Optical polymer thin films with isotropic and anisotropic nano-corrugated surface topologies

Ibn‐Elhaj, Mohammed; Schadt, M.

doi:10.1038/35071039

Cited by 271 publications

(212 citation statements)

References 21 publications

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“…To date, many studies have been devoted to the use of static surface topographies fabricated by wrinkling (1,2), embossing (3), or lithography. However, there is an increasing demand to make these surface structures switchable in modern applications, such as adjustable gas and water flow behavior at corrugated surfaces (4), autonomously adjusting lenses (5), controlled wettability (6), and modulated optics such as scattering, diffraction, or reflection (7)(8)(9). Also, the mechanical properties can be altered by the appearance or disappearance of protrusions at the surface (10,11), such as friction, stick, and adhesion which manifest themselves in, e.g., haptic applications (12).…”

mentioning

confidence: 99%

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

Liu

Onck

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

124

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In this work we propose randomly ordered polydomain nematic liquid crystal polymer networks to reversibly generate notable jagged relief patterns at a polymer coating surface by light illumination. The domain size is controlled by the addition of traces of partly insoluble fluorinated acrylate. The photoresponse of the coating is induced by a small amount of copolymerized azobenzene monomers. Upon exposure to UV light, azobenzene undergoes trans to cis isomerization, resulting in a change in molecular order and packing within each domain. The extent of this effect and its directionality depends on the domain orientation. Localized to domain level, this morphological change forms large 3D spikes at the surface with a modulation amplitude of more than 20% of the initial thickness. The process is reversible; the surface topographical patterns erase within 10 s by stopping the light exposure. A finite element model is applied to simulate the surface topography changes of the polydomain coating. The simulations describe the formation of the topographic features in terms of light absorption and isomerization process as a function of the director orientation. The random director distribution leads to surface structures which were found to be in close agreement with the ones measured by interference microscopy. The effect of domain size on surface roughness and depth modulation was explored and related to the internal mechanical constraints. The use of nematic liquid crystal polydomains confined in a polymer network largely simplifies the fabrication of smart coatings with a prominent triggered topographic response.surface dynamics | self-organization | switchable jagged surfaces | polydomain liquid crystal polymer | light activation I n nature, living creatures have developed a series of motion and surviving strategies based on unique topographic patterns on their surfaces. The surface topographies range from static patterns as, for instance, found on the leaves of the lotus flower, repelling water and dirt particles, to the dynamic structures that appear under certain conditions as found in many mammals. An example is the pilomotor reflex at the skin of mammals which creates insulation in cold conditions and provides protection by scaring away predators when the body appears larger. To date, many studies have been devoted to the use of static surface topographies fabricated by wrinkling (1, 2), embossing (3), or lithography. However, there is an increasing demand to make these surface structures switchable in modern applications, such as adjustable gas and water flow behavior at corrugated surfaces (4), autonomously adjusting lenses (5), controlled wettability (6), and modulated optics such as scattering, diffraction, or reflection (7-9). Also, the mechanical properties can be altered by the appearance or disappearance of protrusions at the surface (10, 11), such as friction, stick, and adhesion which manifest themselves in, e.g., haptic applications (12).Our focus here is to develop dynamic topographic patterns at su...

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mentioning

confidence: 99%

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

Liu

Onck

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

124

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“…The distribution of silica nanoparticles in the film as well as the porosity may result in a final value that is far lower than the value of bulk silica. For some optical applications, anti-reflective coatings are of interest in order to maximize the light transmitted and to minimize that reflected through a certain void [31][32][33][34][35][36]. The principle of antireflection is the destructive interference occurring between the reflected beams at the substrate-film interface and that at the film-air interface [37].…”

Section: Resultsmentioning

confidence: 99%

Addition of silica nanoparticles to tailor the mechanical properties of nanofibrillated cellulose thin films

