Controlling the Wettability of Hierarchically Structured Thermoplastics

Abstract

Surfaces play an important role in defining the properties of materials, controlling wetting, adsorption, or desorption of biomolecules, and sealing/bonding of different materials. We have combined microscale features with plasma-etched nanoscale roughness and chemical modification to tailor the wettability of the substrates. Cyclic olefin polymers and copolymers (COPs/COCs) were processed to make a range of surfaces with controlled superhydrophobic or -hydrophilic properties. The hydrophobic properties of the polymers were increased by the introduction of microstructures of varying geometry and spacing through hot embossing. The COC/COP substrates were functionalized by plasma activation in O(2), CF(4), and a mixture of both gases. The plasma etching introduces nanoscale roughness and also chemically modifies the surface, creating either highly hydrophilic or highly hydrophobic (contact angle >150°) surfaces depending on the gas mixture. The influence of geometry and chemistries was characterized by atomic force microscopy, contact angle measurements, and X-ray photoelectron spectroscopy. Measurements of the contact angle and contact angle hysteresis demonstrated long-term stability of the superhydrophobic/superhydrophilic characteristics (>6 months).

Adhesion of sputter-deposited Cu/Ti film on plasma-treated polymer substrate

“…The surface morphology of the postplasma-etched polymer can vary depending on the plasma power, gas composition and chemical structure of the polymer substrate. In fact, plasma etching has been used to fabricate polymer nanowires [16] and to induce nanoscale roughness of a polymer surface [17]. In order to see whether the plasma chemistry have an effect on the surface morphology of the ABF substrate, O 2 plasma (1.2 kW, 240 s) was used to pretreat the ABF substrate prior to deposition of 10-nm-thick Ti film and the resulting cross-sectional TEM images are shown Fig.…”

Fabrication of superhydrophobic transparent cyclic olefin copolymer (COC)‐SiO2 nanocomposite surfaces

“…Comonomer ratio can be arranged to have low or high glass-transition temperature (T g ) ranging from 33 to 180. [49][50][51][52] COC has excellent properties, such as, resistance to many organic solvents, outstanding biocompatibility, very good melt processability and moldability, low absorption of moisture, high rigidity, strength and hardness, high optical clarity, and so on. It is one of the good candidates for glass in the electrical and optical areas.…”

Controlled Smart Anisotropic Unidirectional Spreading of Droplet on a Fibrous Surface

“…An aligned PET (hydrophobic)/CHI (hydrophilic) fibrous surface (see Figure a) can be easily obtained via electrospinning technique coupled with a high‐speed‐collection drum (see Figure S1a in the Supporting Information). The hydrophobic/hydrophilic property of microstructures on the surface has a large impact on the wetting behavior of droplets, thus the anisotropy of PET/CHI surface can be controlled by tailoring the PET/CHI composition (see Figure S2 in the Supporting Information). As shown in Figure b, compared with a spherical shape (left, hydrophobic) on a pure PET fibrous surface, the ink droplet deforms to a stick‐like shape (middle, strong anisotropy with a length/width ratio ( L / W ) of ≈6.6) when PET/CHI is around 10/2.…”