Subscriber access provided by University of Colorado Boulder
Article
A New Scalable Approach Towards Shape Memory Polymer Composites via ‘Spring-Buckle’ Microstructure Design Xiaodong Wu, Yangyang Han, Zehang Zhou, Xinxing Zhang, and Canhui Lu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b02238 • Publication Date (Web): 30 Mar 2017 Downloaded from http://pubs.acs.org on April 6, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 27
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
A New Scalable Approach Towards Shape Memory Polymer Composites via ‘Spring-Buckle’ Microstructure Design Xiaodong Wu, Yangyang Han, Zehang Zhou, Xinxing Zhang,* and Canhui Lu* State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu 610065, China.
Abstract: Shape memory polymers (SMPs) have attracted tremendous research interests since their discovery. However, most advances in research of SMPs are based on molecular designs, i.e., ‘bottom-up’ strategies. Due to the viscoelasticity of polymers, slow and incomplete shape variations are inevitable for most existing SMPs. Here, we propose a simple and scalable approach to design and fabricate SMP composites (SMPCs) based on a ‘spring-buckle’ microstructure design. Specifically, a highly elastic ‘spring’ is employed as a basic skeleton for the SMPCs, onto which self-adhesive and stimuli-responsive ‘buckles’ are installed as reversible switch units. The resultant SMPCs with such ‘spring-buckle’ microstructure enable quick programming at ambient temperature, ultrafast (2-3 s) and nearly complete (~100%) shape recovery triggered by organic solvents, benefiting from a unique capillary effect. This structural approach provides a novel design philosophy for shape memory materials, and opens up new opportunities for their applications in sensor, actuator, aerospace and other applications.
ACS Paragon Plus Environment
1
ACS Applied Materials & Interfaces
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 27
Keywords: polyurethane sponge, natural rubber, shape memory polymer composite, microstructure design, capillary effect, liquid sensing.
1. Introduction Shape memory materials are a class of smart materials that can memorize temporary shapes and recover to their permanent shapes when triggered by external stimuli1. As an important branch of shape memory materials, shape memory polymers (SMPs) have attracted extensive interests from both fundamental research and technological innovations since its discovery in the 1940s2. Especially during the past two decades, the field of SMPs has witnessed a rapid growth because of their intrinsic versatility in many practical and potential applications, such as heatshrinkable tubes and films, implants for minimally invasive surgery3, drug releasing systems4, self-healing materials5, sensors6, actuators7, aerospace applications8, etc9-17. Generally, the prerequisite for endowing polymers with shape memory effect involves two elements: permanent net-points and reversible switch units. As illustrated in Figure 1a, reversible switch units can be deformed above their transition temperature to program temporary shapes (i.e. programming). The temporary shapes can be hold by crystallization or vitrification (i.e. storage). When triggered by external stimuli (such as heat, light, solvent, magnetic field, electricity, etc), the produced activation energy allows the relaxation of polymer chain segments, and the net-points (including covalent cross-links and physical cross-links) drive SMPs to return to their permanent shapes (i.e. recovery). Hitherto, however, almost all the advances in SMP fields (bulk SMPs, SMP hydrogels, composites, foams, microstructures, etc) are based on molecular designs (i.e. ‘bottom-up’ strategies), including new molecular designs4,6,10,16,18-19, performance optimization through compositional tuning20-21, alternative shape recovery
ACS Paragon Plus Environment
2
Page 3 of 27
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
triggering mechanisms7,18-19 and innovative SMP applications3-5,12-17. Unfortunately, shape memory effect is not an intrinsic property of polymers, but relies heavily on movement and relaxation of polymer chains. Due to the viscoelasticity of polymers, hot and slow programming, unstable shape fixation, slow and incomplete shape recovery are inevitable for most existing SMPs. Moreover, complicated molecular design/synthesis or sophisticated microphase controlling are usually involved in ‘bottom-up’ strategies. These might lead to high-cost and other disadvantages for these SMPs in their practical manufacturing and applications. Alternatively, shape memory composites/hybrids provide another strategy to fabricate shape memory materials with interesting properties22-23. For instance, Huang and co-workers developed shape memory hybrids consisting of plastic sponge and P407 gel. These shape memory hybrids exhibited cooling-responsive and water-responsive shape memory effect24. Venkatraman et al. fabricated shape memory composites comprising radio-opaque filler-filled polymer blend and polymer hydrogel. These composites revealed potential application for temporary vascular occlusion25. Besides, Krishnan and co-workers prepared biodegradable hybrid nanocomposites with shape memory properties based on starch and lysine26. Compared with SMPs, the shape memory effect of these composites/hybrids can be readily tuned, and more phenomena and new features can be realized through rational design. Here, for the first time, we propose an innovative structural approach to fabricate new SMP composites (SMPCs) with a ‘spring-buckle’ structure based on micro-structural design. To further elucidate the general concept, the design philosophy of our structural SMPCs is illustrated in Figure 1b. Specifically, a highly elastic ‘spring’ is employed as a basic skeleton for the SMPCs, onto which self-adhesive and stimuli-responsive ‘buckles’ are installed as reversible switch units. When a finite force is applied onto the ‘spring-buckle’ composites, ‘spring’ is
ACS Paragon Plus Environment
3
ACS Applied Materials & Interfaces
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 27
compressively deformed. Simultaneously, the ‘buckles’ are locked together, which traps the SMPCs in temporary shapes. When subjected to appropriate external stimuli, the ‘buckles’ could be opened and the elastic ‘spring’ drives the deformed composites to recover to their original shapes quickly. With this unique ‘spring-buckle’ microstructure, such SMPCs are expected to attain quick programming, very fast and nearly complete shape recovery and other unique functions. In this work, we explored the feasibility of constructing SMPCs based on the proposed ‘springbuckle’ microstructure design. By carefully selecting, natural rubber (NR) with self-adhesive behavior modulatable by external stimuli was chosen as the ‘buckles’ and coated on highly elastic polyurethane (PU) ‘spring’ via water-based layer-by-layer (LBL) assembly, forming SMPCs. As expected, the as-prepared SMPCs enabled quick programming at room temperature, ultrafast (2-3 s) and nearly complete (100%) shape recovery induced by organic solvents. Furthermore, the SMPCs exhibited fast organic liquid sensing behavior (
