In movies and TV shows, you can sometimes see a storyline in which intelligence agents write on paper with rice soup and send it out when it is dried. And the person who received the information, put this “white paper” in the iodine wine bubble, you can read the secret information on the paper. Writing on ordinary paper with rice soup and using iodine wine is actually a traditional encryption decryption technique.
The principle is that rice soup contains starch, and starch will turn blue when it comes to iodine, which is determined by the characteristics of the molecular structure of the starch itself. This type of encryption decryption technology is of great significance for information protection, security and data storage.
Find more, more secure “color-changing” inks
In recent years, researchers have studied the application of photoluminescent materials such as organic dyes, quantum dots and doped materials with rare earth elements in the fields of information protection, anti-counterfeiting and safety. In general, researchers add photoluminescent materials to solvents to prepare photoluminescence safety inks that can be used for printing and printing.
But this photoluminescent safety ink has more disadvantages. For example, the formulation parameters of inks are usually optimized before use; some inks containing organic dyes have poor light stability; the synthesis of some quantum dot and niobium elementdos doping materials can introduce heavy metals that can cause potentially toxic and environmental problems; although photoluminescent safety inks are invisible to the human eye in ambient light. However, it can be easily detected in ultraviolet or near-infrared light.
Therefore, the safety level of photoluminescence safety inks needs to be further improved in order to be better used for the protection of secret information.
In recent years, the stimulating response material sparking color change through microstructure change has attracted wide attention. The irritants used to trigger color changes include light, steam, mechanical forces, pH, temperature, electric field, magnetic field, etc. However, many stimuli are not readily available in daily life, making it difficult to decrypt encrypted information quickly and easily in practice.
New secret paper: soft fire-resistant roasting, but also hide information
Recently, the scientific research team led by Zhu Yingjie of the Shanghai Silicate Research Institute of the Chinese Academy of Sciences, based on the research work of the new refractory paper, developed a new type of secret paper that can be used for rapid encryption and rapid decryption of secret information, using hydroxyapatite ultra-long nanowires and plant fiber composites.
The new type of secret paper looks as white as plain paper. Its main component is hydroxyapatite. Hydroxyapatite is a natural mineral and a major inorganic component of human bones and teeth. In our human bones, we contain about 70% hydroxyapatite and tooth enamel contains up to 90% hydroxyapatite.
Figure 1 New secret paper based on hydroxyapatite ultra-long nanowires
Zhu Yingjie’s team synthesized ultra-long nanowires of hydroxyapatite, which is about 10 nanometers in diameter and can be several hundred microns in length. It is very fine, about one-tenth of a millionth of a person’s hair. Looking under a high-scanning electron microscope, you can see that these lines can bend naturally, looking like long, thin, soft noodles, with good flexibility.
Figure 2. The new compact paper has good flexibility and can be bent, twisted and folded at will
In recent years, Zhu Yingjie’s team has adopted hydroxyapatite ultra-long nanowires as the main construction material, developed more than 20 kinds of new refractory paper with different functions, and has good application prospects in special fire resistance, functional refractory, flame retardant, thermal insulation, electronic information, energy, environmental protection, biomedical and other fields.
White vinegar as ink, cheap and useful
So, to achieve the function of encryption decryption, this kind of paper with special ink? That’s right, this invisible safety ink is white vinegar. Write with white vinegar on the paper, and when it is dried, it becomes ordinary “white paper”. After a few seconds of burning, the information on the paper becomes clear.
Video 1. Secret information written with white vinegar on new secret paper is invisible to the human eye in visible light, but it is revealed and clearly visible seconds after the fire.
The process is simple and the principle is not complicated. This is because the new type of secret paper is made from hydroxyapatite ultra-long nanowires, plant fibers, two different substances composite. Hydroxyapatite ultra-long nanowires are resistant to high temperatures and fires, while plant fibers are easy to burn.
When roasting paper with fire, the plant fiber part does not burn completely, producing black carbon particles. These black carbon particles are covered in hydroxyapatite-length nanowires, shifting the color of the paper from white to gray-black.
And because the acetic acid molecules in white vinegar have a catalytic effect, the plant fibers in the area written by white vinegar are removed by accelerating the combustion of oxidation oxidation to produce carbon dioxide gas, and there is basically no black carbon particles left on the paper. This leads to areas written in white vinegar that, after burning, show the color of hydroxyapatite ultra-long nanowires or white.
That is to say, the new secret paper with fire only a few seconds, written with vinegar text and patterns appear white, not with vinegar writing areas appear black, so that the new secret paper in the secret information is clearly revealed.
Figure 3. You can use a variety of pens with white vinegar as a writing tool, white vinegar as a security ink to write secret information on the new secret paper (encryption process);
This secret writing technology is simple but very practical, because white vinegar as ink, cheap and do not need to do further processing in advance, decryption process is fast and convenient, with a fire roaston on the line. Therefore, this new type of secret paper has good application prospects in the fields of secret information protection, anti-counterfeiting and security.
Related research on “Secret Paper with vinegar as an Invisible Security Ink and Fire as a Decryption Key for Information Protection” Table in the journal European Chemistry , an international leading academic journal ( Chemistry – A European Journal, 2019, 25, 10918-10925).