Effervescent UV

[Pete Hanlin]

Seems I am the only one out here who wonders "why???" about everything, but here's another one...

Why is it that UV that has been left standing awhile will often either "burp" or, more often, will "erupt" when a lens is dipped into it? I have observed this in nearly every lab I've worked in, and have come to the conclusion that:
A.) the difference in temperature between the lens and UV must be great enough to cause a boiling effect, or
B.) for some reason, bubbles accumulate at the bottom of a tank of UV- these bubbles either escape simulatneously (burp) or in series (when the lens is introduced).

Appreciate any answers to this long puzzling question (I have noticed the same effect in some tints, but not nearly to the degree found in UV... probably because the UV has more solid mass within it, I would guess).

Pete "asker of the inane and mundane" Hanlin

[Darryl Meister]

Hi Pete,

I believe that the effect is related to the surface tension of the solution. I think that the top layer of the surface acts like a shell because of the attraction of the molecules to each other, and once you "poke" through the top layer and break the tension, you release the gas pressure of the hot liquid beneath -- allowing it to boil. Pressure is intimately related to the boiling temperature of a liquid; liquids boil at lower temperatures with reduced pressure, and vice versa.

Best regards,
Darryl Answerer of the inane and mundane" Meister

[Pete Hanlin]

Ah, I see... so the surface of the UV solution acts like the lid of a pressure cooker. That is, as long as the surface lies undisturbed, the solution is kept "under pressure" and therefore has a higher boiling point. However, when I dip the lenses I break the tension and "flip the lid" off the pressure cooker (thus boiling the UV and messing up my counter).

Once again, thanks for providing an answer to one of life's nagging little questions. I'm going to try to observe this surface tension by floating a paper clip on top of the UV (yep, I'm working in the lab for a couple weeks, so I have time for this kind of shananigans).

Pete

[Darryl Meister]

Originally posted by Pete Hanlin:
I'm going to try to observe this surface tension by floating a paper clip on top of the UV (yep, I'm working in the lab for a couple weeks, so I have time for this kind of shananigans).

Actually, that is a very good example of surface tension. The dry paper clip floats on the "elastic" top layer of the solution, which is under tension.

I think that surface tension is also why liquids always fall in or form spherical droplets.

Best regards,
Darryl

[shanbaum]

Originally posted by Darryl Meister:
I believe that the effect is related to the surface tension of the solution. Hmm... I don't think so, at least, I don't think that's the major factor. From what I recall, superheating (the elevation of the temperature of a liquid beyond its boiling point) is related to the lack of "nucleation points" in the liquid - that's why it's common practice to put "boiling chips" in liquids one wants to boil (think back, Darryl... chemistry class... Mr. Drago... the explosion...).

I mostly recall this when I heat the water before adding the rice.

[This message has been edited by shanbaum (edited 08-04-2000).]

[Darris Chambless]

My God, Man! :-)

Pete,

Has anyone ever said that you must have too much time on your hands? :-) I've been told that a few times and perhaps they were right, but why does water boil? You can reduce this effect by "tempering" the heated fluid by inserting a metal spoon into the liquid before dropping the lenses in. Do this slowly at first or warm the spoon before you put it in the pan. This will stop the pan from burping :-)

I can't believe I actually responded to this :-)

Remember: What happens when you throw a cold, wet piece of metal into a smelting unit at full glow? Your loved ones prepare your funeral arrangements :-)

Darris "If I grab the glowing tip of a red hot poke shouldn't the heat simply transfer to the cooler temperature of my skin? :-)" Chambless

[Darryl Meister]

Originally posted by shanbaum:
I don't think that's the major factor. From what I recall, superheating (the elevation of the temperature of a liquid beyond its boiling point) is related to the lack of "nucleation points" in the liquid - that's why it's common practice to put "boiling chips" in liquids one wants to boil[This message has been edited by shanbaum (edited 08-04-2000).]

