School of Chemical Engineering , Purdue University , West Lafayette , Indiana 47907 , United States.
Langmuir. 2018 Apr 24;34(16):4874-4887. doi: 10.1021/acs.langmuir.8b00566. Epub 2018 Apr 10.
Polymers at fluid interfaces are used for a number of applications that include coatings, electronics, separation, energy, cosmetics, and medicines. Here, we present a study on an amphiphilic block copolymer, poly((d,l-lactic acid- co-glycolic acid)- block-ethylene glycol) (PLGA-PEG), at the air-water interface. PLGA-PEG at the air-water interface prepared by using an organic spreading solvent exhibits an extremely high surface pressure without the occurrence of desorption, making it an attractive candidate for a variety of uses in the areas mentioned above. The origin of this high surface pressure increase was shown to be due to the glass transition of the PLGA segments. The temperature at which this glass transition occurs for the PLGA segments of PLGA-PEG at the air-water interface was measured to be about 290 K by thermodynamic analysis based on the two-dimensional Maxwell relations. However, from an applications standpoint, spreading by an organic solvent greatly limits its scope of feasible uses. To explore the possibility of maintaining the excellent surface mechanical properties of the PLGA-PEG at the air-water interface while not using an organic solvent, we investigated the air-water interfacial properties of water-spread PLGA-PEG. When spread with water, it was shown that the initial micelles that form in the aqueous spreading solution remain intact even after being spread onto the air-water interface. Due to this different morphology, the surface pressure and monolayer stability were greatly reduced for the water-spread PLGA-PEG at the air-water interface. We used the Daoud and Cotton's blob scaling model to describe the desorption process of the water-spread PLGA-PEG at the air-water interface. From the scaling concept, it was shown that with higher PEG molecular weight and larger micelle size, the adsorption energy of the water-spread PLGA-PEG to the air-water interface was increased.
聚合物在流体界面上被用于多种应用，包括涂料、电子、分离、能源、化妆品和药物。在这里，我们研究了一种两亲性嵌段共聚物，聚（（D，L-丙交酯-共-乙交酯）-嵌段-乙二醇）（PLGA-PEG），在气-水界面上。使用有机铺展溶剂在气-水界面上制备的 PLGA-PEG 表现出极高的表面压，而不会发生解吸，使其成为上述各领域多种用途的有吸引力的候选物。这种表面压升高的起源被证明是由于 PLGA 段的玻璃化转变。通过基于二维 Maxwell 关系的热力学分析，测量到在气-水界面上 PLGA-PEG 的 PLGA 段发生玻璃化转变的温度约为 290 K。然而，从应用的角度来看，有机溶剂的铺展极大地限制了其可行用途的范围。为了在不使用有机溶剂的情况下保持 PLGA-PEG 在气-水界面上的优异表面机械性能的可能性，我们研究了水铺展 PLGA-PEG 的气-水界面性质。当用水铺展时，表明在水铺展溶液中形成的初始胶束即使铺展到气-水界面上也保持完整。由于这种不同的形态，水铺展 PLGA-PEG 在气-水界面上的表面压和单层稳定性大大降低。我们使用 Daoud 和 Cotton 的blob 缩放模型来描述水铺展 PLGA-PEG 在气-水界面上的解吸过程。从缩放概念来看，表明随着 PEG 分子量和胶束尺寸的增加，水铺展 PLGA-PEG 对气-水界面的吸附能增加。
