Materials and strategies applicable to the dynamic transport of microdroplets are relevant to surface fluidics, self-cleaning materials, thermal management systems, and analytical devices. Techniques based on electrowetting, topographic micropatterns, and thermal/chemical gradients have advanced considerably, but dynamic microdroplet transport remains a challenge. This manuscript reports the fabrication of mechano-tunable, microtextured chemical gradients on elastomer films and their use in controlled microdroplet transport. Specifically, discreet mechanical deformations of these films enabled dynamic tuning of the microtextures and thus transport along surface-chemical gradients. The interplay between the driving force of the chemical gradient and the microtopography was characterized, facilitating accurate prediction of the conditions (droplet radius and roughness) which supported transport. In this work, the use of microtextured surface chemical gradients in mechano-adaptive materials with microdroplet manipulation functionality was highlighted.

wileyonlinelibrary.comThe surface-chemical features (e.g., the pattern, density, and orientation of surface functional groups) of these rigid materials are therefore diffi cult to modify rapidly and reversibly. We desire simple systems with surface-chemical features that can be easily and reversibly modifi ed using mechanical stimuli. The tunable surface properties of these systems will be useful, for example, in controlling surface wettability, reactivity, and assembly.We describe an approach where the surfaces of soft, elastomeric polymers are covalently functionalized with desired chemical moieties that are reversibly modifi ed using mechanical deformations. We demonstrate this approach using soft materials with micrometer-scale patterns of chemical functional groups on their surface. Specifi cally, we homogeneously and heterogeneously functionalized silicone fi lms with small molecules and fl uorophores and demonstrated rational control of critical surface-chemical features (e.g., pattern, area, and molecular density) of these fi lms using stressinduced strain. We applied tensile stress to the fi lms after or during the process of functionalization to decrease or increase (following the release of the stress), respectively, the feature size and periodicity of the chemical patterns on the fi lms. Further, when we applied tensile stress to the polymers during functionalization, we were able to access an array of patterns from one mask design by controlling the axis of stress. This approach will enable functional materials with surface properties (e.g., surface energy) and features (e.g., the size and/or organization of reactive/inert and/or wettable, to select solvents, regions) that can be controlled using mechanical deformation. Finally, we used the chemical and mechanical functionality of these materials to organize and manipulate the geometry of arrays of liquid droplets on their surfaces by stretching the fi lms. These arrays of microdroplets have functionality applicable to microlens and microreactor technologies, and again, by stretching the elastomeric supports, it is possible to tune the geometric properties (and thus function) of the droplet arrays.One of the most common and versatile methods available for chemically functionalizing a surface is to cover it with a layer of self-organizing molecules-self-assembled monolayers (SAMs). [ 1 ] SAMs may be used to produce surfaces Stretchable Chemical Patterns for the Assembly and Manipulation of Arrays of Microdroplets with Lensing and Micromixing FunctionalityJohn J. Bowen , Jay M. Taylor , Christopher P. Jurich , and Stephen A. Morin * The chemical properties of a surface are readily controlled using a layer (or layers) of surface-functional groups that can be generated with, for example, self-assembled monolayers (SAMs) or polymer brushes. These methods have enabled rational control over surface chemistry, which directly impacts surface properties, such as wettability, but generally follow a serial approach to building up surface-functional groups (i.e.,...

Preceramic polymers (PCPs) are a group of specialty macromolecules that serve as precursors for generating inorganics, including ceramic carbides, nitrides, and borides. PCPs represent interesting synthetic challenges for chemists due to the elements incorporated into their structure. This group of polymers is also of interest to engineers as PCPs enable the processing of polymer-derived ceramic products including high-performance ceramic fibers and composites. These finished ceramic materials are of growing significance for applications that experience extreme operating environments (e.g., aerospace propulsion and high-speed atmospheric flight). This Review provides an overview of advances in the synthesis and postpolymerization modification of macromolecules forming nonoxide ceramics. These PCPs include polycarbosilanes, polysilanes, polysilazanes, and precursors for ultrahigh-temperature ceramics. Following our review of PCP synthetic chemistry, we provide examples of the application and processing of these polymers, including their use in fiber spinning, composite fabrication, and additive manufacturing. The principal objective of this Review is to provide a resource that bridges the disciplines of synthetic chemistry and ceramic engineering while providing both insights and inspiration for future collaborative work that will ultimately drive the PCP field forward.

Polymeric microstructures (PMs) are useful to a broad range of technologies applicable to, for example, sensing, energy storage, and soft robotics. Due to the diverse application space of PMs, many techniques (e. g., photolithography, 3D printing, micromilling, etc.) have been developed to fabricate these structures. Stemming from their generality and unique capabilities, the tools encompassed by soft lithography (e. g., replica molding, microcontact printing, etc.), which use soft elastomeric materials as masters in the fabrication of PMs, are particularly relevant. By taking advantage of the characteristics of elastomeric masters, particularly their mechanical and chemical properties, soft lithography has enabled the use of non‐planar substrates and relatively inexpensive equipment in the generation of many types of PMs, redefining existing communities and creating new ones. Traditionally, these elastomeric masters have been produced from relief patterns fabricated using photolithography; however, recent efforts have led to the emergence of new methods that make use of masters that are self‐forming, dynamic in their geometric and chemical properties, 3D in architecture, and/or sacrificial (i. e., easily removed/released using phase changes). These “next generation” soft lithographic masters include self‐assembled liquid droplets, microscale balloons, templates derived from natural materials, and hierarchically microstructured surfaces. The new methods of fabrication supported by these unique masters enable access to numerous varieties of PMs (e. g., those with hierarchical microstructures, overhanging features, and 3D architectures) that would not be possible following established methods of soft lithography. This review explores these emergent soft lithographic methods, addressing their operational principles and the application space they can impact.