Hi Robert,

Good to have you on board during these discussions, as usual. Here are my premises:

I do know this much: Liquids, such as water, boil when their vapor pressure is equal to the external pressure. Vapor pressure increases with the temperature of the liquid. At sea level, the vapor pressure of water is equal to the atmospheric pressure when water has a temperature of 100 deg C. When the external pressure increases, the vapor pressure of the water must be higher for it to boil. This means that the temperature must be hotter. (This is also why water boils at a lower temperatures at higher altitudes.)

Now, we know that liquids maintain surface tension. (The molecules below the top layer of the liquid attract this layer, while they're are no liquid molecules above the layer.)

Now for the conjecture... My reasoning was that the surface tension of the liquid effectively increases the external pressure outside the liquid. This, in turn, allows the liquid to reach a higher temperature before boiling because the vapor pressure must now be higher. However, once the surface tension has been compromised (by a lens piercing through the top layer, for instance), the liquid can immediately start boiling if its temperature had exceeded its normal boiling point.

Does this sound any more believable, or am I completely off base here?

Alas, the only thing about this stuff that I remember from my chemistry class was that solvents added to a solution increase its boiling point (or was it decrease???).

The "spoon" idea might work because metal has a high thermal conductivity (compared to a plastic lens), and would transfer the heat out of the liquid -- reducing its tendency to boil.

Best regards,
Darryl

[Darris Chambless]

Awight Darryl,

It's on now! :-) "The "spoon" idea might work because metal has a high thermal conductivity (compared to a plastic lens), and would transfer the heat out of the liquid -- reducing its tendency to boil." I would like to address the word "might." You would doubt me?!?! I can't believe it. After all these years and you would doubt moi`? :-)

You know what I learned from chemistry (besides how to make gelignite, Tri--Nitro Tolulene, Napalm and corrosives)? I learned that much of it equates back to common sense. The spoon idea comes from canning peaches. You put a spoon in the "Kerr" jar to temper the heated fluid sos not to shatter the jar. As the liquid cools is contracts and causes a vacuum on the lid creating an air tight seal and presto change-o you have a vacuum sealed jar full of nummy peaches that are required by law to sit on a shelf out in the garage for at least 20 years before being discarded :-)

When the temperature drops upon introduction of the cool lens, the cooling effect causes a centralized contraction of molecules in an environment that is expanding due to heat. This is not unlike pushing an inflated balloon under water and then letting go of it. The spoon acts like a vent which equalizes the molecular changes by buffering the reaction caused by rapid temperature changes.

Chemistry didn't teach me that either; my great grandmother did ;-) So you're not only doubting me but my great grandmother as well. That's gratitude for you. I hope you're proud of yourself! :-) It's amazing what necessity can teach you.

Darris "Wisenheimer" Chambless :-)

[Pete Hanlin]

Darris said:
"You can reduce this effect by tempering" the heated fluid by inserting a metal spoon into the liquid before dropping the lenses in. Do this slowly at first or warm the spoon before you put it in the pan. This will stop the pan from burping :-)

Okay, fine... however, this doesn't explain why UV will occasionally "explode" spontaneously (without the introduction of any object whatsoever). I've seen a pot of UV blow its lid plum off the tinting unit when no one was within 10 feet of the thing.
I still think it has something to do with the presence of the UV crystals in the solution creating a layer of hotter solution on the bottom. I think the UV begins to "boil" below this layer and, when enough steam is created, it breaks through the layer- causing the "burp."

Of course, tints sometimes boil when a lens is introduced, so I suppose I see your point... Without all the mumbo jumbo about "centralized contractions" and stuff, the introduction of a cold object causes an increase in the temperature difference between the hot liquid and the cool surface. If the difference between the two surfaces raises above the boiling point of the liquid... viola!

