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持续升温时稀疏CTAC表面活性剂溶液剪切黏度变化的动力及能量分析
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摘要
在恒定的剪切速率下、持续升温,对稀疏CTAC/NaSal表面活性剂溶液进行流变测试,发现不同剪切速率下,即便升温速度相同,同一溶液内分子自组装结构变化的差异也很大。首次发现"双峰"现象,其形成条件为:溶液浓度1.25-2.50 mmol/L、剪切速率5 s~(-1)、升温速度0.0033-0.0333℃/s。建立了棒状胶束尺寸变化速度与温度和剪切速率之间的关系式(见下图),可以发现不管是剪切还是温度,对胶束尺寸变化的作用都具有两面性,因此,试验条件下胶束尺寸大小实际上取决于剪切和温度两种作用的"匹配程度"。此外,引进总自由能变的概念,从能量角度分析了剪切和温度对表面活性剂胶束溶液的协同作用。
Quite dilute CTAC/NaSal surfactant solution has been investigated with increasing temperature under shear.Different shear rates induce very different assembly transitions for the same solution with same temperature increasing rate(r).A special "two peaks" phenomenon appears under the following conditions:concentration of 1.25-2.50 mmol/l,shear rate of 5 s~(-1) and r of 0.0033-0.0333 ℃/s.An equation is established to describe the relations between the change in rodlike micelle size with time(dR/dt) and the combined effects of shear and temperature.It can be found that either effect of shear or temperature has two aspects on dR/dt,therefore,the micellar size actually depends on the "matching-degree" of the two effects under our experimental conditions.Besides,the total free energy change in the surfactant solution system is analyzed to study the simultaneous effects of shear and temperature from energy viewpoint.
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