Butler Michael F
Unilever Research and Development, Colworth House, Sharnbrook, Bedfordshire MK44 1LQ, UK.
Biomacromolecules. 2002 Nov-Dec;3(6):1208-16. doi: 10.1021/bm0255645.
The influence of shear on the structure of a gelatin/maltodextrin mixture was investigated using small-angle light scattering both during phase separation and after phase separation was allowed to occur quiescently. In all cases, phase separation occurred via spinodal decomposition to form a droplet morphology, and a characteristic length scale was formed in the structure that was prevalent during shear, as well as in quiescent conditions. Below the critical shear rate for droplet breakup, shear accelerated the coarsening rate of the droplets. A transient regime of rapid hydrodynamic coarsening was present when shear was initiated after phase separation and at late times in all cases once the droplets attained a certain size. At the critical shear rate for droplet breakup (1 s(-1)), the rapid repetition of breakup and coarsening was postulated to occur, which enabled a microstructure consisting of elongated droplets with a narrow size distribution to form. When the shear rate enabled droplets to extend to such an extent that a percolated structure could form (10 s(-1)), then the structure was relatively stable and changed very slowly over time. At very high shear rates (100 s(-1)), droplet breakup was suppressed and a highly fibrillar morphology formed that was stable only while the system was under shear. Cessation of shear at high rates led to fiber breakup and the formation of many small droplets. For a given shear rate, the final microstructure appeared to be independent of the time that shear was started when the structure consisted of discrete droplets or fibers. When a percolated structure could form, however, the shear history appeared to be important.
利用小角光散射研究了剪切对明胶/麦芽糊精混合物结构的影响，研究过程包括相分离期间以及相分离静止发生之后。在所有情况下，相分离均通过旋节线分解形成液滴形态，并且在剪切过程中以及静止条件下，结构中均形成了一种特征长度尺度。在液滴破碎的临界剪切速率以下，剪切加速了液滴的粗化速率。当在相分离后开始剪切时，以及在所有情况下液滴达到一定大小时的后期，会出现快速流体动力学粗化的瞬态状态。在液滴破碎的临界剪切速率（1 s⁻¹）下，推测会发生破碎和粗化的快速重复，从而形成由尺寸分布窄的细长液滴组成的微观结构。当剪切速率使液滴延伸到能够形成渗流结构的程度（10 s⁻¹）时，那么该结构相对稳定且随时间变化非常缓慢。在非常高的剪切速率（100 s⁻¹）下，液滴破碎受到抑制，形成了仅在系统处于剪切状态时才稳定的高度纤维状形态。在高速率下停止剪切会导致纤维破碎并形成许多小液滴。对于给定的剪切速率，当结构由离散液滴或纤维组成时，最终的微观结构似乎与开始剪切的时间无关。然而，当能够形成渗流结构时，剪切历史似乎很重要。
