Composite Electrophoretic Particles for Low Haze Variable Transmission Films
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Solution Overview
Problem
Existing variable transmission devices face challenges in achieving low haze while maintaining effective optical switching rates, as smaller pigment particles are difficult to control and larger particles increase haze due to scattering.
Innovation Solution
The use of charged composite particles, such as manganese ferrite black spinel, copper chromite black spinel, and carbon black, coated with a polymeric material, which are matched in refractive index to the binder and suspending fluid to minimize light scattering, allowing for controlled movement under an electric field and reduced haze.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If smaller pigment particles are used to reduce haze, then light scattering is reduced and haze decreases, but electrophoretic control becomes difficult and switching speed decreases
Solution Approach 1:
The patent uses composite particles consisting of a core pigment material (such as carbon black or metal oxides) coated with a polymer shell. This composite structure allows the particle to maintain the light-absorbing properties of the pigment core while the polymer coating provides a surface that responds effectively to electrophoretic fields, thus resolving the contradiction between reducing haze and maintaining controllability
Solution Approach 2:
The patent optimizes the size parameter of the composite particles to a specific range (0.5-5.0 micrometers) and adjusts the refractive index parameter by selecting appropriate polymer materials. These parameter changes allow the particles to minimize light scattering while maintaining effective electrophoretic response, thus reducing haze without sacrificing control
2Ease of operation
If larger pigment particles are used to improve electrophoretic control and switching speed, then ease of operation improves, but light scattering increases and haze increases
Solution Approach 1:
The composite particle structure with polymer coating allows for larger particle sizes (0.5-5.0 micrometers) that are easily controlled by electrophoretic fields, while the polymer material is selected to match the refractive index of the suspending fluid, minimizing light scattering and haze despite the larger size
Solution Approach 2:
The patent changes the refractive index parameter of the particle by selecting specific polymer materials that match the suspending fluid, allowing larger particles to be used without increasing haze. Simultaneously, the particle size parameter is optimized to a range that provides good electrophoretic control
3Illumination intensity
If pigment particles are used for light attenuation, then optical switching is achieved, but light scattering occurs and haze is generated
Solution Approach 1:
The patent changes the refractive index parameter of the composite particles by selecting polymer materials that match the suspending fluid, minimizing light scattering. Meanwhile, the pigment core maintains its light-absorbing properties for effective attenuation, thus achieving optical switching without generating haze
Solution Approach 2:
The composite structure separates the functions: the pigment core provides light absorption for attenuation while the polymer coating provides refractive index matching to minimize scattering. This functional separation allows effective light attenuation without haze generation
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
This solution enables bistable electro-optic media with low haze and efficient optical switching, balancing particle size for improved control and reduced scattering, thus enhancing the performance of variable transmission devices.
Implementation Method 1
the charged composite particles move through the suspending fluid under the influence of an electric field
Implementation Method 2
The nature of the light scattering is also affected by the size of the aggregates of these particles. As the aggregates increase in size, more and more of the light is scattered in the forward direction. This scattered light results in the appearance of haze in the window.
Implementation Method 3
Each of the binder, the charged composite particles, and the suspending fluid have an index of refraction, and a difference between the index of refraction of the composite particles and at least one of the binder and suspending fluid is less than or equal to 0.05 at 550 nm
Data Source
AI summary
An electro-optic media includes either a plurality of microcapsules in a binder, a polymeric sheet containing sealed microcells, or droplets in a continuous polymeric phase. Each of the microcapsules, microcells, or droplets contain a dispersion that includes a plurality of charged composite particles and a suspending fluid, and the charged particles move through the suspending fluid under the influence of an electric field. The composite particles include one or more types of pigment particles that are at least partially coated with a polymeric material. Each of the binder, polymeric sheet, continuous polymeric phase, the charged composite particles, and the suspending fluid have an index of refraction, and a difference between the index of refraction of the composite particles and at least one of the binder, polymeric sheet, continuous polymeric phase, and solvent is less than or equal to 0.05 at 550 nm.