The solid fraction f s was calculated based on the actual pattern dimensions measured from the AFM and SEM images see Supplementary Information for f s calculation. The deformed micro- and nanopatterns were subsequently investigated for the surface wetting properties. While hard segments in the polymer chains would migrate to the surface during stretching 46 , the molecular reorientation did not result in a significant change in the surface wettability in our case. Therefore, the changes in CAs on the surface patterns under different tensile strains observed in our study could mainly be attributed to the pattern transformation, rather than surface chemistry.
The CA measurement data for various surface patterns as a function of tensile strain is shown in Fig. Depending on the geometric feature, the CA on a patterned surface varied in different extents with the mechanical strain levels. To illustrate qualitatively, we consider a schematic shown in Fig.
Since the SMP used is intrinsically hydrophobic, the water droplet would not be able to fully intrude into the patterned structure Rather, there would be small air spaces trapped within the grooves. In contrast to the above discussion, the surface wetting characteristic of the holes did not exhibit a systematic relationship between the deformed geometries and the corresponding CAs. This could be associated with the presence of continuous solid surrounding the holes, which hinder the water droplet from wetting the sidewall.
This switchable wetting without changing materials or needing continuous external stress or energy inputs presents an alternative to applications where dynamic control of liquid wetting is needed, for example in fluidic devices, nanoparticle assembly and water collection 15 , 49 , Figure 7 conceptually demonstrates the transfer of a microdroplet from one surface to another. By mechanical modulation, the deformable surface texture can be used to selectively transfer microdroplets of different volumes from one surface to another; and by using SMP the deformation of the surface texture may be kept in a transient stage without resulting in a permanent deformation.
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Water droplet adhesion is known to be dependent on the geometry and length-scale of the surface textures As such, coupling the current research results with surface texture design provides a novel approach to manipulate liquid transport. Although there are many existing examples of surface functionalities such as wetting achieved by surface texturing, this study has shown the shape memory effect to not only be effective at a certain rationale design of surface pattern i. For instance, varying contents of the hard and soft segments in a thermoplastic elastomer can lead to different thermomechanical properties e.
The SMPs can still be deformed and recovered in the similar manners above the respective T trans at a rubbery state.
Mechanics of Materials: Strain » Mechanics of Slender Structures | Boston University
Besides thermal recovery, the understanding gained from this study can also apply to other external stimulation e. Hence, this work can serve as the basis for future studies investigating the role of different geometries of responsive complex structures e. Polyetherurathane-based SMP was thermally imprinted with permanent shape made up of micro- and nanoscale surface textures. The pattern deformation and recovery can be engineered by tailoring surface texture designs including length scale, degree of anisotropicity and shape protruding vs.
While the applied strain and inherent material properties are responsible for the macroscopic bulk deformation, free surface coupled with proportion of mobile chains, surface area-to-volume ratio, dependence of stress distribution on surface geometry are the factors involved in governing the pattern deformation.
Distinct deformations of various pattern geometries under the same applied strain could influence the subsequent recovery. In contrast to bulk behaviours, surface pattern recovery mechanism could be driven by the interplay of the surface area minimization and entropy elasticity of the soft segment. We further reported the control of deformable surface patterns on surface wetting tuning without the need for continuous input of external stresses or energies. Therefore, this new approach would open up an avenue of incorporating shape memory surface pattern into microfluidic devices for manipulating fluid transport.
The silicon moulds used to fabricate the micro- and nanoscale surface textures are listed in Table 1. High-resolution and well-defined surface textures can be controllably fabricated through nanoembossing technique, commonly known as nanoimprinting The moulds were further treated with a fluorosilane release agent 0. Note that the silane-treated moulds underwent a self-cleaning imprint on polycarbonate films to further remove the physisorbed silane if any.
This is to ensure that there is no influence of silane on the subsequent contact angle measurements. Upon demoulding, these patterns were formed permanently on the surfaces of the polymer films.
