耗散粒子动力学模拟Nafion膜和PVA/Nafion共混膜的介观结构

采用耗散粒子动力学模拟方法研究了水化Nafion膜和水化聚乙烯醇(PVA)/Nafion共混膜的微结构.模拟结果表明水化Nafion膜和水化PVA/Nafion共混膜均能形成相分离的微结构.在水化Nafion膜中,水与磺酸根混合形成管状的水团簇.随着膜内水含量增多,管状水团簇的尺寸逐渐变大并在膜内形成连续的水通道.在水化PVA/Nafion共混膜中,PVA、水、磺酸根混合形成亲水性区域.共混膜中PVA的质量分数和水含量共同影响膜的微结构.当膜中PVA质量分数较低时,PVA主要分布在Nafion的磺酸根基团周围;PVA质量分数升高后,PVA会在膜内单独成一相.当膜中的水含量相对较低时,水分子会溶解于PVA中,此时膜内不存在单独的水团簇;膜中的水含量增多后,膜内会形成接近于球形的水团簇.本文工作可为直接甲醇燃料电池用的PVA改性Nafion膜的开发提供参考.

Dissipative Particle Dynamics Simulations on Mesoscopic Structures of Nafion and PVA/Nafion Blend Membranes

Dissipative particle dynamics simulations were performed to study the mesoscopic structures of both humidified Nafion and polyvinyl alcohol(PVA)/Nafion blend membranes.Simulation results show that a phase-segregated microstructure is formed in both humidified Nafion and PVA/Nafion blend membranes.In humidified Nafion membrane,water molecules and sulfonate groups form tubular shaped water clusters.As the water content is increased,the size of water cluster is enlarged and water clusters percolate to form a continuous water channel.In the PVA/Nafion blend membrane,PVA,water molecules, and sulfonate groups together form hydrophilic domains.The mesoscopic structure of the PVA/Nafion blend membrane is affected by both the PVA/Nafion blend ratio and the water content in the membrane. When the PVA mass fraction is relatively low,PVA is predominantly distributed along the sulfonate groups of Nafion and as the PVA mass fraction is increased,PVA alone forms a distinct phase in the membrane. When the water content in the membrane is relatively low,water molecules are predominantly dissolved in PVA and as the water content is increased,spherical water clusters emerge in the membrane.This work provides further guidance for the development of PVA modified Nafion membranes for direct methanol fuel cell applications.