Dirk Broer

Eindhoven University of Technology | TUE · Department of Chemical Engineering and Chemistry

Critical temperature indicators have been extensively utilized in various fields, ranging from healthcare to food safety. However, the majority of the temperature indicators are designed for upper critical temperature monitoring, indicating when the temperature rises and exceeds a predefined limit, whereas the stringently demanded low critical temp...

Fingertip perspiration is a vital process within human predation, to which our species owes its survival and its biological success. In this paper, we recreate the unique human ability of extensive perspiration and controlled friction in self-assembled cholesteric liquid crystals, mimicking the natural processes that occur in the dermis and epiderm...

Secretion of functional fluids is essential for affecting surface properties in ecosystems. The existing polymer membranes that mimic human skin functions are limited to secreting, either apolar or polar, liquid. However, the development of membranes that grant exchange liquid with different polarities remains a grand challenge. This process is pro...

Cholesteric liquid crystals (CLCs) are chiral photonic materials with selective reflection in terms of wavelength and polarization. Helix engineering is often required in order to produce desired properties for CLC materials to be employed for beam steering, light diffraction, scattering, and adaptive or broadband reflection. Here, we demonstrate a...

Artificially created tactile feedback is in high demand due to fast developments in robotics, remote control in medicine, virtual reality, and smart electronics. Despite significant progress, high-quality haptic feedback devices remain challenging mainly due to the lack of stability and spatiotemporal resolution. In this work, we address these issu...

Multiresponsive Liquid Crystal Cilia In article number 2101619, Dirk J. Broer and co‐workers prepare an array of liquid crystal polymer micro‐cilia of well‐defined tapered shape by replicating a track‐etched polyimide. The densely packed self‐standing cilia show patterned and collective out‐of‐plane motion in response to ambient changes. The bendin...

Liquid manipulation at solid surfaces has attracted plenty of interest yet most of them are limited to one or two direction(s), while transport in three dimensions is largely unexplored. Here, we demonstrate three‐dimensionally steered dynamic liquid mobility at nanoporous liquid crystal polymer coatings. To this end, we orchestrate liquid motion v...

Liquid manipulation at solid surfaces has attracted plenty of interest yet most of them are limited to one or two direction(s), while transport in three dimensions is largely unexplored. Here, we demonstrate three‐dimensionally steered dynamic liquid mobility at nanoporous liquid crystal polymer coatings. To this end, we orchestrate liquid motion v...

Coatings with dynamic surface structures are appealing to many applications like haptics and soft robotics. Restrictively, the speed of the surface dynamics in these coatings is often limited to frequencies below 1 kHz, which makes them unsuitable for applications like acoustics and communication optics. This work describes a method to create high‐...

Cilia and flagella are a vital part of many organisms. Protozoa such as paramecia rely on the collective and coordinated beating of tubular cilia or flagella for their transport, while mammals depend on the ciliated linings of their bronchia and female reproductive tracts for the continuity of breathing and reproduction, respectively. Over the year...

Cilia are of vital importance for myriad of natural functions such as the propulsion of microorganisms or the cleaning of the mammalian respiratory system. These cilia often show coupled 3D shape changes, such as waves, to perform their function. Here, we present a versatile platform to fabricate artificial micrometer‐sized azobenzene‐doped liquid...

Control over molecular motion is facilitated in materials with highly ordered nanoscale structures. Here we report on the fabrication of cholesteric liquid crystal networks by circularly polarized light irradiation, without the need for chiral dopant or plasticizer. The polymer network is obtained by photopolymerization of a smectic achiral diacryl...

Control over molecular motion is facilitated in materials with highly ordered nanoscale structures. Here we report on the fabrication of cholesteric liquid crystal networks by circularly polarized light irradiation, without the need for chiral dopant or plasticizer. The polymer network is obtained by photopolymerization of a smectic achiral diacryl...

