Free-Standing Membrane Fabrication via Crosslinking Gradient
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Solution Overview
Problem
Existing membrane fabrication methods fail to produce free-standing membranes with uniform pore size and shape, ordered pore distribution, and controlled morphology, which are essential for precise applications like filtration and catalytic reactions, due to issues such as poor control over pore size, shape, and residual stress.
Innovation Solution
A one-step photolithographic method that controls UV dose and exposure time to create a crosslinking gradient in the photoresist layer, allowing for self-detachment of membranes with well-defined patterns and uniform pore distribution, using either negative or positive photoresists.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithographic methods with sacrificial layers are used, then membranes can be patterned with well-defined pores, but the fabrication cost and complexity increase and membrane quality is impaired
Solution Approach 1:
The patent extracts and eliminates the sacrificial layer component from the fabrication process. By using a self-detaching membrane approach, the method removes the need for additional sacrificial layers that were previously required in conventional photolithographic methods, thereby simplifying the fabrication process while maintaining pore definition quality
Solution Approach 2:
The membrane structure itself provides the detachment function without requiring external sacrificial layers. The self-detaching mechanism allows the membrane to release from the substrate through its own structural properties, eliminating the need for separate sacrificial layer materials and dissolution steps
2Ease of manufacture
If track-etch membranes are used, then membranes are commercially available, but control over pore morphology and size is poor
Solution Approach 1:
The patent changes the key parameter of pore formation from random bombardment-induced tracks to controlled UV exposure patterns. By adjusting UV dose, exposure time, and photomask patterns, precise control over pore size, shape, and distribution is achieved, transforming the manufacturing process from uncontrollable to highly controllable
3Manufacturing precision
If anodic alumina membranes are used, then morphological quality improves, but handling of dangerous reagents is required
Solution Approach 1:
The patent replaces the use of dangerous reagents with a disposable photomask and UV exposure approach. The photomask can be easily replaced to achieve different pore patterns, and the UV exposure process eliminates the need for handling hazardous chemicals while maintaining morphological quality
Solution Approach 2:
The patent substitutes the electrochemical etching mechanism with a photopolymerization-based mechanical detachment system. Instead of using dangerous reagents for membrane formation, UV light initiates crosslinking and subsequent self-detachment, replacing harmful chemical processes with safer optical and mechanical mechanisms
4Ease of manufacture
If soft lithography is used, then fabrication is simple, but membrane surface becomes uneven due to surface tension
Solution Approach 1:
The patent replaces the spin-coating mechanical process that causes surface tension issues with a direct UV exposure and self-detachment mechanism. This substitution eliminates the surface tension problem inherent in liquid prepolymer application while maintaining fabrication simplicity
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 method produces membranes with a low coefficient of variation (0.15%) and precise control over pore shape and size, enabling superior performance in filtration and catalytic reactions, and allows for the synthesis of nanoparticle patterns with tailored pore sizes and shapes.
Implementation Method 1
exposing the photoresist layer from its top to a dose of ultraviolet radiation through a mask having a predetermined pattern, controlling an intensity of the dose of ultraviolet radiation and controlling a time the photoresist layer is exposed to the dose of radiation such that a top portion of the photoresist layer through which the dose of ultraviolet radiation enters the photoresist layer undergoes greater cross linking than a bottom portion of the photoresist layer immediately adjacent to the top surface of the substrate
Data Source
AI summary
The present disclosure discloses a method of fabrication of free standing open pore membranes with uniform pore size and shape and ordered pore distribution, and its use for synthesis of nanoparticle patterns. The method includes applying a photoresist layer to the top surface of a substrate, heating the photoresist layer for a period of time, and exposing the photoresist layer to a dose of ultraviolet radiation through a mask having a predetermined pattern. The dose of ultraviolet radiation is controlled in intensity and time and the photoresist layer is exposed such that a top portion of the photoresist layer through which the dose of ultraviolet radiation enters the photoresist layer undergoes greater cross linking than a bottom portion of the photoresist layer immediately adjacent to the top surface of the substrate such that a cross linking gradient develops through a thickness of the photoresist layer. The mask is removed and the membrane is readily detached from the top surface of the substrate since the portion of the membrane adjacent to the top surface is less cross linked than the top surface of the membrane. The detached membrane forms a free standing patterned membrane having a preselected pattern of open pores. The method can be used with positive photoresist materials as well when deposited on a UV transparent substrate so that the photoresist can be exposed to UV from its top with photomask and UV exposure from its back of the transparent substrate without the photomask.