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The polymer films were placed in a home-built sample holder for uniaxial stretching. For grating-structured films, the stretching direction was orthogonal to the longitudinal axis of the grating. The stretching and recovery experiments on each surface pattern were done in triplicate. Dimensions of surface pattern on 2 fields in independent SEM images were analysed with ImageJ software. For stretched samples, the AFM tip was positioned near the centre of the neck region 46 , Surface pattern dimensions were provided by the software measurement; the values obtained from the AFM software were also cross-checked with the values measured on the SEM images.
Wettabilities of samples were characterized by measuring static water contact angles CAs using a sessile drop method on a contact angle goniometer Kino SLKS. CA values were obtained from the integrated software in the goniometer. How to cite this article : Lee, W. Behl, M. Shape-memory polymers. Today 10 , 20—28 Liu, C. Review of progress in shape-memory polymers. Lendlein, A. Light-induced shape-memory polymers.
Nature , — Multifunctional shape - memory polymers. Kratz, K. Temperature - memory effect of copolyesterurethanes and their application potential in minimally invasive medical technologies.
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Liu, Y. Thermomechanics of shape memory polymers: Uniaxial experiments and constitutive modeling.
Kohlmeyer, R. Remote, local, and chemical programming of healable multishape memory polymer nanocomposites. Nano Lett.
Rodriguez, E. ACS Appl. Interfaces 3 , — Reddy, S. Bioinspired surfaces with switchable adhesion. Sharp, A. Toward a self-deploying shape memory polymer neuronal electrode. Neural Eng. Yakacki, C. Deformation limits in shape - memory polymers. Mohr, R. Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers.
USA , — Yu, K. Reduced time as a unified parameter determining fixity and free recovery of shape memory polymers. Wang, Z. Programmable, pattern - memorizing polymer surface. Chen, C. Directed water shedding on high - aspect - ratio shape memory polymer micropillar arrays. Xu, H. Deformable, programmable, and shape - memorizing micro - optics. Chhatre, S. Scale dependence of omniphobic mesh surfaces.
Langmuir 26 , — Wu, Z. Stimuli-responsive topological change of microstructured surfaces and the resultant variations of wetting properties. Interfaces 5 , — Vrancken, R. Anisotropic wetting and de-wetting of drops on substrates patterned with polygonal posts. Soft Matter 9 , — Lee, S. Tunable anisotropic wettability of rice leaf - like wavy surfaces. Obara, N.
Imbibition of a textured surface decorated by short pillars with rounded edges. E 86 , Liu, N. Formation of micro protrusion arrays atop shape memory polymer. Xie, T. Encoding localized strain history through wrinkle based structural colors. Yang, S. Harnessing surface wrinkle patterns in soft matter. Lee, E. Tilted pillars on wrinkled elastomers as a reversibly tunable optical window. Kim, P. Rational design of mechano - responsive optical materials by fine tuning the evolution of strain - dependent wrinkling patterns. Chou, S. Any international shipping and import charges are paid in part to Pitney Bowes Inc.
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An "effective radius" for the tip was determined from the simulated data, and FEM simulations were conducted from this idealized geometry for comparison with those from the measured geometry. The differences in the stress distributions provide a quantitative measure of the experimental stress uncertainties caused by the non-spherical shape of the tip. Finally, plastic deformation of gold nanowires has received considerable attention recently due to their ability to form single atom chains which results in quantized conductance.
NIST has identified the breaking of such nanowires as a likely candidate for a much needed intrinsic force standard for very small loads, and accurate quantum-mechanics-level simulations have been used to explore the deformation behavior over a wide range of deformation conditions. The figure below shows the atomic configuration of a stretched gold nanowire that was simulated using density functional theory. It was found that single atom chains are easily formed and that the breaking force of these chains is extremely consistent at 1. Summary This project provides new measurement methods, property data and simulations for areas critical to US manufacturing, describing the mechanisms responsible for mechanical behavior.
Download Image info. Major Accomplishments High impact and effective dissemination of NIST measurement capabilities can be achieved by directly incorporating these experimental techniques into national user facilities such as the DOE-operated APS.