Hierarchical patterning of hydrogels by replica molding of impregnated breath figures leads to superoleophobicity

Abstract

The surface chemistry and topography govern the spreading of liquids on a solid. When an oil drop makes a contact angle, θ > 90° on a solid surface, the solid is termed as oleophobic. Adding roughness to an inherently oleophobic surface enhances its oil dewetting and can lead to superoleophobicity when θ > 150°. In this study, we introduce the concept of a two-tier hierarchical roughness on the surface of soft materials such as hydrogels by forming the patterned inverse replica of breath figure polymer films impregnated with nanoparticles. The directed deposition of nanoparticles in the breath figure pores is accomplished by an aerosol assisted technique that exclusively leads to deposition within the pores and filling of the pores. The inverse replica of such impregnated films exhibits a close packed hexagonally structured second tier of surface roughness which directly leads to a superoleophobic surface. Since these structures have well defined geometries, it is possible to estimate the contact angle by assuming a partial wetting of the oil drop in a 'fakir' state on the rough surface. The estimation is in good agreement with the experimental contact angle value. While the work demonstrates a facile method to impart superoleophobicity to a hydrogel surface, it also demonstrates new methods to imbue breath figure pores with functional materials that can be easily transferred to the pores of the inverse replica.

Breath-Figure Self-Assembly, a Versatile Method of Manufacturing Membranes and Porous Structures: Physical, Chemical and Technological Aspects

“…Various experimental techniques were successfully applied for breath-figure self-assembly, including drop-casting [ 66 , 67 , 68 , 69 , 70 , 71 ], spin-coating [ 72 , 73 , 74 , 75 , 76 , 77 , 78 ], the “doctor-blade” technique [ 79 , 80 ], and dip-coating [ 46 , 54 , 58 , 81 , 82 , 83 ]. When breath-figures-inspired patterns are formed under drop-casting, a drop of polymer solution is deposited by a precise micro-syringe (or micro-injector) on a solid substrate and exposed to air flow with a controlled humidity [ 66 , 67 , 68 , 69 , 70 , 71 ].…”

Recent Advances in Bioinspired Gel Surfaces with Superwettability and Special Adhesion

“…[39] The PNIPAAm-nanoclay hydrogels were fabricated by photoinitiated radical polymerization of the mixture of NIPAAm and clay nanoparticles. [41,42] Similarly, to mimic the hydrogel-like mucus layer of S. japonica, Cai et al fabricated calcium alginate (Ca-alginate) hydrogel coating with salt-tolerant oil-repellent features on glass slides through the electrostatic interactions of polyanions and polycations. The interaction of the rigid nanoclay and flexible polymer networks supports the stability of trapped water on the hydrogel surface and contributes to the robust superoleophobicity and low adhesion properties.…”

Breath-Figures Self-Assembly, the Versatile Method of Manufacturing Membranes and Porous Structures: Physical, Chemical and Technological Aspects

“…Various experimental techniques were successfully applied for the breath figures self-assembly, including: drop-casting [66][67][68][69][70][71], spin-coating [72][73][74][75][76][77][78], the "doctor-blade" technique [79][80] and dip-coating [46,54,58,[81][82][83]. When breath-figures inspired patterns are formed under drop-casting a drop of polymer solution is deposited by the precise micro-syringe (or micro-injector) on the solid substrate and exposed to the air flow possessing controlled humidity [66][67][68][69][70][71].…”

“…The substrate is then rotated at high speed in order to spread the evaporated polymer solution by centrifugal force. All the process is performed under controlled humidity [72][73][74][75][76][77][78]. In the doctor-blade technique an immobilized blade applies a unidirectional shear force to the polymer solution that passes through a small gap between the blade and the substrate [79][80]84].…”

“…Multi-scale, hierarchical patterning features the breath-figures self-assembly [14,[76][77][93][94]. The characteristic spatial scales of patterns vary from nanometers to dozens of micrometers.…”