CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa (FCT/UNL), 2829-516 Caparica, Portugal.
ACS Appl Mater Interfaces. 2012 Mar;4(3):1470-7. doi: 10.1021/am201722x. Epub 2012 Mar 2.
Optical memories with long-term stability at high temperatures have long been pursued in azopolymers with photoinduced birefringence. In this study, we show that the residual birefringence in layer-by-layer (LbL) films made with poly[1-[4-(3-carboxy-4 hydroxyphenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) alternated with poly(allylamine hydrochloride) (PAH) can be tuned by varying the extent of electrostatic interactions with film fabrication at different pHs for PAH. The dynamics of both writing and relaxation processes could be explained with a two-stage mechanism involving the orientation of the chromophores per se and the chain movement. Upon calculating the activation energies for these processes, we demonstrate semiquantitatively that reduced electrostatic interactions in films prepared at higher pH, for which PAH is less charged, are responsible for the longer stability at high temperatures. This is attributed to orientation of PAZO chromophores via cooperative aggregation, where the presence of counterions hindered relaxation.
具有光致双折射的偶氮聚合物长期以来一直被用于研究高温下具有长期稳定性的光学记忆体。在这项研究中，我们表明，通过在不同 pH 值下改变与聚[1-[4-(3-羧基-4 羟苯基偶氮)苯磺酰胺基]-1,2-乙二基，钠盐]（PAZO）交替的聚（烯丙基胺盐酸盐）（PAH）的静电相互作用的程度，可以调节层层（LbL）薄膜中的残余双折射。通过使用涉及发色团本身的取向和链运动的两阶段机制，可以解释写入和弛豫过程的动力学。通过计算这些过程的活化能，我们半定量地证明，在较高 pH 值下制备的薄膜中，由于 PAH 的电荷较少，因此减少了静电相互作用，这是在高温下具有更长稳定性的原因。这归因于通过协同聚集使 PAZO 发色团取向，其中抗衡离子的存在阻碍了弛豫。
