Enhanced Water Retention by Using Polymeric Microcapsules to Confer High Proton Conductivity on Membranes at Low Humidity

Abstract

Water retention is a pervasive issue in agriculture and industry. Inspired by the water‐storage mechanisms in plant cells, three kinds of polymeric microcapsules (PMCs) with carboxylic acid, sulfonic acid, and pyridyl groups are prepared using distillation–precipitation polymerization. The size of the lumen of the PMCs may govern the static water uptake by holding water molecules in a free‐water state, and the functional groups in the shell of PMCs may manipulate dynamic water release by holding water molecules in a bound‐water state, thus yielding PMCs with high and tunable water‐retention properties. Incorporation of PMCs into composite membranes gives rise to dramatically enhanced water‐retention properties and proton‐transfer pathway, and consequently increased proton conductivity by up to one order of magnitude over the control polymer membrane, under low relative humidity of 20%. This study may offer a facile and generic strategy to design and prepare a variety of materials with superior water‐retention properties.

Assimilation of highly porous sulfonated carbon nanospheres into Nafion® matrix as proton and water reservoirs

“…After that, the former one kept greater s values by 7e8 times than the latter one over a relatively long duration. It has been proposed by Wang and co-workers that the bound water portions are resilient against dry environment and this is able to maintain its proton conductivity longer [36]. Indeed, Fig.…”

Enhanced water retention and low-humidity proton conductivity of sulfonated poly(ether ether ketone) hybrid membrane by incorporating ellipsoidal microcapsules

“…Under the conditions of 80 C and 100% RH, the water uptake of hybrid membrane with filler content of 30 wt.% increased to 70% from 37% of unfilled membrane and proton conductivity increased by about 141%. Though the poor compatibility and low conductivity problems can be alleviated by proper modification, some other drawbacks of inorganic microcapsules still exist, such as too fast water release, low water uptake, less proton-conducting ability [12]. To solve these problems, polymeric hollow spheres, or polymeric capsules may be more promising candidates.…”

“…To solve these problems, polymeric hollow spheres, or polymeric capsules may be more promising candidates. Wang et al [12] designed a series of polymeric microcapsules (PMCs) and reported a 21.4-fold increase of proton conductivity under 20% RH and 40 C by embedding 15 wt.% of carboxylic acid-functionalized microcapsules into chitosan membrane.…”

“…often suffer from substantial water loss at low humidity, which results in sharp decline of proton conductivity [4,9e11]. Inspired by the waterretention phenomena and principles in plant cells, microcapsules have been designed and filled into membrane bulk as water-retention media, furnishing water to the hydropenic membrane matrix continuously [12]. Compared with solid spheres, microcapsules possess special hollow structure, which affords the following three merits as fillers for PEMs: (I) ensuring the homogeneous dispersion in the polymeric matrix; (II) holding more free water to confer membranes a higher water content; (III) possessing low proton transfer resistance to make proton transport more effective [8,13e15].…”

Embedding of Hollow Polymer Microspheres with Hydrophilic Shell in Nafion Matrix as Proton and Water Micro-Reservoir

“…Grafting hydrophilic oligomeric chains to inorganic particles [3][4][5][6][7][8][9][10][11][12][13][14][15] has furthered the preparation technique of Nafion nanocomposite membranes. With the aim of achieving the forestated goal, use of hydrophilic hollow polymer spheres (HPS) as filler is apparently more attractive [16][17][18][19][20][21] because this particulate structure possesses larger interior space for storing water and the porous hydrophilic polymeric shell prevents quick evaporation of water while the membrane is subjected to dehydration [22,23]. It has also been considered that the Grotthuss mechanism became dominant in the presence of hydrophilic HPS in a PEM matrix [24] because the matrix water strongly associates with pendant hydrophilic functional groups and is therefore immobile.…”