Although thin films are typically manufactured in planar sheets or rolls, they are often forced into three-dimensional (3D) shapes, producing a plethora of structures across multiple length scales. To understand this complex response, previous studies have either focused on the overall gross shape or the small-scale buckling that decorates it. A geometric model, which considers the sheet as inextensible yet free to compress, has been shown to capture the gross shape of the sheet. However, the precise meaning of such predictions, and how the gross shape constrains the fine features, remains unclear. Here, we study a thin-membraned balloon as a prototypical system that involves a doubly curved gross shape with large amplitude undulations. By probing its side profiles and horizontal cross-sections, we discover that the mean behavior of the film is the physical observable that is predicted by the geometric model, even when the buckled structures atop it are large. We then propose a minimal model for the horizontal cross-sections of the balloon, as independent elastic filaments subjected to an effective pinning potential around the mean shape. Despite the simplicity of our model, it reproduces a broad range of phenomena seen in the experiments, from how the morphology changes with pressure to the detailed shape of the wrinkles and folds. Our results establish a route to combine global and local features consistently over an enclosed surface, which could aid the design of inflatable structures, or provide insight into biological patterns.
more »
« less
Wrapping Liquids, Solids, and Gases in Thin Sheets
Many objects in nature and industry are wrapped in a thin sheet to enhance their chemical, mechanical, or optical properties. Similarly, there are a variety of methods for wrapping, from pressing a film onto a hard substrate to inflating a closed membrane, to spontaneously wrapping droplets using capillary forces. Each of these settings raises challenging nonlinear problems involving the geometry and mechanics of a thin sheet, often in the context of resolving a geometric incompatibility between two surfaces. Here, we review recent progress in this area, focusing on highly bendable films that are nonetheless hard to stretch, a class of materials that includes polymer films, metal foils, textiles, and graphene, as well as some biological materials. Significant attention is paid to two recent advances: a novel isometry that arises in the doubly-asymptotic limit of high flexibility and weak tensile forcing, and a simple geometric model for predicting the overall shape of an interfacial film while ignoring small-scale wrinkles, crumples, and folds.
more »
« less
- Award ID(s):
- 1654102
- NSF-PAR ID:
- 10095483
- Date Published:
- Journal Name:
- Annual Review of Condensed Matter Physics
- Volume:
- 10
- Issue:
- 1
- ISSN:
- 1947-5454
- Page Range / eLocation ID:
- 431 to 450
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)We study the wetting of a thin elastic filament floating on a fluid surface by a droplet of another, immiscible fluid. This quasi-2D experimental system is the lower-dimensional counterpart of the wetting and wrapping of a droplet by an elastic sheet. The simplicity of this system allows us to study the phenomenology of partial wetting and wrapping of the droplet by measuring angles of contact as a function of the elasticity of the filament, the applied tension and the curvature of the droplet. We find that a purely geometric theory gives a good description of the mechanical equilibria in the system. The estimates of applied tension and tension in the filament obey an elastic version of the Young–Laplace–Dupré relation. However, curvatures close to the contact line are not captured by the geometric theory, possibly because of 3D effects at the contact line. We also find that when a highly-bendable filament completely wraps the droplet, there is continuity of curvature at the droplet-filament interface, leading to seamless wrapping as observed in a 3D droplet.more » « less
-
more » « less
Abstract Wearable electronics, conformable sensors, and soft/micro-robotics require conductive yet stretchable thin films. However, traditional free standing metallic thin films are often brittle, inextensible, and must be processed in strict environments. This limits implementation into soft technologies where high electrical conductivity must be achieved while maintaining high compliance and conformability. Here we show a liquid metal elastomeric thin film (LET) composite with elastomer-like compliance (modulus < 500 kPa) and stretchability (>700%) with metallic conductivity (sheet resistance < 0.1 Ω/□). These 30–70
