琼脂凝胶中氯化铵结晶生长的形态转化

为了在同一系统中通过改变外部条件得到目前所报道的一些典型的远离平衡态下的几种凝聚形态，研究了NH4Cl在琼脂凝胶中的枝晶生长，实现了在其生长过程中通过改变条件得到不同的形态变化．结果表明，NH4Cl起始质量分数对其结晶形态产生明显的影响，随着起始NH4Cl质量分数的减少，晶体生长形态的不规则程度增加，逐渐由枝晶过渡到密枝；在一定条件下，普通枝晶生长完成以后其生长形态转变为近来人们很感兴趣的曲折(zigzag)结构．产生这种形态转化的原因是琼脂中的NH4Cl结晶有分层生长的现象，随着琼脂凝胶水分的不断蒸发和琼脂表层的干燥和收缩，NH4Cl先在琼脂表层形成枝晶，然后过渡到在琼脂下面结晶成zigzag结构，在不同的结晶层面，生长的结晶体形态不一样．

Morphological Transition of NH4Cl Crytal Growth from Agarose Gel

The morphology and its transition of NH_4Cl crytal growth from agarose gel are studied. It is found that the initial concentration of NH_4Cl played a role in the morphological selection of its crystal growth. Another interesting morphological transition from dendrites to zigzagged branches is observed. Further investigation reveals that the zigzagged branches grow in the agarose gel and contact the slide tightly, while dendrites grow on the surface of the agarose gel. This phenomenon is caused by the drying and shrinking effect of the agarose gel. It is suggested that the growing in different position leads to various crystal morphologies of NH_4Cl.