Imperial College London


Faculty of EngineeringDepartment of Chemical Engineering

Research Postgraduate







517BACE ExtensionSouth Kensington Campus





Publication Type

3 results found

Tan A, Pellegrino L, Ahmad Z, Cabral JTet al., 2022, Tunable structural color with gradient and multiaxial polydimethylsiloxane wrinkling, Advanced Optical Materials, Vol: 10, ISSN: 2195-1071

The generation of structural color from wrinkled polydimethylsiloxane (PDMS) surfaces, fabricated by plasma exposure, subjected to uni- and multi-axial, and sequential strain fields is examined. The approach is based on the well-known, mechanically-induced, buckling instability of a supported bilayer, whereby the top glassy “skin” is formed by plasma oxidation. Surface periodicities 200 nm ≲ d ≲ 3 μm, encompassing the visible spectrum, are investigated in terms of the observed color, intensity spectrum, and color mixing from different diffraction orders, exhibiting good agreement with model predictions. By contrast with complex fabrication methods, color tunability and mechanochromic response are readily achieved by adjusting plasma and strain parameters, and by dynamically varying strain (ε ≲ 50%). Prescribed strain directionality, employing uniaxial, isotropic, gradient strain, and wave-sum wrinkling superposition, as well as skin thickness (and thus d) and amplitude gradients, using facile and scalable fabrication approaches, yield striking spatial color variation, homogeneity, and directionality.

Journal article

Pellegrino L, Tan A, Cabral JT, 2022, Ripple patterns spontaneously emerge through sequential wrinkling interference in polymer bilayers, Physical Review Letters, Vol: 128, ISSN: 0031-9007

We report the formation of “ripple” patterns by the sequential superposition of nonorthogonal surfacewaves excited by the spontaneous buckling of polymeric bilayers. Albeit of a different nature and micronscale compared to the familiar sedimentary ripples caused by gentle wave oscillations, we findcommonalities in their topography, defects, and bifurcations. The patterns are rationalized in terms ofa defect density that depends on the relative angle between generations, and a constant in-plane bendingangle that depends on skin thickness. A minimal wave summation model enables the design of ripple andcheckerboard surfaces by tuning material properties and fabrication process.

Journal article

Tan A, Pellegrino L, Cabral JT, 2021, Tunable phase gratings by wrinkling of plasma-oxidized PDMS: gradient skins and multiaxial patterns, ACS Applied Polymer Materials, Vol: 3, Pages: 5162-5170, ISSN: 2637-6105

Wrinkling instabilities in polymeric bilayers have been exploited as optical phase gratings with tunable performance. Here, we report strain modulated 1D and 2D phase gratings fabricated by the ubiquitous process of plasma-oxidation of polydimethylsiloxane (PDMS). While surface oxidation provides a remarkably facile glassy skin formation approach, minimizing delamination and debonding, it inherently results in a gradient conversion profile emanating from the top film interface. We examine and quantitatively model the consequences of this gradient layer on the optical properties of the resulting strain-tunable phase gratings. Diffraction efficiencies up to 48% are demonstrated. We then develop and validate a surface reconstruction methodology based on the diffraction pattern of our sinusoidal gratings and our model, which we extend to the high deformation regimes and to 2D gratings, obtained by superposition of two wrinkling generations, where both amplitudes and wavelengths can be independently tuned. Overall, this approach provides a rapid, robust and predictive framework for the design and fabrication of tunable, single, and multiaxial surface gratings.

Journal article

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