This web page is all about polymer crystals. No, this page has nothing to execute with polymers as supplied by the new age community, utilizing \"crystals\" to focus psychic energy. We\"re talking around another sort of decision here. The sort of decision we\"re talking about here is any object in i m sorry the molecules space arranged in a consistent order and pattern. Ice cream is a crystal. In ice cream all the water molecules room arranged in a certain manner. Therefore is table salt, sodium chloride. (Oddly, your mother\"s good crystal drink glasses are not decision at all, as glass is one amorphous solid, that is, a hard in i beg your pardon the molecules have actually no bespeak or arrangement.)To recognize all this speak of crystals and also amorphous solids, it helps to go home. Go home? Why? therefore you deserve to look in your sock drawer, that\"s why. Girlfriend see, some world are really neat and orderly. As soon as they put their socks away they fold them and also stack them an extremely neatly. Prefer this:

Other civilization don\"t really care around how practiced their amount say drawers look. Such individual will just throw their socks in the drawer in one huge tangled mess. Their amount say drawers look choose this:

Polymers are as with socks in that occasionally they space arranged in a neat orderly manner, prefer the amount say drawer in the height picture. When this is the case, us say the polymer is crystalline. Other times there is no order, and the polymer chain just kind a huge tangled mess, favor the socks in the bottom picture. When this happens, us say thepolymer is amorphous.We\"re going come talk about the neat and also orderly crystalline polymers ~ above this page.So what type of arrangements carry out the polymers prefer to form?In a perfect component of a perfect world, lock would choose to heat up all stretched out, kind of favor a neat pile of brand-new boards down at the wood yard. An additional analogy is uncooked spaghetti right out that the bag choose in the photo below.

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But they can\"t constantly stretch out that straight. In fact, very few polymers deserve to stretch out perfectly straight favor that. Instead, all the chain entanglements that they have avoids them from doing so. Castle look more like the cook spaghetti below.


There might be some parts like the uncooked noodles above all blended in like once you don\"t line the noodles after you litter them in the pot. Some polymers are especially prone to execute this like ultra-high molecular weight polyethylene, and aramids prefer Kevlar and Nomex. Many polymers have the right to only stretch the end for a short distance prior to they fold back on us or acquire stopped by being all tangled up. You have the right to see this in the picture.

For polyethylene, the length the chains will certainly stretch prior to they fold is around 100 angstroms.But not just do polymers fold prefer this, they also type stacks of those urgently chains. There is a picture of a bunch of stacks which completely are dubbed a lamella, right below.
Of course, that isn\"t always as neat as this. Sometimes component of a chain is consisted of in one crystal, and component of it isn\"t. Once this happens, we acquire the type of chaos you view below. Our lamella is no much longer neat and tidy, however sloppy, through chains hanging out of that everywhere!
Of course, being so combined up, the polymer chains will often decide they want to come ago into the lamella after ~ wandering about outside because that awhile. When this happens, we gain a snapshot like this:
This is the switchboard design of a polymer crystalline lamella. We have to tell girlfriend that as soon as a polymer chain doesn\"t wander approximately outside the crystal, however just wrinkle right ago in ~ above itself, choose we witnessed in the very first pictures, the is referred to as the adjacent re-entry model. Ns guess the other kind would simply be the messy re-entry model, no?

Amorphousness and also Crystallinity

Are you wondering about something, spring at these pictures? of course, you have the right to see that several of the polymer is crystalline, yet then, part is not! yes folks, most crystalline polymers are not entirely crystalline. In fact, most are largely not crystalline. The chains, or parts of chains, that aren\"t in the crystals have no order to the arrangement of their chains. We scientists say the they room in the amorphous state. Therefore a crystalline polymer really has actually two components: the crystalline portion and the amorphous portion. The crystalline section is in the lamellae notified regions, and also the amorphous potion is external the lamellae and between the layers. If we look at a wide-angle photo of what a lamella watch like, we can see exactly how the crystalline and amorphous sections are arranged. So currently you can see, lamella flourish like the spokes the a bike wheel native a main nucleus. Periodically we contact these spokes \"lamellar fibrils\". The fibrils grow out in 3 dimensions, so they really look much more like spheres 보다 wheels. The totality assembly is dubbed a spherulite. In a sample that a crystalline polymer weighing only a few grams, over there are plenty of billions of spherulites.In between the crystalline lamellae, there are areas where there is no order come the setup of the polymer chains. These disordered areas are the amorphous areas we were talk about. As you can also see in the picture, a single polymer chain may be partly in a crystalline lamella, and partly in the amorphous state. Some chains even start in one lamella, overcome the amorphous region, and also then join an additional lamella. These chains are referred to as tie molecules. They carry out a distinct property of, girlfriend guessed it, tying the lamellae to each other. In a sense, castle act prefer crosslinks and also strengthen the hard polymer, offering it better mechanical properties.The crucial point here is that no polymer is totally crystalline. If you\"re do plastics, this is a great thing. Crystallinity provides a product strong, but it additionally makes that brittle. A totally crystalline polymer would be as well brittle to be offered as plastic. The amorphous regions give a polymer toughness, that is, the capacity to bending without breaking and also the capacity to absorb impact energy. These are both great properties to have.However, because that making fibers we prefer our polymers to be as crystalline as possible. This is due to the fact that a fiber is really a long crystal, in a sense. Want to know more? climate visit the Fiber Page!Ok, then, many \"crystalline\" polymers have a mix the amorphous and crystalline regions, yet some are much more highly crystalline and also some are an ext highly amorphous. Right here are some of the polymers that have tendency toward the extremes:Some highly Crystalline Polymers:Some highly Amorphous Polymers:PolypropylenePoly(methyl methacrylate)Syndiotactic polystyrene Atactic polystyreneNylonPolycarbonateKevlar and NomexPolyisoprenePolyketonesPolybutadiene


