Effects of electric field and temperature on the shape of chlorophyll aggregates in casting films

Highlights: • Influence of temperature/electric field on chlorophyll aggregate form was studied. • Fractal dimensions of chlorophyll aggregates ranged from 1.54 to 1.66. • Electric field application induced a Brownian-tree to chain-shaped form change. • Morphology variation changed the wettability of film surfaces. -- Abstract: We have prepared chlorophyll (Chl) casting films and characterized the effects of temperature and electric field on the fractal forms of Chl aggregates formed therein. The amount of fractal aggregates increased with increasing temperature. Their fractal dimensions (1.54–1.66) were close to those predicted by the diffusion-limited aggregation model. The surface morphology change of Chl films with temperature did not affect their wettability, i.e., these films remained hydrophilic, exhibiting contact angles θ_C of 35.3 ± 4.9°. The application of an electric field induced a Brownian-tree to chain-shaped aggregate form change, which was rationalized by the effect of electric drag on diffusion of Chl molecules. In contrast to the case of temperature-induced morphology change, the corresponding variation caused by the applied electric field have changed the film wettability and turned the originally hydrophilic (θ_C = 35.3 ± 4.9°) films into hydrophobic (θ_C = 86.6 ± 4.0°) ones. This find was consistent with the change in shape of the fractal aggregates.