Nafion makes the water around it very acidic, about as acidic as 1.2 M sulfuric acid, which helps explain why particles are repelled from its surface.
Scientific Claim
Nafion creates a significant pH gradient in surrounding water, with internal acidity equivalent to approximately 1.2 M sulfuric acid, which is consistent with diffusiophoresis theory explanations for EZ formation.
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
definitive
Can make definitive causal claims
Assessment Explanation
The study reports specific experimental measurements of Nafion's acidity using methylene blue, which is a factual observation. The language accurately reflects the experimental findings.
Source Excerpt
“Using methylene blue the internal acidity of Nafion has been estimated to be equivalent to 1.2 M sulphuric acid. The excess protons inside Nafion are of two types—'fixed' ions which can 'hop' between sulfonic groups, and 'mobile' ions which can can freely diffuse away. Thus water around Nafion becomes acidic, with a pH gradient approaching neutral (7) further away from the memberane.”
Evidence from Studies
Supporting Evidence (1)
The study reports specific measurements of Nafion's acidity using methylene blue, estimating it equivalent to 1.2 M sulfuric acid, and describes the resulting pH gradient. This is presented as evidence supporting diffusiophoresis theory.