Temperature and relative humidity dependency of film formation of polymeric latex dispersions.
Temperature and relative humidity dependency of film formation of polymeric latex dispersions.
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DOI：
10.1021/la202300p
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发表时间：
2011-10
期刊：
影响因子：
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通讯作者：
Xuelian Chen;S. Fischer;Yongfeng Men
中科院分区：
文献类型：
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作者：
Xuelian Chen;S. Fischer;Yongfeng Men
采用热重分析和同步辐射小角X射线散射技术表征了聚合物胶乳分散体在不同温度和相对湿度下成膜的前三个阶段的结构演变。鉴定了三个中间阶段：（1）阶段I*，（2）阶段I**，和（3）阶段II*。阶段I* 是常规定义的阶段I和II的中间阶段，其中胶乳颗粒开始结晶。干燥温度的变化会影响有序化开始的位置，而相对湿度则不会。阶段I** 是胶乳颗粒与其在fcc结构中的抗衡离子的扩散壳彼此接触的地方。这些层的重叠导致由于有效电荷的减少而加速晶格收缩。阶段II* 是其中胶乳颗粒，在其T（g）以上充分干燥，由于胶乳膜中的水的不完全蒸发，在成膜期间仅部分变形和填充。这是因为软乳胶颗粒在液体/空气界面处快速变形，使得一定量的水不能从乳胶膜有效地蒸发。对于在接近其最低成膜温度的温度下干燥的胶乳分散体，阶段II和III之间的过渡可以是连续的，因为胶乳颗粒以慢得多的速率变形，为水蒸发提供足够的表面积。
Thermogravimetric analysis and a synchrotron small-angle X-ray scattering technique were employed to characterize the structural evolution of a polymeric latex dispersion during the first three stages of film formation at different temperatures and relative humidities. Three intermediate stages were identified: (1) stage I*, (2) stage I**, and (3) stage II*. Stage I* is intermediate to the conventionally defined stages I and II, where latex particles began to crystallization. The change of drying temperature affects the location of the onset of ordering, whereas relative humidity does not. Stage I** is where the latex particles with their diffuse shell of counterions in the fcc structure are in contact with each other. The overlapping of these layers results in an acceleration of the lattice shrinkage due to a decrease of effective charges. Stage II* is where the latex particles, dried well above their T(g), are deformed and packed only partially during film formation due to incomplete evaporation of water in the latex film. This is because of a rapid deformation of the soft latex particles at the liquid/air interface so that a certain amount of water is unable to evaporate from the latex film effectively. For a latex dispersion dried at a temperature close to its minimum film formation temperature, the transition between stages II and III can be continuous because the latex particles deform at a much slower rate, providing sufficient surface area for water evaporation.