Glassy polymers are extremely difficult to self-heal below their glass transition temperature (Tg) due to the frozen molecules. Here, we fabricate a series of randomly hyperbranched polymers (RHP) with high density of multiple hydrogen bonds, which showTgup to 49 °C and storage modulus up to 2.7 GPa. We reveal that the hyperbranched structure not only allows the external branch units and terminals of the molecules to have a high degree of mobility in the glassy state, but also leads to the coexistence of “free” and associated complementary moieties of hydrogen bonds. The free complementary moieties can exchange with the associated hydrogen bonds, enabling network reconfiguration in the glassy polymer. As a result, the RHP shows amazing instantaneous self-healing with recovered tensile strength up to 5.5 MPa within 1 min, and the self-healing efficiency increases with contacting time at room temperature without the intervention of external stimuli.
To
mimic the velocity-sensitive ability of the human skin, we fabricate
a class of “solid–liquid” elastomers (SLEs) by
interpenetrating polyborosiloxane (PBS) with polydimethylsiloxane
(PDMS). PBS forms a dynamic network through boron/oxygen dative bonds,
while PDMS is covalently cross-linked to form a permanent network.
The permanent network affords a scaffold for the dynamic network,
endowing SLEs with high elasticity and structural stability, thereby
overcoming the inherent drawbacks such as fluidity and irreversible
deformation of conventional solid–liquid materials. Meanwhile,
the dissociation and association of the dynamic network is time-dependent.
Thus, the modulus of SLEs varies with strain rates, and if the SLEs
contain carbon nanotubes, their electric conductivity is also responsive
to strain rates. This property can be utilized to fabricate skin-like
sensors with the ability to distinguish different contact velocities.
Moreover, the dynamic network can dissipate energy and be repaired,
leading to the high stretchability and self-healing performance of
SLEs.
Growing
interest has been received in metallic foams for their
combined features of metals and porous structures. Coating metals
on polymers have been the most prevalent method to fabricate hybrid
metallic foams to inherit both the merits of metals and the mechanical
flexibility of polymers. However, direct coating metals on foams is
challenging and requires tedious synthesis, such as electrolysis and
chemical reduction. This work reported a facile strategy to build
hybrid metallic foams via in situ foaming of liquid metals (LM) and
polyurethane. The fluidity and incompatibility of LM with porous polyurethane
allow the coating of LM on polymers. LM-Foams exhibit high electrical
conductivity (3.9 × 104 S/m), low density (ρ
< 1 g/cm3), phenomenal elasticity (recover at 95% strain),
and excellent mechanical stability (stable with 1000 compressive cycles).
Interestingly, the ease of deformation for fluidic fillers in elastic
polyurethane generates additional resistive change under pressure,
showing unique sensory behaviors which were not observed in conventional
conductive foams, such as high response sensitivity (gauge factor
>25), short response time (202 ms), and outstanding electrical
stability.
The nonuniform size distribution of pores leads LM-Foams to show unusual
position-dependent sensitivity, enabling advanced applications as
password pads and electrical protection foams.
Liquid metal (LM) is used as fillers gradient dispersed in polymer matrix to prepared LM fiber. Such LM fiber showed distinguished thermally programmable shapes and electrical conductivities.
Metal–polymer composites (MPCs) with combined properties of metals and polymers have achieved much industrial success. However, metals in MPCs are thought to be ordinary and invariable electrically conductive fillers in supportive polymers to show limited use in modern technologies. This work that is disclosed here, for the first time, introduces stimuli‐driven transition from biphasic to monophasic state of liquid metal into polymer science to form dynamic soft conductors from the binary metal–polymer composites. The binary metal that exhibits temperature‐driven reversible transition between solid and liquid states via a biphasic state is fabricated. A conducting stretchable polymer composite is developed using the judiciously chosen biphasic binary metal that undergoes conductor to insulator transition upon stretching. Insulating stretched films become conducting upon heating. A “tube” model elegantly describes such distinctive deformation/temperature‐dependent behaviors. Moreover, the conducting polymer composite shows decrease in its resistance upon increasing the sample temperature. The resistance can be tuned from 1 to 108 Ω depending on the state of binary metal in the phase diagram. This work would build the intimate and interesting connection between metal phases and polymer science toward next‐generation soft conductors and beyond.
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