Coarsening of the pore network in drying latex films upon interparticle aggregation.
Coarsening of the pore network in drying latex films upon interparticle aggregation.
复制标题
颗粒间聚集时干燥乳胶膜中孔网络的粗化。
DOI：
10.1021/la501354k
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
D. Johannsmann
中科院分区：
文献类型：
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作者：
K. Pohl;Rebekka König;Heike Römermann;M. Schulz;D. Johannsmann
在聚合物 Tg 约为室温的乳胶分散体成膜过程中观察到的横向干燥前沿由三条不同的线组成。这些线的特征是浊度降低、浊度重新急剧增加、以及在所谓的“光晕”结束时浊度逐渐降低。具有人字形形态的微裂纹在第一行出现，浊度降低。如果存在宏观裂纹，这些裂纹会在晕环末端附近成核。在浊度急剧增加的线上，我们还观察到应力双折射的增加。干燥前沿的子结构在特征上不同于先前描述的用于从硬颗粒干燥薄膜的结构。特别是，浊度的重新增加不能解释为孔隙张开，而是颗粒跳跃接触后孔隙网络变粗的结果。毛细管不稳定性开始出现，小孔在聚合物/水界面能的作用下塌陷，而较大的孔相应地膨胀。这种不稳定性（与液体射流的瑞利不稳定性有关）使薄膜显得浑浊。此外，引起的机械不均匀性会阻止直的宏观裂纹渗透到晕中，因为会导致裂纹偏转和裂纹分支，这在能量上是不利的。
The lateral drying front observed during film formation from latex dispersions with a Tg of the polymer around room temperature is composed of three three distinct lines. The lines are characterized by a decrease in turbidity, a renewed sharp increase in turbidity, and a more gradual decrease in turbidity at the end of what can be called a "halo". Microcracks with herringbone morphology develop at the first line, where the turbidity decreases. If macrocracks are present, these nucleate close to the end of the halo. At the line, where the turbidity sharply increases, one also observes an increase in stress birefringence. The substructure of the drying front is characteristically different from the structures described previously for films drying from hard particles. In particular, the renewed increase in turbidity cannot be explained as pore-opening, but rather is the consequence of a coarsening of the pore network after the particles jump into contact. A capillary instability sets in, by which the small pores collapse under the polymer/water interfacial energy, while the larger pores expand correspondingly. The instability (related to the Rayleigh instability of liquid jets) makes the films appear turbid. Also, the induced mechanical heterogeneity prevents straight macrocracks from penetrating into the halo because crack deflection and crack branching would result, which is energetically unfavorable.