Arnaud Chiche

Complex micropatterning of periodic structures on elastomeric surfaces

We report a simple methodology to fabricate complex sub-micrometre periodic structures in poly(dimethylsiloxane) over large surface areas (several cm2). Single-frequency, uni- and multi-axial sinusoidal surface modulations, with tunable amplitude and wavelength, in the nano- to micrometre range, are readily demonstrated. The technique builds upon a buckling instability of a stiff layer supported by an elastomeric membrane (reported earlier), induced by surface oxidation of a pre-stretched elastomer coupon followed by removal of the applied mechanical strain. Plasma oxidation yields model surfaces with single wavelengths, sub-micrometre periodicity, achieving a dynamic range from sub-200 nm to 10s of µm, which UV ozonolysis extends to 100s of µm. We find that a single ‘dose’ parameter (exposure time × power) characterizes the surface conversion. The strain control provides unprecedented tunability of surface pattern amplitude and morphology, ranging from lines to complex periodic topologies induced under multi-axial deformation. We introduce a novel multiple strain–exposure and replication approach that extends surface topologies beyond lines, chevron and spinodal patterns (isotropic structures with a dominant wavelength). The resulting structures exhibit a glass-like surface, which is easily grafted with self-assembled monolayers to enhance functionality. Applications of this inexpensive and fast methodology include stamps for soft lithography, micromolding, templating and surface patterning.

Crystallization -induced switching of the morphology of poly(ethylene oxide)- block -polybutadiene micelles

We studied the morphology of micelles formed by a well-defined poly(1,2-butadiene)-block-poly(ethylene oxide) diblock copolymer (PB-b-PEO). Dissolved in n-heptane at 70 °C, that is, above the melting point of PEO, spherical micelles are formed due to the selectivity of the solvent for the PB-block. If the solutions are cooled down to low temperatures, the liquid PEO-block crystallizes within the cores of the spherical micelles that remain stable. If, however, the solutions are quenched to 30 °C, the spherical micelles aggregate to a novel meander-like structure within several minutes. In its final state, the meander-like super-structure is crystalline, as revealed by time-resolved wide-angle X-ray scattering. The super-structure is shown to result from crystallization-induced aggregation of spherical micelles. Moreover, crystallization leads to well-defined angles between subsequent aggregating units. A quantitative Avrami-type analysis of the crystallization kinetics demonstrates that the formation of the meander-type structure resembles a 2D growth process combined with a breakout crystallization, showing an Avrami-exponent of 2.5. In contrast to this, crystallization at low temperatures resembles a confined crystallization with a low Avrami-exponent of 0.7. All data demonstrate that the morphology of block copolymers having a crystallizable block can be switched by the competition of aggregation and crystallization.

Controlled solvent vapour annealing for polymer electronics

Solvent vapour annealing (SVA) is demonstrated as an attractive method to anneal polymer blend and block copolymer thin films at low temperatures. It is especially suitable for organic electronics, where sensitive materials with strong intermolecular interactions are used. We demonstrate the effect of solvent vapour exposure on the film properties of a perylene bisimide acrylate (PPerAcr) side-chain polymer with strong crystallinity at the perylene bisimide moieties. We record the film thickness, light absorption and fluorescence as a function of the relative solvent vapour pressure. At a certain threshold of relative solvent vapour pressure, we observe a disruption of the π–π stacking, which is responsible for perylene bisimide crystallisation. This leads to an increase in the polymer-chain mobility and therefore to changes in the film morphology. The results are applied to a film of a donor–acceptor block copolymer carrying PPerAcr segments, and the influence of solvent annealing on the nanoscale morphology is demonstrated.

Nanostructured wrinkled surfaces for templating bionanoparticles—controlling and quantifying the degree of order

We present a novel method to align the tobacco mosaic virus (TMV) on topographically structured surfaces. In order to gain defined patterns we use wrinkled polydimethlysiloxane (PDMS) sheets as templates. We aligned the virus with a simple spin-coating procedure on the PDMS sheet. The concentration of the virus solution and the spin speed are varied in order to identify ideal conditions for the arrangement of the viruses on the wrinkled templates. Here, we establish a simple analytical approach which allows quantifying the degree of order of the patterns, which is the basis for a quantitative discussion of templating efficiency. Furthermore, we discuss the role of dewetting processes for the particle assembly. TMVs can be used as reactive nanoparticles due to their well-defined surface chemistry. They can as well serve as a model system for alignment of anisotropic particles via spin coating from solution.

Evaluation of temperature-dependent adhesive performance via combinatorial probe tack measurements

We describe the design and application of a temperature gradient probe tack apparatus for investigating the adhesive performance of model pressure-sensitive adhesives (PSAs). In particular, we illustrate a probe tack apparatus for studying the effect of temperature on three critical adhesion identifiers: adhesion energy, elongation at break, and debonding mechanisms. The measurement temperature is varied across the PSA film using a gradient temperature stage constructed from a transparent sapphire plate with a heating and cooling source positioned at opposite ends. The transparent substrate allows visualization of the contact area and debonding mechanisms during the test. The gradient temperature stage is integrated onto a motorized x-y stage, enabling a matrix of probe tack tests to be conducted across the PSA film at different sample temperatures. We use a spherical probe to evaluate the adhesive performance of a 150μm thick model poly(styrene-b-isoprene-b-styrene) PSA film between a temperature range of 10 °C to 100 °C. We demonstrate that this apparatus is a viable combinatorial design for tack measurements and may be extended to more complicated two-dimensional gradient films.We describe the design and application of a temperature gradient probe tack apparatus for investigating the adhesive performance of model pressure-sensitive adhesives (PSAs). In particular, we illustrate a probe tack apparatus for studying the effect of temperature on three critical adhesion identifiers: adhesion energy, elongation at break, and debonding mechanisms. The measurement temperature is varied across the PSA film using a gradient temperature stage constructed from a transparent sapphire plate with a heating and cooling source positioned at opposite ends. The transparent substrate allows visualization of the contact area and debonding mechanisms during the test. The gradient temperature stage is integrated onto a motorized x-y stage, enabling a matrix of probe tack tests to be conducted across the PSA film at different sample temperatures. We use a spherical probe to evaluate the adhesive performance of a 150μm thick model poly(styrene-b-isoprene-b-styrene) PSA film between a temperature range o...

A new design for high-throughput peel tests: statistical analysis and example

The peel test is one of the most common techniques to investigate the properties of pressure sensitive adhesives (PSAs). As the demand increases for combinatorial tools to rapidly test material performance, designing a high-throughput peel test is a critical improvement of this well-established technique. A glaring drawback to adapting conventional peel tests to study combinatorial specimens is the lack of sufficient statistical information that is the foundation of this type of measurement. For example, using a continuous gradient of sample properties or test conditions in the peel direction implies that each data point (force) corresponds to a given test condition, thus prohibiting the average force to be calculated for a given condition. The aim of this paper is both to highlight the potential problems and limitations of a high-throughput peel test and suggest simple experimental solutions to these problems based on a statistical analysis of the data. The effect of the peel rate on the peel force is used to illustrate our approach.