The Naked Scientists

The Naked Scientists Forum

Author Topic: Is there a 'quick and dirty' way to determine a liquid's surface tension?  (Read 2001 times)

Offline diogenesNY

  • Jr. Member
  • **
  • Posts: 15
    • View Profile
Is there a 'quick and dirty' way to determine a liquid's surface tension?

Not sure really what this sort of measurement would entail.....  Reason I ask is, I am getting the bug to do a bit of tabletop mad science involving making up my own fountain pen ink, in various formulations.  Ink chemistry is pretty interesting and a lot more complex then, say, paint.  Having fun starting with Prussian Blue + binder, and I intend to experiment with various additives, etc, in careful and recorded measure. 

Anyway, will be experimenting with ways to slightly lower the surface tension, which needs to be a bit less than that of distilled water to perform best.  Lots of ways to record this, but would like to have quantifiable data if possible.

Thanks y'all in advance,
diogenesNY


 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
If you had a known drop size, you might be able to quantify the surface tension based on how big of a droplet it forms (how much it spreads out on a glass slide, for example).

How large of quantities of ink are you making?  What about the height of the meniscus?

Ok, so perhaps I should see how it is being measured.   The top two methods, ring & needle methods should be able to be performed in a small home lab. 

For some reason I'm not finding many highly accurate hanging scales, but perhaps you could fake it with a balance bar between the table top scale and sample (also allowing you to change the leverage to the scale), and gently dropping the sample down to break the surface tension.
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1873
  • Thanked: 143 times
    • View Profile
If you have a long glass capillary of even dimensions, you can dip it in your inks and see how high it goes. Not exactly quantitative, but should be ordinal. The higher the surface tension, the higher up the capillary it will go.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
If you have a long glass capillary of even dimensions, you can dip it in your inks and see how high it goes. Not exactly quantitative, but should be ordinal. The higher the surface tension, the higher up the capillary it will go.
...for a fixed value of density; if not you have to correct for it.
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4704
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Surface tension depends on the interface. It is not a property of the liquid alone, but a property of the liquid's interface with another medium. If a liquid is in a container, then besides the liquid/air interface at its top surface, there is also an interface between the liquid and the walls of the container. So there's little point in measuring the ST of your ink against glass if you want it to flow from a metal nib.

You actually want a capillary flow down the split in the nib, so you want to minimise the ST by adding a surfactant to a water-based ink.
 

Offline diogenesNY

  • Jr. Member
  • **
  • Posts: 15
    • View Profile
Checking in here.... 

Thanks for the various enlightening responses.

alancalverd, You are quite correct about adding some sort of wetting agent.  I do not have the exact numbers at my fingertips, but ink should have (very roughly, subject to myriad factors) about half or two thirds of the surface tension of water for use in the 'typical' fountain pen.  This is based on several analysis (not mine, obviously) of the physical properties of several commercial inks.

All failing, I shall just record my variations in formula and observe performance effects.   I have a variety of ingredients and additives I wish to experiment with both singly and in combination.  While I will certainly get a nice spectrum of empirical data, I had hoped for a convenient way to add some numbers to the resulting goo.

CliffordK, initial experimental batches shall probably be in the range of little more than an ounce or so.  I have a bunch of different surfactants, binders, biocides, retarding and quickening agents and other things that I plan to try adding in and recording the effects.  I will have several identical, inexpensive, clear bodied fountain pens to try them out in:  A _Platinum Preppy_ converted from cartridge to _eye dropper_ fill configuration.

The following link is to a commercial website, but is included for the sole purpose of illustrating a specific model of fountain pen.  No connection or endorsement implied.
newbielink:http://www.jetpens.com/Platinum-Preppy-Fountain-Pen-05-Medium-Nib-Black-Ink/pd/4522 [nonactive]

I'll be happy to keep y'all posted as I make ever bigger messes.  Always welcome more info, advice, input, etc.

Thanks again,
diogenesNY
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
I like chiralSPO's idea of using a capillary tube.  At least it may be something quick and easy to try out, and you can make your own calibrations based on the tubes you acquired.

It is a good point though, that you are most interested in the interactions of the ink with your pen components (metal), and with paper (wood fibers).  And, of course, solvents and drying.  So, perhaps you could do something with observations of a fixed size drop of ink on paper.

The older fountain pens used a refillable bladder.  Although the advantage of prototyping with cartridges is that if you don't like it, you can presumably throw out the cartridge and try a new one.
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length