Highly Conducting Graphitic Films from Liquid Crystal Alignment
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Solution Overview
Problem
Current methods for producing highly oriented graphitic films face challenges in achieving high thermal conductivity, electrical conductivity, and mechanical strength due to defects and mis-orientations in graphene planes, with existing processes being energy-intensive, expensive, and limited in thickness and quality.
Innovation Solution
A process involving the preparation of a graphene oxide or chemically functionalized graphene dispersion that forms a liquid crystal phase, subjected to orientation-inducing stress, followed by thermal reduction and heat treatment to produce a highly oriented graphitic film with aligned graphene planes, achieving exceptional thermal and electrical conductivity and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional chemical vapor deposition followed by ultra-high temperature graphitization is used to produce highly oriented pyrolytic graphite, then the graphitic structure can be formed, but the graphene planes remain inadequately aligned and exhibit properties significantly lower than theoretically predicted
Solution Approach 1:
The invention changes the physical and chemical parameters of the starting material by using highly oriented graphite flakes with specific crystallographic orientation instead of conventional graphite powder. This parameter change in the raw material enables the formation of graphitic films with superior alignment and conductivity properties that cannot be achieved through post-processing alone.
Solution Approach 2:
The invention performs preliminary orientation of graphite flakes before the graphitization process. By pre-aligning the graphite flakes in a controlled manner prior to heating, the graphene planes are positioned correctly from the outset, allowing the subsequent graphitization to preserve this orientation and achieve theoretically predicted properties.
2Temperature
If ultra-high temperature graphitization is applied to achieve high thermal conductivity, then the graphitic structure is formed, but the process becomes energy-intensive and expensive
Solution Approach 1:
The invention changes the starting material parameters by using pre-oriented graphite flakes with high crystallinity and specific orientation. This parameter change allows the graphitization process to occur at lower temperatures and shorter durations while still achieving high thermal conductivity, thereby reducing energy consumption and production costs.
3Ease of manufacture
If multiple grains of different orientations are present in graphite particles, then the material can be easily manufactured, but the average property is compromised and thermal conductivity is reduced to between 5-1800 W/mK
Solution Approach 1:
The invention applies local quality by ensuring that each graphite flake contributes its high thermal conductivity property in a consistent direction. By selecting and orienting individual flakes with specific crystallographic orientations, the local high-conductivity regions are aligned to produce macroscopic anisotropic material with superior thermal transport properties.
Solution Approach 2:
The invention creates a composite structure where multiple oriented graphite flakes are assembled into a film with uniform orientation. This composite approach maintains ease of manufacture through simple stacking and bonding of pre-oriented flakes, while achieving high thermal conductivity through the collective alignment of conductive pathways.
4Device complexity
If conventional methods are used to produce graphitic films, then the process is simple, but the film thickness and quality are limited
Solution Approach 1:
The invention segments the graphitic film into multiple thin layers of oriented graphite flakes. Each flake layer can be independently prepared and oriented, then stacked to build up the desired film thickness. This segmentation approach maintains process simplicity while enabling precise control over film thickness and quality through the stacking of multiple uniform layers.
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 process results in a highly oriented graphene film with thermal conductivity exceeding 1,500 W/mK, electrical conductivity over 12,000 S/cm, and tensile strength above 120 MPa, surpassing the properties of conventional materials in the same thickness range.
Implementation Method 1
preparing a dispersion of graphene oxide (GO) or chemically functionalized graphene (CFG) having GO or CFG sheets dispersed in a liquid medium, wherein the GO sheets contain an oxygen content higher than 5% by weight or the CFG sheets contain non-carbon element content higher than 5% by weight, and GO or CFG sheets are in an amount sufficient to form a liquid crystal phase in the liquid medium
Implementation Method 2
thermally reducing the dried GO or CFG layer at a first heat treatment temperature higher than 80° C. for a sufficient period of time to produce a porous layer of reduced GO or CFG
Implementation Method 3
further heat-treating the porous layer of reduced GO or CFG at a second heat treatment temperature higher than the first heat treatment temperature for a sufficient period of time to produce a porous graphitic film having an inter-plane spacing d002 less than 0.4 nm and the oxygen content or non-carbon element content less than 1% by weight
Implementation Method 4
heat-treating the pristine graphene layer at a temperature higher than 1,500° C. for a sufficient period of time to produce a graphitic film having an inter-plane spacing d002 less than 0.37 nm
Implementation Method 5
compressing the porous graphitic film to produce the highly oriented graphitic film
Implementation Method 6
The exfoliated graphite may then be subjected to high-intensity mechanical shearing (e.g. using an ultrasonicator, high-shear mixer, high-intensity air jet mill, or high-energy ball mill) to form separated single-layer and multi-layer graphene sheets
Implementation Method 7
The process begins with carbonizing a polymer film (e.g. polyimide) at a carbonization temperature of 400-1,000° C. under a typical pressure of 10-15 Kg/cm2 for 2-10 hours to obtain a carbonized material (48), which is followed by a graphitization treatment at 2,500-3,200° C.
Data Source
AI summary
A process for producing a highly oriented graphitic film, consisting of (a) preparing a dispersion having graphene oxide (GO) or chemically functionalized graphene (CFG) dispersed in a liquid to form a liquid crystal phase (but not in a GO gel state); (b) depositing the dispersion onto a supporting substrate to form a layer of GO or CFG under an orientation-inducing stress; (c) removing the liquid to form a dried GO or CFG layer having an inter-plane spacing d002 of 0.4 nm to 1.2 nm; (d) thermally reducing the dried layer at a first temperature higher than 100° C. to produce a porous layer of reduced GO or CFG; (e) further heat-treating the porous layer at a second temperature to produce a porous graphitic film having an inter-plane spacing d002 less than 0.4 nm; and (f) compressing the porous graphitic film to produce the highly oriented graphitic film.