So why is it that part polymers are much more highly crystalline and also some are an ext highly amorphous? There space two important factors, polymer structure and intermolecular forces.

Crystallinity and also polymer structure

A polymer\"s molecular framework strongly influence crystallinity. If it\"s regular and orderly, extremely symmetrical, it will certainly pack into crystals much more easily. In a way, the molecules want to get next come each other in crystalline domains. If the molecular structure is not highly regular and symmetrical, the won\"t. Let\"s take it a look in ~ polystyrene in it\"s various forms to help us understand just how this works.
As you deserve to see in the list above, there space two type of polystyrene. Over there is atactic polystyrene, and also there is syndiotacticpolystyrene. The former is completely amorphous and the later on is very crystalline.
Syndiotactic polystyrene has actually a very regular and also orderly structure, v the phenyl groups falling on alternative sides the the direct carbon backbone. This way it have the right to pack very easily right into crystals due to the fact that the backbones deserve to come close together without the phenyl groups acquiring in the way. In fact, the phenyl teams are able to likewise come an extremely close to every other, i beg your pardon they like to do an extremely much. That interaction is called \"pi-stacking,\" and also occurs in lots of polymers with fragrant rings in the backbone or pendent to the polymer chains.But atactic styrene has actually no such order. The phenyl groups come on any type of which next of the chain they please going down the backbone. Through no order, the chains can\"t pack very well to add the pi-stacking isn\"t there together much. For this reason atactic polystyrene is an extremely amorphous. Walk that mean it has lousy properties? Of course not! Atactic polystyrene is among the many widely used commercial polymers in products today. Take it a look at the shop in level one and see how numerous items contain this polymer. Various other atactic polymers prefer poly(methyl methacrylate) and poly(vinyl chloride) are likewise amorphous. And as you might expect, stereoregular and also symmetrical polymers like isotactic polypropylene andpolytetrafluoroethylene are extremely crystalline. Yet of course, not completely so. That\"s why these polymers have such remarkable combinations of properties, solid AND tough.Polyethylene is another good example. It deserve to be crystalline or amorphous. Direct polyethylene can be practically 100% crystalline, depending on how it\"s processed and handled. But the branched stuff simply can\"t fill the method the linear stuff can, with the branch points getting in the way, so the is much more highly amorphous. The still has some crystalline domains, though, and those act as physical crosslinking sites. Low thickness polyethylene (highly branched version) is weaker 보다 the other, much more linear kinds, but still advantageous for sandwich bags and food wrap.

Crystallinity and also intermolecular forces

Intermolecular pressures can be a huge help because that a polymer if it wants to type crystals. A an excellent example is nylon. You have the right to see indigenous the picture below that the polar amide teams in the backbone chain the nylon 6,6 room strongly attractive to every other. They kind strong intermolecular hydrogen bonds. This strong binding holds chain together, and also because those chains room so symmetrical, they\"re also type crystals. This raises the melting suggest of the crystals compared to polymers there is no such solid intermolecular interactions. That\"s why nylons have much higher melting points than, say, polyethylene or polypropylene.
Polyesters are one more example. Let\"s look at the polyester we contact poly(ethylene terephthalate) or PET.
The polar ester teams make for strong interactions, just like the poles of a magnet pull towards each other. In addition, the fragrant rings choose to stack with each other in one orderly fashion (remember pi-stackin?), making the crystal also stronger. These strong interaction again raise the Tm of pet much greater than the of polyethylene.

And now you can be asking yourself, \"If those intermolecular forces impact crystallinity and Tm, don\"t lock also influence Tg? Wouldn\"t more powerful interactions causing a higher Tm additionally lead come a higher Tg?\"

Wow! You\"ve come a long method already. Great questions and also the answer come both is \"Yes!\" In fact, for countless polymers, there\"s a more-or-less straight relationship in between Tg and Tm (degrees Kelvin). Take it a look at the plot below for few of the more common polymers that space at the very least semi-crystalline. And as you might have guessed, Tm is constantly greater than Tg.


