Liquid Crystal-Based Organosilicone Elastomers with Supreme Mechanical Adaptability.

Zhe Liu,Wei Chen,Hao Zhang,Hua Wang,Jinghao Hao,Chuanjian Zhou,Xiao Cheng,Yuqi Xiong

doi:10.3390/polym14040789

Zhe Liu, Wei Chen + Show 6 more

Open Access

https://doi.org/10.3390/polym14040789

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Abstract

Elastomers with supreme mechanical adaptability where the increasing stress under continuous deformation is significantly inhibited within a large deformation zone, are highly desired in many areas, such as artificial muscles, flexible and wearable electronics, and soft artificial-intelligence robots. Such system comprises the advantages of recoverable elasticity and internal compensation to external mechanical work. To obtain elastomer with supreme mechanical adaptability, a novel liquid crystal-based organosilicon elastomer (LCMQ) is developed in this work, which takes the advantages of reversible strain-induced phase transition of liquid crystal units in polymer matrix and the recoverable nano-sized fillers. The former is responsible for the inhibition of stress increasing during deformation, where the external work is mostly compensated by internal phase transition, and the latter provides tunable and sufficient high tensile strength. Such LCMQs were synthesized with 4-methoxyphenyl 4-(but-3-en-1-yloxy)benzoate (MBB) grafted thiol silicone oil (crosslinker-g-MBB) as crosslinking agent, vinyl terminated polydimethylsiloxane as base adhesive, and fumed silica as reinforcing filler by two-step thiol-ene “click” reaction. The obtained tensile strength and the elongation at break are better than previously reported values. Moreover, the resulting liquid crystal elastomers exhibit different mechanical behavior from conventional silicone rubbers. When the liquid crystal content increases from 1% (w/w) to 4% (w/w), the stress plateau for mechanical adaptability becomes clearer. Moreover, the liquid crystal elastomer has no obvious deformation from 25 °C to 120 °C and is expected to be used in industrial applications. It also provides a new template for the modification of organosilicon elastomers.

Highlights

Elastomers with supreme mechanical adaptability have been used and developed for several years [1,2,3], which have recoverable large deformation capacity, and ability to compensate external work during continuous deformation [4,5]
Compared to the traditional liquid crystal elastomers synthesized by hydrosilylation reaction using Pt complex catalysts, our technology has three important advantages: (1) it avoids costly metal platinum catalyst and the reaction conditions are milder and more convenient [33,34]; (2) the hydrosilylation reaction usually results in a mixture of Markovnikov and anti-Markovnikov addition products, which complicate the characterization of the product [35], but thiol-ene “click” reaction is difficult to produce markovnikov addition product [36]; (3) compared to the previous one-step strategy [37,38], we can improve the mechanical strength of the elastomers to more than 4 MPa by using the reinforcing filler
Compared with the traditional thermal deformation liquid crystal elastomers, the LCMQs in this work have no obvious deformation from 25 ◦C to 120 ◦C (Figure S4), which is critical for industrial applications

Summary

Introduction

Elastomers with supreme mechanical adaptability have been used and developed for several years [1,2,3], which have recoverable large deformation capacity, and ability to compensate external work during continuous deformation [4,5]. We developed a new method for preparing liquid crystal-based organosilicon elastomers with excellent mechanical adaptability and strength. Compared to the traditional liquid crystal elastomers synthesized by hydrosilylation reaction using Pt complex catalysts, our technology has three important advantages: (1) it avoids costly metal platinum catalyst and the reaction conditions are milder and more convenient [33,34]; (2) the hydrosilylation reaction usually results in a mixture of Markovnikov and anti-Markovnikov addition products, which complicate the characterization of the product [35], but thiol-ene “click” reaction is difficult to produce markovnikov addition product [36]; (3) compared to the previous one-step strategy [37,38], we can improve the mechanical strength of the elastomers to more than 4 MPa by using the reinforcing filler. The liquid crystal-based organosilicon elastomers were tested for tensile strength and elongation at break according to the GB/T528-2009 standard with a loading speed of 500 mm/min and the gauge length of 20 mm.

Synthesis of Crosslinker

Synthesis of Crosslinker-g-MBB

Results and Discussion

Mechanical Adaptability of MQ 1 and the LCMQs

The Viscoelastic Properties of MQ 1 and the LCMQs

Conclusions