To make a comparison: how is CO 2 dissolved in water? Always as the acid? Or as well through hydrogen bonds to CO 2 's symmetric oxygens? Hi, small doubt relating to this. How fluorinated molecules reduce the surface energy? Corribus Chemist Sr. I apologize in advance for the length of this post, but this is such an interesting topic to mull over. I'll stating up front that these are just my speculations. I haven't delved into the literature to verify whether anything here is true or false, so YMMV.
Why is this an apparent discrepency? Well, let's look briefly at the two facts: 1 Most websites and other popular literature sources point to the very low magnitude of van der Waals London dispersion forces in PTFE as being responsible for the nonreactivity and low friction coefficient of PTFE surfaces. I don't think we have any reason to doubt this latter fact about Geckos. In turn, the lack of susceptibility of the PTFE surface to instantaneous induced dipole moment changes - that is, the lack of van der Waals forces at the PTFE surface - is usually attributed to the very strong C-F single bond, and the extremely low polarizeability of fluorine.
Fluorine is so electronegative that it holds its electrons very close to the nucleus, which lowers the probability that some other nearby dipole can temporarily pull an electron farther away. Hence the "nonstickiness" of perfluorinated polymer materials.
Sounds good, right? Uh-oh: 2 PTFE has a very high melting point. The temperature at which a phase change for a substance occurs is well known to all chemists to be highly influenced by the amount of intermolecular forces holding it together, and typically a higher phase change temperature means MORE and STRONGER intermolcular forces - all things being equal of course. So, if the non-stickiness of PTFE is attributed to very low magnitude intermolecular forces and the high melting point of PTFE is attributed to very high magnitude intermolecular forces, something clearly ain't right.
The author of the article I linked to solves this discrepency by essentially rejecting 1 completely. From the horse's mouth - er, fingers - "However. That has got to be completely untrue. If it had very weak van der Waals forces, it would be a gas - not a fairly high melting point solid! After all, the melting point is an actual piece of indisputable data that is hard to rationalize without assuming that the intermolecular forces in PTFE must substantial in magnitude.
However, I maintain that this discrepency is due to an inappropriate comparison of bulk and surface properties, as well as a need to explore in more detail what gives rise to the high melting point of PTFE. Let me address these one at a time. A Phase changes and intermolecular forces.
The temperature at which a phase change occurs for a substance is due to the strength of the intermolecular forces that hold the substance together. For boiling points, applying this rule is usually pretty simple. You look at the structure of the molecules making up the substance, determine whether there are likely to be dipole-dipole interactions, hydrogen bonds, or London forces, and make some arbitrary but straightforward assessment of the overall strength of these interactions based on the magnitude and number of the forces identified as important.
It's typically understood that a higher molecular weight corresponds to higher boiling point, for example, because higher molecular weight substances tend to have more overall molecular-scale surface area - more places for molecules to stick together due to transient dipoles. Many students assume higher weight substances are harder to boil because of gravity, but this couldn't be more wrong. Melting points, while still generally dependent on intermolecular forces, are not so straightforward to explain.
No longer can we just look at the constituent molecule and make an assessment of the relative strength of intermolecular forces expected, because the way a solid is put together matters. The crystal structure, density, particle size, and so forth all make a huge difference on bulk properties, even among solids which are compositionally identical and moreso if they aren't. Essentially the point that is being made there is that while two substances may be chemically similar with respect to molecular polarity, the number of relevant intermolecular forces in the solid state can vary substantially simply because of the way the molecules pack together.
A branched alkane, for example, will have a higher melting point than a linear alkane of the same molecular weight due to the effeciency of packing in the former: linear alkanes pack much more closely together than branched alkanes, which means the shared surface area is larger or, the average distance between molecules is smaller.
Strength of intermolecular interactions is due not only to relative differences in charges permanent or transient but also to the distances between them. The resins within these coatings are the toughest within the fluoropolymer range and can be applied at film builds up to 1, micrometers. We are experts in precision engineering plastics with an unrivalled level of ability. One of our main strengths is the vast range of fluoropolymer materials we have available.
We can even work with you to create a bespoke material that's ideal for your application. Polytetrafluoroethylene or PTFE is a particularly versatile ivory-white and opaque plastic fluoropolymer; it is made by the free-radical polymerisation of many tetrafluoroethene molecules, and is suitable for a wide range of applications in industries as diverse as aerospace, the food and drink industry, pharmaceuticals and telecoms.
