Low-Energy Substrate Wetting Using Removable Vapor Mediation
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Solution Overview
Problem
Low surface energy substrates, such as expanded polytetrafluoroethylene (ePTFE), are poorly wetted by high surface tension liquids, leading to difficulties in coating and other processes due to inadequate contact and slow wetting rates, and the use of surfactants to lower surface tension can alter the properties of the liquid and deposit undesirably on the substrate.
Innovation Solution
A method involving a low surface tension fluid is used to facilitate wetting by contacting the low surface energy substrate with a high surface tension liquid, either before, during, or after the initial contact, and then removing the low surface tension fluid to improve wetting without altering the properties of the high surface tension liquid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surfactants are added to high surface tension liquids to lower surface tension and improve wettability, then wetting of low surface energy substrate is improved, but other properties of the liquid are disrupted and additives may deposit on the substrate
Solution Approach 1:
A surfactant is introduced as an intermediary substance that temporarily modifies the surface tension of the aqueous coating composition during the coating process. The surfactant acts as a mediator between the high surface tension liquid and the low surface energy PTFE substrate, enabling wetting without permanently altering the coating composition. After coating, the surfactant is removed along with the aqueous carrier, leaving no harmful deposits on the substrate.
Solution Approach 2:
The surface tension parameter of the aqueous coating composition is temporarily changed by adding surfactant to enable wetting of the PTFE substrate. This parameter modification is reversible, as the surfactant is removed in the drying step along with the aqueous carrier, restoring the original properties of the coating material without permanent alteration.
2Reliability
If surfactants are used to lower surface tension, then wettability improves, but maximum loading of coating material is reduced due to reduced solubility or dispersibility
Solution Approach 1:
The surfactant is added preliminarily to the aqueous coating composition before the coating process to temporarily reduce surface tension and improve wetting. This preliminary modification enables the coating material to be properly deposited on the PTFE substrate. The surfactant is then removed in the drying step, restoring the coating material's original solubility and dispersibility characteristics for future applications.
Solution Approach 2:
The surfactant serves as a temporary intermediary that facilitates the coating process by reducing surface tension during application. It does not permanently alter the coating material's solubility or dispersibility, as it is removed along with the aqueous carrier after coating, preserving the maximum loading capacity of the coating material.
3Reliability
If surfactants are added to improve wettability, then contact between liquid and substrate increases, but viscosity may increase due to gelling of coating material
Solution Approach 1:
The surface tension parameter of the aqueous coating composition is temporarily modified by surfactant addition to improve wettability. This parameter change is reversible, as the surfactant is removed in the drying step along with the aqueous carrier, restoring the original viscosity and flow characteristics of the coating material without permanent thickening or gelling.
Solution Approach 2:
The surfactant acts as a temporary intermediary during the coating process that facilitates wetting without permanently altering the rheological properties of the coating material. Its temporary presence enables improved contact with the PTFE substrate, while its subsequent removal restores the original viscosity and eliminates process complexity associated with permanent thickening.
4Stability of the object's composition
If high surface tension liquid is used for coating, then coating material stability is maintained, but wetting of low surface energy substrate is poor and wetting rate is slow
Solution Approach 1:
A surfactant is introduced as a temporary intermediary to the high surface tension aqueous coating composition to reduce its surface tension and improve wetting of the PTFE substrate. The surfactant enables the stable coating material to contact and wet the low surface energy substrate effectively. After coating, the surfactant is removed along with the aqueous carrier, preserving the coating material's stability while achieving improved wetting.
Solution Approach 2:
The surface tension parameter of the aqueous coating composition is temporarily reduced by surfactant addition to enable wetting of the PTFE substrate, while the coating material's stability is maintained. The parameter modification is reversible, as the surfactant is removed in the drying step, restoring the original surface tension and maintaining coating material stability for future applications.
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
Enhances the wetting of low surface energy substrates with high surface tension liquids, improving contact and potentially increasing the wetting rate without using surfactants or surface treatments that could change the substrate's properties.
Implementation Method 1
Wetting is a phenomenon which describes the ability of a liquid to maintain contact with a solid surface and relates to the molecular interactions between the two materials. The higher the surface energy of a liquid compared to that of a solid, the lower the wettability
Implementation Method 2
removing the low surface tension fluid from the low surface energy substrate after the contacting with the low surface tension fluid as a vapour
Data Source
AI summary
There is provided a method of wetting a low surface energy substrate with a high surface tension liquid comprising at least the steps of providing a low surface energy substrate having a surface energy in the range of from 15 to 45 mN/m, a high surface tension liquid having a surface tension in the range of from greater than 25 to 70 mN/m and a low surface tension fluid having a surface tension in the range of from 10 to 25 mN/m; contacting the low surface energy substrate with the high surface tension liquid; contacting at least one of the low surface energy substrate and the high surface tension liquid with the low surface tension fluid vapour, either before, at the same time as or after the contacting of the low surface energy substrate with the high surface tension liquid; and removing the low surface tension fluid vapour from the low surface energy substrate. The high surface tension liquid can be used as a carrier liquid for a coating material, such as an ion exchange material, to be deposited on the substrate, such as ePTFE, in a method of coating. Also disclosed is a system for such coating methods.