In the flourishing field of soft robotics, strategies to embody communication and collective motion are scarce. Here we report the synchronized oscillations of thin plastic actuators by an approach reminiscent of the synchronized motion of pendula and metronomes. Two liquid crystalline network oscillators fuelled by light influence the movement of...

Alignment layers are vital to the function of numerous devices based on liquid crystal (LC) materials. The pursue of versatile, effective and even flexible alignment layers, preferably prepared by simple methods, is still actively ongoing. Herein, we propose a facile one-step method by mixing silanes into the starting LC mixtures, which in contact...

Photoembossing is a powerful photolithographic technique to prepare surface relief structures relying on polymerization-induced diffusion in a solventless development step. Conveniently, surface patterns are formed by two or more interfering laser beams without the need for a lithographic mask. The use of nanosecond pulsed light-based interference...

The reverse mode polymer dispersed liquid crystal (PDLC) is an emerging smart window technology. Unlike traditional PDLCs, a reverse mode PDLC can be transparent and opaque in the absence and presence of an external electric field. This report provides a brief introduction to several reverse modes PDLC smart window technologies, focusing on polymer...

This work describes a method to create dynamic pre-programmed surface textures by an alternating electric field on coatings that consist of a silicon oxide reinforced viscoelastic siloxane network. Finite element...

Although switchable adhesive surfaces are important and desirable for soft robotics, it is still challenging to replicate nature's switchable adhesion capability on artificial surfaces, especially for underwater applications. Here polymeric coatings with fingerprint topographies that are capable of switching the surface adhesion upon light illumina...

Morphological properties of surfaces play a key role in natural and man‐made objects. The development of robust methods to fabricate micro/nano surface structures has been a long pursuit. Herein, an approach based on molecular self‐assembling of liquid crystal polymers (LCPs) is presented to directly translate 2D molecular director profiles obtaine...

'Smart' windows which reversibly increase their reflectivity upon heating are attracting considerable attention as devices for maintaining comfortable indoor environmental conditions. In this work, twisted nematic semi‐interpenetrating liquid crystal networks which lose their order upon heating are sandwiched between reflective linear polarizers. T...

By exploiting the dynamic chirality, directionality of motion and shape change of a single light‐driven motor embedded in a liquid‐crystal network, complex mechanical motions including bending, walking and helical motion, in soft polymer materials are achieved which offers fascinating opportunities toward inherently photo‐responsive materials. Abs...

Controlling sophisticated motion by molecular motors is a major goal on the road to future actuators and soft robotics. Taking inspiration from biological motility and mechanical functions common to artificial machines, responsive small molecules have been used to achieve macroscopic effects, however, translating molecular movement along length sca...

Major research challenges for materials science and technology include the design of tailor-made materials with deliberately controlled and multifunctional performance attributes. In the field of composite materials, powerful methods have been developed to control and dynamically modulate the distribution of components to facilitate synergistic pro...

Control over main‐chain motion of chiral π‐conjugated polymers can lead to unexpected new functionalities. Here, it is shown that by combining photoswitchable azobenzene units in conjugation with chiral fluorene comonomers and appropriate plasticizers, the polymer organization and chiroptical properties of these alternating copolymers steered by li...

In recent years, light‐responsive liquid crystal (LC) polymers have been studied as promising materials for the fabrication of untethered soft actuators. The underwater behavior of these advanced materials has, however, been rarely investigated. This paper reports on the fabrication of light‐responsive amphibious LC‐actuators via direct ink writing...

Responding to external stimuli is a trait observed in all living organisms. Modern artificial materials have adopted this profound characteristic, thereby commencing the field of stimuli–responsive systems. Liquid crystal polymers are attractive members of this family of systems owing to the available control on their anisotropic properties capable...

Surface coatings, as interfaces between functional devices and targeted objects, are critical in the performance of functional devices. Switchable topographies bring opportunities to regulate the functionality of surfaces, ranging from morphing and controllable friction to object lifting and debris removal. Various responsive materials have been in...

