Background: silicone gel and elastomer have very low Tg (-122 C), excellent flexibility and adhesion at high temperature and low temperature, thus becoming an excellent sealant and adhesive. Because of the low surface energy, organosilicon is difficult to be wetted by water, which shows excellent waterproof performance. Therefore, this kind of material is widely used in the sealing of construction gap, and it is also particularly suitable for underwater applications, such as pipeline seals, ship coatings, etc. Traditional curing mechanisms of organosilicon include free radical curing, moisture curing (hydrolysis / condensation, room temperature vulcanization, RTV) and platinum catalyzed hydrogenation curing, but these curing processes can not be carried out under water. For example, in the process of tin catalyzed RTV curing, too much water will lead to the hydrolysis of crosslinker and failure; in the process of silicon hydrogenation curing, too much water will lead to the hydrolysis of SIH group The crosslinking efficiency is reduced. Therefore, silicone gel and elastomers must be solidified in the air before being applied underwater. The curing process varies from a few minutes to several days. If it is not cured, it will be applied underwater. Miserable results will be made. And the above curing mechanism generally needs heavy metal as catalyst, which is obviously not in line with the concept of green chemistry. Based on the above analysis, based on the above analysis, the research group of Michael A. Brook of McMaster University, Canada, based on the reaction of aldehydes and amino groups, achieved the rapid gel of silicone elastomers under water without catalyst. By adjusting the molecular weight of amino propyl siloxane (that is, the concentration of amino) and the type of small aldehydes, the performance of the elastomer can be adjusted conveniently. When formaldehyde was used as cross-linking agent in air, the gel time of siloxane with molecular weight of 3000 g? Mol-1 was only 4 S. In the underwater plugging experiment, the formaldehyde cross-linked siloxane mixture can plug the hole with a diameter of 1 cm within 5 s, and no leakage was observed within 14 days. The research results of this paper will have a very broad application prospect in the field of 3D printing and underwater sealing. The gelation and solidification diagram of ammonia propyl siloxane and aldehydes in air 1. the reaction of amino propyl silicon with aldehydes. (A) : glutaraldehyde, glu-t; (b): glyoxal, gly-t; (c): formaldehyde, for-t. Using aminopropylsiloxane, glutaraldehyde, glyoxal and formaldehyde as reactants, the researchers carried out cross-linking reaction in air without catalyst. It is found that the reaction rate between them is very fast, and the time needed to form gelling is related to the concentration of ammonia, aldehyde and the type of aldehyde. The gelation time of glutaraldehyde and glyoxal was 10-15 s and 30 s respectively. In contrast, when formaldehyde is used as crosslinking agent, the mixture can form gelling within 2 s. In addition to gelation time, the researchers determined the complete curing time of the mixture by tracking the increase of Young modulus. When the young modulus was not increased, the curing was complete. It is found that it takes about 3 hours for Gly (glyoxal elastomer) and Glu (glutaraldehyde elastomer) to fully cure, while only 1.5-2 hours for for for (formaldehyde elastomer) to fully cure in air. For glutaraldehyde system, the optimal [NH2]: [Cho] molar ratio is 1:2, glyoxal is 3:4, formaldehyde is 1:1. The elastomer prepared with this ratio has the best performance. Comparison of gelation time between ammonia propyl siloxane and aldehydes in air and water
Fig. 3. the rheological curves of emulsion in air (without solvent) or 50/50 wt 3000 g. Mol-1 amino propyl silane emulsion, where A: formaldehyde, B: B two aldehyde, C: glutaraldehyde, 50000 G. Mol-1 propyl silane and D: formaldehyde, E: B two aldehyde, F: Glutaraldehyde reaction. The researchers compared the gel reaction of organosilicon in air and water. It was found that the gelation rate of aqueous solutions of three aldehydes in air was very fast: when the amino siloxane with molecular weight of 3000 g? Mol-1 was cross-linked, the gelation time was less than 20 s (Figure 3A-C); with the increase of molecular weight from 3000 to 50000 g mol-1, the gelation time was highest to 532 s (Fig. 3D-F). Taking formaldehyde as an example, when the molecular weight of siloxane increases, the gelation time of formaldehyde system only slightly increases from 4 s to 16 s. The gelation time of glyoxal and glutaraldehyde system was longer after the molecular weight of siloxane was increased, which indicated that the reaction of formaldehyde to amino group was higher. The gel time of silicone in water is generally higher than that in air. When the molecular weight of organosilicon is 3000 g. Mol-1, the gelation time of formaldehyde, ethylene two aldehyde and glutaraldehyde in water is 12 s, 75 s and 21 s respectively. With the increase of molecular weight of organosilicon to 50000 g / mol-1, this time increased to 55 s, 605 s and 775 s. Experiment of silicone elastomer plugging under water
