Sir Peter Mansfield Imaging Resonance Centre, School of Medicine, University of Nottingham, Nottingham, NG2 7RD, UK.
NIHR Nottingham Biomedical Research Centre, Nottingham University Hospitals NHS Trust, Queen's Medical Centre, Derby Road, Nottingham NG7 2UH, UK.
Soft Matter. 2023 May 3;19(17):3228-3237. doi: 10.1039/d2sm01381a.
Na multiple quantum filtered (MQF) rheo-NMR methods were applied to probe the molecular foundation for flow induced self-assembly in 0.5% -carrageenan fluid. This method is sensitive enough to utilize an endogenous sodium ion concentration of approximately 0.02%. Rheo-NMR experiments were conducted at different temperatures and shear rates to explore varying molecular dynamics of the biopolymer in the fluid under shear. The temperature in the rheo-NMR experiments was changes from 288 K to 313 K to capture transition of κ-carrageenan molecules from helices to coils. At each temperature, the fluid was also tested for flow and oscillatory shear behaviour using bulk rheometry methods. It was found that the Na MQF signals were observed for the 0.5% -carrageenan solution only under shear and when the fluid demonstrated yielding and/or shear-thinning behaviour. At temperatures of 303 K and above, no Na MQF signals were observed independent of the presence or absence of shear as the molecular phase transition to random coils occurs and the fluid becomes Newtonian.
采用多量子过滤（MQF）流变核磁共振方法研究了 0.5%卡拉胶溶液中流动诱导自组装的分子基础。该方法的灵敏度足以利用约 0.02%的内源性钠离子浓度。在不同的温度和剪切速率下进行流变核磁共振实验，以探索剪切下生物聚合物在流体中的不同分子动力学。流变核磁共振实验中的温度从 288 K 变化到 313 K，以捕捉κ-卡拉胶分子从螺旋到线圈的转变。在每个温度下，还使用体流变学方法测试了流体的流动和振荡剪切行为。结果发现，只有在剪切下，并且当流体表现出屈服和/或剪切变稀行为时，才观察到 0.5%卡拉胶溶液的 Na MQF 信号。在 303 K 及以上的温度下，无论是否存在剪切，都没有观察到 Na MQF 信号，因为分子相转变为无规线团，流体呈现牛顿行为。
