Wetting on a corrugated surface that is formed via wrinkling of a hard skin layer formed by UV oxidation (UVO) of a poly(dimethylsiloxane) (PDMS) slab is studied using advancing and receding water contact angle measurements. The amplitude of the wrinkled pattern can be tuned through the pre-strain of the PDMS prior to surface oxidation. These valleys and peaks in the surface topography lead to anisotropic wetting by water droplets. As the droplet advances, the fluid is free to move along the direction parallel to the wrinkles, but the droplet moving orthogonal to the wrinkles encounters energy barriers due to the topography and slip-stick behavior is observed. As the wrinkle amplitude increases, anisotropy in the sessile droplet increases between parallel and perpendicular directions. For the drops receding perpendicular to the wrinkles formed at high strains, the contact angle tends to decrease steadily towards zero as the drop volume decreases, which can result in apparent hysteresis in the contact angle of over 100°. The wrinkled surfaces can exhibit high sessile and advancing contact angles (>115°), but the receding angle in these cases is generally vanishing as the drop is removed. This effect results in micrometer sized drops remaining in the grooves for these highly wrinkled surfaces, while the flat analogous UVO-treated PDMS shows complete removal of all macroscopic water drops under similar conditions. These wetting characteristics should be considered if these wrinkled surfaces are to be utilized in or as microfluidic devices. 相似文献
In numerous applications in microfluidics, cell growth, soft lithography, and molecular imprinting, the surface of poly(dimethylsiloxane) (PDMS) is modified from a hydrophobic methyl-terminated surface to a hydrophilic hydroxyl-terminated surface. In this study, we investigated molecular structural and orientational changes at the PDMS-air interface in response to three commonly used surface modification processes: exposure to long-wavelength ultraviolet light (UV), exposure to short-wavelength UV that generates ozone (UVO), and exposure to oxygen plasma (OP). The surfaces of two PDMS compositions (10:1 and 4:1 of base polymer/curing agent) were probed during modification, using monolayer-sensitive IR + visible sum frequency generation (SFG) vibrational spectroscopy, with two different polarization combinations. During PDMS surface modification, the peak intensities of CH3 side groups and CH2 cross-link groups decreased, while peak intensities of Si-OH groups increased. There was no significant change in the average orientation of the CH3 groups on the PDMS surface during modification. The concentration of CH3 groups on the surface decreased exponentially with time, for all three UV, UVO, and OP modification processes, with first order kinetics and time constants of approximately 160, 66, and 0.3 min, respectively. At steady state, residual CH3 groups were detected at the PDMS surface for UV and UVO treatments; however, there were negligible CH3 groups detected after OP modification. 相似文献
Soft skin layers on elastomeric substrates are demonstrated to support mechano-responsive wrinkle patterns that do not exhibit cracking under applied strain. Soft fluoropolymer skin layers on pre-strained poly(dimethylsiloxane) slabs achieved crack-free surface wrinkling at high strain regimes not possible by using conventional stiff skin layers. A side-by-side comparison between the soft and hard skin layers after multiple cycles of stretching and releasing revealed that the soft skin layer enabled dynamic control over wrinkle topography without cracks or delamination. We systematically characterized the evolution of wrinkle wavelength, amplitude, and orientation as a function of tensile strain to resolve the crack-free structural transformation. We demonstrated that wrinkled surfaces can guide water spreading along wrinkle orientation, and hence switchable, anisotropic wetting was realized. 相似文献
Soft skin layers on elastomeric substrates are demonstrated to support mechano-responsive wrinkle patterns that do not exhibit cracking under applied strain. Soft fluoropolymer skin layers on pre-strained poly(dimethylsiloxane) slabs achieved crack-free surface wrinkling at high strain regimes not possible by using conventional stiff skin layers. A side-by-side comparison between the soft and hard skin layers after multiple cycles of stretching and releasing revealed that the soft skin layer enabled dynamic control over wrinkle topography without cracks or delamination. We systematically characterized the evolution of wrinkle wavelength, amplitude, and orientation as a function of tensile strain to resolve the crack-free structural transformation. We demonstrated that wrinkled surfaces can guide water spreading along wrinkle orientation, and hence switchable, anisotropic wetting was realized. 相似文献
In this paper,we present a simple method by combining surface wrinkling and template replication to create a series of hierarchical structures on polydimethylsiloxane(PDMS) elastomer.The primary stable lined patterns are formed by duplicating commercialized compact disk and digital versatile disk with PDMS.The secondary microscale patterns are from surface wrinkling,which is elicited by oxygen plasma(OP) treatment of the prestrained PDMS stamp followed with the prestrain release.By systematically varying the OP exposure duration,the prestrain,and the angle(θ) between the primary pattern orientation and the prestrain direction,we obtain highly ordered well-organized composite patterns from different patterning techniques and with different length scales and mechanical stabilities. 相似文献
Here, a simple combined strategy of surface wrinkling with visible light irradiation to fabricate well tunable hierarchical surface patterns on azo‐containing multilayer films is reported. The key to tailor surface patterns is to introduce a photosensitive poly(disperse orange 3) intermediate layer into the film/substrate wrinkling system, in which the modulus decrease is induced by the reversible photoisomerization. The existence of a photoinert top layer prevents the photoisomerization‐induced stress release in the intermediate layer to some extent. Consequently, the as‐formed wrinkling patterns can be modulated over a large area by light irradiation. Interestingly, in the case of selective exposure, the wrinkle wavelength in the exposed region decreases, while the wrinkles in the unexposed region are evolved into highly oriented wrinkles with the orientation perpendicular to the exposed/unexposed boundary. Compared with traditional single layer‐based film/substrate systems, the multilayer system consisting of the photosensitive intermediate layer offers unprecedented advantages in the patterning controllability/universality. As demonstrated here, this simple and versatile strategy can be conveniently extended to functional multilayer systems for the creation of prescribed hierarchical surface patterns with optically tailored microstructures.
