Nodular structure

Departing from the known fact that PVC melts have a nodular structure, about 1 micron in size, the authors assumed that white ash particles invaded the inter-nodular spaces, thereby causing the nodules to move apart and the chains between them to be broken as a result the nodules acquire more freedom to move. As the filler concentration is increased, the contribution to viscosity increase... 

As a consequence, the overall penetrant uptake cannot be used to get direct informations on the degree of plasticization, due to the multiplicity of the polymer-diluent interactions. The same amount of sorbed water may differently depress the glass transition temperature of systems having different thermal expansion coefficients, hydrogen bond capacity or characterized by a nodular structure that can be easily crazed in presence of sorbed water. The sorption modes, the models used to describe them and the mechanisms of plasticization are presented in the following discussion. 

Pre-crystalline order in PET has been investigated by a number of different groups and in the present volume the issue is reviewed under different perspectives in two other contributions [25,26]. Nodular structures measuring ca. 7.5 nm and ca 15 nm apart in PET quenched from the melt close to Tg were first described by Geil [27,28]. Such structures are essentially amorphous, albeit characterized by some degree of orientational order and by a significantly higher density as compared to the fully isotropic polymer. They are indeed qualitatively compatible with the bundle model we propose [29]. Apparently... 

Our previous studies showed that CNTs exhibit marked cytotoxicity (Cui et al., 2005 Tian et al., 2006). For example, SWCNTs can inhibit HEK293 cell proliferation, decrease cell adhesive ability in a dose-and time-dependent manner as shown in Fig. 9.7. HEK293 cells also exhibit active responses to SWCNTs such as secretion of some 20-30 kd proteins to wrap SWCNTs, aggregation of cells attached by SWCNTs and formation of nodular structures as shown in Fig. 9.8. Cell cycle analysis showed that 25pg/ml SWCNTs in medium induced Gt arrest and cell apoptosis in HEK293 cells as shown in Fig. 9.9. Biochip analysis showed that SWCNTs can induce up-regulation expression of cell cycle-associated genes such... 

Nodular. Because of their appearance, nodular structures are often referred to as cauliflower type. Although the phenomenon has been attributed to a number of factors (such as impurities), the origin and growth mechanism of this feature are still not well understood. 

The solvent-etched fracture surface of folly cured PEI modified epoxy with different composition is shown in Figure 3.8. For PEI content smaller than 10wt%, the PEI-rich phase is dispersed in a continuous epoxy-rich matrix [i.e., sea-island morphology is observed (a and b)]. Above 25 wt% PEI content, nodular structure was observed (e and f) where the epoxy-rich phase forms spherical nodules and the PEI rich phase forms the matrix. With PEI content between 15 wt% and 20 wt%, dual phase morphology, where sea-island morphology and epoxy nodular structure coexist, is present (c and d). Similar morphology was observed in PEI/BPACY blend [47],... 

Poly(bithiophene) films from these two ionic liquids are morphologically similar (Figure 7.14), even though the redox behavior (Figure 7.9) is markedly different, suggesting that the dominant differences in the films produced are on an atomic or sub-micron rather than macroscopic level. The morphology ofthe poly (bithiophene) films appears to be similar to that described by Roncali et al. [74] who reported a thin film on the surface of the electrode, covered by a thick brittle powdery deposit, from the galvanostatic polymerization of bithiophene in acetonitrile. The nodular structures are smaller in the poly (bithiophene) films than in the poly (thiophene), which is consistent with the formation of shorter chain polymers [73], but this does not... 

A basal type of deposit is also obtained in the presence of impurities like Co, Ni and Sb, which deposit in between the stacks of platelets resulting a nodular structure.109,110 Such morphology is found in the presence of high concentrations cetylpyrridinium chloride. Cetylpyrridinium chloride produces basal type deposits (Fig. 13), because... 

Figure 2. Nodular structure in polycarbonate with apparent internodular crosslinks (transmission electron micrograph, unshadowed)...

In an earlier analysis, it was shown that the main argument for the existence of inhomogeneous crosslinking — the appearance of nodular structure particularly when etched fracture surfaces are examined — is not at all characteristic of cured epoxies. Similar nodular structures could also be seen in other amorphous polymers. 

Evidence for heterogeneities in PC has also been derived from electron microscopy (EM). Extensive work has been published on the existence of a nodular structure in the range of 3-10 nm (see e.g. According to Yeh et al. craze fibrils are... 

In the first section, up to Uhlmann s paper, we arc concerned with polymer melts in equilibrium. In dilute solution, the dominant restriction on randomness, apart from the very fact that the polymer molecule is a chain, is self-exclusion, and Paul Flory taught us how to cope with that many years ago. In the interior (and I emphasize interior) of the pure amorphous phase, mutual exclusion has a large effect on the total entropy, but its effect on molecular conformations is the relatively minor one of virtually cancelling the effects of self-exclusion. That knowledge we also owe to Flory. Hence a limited number of parameters suffice both to describe and explain the conformations in this case. Uhlmann s paper dismisses for us the aberrant nodular structures which have been proposed there only remains to ask how in certain circumstances the appearance of nodular structure can be produced. 

Opdahl and Somorjai studied the surface deformation and surface elastic properties of stretched polyethylene in a device depicted in Fig. 3.73. It was found that the surface textures of both HDPE and LDPE changed and that the nodular structures present at the surface lengthened in the direction of the stretch and contracted perpendicular to the stretch at various elongations. This resulted in a roughening of the surface. 

Several studies have shown that electrochemically prepared films have an inhomogeneous nodular (or cauliflower ) structure.125 A number of studies have reported the morphology of PPy films as a function of various processing variables however, little is known of the mechanism of formation of the nodular structure or the effect of this structure on mechanical properties. 

Figure 1.15 Scanning electron micrographs of the fine structure of two phese inversion membranes (a) sponge-type structure consisting of spherical cells (b nodular structure consisting of small polymer beads fused together to form a randomly porous structure.

Figure 1.16 Scanning electron micrograph of a membrane showing a nodular structure at the surface which converts into a cellular structure towards the bottom side of the membrane.

Cellular and Nodular Membrane Fine Structure. Several authors have commented on the two different structures shown in Figure 1.15. It is generally assumed that a fine structure is already predetermined in the casting solution prior to the actual phase separation. 4 A cellular structure will be obtained when in the beginning state of the phase separation, i.e., before the solidification of the polymer-rich phase, the continuous phase is formed by the polymer-rich phase. A nodular structure is obtained when the precipitant-rich phase is continuous, completely surrounding droplets of the polymer-rich phase. 

Figure 5.5 Cross section and surface of a microporous polysulfone sheet used in composite reverse osmosis membranes (a) total cross section of a polysulfone sheet cast on a nonwoven polyester fabric, then delaminated prior to freeze-fracture for SEM (note fiber trecks on backside of the sheet) (b) backside of sheet showing cellular structure, which extends through 85% of the sheet thickness (c) transition region from cellular to nodular structure near film surface (d) dense nodular structure at the surface (e) high magnification of the extreme top surface cross section (f) high magnification view of the surface structure showing tha texture of the top surface.

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