Scientists Just Figured Out How Washing Machines Work?!
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Scientists Just Figured Out How Washing Machines Work?!

[♪ INTRO] There are all kinds of inventions that make
modern living possible, but some fly under the radar. Some so much so that we’ve only just figured
out how they truly work. Case in point: the washing machine. Because apparently, no published paper was
able to totally explain how these things got your clothes clean; not
until 2018. Now, to be clear, it’s not like we had no
idea how these machines worked. The oldest washing machines that resemble
our modern appliances date back to the 19th century, so these things have been around for quite
a while. And for years, we’ve had a really good understanding of how they use soap and detergent to get stuff
off the surface of your clothes. Soap is a surfactant, which is short for surface
active agent. That means its molecules can attach to two
substances that don’t normally interact, for example, oil and water. Usually, one end of the molecule is hydrophobic,
meaning it repels water, and the other end is hydrophilic and regularly
bonds with water. So, when soap is dumped into a big bath of water, the surfactant molecules group together to
form spherical structures called micelles. The hydrophilic ends stick out toward the
water, and the hydrophobic ends hide inside. When a micelle lands on a dirty section of
fabric, the hydrophobic ends pop out and attach to
the dirt, or whatever is soiling your clothes. Then, the hydrophilic ends pull the rest of
the micelle off the fabric’s surface, and the micelle reforms with the soil it’s
“eaten” in its center. Detergents like the ones we use for washing
clothes use anionic surfactants, meaning the hydrophilic end has a negative
electrical charge. But, while there are different types of surfactants,
they generally all work the same way. The reason washing machines spin everything
around is to help the soap solution flow through your fabric and pick up all the
dirt hiding in the crevices. But here’s where the mystery came in: Water
can’t flow through every spot in your clothes. That’s because fabric is usually made of
yarn, which is itself made of multiple fibers. Soap generally has no problem getting into
inter-yarn pores, or the spaces between separate strands of yarn. But it does have a problem getting into intra-yarn
pores, or the spaces between the fibers in a single
strand. These pores are at least an order of magnitude
smaller than the inter-yarn ones, and only about 0.1 percent of the soap solution
can actually get inside them, and even then, it doesn’t get in all the way. Micelles actually get stuck in there and are
only able to move when they’re struck by nearby water molecules. According to the math, all of the micelles
would eventually get knocked out, and that soap and dirt would go flowing down
the drain. But this process would take several hours. And that’s just not how washing machines work. They get the soap and crud off your clothes
in usually under one hour. This phenomenon was called the “stagnant
core problem”, and its what scientists hadn’t been able
to explain until that 2018 paper. In their research, the authors learned that
the solution to getting dirt out of those intra-yarn pores
wasn’t the soap, which is kind of surprising. Instead, it was the rinse cycle, along with
a process called diffusiophoresis. Diffusiophoresis is the movement of colloidal
particles caused by a gradient. In other words, it’s the movement of tiny
particles suspended but not dissolved in a fluid. When you swap out the soapy water with the
clean stuff, the surfactant micelles are way more concentrated
in the fiber pores than they are elsewhere. And when you’re using anionic surfactants,
this creates an electric field that makes the micelles migrate out of those
intra-yarn pores. In their paper, scientists figured this out
by doing a series of experiments. Instead of dirt, they used micrometer-sized,
fluorescent balls, and they picked a standard detergent called
sodium dodecyl sulfate. It also goes by sodium lauryl sulfate, and you can probably find it in most of the
cleaning products you own. The team did one trial with no detergent at all, just to see how much cleaning the water and
agitation could do all by itself. Then, they did a trial that rinsed sudsy fabric
with detergent-filled water, and no diffusiophoresis was observed. Finally, their third run mimicked a regular
wash/rinse cycle, where the soapy fabric was rinsed with clean
water. This time, the team observed that the fabric pores nearly emptied out after just 10 minutes of rinsing, cleaning out the intra-yarn pores over 100
times faster than in the soapy run. So yeah, surfactants get the dirt off your
clothes, but you need clean water to actually get dirt
out of them. This research doesn’t answer all the questions
about cleaning your clothes, for example, why some stains are far more
persistent than others, but it does have some worthwhile applications. With knowledge like this, we might be able
to maximize detergent efficiency and minimize the amount of water and energy
we use to do our laundry. That would make washing machines, both in
your home and in industry, much better for the planet. Which is kind of a big deal, considering how
much water this process takes. On a different note, other research suggests
that faster rinsing speeds could also create a better diffusiophoresis
effect. So there may be turbo-charged washers in our
future that get clothes clean even faster. But, hey. As long as my laundry
comes out smelling fresh, I’m all for it. Thanks for watching this episode of SciShow! If you want to learn more about laundry science, you can check out our episode about fabric
brighteners. Apparently, they don’t just make the colors
in your fabric more vibrant, they make your clothes glow. [♪ OUTRO]

100 thoughts on “Scientists Just Figured Out How Washing Machines Work?!

  1. For over a decade we’ve used an ozone generator that infuses ozone into the wash in place of detergent. It’s worked really well, would like to hear your comments/research on this method 🙂.

  2. my-CELL, not MY-cell,
    col-LOYD-al, not col-LIED-al.

    I love the videos! I love all the hosts! and I'm not suggesting re-dubbing or anything, like when you guys re-uploaded that one video to fix the weird brick analogy. But you could make a note in the video description or the closed-captioning, or even pin the most polite person to point it out. :/
    (Merriam-Webster's website will pronounce words for you if you aren't sure!)

