Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: alancalverd on 01/06/2023 11:17:02
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It seems to me that the three components of a dishwasher sachet are required to "do their thing" at different times and temperatures, but the soluble sachet is dumped into the bowl all at once and there are several fill and drain cycles in a 2-hour wash, so there can't be much of number three by the time you need it.
I misspent part of my youth as a physical chemist in a detergent laboratory but 60 years ago we only worked on one surfactant material at a time - the job was to tailor its molecule, concentration and solvent viscosity to a particular application. This new stuff looks like magic in comparison!
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I worked in a detergent manufacturing facility(50years ago) but our products were for the catering industry and not the domestic market. Our dishwasher products were for a much shorter cycle, I think about 10-15 mins. A typical detergent would consist of sodium hydroxide and edta or nta. Subsequent to the wash a rinse aid was added to stop streaking which was usually isopropanol and a low foam surfactant(non-ionic). Unfortunately I have no idea what goes into the domestic detergent but the damage I have seen on glassware arouses suspicion of a labile fluorine compound, but that can't be , can it?.
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How do "all in one" dishwasher sachets work?
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Hi.
I don't know but I have built a theory while doing housework. Some of the all-in-one tablets have 4 fairly separate looking chambers full of fluid, powder and some solid ball of stuff. The walls of the chambers can be made to dissolve at different rates thus releasing detergent, salt or rinse aid at different times in the cycle. Even when the walls have dissolved, the ball of solid stuff is only slowly dissolved into the water throughout the whole cycle.
Experience based on: Seeing what happens to these tablets if you have accidently picked them up with wet hands and then returned them back to the packet for later use; Putting the dishwasher on a fast wash cycle that is just too fast and having gloopy stuff and undissolved bits left in the bottom (while other bits do seem to have dissolved) etc.
Theorised improvements: Have the walls of the tablet act more like semi-permeable membranes that don't dissolve away at all quickly. Water should get into the membrane eventually and the internal concentration should then be maintained at ~ saturated with solute. Meanwhile, outside the tablet the concentration ~ 0, so you have a fixed concentration gradient over a semi-permeable membrane and thus a fixed rate of diffusion across the membrane throughout the wash cycle.
Best Wishes.
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do "all in one" dishwasher sachets work?
Remarkably well! I am intensely lazy (synonym for extremely intelligent, in my book) and have finally convinced the Boss that rinsing or scrubbing dishes before putting them in the dishwasher is a waste of life, water and energy. Having now switched to a 3-part "premium" sachet, the reject rate ("it was cleaner than this when it came out of the factory") has dropped to zero and normal human relations have been re-established.
So having established the fact, I'm curious about the mechanism. I recall earlier solid pellets having two parts, one of which dissolved in cold first-rinse water and the other being activated at 80 deg C, but that's physics - liquids is different, and chemistry.
ES's hypothesis is beginning to make sense in my mind.