Dingcai Wu,*,† Fei Xu,† Bin Sun,† Ruowen Fu,† Hongkun He,‡ and Krzysztof Matyjaszewski*,‡ †Materials Science Institute, Key Laboratory for Polymeric Composite and Functional Materials of Ministry of Education, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, People's Republic of China ‡Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States

Design and Preparation of Porous Polymers

Finding new materials with targeted properties has traditionally been guided by intuition, and trial and error. With increasing chemical complexity, the combinatorial possibilities are too large for an Edisonian approach to be practical. Here we show how an adaptive design strategy, tightly coupled with experiments, can accelerate the discovery process by sequentially identifying the next experiments or calculations, to effectively navigate the complex search space. Our strategy uses inference and global optimization to balance the trade-off between exploitation and exploration of the search space. We demonstrate this by finding very low thermal hysteresis (ΔT) NiTi-based shape memory alloys, with Ti50.0Ni46.7Cu0.8Fe2.3Pd0.2 possessing the smallest ΔT (1.84 K). We synthesize and characterize 36 predicted compositions (9 feedback loops) from a potential space of ∼800,000 compositions. Of these, 14 had smaller ΔT than any of the 22 in the original data set.

/pdf/accelerated-search-for-materials-with-targeted-properties-by-2gaob66a72.pdf

Accelerated search for materials with targeted properties by adaptive design.

Gas permeation parameters and other physicochemical properties of a polymer of intrinsic microporosity: Polybenzodioxane PIM-1

Functional shape memory alloys need to operate reversibly and repeatedly. Quantitative measures of reversibility include the relative volume change of the participating phases and compatibility matrices for twinning. But no similar argument is known for repeatability. This is especially crucial for many future applications, such as artificial heart valves or elastocaloric cooling, in which more than 10 million transformation cycles will be required. We report on the discovery of an ultralow-fatigue shape memory alloy film system based on TiNiCu that allows at least 10 million transformation cycles. We found that these films contain Ti2Cu precipitates embedded in the base alloy that serve as sentinels to ensure complete and reproducible transformation in the course of each memory cycle.

http://science.sciencemag.org/content/sci/348/6238/1004.full.pdf

Ultralow-fatigue shape memory alloy films

Highly permeable polymers for gas separation membranes

Ultralow-fatigue Ti54Ni34Cu12 shape memory alloy films allow at least 10 million transformation cycles.

Ultralow‐Fatigue Shape Memory Alloy Films.

Micropatterned freestanding superelastic TiNi films in the thickness range between 20 and 100 µm are attractive materials for medical in vivo applications. Micropatterning of these materials by UV lithography and etching is a challenging task, as wet etching has severe design limitations due to its isotropic nature while dry etching shows much to low etching rates. This study presents a method to fabricate freestanding TiNi films (with thicknesses higher than 20 µm) with a minimum feature size 5 µm based on UV lithography, sacrificial layer and wet etching technology. This method was successfully applied to the fabrication of TiNi films with 50 µm thickness and 25 µm feature size. These superelastic films showed remarkable tensile strengths up to 1100 MPa and elongations upon fracture of more than 40%.

Micropatterned Freestanding Superelastic TiNi Films

The performance of polymeric membranes for gas separation is mainly determined by the free volume. Polymers of intrinsic microporosity are interesting due to the high abundance of accessible free volume. We performed measurements of the temperature dependence of the positron lifetime, generally accepted for investigation of free volume, in two polymers of intrinsic microporosity (PIM-1 and PIM-7) in the range from 143 to 523 K. The mean value of the free volume calculated from the ortho-positronium lifetime is in the range of typical values for high free volume polymers. However, the temperature dependence of the local free volume is non-monotonous in contrast to the macroscopic thermal expansion. The explanation is linked to the spirocenters in the polymer.

Unusual temperature dependence of the positron lifetime in a polymer of intrinsic microporosity

Self-expanding vascular implants are typically manufactured from Nitinol tubing, using laser cutting, shape setting, and electropolishing processes. The mechanical and fatigue behavior of those devices are affected by the raw material and its processing such as the melting process and subsequent warm and cold forming processes. Current trends focus on the use of raw material with fewer inclusions to improve the fatigue performance. Further device miniaturization and higher fatigue life requirements will drive the need toward smaller inclusions and new manufacturing methods. As published previously, the high-cycle fatigue region of medical devices from standard processed Nitinol is usually about 0.4-0.5% half-alternating strain. However, these results highly depend on the ingot and semi-finished materials, the applied manufacturing processes, the final dimensions of test samples, and applied test methods. Fabrication by sputter deposition is favorable, because it allows the manufacturing of micro-patterned Nitinol thin-film devices without small burrs, heat-affected zones, microcracks, or any contamination with carbides, as well as the fabrication of complex components e.g., 3D geometries. Today, however, there is limited data available on the fatigue behavior for real stent devices based on such sputter-deposited Nitinol. A detailed study (e.g., using metallographic methods, corrosion, tensile, and fatigue testing) was conducted for the first time in order to characterize the micro-patterned Nitinol thin-film material.

Rodrigo Lima de Miranda

Papers

Ultralow-fatigue shape memory alloy films

Ultralow‐Fatigue Shape Memory Alloy Films.

Micropatterned Freestanding Superelastic TiNi Films

Unusual temperature dependence of the positron lifetime in a polymer of intrinsic microporosity

Comparison of the Fatigue Performance of Commercially Produced Nitinol Samples versus Sputter-Deposited Nitinol