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Chain Entanglement and Its Effect on Diffusion

March 15, 2011

Q: How can Novinium achieve effective cable-life extension without a soak period? It would seem to me that Novinium puts less fluid into the cable than one would get with a soak period.

A:  When Novinium founders conceived of the first generation of treatment fluid over two decades ago, they failed to check the relative diffusion rates of the phenylmethyldimethoxysilane (PMDMS) monomer and the condensation catalyst that we had chosen to provide long cable life.

This turned out to be a grave mistake, which we have since corrected. The post named Catalytic Considerations — Component I describes the inefficiency of the soak period. Novinium solved the problem with US Patent 7,700,871. Additional posts, including Catalytic Considerations II, explain the elegance of that solution. Also key to understanding the functional improvement of the five kinds of ingredients in Cablecure® 732 fluid is the concept of chain entanglement. To illustrate chain entanglement, this discussion focuses on one of the tailored molecules found in Cablecure 732 fluid called tolylethylmethyldimethoxysilane or TEM for short.

TEM chain entanglement 1 Figure 1

Figure 1 shows the rather boring structure of cross-linked polyethylene (XLPE). The carbon-carbon chains are typically several thousand carbon atoms long. About once every 1,000 carbons, there is a cross-link site.

TEM chain entanglement 2 Figure 2

In figure 2, an electron micrograph* at 40,000X magnification illustrates the structure of the crystalline and amorphous phases of the polymer. Roughly half of the PE is crystalline; the balance is amorphous. The lightly shaded, generally parallel lines are crystalline platelets. The darker areas between the crystalline regions are amorphous.

PE platelets Figure 3

Individual polyethylene chains—represented as squiggly lines in figure 3—snake their way through and between crystalline and amorphous areas. The carbon-carbon chains are tightly packed serpentines in the crystalline region and wander randomly in the amorphous region. Each crystalline platelet is about 10 nanometers thick, or about 75 carbon-carbon bonds. The amorphous layer sandwiched between platelets is roughly the same thickness. The vast majority of diffusion that occurs does so in the amorphous region, but even crystalline polymers are not impervious to diffusion.

TEM chain entanglement 4 Figure 4

Figure 4 shows a 3-D section of two crystalline platelets and an anatomically accurate representation of the tangle of carbon-carbon chains that make up the amorphous cream filling—think about one of those chocolate cookies with the sugary white filling. A water molecule is illustrated in the upper-right corner and to the same scale. It’s pretty easy to visualize the water diffusing through the intramolecular spaces of the amorphous polymer. On the left of the “cream filling” is a monomer of the aforementioned tolylethylmethyldimethoxysilane or TEM monomer. Considerably larger than water, the TEM monomer can squeeze through the amorphous layer, but it must bend and rotate tortuously to diffuse.

The monomer reacts with water it encounters, and it grows as it does so (see Catalytic Considerations I and Catalytic Considerations II). Six monomers plus seven waters yield a hexamer. If you look closely at the TEM molecules, you’ll notice rings of six carbon atoms. These rings include what chemists call conjugated double bonds. This ring structure is quite rigid. Furthermore, the rings have a two-carbon chain to the silicone backbone and another carbon hanging off the end of the ring. These structures stick out from the molecule and slow diffusion. It’s a bit like holding your arms out to the side of your body and then pushing your way through a crowd. Your movement is slow (and you are unlikely to make any friends). Likewise, in figure 4, the six-unit TEM hexamer will become entangled in the PE chains: it will move, but very slowly.

Because of the chain entanglement resulting from these “rude arms,” the TEM molecule was custom designed for the rejuvenation application. The TEM class of materials is available only in Novinium’s Cablecure 732 formulation and is protected by US Patent 7,643,977, other pending applications, and foreign equivalents. It has no other commercial uses.

This is in contrast to the legacy class of materials in use prior to the introduction of Cablecure 732 fluid. Those older materials, which have dozens of applications and hence were readily available, are not optimized for cable-life extension. The molecular optimization included in TEM facilitates a significant increase in the anticipated life postinjection or reduces the volume of fluid required for more modest life-extension periods.

*Kindly provided by Fred Steennis of KEMA in the Netherlands.