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Molding samples from gels
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Photoelastic samples can also be cast from more common materials than [urethane](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/molding-urethane). For example gelatin is a very good photoelastic material, with a high photoelastic constant, which means that a small stress induces a large photoelastic effect ([Kuske & Robertson, "Photoelastic Stress Analysis"](https://books.google.com/books?id=qsdRAAAAMAAJ&redir_esc)). Gelatin is most likely the most used photoelastic gel but many others like agar or konjac exist ([Tomlinson and Taylor](https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-54/issue-8/081208/Photoelastic-materials-and-methods-for-tissue-biomechanics-applications/10.1117/1.OE.54.8.081208.short?SSO=1)). In this section we focus on making samples out of gelatin but similar processes can be applied to other type of hydrogels.
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Photoelastic samples can also be cast from more common materials than [urethane](/molding-urethane). For example gelatin is a very good photoelastic material, with a high photoelastic constant, which means that a small stress induces a large photoelastic effect ([Kuske & Robertson, "Photoelastic Stress Analysis"](https://books.google.com/books?id=qsdRAAAAMAAJ&redir_esc)). Gelatin is most likely the most used photoelastic gel but many others like agar or konjac exist ([Tomlinson and Taylor](https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-54/issue-8/081208/Photoelastic-materials-and-methods-for-tissue-biomechanics-applications/10.1117/1.OE.54.8.081208.short?SSO=1)). In this section we focus on making samples out of gelatin but similar processes can be applied to other type of hydrogels.
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Making cross-linked gelatin discs
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Gelatin samples can be molded in the same way as [urethane](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/molding-urethane) ones. To make gelatin discs, first dissolve gelatin in water. To do so let first the gelatin softness in cold water during few minutes. Then heating it up higher than 50 degrees but lower than 90 degrees. Depending on the required rigidity, the concentration of gelatin can be tuned. A typical concentration is 10 weight percent. The gelatin will set at a temperature around 35 degrees. After pouring the warm gelatin solution in the rubber molds, store the molds in the refridgerator for around 3 hours, to make sure the gels are fully set.
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Gelatin samples can be molded in the same way as [urethane](/molding-urethane) ones. To make gelatin discs, first dissolve gelatin in water. To do so let first the gelatin softness in cold water during few minutes. Then heating it up higher than 50 degrees but lower than 90 degrees. Depending on the required rigidity, the concentration of gelatin can be tuned. A typical concentration is 10 weight percent. The gelatin will set at a temperature around 35 degrees. After pouring the warm gelatin solution in the rubber molds, store the molds in the refridgerator for around 3 hours, to make sure the gels are fully set.
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The samples can be used as such but they are not stable for long observation. If they stay in the air they will dry and solidify, and if they stay into water they will swell it and dissolve. In both cases this changes the photoelastic properties of the material. To stabilize them we can cross-link the gelatin. We also note that bacteria can develop in the gelatin ruining its properties.
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... | ... | @@ -37,4 +37,4 @@ Gelatin spheres made using the technique published by ([Workamp et al](https://a |
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Photoelastic response of a suspension of bidisperse gelatin spheres in a Couette geometry. For more details see [Workamp et al](https://doi.org/10.1051/epjconf/201714003020).
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[<go back to home](https://git-xen.lmgc.univ-montp2.fr/PhotoElasticity/Main/wikis/home) |
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[<go back to home](/home) |
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