Super-hydrophobic surfaces have attracted great research interest dueto their novel performance as self-cleaning

anti-fog

and antioxidation.In this work

a new approach

based on elastomeric templates and UV-curable resins

has been developed to prepare super-hydrophobic surfaces.Poly(dimethylsiloxane) (PDMS

Sylgard 184) was purchased from Dow Corning and used to replicate lotus-leaf surfaces.In the replication step

PDMS blocks were prepared through replica molding against lotus-leaf surfaces.PDMS prepolymer was prepared by mixing the elastomer base and curing agent in a ratio of 10:1.After 20 min

the PDMS prepolymer was poured into molds within fresh lotus-leaf surfaces as masters.Then the prepolymer was cured in 40℃ oven for 4 h.After curing and peeling off

the PDMS blocks with negative lotus-leaf surfaces’ structures were obtained.Microscope observation indicates that the PDMS blocks’ surfaces were featured with hollow cavities of 7~12 microns in diameter.The PDMS blocks could be used as stamps in the following curing step of ultraviolet (UV)-curable prepolymers

which consist of oligomer

cross-linking agent

reactive monomer

and photo-initiator.In the experiment

isobornyl acrylate

siliconized urethane acrylate

benzoin dimethyl ether and dipentaerythritol pentaacrylate were used as monomer

oligomer

photoinitiator and crosslinking agent

respectively.In a typical process

UV-curable prepolymer was prepared by mixing monomer

oligomer

photoinitiator and crosslinking agent in a ratio of 10:68:2:20 Then the prepolymer was put into a 0.085 MPa vacuum oven to remove air bubble.The prepolymer was spread on substrates (silicon wafer or glass slide)

pressed by the PDMS stamp with replicated lotusleaf surface.Finally

the UV-curable prepolymer covered with the PDMS stamp was exposed to UV-light (500 μW/cm2).After curing for 15 min

the PDMS stamp was peeled off

and the cured sample was store in 40℃ oven for 5 h before further experiments.Measured by scanning electron microscopy (SEM

Hitachi S-4500)

a large amount of papillary microstructures with an average diameter of about 7~10 microns and average height of 10~18 microns could be seen on the surfaces.These papillary microstructures are replicas of the surface patterns of the lotus leaves.The obtained surfaces had water contact angles larger than 150° and small sliding angles

exhibiting fascinating super-hydrophobicity like lotus-leaf surfaces.Obviously

the replicated papillary microstructures played important role in the increase of surface hydrophobicity from about 105° (smooth film surface) to 157°.This result can be explained with the Wenzel theory.Factors influencing the wettability of resulted surfaces

such as content of monomer

cross-linking agent

initiator and light irradiation time

were also studied in detail.Experiments showed that the surface contact angles increase with the content of photoinitiator before 0.7%

and decrease with the content of crosslinking agent when larger than 20%.A monomer content of about 10% and irradiation time longer than 10 min were also preferable for achieving high hydrophobicity.Combining the advantages of soft-lithographic and UV-curing techniques

this approach can be potentially applied in fabrication of large-area super-hydrophobic surfaces.