Since you are on a "roll," however :rolleyes: , why not explain why polycarb causes swarf and resins do not... or why do high index materials tend to stink in proportion to their expensiveness (i.e., the more they cost, the more they smell)... heh, heh.

Hey, have a good weekend dude! I'm just going into my garage to swap out my engines (this may take a few minutes :) ).

Pete

[Pete Hanlin]

Darryl observed:
"I think that surface tension is also why liquids always fall in or form spherical droplets.

I believe surface tension is also the reason why soap bubbles are capable of lifting dirt off of a surface...

Pete

[shanbaum]

Originally posted by Darryl Meister:
Does this sound any more believable, or am I completely off base here?

It's completely believable, and I think it's generally agreed that the effect you describe occurs; but I don't think it is the prime contributor to the particular effect Pete described; that is, it's not so much the breaking of the surface of the liquid that precipitates boiling, but the introduction into the liquid of a surface that provides nucleation sites where vapor bubbles form. It would be interesting to see the difference between introducing a lens, and introducing, for instance, some rice. Because the rice would present many more nucleation points, I'd expect the sudden boil to be more violent.

This may be the point at which a guy wearing a white coat, holding a beaker of frothing liquid, enters and says, "Stop! You're both right!"

As far as the efficacy of soap bubbles (as opposed to the bubbles themselves) resulting from surface tension is concerned, I sorta doubt it, given that a detergent lowers the wetting angle of a liquid (doesn't it?), which is one way to measure surface tension (isn't it?).

[Darris Chambless]

SMACK! Wake up and smell the neutralizer :-)

Let's go back to the early days of elementary science. What happens to fluids that are heated as the heat rises to the top surface? It begins to cool at the top which makes it condense and become heavier which will cause it to then sink to the bottom where it is then reheated and the whole process starts over again.

The rate at which the surface of the fluid cools can vary depending on the ambient temperature (or that of the room the unit is in). If the surface cools rather quickly and sinks faster than is stable for the temperature of the surrounding fluid you get the same reaction as dropping in a cool lens. The "I was just standing there and the lid blew off the UV."

You can and will get the same reaction out of a tint pot, but not as readily as you will in a UV pot. The reason for this is because tints are usually more viscous and therefore heat exchange takes place on a more even plane lessening the effect of the "BURP!" (I have just utilized some of my refrigeration knowledge on heat exchange to further the information pertaining to optical tint pots and why they explode on occasion :-). UV being thinner can have quicker temperature changes and thus perform it's "Wounded Swan Ballet" on a more frequent basis :-)

I must address "mumbo jumbo" ;-) I try to keep the explanations on a "regular guy" basis but sometimes the technical stuff has to come out. Darryl is the "technical guy" and I'm the "regular guy". Bran muffin anyone? :-)

"Since you are on a "roll," however , why not explain why polycarb causes swarf and resins do not... or why do high index materials tend to stink in proportion to their expensiveness (i.e., the more they cost, the more they smell)... heh, heh."

Okay, I didn't want to get technical but I have to in order to answer this one. Poly carbonate is a fibrous material which lends itself to "binding" as it is cut and cooled. It's molecular structure is interconnected and thus does not turn to powder. As it cuts it melts because it will build up and retain heat causing it to soften. Think of what happens to a rubber eraser. If it is cool or cold and you rub it on a piece of paper you get a rubbery powder. If you heat it up before rubbing it on paper it will smear all over the place and ruin whatever you're trying to fix. That might be a good excuse for not having your homework though, "I'm sorry teacher, but I was doing an experiment and my eraser ate my homework." :-)

Resigns do not share the same molecular structure as polycarbonate. The molecular structure of a resign is not interconnected and will "break apart" or "fracture" as it were, not unlike a piece of Sandstone. In other words resign is made up of individual particles and uses a bonding medium (also of individual particles) that flows in between to form a solid structure. When resign is cut the particles are dislodged from the bonding agent and the result is a powderery substance. Resign also dissipates heat more readily during the cutting process and therefore requires more heat in order to melt than a polycarbonate lens does

Polymer lenses are similar to resigns when cut, but do not share the same molecular structure. The molecular structure of polymer is more like overlapping plates that will bond to the surface of itself creating a brickwork, so to speak, of material. The bonding agent actually fuses these plates to themselves instead of a suspension bonding agent like that used in resign.

