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...

The surface roughness of polyelectrolyte multilayers made from poly(diallyldimethylammonium chloride), PDADMAC, and poly(styrene sulfonate), PSS, was measured as a function of film deposition conditions. For dry multilayers, the significant roughness which builds up for thicker films is much more apparent for multilayers terminated with PSS. Corresponding roughness for PDADMA-capped multilayers may be seen by imaging in situ under electrolyte. Roughness may be substantially reduced, but not eliminated, by annealing in salt. Annealing does not lead to loss of polyelectrolyte from the film, even under conditions where the salt concentration is high enough to place the film properties beyond the glass transition. Roughness does not correlate with the molecular weight of the polyelectrolyte and is thus not caused by solution or film polymer chain conformations. The wavelength of the roughness features is approximately proportional to film thickness, which supports a mechanism whereby roughness is generated by anisotropic swelling due to water and polyelectrolyte addition in a manner similar to water uptake in hydrogels. Roughness is preserved by the glassy PSS layer and probably incorporated within the film as it grows.

A series of copolyelectrolytes with randomly positioned fluorinated (hydrophobic) and zwitterionic (hydrophilic) repeat units was synthesized and used to assemble multilayers. Regular layer-by-layer growth was observed for polymers with a charge density as low as 6%. The hydrophobicity of these "schizophobic" surfaces increased with increasing fluorine content. Polymer-on-polymer stamping was used to create patterned areas of low and high friction, probed by lateral force microscopy using a modified hydrophobic tip. "Contractile" A7r5 smooth muscle cells adhered to the fluorinated surfaces, but the introduction of zwitterion functionality induced a motile, less firmly attached morphology consistent with the "synthetic" motile phenotype of this cell line. In contrast with cells well adhered (on fluorinated) or completely nonadhering (on zwitterionic) films, incorporation of closely spaced repeat units with strongly contrasting hydrophobicity appears to generate intermediate cell adhesion behavior.

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, 4....