µ m thin films are highly conformable, free standing, and display a unique Janus microstructure, where a fully conductive activated side is accompanied with an opposite insulated face. LETs display exceptional electro-mechanical characteristics, with a highly linear strain-resistance relationship beyond 700% deformation while maintaining a low resistance. We demonstrate the multifunctionality of LETs for soft technologies by leveraging the unique combination of high compliance and electrical conductivity with transfer capabilities for strain sensing on soft materials, as compliant electrodes in a dielectric elastomeric actuator, and as resistive heaters for a liquid crystal elastomer. -
more » « less
ABSTRACT Cationic photopolymerization has become increasingly important in thin‐film applications for advantages including no oxygen inhibition and rapid polymerization rates. Photocurable cationic thin film properties are often modulated by incorporation of oligomeric and prepolymer materials, but little work has directly examined the effect of prepolymer structure and reactive group placement on the thermomechanical properties of the final material. To explore the role of molecular architecture, epoxy functionalized butyl acrylate gradient copolymers were synthesized with reactive groups in end segments or randomly distributed along the prepolymer chain. Polymerized end functionalized formulations exhibit moduli almost double that of random functionalized oligomer formulations. In addition, inclusion of end functionalized prepolymers decreases creep of resulting thin films by a factor of 10. Furthermore, decreasing the concentration of the cross‐linking diluent in end functionalized prepolymer systems results in amorphous networks with significantly lower mechanical strength. Increasing reactive groups at the ends of prepolymers produces stronger materials without affecting tensile elongation at break. These properties indicate that the structured oligomers facilitate the formation of continuous hard domains with high cross‐link density with inclusions of soft, flexible domains of low cross‐link density. This study demonstrates that the prepolymer architecture governs network formation and ultimate properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.
2017 ,55 , 144–154 -
more » « less
Abstract Two-dimensional (2D) ternary materials recently generated interest in optoelectronics and energy-related applications, alongside their binary counterparts. To date, only a few naturally occurring layered 2D ternary materials have been explored. The plethora of benefits owed to reduced dimensionality prompted exploration of expanding non-layered ternary chalcogenides into the 2D realm. This work presents a templating method that uses 2D transition metal dichalcogenides as initiators to be converted into the corresponding ternary chalcogenide upon addition of copper, via a solution-phase synthesis, conducted in high boiling point solvents. The process starts with preparation of VSe2nanosheets, which are next converted into Cu3VSe4sulvanite nanosheets (NSs) which retain the 2D geometry while presenting an X-ray diffraction pattern identical with the one for the bulk Cu3VSe4. Both the scanning electron microscopy and transmission microscopy electron microscopy show the presence of quasi-2D morphology. Recent studies of the sulfur-containing sulvanite Cu3VS4highlight the presence of an intermediate bandgap, associated with enhanced photovoltaic (PV) performance. The Cu3VSe4nanosheets reported herein exhibit multiple UV–Vis absorption peaks, related to the intermediate bandgaps similar to Cu3VS4and Cu3VSe4nanocrystals. To test the potential of Cu3VSe4NSs as an absorber for solar photovoltaic devices, Cu3VSe4NSs thin-films deposited on FTO were subjected to photoelectrochemical testing, showing p-type behavior and stable photocurrents of up to ~ 0.036 mA/cm2. The photocurrent shows a ninefold increase in comparison to reported performance of Cu3VSe4nanocrystals. This proves that quasi-2D sulvanite nanosheets are amenable to thin-film deposition and could show superior PV performance in comparison to nanocrystal thin-films. The obtained electrical impedance spectroscopy signal of the Cu3VSe4 NSs-FTO based electrochemical cell fits an equivalent circuit with the circuit elements of solution resistance (Rs), charge-transfer resistance (Rct), double-layer capacitance (Cdl), and Warburg impedance (W). The estimated charge transfer resistance value of 300 Ω cm2obtained from the Nyquist plot provides an insight into the rate of charge transfer on the electrode/electrolyte interface.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1146/annurev-conmatphys-031218-013533
