Fuchs Christian, Hussain Hazrat, Schwieger Christian, Schulz Matthias, Binder Wolfgang H, Kressler Jörg
Martin Luther University Halle-Wittenberg, Department of Chemistry, D-06099 Halle (Saale), Germany.
Martin Luther University Halle-Wittenberg, Department of Chemistry, D-06099 Halle (Saale), Germany.
J Colloid Interface Sci. 2015 Jan 1;437:80-89. doi: 10.1016/j.jcis.2014.09.050. Epub 2014 Sep 28.
The behavior of a series of amphiphilic triblock copolymers of poly(ethylene oxide) (PEO) and poly(isobutylene) (PIB); including both symmetric (same degree of polymerization (DP) of the terminal PEO blocks) PEOm-b-PIBn-b-PEOm and non-symmetric (different DP of the terminal PEO blocks) PEOm-b-PIBn-b-PEOz, is investigated at the air/water interface by measuring surface pressure vs mean molecular area isotherms (π vs mmA), Langmuir-Blodgett (LB) technique, and infrared reflection-absorption spectroscopy (IRRAS). The block copolymer (PEO32-b-PIB160-b-PEO32) with longer PEO segments forms a stable monolayer and the isotherm reveals a pseudo-plateau starting at π∼5.7 mN/m, also observed in the IRRAS, which is assigned to the pancake-to-brush transition related to the PEO dissolution into the subphase and subsequent PEO brush dehydration. Another plateau is observed at π∼40 mN/m, which is attributed to the film collapse due to multilayer formation. The pancake-to-brush transition could not be observed for samples with smaller PEO chains. The isotherms for block copolymers, with short PEO chains, both symmetric (PEO3-b-PIBn-b-PEO3) and non-symmetric (PEO12-b-PIBn-b-PEO3), reveal another transition at π∼20-25 mN/m. This is interpreted to be due to the conformational transition from a folded state where the middle PIB block is anchored to the water surface at both ends by the terminal hydrophilic segments to an unfolded state with PIB anchored to the water surface at one end. It is assumed that this transition involves the removal of PEO3 chains from the water surface in case of non-symmetric PEO12-b-PIB85-b-PEO3 and in case of symmetric, probably one PEO3 of each PEO3-b-PIB85-b-PEO3 chain. Because of the weaker interaction of the short PEO3 chains with the water surface as compared with the relatively longer PEO12 chains, the film of PEO3-b-PIB85-b-PEO3 collapses at much lower surface pressure after the transition as compared with the PEO12-b-PIB85-b-PEO3. The AFM images reveal the formation of microdomains of almost uniform height (6-7 nm) in LB films of PEO3-b-PIB85-b-PEO3 and PEO12-b-PIB85-b-PEO3 after transferring onto silicon surfaces. These domains are assumed to be the mesomorphic domains of ordered and folded PIB chains.
研究了一系列聚环氧乙烷（PEO）和聚异丁烯（PIB）的两亲性三嵌段共聚物的行为，包括对称的（末端PEO嵌段聚合度（DP）相同）PEOm-b-PIBn-b-PEOm和非对称的（末端PEO嵌段DP不同）PEOm-b-PIBn-b-PEOz。通过测量表面压力与平均分子面积等温线（π对mmA）、朗缪尔-布洛杰特（LB）技术和红外反射吸收光谱（IRRAS），在空气/水界面进行了研究。具有较长PEO链段的嵌段共聚物（PEO32-b-PIB160-b-PEO32）形成稳定的单分子层，等温线显示在π5.7 mN/m处开始出现一个假平台，在IRRAS中也观察到了，这归因于与PEO溶解到亚相以及随后的PEO刷脱水相关的煎饼状到刷状转变。在π40 mN/m处观察到另一个平台，这归因于由于多层形成导致的膜塌陷。对于具有较短PEO链的样品，未观察到煎饼状到刷状转变。对称的（PEO3-b-PIBn-b-PEO3）和非对称的（PEO12-b-PIBn-b-PEO3）具有短PEO链的嵌段共聚物的等温线在π~20 - 25 mN/m处显示出另一个转变。这被解释为是由于构象转变，从中部PIB嵌段两端通过末端亲水性链段锚定在水面的折叠状态转变为PIB一端锚定在水面的展开状态。假定这种转变在非对称的PEO12-b-PIB85-b-PEO3情况下涉及从水面去除PEO3链，在对称情况下，可能是每个PEO3-b-PIB85-b-PEO3链中的一个PEO3。由于与相对较长的PEO12链相比，短PEO3链与水面的相互作用较弱，与PEO12-b-PIB85-b-PEO3相比，PEO3-b-PIB85-b-PEO3的膜在转变后在低得多的表面压力下塌陷。原子力显微镜（AFM）图像显示，在转移到硅表面后，PEO3-b-PIB85-b-PEO3和PEO12-b-PIB85-b-PEO3的LB膜中形成了高度几乎均匀（6 - 7 nm）的微区。这些区域被认为是有序和折叠的PIB链的介晶区。
