arXiv subjects

Alfred J. Crosby

Publications and source records attributed to Alfred J. Crosby.

10 recordsLinked to original sources

arXiv2026

Supercritical Snapping and Controlled Launching via Dual Latch Gels

Natural organisms have evolved integrated Latch-Mediated Spring Actuation systems (LaMSA) that consist of multiple latches and springs to enhance power output and adapt to diverse environmental conditions. Similar designs are appealing yet largely unexplored in engineered materials due to the complexity of integrating multiple components into a single material platform. Here, we report a dual-latched magneto-elastic shell device capable of selectively activating the latches to regulate snapping pathways and energy output based on specific actuation requirements. Differential deswelling across the thickness acts as the motor to load the elastic energy into the shell, which is then released via the snap-through instability once the loading reaches the critical threshold, constituting an intrinsic mechanical latch. Activation of the external magnetic latch delays snapping onset beyond the threshold of the intrinsic latch, leading to a power-amplified supercritical snap-through instability as well as a bifurcation instability. The combined function of both latches allows for flexible control over energy storage and release. Additionally, this integrated LaMSA system possesses an untethered anchoring mechanism, enabling the device to launch in arbitrary directions from the substrate, driven by the energy released during snapping. We envision that the design principles of dual-latched LaMSA systems will create opportunities for power-dense actuation in engineered materials and robotic devices.

physics.app-ph↗

arXiv2026

Modulus and confinement effects on self-repeating, power-amplified snapping of soft, swollen beams

Latch-mediated Spring Actuation (LaMSA) is a mechanism found in nature, employed by organisms that generate the highest levels of power density through repeatable, rapid energy release. While LaMSA has been used in engineered systems like archery bows, catapults, and jumping robots, most such technologies require external power for self-repeating motion. Recent advances in soft actuators have demonstrated that engineered gels swollen with a volatile solvent are capable of self-repeating, high specific-power generation by taking advantage of balances between environmental interaction (evaporation) and elasticity. These systems rely upon snap-through instabilities. Due to the complex coupling between material properties and geometry, both of which evolve as self-repeating motion continues, an understanding of how polymer properties and boundary conditions control the lifetime, count, and magnitude of power generating events for a given amount of solvent remains unrealized. We overcome the challenges in characterizing the performance of evaporation-driven, power-generating gels by measuring accumulating force response from evaporation in parallel with the profile deformation of the structure. By optimizing the balance between swelling properties and elasticity, the lifetime of snapping is increased by 445% from previous literature, snapping at a maximum power density of about 87 W/kg. This power is achieved with swollen beams 50 mm in length after 53 mg of solvent had evaporated and is comparable to the power output of adult jumping mantises at 68 W/kg at a similar size scale.1 We develop scaling relationships that balance Flory-Rehner swelling theory with buckling mechanics to generate insight into optimizing lifetime and power of autonomous power-generating systems.

cond-mat.soft↗

arXiv2025

Poroelasticity of bottlebrush and linear polymer networks

The transport of solvent molecules through soft, swollen networks is critical in both natural and engineered systems. While this poroelastic flow has traditionally been explored in networks where the mesh size is comparable to the solvent molecule size, the effect of network architecture on permeability remains underexplored. Here we investigate solvent transport in linear polymer networks (LPN) and highly elastic bottlebrush elastomer networks (BBN), where the presence of densely grafted sidechains allows for control over swelling and mechanical properties. By synthesizing BBNs with systematically varied crosslinking density while maintaining constant sidechain length and grafting density, we probe the poroelastic response in the stretched backbone regime (SBB). Poroelastic relaxation indentation experiments, performed in toluene, reveal how permeability scales with crosslink density and polymer volume fraction. Compared to LPN with identical chemistry, the BBN exhibited a lower permeability scaling exponent with polymer volume fraction that closely matches the theoretical exponent. Despite architectural differences, permeability data for both networks collapse onto a single curve when plotted against dry shear modulus. Our findings demonstrate that molecular network architecture significantly influences permeability, offering new routes to tailor solvent transport in soft, swollen networks. These insights highlight BBNs as a promising platform for applications in permeable membranes, filtration, and microfluidic systems, and pave the way for further studies on how network parameters, such as sidechain length, impact permeability in these highly tunable materials.

