Pressure tunable adhesion of rough elastomers

Deneke, Naomi; Chau, Allison L.; Davis, Chelsea S.

doi:10.1039/d0sm01754j

Cited by 12 publications

(10 citation statements)

References 47 publications

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“…Although we have initially performed this annealing in an inert atmosphere, our later experiments (vide infra) have demonstrated that the ambient atmosphere annealing is also possible, thanks to the good thermal stability and the robust chemical structure of 2EHO-TPA-CNPE. While heating above glass transition at relatively high temperatures (>200-250 °C) was typically required for the formation of dewetted structures in polymer thin films, [53,55,56] the dewetting dynamics are quite different in the case of nanoscopic molecular thin-films. The solid-state of molecular semiconductor thin-films, from the cumulative cohesive energetics perspective, are bound by relatively weak π-interactions and van der Waals forces, especially when compared with polymeric materials.…”

Section: Resultsmentioning

confidence: 99%

Organic Light‐Emitting Physically Unclonable Functions

Kayacı

Özdemir

Kalay

et al. 2021

Adv Funct Materials

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The development of novel physically unclonable functions (PUFs) is of growing interest and fluorescent organic semiconductors (f‐OSCs) offer unique advantages of structural versatility, solution‐processability, ease of processing, and great tuning ability of their physicochemical/optoelectronic/spectroscopic properties. The design and ambient atmosphere facile fabrication of a unique organic light‐emitting physically unclonable function (OLE‐PUF) based on a green‐emissive fluorescent oligo(p‐phenyleneethynylene) molecule is reported. The OLE‐PUFs have been prepared by one‐step, brief (5 min) thermal annealing of spin‐coated nanoscopic films (≈40 nm) at a modest temperature (170 °C), which results in efficient surface dewetting to form randomly positioned/sized hemispherical features with bright fluorescence. The random positioning of molecular domains generated the unclonable surface with excellent uniformity (0.50), uniqueness (0.49), and randomness (p > 0.01); whereas the distinctive photophysical and structural properties of the molecule created the additional security layers (fluorescence profile, excited‐state decay dynamics, Raman mapping/spectrum, and infrared spectrum) for multiplex encoding. The OLE‐PUFs on substrates of varying chemical structures, surface energies and flexibility, and direct deposition on goods via drop‐casting are demonstrated. The OLE‐PUFs immersed in water, exposed to mechanical abrasion, and read‐out repeatedly via fluorescence imaging showed great stability. These findings clearly demonstrate that rationally engineered solution‐processable f‐OSCs have a great potential to become a key player in the development of new‐generation PUFs.

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Section: Resultsmentioning

confidence: 99%

Organic Light‐Emitting Physically Unclonable Functions

Kayacı

Özdemir

Kalay

et al. 2021

Adv Funct Materials

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“…Each film was then transferred onto the surface of a bulk elastomer, PDMS (Dow Sylgard 184) using a film transfer method detailed in the previous publication. [ 13 ] The bilayer polymer sample is thermally annealed at 160 °C (above the glass transition temperature of PS) for 24 h. The now mobile PS polymer chains dewet from the PDMS substrate to minimize surface area. The droplets arrange into a polygonal pattern that is characteristic of thin film dewetting and solidify upon quenching to leave stiff asperities on the substrate surface.…”

Section: Methodsmentioning

confidence: 99%

“…A scalable and universal strategy, which enables the modification of any adhesive surface for pressure‐tunable adhesion and easy release on a variety of substrate materials and geometries, has yet to be realized. Previously, [ 13 ] we presented a new and generalized approach to obtain a material with pressure‐tunable adhesion. This new pressure‐tunable adhesive (PTA) is a surface patterned material that utilizes polymer thin film dewetting.…”