本发明公开了两性离子化合物在制备基于动态散射模式的液晶材料中的应用。本发明还公开了一种液晶混合物，这种液晶化合物包括主体液晶和掺杂剂，其中掺杂剂为两性离子化合物。本发明也公开了一种包括该液晶化合物的液晶调光器件，同时也公开了这种液晶调光器件的应用。本发明使用两性离子化合物作为掺杂剂稳定液晶材料的动态散射，解决了现有技术中掺杂剂存在具有良好的DSM特性但低阈值电压的问题，延长了DSM基光学器件的使用寿命。

The remote light exposure of photo-responsive liquid crystalline polymers has drawn a great attention over the last years as an attractive strategy to generate mechanical work with high spatial resolution. To tailor these materials into practical engineering devices, it is of key importance to gain control over their morphology and thus precisely p...

Liquid-releasing artificial skins are made from films of a smectic liquid crystal polymer network (LCN) photopolymerized in the presence of a photo-active azobenzene chromophore and a liquid crystal porogen. The porogen phase separates during the polymerization process and the polymer forms a spongy polymer network filled with liquid. The liquid is...

The integration of light tracking and light guiding within fiber arrays is an intriguing challenge. In this study, an advanced drop casting/drawing method is applied to fabricate a fiber array capable of not only performing sunflower‐inspired light tracking, but also light guiding. The fiber arrays are constructed with various liquid crystal networ...

Living organisms enhance their survival rate by excreting fluids at their surface, but man-made materials can also benefit from liquid secretion from a solid surface. Known approaches to secrete a liquid from solids are limited to passive release driven by diffusion, surface tension, or pressure. Remotely triggered release would give active control...

Prof. Dirk Broer is among the pioneers and most active researchers in the field of stimuli-responsive liquid crystal (LC) networks. He is the inventor of reactive mesogens, a class of materials with far-reaching implications in liquid-crystal photonics and in the triumph of LC-based shape-shifting polymers. Together with his team, Prof. Broer conti...

Shape-shifting liquid crystal networks (LCNs) can transform their morphology and properties in response to external stimuli. These active and adaptive polymer materials can have impact in a diversity of fields, including haptic displays, energy harvesting, biomedicine and soft robotics. Electrically driven transformations in LCN coatings are partic...

An approach is proposed to create robust liquid crystalline polymer coatings that exhibit sensitivity and dynamic reversibility toward multiple external stimuli including UV irradiation and electrical input. This coating spontaneously alters its surface topographic texture and thickness in response to each of these signals. The corresponding deform...

Liquid crystal networks doped with azobenzene molecular photo-switches have been commonly used as responsive polymers in untethered soft/micro robots. Understanding the underlying actuation mechanism of azobenzene chromophores in aqueous and ambient environments is crucial for the control of deformation speed and amplitude of the photo responsive a...

The paper presents a methodology to control the motion and orientation of suspended reflective cholesteric flakes in a nematic liquid crystal matrix. The flakes exhibit a dielectric anisotropy which controls their alignment with their in-plane axes parallel to an external electrical DC field. The elastic forces imposed by the liquid crystal host af...

Nature employs travelling waves to generate propulsion of fluids, cells and organisms. This has inspired the development of responsive material systems based on different external triggers. Especially light-actuation is suitable because of its remote control and scalability, but often complex, moving light sources are required. Here, we developed a...

Surface topography variations of liquid crystal networks in their functional coatings provide unique properties in these systems. Chiral-nematic polymer coatings self-organize in a fingerprint texture with the molecular helices parallel to the substrate with alternating domains of molecular units with parallel and perpendicular director orientation...

Recent developments in soft matter science provide options to add mobility and motility to polymer films and surfaces. Restrictively, the dynamics in these materials are modulated by a pulsated trigger and the route to autonomous dynamics is still a most intriguing challenge. Here, is the design of a self‐sustaining oscillating surface is reported...