The authors report the formation of highly oriented wrinkling on the surface of the bilayer [polystyrene (PS)/poly(vinyl pyrrolidone) (PVP)] confined by a polydimethylsiloxane (PDMS) mold in a water vapor environment. When PVP is subjected to water vapor, the polymer loses its mechanical rigidity and changes to a viscous state, which leads to a dramatic change in Young's modulus. This change generates the amount of strain in the bilayer to induce the wrinkling. With a shape-controlled mold, they can get the ordered wrinkles perfectly perpendicular or leaned 45 degrees to the channel orientation of the mold because the orientation of the resultant force changes with the process of water diffusion which drives the surface to form the wrinkling. Additionally, they can get much smaller wrinkles than the stripe spacing of PDMS mold about one order. The wrinkle period changes with the power index of about 0.5 for various values of the multiplication product of the film thicknesses of the two layers, namely, lambda approximately (h(PS)h(PVP))(1/2). 相似文献
Surface wrinkling is a promising route to control the mechanical, electrical, and optical properties of materials in a wide range of applications. However, previous artificial wrinkles are restricted to single or random orientation and lacks selectivity. To address this challenge, this study presents multidirectional wrinkle patterns with high selectivity and orientation through sequential uniaxial strain with conformal polymeric shadow masks. The conformal but nontraceable polymeric stencil with microapertures are adhered to a flat substrate prior to oxidation, which forms discrete and parallel wrinkles in confined domains without any contamination. By fully investigating the process, this study displays compound topography of wrinkles consisting of wrinkle islands and surrounding secondary wrinkles on the same surface. With this topography, various diffusion properties are presented: from semi‐transparent yet diffusive films to multidirectional diffusive films, which will be available for new types of optical diffuser applications. 相似文献
An in-plane constrained cross-linked gel layer absorbs an equilibrium amount of solvent and experiences in-plane compressive stress. A stability analysis of such an elastic gel layer that is attached to either a viscous or an elastic bottom layer atop a rigid substrate is considered. The effects of the top and bottom layer moduli (E(t) and E(b)), the bottom-to-top layer thickness ratio (H/h), and the polymer solvent interaction parameter (chi) on the critical condition of wrinkling, wrinkle wavelength, and amplitude are examined. When the bottom layer is viscous, the compressed top layer is always unstable, and wrinkling is rate-controlled. The viscous flow of the bottom layer governs the rate and determines the fastest growing wavelength. As E(t) rises, the bending stiffness of the elastic layer does as well, and so the fastest growing wavelength (lambda(m)) rises and the equilibrium amplitude (A(e)) falls. As H/h rises, the constraint of the rigid substrate diminishes, and so lambda(m) and A(e) rise. As chi falls or as the solvent has higher affinity for the polymeric gel, lambda(m) falls and A(e) rises because better solvents create higher compressive strain that promote low-wavelength, high-amplitude wrinkles. When the bottom layer is elastic, a critical compressive stress exists. If the generated compressive stress by solvent absorption is greater than the critical stress, the top layer wrinkles. It was found that wrinkling is most likely at intermediate E(t), low E(b), high H/h, and low chi. Further, lower chi, higher H/h, and lower E(b) were found to promote higher equilibrium amplitude and higher wavelength wrinkles. 相似文献