cond-mat.soft↗

arXiv2025

Architected Dual-Network Solvent-free Adhesives for Stretchable Fabrics

Natural systems, such as tendons and spider silk, demonstrate how the combination of strength and stretchability can be effectively achieved by integrating stiff and flexible network structures. Inspired by these systems, we developed a novel, solvent-free dual-network adhesive based on a self-assembling ABA triblock copolymer, poly(methyl methacrylate)-poly(n-butyl acrylate)-poly(methyl methacrylate) (PMMA-b-PnBA-b-PMMA), designed for applications requiring both high strength and stretchability. The triblock copolymer forms a physically crosslinked network through microdomains of PMMA end-blocks that provide structural integrity, while the PnBA mid-block forms a soft, stretchable matrix. To further enhance mechanical performance, a second poly(n-butyl acrylate) (PnBA) network is polymerized in situ, locking the PMMA microdomains in place and creating a load-bearing system. By varying the crosslinking density of the secondary network, we tailor the adhesive's mechanical properties (Young's modulus: 0.17 - 1.18 MPa) to suit different substrates, creating a mechanically transparent seam. The resulting dual-network system combines different strategies to achieve high strength and stretchability, with adhesive performance comparable to industrial methods such as sewing, particularly in bonding neoprene fabric composites and sealing the joints. Our solvent-free approach also eliminates the need for lengthy solvent evaporation steps, offering an eco-friendly and more efficient alternative for flexible adhesive applications in fields such as soft robotics, flexible electronics, and sports apparel.

cond-mat.mtrl-sci↗

arXiv2024

Mesoscale Polymer Arrays: High Aspect Ratio Surface Structures and Their Digital Reconstruction

Inspired by adhesive bio-filamentous structure, such as bacterial pili, this work details the methods used to fabricate and characterize a surface-anchored array of thin, flexible and shape-responsive mesoscale polymer ribbons with a length-to-thickness aspect ratio of up to 100,000. The resulting structures exhibit geometrically complex and dynamic morphologies consistent with elastocapillary bending that experience an increase in curvature over hours of aging due to creep. We develop a computational image analysis framework to generate 3D reconstructions of these densely crowded geometries and extract quantitative descriptors to demonstrate morphological changes due to aging. We demonstrate the robustness of this quantitative method by characterizing the creep-induced change in an aging ribbon array's shape and develop a scaling relationship to describe the importance of ribbon thickness for shape and dynamical observations. These methods demonstrate an essential baseline to probe morphology-property relationships of mesoscale polymer ribbon arrays fabricated from a variety of materials in numerous environments. Through the introduction of perfluorodecalin droplets, we illustrate the potential of these ribbon arrays towards applications in adhesive, microrobotic, and biomedical devices.

cond-mat.soft↗

arXiv2022

Shaping Nanoscale Ribbons into Micro-Helices of Controllable Radius and Pitch

We report fabrication of highly flexible micron-sized helices from nanometer-thick ribbons. Building upon the helical coiling of such ultra-thin ribbons mediated by surface tension, we demonstrate that the enhanced creep properties of highly confined materials can be leveraged to shape helices into the desired geometry with full control of the final shape. The helical radius, total length and pitch angle are all freely and independently tunable within a wide range: radius within $\sim$ 1-100 micrometer, length within $\sim$ 100-3000 micrometer, and pitch angle within $\sim$ 0-70°. This fabrication method is validated for three different materials: poly(methyl methacrylate), poly(dimethylaminoethyl methacrylate), and transition metal chalcogenide quantum dots, each corresponding to a different solid-phase structure: respectively a polymer glass, a crosslinked hydrogel, and a nanoparticle array. This demonstrates excellent versatility with respect to material selection, enabling further control of the helix mechanical properties.

