Thermo‐Responsive Jamming of Nanoparticle Dense Suspensions towards Macroscopic Liquid–Solid Switchable Materials

Abstract

Nanoparticle aggregation for constructing functional materials has shown enormous advantages in various applications. Most efforts focused on ordered nanoparticle aggregation for specific functions but were often limited to irreversible aggregation processes due to the thermodynamic equilibrium. Herein, we report a reversible disordered aggregation of SiO2‐PNIPAAm nanoparticles (SPNPs) through thermo‐responsive jamming, obtaining smart liquid–solid switchable materials. The smart materials can display a switch between liquid‐like state and solid‐like state responding to a temperature change. This unique macroscopic behavior originates from the reversible disordered aggregation modulated by temperature‐dependent hydrophobic interactions among the SPNPs. Notably, the materials at the solid‐like state show anti‐impact properties and can withstand the impact of a steel sphere with a speed of 328 cm s−1. We envision that this finding offers inspiration to design smart liquid–solid switchable materials for impact protection.

Two‐Dimensional Polymer Networks Locking on Inorganic Nanoparticles

“…Tunable surface functionalization is critical for the processing, long‐term storage, applications of inorganic NPs [56–60] . Inorganic NPs can be functionalized with a variety of ligands, such as small molecules, [61] surfactants, [62] dendrimers, [63] polymers, [64] and biomolecules, by covalent or non‐covalent conjugation between inorganic NPs and ligands.…”

Thermally Responsive Fibers for Versatile Thermoactivated Protective Fabrics

“…[11][12][13][14] The addition of responsive nanofillers is an alternative approach because nanofillers significantly improve the mechanical strength during the hardening process, but the complex preparation method and easy agglomeration substantially limit their scalability and applicability. [15][16][17][18] Recently, inspired by thermostable proteins, researchers have synthesized an isovolumetric self-adaptive polymer to solve the poor controllability, long response time, and low response level. [19] Nevertheless, continuous processing of self-adaptive materials to fibers is difficult owing to the influence of viscosity, solubility, and molecular weight.…”

Entropy‐Mediated Polymer–Cluster Interactions Enable Dramatic Thermal Stiffening Hydrogels for Mechanoadaptive Smart Fabrics

“…However, such a design usually leads to reduced modulus change amplitudes (generally <20 times) and the maximum moduli at the stiffened state are also low (<1 MPa). Grafting LCST‐type polymers on nanoparticles to thermally induce percolating reinforcing network or particle jamming may greatly enhance material's mechanical strength at the stiffened state, yet the complicated manufacturing and elaborate control over particle assemblies largely limit their extensive applications [4, 19] . As an alternative, Gong et al.…”

“…Grafting LCST-type polymers on nanoparticles to thermally induce percolating reinforcing network or particle jamming may greatly enhance material's mechanical strength at the stiffened state, yet the complicated manufacturing and elaborate control over particle assemblies largely limit their extensive applications. [4,19] As an alternative, Gong et al recently reported a simply prepared, thermal stiffening, and isochoric poly(acrylic acid) (PAA)/calcium acetate hydrogel which showed 1800 times Young's modulus enhancement ( � 350 times storage modulus change) as well as high storage modulus at the stiffened state ( � 35 MPa). [20] The thermal stiffening effect is believed to arise from the reduced permittivity of calcium acetate and enhanced interchain interactions at high temperatures, and has enabled a few fascinating applications like thermoactivated protection, [20] switchable lubrication, [2] and cold-induced shape recovery.…”