Zinc Oxide Superstructures in Colloidal Polymer Nanocomposite Films: Enhanced Antibacterial Activity through Slow Drying

Abstract

Achieving control over the distribution of biocides across the thickness of polymer nanocomposite films is one of the largest challenges to develop efficient antibacterial surfaces. In such applications, it is key to maximize the biocide presence at the film top surface to ensure contact with bacteria. Here, we make use of evaporation driven colloidal self-assembly to control the vertical distribution of biocides in polymer composite films cast from colloidal blends of polymer and zinc oxide (ZnO) nanoparticles. We present a thorough study which shows that the evaporation rate and ZnO volume fraction have a strong impact on the final film architecture and on its wetting and antibacterial properties. For high enough ZnO volume fraction, the ZnO nanoparticles assemble in superstructures on top of the film, which are higher the slower the evaporation rate used, and maximum ZnO surface coverage achieved through slow film drying. At high ZnO volume fraction (ϕ = 0.29), the zone of inhibition diameter against Escherichia coli increases as evaporation rate decreases, with the nanocomposite films having the strongest antibacterial activity when formed at slow evaporation rate. We propose a model for the formation of these colloidal superstructures based on the segregation of large (polymer) and small (ZnO) particles during drying, followed by the assembly of small particles around packed large particles due to differences in the surface charge of the two populations. Our work provides valuable guidelines for the design and assembly of not only antibacterial colloidal films but also a wider range of functional colloidal polymer films including abrasion resistant, self-cleaning, and others.

Evaporation-driven self-assembly of binary and ternary colloidal polymer nanocomposites for abrasion resistant applications

“…Drying at moderate evaporation rates results in much more heterogeneous structures, with higher silica coverage, as seen in Figure 1(e). These structures more closely resemble those reported by Dong et al in blends of latex and zinc oxide 40 . Drying at even faster evaporation rates results in further alterations to the final silica superstructure.…”

“…This is the case for bactericidal nanofillers, which need to be at the film surface to impart antimicrobial activity 39 . Recently, Dong et al harnessed the stratification process to fabricate antibacterial coatings with an optimized zinc oxide coverage at the surface 40 . Reinforcing particles are also primarily required at the surface of polymer films to improve hardness.…”

Colloidal assembly of polydisperse particle blends during drying

“…The zeta potential of P(MMA-BA) particles is À43 AE 1 mV, and they have a glass transition temperature T g of 19 1C, as measured by DSC. 32 The zeta potential of the zwitterionic particles is À19.8 AE 0.5 mV, and the measured T g of the butyl/hexyl methacrylate core is À8 1C as measured by DSC (see Fig. S3, ESI †).…”

“…An aqueous dispersion of surfactant-free polymer particles was synthesized via emulsion polymerization of poly(methyl methacrylate/butyl acrylate) (MMA/BA: 1/1 by weight) and 1 weight% based on monomer of sodium styrene sulfonate (NaSS), as described elsewhere. 31 The glass transition temperature (T g ) was 19 1C, 32 and the solids content of the dispersion was 50 wt%.…”

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphologies

“…Once doped, they display new properties, e.g., electrical conductivity, magnetic, magneto-optical, photocatalytic, antibacterial and optical [ 74 , 161 , 220 , 221 , 222 , 223 , 224 , 225 , 226 , 227 , 228 , 229 , 230 , 231 , 232 ]. At present, various ZnO nanostructures are being used in attempts to produce a new generation of light-emitting diodes [ 233 , 234 ], lasers [ 235 ], field emission devices [ 236 , 237 ], memory carriers [ 238 , 239 ], solar cells [ 240 , 241 , 242 , 243 , 244 , 245 , 246 ], liquid crystals [ 247 ], polymer nanocomposites [ 248 , 249 , 250 , 251 ], food packaging materials [ 252 , 253 , 254 , 255 , 256 , 257 , 258 ], transparent ultraviolet light absorbers in unplasticised polymers [ 259 ], catalysts [ 260 ], photoluminescent NPs [ 261 ], photocatalysts ...…”