cond-mat.soft↗

arXiv2022

Interfacial Cavitation

Cavitation has long been recognized as a crucial predictor, or precursor, to the ultimate failure of various materials, ranging from ductile metals to soft and biological materials. Traditionally, cavitation in solids is defined as an unstable expansion of a void or a defect within a material. The critical applied load needed to trigger this instability - the critical pressure - is a lengthscale independent material property and has been predicted by numerous theoretical studies for a breadth of constitutive models. While these studies usually assume that cavitation initiates from defects in the bulk of an otherwise homogeneous medium, an alternative and potentially more ubiquitous scenario can occur if the defects are found at interfaces between two distinct media within the body. Such interfaces are becoming increasingly common in modern materials with the use of multi-material composites and layer-by-layer additive manufacturing methods. However, a criterion to determine the threshold for interfacial failure, in analogy to the bulk cavitation limit, has yet to be reported. In this work we fill this gap. Our theoretical model captures a lengthscale independent limit for interfacial cavitation, and is shown to agree with our observations at two distinct lengthscales, via two different experimental systems. To further understand the competition between the two cavitation modes (bulk versus interface) we expand our investigation beyond the elastic response to understand the ensuing unstable propagation of delamination at the interface. A phase diagram summarizes these results, showing regimes in which interfacial failure becomes the dominant mechanism.

cond-mat.soft↗

arXiv2021

Programmed Wrapping and Assembly of Droplets with Mesoscale Polymers

Nature is remarkably adept at using interfaces to build structures, encapsulate reagents, and regulate biological processes. Inspired by Nature, we describe flexible polymer-based ribbons, termed "mesoscale polymers" (MSPs), to modulate interfacial interactions with liquid droplets. This produces unprecedented hybrid assemblies in the forms of flagellum-like structures and MSP-wrapped droplets. Successful preparation of these hybrid structures hinges on interfacial interactions and tailored MSP compositions, such as MSPs with domains possessing distinctly different affinity for fluid-fluid interfaces as well as mechanical properties. In situ measurements of MSP-droplet interactions confirm that MSPs possess a negligible bending stiffness, allowing interfacial energy to drive mesoscale assembly. By exploiting these interfacial driving forces, mesoscale polymers are demonstrated as a powerful platform that underpins the preparation of sophisticated hybrid structures in fluids.

cond-mat.soft↗

arXiv2018

Size-scaling limits of impulsive elastic energy release from a resilin-like elastomer

Elastically-driven motion has been used as a strategy to achieve high speeds in small organisms and engineered micro-robotic devices. We examine the size-scaling relations determining the limit of elastic energy release from elastomer bands with mechanical properties similar to the biological protein resilin. The maximum center-of-mass velocity of the elastomer bands was found to be size-scale independent, while smaller bands demonstrated larger accelerations and shorter durations of elastic energy release. Scaling relationships determined from these measurements are consistent with the performance of small organisms which utilize elastic elements to power motion. Engineered devices found in the literature do not follow the same size-scaling relationships, which suggests an opportunity for improved design of engineered devices.

cond-mat.soft↗

arXiv2015

Deformation and shape of flexible, microscale helices in viscous flow

We examine experimentally the deformation of flexible, microscale helical ribbons with nanoscale thickness subject to viscous flow in a microfluidic channel. Two aspects of flexible microhelices are quantified: the overall shape of the helix and the viscous frictional properties. The frictional coefficients determined by our experiments are consistent with calculated values in the context of resistive force theory. Deformation of helices by viscous flow is well-described by non-linear finite extensibility. Under distributed loading, the pitch distribution is non-uniform and from this, we identify both linear and non-linear behavior along the contour length of a single helix. Moreover, flexible helices are found to display reversible global to local helical transitions at high flow rate.

physics.flu-dyn↗