And just in instance you\"re wondering around physical properties, here\"s a brief an overview of several properties because that a pair dozen usual polymers. These encompass some nice high perfomance materials and also some the aren\"t (like low density PE).

Acronym Polymer surname Tg (oC) Tm (oC) TGA* direct CTE** Flex Modulus advantageous Conversions
ABS Acrylonitrile-Butadiene-Styrene 110-125 ----- 375 65-95 2.07 - 4.14 1 Pa = 10 dynes/cm2
PMMA Poly(methyl methacrylate) 85-110 ----- 313 50-90 2.24 - 3.17 1 psia = 6.895 kPa
AN Polyacrylonitrile 95 135 ---- 66 3.45 - 4.07 1 kPa = 0.145 psia
PTFE Polytetrafluoroethylene 126* 327 525 70 - 120 0,525 1 MPa = 1,000,000 Pa
PVDF Poly(vinylidene fluoride) -60 come -20 170 - 178 470 70 - 142 1.72 - 2.89 1 GPa = 1,000 MPa
Nylon 6 Polycaprolactam 40 - 87* 210 - 220 400 80 - 83 2.69 1 Newt = 101.97 G force
Nylon 66 Nylon 66 50* 255-265 426 80 2.83-3.24 1 Joule = 0.239 calories
PC Polycarbonate 140 - 150 ---- 473 68 2.35 1 calorie = 4.184 Joules
PBT Poly(butylene terephthalate) 30 - 60 220 - 287 386 60 - 95 2.28 - 2.76 oF = 9/5(oC) + 32
PET Poly(ethylene terephthalate) 73 - 80 245 - 265 414 65 2.41 - 2.10 oC = 5/9(oF - 32)
PEEK Poly(ether ether ketone) 150 334 575 40 - 108 3.86 10 Poise = 1 Pa-sec
PEI Poly(ether imide) 215 - 217 ---- ---- 47 - 56 3.31
LDPE Low density polyethylene -133 to -100 98 - 115 459 100 - 220 2.40 - 3.30
HDPE High thickness polyethylene -133 come -123 130 - 137 469 59 - 110 1.00 - 1.55
PI Polyimide ---- 310 - 365 ---- 45 - 56 3.10 - 3.45
PPO Poly(phenylene oxide) 100 - 142 ---- 400 38 - 70 2.25 - 2.76
PPS Poly(phenylene sulfide) 88 285 - 290 508 49 3.79
PP Polypropylene -15 160 - 175 417 81 - 100 1.17 - 1.72
PS Polystyrene 74 - 109 ---- 351 50 - 83 2.62 - 3.38
PSO Polysulfone 190 ---- 510 56 2.69
PES Poly(ether sulfone) 220 - 230 ---- ---- 55 2.40 - 2.62
PVC Poly(vinyl chloride) 75 - 105 ---- 265 50 - 100 2.07 - 3.45

Source: modern-day Plastic Encylopedia, McGraw Hill, Inc., brand-new York, NY, 1989.

*data taken from Polymer Handbook, second Edition, J. Brandup, E.H.Imergut, john Wiley and also Sons, brand-new York, NY, 1975

**data from TA instruments Library (heating price of 20 oC/min)

How lot Crystallinity?

Remember we said that numerous polymers contain several crystalline material and lots that amorphous material. Practically no polymer is 100% crystalline and, in fact, most polymers space only approximately 10-30% crystalline. There\"s a method we can uncover out how much that a polymer sample is amorphous and also how lot is crystalline. This an approach has its own page, and also it\"s referred to as differential scanning calorimetry. It uses an analytical instrument to actually measure the glass shift and melt temperatures. Much more importantly, it have the right to measure exactly how much of every is in a provided sample. This kind of \"quantitation\" is an extremely important in understanding exactly how well any kind of polymer will certainly behave and also what it deserve to be offered for. Lesson here is: the an ext you know, the an ext you understand.

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There are other approaches that have the right to tell friend something about what sort of crystallinity is present, such together neutron and also x-ray scattering. Solid state NMR has recently become vital tool for looking at the species and amounts of crystalline and amorphous domain names present. Us don\"t have actually time or room to tell girlfriend all about these powerful tools here, yet if you\"re interested, you can discover tons of info on the web.

using a mix of these techniques, it\"s even feasible to identify amorphous domains from what\"s referred to as rigid amorphous areas. The previous makes a polymer tougher and an ext flexible when the latter makes the stronger. Didn\"t know there were that many different areas inside a perfectly simple polymer, go you?

(Spherulite number after Odian, George; principles of Polymerization, third ed., man Wiley & Sons, new York, 1991, p.27.) go back to Level Three brochure Return toMacrogalleria Directory