Fig. 4. (a) two syringes extrude formaldehyde or glutaraldehyde to solidify with aminopropylsiloxane; (b) extrude glutaraldehyde ("McMaster") or formaldehyde ("Chemistry") from the mixing syringe, and use the elastomer made of 3D printing (three times, film thickness 0.1cm); C: I) cut an opening of 5cm × 1cm in the polypropylene barrel, the barrel size is 42cm (W) x 29 cm (L) x 14.5 cm (H); ii) extrude formaldehyde based silicone elastomer during water flow; iii) the opening is completely sealed; IV) insert the plug into the hole with the syringe in a; V) water flows out of five holes; VI) inject sealant underwater; VII) no water flows out of the barrel. The researchers added 5% mole of propyl siloxane and glutaraldehyde in a double barrel syringe. Only two materials were manually allocated from the syringe, and two materials could be deposited on a layer by layer. The gel time of each extrusion layer was less than 15 s. In order to test whether the silicone elastomer can be formed under water, the researchers drilled five holes with a diameter of 1 cm at the bottom of a 1.5-litre polypropylene container. When filled with water, the water quickly discharged from the five holes with a flow rate of about 0.5 L · min-1. While filling the container with water, the researchers squeezed the formaldehyde / siloxane mixture out of the syringe under water, and the mixture was A white elastomer of 1.25 cm was formed in s, which blocked the hole and effectively prevented water from flowing out of the container. Although it took about 6 hours for organosilicon to fully cure in water, no leakage was observed in the container within 14 days after the elastomer was formed. Adhesion of silicone elastomer on different surfaces
Figure 5. Stress-strain curve of elastomer with higher adhesion to polar substrate. （A）：For-PDMS；（B）：Glu-PDMS。 The sample is pre strained (0.002 n) to 100% before starting to stretch. The researchers found that the silicone elastomers crosslinked by glutaraldehyde and formaldehyde can effectively bind to various surfaces. The adhesion properties of the elastomers to different surfaces were tested by tensile test. It is found that there is no significant difference in the fracture stress on the surface of plexiglass, polystyrene, glass and Teflon, but the fracture strain value is significantly different. The adhesion properties of materials with higher polarity (such as glass, plexiglass and polystyrene) are better than those of Teflon. The adhesion of glutaraldehyde cured elastomer is stronger than that of formaldehyde elastomer. Summary: in order to solve the problem that silicone elastomers can not be solidified underwater, the research team of Michael A. Brook of McMaster University, Canada, has successfully achieved the rapid gel and curing of silicone elastomers under water under the condition of no catalyst, using the amino propyl siloxane and formaldehyde, glutaraldehyde and ethyl two aldehyde as raw materials. It was found that formaldehyde and silicone had the most rapid reaction in the three kinds of small aldehydes. The gelation time of formaldehyde in air was only 4 S. When the molecular weight increased to 50000 G. Mol-1, the time increased slightly to 16 S. The gel time of organosilicon system was 12 and 55 s at 3000 and 50000 g mol-1 respectively. The formaldehyde / siloxane mixture can close the hole with a diameter of 1 cm in only 5 seconds under water, and it can keep water free for 14 days. About the author: Professor Michael A. brook is an expert in silicon chemistry, silica and organosilicon. He has made many achievements in scientific research, education and teaching. In 2016, he won the Frederic Stanley Kipping award of the American Chemical Society (ACS), the world's highest award in silicon chemistry, known as the Nobel Prize in the field of silicon chemistry. Professor brook has been nominated as the excellent teaching award and won the second prize by McMaster University Students' Union seven times. He is also the winner of the teacher president award of McMaster University. During the visit, he won many honors: he was awarded the title of outstanding visiting scientist by the highest scientific research institution in Australia and the federal scientific and industrial research organization in 2011; he was awarded the ETS of Irish Science Foundation in 2007 Walton Visiting Professor Award; 2003-2004 winner of the killa award of the Canadian Council of Arts and Sciences; 1996 winner of the collaboration award of the National Advisory Board of Canada and the National Institute of science and engineering; 1992-93 winner of the foreign expert award of the National Science Foundation of the Netherlands. He has published more than 100 academic papers in J. am. Chem. SOC. And other important chemical journals. Original link: https://onlinelibrary.wiley.com/doi/10.1002/adfm.202000737 advanced polymer science established "adhesive" and other communication groups, added small editors as friends (micro signal: polymer Xiang, please note: name unit Title Research direction), invited to join the group.
Source: polymer science frontier
Statement: only on behalf of the author's personal point of view, the author's level is limited, if there is any unscientific, please leave a message below for correction!
---Nanocellulose looking for the northern Century---
---Table interface tensiometer / contact angle tester to find Zhonghao Qingyuan---
Wechat plus group:
"Polymer science frontier" brings together 200000 experts and scholars, researchers and researchers in polymer field. We have established more than 80 comprehensive communication groups (including teachers, business executives, master's doctorate, North America, Europe, etc.), professional exchange groups (plastics, rubber and plastic elastomers, fibers, coating adhesives, inks, gels, biomedical polymers, polymer synthesis, membrane materials, Shi Moxi, nanomaterials, Characterization Technology, automotive polymers, foaming, polyimides) , antibacterial, bionic, tumor treatment).
Add editor in chief as a friend (wechat: polymer Xiang, please note: name unit Title Research direction) or long press QR code to add editor in chief as a friend and invite to the group.
Add a small wechat (please note: name unit Title Research direction)
Invite you to the discussion group
(add wechat QR code scanning)
Our microblog: polymer science frontier, welcome to interact with us.
Our QQ communication group: 451749996 (please note: name unit research direction)
Contribution recommendation cooperation: editor@polysci.cn