- Run UV-vis on salt-exchanged PVOH(22K) + GA + PP films.
UV-Vis of Salt-Exchanged PVOH Films
- Place film in 20 mL 10 mM Fe2(SO4)3.
- Time how long it takes for the film to change color from green to pink.
- Remove film from salt solution, pat dry with KimWipes, and cut with a 3.5 mm film cutter.
- Measure the thickness of the film with calipers, then place it in a quartz cuvette and take a spectrum from 200 nm to 800 nm.
- Place the film back in its H2SO4 solution.
- Discard the salt solution into a waste container.
- Repeat the above steps in 20 mL solutions of 10 mM Al2(SO4)3 and 10 mM Na2SO4.
- The following films were analyzed with this protocol:
- PVOH(22K) 1.0067 g + 1 mL GA + 1 mL PP + HCl
- PVOH(22K) 1.0073 g + 1 mL GA + 1 mL PP
- PVOH(22K) 1.05225 g + 0.5 mL GA + 1 mL PP
- Note that all films were stored in 2 wt% H2SO4 solution prior to being soaked in the salt solutions.
- Immediately after being placed in the three salt solutions, the PVOH(22K) 1.05225 g + 0.5 mL GA + 1 mL PP films became colorless.
||Salt Solution 
||Film Thickness [mm]
||Time in Solution [min]
| PVOH(22K) 1.0073g, 1mLGA, 1mLPP||Al2(SO4)3||0.6||Green||174
| PVOH(22K) 1.0073g, 1mLGA, 1mLPP||Na2SO4||0.5||Pink||189
| PVOH(22K) 1.0073g, 1mLGA, 1mLPP||Fe2(SO4)3||0.6||Pink||189
| PVOH(22K) 1.05225g, 0.5mLGA, 1mLPP||Al2(SO4)3||0.6||Transparent||135
| PVOH(22K) 1.05225g, 0.5mLGA, 1mLPP||Na2SO4||0.1||Transparent||135
| PVOH(22K) 1.05225g, 0.5mLGA, 1mLPP||Fe2(SO4)3||0.4||Transparent||135
| PVOH(22K) 1.0067g, 1mLGA, 1mLPP, HCl||Al2(SO4)3||0.9||Green||152
| PVOH(22K) 1.0067g, 1mLGA, 1mLPP, HCl||Na2SO4||1||Pink||160
| PVOH(22K) 1.0067g, 1mLGA, 1mLPP, HCl||Fe2(SO4)3||0.9||Pink||162
- In all spectra, a peak at around 420 nm is visible. Based on spectra of porphine in the salt solutions alone, it is likely that this peak is due to the presence of porphine in the films. The peak absorbance at 420 had the highest value for films soaked in 10 mM Na2SO4, while the peak absorbance was the lowest for films soaked in Al2(SO4)3. This corresponds to the fact that all films soaked in the latter solution remained green in color and did not become pink, even after soaking for several hours.