NCAP PDLC (Liquid Crystal Window)
SFI NCAP (Nematic Curvilinear Aligned Phases) PDLC technology relies on a polymer matrix film containing droplets of liquid crystal.
This film is fabricated by coating a water-based fluid using conventional coating processes. Today it is used as Switchable Window (also named Liquid Crystal Window or PDLC Smart Glass).
The main advantages of our Liquid Crystal Window are:
- Best transparency compared to all other film manufacturers.
- Consistency over batches.
- Electro-Optical long last stability.
- Easy to customize.
Principles of Liquid Crystal Window
Harnessing the Characteristics of Liquid Crystals Window.
The secret of the transformation between clear or translucent PDLC Smart Glass is found in the Liquid Crystal Sheet (figure 1). The randomly aligned Liquid Crystal molecules is such that it disperses light. When voltage is applied, however, these same molecules arrange themselves in a specific direction in such a way as to permit parallel light to pass through the glass (figure 2).
SFI PDLC Smart Glass is a laminated glass that contains Liquid Crystal sheet between two pieces of glass.
The transparency of glass is controlled by utilizing the properties of Liquid Crystal whose molecules align with voltage. SFI's Liquid Crystal has a property, which is randomly aligned LC molecules align with voltage (figure 3), the light can not pass through at randomly aligned phase while it can easily pass through when LC molecules align. This the secret from clear to translucent phenomenon.
Principles of SFI NCAP PDLC
|SFI Extra Clear Liquid Crystal Window||Other PDLC|
Non-Spherical Micro-droplet Morphology
|Spherical Micro-droplet Morphology|
Always requires matrix & LC index-matching improvements
Matrix Structure - PVA
Matrix Structure - UV cureable
|Very Low Matrix Plasticization|
Due to incompatibility of LC with solvent (H2O), almost all LC remains in micro-droplets & does not affect the optical performance or mechanical properties of matrix.
High Matrix Plasticization
|Possible Dye doping|
Due to micro-emulsion process, almost all dyes remain in LC droplets, which allows for making colored film products with high optical contrast, i.e. On-state transparency & Off-state darkness.
Not possible Dye doping
SFI Extra Clear NCAP PDLC
Historically, the development of NCAP PDLC based technology has arisen out of the extensive work on composite films of liquid crystals and polymers. These systems were the subject of intense work for over a decade in the mid-1980’s through mid-1990’s, attracting the attention of major display companies, small start-ups, and numerous academic groups. These systems went by a variety of names: NCAP, PDLC, PNLC, liquid crystal gels, and others. All these systems were based around the common theme of a liquid crystal cell in which a polymer network produced droplets or domains of liquid crystal. The optical properties of the cell depended on the alignment of the liquid crystals within each domain, with this alignment being determined by the balance of local alignment forces by the bounding polymer network, and any applied electric field. Nearly all of these devices could be switched between a turbid, scattering state and a transparent, non-scattering state. Over 1,000 technical papers and patents were published during the history of these materials.
There were two major material systems used for the fabrication of these systems. The first relied on a single-phase solution of the liquid crystal and the polymer precursor that was induced to phase separate into a polymer network and liquid crystal domains. Photo-polymerization of reactive monomers and oligomers was by far the most popular pathway, given the versatility of photo-polymerization chemistry and ease of processing. The vast majority of groups working on liquid crystal dispersion displays used phase separation methods to form their devices.
These phase separation methods, though, possessed several fundamental limitations. For the purposes of this background, the most serious flaw is a serious incompatibility with dichroic liquid crystal materials. Dichroic dyes tend to absorb light very strongly in the ultraviolet and visible regions of the spectrum, and so significantly reduce the amount of radiation available to initiate the photo-polymerization process. These dyes also tend to remain in the polymeric matrix and as such are un-switchable, causing relatively high adsorption even when the material is powered.
Any un-switched dye molecules will greatly degrade. More importantly, dichroic dyes can interfere with the actual polymerization chemistry through reaction with the growing polymers used to induce phase separation. Rather than being cured in seconds, dichroic dyes force irradiation times of an hour or more, totally impractical in manufacturing.
Dichroic dyes dissolved in a liquid crystal provide the most attractive route for the fabrication of smart films for energy saving and other innovative based products. The absorbance of the dye depends on the alignment of the dye molecules, which tends to follow the alignment of the liquid crystal. In this way, dichroic based devices provide both a controllable absorption and a controllable scattering effect, leading to an attractive smart film product.
The other major approach towards dispersed liquid crystals used a water-based emulsion to form the composite film. An emulsion of liquid crystal droplets was dispersed into a water-based, film-forming polymer. This electro-optical “paint” was coated onto a conductive substrate, dried, and then laminated to a counter electrode. Both scattering mode devices (made with liquid crystal mixtures) and dye-based devices (using liquid crystals containing a dichroic dye) could be constructed with this system.
It became possible to make devices using either the photo-polymerization or emulsion approach. Interestingly, nearly 100% of the groups working on liquid crystal dispersed systems took up photo-polymerization systems as their development platforms. The barrier to entry for making photo-polymerization-based systems was relatively low. Several good recipes for photo-polymerized liquid crystal systems had been published, and the infrastructure required to make these systems was small. The ability to make a switchable scattering system was still relatively novel and applications in switching windows and in projection displays appeared attractive.
In contrast, the emulsion-based NCAP systems are difficult systems to control, and required a reasonably significant infrastructure to make and characterize emulsions. Other groups tended to shy away from these systems. No publications (including the book Liquid Crystal Dispersions) provided a recipe for a practical emulsion-based system that could be easily built and provide good performance. Up to date there is no clear pathway for competitors to follow.
A key point is that while there has been an intense amount of effort on liquid crystal/polymer dispersions by numerous groups, the core technology that has been the focus of this development is poorly-suited for the construction of innovative platform for smart films. The know-how that has been generated on scattering-mode liquid crystal/polymer composites cannot be applied to compete effectively with the NCAP-based platform.
Even after 25 years of development, there is no practical approach to manufacture a dichroic based liquid crystal composite system by photo polymerization-based methods. Dichroic dyes strongly absorb UV light, and they readily interfere with the polymerization chemistries used in PDLC systems. For the foreseeable future, dichroic-based liquid crystal dispersion for innovative smart films will remain practical only in emulsion-based systems.
We produce the SFI2 Extra Clear in roll to roll process (figure 4).