Xiang Fangming, Ward Sarah M, Givens Tara M, Grunlan Jaime C
Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123, USA.
Soft Matter. 2015 Feb 7;11(5):1001-7. doi: 10.1039/c4sm02363c.
Hydrogen bonded poly(acrylic acid) (PAA)/poly(ethylene oxide) (PEO) layer-by-layer assemblies are highly elastomeric, but more permeable than ionically bonded thin films. In order to expand the use of hydrogen-bonded assemblies to applications that require a better gas barrier, the effect of assembling pH on the oxygen permeability of PAA/PEO multilayer thin films was investigated. Altering the assembling pH leads to significant changes in phase morphology and bonding. The amount of intermolecular hydrogen bonding between PAA and PEO is found to increase with increasing pH due to reduction of COOH dimers between PAA chains. This improved bonding leads to smaller PEO domains and lower gas permeability. Further increasing the pH beyond 2.75 results in higher oxygen permeability due to partial deprotonation of PAA. By setting the assembling pH at 2.75, the negative impacts of COOH dimer formation and PAA ionization on intermolecular hydrogen bonding can be minimized, leading to a 50% reduction in the oxygen permeability of the PAA/PEO thin film. A 20 bilayer coating reduces the oxygen transmission rate of a 1.58 mm natural rubber substrate by 20 ×. These unique nanocoatings provide the opportunity to impart a gas barrier to elastomeric substrates without altering their mechanical behavior.
氢键连接的聚丙烯酸（PAA）/聚环氧乙烷（PEO）逐层组装体具有高弹性，但比离子键合薄膜的渗透性更强。为了将氢键连接组装体的应用扩展到需要更好气体阻隔性能的领域，研究了组装pH值对PAA/PEO多层薄膜氧气渗透性的影响。改变组装pH值会导致相形态和键合发生显著变化。由于PAA链之间COOH二聚体的减少，PAA和PEO之间分子间氢键的数量随pH值升高而增加。这种改善的键合导致PEO域更小且气体渗透性更低。将pH值进一步提高到2.75以上会由于PAA的部分去质子化而导致氧气渗透性更高。通过将组装pH值设定为2.75，可以将COOH二聚体形成和PAA电离对分子间氢键的负面影响降至最低，从而使PAA/PEO薄膜的氧气渗透性降低50%。20层涂层可使1.58毫米天然橡胶基材的氧气透过率降低20倍。这些独特的纳米涂层提供了在不改变弹性体基材机械性能的情况下赋予其气体阻隔性能的机会。
