Synthesis and cement performance of thermoresponsive core-shell microgel superplasticizers with size modulation.

Four microgels (MG) with different carboxyl contents were designed and prepared by using two monomers of methacrylic acid (MAAc), the thermosensitive monomer N-isopropylacrylamide (NIPAM), and the crosslinker N,N'-methylenebisacrylamide (BIS). NH2-functionalized HPEG2400 (HPEG-NH2) was grafted onto the carboxyl groups around the microgel shell through amide linkage, and thermoresponsive core-shell microgel superplasticizers with size modulation were successfully synthesized, named MG-HPEG. The formation of the core-shell structure was confirmed by FTIR, while DLS and SEM confirmed that the obtained MG-HPEG possessed a spherical structure with particle sizes ranging from 1000-2000 nm. Water absorption tests in cement mortar showed that the MG-HPEG samples with different carboxyl contents all exhibited water absorption to varying degrees. Further flowability and mechanical property tests of cement mortar were carried out to show a superior performance which was observed at a carboxyl content of 6.6%, resulting from an optimal balance between swelling capacity and carboxyl density. Compared with the blank sample and other microgel superplasticizers, this superplasticizer exhibited a water-reducing rate of 11.3% and a flow spread of 241 mm. Moreover, the compressive strengths of cement specimens at 7 and 28 days were increased by 19% and 32%.