Now, Why does polymer smell bad while it cuts? Here is the really technical stuff. There's this smelly guy named Sal that operates the casting equipment. Sal has a medical problem involving over active sweat glands that inadvertently, will cause Sal to sweat into the liquid thus producing the same odor that you will find on Sal if you are unfortunate enough to get close enough to him to smell him. Yup. Sal is the reason all polymer lenses smell "funny" when you cut 'em. By the way, Sal doesn't like to be told he has "over active sweat glands." He prefers being told he is "endowed with well producing bodily fluid expulsion devices." :-)

I do hope this will answer some of those nagging questions that are on so many minds these days :-)

Take care,

Prof. Chambless :-)

PS. Professor Chambless can be seen at the Physical Science Auditorium speaking in front of hundreds of empty chairs this Tuesday night at 8:00 PM. So please feel free to not stop by so that we don't break his record of forty million "no shows" :-)

[Darryl Meister]

Originally posted by Pete Hanlin:
Since you are on a "roll," however :rolleyes: , why not explain why polycarb causes swarf and resins do not... or why do high index materials tend to stink in proportion to their expensiveness (i.e., the more they cost, the more they smell)... heh, heh.
Pete

Hi Pete,

I look at poly swarf a little more simply than Darris does (and this is again conjecture on my part)... Poly is a softer material and is also a thermoplastic, which means that it will melt at high temperatures. Normal CR-39 is a harder material and is also a thermoset, which means that it won't melt at high temperatures but start to burn instead. The heat created while grinding the poly during the edging process causes the material to melt/soften. When the removed material cools again, it hardens back into strands of swarf.

Many high-index polyurethanes (such as 1.6 MR-6 and 1.66 MR-7) contain sulfur-like ingredients, which give them their characteristic odor.

Best regards,
Darryl

[This message has been edited by Darryl Meister (edited 08-06-2000).]

[Darris Chambless]

Hey Darryl,

"Many high-index polyurethanes (such as 1.6 MR-6 and 1.66 MR-7) contain sulfur-like ingredients, which give them their characteristic odor."

Sal's sweat has been called a lot of things but never "sulfur-like ingredients." :-)

Darris "Didn't I just say that?" Chambless

[Darryl Meister]

Originally posted by Darris Chambless:
Sal's sweat has been called a lot of things but never "sulfur-like ingredients." :-)

Well, we've had our top chemical engineers trying to analyze the exact composition of Sal's sweat using FTIR (Fourier Transform Infrared) analysis. Consequently, we have a much better understanding of Sal's sweat than a lot of those "other guys." ;)

Best regards,
Darryl

[shanbaum]

Originally posted by Darris Chambless:
Polycarbonate['s] molecular structure is interconnected and thus does not turn to powder... The molecular structure of a [resin] is not interconnected and will "break apart" or "fracture" as it were, not unlike a piece of Sandstone. In other words resign is made up of individual particles and uses a bonding medium (also of individual particles) that flows in between to form a solid structure.

That's quite wrong, Darris; CR-39 is in fact a long-chain polymer. I think it's the case that all plastic materials used in ophthalmics (including polycarb) fall under the general categorization of "polymer". I also think it's the case that the differences among these materials derive from the way in which these long chains are cross-linked (that is, links among chains).

