title: Shaping calcite crystals by means of comb polyelectrolytes having neutral hydrophilic teeth.
abstract: Comb polyelectrolytes (CPs) having neutral hydrophilic teeth, similar to double hydrophilic block copolymers, are a powerful tool to modify the chemical-physical properties of inorganic crystalline materials. One of their main applications is in concrete technology, where they work as superplasticizers, particle-dispersing agents. Here, CPs, having the same poly(acrylic acid)  (PAA) backbone chain and differing in the grafting with methoxy poly(ethylene glycol) chains (MPEG) of two molecular weights, were used to investigate the influence of tooth chains in polymer aggregation and in  control on morphology and aggregation of calcite particles. These polymers aggregate, forming interpolymer hydrogen bonds between carboxylic groups and ether oxygen functionalities. The presence of calcium ions in solution further enhances aggregation. Crystallization experiments of calcite in the presence of CPs show that the specificity of interactions between polymers and crystal planes and  control on aggregation and size of particles is a function of the content and chain length of the MPEG in the PAA backbone. These parameters limit and can make specific the electrostatic interactions with ionic crystalline planes. Moreover, the mechanism of crystallization, classical or nonclassical, is addressed by the CP structure and concentration. These findings have implications in the understanding of the complex chemical processes associated to concrete superplasticizers action and in the study of the biomineralization processes, where biological comb polyelectrolytes, the acidic glycoproteins, govern  formation of calcitic structures.
authors: Centro Interdipartimentale di Ricerca in Scienze Ambientali Sede di Ravenna-Università di Bologna, via S. Alberto 163, 48100 Ravenna, Italy.
authors: Danilo
authors: D
authors: Malferrari
authors: Simona
authors: S
authors: Fermani
authors: Paola
authors: P
authors: Galletti
authors: Marco
authors: M
authors: Goisis
authors: Emilio
authors: E
authors: Tagliavini
authors: Giuseppe
authors: G
authors: Falini