"I am not sure whether this relates to dark reaction. I don't see dark reaction taking place within such a short period of time. If I am not misled some papers (?) advocated applying a 0,5% am. dich. bath for some 5 - 10 min. Though I am not sure I would rather speculate this step is supposed to enhance hardening (Cr3 formation) on the exposed sites."
I agree. I don't think there's enough time for dark reaction.I still don't see a mechanism for the extra dichromate to preferentially reduce only at the hardened sites. Could it be some form of diffusion where the velocity of the dichromate is slowed down by the harder sites causing greater a probability of reduction at these sites? Could the already formed Cr3+ act as a catalyst for the further reduction of fresh dichromate?
"So you were using chrome alum + "part B"?"
Yes. The film went very cloudy. I suspect that I overhardened it and the structure was no longer capable of holding the dissolved gelatin, so causing precipitation. Interestingly I told Hans Bjelkhagen about my attempt to use Chrome Alum and, before I could tell him my result, he said "Went cloudy, didn't it" with a smile!
DCG Latensification
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Danny bruza
DCG Latensification
you use dichromate and sulfuric acid as a bath right after exposer
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Martin
DCG Latensification
"I don't think there's enough time for dark reaction.I still don't see a mechanism for the extra dichromate to preferentially reduce only at the hardened sites."
Nor do I.
"Could it be some form of diffusion where the velocity of the dichromate is slowed down by the harder sites causing greater a probability of reduction at these sites? Could the already formed Cr3+ act as a catalyst for the further reduction of fresh dichromate?"
Frankly, I don't know. Instinctively, I would opt for the latter. There must be some reason why general wisdom suggests 0,5% am. dich. and not 5%. Curiously, some papers suggest a 10s rinse only in the 0,5% am. dich. solution.
Maybe there is also some pH issue involved - given Cr3 hardening is pretty fragile with respect to pH.
Nor do I.
"Could it be some form of diffusion where the velocity of the dichromate is slowed down by the harder sites causing greater a probability of reduction at these sites? Could the already formed Cr3+ act as a catalyst for the further reduction of fresh dichromate?"
Frankly, I don't know. Instinctively, I would opt for the latter. There must be some reason why general wisdom suggests 0,5% am. dich. and not 5%. Curiously, some papers suggest a 10s rinse only in the 0,5% am. dich. solution.
Maybe there is also some pH issue involved - given Cr3 hardening is pretty fragile with respect to pH.
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Sergio
DCG Latensification
Returning my original proposed idea, the DCG latensification is analogue to silver halide one, this is a predeveloping procedure, but the main target of the system is the quantum efficiency, probably a blue excited dichromate molecule hava more probability of receive an electron from (originally from red photon) a high reducing agent than from gelatin environment.
Is sure that Kst rate of electron trnasference is lower in gelatin than the optimized electron transfer versions, so is clear here that DCG excitation-reduction quantum efficiency is poor in blue green region, exactly due the electron tranference gap.
Another idea: what happen if you insere an efficient electron donor instead use the pure gelatin (I suppose the mechanism is the transformed hexavalent chromium to trivalent, analogue to Jeff Blyte MB chromium reduction)? Here we surpass the gelatin molecules sure due the very high efficiency tranfer, per example with Corcat P-600 branched polyethylenimine from Bayer. WDYT?
"Hence the gelatin already cross linked would further cross link faster than uncrosslinked gelatin."
I don't believe in this bias diferential, maybe you could find chemically one increase but nise is problem in development.
Is sure that Kst rate of electron trnasference is lower in gelatin than the optimized electron transfer versions, so is clear here that DCG excitation-reduction quantum efficiency is poor in blue green region, exactly due the electron tranference gap.
Another idea: what happen if you insere an efficient electron donor instead use the pure gelatin (I suppose the mechanism is the transformed hexavalent chromium to trivalent, analogue to Jeff Blyte MB chromium reduction)? Here we surpass the gelatin molecules sure due the very high efficiency tranfer, per example with Corcat P-600 branched polyethylenimine from Bayer. WDYT?
"Hence the gelatin already cross linked would further cross link faster than uncrosslinked gelatin."
I don't believe in this bias diferential, maybe you could find chemically one increase but nise is problem in development.
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Dinesh
DCG Latensification
"Another idea: what happen if you insere an efficient electron donor instead use the pure gelatin"
This was my first idea, but in a photorefractive sense. That is, inject electron donors into the gelatin and have them fall into the "electron traps" caused by the excitation state of the reduced dichromate. I thought this would be hard because the electron would have to have just the right energy and the gelatin would have to have some elements of a photorefractive compound so that the electron would migrate into the bright fringes. I did not think of chemical donors. I think I like the MB idea better (but not too much better!). These chemical (non MB) donors would have to provide electrons at the correct site during exposure (or at least during the excitation time of the dichromate). If these electrons are actinic, they must be blue sensitive but must either go to a higher energy state than the excitation state of DC and then cascade into the dc excited state, much like a two-stage laser, or rise up to the excited DC state and compete with electrons from the gelatin. If these electrons are not actinic, they must either be free (metal) or loosely bound so that the bias exposure releases them into the gelatin. Another possibility: Since gelatin has a crystal structure, is it possible to dope it with a type V dopant that releases electrons that stay within the crystal structure. Use the crystal as a sort of "band gap" a la semiconductors?
