The team of Professor Li Chenghui of Nanjing University "ACS AMI": High...

Background introduction

The ability to repair damage spontaneously, also known as self-repair or self-healing, is a unique function inherent in most organic life forms in nature
.

Inspired by the self-healing phenomenon of living organisms, in recent years, researchers have started from the molecular level and used physical or chemical strategies to give traditional materials the ability to quickly recover, and design and synthesize many new self-healing polymer materials.
The service life of materials, improving material safety, reducing waste and optimizing economic benefits provide an ideal way.

At present, both foreign aid self-healing materials based on microcapsules or microvessels ^1-3 , or intrinsic self-healing materials that rely on dynamic covalent bonds or non-covalent interactions have made great progress ^4-6
.

However, for the large-scale practical application of existing self-healing materials, there are still the following difficulties and challenges: ( 1 ) Most self-healing materials require external stimuli such as heating, light, and solvents to assist in the repair ; ( 2 ) Spontaneous repair at room temperature The repair speed is slow, and it often takes tens of hours or even days to complete the repair process; ( 3 ) The external environment interferes greatly with the self-repair process, and it is difficult to achieve under various unconventional environmental conditions ( aqueous phase, organic solvent, strong acid).
, Strong bases, oxidants, reducing agents, etc.
) self-repair

Article summary

Recently, the face of these scientific questions, School of Chemistry and Chemical Engineering Professor Li Chenghui team by using micro urea bond ( 0 .

26 wt% ) enhance the flexibility of polydimethylsiloxane (induction PDMS inter) polymer chain is wound and diffusion According to the strategy, a self-healing polymer network HPUrea cross-linked by physical reversible entanglement interaction was successfully prepared (Figure 1 )

Figure 1.

The structural composition of HPUrea , a polysiloxane polymer that can quickly and spontaneously repair in multiple environments .

main content

First, the author used the high molecular weight bis (3 -aminopropyl ) -terminated polydimethylsiloxane HPDMS-NH2 ( M _n = 20000) and the polycondensation reaction between hexamethylene diisocyanate HDI and succeeded in linear Introducing a small amount of urea bond units ( 0.

26 wt% ) into the PDMS chain , through which a trace amount of hydrogen bond interactions can induce a higher density of polymer chain entanglement, and a colorless, transparent and uniform polymer film HPUrea ( Figure 2a ) .
The successful synthesis of the material was confirmed by characterization methods such as infrared spectroscopy (Figure 2b ), nuclear magnetic and gel permeation chromatography .

Figure 2.

( a ) Transparency test of HPUrea in the visible light region; ( b ) Infrared spectrum test curve of raw material HDI and product HPUrea .

Subsequently, the author conducted a detailed test
on the mechanical properties of HPUrea , and first carried out a tensile test at different tensile rates .

When the stretching rate is 10 mm/min , the HPUrea polymer material can be slowly stretched to more than 70 times the original length , and when the stretching rate is increased to 200 mm/min , its elongation at break can still be maintained at 2000 Around

Figure 3.

Demonstration of the self-healing process of HPUrea samples at room temperature .

In order to visually test the self-healing properties of HPUrea , the author first demonstrated its cutting - contact - repair - stretching process at room temperature (Figure 3 )
.

The results show that after being damaged and repaired at room temperature for 30 minutes , it can withstand 500% of the tensile strain manually .
In addition, the author passed mechanical tensile tests on its performance in different environments (underwater, salt solution, oil phase, ethanol, acetone, dimethyl sulfoxide, strong acid, strong alkali, low temperature, strong oxidant, strong reducing agent).
The self-repair performance was quantitatively compared and analyzed .
As shown in Figure 4 , the mechanical properties of the damaged HPUrea sample after 30 minutes of repair in the above ten environments can be quickly restored to the initial level, and the corresponding self-repair efficiency can reach 63.
3~3.

FIG .
4 .
HPUrea in a self-healing in many different environments 30 min self-repairing efficiency of the mechanical tensile curve and the corresponding rear
.

Finally, based on the characteristics of the HPUrea a flexible base material, selected liquid metal gallium indium alloy having high electrical conductivity (eGain) as a conductive layer, coated by a cold way to obtain a successfully prepared having a " sandwich " structure Flexible electronic sensor HPUrea-EGaIn
.
Thanks to HPUrea’s excellent mechanical stretchability, various environmental stability and self-healing properties, HPUrea-EGaIn strain sensor has achieved the organic unity of flexibility, elasticity, stability, sensitivity and repairability, and has a great advantage in the field of flexible electronic devices.
Potential application value (Figure 5 )
.

Figure 5.
HPUrea-EGaIn strain sensor's multi-environment repairability and cycling stability test : ( a ) The test sample is immersed in a different pH environment - destruction - contact - repair process; ( b ) strain - resistance of the sensor after repair Response curve; ( c ) 1000 cycles test process of initial sample under 20% strain ; ( d ) Cycle stability test of sample after complete restoration under strong acid and ( e ) strong alkali environment .

references

1 KS Toohey, NR Sottos, JA Lewis, JS Moore and SR White, Nat.
Mater.
, 2007 , 6, 581-585.

2 RP Wool, Soft Matter , 2008 , 4, 400-418.

3 DY Zhu, MZ Rong and MQ Zhang, Prog.
Polym.
Sci.
, 2015 , 49, 175-220.

4 Y.
Yang and MW Urban, Chem.
Soc.
Rev.
, 2013 , 42, 7446-7467.

5 W.
Zou, J.
Dong, Y.
Luo, Q.
Zhao and T.
Xie, Adv.
Mater.
, 2017 , 29, 1606100.

6 S.
Wang and MW Urban, Nat.
Rev.
Mater.
, 2020 , 5, 562-583.

Original link
https://doi.
org/10.
1021/acsami.
1c06521