Liquid crystalline networks of specific geometry are observed to undergo thermally triggered chaotic continual rocking motion and light triggered rolling.

A temperature‐responsive polarization converter, which reversibly changes from a full‐wave to a half‐wave plate upon heating, is developed. The polymer wave plate has a controlled thickness and is based on a uniaxial aligned nematic semi‐interpenetrating network coating containing a specific concentration of a non‐crosslinked liquid crystal elastom...

Engineering the helical structure of chiral photonic materials in three dimensions remains a challenge. 3D helix engineered photonic materials are fabricated by local stratification in a photopolymerizable chiral nematic liquid crystal. The obtained chiral photonic materials reflect both handedness of circular polarized light and show super‐reflect...

Liquid crystal surfaces can undergo topographical morphing in response to external cues. These shape-shifting coatings promise a revolution in various applications, from haptic feedback in soft robotics or displays to self-cleaning solar panels. The changes in surface topography can be controlled by tailoring the molecular architecture and mechanic...

Azobenzene‐containing liquid crystal polymer networks (LCNs) are developed for temperature‐ and light‐regulated gas permeation. The order in a chiral‐nematic LCN (LCN*) is found to be essential to couple the unique structure of the membrane and its gas permeation responses to external stimuli such as temperature and varying irradiation conditions....

A new principle is developed to fabricate temperature-responsive multi-color photonic coatings that are capable to switch color. The coating is composed of a non-crosslinked liquid crystal siloxane-based elastomer that is interpenetrated through an acrylate-based liquid crystal network. Discrete temperature changes induce phase separation and mixin...

Photo-responsive liquid crystal polymer networks offer promising means to generate useful functional devices, but many of them focus on their mechanical response so as to generate surface features or shape change. Here we investigate the photomechanical effect of the polymer network for molecular transport purposes. Dual wavelength illumination of...

An easy approach to pattern angular-independent, multi-color reflective coatings based on cholesteric liquid crystalline (CLC) particles is presented. CLC particles are fabricated by emulsification, which is a scalable, cost-effective and environmentally-friendly synthesis process. The photonic particles can be easily dispersed in a binder to produ...

In article number 1803274, Dirk J. Broer, Albertus P. H. J. Schenning, and co‐workers fabricate multi‐stable, re‐ and pre‐configurable visible light responsive surface topographies by using low illumination doses. Preliminary studies reveal that these light responsive polymers are suitable as adaptive biological surfaces. The authors would like to...

Light responsive materials that are able to change their shape are becoming increasingly important. However, preconfigurable bistable or even multi‐stable visible light responsive coatings have not been reported yet. Such materials will require less energy to actuate and will have a longer lifetime. Here, it is shown that fluorinated azobenzenes ca...

The ability to induce oscillating surface topographies in light‐responsive liquid crystal networks on‐demand by light is interesting for applications in soft robotics, self‐cleaning surfaces, and haptics. However, the common height of these surface features is in the range of tens of nanometer, which limits their applications. Here a photoresponsiv...

The induction of electrohydrodynamic instabilities in nematic liquid crystals through light illumination are reported. For this purpose, a photochromic spiropyran is added to the liquid crystal mixture. When an electrical field is applied in the absence of UV light, the homeotropic liquid crystal reorients perpendicular to the electrical field driv...

The original version of this Article contained errors in Figs. 1a, 2a, 3a, and 4b, in which the units on the scale bars incorrectly read 'µm' rather than the correct 'nm.' This has been corrected in both the PDF and HTML versions of the Article.

Many publications report on stimuli responsive coatings, but only a few on the controlled release of species in order to change the coating surface properties. A sponge-like coating that is able to release and absorb a liquid upon exposure to light has been developed. The morphology of the porous coating is controlled by the smectic liquid crystal...