Controlled Fabrication Of Superhydrophobic Al Foil With Anti-dew And Anti-frosting Properties

Aluminum foil has good heat conductivity and is widely used in heat exchangers as well as a variety of electrical equipments. However, the formation of the drops and frost by water vapor condensation in the surface will produce a high thermal resistance, which will greatly reduce heat transfer efficiency of the heat exchanger, and thus waste enormous energy. It is reported that superhydrophobic surface with special micro-and nano-structures is an effective way to inhibit or even eliminate condensation and frost. Although there are already a large number of experimental reports about successfully preparing of superhydrophobic aluminum surfaces, but it is difficult to achieve the performance of anti-dew and anti-frosting due to the condensed water trapped into the aluminum surfaces’gap of the micro-and nano-structures. In this paper, we use a simple, inexpensive, one-step variable voltage electrochemical anodic oxidation method, choosing phosphoric acid as the electrolyte to fabricate the nanopores with nano-protuberances composite array structures on the aluminum surface. Studies show that after modifying with the low surface energy material, the structure has perfect ultra-hydrophobic properties, with an extremely low adhesion to the water droplets. The water droplets formed in the condensation process can be quickly detached from the surface and the time of beginning to frost may be considerably delayed. Specific research contents are as follows:1. Controllable preparation of nanostructure arrays on Al foil surface. We use one-step variable voltage electrochemical anodic oxidation method to fabcricate nano-pore with nano-protuberances composite array structures on aluminum foil surface. Through studying the influence of each of the experimental parameters in the reaction process (the pretreatment conditions, the concentration of the electrolyte, reaction starting voltage, the reaction temperature, the continue oxidation time after the current rises to1.0A, the distance between the electrode and the aluminum foil, the rise voltage rate) on the sample surface morphology and performance to explore the formation mechanism of the aluminum surface with nano composite array structure, achieving the low cost, large area and controllable preparation of the superhydrophobic aluminum surface with nanostructures.2. Anti-dew performance test of superhydrophobic aluminum foil. After modifying with the low surface energy material FAS, the alumina nanopore with nano-protuberances composite array structure having stable, non-sticky ultra-hydrophobic properties, the static contact angle is greater than160°, the roll angle is close to0°, and adhesive force is about6μN. It can maintain good stability under the raindrop impact and even harsher conditions. Under the condition of high humidity and low temperature, the sample’s anti-dew performance was tested by comparing with the ordinary aluminum foil and a hydrophobic aluminum foil. We found that the water droplets formed on the samples can bounce off from the surface and they can take away a large number of other water droplets on the sample in the rolling process to keep surface dry.3. Anti-icing/anti-frosting performance test of the superhydrophobic Al foil. Simulating natural icing/frosting conditions, we test the anti-icing/anti-frosting performance of the superhydrophobic Al foil in comarison with smooth aluminum foil. The results show that, under the same conditions, icing/frosting occurs latest on the superhydrophobic Al foil surface. The times for initiating icing/frosting on the samples’surfaces are obviously shortened after adding external disturbances. At the same temperature and the same icing/frosting time, the quality of ice/frost is smallest on superhydrophobic Al foil surface. These results revealed that the superhydrophobic surface has the best anti-icing/anti-frosting effect. At different temperature but the same icing/frosting time, ice/frost quality on the super-hydrophobic Al foil is not the same:the lower the temperature, the more quality of the ice/frost. This phenomenon indicates that the anti-icing/anti-frosting effect of the superhydrophobic Al foil is decreased, with decreasing of the temperature.