PTFE is produced by AFT Fluorotec in rods or tubes of any size, or filled with glass, carbon, stainless steel or many other materials to increase wear resistance and strength, whatever your project or build, we are sure to have a material that will work for you.
In fact, beyond reaction to some chemical agents and solvents for example, chlorine trifluoride, cobalt III fluoride, xenon difluoride or elementary fluorine if at a high pressure and temperature , the only factor to be taken into consideration when using PTFE is that it does not have a good resistance to high energy radiation, which will cause breakdown of the PTFE molecule.
PFA or Perfluoroalkoxy has very similar properties to PTFE in that it is very chemically resistant, flexible and thermally stable with continuous use up to degrees C , but while PTFE does have some tendency to creep, PFA is creep resistant and is excellent for melt-processing, injection moulding, extrusion, compression moulding, blow moulding, and transfer moulding.
Pure or virgin PTFE can deform badly under a load, but the use of fillers can help with this, though it should be noted that not all filled PTFE is suitable for use with food. Adding a filler to PTFE can increase its strength, improve resistance to abrasion, add electrical conductivity and more; however, adding fillers can also reduce some of the advantageous PTFE properties, such as chemical resistance which will be limited by that of the filler.
Fillers used can range from glass in various percentages , stainless steel , molybdenum disulphide, carbon or graphite, depending on which properties are to be improved. The biggest advantage of PTFE is its versatility, and the range of applications over so many products and different industries for this material is staggering.
The use of PTFE can have massive benefits in manufacturing and engineering, not just in making tubes or liners for handling or storing corrosive chemicals, but by coating parts such as bearings or screws to increase the lifetime of both the parts themselves and the machinery they are part of.
Friction and wear can also be factors with bearings, and a PTFE coat can give the same benefits as with coating screws, with the additional advantage that the coating will also be heat-resistant. This will also reduce maintenance needs as there are less likely to be faults with the equipment, and also greatly reduce, or even eliminate, any expensive manufacturing downtime due to faults or repairs.
Cleaning of equipment can also be reduced in some cases as a PTFE coat is non-wetting, facilitating self-cleaning of parts. And Teflon textile finishes can even help the environment, because, when applied to fabric, the finish will repel water and oil stains, reducing the need to use dry cleaning, and fabrics will also dry more quickly, using less energy with tumble drying, and last longer due to reduced wear.
With the added advantages that PTFE is non-toxic, has only a minor contraindication for humans from polymer fume fever only if the temperature of any Teflon-coated pans reaches degrees C and is FDA approved and food-safe, this material really is of great benefit in many different areas. The polymer is used frequently as a coating on catheters to inhibit bacteria and infections and is also used as a graft material in surgery.
Call: Search Search. Corrosion-resistant PTFE coatings are used to protect metal components. Our aluminium thermal spray coatings offer excellent corrosive resistance on a metal surface. We know that not all coatings applications have a one size fits all solution. Frac balls made from PEEK or glass filled nylon can be manufactured in any size you need.
We can produce fluoropolymer tubes and rods in any size, shape or material type. We design and manufacture world-class plastic, rubber and elastomer seals. Sign Up. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options. Continue reading with a Scientific American subscription. Subscribe Now You may cancel at any time.
The second option, more novel and that is beginning to be introduced in the industry, consists in changing the interaction between water and material physically. If, in the case of the chemical modification we focus on the bonding forces between the water and the surface of the material, the physical modification acts on the surface tension between a solid material and a liquid.
These surface tension forces are the same than when we play soap bubbles with a hoop, the layer of soap water stays inside the hoop and then we can blow to make the bubble. In theory, because of the weight of the soapy water, it should be impossible, but surface tension is present to keep the water from falling. It is also the surface tension that causes some mosquitoes to walk above the water without sinking, since it generates an upward force that is greater than its weight.
As we have seen, there are certain materials and animals that due to the surface tension between water and them can generate hydrophobicity. In order to modify this surface tension, we only have to modify the contact surface between the material and the water, creating peaks or lines in the material, of micrometric or nanometric size, between which the water is floating in the air.
The foundation is similar to a bed of a fakir. If they lay on a board with a single nail, they would nail it, but since they lie on many, the weight is distributed among many points and they remain in the air. The same thing happens to water and it stays in the air, with a very weak interaction between the skewers of the surface and the water, giving spherical shape to the drops of water and causing them to roll on the surface without wetting it.
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