[Darris Chambless]

Hello Mr. Shanbaum,

I respect your intellect and you could be correct but I'll have to do a little re-upping on my studies (it's been a while sense I've messed with any of this stuff) If I recall correctly though each resign uses a different catalyst in order to bond the molecules of the starting substances. Each catalyst has to be specifically suited for each material because of the unique propperties of each. Before I can say anything any more definitive I'll have to double check, but I'm pretty sure I'm correct in my analogy. If I find any inconsistancies in my analogies vs. the real information I'll let you know.

Take care and thanks for your input.

Darris c.

[Jeff Trail]

Skipping all the chemistry :-) .. is it just this one tint unit that is "blowing" it's top? or was it every place you were at?
Reason being it may just be the lid and pot fit together "to well".. sounds dumb I know.. but I had the same thing on my 9 unit tinter and I couldn't figure it out and we switched the lids around and it hasn't done it since :rolleyes: .. of course all those other "theories" everyone is posting sounds alot more scientific...

Jeff "must have left my "Mr.Wizard" hat at the office" Trail

[Pete Hanlin]

Good answer, Jeff (ever the practical man). Actually, I've seen UV pop its top in almost every lab I've been in. My personal observation has been that UV with more "crystals" (or solid matter) in it tends to spontaneously vent more often- thus my original query.

Moving beyond that query, now. If the poly is "melting" while being edged, am I to assume that, if a cool enough temperature could be kept at the point of edging, the poly would act like any other resin? I know that tri-axial "burr" generators use a jet of very cool air to maintain a cool temperature at the burr. Could the same be done in an edger?

BTW, thanks for continually providing me with more input, fellas... you are all a fount of knowledge and I will aspire to be like Plato soaking up Socrate's knowledge.

Pete "the objects we see are merely reflections of the truth" Hanlin

[Darris Chambless]

Hey Pete,

You are absolutely correct about the poly and cooling. In theory if you could use a cooling agent that would bring the temperature down to a level that would cause the poly to become more rigid it would cut more like a conventional plastic lens, but probably not quite as powerdery. You change the molecular properties of the material.

Here's a good example: Take a childs rubber kickball and bounce it on the ground. What happens? It bounces back and usually (if you're a guy) hits you in the nether region :-) Now take that same ball and roll it around in liquid nitrogen (which most of us have lying around the house in a large vacuum seal thermosealed container somewhere. Or at least I do anyway :-) and try to bounce it. It will shatter, like glass, into many pieces.

Disclaimer: If you should attempt to try this experiment without the proper safety gear you are an idiot and should be shot immediately. If you have the proper safety gear and supervision make sure that the liquid nitrogen does not come in contact with your skin or you will lose a little of yourself that you may be rather fond of. Recommendation - Don't try this at home (unless you want to be shot for being an idiot :-)

Darris "What does this chemical taste like?" Chambless

[beta chem]

May I ask what the solvent is when you are doing this procedure and also what the components of the solute are? When you super heat a substance and add a boiling stone it will "bump" suddenly. This poses more of a problem with polar solvents such as water because of the amount of surface tension(cohesion) and adhesion at the bottom of the vessle. When using a boiling stone you should use one that is porous. With some substances there is a adhesive force between a liquid and a solid such as glass. With the addition of a porous stone you are breaking that adhesive force at the bottom of the vessle and giving it more surface area to boil off from. Wood it seems is the best for controlling bumping in a non-ionized polar solvent such as water because of its highly porous structure. Also when you cover a system with a lid you allow it to superheat because the vaporpressure is increased for the solvent. This is basically right out of my organic lab text book.

http://www.angelfire.com/scifi/HIFI4/w.gif



[This message has been edited by beta chem (edited 09-25-2000).]

[Pete Hanlin]

Beta Chem,
To be honest, I haven't a clue what the actual chemical composition of UV dye is (Darryl?). I might be able to find it on the solution's MSDSheet (I doubt it, though). Usually, there seems to be solid particles suspended in the solution... Observation has shown that, the more particles suspended in the solution, the greater the tendency for the solution to "erupt." Also, the temperature of the object being introduced to the solution seems to have great bearing on the reaction of the solution. I had come to the conclusion that introducing a cool object must cause a section of the solution to cool and fall to the bottom- which sets off a chain reaction of the solution expanding and contracting as a current becomes established in the solution...

