Phase Separation of Several Kinds of Polyethylene Solution under the Gelation/Crystallization Process

Abstract

The gelation mechanism of polyethylene solutions was investigated by using light scattering and X-ray diffraction techniques in terms of the liquid−liquid phase separation. Three kinds of polyethylene, ultrahigh molecular weight polyethylene (UHMWPE), low molecular weight linear polyethylene (L-LMWPE), and low molecular weight branched polyethylene (B-LMWPE), were used as test specimens. When an incident beam of He−Ne gas laser was directed to the UHMWPE and B-LMWPE solutions quenched to a desired temperature, the logarithm of scattered intensity increased linearly in the initial stage and tended to deviate from this linear relationship in the latter stage. If the linear increase in the initial stage can be analyzed within the framework of the linear theory of spinodal decomposition proposed by Cahn, the gelation is obviously attributed to the phase separation leading to the concentration fluctuation of the solution. Furthermore, in the later stage showing the deviation from the linear relationship, light scattering from the UHMWPE solution with 0.5% concentration under Hv polarization condition showed an X-type pattern, indicating the appearance of optically anisotropic rods. On the other hand, the scattering from the B-LMWPE solution with 3% concentration showed a four-leaf clover pattern, indicating the appearance of optically anisotropic spherulites. No crystallite was confirmed by the X-ray diffraction measurements, when the rods and spherulites appeared. With further lapse of time, the Hv patterns became clearer and the corresponding X-ray diffraction intensity curves showed a very small diffraction peak from the (110) plane. In contrast, for the L-LMWPE solutions, the logarithm of scattered intensity against time showed a rapid increase and tended to level off because of rapid change from slightly transparent to whiten gels. In such a process, any quantitative analysis of the scattered light intensity was impossible. The corresponding X-ray diffraction revealed the strong reflections from the (110) and (200) planes, indicating the rapid formation of stable crystallites. Through a series of experiments for the three kinds of polyethylene solution, it turned out that gelation mechanism of polyethylene solutions is strongly affected by molecular weight and the degree of branching.

Gelation mechanism of ultra-high-molecular-weight polyethylene (UHMWPE) chains in dispersion solutions containing multiwall carbon nanotubes (MWNTs) analyzed in terms of liquid-liquid phase separation

“…In accordance with the previous paper [16], the linear relationship is obviously related to the liquid-liquid phase separation of the solution. Namely, the UHMWPE solutions at elevated temperature are thermodynamically unstable at the gelation temperature and tend to incur phase separation by UHMWPE chain diffusion immediately.…”

“…In spite of the detailed analysis for the UHMWPP, the time dependence of crystallite formation after rapid temperature dropping could not be measured by X-ray diffraction. For UHMWPE-quenched solution [16], it was confirmed by X-ray diffraction that there existed no ordered structure like para-crystallite with large fluctuation of lattice distance in the initial stage, but the optically anisotropic structures like rods or spherulites appeared in the later stage of the phase separation.…”

“…Since then, more detailed analysis has been reported for several kinds of polymer. By using successful analysis of the linear theory of spinodal decomposition by Cahn [9,10], Matsuo et al extended to some crystalline polymer solutions such as PVA [11,12], polypropylene [13], agarose [14,15], and polyethylene [16] in order to investigate whether the gelation by the quenching is attributed to the phase separation of solution by the concentration fluctuation.…”

“…On the basis of a series of established results [11][12][13][14][15][16], this paper deals with the admixed effect of multiwall carbon nanotubes (MWNTs) on the gelation/crystallization mechanism of UHMWPE solutions. This is very important to make clear the evidence that well-blended UHMWPE-MWNT composites prepared by gelation/crystallization provide characteristics of high modulus and high electric conductivity.…”

Spatiotemporal Evolution in Morphogenesis of Thermoreversible Polymer Gels with Fibrillar Network

“…The point to observe is that the characteristic fluctuation length-scale (∼0.5 μm) was also shown in other polymer gel systems. [36][37][38][39][40][41] This would be considered later. Figure 7 shows the result of a systematic stepwise survey of the time-resolved scattering patterns.…”