Eita

Arwin

Granberg³

et al. 2011

Journal of Colloid and Interface Science

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Over the last decade, the use of nanocellulose in advanced technological applications has been promoted both due the excellent properties of this material in combination with its renewability.In this study, multilayered thin films composed of nanofibrillated cellulose (NFC), polyvinyl amine (PVAm) and silica nanoparticles were fabricated on polydimethylsiloxane (PDMS) using a layer-by-layer adsorption technique. The multilayer build-up was followed in situ by quartz crystal microbalance with dissipation, which indicated that the PVAm-SiO 2 -PVAm-NFC system adsorbs twice as much wet mass material compared to the PVAm-NFC system for the same number of bilayers. This is accompanied with a higher viscoelasticity for the PVAm-SiO 2 -PVAm-NFC system. Ellipsometry indicated a dry-state thickness of 2.2 and 3.4 nm per bilayer 2 for the PVAm-NFC system and the PVAm-SiO 2 -PVAm-NFC system, respectively. Atomic force microscopy height images indicate that in both systems, a porous network structure is achieved.

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“…SiW, UC and CG exhibited isotropic surfaces with a low average roughness compared to MS. MS was the only substrate investigated that exhibited anisotropic topology 30 NIR analysis was performed to probe the molecular interactions in the spherulites and spectra were acquired for the spherulites deposited on each substrate (Figure 3d). Similar bands were observed for all the spherulites, but with apparent differences in intensity.…”

Section: 1±05° and The Values Of This Parameter Increased In The mentioning

confidence: 99%

Impact of Substrate Properties on the Formation of Spherulitic Films: A Case Study of Salbutamol Sulfate

Serrano

Mugheirbi

O’Connell

et al. 2016

Crystal Growth & Design

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Spherulitic assemblies have applications as carriers for drug delivery and as targeting vectors. Presently, the driving force behind the formation of spherulites comprising small drug molecules is not fully understood. Herein, the impact of different substrate types on spherulitic crystallization of salbutamol sulfate (SS) was investigated. Freshly cleaved mica, silicon (111) wafer (SiW), uncoated borosilicate glass (UG), silane coated glass (CG) and stainless steel (MS) were used as substrates. It was demonstrated that the spherulite growth can be controlled via the substrate selection. Spherulite formation was inhibited on hydrophilic substrates, such as mica, possibly due to stronger intermolecular interactions between SS and the substrate than SS-SS interactions. Contact angle measurements established that mica possessed the lowest contact angle (15.1±0.5°) and the values of this parameter increased in the order of UC˂SiW˂CG˂MS. Substrate roughness also played a key role in controlling spherulite formation. SiW, UC and CG had isotropic surfaces with low average roughness, facilitating spherulite formation. Overall, this work demonstrates that it is possible to successfully produce SS spherulites using a single step process at room temperature. Furthermore, the formation of SS spherulites can be tuned by the hydrophobicity of the substrate, an approach that could be applied to assembling spherulites of other small organic molecules. Presently, the driving force behind the formation of spherulites comprising small drug molecules is not fully understood. Herein, the impact of different substrate types on spherulitic crystallization of salbutamol sulfate (SS) was investigated. Freshly cleaved mica, silicon (111) wafer (SiW), uncoated borosilicate glass (UG), silane coated glass (CG) and stainless steel (MS) were used as substrates. It was demonstrated that the spherulite growth can be controlled via the substrate selection. Spherulite formation was inhibited on hydrophilic substrates, such as mica, possibly due to stronger intermolecular interactions between SS and the substrate than SS-SS interactions. Contact angle measurements established that mica possessed the lowest contact angle (15.1±0.5°) and the values of this parameter increased in the order of UC˂SiW˂CG˂MS. Substrate roughness also played a key role in controlling spherulite formation. SiW, UC and CG had isotropic surfaces with low average roughness, facilitating spherulite formation. Overall, this work demonstrates that it is possible to successfully produce SS spherulites using a single step process at room temperature. Furthermore, the formation of SS spherulites can be tuned by the hydrophobicity of the substrate, an approach that could be applied to assembling spherulites of other small organic molecules.

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Optical polymer thin films with isotropic and anisotropic nano-corrugated surface topologies

Cited by 271 publications

References 21 publications

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

Addition of silica nanoparticles to tailor the mechanical properties of nanofibrillated cellulose thin films

Impact of Substrate Properties on the Formation of Spherulitic Films: A Case Study of Salbutamol Sulfate

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