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

Abstract

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%.