This was my first idea, but in a photorefractive sense. That is, inject electron donors into the gelatin and have them fall into the "electron traps" caused by the excitation state of the reduced dichromate. I thought this would be hard because the electron would have to have just the right energy and the gelatin would have to have some elements of a photorefractive compound so that the electron would migrate into the bright fringes. I did not think of chemical donors. I think I like the MB idea better (but not too much better!). These chemical (non MB) donors would have to provide electrons at the correct site during exposure (or at least during the excitation time of the dichromate). If these electrons are actinic, they must be blue sensitive but must either go to a higher energy state than the excitation state of DC and then cascade into the dc excited state, much like a two-stage laser, or rise up to the excited DC state and compete with electrons from the gelatin. If these electrons are not actinic, they must either be free (metal) or loosely bound so that the bias exposure releases them into the gelatin. Another possibility: Since gelatin has a crystal structure, is it possible to dope it with a type V dopant that releases electrons that stay within the crystal structure. Use the crystal as a sort of "band gap" a la semiconductors?
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Sergio
DCG Latensification
"Another idea: what happen if you insere an efficient electron donor instead use the pure gelatin"
This was my first idea, but in a photorefractive sense. That is, inject electron donors into the gelatin and have them fall into the "electron traps" caused by the excitation state of the reduced dichromate. I thought this would be hard because the electron would have to have just the right energy and the gelatin would have to have some elements of a photorefractive compound so that the electron would migrate into the bright fringes.
>>If I understand the gelatin will behave as a "leuco" element or high state energetic reacted between molecules? Difficult to change the refractive index in this way, I think only with crosslink hardening effect it will be useful.
I did not think of chemical donors. I think I like the MB idea better (but not too much better!). These chemical (non MB) donors would have to provide electrons at the correct site during exposure (or at least during the excitation time of the dichromate).
>> Yes, the chemical donor may be a hydrogen from amines, that will react with the environment to deprotonate the molecule generating a reduce radical (reducing the dichromate), moreover, the amine (TMG?) will act as oxygen scavenger that will consume the last and form more radicals that will reduce dichromate, note that TMG itself will not chelate with dichromate directly.
If these electrons are actinic, they must be blue sensitive but must either go to a higher energy state than the excitation state of DC and then cascade into the dc excited state, much like a two-stage laser, or rise up to the excited DC state and compete with electrons from the gelatin.
>>The blue energy will cascade into DC but the electron transfer is independent from light exitation or just the energy must be equivalent?
If these electrons are not actinic, they must either be free (metal) or loosely bound so that the bias exposure releases them into the gelatin. Another possibility: Since gelatin has a crystal structure, is it possible to dope it with a type V dopant that releases electrons that stay within the crystal structure. Use the crystal as a sort of "band gap" a la semiconductors?
>>Yes, you can make the gelatin conductive with silver halide or TiO2, an electron can be injected by MB, radicals, electrical current into this semiconductor band gap to the dichromate or traped by silver halide, it may open the way for cyanine dye dichromate sensitization, introducing dichromate reduction by silver halide development.
This was my first idea, but in a photorefractive sense. That is, inject electron donors into the gelatin and have them fall into the "electron traps" caused by the excitation state of the reduced dichromate. I thought this would be hard because the electron would have to have just the right energy and the gelatin would have to have some elements of a photorefractive compound so that the electron would migrate into the bright fringes.
>>If I understand the gelatin will behave as a "leuco" element or high state energetic reacted between molecules? Difficult to change the refractive index in this way, I think only with crosslink hardening effect it will be useful.
I did not think of chemical donors. I think I like the MB idea better (but not too much better!). These chemical (non MB) donors would have to provide electrons at the correct site during exposure (or at least during the excitation time of the dichromate).
>> Yes, the chemical donor may be a hydrogen from amines, that will react with the environment to deprotonate the molecule generating a reduce radical (reducing the dichromate), moreover, the amine (TMG?) will act as oxygen scavenger that will consume the last and form more radicals that will reduce dichromate, note that TMG itself will not chelate with dichromate directly.
If these electrons are actinic, they must be blue sensitive but must either go to a higher energy state than the excitation state of DC and then cascade into the dc excited state, much like a two-stage laser, or rise up to the excited DC state and compete with electrons from the gelatin.
>>The blue energy will cascade into DC but the electron transfer is independent from light exitation or just the energy must be equivalent?
If these electrons are not actinic, they must either be free (metal) or loosely bound so that the bias exposure releases them into the gelatin. Another possibility: Since gelatin has a crystal structure, is it possible to dope it with a type V dopant that releases electrons that stay within the crystal structure. Use the crystal as a sort of "band gap" a la semiconductors?
>>Yes, you can make the gelatin conductive with silver halide or TiO2, an electron can be injected by MB, radicals, electrical current into this semiconductor band gap to the dichromate or traped by silver halide, it may open the way for cyanine dye dichromate sensitization, introducing dichromate reduction by silver halide development.