Hydrophobic and Ultrahydrophobic Multilayer Thin Films from Perfluorinated Polyelectrolytes

Abstract

Interest in surfaces exhibiting large water contact angles is stimulated both by important technological implications and by novel aspects of surface physics. Since wetting can be controlled by a single monolayer of material, novel materials or surface treatments can yield a fascinating range of properties. Such treatments, which are capable of generating particularly hydrophobic surfaces, include conventional coating processes such as spraying or dipping, [1a] vacuum deposition techniques, [1b] and such surface-modification technologies as diffusion, [1c] laser and plasma processes, [1d] chemical plating, [1e] grafting [1f] or bonding hydrogel encapsulation, [1g] and bombardment with high-energy particles. [1h] The use of the layer-by-layer sequential adsorption [2] method for the assembly of an ultrathin film has very recently been reported for making ultrahydrophobic surfaces. [3,4] These studies address the critical issue of inducing surface roughness, which is required for true ultrahydrophobic behavior. [5][6][7][8][9][10][11][12][13][14][15] Soeno et al. [3] described a multilayered polyelectrolyte/silica nanoparticle system which was heated to sinter the particles and burn off the polymer, then treated with a fluorosilane to induce the required hydrophobicity. Zhai et al. [4] reported the formation of a pH-sensitive multilayer which undergoes a porosity-inducing phase transition in acidic solutions. Additional treatment steps, including crosslinking, deposition of silica nanoparticles, fluorosilane treatment, and thermal annealing, yielded stable ultrahydrophobic materials. Although the targeted surface properties were obtained, multiple processing steps are not desirable. Herein, we describe a multilayering process that uses both fluorinated polyanions and polycations, with a roughening step, by utilizing a naturally occurring nanorod that can be inserted conveniently into the layering sequence.The polyelectrolytes used were nafion (Scheme 1), which is a commercially available sulfonated fluorinated material, and a polycation synthesized from poly(vinylpyridine) and a fluorinated alkyl iodide. Polyelectrolyte components were deposited on silicon wafers under ambient conditions using dilute solutions/dispersions. Although fluorinated solvents, such as trifluoroethanol, were useful for dispersing the polyelectrolytes, we were interested in employing more common solvents as vehicles for manipulating all the components. Methanol was effective in this respect. Figure 1 shows the layer-by-layer build-up of the fluorinated polyelectrolytes. The regular growth of the multilayer alleviated our concerns that the polyelectrolytes, probably existing as micellar, nanoparticulate dispersions rather than true solutions, might not produce acceptable multilayering behavior. Some curvature of the build-up curve hints at exponential growth (a topic of recent interest [16,17] ), but the fact that such curvature is so slight suggests it might result from increasing surface roughness, which was found to be 2.9, 3.2...

Bioinspired Materials for Self-Cleaning and Self-Healing

“…Others have focused on a toolbox of methods for creating these materials. A variety of superhydrophobic surfaces obtained using dry methods such as plasma modification, 26,40 laser etching, 41 and templating 42 and wet methods such as layer-by-layer deposition, 43 colloidal assembly, 44 electrospinning, [45][46][47] and solvent evaporation 48 have been reported.…”

Design and Creation of Superwetting/Antiwetting Surfaces

“…[80] The methods mentioned above are some of the convenient approaches for the construction of special rough surfaces with superhydrophobicity. In addition to these, many other methods have also been developed, including chemical vapor deposition (CVD), [18,81] plasma polymerization/etching of polymer films, [82,83] laser ablation and photolithography-based microfabrication, [84] self-assembly, [85][86][87] glancing-angle deposition, [88] and wet chemical deposition routes. [89][90][91] …”

Preparation and characterization of self-cleaning stable superhydrophobic linear low-density polyethylene

“…Because of their self-cleaning property and limited contact area between solid surfaces and water, superhydrophobic surfaces have great potential applications in both industrial and agriculture fields [7]. Recently, the preparation of artificial superhydrophobic surfaces has attracted much attention, and many methods of fabricating superhydrophobic surfaces, such as the solution method [8], sol-gel method [9][10][11][12], plasma fluorination method [13][14][15][16][17], electrospinning method [18][19][20][21][22][23][24][25], template method [26][27][28][29], layer-by-layer self-assembly [30][31][32][33][34], and other methods [35][36][37][38][39][40][41][42][43] have been proposed. However, most of these methods are rather complicated.…”