CCAs provide dispersity and suspension to particles because the hydrophobic side of the CCA dissolves and disperses in nonpolar solvents, and the hydrophilic side is adsorbed to the particles while CCAs assemble in reversed micelles RMs so that the sedimentation and agglomeration would not happen with particles.
When an external electric field is applied, the separation of electronic ink and RMs occurs. Then the particles can move around with specific direction. The rheology of the electronic ink particles within the micro-chamber is really complex. One of the strategies is only reducing the viscosity of suspending liquid while applying the voltage, and to recover the viscosity after removing the voltage, which is called the inversed electrorheological IER effect.
Another strategy is to use liquid crystal to activate charging and optimize the IER effect. The mobility of E Ink is much better than regular ink. Bistability freezes the distribution of particles in place after removing the external driving voltage. At this time, particles are acted upon by many forces, such as buoyancy, van der waals force, coulombic force, frictional force, gravity, and solubility.
This is the balance that keeps the particles in the same place and the reason why E-Ink saves so much power between switching pages. However, the electric field of opposite particles could cause the degeneration of grayscale. We can achieve this multi-grayscale by using pulse amplitude modulation PAM , controlling the polarity and the amplitude of the voltage, or pulse width modulation PWM , controlling the polarity and the duration of the voltage.
Now we understand these technological challenges that E Ink is facing. It is a one-pigment system which means only 1 color can be shown. The black pigment could move to the side and the capsule would show a transparent area when a charge is applied. One pigment ink system. Each microcapsule contains negatively charged white particles highly scattered particles and positively charged black particles light absorbing particles suspended in a clear fluid.
When an external positive or negative electric field is applied, corresponding particles move to the top or the bottom of the microcapsule. Then the viewer can see the surface spot as black or white. This two pigment system is more challenging because both two sets of particles must to be surfaced treated to avoid agglomeration.
Two pigment ink system. This ink was engineered specifically for Electronic Shelf Labels ESL and is offered in black, white and red, and black, white and yellow. In other words, E-Ink is just one specific kind of E-Paper technology. The Pebble smartwatch is arguably the most popular example of an E-Paper display that doesn't use E-Ink.
Instead, it uses an extremely low-power LCD display with a reflective layer that looks like paper. Other technologies include Mirasol and Electrowetting, but these have generally been relegated to niche usage. In an E-Ink display, a clear fluid is used to suspend millions of tiny capsules filled with black and white pigment.
The black pigment is negatively charged while the white pigment is positively charged, and the fluid layer is sandwiched between two electrode layers which are divided up into regions. Each region is one "pixel" in the display. This whole process is called electrophoresis.
Depending on how the electrode layers are charged, the ratio of pigment in each region changes, and that ratio is what products varying degrees of grayscale on the screen. So when the bottom electrode creates a positive electric field, the positively-charged white pigment is pushed to the top of the fluid layer, thus obscuring the negatively-charged black pigment that moves to the bottom of the fluid layer.
Together, all of the white pigment appears as a white pixel. Conversely, when the bottom electrode creates a negative electric field, the negatively-charged black pigment is pushed to the surface of the capsule, thus obscuring the white pigment. This results in a black pixel on the display. But when the bottom electrode creates both positive and negative electric fields, a mixture of black and white pigment is pushed to the surface of the capsule, resulting in a shade of gray that can be darker or lighter depending on how much white and black is on display for that pixel.
Unlike an LCD display, which requires constant power to keep the contents of the display on screen, E-Ink only requires power to change the polarity of electrodes on a per-region basis.
This means that your e-reader only uses power when it turns pages, and that's how an e-reader can last for up to one month on a single charge. E-Ink devices can reduce power consumption even more by only changing the pixels that need to be changed per page turn. In other words, if a particular pixel stays black from one page to the next, nothing needs to be changed and no power needs to be expended.
However, over time, some pixels may become stuck and refuse to change even with a new polarity, and this results in an imprint of text which stays even after the page has been turned. This phenomenon is known as "ghosting" and is usually fixed by a full-page refresh. That's why every so often the screen flashes completely black, then white, then back to the page. E-Ink's reflective nature makes it perfect for reading in bright light, but because it can't emit any light by itself, it can't be read in the dark.
In earlier models, reading in the dark meant using a lamp or some other external light source, just as you would with a regular paper book. Nowadays, upmarket e-readers have a built-in lighting feature which lets you to read in the dark. Lighting is also useful during the daytime when you need to adjust contrast. E Ink displays are referred to as "reflective displays. In an E Ink display, no backlight is used; rather, ambient light from the environment is reflected from the surface of the display back to your eyes.
As with any reflective surface, the more ambient light, the brighter the display looks. This attribute mimics traditional ink and paper, and users of E Ink displays have said that they do not have the same eye fatigue as with LCDs when reading for long periods of time. Therefore, eliminating the need for a backlight significantly increases the battery life versus using a traditional LCD.
0コメント