  3. 0:31 — Naming your new washing-machine invention, "Woman's friend." Yeah, times have definitely changed since the late 1800s… 😂

  4. scishow how about a show on "How does a hair know when to grow?" If a hair grows to its finite length and then you shave it, what triggers its restimulation?

  5. I was listening to her with my eyes closed. It sounded like she has a lot of stress in her voice. It made me jump. I hope she is okay.

  6. I guess it's not quite clickbait…but the title could have been less "omg crazy!"-sounding. Rather unprofessional from a channel with a reputation for treating the audience with respect while teaching them at the same time. I really hate seeing good channels losing the things that made them so good by trying to be more "trendy".

  7. 'The Womans Friend' washing machine . . . . . . . . See, it was a different time back then but dont worry, theres plenty of knuckle draggers that havent realised that yet . . . . . . . My washing machine is 20 years old and i found it on the side of the road: works perfectly, bit old and makes a lot of odd sounds, rough around the edges and looks worn out . . . . . . Bit like me really and i can occasionally find myself on the side of the road, thrown out last night but then the wife finds out she still needs me . . . . . . Which is weird cos im not married.

  8. More of a quality comment here – I haven't watched Sci Show in quite a while and the last video you actually presented. I went back to the old one and then watched this one since it was on the feed and the difference between them is astonishing. You seem way more comfortable presenting now than you used to. Tell the guys you want more screen time! Whatever you're doing is working!

  9. "Scientists just figured out how washing machines work,"
    Me: you mean that we've been using alien technology this entire time?

  10. Why are they saying "Using less water would be better for the planet", it's not as if the water gets launched into space when we are done. Wouldn't only the energy cost matter here or am I missing something? It seems like "better for the planet" is just becoming a non-sense phrase thrown around anywhere it 'sounds good'.

  11. Parts of the video seem unintentionally confusing. The heads of the molecule are identified as hydrophilic, but then it's stated that the hydrophobic ends stick to the dirt, while showing the hydrophilic ends attaching to the dirt instead.

    It's also asserted that soap isn't what cleans the intra-yarns, but rather diffusiophoresis. However, it sounds like it's the concentrated soap being flushed away by the clean water that causes the electric field, so the soap is still an integral component of getting the intra-yarns cleaned; it just isn't the only component.

    I think I get the gist, but I believe the video could've been more informative if it was a little more clear.

  12. Scientists only figured this out now? I'll consider releasing a paper next month for all the missing information they couldn't understand..

  13. I don't like laundry that smells fresh, because this usually means it is over perfumed. I prefer to have the odours washed out and the clothes smelling neutral, than have the odours screened by another odour.

  14. We need better means of desalinating ocean water on a larger scale. Most cities in the US are on or near the coastline. Water wouldn't be a problem if we could use the ocean instead of inland springs and rivers. We should be looking into geothermal power more as well. We already have a giant caldera we could surround with geothermal plants that would generate enough electricity to power the whole country. And you could do that without damaging the park therein.

  15. That's so funny. I double rinse my clothes sometimes because I think it makes them cleaner. I figured it got more of the detergent out.

  16. have known for a long time that it was the rinse cycle that really got the clothes clean, but didn't fully "know" the reason WHY that was. cool vid.

  17. But can anyone tell me how “efficient” detergent takes like 1 drop (supposedly, I don’t believe it) but original needs like a gallon to clean?

  18. You actually finally explained to me why a stuffed washer is not a good thing, leaving clothes feeling and smelling half-washed. Given that they don't have enough room for the clean water reaction you mentioned, it now makes perfect sense.

  19. FUN FACT: Sodium Lauryl Sulfate can also be found in your toothpaste and your soap (shampoo, body wash, etc.) among other products you use. There was a study that I clearly remember mentioned in middle school during oral report day linking Sodium Lauryl Sulfate to cancer.

  20. Well, it's always been known that they work pretty much the same way as hand washing clothing. So the "mystery" isn't what the title might suggest.

  21. So I’ve been saying this for years. I have horses and therefore saddles. When you clean a saddle you use a glycerin based soap and a little water. This creates a foam.
    Most people just wipe the dirty foam up with a dry cloth. Not me! I used soaking wet sponge to “float out” the dirt. Otherwise it just doesn’t get removed, just moved around.
    Nice to know I was right! It’s all in the rinse!

  22. Wow! So the Bible really knew what it was talking about when it said to wash with running water!

    And some people say it isn't scientific. Hmm………

  23. And next week a team of scientists from Japan will disprove EVERYTHING stated in this video and interject their own theory and have a paper PROVING that none of the content of this video is actually what happens when you wash your clothing and that in fact your clothing isn't real to begin with, then about 400 years from now THAT paper from Japan will again be disproved and so on and on!! That is what way science seems to work anymore!! And honestly HOW THE HELL CARES when you have dirty clothes and the wash machine DOES IN FACT clean them isn't that "all we actually need to know" but sciences loves to waste time "solving problems" that really do not need to actually "be solved" in the first place!! And besides isn't there more "pressing issues" science COULD be working on??? For example I wish science would finally develop a microwave oven that cooks the "middle of my burrito" which is still a block of ice after a minute and yet the ends are so over cooked they are like trying to bite through a cinder block……..NOW that would be a "feat of science" to make a microwave cook more evenly!!

  24. Aside from the clickbaity title, this video perfectly showcases how science works. Everyone can understand that washing machines are good at washing clothes, but the scientists here were trying to better understand the 'how' (and eventually the 'why') these things happen.
    Most people would have no problem saying that they absolutely know how a washing machine washes, but not scientists. They work tirelessly on seemingly simple things to bring us to a conclusion of absolute certainty.
    Now we all have the best working knowledge on how things are the way they are… or at least why washing machines work! Very informative

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