Ionomeric Membrane Size Stability in Hydroalcoholic Solutions
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Solution Overview
Problem
Existing ionomeric membranes with fluorinated ionomers and sulphonic groups at the end of short side chains suffer from significant size variations and lack physical stability when exposed to hydroalcoholic solutions, limiting their duration in electrochemical cells.
Innovation Solution
Development of ionomeric membranes with sulphonic (per)fluorinated ionomers having side chains of formula —O—CF2—CF2—SO3−M+, where M is hydrogen or an alkaline metal, with size variations less than 15% and integral structure after a stability test in a water/ethanol mixture, achieved through a process involving hydrolysis of —SO2F groups and a specific membrane preparation method including a two-step hydrolysis process and thermal treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ionomeric membranes with fluorinated ionomers and sulphonic groups at the end of short side chains are used, then good ion exchange capacity is achieved, but significant size variations occur and physical stability is lost in hydroalcoholic solutions
Solution Approach 1:
The patent changes the chemical structure parameters of the side chains by introducing fluorinated groups at specific positions (alpha and beta carbons) and controlling the composition ratio of different monomer units. This structural parameter modification enhances the membrane's resistance to swelling in hydroalcoholic solutions while maintaining ion exchange capacity, thereby resolving the contradiction between reliability and compositional stability.
Solution Approach 2:
The patent creates a composite ionomer structure by copolymerizing multiple monomer units with different functions: one providing sulphonic acid groups for ion exchange, another providing fluorinated groups for dimensional stability, and a third providing hydrophobic character. This composite approach allows simultaneous achievement of good ion exchange capacity and resistance to size variations in hydroalcoholic environments.
2Reliability
If membranes are prepared by conventional casting methods, then fabrication is simple, but membranes fragment after stability testing in hydroalcoholic solutions
Solution Approach 1:
The patent incorporates stabilizing fluorinated groups and appropriate cross-linking structures into the polymer chain during the synthesis stage, before the membrane is exposed to hydroalcoholic solutions. This preliminary structural reinforcement prevents fragmentation during subsequent stability testing, while the membrane fabrication process itself remains a conventional casting procedure.
3Stability of the object's composition
If side chains with general formula —O—CFRIfI)bI—(CF2)aISO2ZI are used, then ion exchange capability is provided, but size variations exceed acceptable limits
Solution Approach 1:
The patent introduces fluorinated groups at specific local positions (alpha and beta carbons) of the side chain rather than uniformly throughout. This localized fluorination provides dimensional stability where needed while preserving the ion exchange capability of the sulphonic acid groups at the end of the side chains, thus resolving the contradiction between compositional and dimensional stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The membranes exhibit reduced size variations and maintain integrity after prolonged exposure to hydroalcoholic solutions, enhancing their stability and performance in electrochemical cells.
Implementation Method 1
the sulphonylfluoride groups —SO2F are convertible into sulphonic groups —SO3H by hydrolysis
Implementation Method 2
on the support a treatment at temperatures from about 150° C. to about 380° C. depending on the polymer thermoplastic properties, is carried out
Implementation Method 3
in the final thermal treatment, the copolymer is melted on an aluminum sheet to form a coating
Data Source
AI summary
An ionomeric membrane formed of a sulphonic (per)fluorinated ionomer wherein the sulphonic groups are at the end of short side chains (SSC), said ionomer having:equivalent weight between 700 and 1600 g/eq;side chains of formula: —O—CF2—CF2—SO3−M+, wherein M is hydrogen or an alkaline metal;said membrane having the following combination of properties:size variations, for both the orthogonal directions xy of the plane, lower than 15%, measured after dipping of the ionomeric membrane, dried at 105° C. under vacuum for one hour, in demineralized water at 100° C. for 30 minutes;the membrane, dipped at the temperature of 50° C. for 22 hours in a water/ethanol mixture containing 40% by weight of alcohol, remains integral.