A strategy for enhancing mechanical properties of electrically controlled solid propellant via in-situ-induced microphase separation

Electrically controlled solid propellant (ECSP), a type of ionogels, has significant potential for working as a power source for missiles, satellites and spacecrafts. However, ECSP exhibits poor mechanical properties, which severely limit its industrial application. Here, we propose a strategy to enhance mechanical properties of ECSP via the combination of Hofmeister effect and microphase separation. First, during the freeze-thaw cycles process, 1,3-cyclohexanedione (CHD) and hydroxylamine nitrate (HAN) undergo oximation reaction by α-H to synthesize oxime groups in the acidic system. The consumption of hydroxylamine ions during the oximation reaction triggers the Hofmeister effect, facilitating the strong aggregation on polyvinyl alcohol (PVA) chains. Second, during the thermal curing process, the oxime groups undergo Beckmann rearrangement to form amide groups. Due to the strong aggregation of PVA chains, the spatial repulsion effect is increased, restricting the diffusion of amide substances formed by Beckmann rearrangement, thereby accelerating local supersaturation and inducing microphase separation. Such ECSP exhibits significantly enhanced mechanical properties, with tensile strength of 2.34 MPa, and elongation at break reaching 701 %. Remarkably, on the basis of the repeated on-off ignition character, its combustion properties are also improved compared to the control test specimen without CHD, with gas production increasing by ∼57 times, the combustion rate in N₂ atmosphere under pressure of 2 MPa rising by ∼2.9 times and the ignition delay time reducing by ∼4.3 time. The presented strategy offers potential applications in its propellant and serves as a reference for enhancing mechanical properties of ionogels in other fields.