I am currently employing the freeze thaw method to synthesize 10% w/v polvinyl alcohol. However, I cannot get the solution to gel. It becomes a sticky paste instead. I am only using a refrigerator freezer. Is this enough? I am freezing it for 12 hours and thaw it at 12 h as well. Thank you.
Hi, I can provide you our method. Hydrolisis degree, Mw and freeze-thaw times are very important. A -20°C freezer is fine. Good luck!
- 10% (w/v) solution of PVA (99% hydrolyzed, Aldrich, Milan, Italy) in distilled water was prepared using autooclaving (at 120 °C for 20 min).
- The PVA solution was cooled down to 60 °C under magnetic stirring (keep it heated to handle a solution with reduced viscosity, otherwise you will need a special pipetter for viscosus liquids), and complemented with distilled water to reach a final PVA concentration of 2.5% (w/v). The solution was poured in multiwell plates.
- We use 8 freeze-thawing cycles. The first cycle consisted of overnight freezing at −20 °C, followed by 30 min defrosting at room temperature (RT). The first cycle enables the crystalite structures, so it is very important. The subsequent 7 cycles consisted of −20 °C freezing for 1 h, followed by 30 min deforsting at RT.
From your result (sticky paste), I think that is not a good result to do the hydrogel. So many researchers produced hydrogel using freezing and thawing method. Peppas in 1975 was the first person using freezing and thawing to produce hydrogel from PVA. In his work, aqueous solutions, 2.5 and 15% wt of PVA, were frozen at -20 degree celcius and thawed back to room temperature resulting in the formation of crystallites. Nambu (1984) used of pure PVA gels produced by freezing and thawing processes for biomedical applications. His freeze-drying technique consisted of cooling a PVA solution to below -3 degree celcius followed by the vacuum evaporation of water.
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HI Ruth. It sounds to me as if the PVA you are using may have a low degree of hydrolysis. You should be using a PVA that is at least 98-99% hydrolyzed. These can be purchased from companies like Sigma. You also should be using a PVA with a high molecular weight (~500-750 kDa) in order to get a cryogel with any decent mechanical properties. To dissolve these high Mw PVAs in water you will need to boil the solution under reflux.
Hi, I can provide you our method. Hydrolisis degree, Mw and freeze-thaw times are very important. A -20°C freezer is fine. Good luck!
- 10% (w/v) solution of PVA (99% hydrolyzed, Aldrich, Milan, Italy) in distilled water was prepared using autooclaving (at 120 °C for 20 min).
- The PVA solution was cooled down to 60 °C under magnetic stirring (keep it heated to handle a solution with reduced viscosity, otherwise you will need a special pipetter for viscosus liquids), and complemented with distilled water to reach a final PVA concentration of 2.5% (w/v). The solution was poured in multiwell plates.
- We use 8 freeze-thawing cycles. The first cycle consisted of overnight freezing at −20 °C, followed by 30 min defrosting at room temperature (RT). The first cycle enables the crystalite structures, so it is very important. The subsequent 7 cycles consisted of −20 °C freezing for 1 h, followed by 30 min deforsting at RT.
physical hydrogels are having such characteristics but chemical cross linked gels are not having such property
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