Conductive Adhesive Humectant Low Humidity Stability
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Solution Overview
Problem
Conductive adhesives used in biomedical electrodes degrade rapidly under low humidity conditions, leading to a loss of electrical properties due to evaporative water loss, compromising the ionically conductive phase and affecting the adhesive's ability to maintain skin contact and electrical conductivity.
Innovation Solution
A conductive adhesive composition comprising a pressure-sensitive adhesive, up to 10 parts by weight of a water-soluble organic chloride electrolyte, and a humectant, which forms a bicontinuous structure to maintain electrical conductivity even under low humidity conditions, preventing the degradation of electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional conductive adhesive with inorganic electrolyte (e.g., potassium chloride) is used, then initial electrical conductivity is achieved, but electrical properties degrade rapidly under low humidity conditions due to evaporative water loss
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte from inorganic salts (potassium chloride, sodium chloride) to organic salts (choline chloride, betaine, phosphocholine). This parameter change fundamentally alters the solubility characteristics and hygroscopic properties of the adhesive, enabling it to maintain electrical conductivity under low humidity conditions where conventional inorganic electrolytes fail.
Solution Approach 2:
The patent creates a composite adhesive system combining organic electrolyte salts with specific polymeric binders and humectants. This composite formulation synergistically maintains water content and ionic conductivity, where the organic electrolyte provides ion conduction pathways while the humectant prevents excessive water loss, solving the instability problem of conventional single-component adhesive systems.
2Stability of the object's composition
If water content in the adhesive is reduced to prevent evaporative loss, then stability under low humidity improves, but electrical conductivity decreases due to reduced ion mobility
Solution Approach 1:
The patent introduces humectants (glycerol, propylene glycol, polyethylene glycol) as intermediary substances that actively bind and retain water molecules within the adhesive matrix. These humectants act as water reservoirs, maintaining adequate water content for ion mobility even in low humidity environments, thereby decoupling the relationship between environmental humidity and adhesive water content.
Solution Approach 2:
The patent changes the electrolyte from inorganic to organic salts, which have different hydration characteristics and solubility profiles. Organic electrolytes like choline chloride maintain effective ionic dissociation and conductivity at lower water contents compared to inorganic salts, allowing the adhesive to function across a broader humidity range without sacrificing electrical properties.
3Stability of the object's composition
If humectant concentration is increased to slow evaporative loss, then water retention improves, but electrical conductivity decreases because alkali halides are poorly soluble in humectants
Solution Approach 1:
The patent fundamentally changes the electrolyte chemistry from inorganic alkali halides to organic salts (choline chloride, betaine, phosphocholine). These organic electrolytes exhibit high solubility in humectants like glycerol and polyethylene glycol, maintaining effective ionic concentration and electrical conductivity even at elevated humectant levels where inorganic salts would precipitate.
Solution Approach 2:
The patent develops a composite formulation where organic electrolyte salts and humectants are synergistically combined. The organic electrolyte molecules are compatible with the humectant molecular structure, allowing them to coexist in high concentrations without phase separation or precipitation, thereby maintaining both water retention and ionic conductivity simultaneously.
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 proposed adhesive composition effectively maintains electrical conductivity and adhesion to the skin over time, even in low humidity environments, ensuring the reliability of biomedical electrodes for diagnostic and therapeutic applications.
Implementation Method 1
The ionically conductive phase of the adhesive consists of an alkali or alkaline earth metal chloride (typically potassium or sodium chloride) dissolved in water... the electrical properties are related to the conductance of dissolved salt in the water/humectant mixture of the adhesive
Implementation Method 2
humectant added to slow down evaporative loss... under low humidity conditions (which can be as low as 20% R.H in hospitals), rapid evaporative loss of water occurs
Data Source
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Figure 4
AI summary
A conductive adhesive composition is provided and articles that include the adhesive composition as a component thereof. The conductive adhesive composition comprises: (a) pressure sensitive adhesive; (b) electrolyte comprising water soluble or water dispersible organic chloride; and (c) humectant. In some embodiments, the conductive adhesive composition is a bicontinuous composition comprising an aqueous phase and an oil phase, and the bicontinuous composition may be derived from a polymerizable microemulsion composition, the microemulsion composition comprising: an aqueous phase comprising one or more hydrophilic monomers or oligomers and/or one or more amphiphilic monomers or oligomers in water, the water-soluble or water-dispersible organic chloride, surfactant and humectant; and an oil phase comprising one or more hydrophobic monomers or oligomers. Biomedical articles such as biomedical electrodes, may incorporate the foregoing adhesive as a component.