Placeholder Image

字幕表 動画を再生する

  • - [Instructor] Let's talk a little bit

  • about crystalline and amorphous polymers.

  • Now, in previous videos, we talked about crystalline

  • versus amorphous solids.

  • Crystalline solids have a very regular pattern,

  • maybe they look something like this.

  • If you imagine the particles,

  • each of these circles being an atom,

  • an ion, or a molecule,

  • while in an amorphous solid,

  • it's a little bit more irregular.

  • It's still solid, so these things aren't moving

  • past each other, like they would in a liquid,

  • but it is an irregular pattern.

  • So this is crystalline,

  • and this is amorphous solids, generally.

  • Now, the focus of this video is to talk

  • about crystalline and amorphous solids made from polymers.

  • Polymers can actually exist in a spectrum

  • someplace between being crystalline

  • and being amorphous.

  • So just as a review, what is a polymer?

  • Well, a polymer is a molecule

  • that's made up of repeated subunits,

  • so you have a subunit, and then it's bonded

  • to another unit, and another unit,

  • and it makes these molecules,

  • which on a molecular scale, are long,

  • made up of these repeating units.

  • And so I can represent them,

  • if I were to zoom out a little bit,

  • as kind of a string-like thing,

  • but just remember, these are made up

  • by these repeating units.

  • Now, in previous videos, we talked

  • about how polymers can be amorphous

  • because these long strings of these repeating units

  • can get all intertwined like this

  • and form this messy ball,

  • and we've talked about things like elastomers,

  • where natural rubber is like this,

  • where you can pull on it,

  • and as long as you don't pull too much,

  • it'll get back to this form.

  • But it turns out that these polymers

  • can also align to various degrees,

  • and become a little bit more crystalline.

  • For example, even with rubber, if you were to pull on it,

  • it's possible that the individual chains

  • get a little bit more aligned.

  • And then the intermolecular forces between them

  • are going to be a little bit stronger,

  • because they are a little bit more aligned.

  • And so this form would be more crystalline,

  • not perfectly crystalline, but more crystalline

  • when you have this alignment.

  • And to just see examples of different polymers

  • that sit on that spectrum,

  • let me draw a spectrum right over here,

  • where at this end, we have something

  • that is very amorphous, and at this end,

  • we have something that is very crystalline,

  • we can see examples from our everyday life.

  • If we focus on plastics,

  • for example, polystyrene, which you might be familiar

  • as foam packaging, right over here,

  • this is reasonably amorphous.

  • I'm not gonna go into the exact numbers,

  • but let's say we could put it right over here.

  • So this is made up of polymers, repeating units,

  • but they're going to be fairly disordered,

  • and something like that,

  • and that's what gives it kind of its softness,

  • that's why it's good as a packaging material.

  • It can absorb jolts.

  • Now, if we go a little bit further down the spectrum,

  • something that is still amorphous,

  • but has more of a crystalline nature,

  • you can look at things like plastic water bottles.

  • Often known as PET bottles,

  • PET stands for polyethylene terephthalate,

  • anything, like polystyrene, polyethylene,

  • the fact that they start with the word poly

  • is the clue that these are polymers.

  • Polystyrene is made up by a bunch of styrenes in a chain.

  • Polyethylene is made up by a bunch of ethylenes in a chain,

  • and so polyethylenes, depending on which version

  • of you look at it,

  • it's someplace between amorphous and crystalline.

  • For example, it might be someplace over here.

  • And if you wanna do further research on it,

  • you can actually look up how crystalline something is,

  • the degree of crystallinity,

  • and you'll see numbers like 30%, or 40% crystallinity.

  • And if you wanna look at especially plastic polymers

  • that are even more crystalline,

  • you can look at something like Kevlar,

  • and Kevlar, depends on the Kevlar you are looking at,

  • it could be someplace in this range here,

  • I'll just put the Kevlar right over there.

  • And if you don't know what Kevlar is,

  • Kevlar is used for making things like bulletproof vests.

  • And so the degree of crystallinity,

  • it's not just the degree of crystallinity,

  • but the degree of crystallinity is how aligned

  • these things are.

  • Kevlar, the polymers are very, very aligned

  • with each other, and so you're able to have

  • these intermolecular forces get reasonably strong,

  • and that's why it is good at stopping bullets,

  • while you would never want packaging foam

  • to stop a bullet for you,

  • but these are all polymers.

- [Instructor] Let's talk a little bit

字幕と単語

動画の操作 ここで「動画」の調整と「字幕」の表示を設定することができます

B1 中級

結晶性および非晶質ポリマー (Crystalline and amorphous polymers)

  • 0 0
    林宜悉 に公開 2021 年 01 月 14 日
動画の中の単語