Ep22 Mechanical properties of polymers & viscoelastic models NANO 134 UCSD Darren Lipomi

Mechanical properties of polymers, stress-strain behavior, temperature dependence. Creep and step-strain experiments. Simple models of viscoelasticity: Voigt-Kelvin and Maxwell.
The plot I drew around 42:00 is a bit off after the step strain is removed. It should be the Burgers model. See the plot on this page: openi.nlm.nih....
lipomigroup.org

[@ri3oz]

I wish my teacher explained as clearly. Good work man!

[@abdelmounaimsiffour3783]

people like you makes students love science thanks sir

[@djlipomi]

Thanks!!

[@smitashivraj1793]

Hello Dr. Darren Lipomi. I really enjoy all of your videos. I was always interested in polymers and material science. Thank you for all the helpful videos!
Regards
Smita

[@djlipomi]

Thanks!

[@parimisreekar]

Awesome lecture… was struggling with leathery vs rubbery vs rubbery flow comparison. Those graphs on right side and explanations really demystified it. Thank you Liporni.

[@MrClaycorn]

Thank you from the UK bruv

[@djlipomi]

Glad it was helpful!

[@enescaglarkorkmazgoz7897]

STUNNING! Thanks for the content; I am glad to see something real before the midterm exam

[@missamy3727]

19:31
"So when you are talking to somebody who has faced a lot of adversity and overcome a lot of challenges, and someone calls them 'That's a stong person', you said 'No. That's a TOUGH person.'"
Love it.

[@djlipomi]

:)

[@RidheshChachapara]

one of the great lectures i have ever attended.....

[@djlipomi]

Thanks!

[@asyuki193]

Thank you, this lecture was so precise and clean.

[@duylinhpham4139]

Great explanation. can't wait for your talk in emts2018 Hanoi.

[@djlipomi]

Thanks!

[@PavanKumarPonnekanti]

Dr. Lipomi, Thankyou for the great lecture, but, at what regime does the complex model accomodate in the relaxation modulus graph.

[@matthieumanghardt4362]

I think your student was right. If the response of the top spring was instantaneous when you applied the force (leading to a vertical line on the graph) then you should have an instantaneous response when the force is removed. The length of the vertical line after the force is removed should be equal to the length of the first vertical line. There is also no reason why the final strain should be equal to the elastic strain (the strain at the top of the first vertical line). It could be higher or lower. Apart from this your explanations were remarkably clear, thanks!

[@djlipomi]

Thanks for the kind words. I should have been more consistent in the response and recovery phases. The responses are never truly instantaneous, since all of the components are acting at the same time. You're right that the final strain does not necessarily equal the initial strain, since the Maxwell dashpot will never recover. The Voigt-Kelvin dashpot will recover fully, however. This is called the Burgers 4-element model. A more accurate drawing is here: pocketdentistry.com/4-rheology/#f0060

[@JAlanne]

thank you. This really helps me understand it much better.

[@rufigeisa18]

Thank so much !! Now, I actually understand :)

[@djlipomi]

Thanks!

[@stochioiuconstantin546]

Good day,
Really comprehensive explanation.
I would like to comment on the last model, as I agree with the student on the elastic deformation . It should be equal in amplitude with the deformation on the beginning of the load.

[@djlipomi]

Thanks. See my comment on this issue in the description.

[@HenoMarkarian]

Thanks from Iran

[@djlipomi]

Thanks for watching!

[@smallfish2354]

Hi Darren,
I have a question; 34:35 where you describe the behaviour of the polymers in the different regions, in the glassy region you described the behaviour as having "complete elastic recovery", wouldn't that only be the case in hypothetical purely crystalline polymers?, in reality wouldn't the amorphous regions of a given polymer still give some losses there?
Many Thanks and I really enjoyed the video,
Tom

[@adamneil4576]

Yes.

[@Mike71857]

Wow, very great lecture! I wonder for what happens microscopically at a semi-crystalline polymeric sample between the proportionality limit and the elastic limit. Why if the sample deformation is still reversible the stress in that region is not linearly proportional to strain?

[@ainunzulfikar]

thank you prof. Lipomi

[@klemenmlakar96]

Superb explanation! :D

[@nanak3363]

at 7:20 what if we take polymer which has more ionic character than covalent character , will the graph be still same ?
at 19:45 why the extra strong one is not tough one ?

[@user-ex1yd3mo1c]

Very clear! Thank you so much !

[@cosanostra8341]

Hello, thank you very much for the explanation!!
I did nanoidentation on a same photoresist (CAR) with 3 different layer thicknesses (4.5um, 5.2um and 6.5um) with a penetration depth of 500nn. i'v come to the conclusion that when the thickness of the photo resist is bigger, then the foto resist is harder. Do you have an idea why?? Thank you very much!!!

[@sashasooshi393]

Thank you so much for your superb explanation.
I am wondering about the difference between Visco-Elasticity and Visco-Plasticity. It would be really kind if someone can please explain them to me.

[@ramprasath9835]

Dear Prof
I need what is the right method to find viscosity for high concentrated PEO Polymer solution, I used Plate and cone method but at high conc the viscoity is fluctuating at high shear rate but at low conc it is constant

[@zainnano5388]

Sir I need all lectures about polymer chemistry that u have done.

[@ramonr.5957]

Can this model be applied to EVA (Ethylene Vinyl Acetate) ?

[@aniawo5119]

Thank you sir ☺

[@brendansullivan4872]

Like a champ

[@romeokoolsoul]

Hi Prof. Lipomi,
I'm just wondering if you can provide a reference regarding breaking/rupture of covalent bonds at ultimate tensile stress, at your earliest convenience please . Thank you

[@DrR1pper]

"e-ta" not "a-da".