined to nanoporous hard templates. 

It should be free from contamination. Contamination can result from mixing different polymers, non-polymeric materials such as paper, and metal as foreign objects. 

Low temperature properties will also be affected by another polymer characteristic, the ability or otherwise of a polymer to crystallize Such crystallization should not be confused with the common and popular concept of a crystal which normally implies a single crystal—a particle that has grown without interruption from a single nucleus, has a definite external shape and is relatively free from defects. Many polymers exhibit polycrystallinity (a property which may also be seen in non-polymeric materials). In such substances aggregates of tiny crystals have been developed, often interlocked with amorphous material. Regions of high order are discernible and unit cell structures may be elucidated. 

The major areas of application of ion beam techniques to polymer surface and interface problems concern (i) segregation at polymer surfaces and interfaces (ii) polymer-polymer interfaces and diffusion and (Hi) transport of non-polymeric materials through thin polymer films. A prototypical case of the latter application is swelling of an amorphous polymer by a small molecule solvent. Kramer et al. [223,224] probed the diffusion front in swelling of PS, PMMA and other polymers by halo-genated solvents. Adhesion problems, glass/polymer interfaces, and polymer surfaces have been studied. 

So much can be achieved in altering the mechanical, thermal or surface properties of polymers by the addition of relatively minor quantities of other polymeric or non-polymeric materials that frequently the problem of choice becomes that of choosing from a range of materials based essentially on the same adhesive but formulated with different additives or cross-linked by a different temperature and time sequence. However, with all these caveats stated it is still necessary to start the process of selection from a consideration of adhesive-substrate compatibility and to proceed from that decision to others involving the use for which the structure is intended, the method whereby it is to be made and the environment in which it must function for a greater or lesser period of time. 

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