Controlled coagulation and redispersion of thermoresponsive poly di(ethylene oxide) methyl ether methacrylate grafted
César Brinatti1, Seyedeh Parinaz Akhlaghi1, Rafael Pires-Oliveira1
1Institute of Chemistry - Universidade Estadual de Campinas (UNICAMP), CP 6154, CEP 13083-970 Campinas, SP, Brazil.
Hypothesis:
Cellulose nanocrystals (CNCs) undergo precipitation in the presence of high concentrations of cationic surfactants in aqueous solutions. To avoid such behavior and/or to promote redispersion of CNC/surfactant mixtures, the CNC surface was grafted with poly di(ethylene oxide) methyl ether methacrylate, P(MEO2MA).
Experiments:
CNC-g-P(MEO2MA) was characterized using the following techniques 13C solid-state nuclear magnetic resonance (13C SSNMR), Fourier-transform infrared spectroscopy - attenuated total reflection spectroscopy (FTIR-ATR) and thermal gravimetric analysis (TGA). Isothermal titration calorimetry (ITC), electrophoretic mobility, light scattering and high sensitivity differential scanning calorimetry (HSDSC) were used to study the interaction between CNC-g-P(MEO2MA) and ionic surfactants, dodecyltrimethylammonium bromide (C12TAB, cationic) and sodium dodecylsulfate (SDS, anionic) at temperatures below and above the LCST.
Findings:
CNC-g-P(MEO2MA) underwent phase separation above its lower critical solution temperature (LCST ∼ 25 °C) and precipitated from solution as seen by HSDSC and transmittance experiments. When C12TAB was added to CNC-g-P(MEO2MA) it induced the precipitation that prevented the redispersion due to strong electrostatic interactions with the negative charges on the CNC surface. With increasing concentrations of SDS, the polymer phase transition temperature was increased, which can be used to redisperse the CNC complexes. By removing SDS from the mixture via dialysis, the CNC-g-P(MEO2MA) underwent subsequent phase transition.
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