Entangled nuclei

When the diluent is a nonsolvent, there is no comparable swollen state and the final structure is one in which large entangled nuclei are connected by a relatively small number of coiled and crumpled internuclear chains and the polymer and diluent phases are segregated. As with the solvent-modified materials, collapse of the system of interconnected nuclei occurs as the diluent is removed, but the large size of the nuclei will lead to the appearance of macroporosity at considerably lower DVB contents and dilutions. In fact, the macroporosity appears at lower DVB contents... 

A rep < 1, Des < 1, the nucleation dynamics is stochastic in nature as a critical fluctuation in one, or more, order parameters is required for the development of a nucleus. For DeYep > 1, Des < 1 the chains become more uniformly oriented in the flow direction but the conformation remains unaffected. Hence a thermally activated fluctuation in the conformation can be sufficient for the development of a nucleus. For a number of polymers, for example PET and PEEK, the Kuhn length is larger than the distance between two entanglements. For this class of polymers, the nucleation dynamics is very similar to the phase transition observed in liquid crystalline polymers under quiescent [8], and flow conditions [21]. In fast flows, Derep > 1, Des > 1, A > A (T), one reaches the condition where the chains are fully oriented and the chain conformation becomes similar to that of the crystalline state. Critical fluctuations in the orientation and conformation of the chain are therefore no longer needed, as these requirements are fulfilled, in a more deterministic manner, by the applied flow field. Hence, an increase of the parameters Deiep, Des and A results into a shift of the nucleation dynamics from a stochastic to a more deterministic process, resulting into an increase of the nucleation rate. 

Fig. 5.3 Schematic illustration of initial crystallization precursor structure (stable critical nucleus) formation in HMW-iPP/LMW-LLDPE blends after cessation of flow. Before flow, HMW-iPP chains solid lines) form a network with a given entanglement density in the LMW-LLDPE matrix blank area). During shear, stretched chain segments begin to form initial erystallization precursor structure via local parallel packing, r and t represent the sizes of initial precursor and critical nucleus for crystallization, respectively. When r > r, the precursors can furthta develop into crystals [21]...

Demonstration of entanglement between the spins of a nucleus and the electron, in the same molecule,... 

The creation of a stable 3-D structure from a disordered state (i.e. a po er melt) is generally considered a two step process. The first step is called mcieation and involves the creation of a stable nucleus from the entangled polymer melt Most technical processes involve secondary or heterogeneous nucleation either from specially added surfiices, nucleating agents, or adventitious surfiices, such as dust piarticles. 

Figure 439 Schematic illustration to suggest how nucleation and growth are suppressed by the entanglements. The entanglements on the interface between the nucleus and hquid create a pinning effect. ...

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