Flocculation

[ThrillaMozilla]

Websnail was interested in my previous remarks on flocculation, and asked me what else I knew about it. He mentioned that he may have experienced a problem due to flocculation. Flocculation is an aggregation of particles that affects colloids. Pigment ink is a colloidal suspension. Flocculation should not affect dye ink.

You can see flocculation in this post. The ink on the right side of each image is pigment ink. You can easily see how uneven the coverage of particles is compared to the other dye inks.

When I diluted the ink, it promptly flocculated. I could even see it on the (clean!) glass slide. I thought I used distilled water to dilute the ink, but when I tried later, I couldn't duplicate it with either distilled water or tap water. I hate to publish results that I can't duplicate, but in this case there's no doubt that it happened. It may be that there was a little tap water residue on the vessel I used (although we have soft water, and impurities would be minimal).

Unfortunately, I don't know enough about flocculation of ink, but I'll tell you what I do know. Generally, colloidal particles have a surface charge that is supposed to keep the particles apart and dispersed. The charge is highly dependent on the solution composition. If the charge becomes neutralized, the particles can attract each other by a force known as Van der Waal's force, and the particles can aggregate. Also, in some colloids, different surfaces on the particles can have opposite charges, and this will cause particles to aggregate into larger particles that will settle.

The surface charge can be either positive or negative, depending on pH and other aspects of the solution composition. For most colloids there is a pH called the zero point of charge. Dissolved salts also have an effect, as ions are attracted or repelled from the surface, and themselves cause a second layer of charge. Certain ions can be bound to the surface and affect the charge. Dissolved organic solvents may also have an effect. The point is that all this is complicated and somewhat difficult to predict.

I don't know to what extent flocculation might be a problem in practice, but if it did occur in a cartridge or print head, I believe it would be a major problem.

 

[websnail]

.. and just to note on the reason I asked TM to post on this.

Roughly a year ago I used a cleaning solution to clear out a set of tubing I used to use for rebottling. At the time it was a mistake and for whatever reason I neglected to flush the tubing afterwards with water. Whether this was the cause of what followed or not is something I can answer as the result wasn't noticed for a few weeks and then disposed of.

Anyway, net result appears to have been two litres of an Epson pigment where one completely separated out and the other (a different ink type) had some settling but not to the same extent. I didn't put two and two together at the time but it was a salutary (albeit expensive!) experience that resulted in a lot of tightening up of procedures.

When the topic of flocculation came up I put two and two together and realised I may have a culprit so it's worth bearing in mind when considering what chemicals, solutions and what not you use to clean out your cartridges and/or refilling equipment.

Just to add further the advice on rebottling is that you should use water, preferably distilled, when cleaning out tubes, syringes or similar. Cleaning solutions should be specifically formulated for the purpose and avoid the mistake of assuming one cleaning solution is as good for printhead cleaning as it is for cartridges flushing. It'd be the equivalent of assuming vinegar and Hydrochloric acid both being acids makes them ok to put your chips/fries... Erm... no!