In contrast, your diagram indicates that there is an attraction of the liquid to the bottom of the container that is weakened when an object pierces the top of the liquid- thus causing a pocket to form... My next question would be, "What is the nature of the attraction?"

Thanks,
Pete

[Darryl Meister]

Originally posted by Pete Hanlin:
To be honest, I haven't a clue what the actual chemical composition of UV dye is (Darryl?).

We work with UV inhibitors at SOLA, but I don't think that it's the same stuff used in UV dyes. It would probably be best to check with SeeGreen or BPI or someone.

My next question would be, "What is the nature of the attraction?"

I would guess 'hydrogen bonding' or some other similar chemical bond.

Best regards,
Darryl

[Jeff Trail]

Originally posted by Darris Chambless:
Hey Pete,

You are absolutely correct about the poly and cooling. In theory if you could use a cooling agent that would bring the temperature down to a level that would cause the poly to become more rigid it would cut more like a conventional plastic lens, but probably not quite as powerdery. You change the molecular properties of the material.
Darris "What does this chemical taste like?" Chambless

Maybe this is the "lets pick on Darris thread" :) BUT you are looking at it on a "chemical" level and forgetting the way it is produced. A poly is produced in a high pressure injection press, not like CR39.. it is pressed in layers, not unlike looking at a cross section of plywood :) .. so even if you did edge it cool, the nature of the way the lens was produced it would still "peel" back..(I think :))
Maybe I'll give it a try and see.. what emp do you figure would work ? I could always hook up my chiller and let that cool it..

Jeff "just one more thing to tinker with" Trail

[Clive Noble]

And I thought I was the only one this happened to... that's what my UV supplier told me

"Nobody has ever complained about 'exploding UV' only you Clive!"

Well, I have sorted it out.

Fistly it doesn't happen when the UV mix is new, it only has the burp effect after 5 or 6 pairs of lenses have been dipped, but if you stir the solution as it's heating up, like every couple of minutes, it won't burp and will remain at the useable temp for hours on end without a problem ...

Try it.

[beta chem]

Yup, stiring is going to break them H bonds.
Try throwing a piece of pourous glass or even a small shard of glass in it. Sounds like the H bonds arn't that bad.The more you dip it the worse it gets, its as if the lenses are taking some of the chemical that is making the H bonds "slippery," out.


beta chem

[Darryl Meister]

After watching a news special the other night on superheating fluids in a microwave oven, I decided to revive this old topic with another response!

The effect described on the show was very similar to our boiling UV question. The investigators ascribed the cause to a lack of nucleation points in the liquid... An explanation first proposed on this site by our own Robert Shanbaum! (Let's all give Robert a hand here.)

Best regards,
Darryl

[Jackie L]

Applause to Shanbaum for knowing this and to Darryl for remembering the post back in August!

Jackie O

------------------

Still a Maina for now

[chip anderson]

Damnitt, Darris you done mentioned all dem Xplosives and you gonna have The ATF, The FBI, The CIA, and God knows who else checking Optiboards now!

Chip

[morinput]

Although I enjoyed reading all the wonderful posts on the subject. I think you all are thinking way too hard into this, the answer is simply that when the uv ages and solids begin to form on the bottom, it creates a "lid" on top of liquid uv that is already boiling on the bottom of the tank, closest to the heating element. At this point any disturbance,whether it be inserting a lens or just knocking into the unit will allow those gases traped under the "lid" of solids to rapidly rise to the top, hence the burping. This also explains why uv will burp on occasion without any provocation, the gases just expand to the point that they break through all by themselves. Also explains why new uv wont do it and why if you stir frequently it does'nt occur. New to the board... I love this stuff!