Double locked: Polymer hydrogels secure confidential information

Date:
March 1, 2022
Source:
Wiley
Summary:
The development of highly secure but simple and inexpensive
encryption technology for the prevention of data leaks and forgeries
is decidedly challenging. A research team has now introduced a
'double lock' based on thermoresponsive polymer hydrogels that
encrypts information so that it can only be read at a specific
window in temperature and time.



FULL STORY ==========================================================================
The development of highly secure but simple and inexpensive encryption technology for the prevention of data leaks and forgeries is decidedly challenging. In the journal Angewandte Chemie, a research team has
introduced a "double lock" based on thermoresponsive polymer hydrogels
that encrypts information so that it can only be read at a specific
window in temperature and time.


==========================================================================
In addition to digital encryption methods, physical methods play an
important role. Their decoding is typically based on external stimuli such
as light or heat. Multiple stimuli offer more security, but make reading
the data cumbersome and complex. "Addition of the time domain greatly
raises the chance to achieve the unity of security and simpleness,"
according to the team led by Zhikun Zheng, Xudong Chen, and Wei Liu,
at Sun Yat-sen University (Guangzhou, China). "We were inspired by the
baking of bread: delicious bread can only be produced if the baking
temperature is not too low or too high and the baking time is not too
short or too long." For their novel "double encryption system" they
use thermoresponsive polymer hydrogels -- cross-linked chain molecules
with water incorporated into their "gaps." Above or below a specific temperature, the clear gels become opaque due to partial unmixing. There
are LCST and UCST gels, which have lower or upper critical solution temperatures, respectively. The phase retention and critical temperature
can be controlled via the content of -CO-NH2 groups in the main chain
of the polymer hydrogels. The density of cross-linking determines the
rate of the phase transition.

As an example of a locked label, the team used transparent acrylic plates
with grooves in the pattern of a QR code. Three different gels were put
in defined areas of the pattern; a UCST gel with a phase change around
40 DEGC, and two LCST gels with a phase change at 33 DEGC (one with a
fast phase transition, and one with a slow phase change). Below 20 DEGC,
the UCST gel is opaque, but highly shrinking. The pattern is deformed
and unreadable. Between 20 and 33 DEGC, it swells and the part of the
code formed by this gel becomes readable.

The second part of the code, formed by the "fast" LCST gel, still cannot
be read. Only heating to over 33 DEGC makes both LCST gels opaque. Now the timing comes into play; only the pattern of the "fast" LCST gel has the
correct second part of the information. At 37 DEGC, it becomes readable
after about half a minute and the complete code can be read. However,
a brief three minutes later, the "slow" LCST gel becomes opaque and
adds false information that makes the codes unreadable. Above 40 DEGC,
both LCST gels become opaque simultaneously.

In addition, the UCST gel becomes transparent and unreadable.

This encryption can only be decoded if the specific temperature and
time windows are known. The source of heat for decoding in this example
could be an infrared lamp, a water bath, a hair dryer, or even the human
body. If sealed to prevent the evaporation of water, these inexpensive
labels are theoretically suitable for long-term use.

========================================================================== Story Source: Materials provided by Wiley. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Dongyang Lou, Yujing Sun, Jian Li, Yuanyuan Zheng, Zhipeng Zhou,
Jing
Yang, Chuxuan Pan, Zhikun Zheng, Xudong Chen, Wei Liu. Double
Lock Label Based on Thermosensitive Polymer Hydrogels for
Information Camouflage and Multilevel Encryption. Angewandte Chemie
International Edition, 2022; DOI: 10.1002/anie.202117066 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220301131039.htm

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