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Polyaniline-Coated Polysulfone Membranes as Flexible Optical pH Sensors
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1  Department of Chemical and Process Engineering Technology, Jubail Industrial College, Jubail Industrial City 31961, Saudi Arabia


A new optical pH sensor based on Polysulfone (PSU) and Polyaniline (PANI) was developed. The transparent and flexible PSU membrane was employed as a support. The electrically conductive and pH-responsive          PANI was deposited onto the membrane surface by in situ chemical oxidative polymerization (COP). The absorption spectra of the PANI-coated PSU membranes exhibited sensitivity to pH changes in the range of 4-12, which allowed for designing dual wave length pH optical sensor. The performance and durability of the membranes were assessed by measuring their response starting from high pH and going down to low pH, and vice versa. The effect of synthesis conditions and film thickness were investigated. The effect of the membrane's storage conditions on the reproducibility of the results was also investigated

Comments on this paper
Amélie Wannebroucq
thickness effect on the response
Dear authors,

Do you know the thickness of the different polymeric layers that you prepared for pH sensing?

Did you see an effect of the thickness on the shape of the absorbance = f(pH) curve?


Amelie Wannebroucq and Marcel Bouvet
Nedal Abu-Thabit
We have not investigated this yet. However, we expect that the thickness is in the order of <500 nm, based on literature reports. Actually, if the polymer coating is too thick, then the absorbance will be less or even blocked.
Nedal Abu-Thabit
For example, sample with absorbance of 2.6 should have higher thickness (as visually observed) and the recorded spectrum was not good (a lot of noise due to high concentration of the polymer sample).
Nedal Abu-Thabit
to clarify what is written in our paper:

"PSU membranes with different thicknesses in the range of 40-400 m were coated with polyaniline

and tested for its optical pH sensitivity. The effect of the membrane thickness on the optical response

was found to be insignificant, even at thickness of 400 m. This result is important for the feasibility
of the practical applications that require tough membranes with superior mechanical properties"

in the above paragraph, we discussed the thickness of support polymer membrane (polysulfone). But in my above two answers, I was talking about thickness of resposnive Polyaniline coating.

Wish this clarify your questions.

Alberto Vallan
usage of plastic optical fibers
Is it possible to use a plastic optical fiber made of PMMA as a support in order to develop a fiber-based pH sensor?
Nedal Abu-Thabit
In principle, yes, it can be used as a polymeric coating, but you have to try it and fine tune the conditions such as doping acid, concentration, reaction time , etc....But also you have to make sure that the coating is from outside ONLY and not outside. I'm not sure about the difference in refractive index between PMMA and polyaniline.? and how much the thickness of cladding layer should be? note also that polyaniline is a conductive polymer and is used for electrostatic charge dissipation and magnetic shielding applications.
Nedal Abu-Thabit
from outside ONLY and not inside
Nedal Abu-Thabit
these links might be useful:

Alberto Vallan
thanks for your suggestions and for the links. About the refractive index, as an example, Rayo Eska SH-4001 plastic fiber produced by Mitsubishi, has a core refractive index of 1.495 and a cladding refractive index of 1.403. The cladding is typically a fluorinated polymer having a thickness of about 10 um.