Surface orientation of polystyrene based polymers: steric effects from pendant groups on the phenyl ring.
- Langmuir : the ACS journal of surfaces and colloids
- Published over 7 years ago
Near edge X-ray absorption fine structure (NEXAFS) coupled with molecular dynamics simulations were utilized to probe the orientation at the exposed surface of the polymer film for polystyrene type polymers with various pendant functional groups off the phenyl ring. For all the polymers, the surface was oriented so that the rings are nominally normal to the film surface and pointing outward from the surface. The magnitude of this orientation was small and dependent on the size of the pendant functional group. Bulky functional groups hindered the surface orientation, leading to nearly unoriented surfaces. Depth dependent NEXAFS measurements demonstrated that the surface orientation was localized near the interface. Molecular dynamics simulations showed that the phenyl rings were not oriented strongly around a particular “average tilt angle”. In contrast, simulations demonstrate that the phenyl rings exhibit a broad distribution of tilt angles, and that changes in the tilt angle distribution with pendant functionality give rise to the observed NEXAFS response. The more oriented samples exhibit a higher probability of phenyl ring orientation at angles greater than 60 degrees relative to the plane of the films surface.
ZnO particles were synthesized by hydrothermal route at 95 °C, with different ethylammonium nitrate (EAN) : water volume ratio (0.01 to 1) in reaction media. Morphology of ZnO particles changed from initial cylindrical to intermediate spindle and finally to spherical with increasing concentration of EAN in reaction media whereas pH of aliquots remained within range of 7-7.5. Aggregates of EAN bind to Zn(2+) enriched both terminal planes as well as to Zn(2+) and O(2-) enriched side planes of basis units which finally resulted to formation of spherical ZnO superstructures. Favorable H-bond and electrostatic interaction helped to bind EAN aggregates with surfaces of ZnO crystals. It was found that the spherical ZnO superstructures showed novel photoluminescent property and enhanced photocatalytic activity compared to that of the commercially available ZnO.
Surfactant-induced Polymer Segregation to Produce Anti-fouling Surfaces via Dip-coating with an Amphiphilic Polymer
- Langmuir : the ACS journal of surfaces and colloids
- Published over 5 years ago
We propose a rational strategy to control the surface segregation of an amphiphilic copolymer in its dip-coating with a low-molecular-weight surfactant. We synthesized a water-insoluble methacrylate-based copolymer containing oligo(ethylene glycol) (OEG) (copolymer 1) and a perfluoroalkylated surfactant (surfactant 1) containing OEG. The dip-coating of copolymer 1 with surfactant 1 resulted in the segregation of surfactant 1 on the top surface of the dip-coated layer due to the high hydrophobicity of its perfluoroalkyl group. OEG moieties of surfactant 1 were accompanied by those of copolymer 1 in its segregation, allowing the OEG moieties of copolymer 1 to be located just below the top surface of the dip-coated layer. The removal of surfactant 1 produced the surface covered by the OEG moieties of the copolymer that exhibited anti-fouling properties. Using this strategy, we also succeeded in the introduction of carboxy groups on the dip-coated surface and demonstrated that the carboxy groups were available for the immobilization of functional molecules on the surface.
- IEEE transactions on pattern analysis and machine intelligence
- Published over 3 years ago
This paper presents two new computationally efficient direct methods for fitting n-dimensional ellipsoids to noisy data. They conduct the fitting by minimizing the algebraic distance in subject to suitable quadratic constraints. The hyperellipsoid-specific (HES) method is an elaboration of existing ellipse and 3D ellipsoid-specific fitting methods. It is shown that HES is ellipsoid-specific in n-dimensional space. A limitation of HES is that it may provide biased fitting results with data originating from an ellipsoid with a large ratio between the longest and shortest main axis. The sumof- discriminants (SOD) method does not have such a limitation. The constraint used by SOD rejects a subset of nonellipsoidal quadrics, which enables a high tendency to produce ellipsoidal solutions. Moreover, a regularization technique is presented to force the solutions towards ellipsoids with SOD. The regularization technique is compatible also with several existing 2D and 3D fitting methods. The new methods are compared through extensive numerical experiments with n-dimensional variants of three commonly used direct fitting approaches for quadratic surfaces. The results of the experiments imply that in addition to the superior capability to create ellipsoidal solutions, the estimation accuracy of the new methods is better or equal to that of the reference approaches.
Crystalline, yet smooth, sphere-like morphologies of small molecular compounds are desirable in a wide range of applications but are very challenging to obtain using common growth techniques, where either amorphous films or faceted crystallites are the norm. Here we show solvent-free, guard flow-assisted organic vapour jet printing of non-faceted, crystalline microspheroids of archetypal small molecular materials used in organic electronic applications. We demonstrate how process parameters control the size distribution of the spheroids and propose an analytical model and a phase diagram predicting the surface morphology evolution of different molecules based on processing conditions, coupled with the thermophysical and mechanical properties of the molecules. This experimental approach opens a path for exciting applications of small molecular organic compounds in optical coatings, textured surfaces with controlled wettability, pharmaceutical and food substance printing and others, where thick organic films and particles with high surface area are needed.
