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Effect of Ionic Surfactants on the Viscoelastic Properties of Chiral Nematic Cellulose Nanocrystal Suspensions.
Langmuir ( IF 3.9 ) Pub Date : 2019-12-31 , DOI: 10.1021/acs.langmuir.9b03437
Damoon Ranjbar 1 , Savvas G Hatzikiriakos 1
Affiliation  

The gelation of cellulose nanocrystal (CNC) suspensions is explored in the presence of two ionic surfactants, namely, sodium dodecyl sulfate (SDS) with a negatively charged head and cetyltrimethylammonium bromide (CTAB) with a positively charged head. The viscosity profile of pure CNC suspensions indicated that at concentrations greater than 5 wt %, they exhibit gel-like behavior, where the viscosity shows a single shear-thinning profile. However, at concentrations lower than 1 wt %, the suspension shows isotropic behavior and experiences a transition to chiral nematic biphasic domains at increasing CNC concentration. In addition, the effect of CTAB, SDS, and NaCl on the surface charge of CNCs is analyzed and coupled with rheological measurements in order to study the relative importance of surfactants and ionic strength on the viscoelastic properties of the CNC suspensions. The mechanism of CNC/surfactants and CNC/CNC interactions leading to the gelation of CNC suspensions is also investigated. It was found that the addition of both ionic surfactants results in the gelation of biphasic chiral nematic CNC suspensions by fostering cross-linking between individual CNCs at smaller concentrations. In the case of CTAB, a gradual and ongoing increase in the viscoelastic moduli was observed with the increase of surfactant concentration, implying the induction of dominant attractive forces between CNCs by surfactant molecules. However, the presence of SDS stimulates both attractive and repulsive forces whose relative dominance controls the viscoelastic properties and gelation.

中文翻译:

离子表面活性剂对手性向列纤维素纳米晶体悬浮液粘弹性的影响。

在两种离子表面活性剂的存在下,研究纤维素纳米晶体(CNC)悬浮液的凝胶化,即带有带负电头的十二烷基硫酸钠(SDS)和带正电头的十六烷基三甲基溴化铵(CTAB)。纯CNC悬浮液的粘度曲线表明,浓度大于5 wt%时,它们表现出凝胶状行为,其中粘度表现出单一的剪切稀化曲线。但是,当浓度低于1 wt%时,悬浮液会表现出各向同性的行为,并且在CNC浓度增加时会经历向手性向列双相域的转变。此外,CTAB,SDS,为了研究表面活性剂和离子强度对CNC悬浮液粘弹性的相对重要性,分析了氯化钠和氯化钠对CNCs表面电荷的影响,并与流变学测量相结合。还研究了CNC /表面活性剂和CNC / CNC相互作用导致CNC悬浮液胶凝的机理。发现两种离子表面活性剂的加入通过促进较小浓度的各个CNC之间的交联而导致双相手性向列型CNC悬浮液的凝胶化。在CTAB的情况下,随着表面活性剂浓度的增加,粘弹性模量逐渐增加,这表明表面活性剂分子在CNC之间诱导了主要的吸引力。然而,
更新日期:2019-12-31
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