Dispersion, fluidity retention and retardation effect of polyacrylate- based ether superplasticizer nanomicelles in Portland cement

摘要

The superplasticizers with a high-order configuration including star, branched, clawed or corosslinked shape, have exhibited superior fluidity retention effect in cementitious mixes, but are often prepared with tedious routes. This paper employed a facile and proven emulsion polymerization technology to prepare nanomicellar polyacrylate ether superplasticizer (PAE). The precise tri-copolymer structure of PAE of poly(tert-butyl acrylate)& ndash;co-polycarboxylate-co-poly(isoprenyl polyethenoxy ether) (PtBA-co-PAA-coPTPEG) was confirmed by 1H nuclear magnetic resonance (NMR). High-resolution transmission electron microscopy (TEM) verified the core & ndash;shell configuration of PAE and further measured colloidal nanomicelles had an average size diameter at 18 & ndash;35 nm. Based on the special configuration, masses of carboxyl groups were pre-reserved in nanocores via PtBA and encapsulated PAA segments, which would be released into the paste to disperse cement particles over 4 h, during the hydrolysis of PtBA pendent chains and dissociation of nanomicelles. This process was revealed by time-dependent evaluation of spread flow and Zeta potential. Furthermore, the action mechanism of micellar PAE dispersing cement and hydrate by adsorbing onto their surfaces was directly observed by TEM testing. The retardation effect of PAE in Portland cement was evaluated by the delayed hydration heat, lower hydration rate and longer setting time, in comparison with control sample. This work offers a superior fluidity retention superplasticizer for reducing the fluidity loss of cement paste, and demonstrates the fluidity retention mechanism of colloidal PAE via nanomicelle dissociation, carboxyl release, and redispersion in alkaline cement paste.(c) 2021 Elsevier Ltd. All rights reserved.