- Langmuir : the ACS journal of surfaces and colloids
- Published about 3 years ago
Superhydrophobic surfaces require extremely rough micro-/nanostructures, but these are easily damaged, especially by scratching with sharp objects. Then, water repellency will be lost depending on the degree of destruction. We introduce a novel approach to restore the original surface properties after mechanical damage: skin shedding. This is demonstrated with a three-layer stack as a proof-of-principle system: When the original, superhydrophobic surface layer is damaged, this leads to dissolution of a sacrificial layer below. Thus, the damaged layer is shedded, a new, unharmed surface is uncovered, and superhydrophobicity can easily be restored by washing. This working principle promises to be easily extendable to multilayer systems, which would allow for multiple regeneration steps, and it is not limited to superhydrophobic surfaces.
- Journal of the Royal Society, Interface / the Royal Society
- Published over 6 years ago
The exceptionally adhesive foot of the gecko remains clean in dirty environments by shedding contaminants with each step. Synthetic gecko-inspired adhesives have achieved similar attachment strengths to the gecko on smooth surfaces, but the process of contact self-cleaning has yet to be effectively demonstrated. Here, we present the first gecko-inspired adhesive that has matched both the attachment strength and the contact self-cleaning performance of the gecko’s foot on a smooth surface. Contact self-cleaning experiments were performed with three different sizes of mushroom-shaped elastomer microfibres and five different sizes of spherical silica contaminants. Using a load-drag-unload dry contact cleaning process similar to the loads acting on the gecko foot during locomotion, our fully contaminated synthetic gecko adhesives could recover lost adhesion at a rate comparable to that of the gecko. We observed that the relative size of contaminants to the characteristic size of the microfibres in the synthetic adhesive strongly determined how and to what degree the adhesive recovered from contamination. Our approximate model and experimental results show that the dominant mechanism of contact self-cleaning is particle rolling during the drag process. Embedding of particles between adjacent fibres was observed for particles with diameter smaller than the fibre tips, and further studied as a temporary cleaning mechanism. By incorporating contact self-cleaning capabilities, real-world applications of synthetic gecko adhesives, such as reusable tapes, clothing closures and medical adhesives, would become feasible.
A water surface acts not only as an optic mirror but also as an acoustic mirror. Echolocation calls emitted by bats at low heights above water are reflected away from the bat, and hence the background clutter is reduced. Moreover, targets on the surface create an enhanced echo. Here, we formally quantified the effect of the surface and target height on both target detection and -discrimination in a combined laboratory and field approach with Myotis daubentonii. In a two-alternative, forced-choice paradigm, the bats had to detect a mealworm and discriminate it from an inedible dummy (20 mm PVC disc). Psychophysical performance was measured as a function of height above either smooth surfaces (water or PVC) or above a clutter surface (artificial grass). At low heights above the clutter surface (10, 20, or 35 cm), the bats' detection performance was worse than above a smooth surface. At a height of 50 cm, the surface structure had no influence on target detection. Above the clutter surface, also target discrimination was significantly impaired with decreasing target height. A detailed analysis of the bats' echolocation calls during target approach shows that above the clutter surface, the bats produce calls with significantly higher peak frequency. Flight-path reconstruction revealed that the bats attacked an target from below over water but from above over a clutter surface. These results are consistent with the hypothesis that trawling bats exploit an echo-acoustic ground effect, in terms of a spatio-temporal integration of direct reflections with indirect reflections from the water surface, to optimize prey detection and -discrimination not only for prey on the water but also for some range above.
Patches on the surfaces of colloidal particles provide directional information that enables the self-assembly of the particles into higher-order structures. Although computational tools can make quantitative predictions and can generate design rules that link the patch motif of a particle to its internal microstructure and to the emergent properties of the self-assembled materials, the experimental realization of model systems of particles with surface patches (or ‘patchy’ particles) remains a challenge. Synthetic patchy colloidal particles are often poor geometric approximations of the digital building blocks used in simulations and can only rarely be manufactured in sufficiently high yields to be routinely used as experimental model systems. Here we introduce a method, which we refer to as colloidal fusion, for fabricating functional patchy particles in a tunable and scalable manner. Using coordination dynamics and wetting forces, we engineer hybrid liquid-solid clusters that evolve into particles with a range of patchy surface morphologies on addition of a plasticizer. We are able to predict and control the evolutionary pathway by considering surface-energy minimization, leading to two main branches of product: first, spherical particles with liquid surface patches, capable of forming curable bonds with neighbouring particles to assemble robust supracolloidal structures; and second, particles with a faceted liquid compartment, which can be cured and purified to yield colloidal polyhedra. These findings outline a scalable strategy for the synthesis of patchy particles, first by designing their surface patterns by computer simulation, and then by recreating them in the laboratory with high fidelity.
The motion of a single rigid or elastic particle inside a corrugated narrow channel is investigated by means of Brownian dynamics simulations. Periodic oscillations of one of the asymmetric channel surfaces induce directed particle transport. For different surface structures of the resting channel surface, we determine optimal transport properties in terms of the driving frequency, particle size, and corrugation amplitude. The transport direction is changed when switching from perpendicular motion of the oscillating surface to parallel motion with respect to the resting surface, which can be rationalized by a transition from a flashing to a pushing ratchet effect. We also study the diffusion behavior and find strongly enhanced diffusion for parallel oscillatory motion with a diffusivity significantly larger than for free diffusion. Elastic large particles exhibit suppressed transport with increasing rigidity. In contrast, for small particles, increasing rigidity enhances the particle transport both in terms of particle velocity and diffusivity.