Effect of counterions on ordered phase formation in suspensions of charged rodlike cellulose crystallites
Effect of counterions on ordered phase formation in suspensions of charged rodlike cellulose crystallites
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DOI：
10.1021/la960724h
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发表时间：
1997-04-16
期刊：
影响因子：
3.9
通讯作者：
Gray, DG
中科院分区：
文献类型：
--
作者：
Dong, XM;Gray, DG
用滤纸酸水解法制备了表面带负电荷硫酸根的纤维素微晶的稳定胶体悬浮液。悬浮液，这是免费的添加电解质，形成手性有序相高于临界浓度。观察到一个尖锐的边界之间共存的手性和各向同性相，使测量的相对量的每一个阶段作为总纤维素浓度的函数。的各向同性的手性反相平衡是敏感的性质存在于悬浮液中的抗衡离子。用钠、钾、铯、铵、四甲基铵、四乙基铵、四丙基铵、四丁基铵、三甲基铵和三乙基铵抗衡离子制备样品。悬浮液与H+抗衡离子形成一个有序的相在最低浓度的微晶。对于无机反离子，有序相形成的临界浓度按H+ < Na+ < K+ < Cs+的顺序增加。对于有机抗衡离子，临界浓度一般随抗衡离子尺寸的增加而增加，表明平衡受疏水吸引力和空间排斥力之间的平衡支配。抗衡离子的性质也影响悬浮液的其它性质，例如它们的稳定性、相分离和手性双组分沥青的温度依赖性，以及由悬浮液制成的干燥样品的再分散性。
Stable colloidal suspensions of cellulose crystallites with negatively charged sulfate groups on their surface were prepared by acid hydrolysis of filter paper. The suspensions, which were free of added electrolyte, formed chiral nematic ordered phases above a critical concentration. A sharp boundary was observed between coexisting chiral nematic and isotropic phases, enabling measurements to be made of the relative amounts of each phase as a function of total cellulose concentration. The isotropic-to-chiral nematic phase equilibrium was sensitive to the nature of the counterions present in the suspension. Samples were prepared with sodium, potassium, cesium, ammonium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, trimethylammonium, and triethylammonium counterions. Suspensions with H+ counterions formed an ordered phase at the lowest concentrations of crystallites. For inorganic counterions, the critical concentration for ordered phase formation increases in the order H+ < Na+ < K+ < Cs+. For the organic counterions, the critical concentration in general increases with increasing counterion size, suggesting that the equilibrium is governed by a balance between hydrophobic attraction and steric repulsion forces. The nature of the counterions also influences other properties of the suspensions, such as their stability, the temperature dependence of the phase separation and of the chiral nematic pitch, and the redispersability of dried samples made from the suspensions.