Dense packing of molecules

The mechanism of improving hardness and wear resistance is supposed to be the dense packing of molecules induced by chain scission at the Tg. The original PC has an amorphous structure, where the free volume may exist among the entanglanent molecules. The small amount of chain scission at Tg temperature induces the molecular rearrangement to result in an increase of density, that is, dense packing of molecules. 

The chemical properties for PC teeth improved with the increase of hardness and wear resistance. BPA extraction from PC teeth was less than the detection limit, and the content did not increase by irradiation. The decrease of denture plaque (adhesion of mucin) was remarkable. The mechanisms of the major changes were estimated to be the dense packing of molecules in amorphous matrix... 

SAMs on metal oxide surfaces, a model assuming a uniform, dense packing of molecules tilted by an angle of 30° to the surface normal was used (Figure 9). 

Initially, the compression does not result in surface pressure variations. Molecnles at the air/water interface are rather far from each other and do not interact. This state is referred to as a two-dimensional gas. Farther compression results in an increase in snrface pressure. Molecules begin to interact. This state of the monolayer is referred as two-dimensional liquid. For some compounds it is also possible to distingnish liqnid-expanded and liquid-condensed phases. Continnation of the compression resnlts in the appearance of a two-dimensional solid-state phase, characterized by a sharp increase in snrface pressure, even with small decreases in area per molecule. Dense packing of molecnles in the mono-layer is reached. Further compression results in the collapse of the monolayer. Two-dimensional structure does not exist anymore, and the mnltilayers form themselves in a non-con trollable way. 

In orthorhombic a-sulfur, the modification stable at normal conditions, S8 rings are stacked to form columns. Consecutive rings are not stacked one exactly above another (as in a roll of coins), but in a staggered manner so that the column looks like a crank shaft (Fig. 11.3). This arrangement allows for a dense packing of the molecules, with columns in two mutually perpendicular directions. The columns of one direction are placed in the recesses of the perpendicular crank shafts . In S6 and in S12 the rings are stacked exactly one above another, and the rolls are bundled parallel to each other. In the structures a... 

Fig. 19. Recrystallization of arborescent graft polyethylenes from dense packing of spheres to fibers of linearly aligned molecules upon annealing...

Figure 9-43. (a) Dove-tail dense packing of 1,3,5-triphenylbenzene molecules [64] (b) Chinese decoration on a sculpture in the sculpture garden of the Ming tombs, near Beijing and (c) Detail of the armor (photographs by on the authors). 

The dense arrangement of the chains points to the action of other forces that can control the molecular conformation of adsorbed macromolecules in addition to the interaction with the substrate. Capillary forces and dewetting during evaporation of the solvent can cause condensation and dense packing of the molecules in monolayer patches,147 148 150 For large molecules with a diameter of ca. 5 nm, capillary forces are in the range of a few nN, which is sufficient to... 

Another important use of the PHS-PEO-PHS block copolymer is the formation of a viscoelastic film around water droplets [11, 12] this results from the dense packing of the molecule at the W/O interface, which leads to an appreciable interfacial viscosity. The viscoelastic film prevents transport of water from the internal water droplets in the multiple emulsion drop to the external aqueous medium, and this ensures the long-term physical stability of the multiple emulsion when using polymeric surfactants. The viscoelastic film can also reduce the transport of any a.i. in the internal water droplets to the external phase. This is desirable in many cases when protection of the ingredient in the internal aqueous droplets is required and release is provided on application of the multiple emulsion. 

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