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  • Viscosity, density and stickiness

    Posted by Aanchal on September 24, 2019 at 9:24 pm

    This query could be under chemistry or even physics or both I guess.

    A thick liquid (say L1) is present in a closet - say a bowl and appears very thick on stirring , even on pouring it with a spoon. The same liquid is put into a pin-hole dispenser and the apparently thick liquid falls in not-so -slow stream, much less than it’s apparent thickness promised.

    I compared this speed of flow of stream (all judgements with naked eyes, no devices used) of the above mentioned L1 with L2 which doesn’t appear as thick as L1 on stirring but speed of stream is less and the liquid appears to be sticky hence resistant to gravity (hence slow).

    I am trying to understand why is L1 stream faster than L2 despite L1 being thicker?

    Are viscosity, stickiness and density playing their roles? How? The liquids discussed are dishwashing gels. 

    Pardon me if this query seems to be out of context or complicated or weird.

    Aanchal replied 4 years, 5 months ago 3 Members · 9 Replies
  • 9 Replies
  • das

    Member
    September 25, 2019 at 3:52 am

    Yup, that’s thixotropy. What you describe is commonly used on filling machines to accelerate the process. In this case, to make the user spend more. Cute trick right?. 

  • Aanchal

    Member
    September 26, 2019 at 12:49 pm

    Thanks @DAS
     I looked up thixotropy. Just a few notes so far.

    So this phenomenon is not just my observation but is much in practice . 

    Now , I prepared a dishwashing liquid which was very very thick. When I stirred it in a bowl, I could see the viscosity and again while I poured back the liquid after filling it in a 10-15 ml spoon, it was very  viscous. 

    The same liquid , when put in a dishwashing dispenser bottle (those with a nozzle) didn’t appear as viscous as it was in the bowl. I believe the first calculation of viscosity a consumer shall have will be by judging the steam of liquid that falls off dispenser, and second by the way it settless on the surface on which it falls.

    So how do I achieve that? 

  • Aanchal

    Member
    September 26, 2019 at 1:33 pm

    Judging the stream not steam I meant above.

  • Aanchal

    Member
    September 26, 2019 at 1:45 pm

    Correction- stream not steam 
    Settles- not settless 

    Typos.

  • Aanchal

    Member
    September 26, 2019 at 2:10 pm

    Correction 
    Stream not steam I meant above.
    Settles not settless. 

  • bill_toge

    Member
    September 27, 2019 at 7:30 pm

    from your description, it sounds as if L1 is shear-thinning (viscous at rest, becomes less viscous under shear) and L2 is more Newtonian (same viscosity regardless of shear)

  • Aanchal

    Member
    September 27, 2019 at 7:33 pm

    Thanks @Bill_Toge.

    Yes. Exactly! Now, how to make Newtonian fluids? 

  • bill_toge

    Member
    September 27, 2019 at 7:37 pm

    surfactants thickened with salt are generally Newtonian, you could try formulating your product that way

  • Aanchal

    Member
    September 27, 2019 at 7:45 pm

    @Bill_Toge

    Thanks again. The L1 I mentioned above is the liquid I prepared using salt. It was much thick in the stable state than L2 the commercially available dishwash liquid. 

    I guess I need to increase the active ingredients’ concentration. 

    I feel the molecules of the liquid need to have stronger bonding while under gravity for the liquid to appear thick rather than thinned down. I am no expert in either Physics or Chemistry though. This was my layman logic, if at all it is. 

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