Structure-property relationships of Kaolin-nanocomposite beads decorated with tertiary amines: Influence of shape on network elasticity and multi-responsivity

Aluminosilicate mineral Kaolin-loaded nanocomposite beads containing cationic 2-(dimethylamino)ethyl methacrylate (DMAEMA) and thermoresponsive N-isopropylacrylamide (NIPA) have been successfully synthe-sized by combined method of dropwise freezing into cryogenic liquid and sedimentation cryogelation. Hertzian elasticity, thermal stability, and responsive-swelling properties were investigated. The nanocomposite gels exhibited better mechanical properties and thermal stability than neat copolymer gels. The stress and displacement distribution on surface of Kaolin-loaded nanocomposite beads were evaluated with classical Hertz theory, and the results were compared with the results obtained from Rubber elasticity theory. The scaling relationship for contact stress and surface displacement was obtained assuming Hertz's small contact area, and the compression force was scaled with displacement with an exponent of 1.34 +/- 0.08. The elastic properties directly attributed to effective potential showed that Hertz potential is valid for small deformations and the elastic modulus decreased with the swollen bead diameter. Addition of Kaolin and NIPA to PDMAEMA-based network has opposite effect on the mechanical properties. The elastic modulus increased, but the swelling ratio decreased with addition of Kaolin. The opposite behavior was observed when NIPA was added, the swelling increased and the mechanical properties weakened. All gels showed significant temperature sensitivity as a result of combination of PDMAEMA and PNIPA, while the swelling was higher at acidic pH than alkaline pH. An overshooting effect attributed to the dynamic conformational changes of tertiary amine of DMAEMA was observed during swelling in pH 3.6. The increase in network density of nanocomposite gel with addition of Kaolin leads to slower relaxation of molecules, and water absorption tends to become relaxation-controlled. An increase in diffusion exponent is observed as diffusion changes from Fickian to non-Fickian. Influence of single salts; NaCl, KCl and K2CO3 on swelling of nanocomposites was investigated. The swelling of Kaolin-loaded nanocomposites decreased with increasing ionic strength, and a salting-out effect was observed. The use of naturally occurring nanoscale particles in such structural material design is an important method for biomedical applications and separation technology.

Automated summary

In this study, aluminosilicate mineral kaolin-loaded nanocomposite beads were successfully synthesized using a combined method of dropwise freezing into cryogenic liquid and sedimentation cryogelation. The nanocomposite gels exhibited better mechanical properties and thermal stability than neat copolymer gels. The addition of kaolin and N-isopropylacrylamide (NIPA) had opposite effects on the mechanical properties. An overshooting effect attributed to the dynamic conformational changes of tertiary amine of dimethylaminoethyl methacrylate (DMAEMA) was observed during swelling at pH 3.6. The increase in network density of the nanocomposite gel with addition of kaolin led to slower molecule relaxation and the diffusion mechanism changed from Fickian to non-Fickian.