Semi-rigid solid

A sol is a colloidal suspension of particles in a liquid for the materials being discussed here, these particles will typically be 1 to 100 nm in diameter. A gel is a semi-rigid solid in which the solvent is contained in a framework of material which is either colloidal (essentially a concentrated sol) or polymeric. 

FIG. 13 Average center-of-mass position of flexible chains of length / with respect to the nearest solid surfaces for different /. Diamonds denote a system of semi-rigid chains in which the opposite effect is observed [28]. 

Gas-filled plastics are polymer materials — disperse systems of the solid-gas type. They are usually divided into foam plastics (which contain mostly closed pores and cells) and porous plastics (which contain mostly open communicating pores). Depending on elasticity, gas-filled plastics are conventionally classified into rigid, semi-rigid, and elastic, categories. In principle, they can be synthesized on the basis of any polymer the most widely used materials are polystyrene, polyvinyl chloride, polyurethanes, polyethylene, polyepoxides, phenol- and carbamideformaldehyde resins, and, of course, certain organosilicon polymers. 

Plasticisers are added to PVC to achieve flexibility and workability. The flexibility or softness is determined by the type of plasticiser and level used in relation to the PVC (phr). They also operate as an internal lubricant between the PVC molecules. Based on organic esters, e.g., phthalates, adipates, trimellitates, phosphates, etc., addition levels can be as low as 20 phr for semi-rigid to 100 phr for very flexible applications. The effect on the thermal stability significantly depends on the physical state of the PVC-plasticiser system (260). The relative amount of crystalline PVC in PVC/diethylhexyl phthalate has been identified on the basis of a combination of carbon-13 solution and solid state nuclear magnetic resonance (NMR) (361). 

Changes in strawberry cell wall components upon ripening were studied by solid-state 13C NMR.162 The separation between semi-rigid (primarily poly-galacturonic acid) and semi-mobile (non-cellulosic substances) domains became more distinct with ripening, whereas the ratio of non-cellulosic material (pectins and hemicellulose) to rigid cellulose decreased. The basic crystallite of strawberry cell walls appeared to be exceptionally small compared with other systems studied.162... 

The variable temperature capability of solid-state NMR spectrometers was exploited in order to obtain narrow NMR spectral resonances of rigid/semi-rigid polymeric materials. Acquisition of NMR spectra of polymeric materials in a soft/viscous state is possible by alteration of the physical state of the sample by any combination of temperature and plasticizing solvent. 

Above amorphous liquid appears, while a semi-crystalline solid appears below Tm. Above Tg, the amorphous phase shows a high mobility leading to high elasticity and deformity. On the other hand, below Tg most polymers behave like rigid solids, and are frequently brittle (glass-like). Exten-sivity is drastically reduced, together with the capacity to resist the effect of blows and oscillation (impact strength). 

The regularity of the polymer backbone is the key factor isotactic polypropylene crystallizes forming a rigid stable solid, whereas atactic polypropylene does not and forms a rubbery elastic solid. For flexible polymers, the structure of the solid is dictated by the symmetry of the polymer backbone. For the formation of a semi-crystalline solid it is necessary for there to be either an element of symmetry in the repeat unit chemical structure or strong interactions to aid the packing of the molecule and initiate the alignment that is required for the crystal growth process. 

We focus on the case of a drop of liquid L sandwiched between a rigid solid S of low energy (e.g., silanized glass) and a semi-infinite rubber R. We assume the elastomer to be homogeneous and isotropic. This material is soft in the sense that it can easily be deformed. If we apply a stress cr, the resulting deformation e is given by Hooke s law ... 

In gel electrophoresis, migration takes place through a slab of a porous gel, a semi-rigid dispersion of a solid in a liquid. Because the molecules must pass through the pores in the gel, the larger the macromolecule, the less mobile it is in the electric field and, conversely, the smaller the macromolecule, the more swiftly it moves through the pores. In this way, gel electrophoresis allows for... 

The scaling approach allows one to predict that the structure of an adsorption layer weakly depends on the volume concentration of polymer, if the adsorption energy is not too high. De Gennes emphasizes that the relationships derived are only valid for an equilibrium adsorption, which, however, can hardly be attained due to hindrance of the reorientation of chains, bonded to the surface. The concentration profile, 0(z), may also be estimated for semi-rigid chains near the solid wall. In this case, the chain is characterized by its persistent length, L, whereas the profile is determined by the value of Oq (z) obtained in the mean-field theory, accounting for the value L,0(z) = o(z + D). 

MACROMOLECULAR ORDER AND CONFORMATION IN THE SOLID AND NEMATIC PHASES OF SEMI-RIGID POLYMERS AND POLYMER-MONOMER MIXTURES—NMR STUDY... 

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