Section: Introductionmentioning

confidence: 99%

Self‐Assembled Asperities for Pressure‐Tunable Adhesion

et al. 2022

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and medical devices [4] that must be removed from skin without causing pain. Additionally, many of these applications involve adhesion to nonplanar surfaces that span large areas, implying that scalability is another requirement. Conventional pressure sensitive adhesives (PSAs) satisfy the first requirement. They can sustain large loads due to their ability to flow and establish conformal contact without significant applied pressure. [5] While PSAs require a relatively low threshold pressure for contact formation, there is little to no change in their adhesive response if the applied pressure is above this threshold. These materials are far from ideal as large deformations are required for interfacial separation and, if the adhesive fails cohesively, permanent damage of the interface will limit its reusability and contaminate the target substrate.Significant advances have been made in the development of new adhesive systems. Surface modification, such as patterning with microscopic wrinkles [6][7][8] or fibrillar posts, [9][10][11][12] have been demonstrated to enhance adhesion strength or release with some success. These materials are advantageous as they can be designed with stiffer and more elastic properties relative to PSAs, which can yield switchable [11,12] or even tunable adhesives. [8] However, these surface modification approaches remain limited either by scalability or the inability to be adapted to a diverse range of surface chemistries. A scalable and universal strategy, which enables the modification of any adhesive surface for pressure-tunable adhesion and easy release on a variety of substrate materials and geometries, has yet to be realized. Previously, [13] we presented a new and generalized approach to obtain a material with pressure-tunable adhesion. This new pressure-tunable adhesive (PTA) is a surface patterned material that utilizes polymer thin film dewetting. This phenomenon can be realized in a host of materials, which we leverage here to form selfassembled stiff asperities on an elastomeric substrate to control adhesion. In the present work, we study the adhesive properties of these materials and demonstrate the control of their pressure-tunable behavior by changing the size of the stiff asperities. As thin film dewetting can be designed to occur in various materials systems, we anticipate that our present strategy to generate a patterned adhesive can displace existing surface patterning approaches and be applied over large surface areas.Polymer thin film dewetting is an interfacial phenomenon associated with an energetically favorable breakdown of a polymer film into droplets due to an external thermodynamic driving force such as temperature or solvent annealing. [14] Control of adhesion is important in a host of applications including soft robotics, pick-and-place manufacturing, wearable devices, and transfer printing. While there are adhesive systems with discrete switchability between states of high and low adhesion, achieving continuously variable adhesion strength remains a challe...

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“…Periodic features in the surface morphologies of natural and artificial soft materials are known to effectuate morphology-driven DOI: 10.1002/mame.202200247 and stimuli-responsive functionality through switchable or tunable adhesion, wettability, and optical responses. [1][2][3][4][5] Easy and robust methods to prepare soft surface wrinkles with controlled structural features are required for customizing and optimizing the application of soft materials in various technological disciplines. Patterning thin polymer films in 3D morphologies is an active research area as these materials find applications in various areas such as stretchable electronics, functional skins, tunable optical devices, tunable surface wetting, adhesion, water collection, triboelectric nanogenerators (TENGs), and biomedical applications.…”

Section: Introductionmentioning

confidence: 99%

Compositionally Homogeneous Soft Wrinkles on Elastomeric Substrates: Novel Fabrication Method, Water Collection from Fog, and Triboelectric Charge Generation

Raj

Davis

Viswanathan

et al. 2022

Macro Materials & Eng

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Functionality and stimuli-response of natural and artificial elastomeric materials depend significantly on the morphology of their surfaces. Structural transformability and tunable responsiveness of wrinkles on elastomeric materials can enable numerous applications in flexible electronics, optics, and adhesives. Currently existing fabrication techniques rely on sophisticated instrumentation, complex experimental setups, and expensive reagents. These methods are limited in terms of mechanical robustness of the wrinkles produced. Here, a simple, inexpensive, scalable, and reproducible strategy, making use of buckling instability for the creation of soft surface wrinkles on polydimethylsiloxane (PDMS), is presented. PDMS with lower elastic modulus is spin-coated onto a mechanically stretched film of PDMS with a higher elastic modulus. Thermal curing followed by the release of prestrain resulted in the formation of wrinkles in the top layer of the PDMS. The hydrophobic soft surface wrinkles with compositional homogeneity exhibit efficient fog water collection and triboelectric charge generation useful for the preparation of triboelectric nanogenerator devices. Furthermore, the substrates show high mechanical stability and mechanoresponsive optical behaviors. The simplicity and general applicability of the method presented here is expected to establish a promising pathway toward the formation of soft wrinkles in other elastomeric systems also, facilitating important applications in various fields.

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Pressure tunable adhesion of rough elastomers

Abstract: The adhesion of rough surfaces comprised of dewetted thermoplastic asperities on an elastomer is controlled by changing the applied compressive load.

Cited by 12 publications

References 47 publications

Organic Light‐Emitting Physically Unclonable Functions

Organic Light‐Emitting Physically Unclonable Functions

Self‐Assembled Asperities for Pressure‐Tunable Adhesion

Compositionally Homogeneous Soft Wrinkles on Elastomeric Substrates: Novel Fabrication Method, Water Collection from Fog, and Triboelectric Charge Generation

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