ABSTRACT Liquid crystal (LC) concentrations in stratified holographic polymer-dispersed liquid cr... more ABSTRACT Liquid crystal (LC) concentrations in stratified holographic polymer-dispersed liquid crystal (PDLC) films have been quantified from depth profiles obtained by time-of-flight secondary ion mass spectrometry (SIMS). The volatile nature of the LCs was hindered during SIMS analysis by capping the PDLC samples with poly(vinyl alcohol) and cooling to cryogenic temperatures. It remains difficult to gain quantitative results from SIMS analysis due to matrix effects yielding complex SIMS fingerprint spectra. With the multivariate statistical method discriminant function analysis the LC contents in the stratified holographic PDLC films were quantified. The concentration of the LC-rich layers was determined to be 32.9 ± 3.4 wt % LC, and for the polymer-rich layers it was 28.8 ± 2.7 wt % LC. The low concentration difference was supported by imaging analysis and modeling results.
In light-driven liquid-crystal network (LCN) actuators, large performance improvements are obtain... more In light-driven liquid-crystal network (LCN) actuators, large performance improvements are obtained by varying the orientation of the molecular director through the thickness of the film actuator. Experiments show that sub-millimeter bending radii are achieved using a splayed molecular orientation. Systems with a splayed or twisted nematic (TN) director profile drive greater amplitude and faster bending than uniaxial planar systems with the same chemical composition. The bending radii of these systems are predicted using a simple model including effects of light intensity, material composition and actuator thickness.
Controlled shape changes of polymerized liquid crystalline coatings is often achieved via prepatt... more Controlled shape changes of polymerized liquid crystalline coatings is often achieved via prepatterning the molecular orientation of liquid crystal (LC) monomers at the stage of preparation. In this work, using the so-called hybrid alignment of the LC, we produce surface structures of positive Gaussian curvature of coatings without complex techniques such as photoalignment. A mixture of LC monomers coated onto a glass plate with planar alignment of the director is exposed to air, which promotes vertical alignment. The competing planar and homeotropic boundary conditions result in a) thickness dependent director and b) spontaneous formation of spindle-like regions, limited by disclination loops, that are called the reverse tilt domains (RTDs). The disclination separates different director configurations inside and outside the RTD. The RTDs produce relatively big protrusions (100 − 600 nm) of the LC network coating. Actuation of the coating by heat increases the amplitude of RTD protrusions.
UV-curable polyetherurethane acrylates and poly- (dimethyl-co-methylphenyl siloxane) acrylates ha... more UV-curable polyetherurethane acrylates and poly- (dimethyl-co-methylphenyl siloxane) acrylates have been investigated for the primary buffer coating of optical fibers. Curing behavior, Emodulus, glass transition temperature and refractive index have been studied in relation to the molecular structure of both acrylate types. The benefits of the appropriate composition with respect to fiber drawing speed and performance are ultrafast curing, low operation
ABSTRACT Inkjet printing and spin-coating have been used to prepare patterns using a silver-conta... more ABSTRACT Inkjet printing and spin-coating have been used to prepare patterns using a silver-containing metallo-organic decomposition ink. The patterned ink was reduced to silver by exposure to UV light and subsequent treatment with hydroquinone solution. This process, which took less than a minute, was performed at room temperature, which allowed low glass transition temperature polymeric substrates, such as PET, to be used. The conductivity of the silver patterns was found to be 10% that of bulk silver. The mechanical stability was also measured, with a linear increase in resistance seen for increasing strain, and no significant change in resistance seen after 12 000 cyclic deformations.
A review with 35 refs. on various possibilities of making structured, oriented polymer films by i... more A review with 35 refs. on various possibilities of making structured, oriented polymer films by in situ photopolymn. of pre-ordered liq.-cryst. monomers. Formation of uniaxially oriented films and their basic process parameters and the formation of superstructures with high degrees of director control are discussed. Photoinitiated polymn. of pre-oriented mesogenic polyfunctional monomers yields films of densely crosslinked polymers with a monodomain liq.-cryst. mol. order. The morphol. of the monomer mesogenic phase is fixed by the rapid photocrosslinking, which enables the formation of either nematic or one of the various smectic structures, depending on the phase behavior of the monomers. The desired macroscopic mol. order in the monomeric state can be accomplished by using techniques such as external fields or surface-induced orientation. Surface structures are also produced by replication polymn., and combinations of these techniques enable the modulation of the orientational director in the plane of the films and also into the third dimension perpendicular to the film surface. Photocrosslinking enables lithog. techniques to fix the director selectively by local polymn., before permanently fixing the total structure. The introduction of chiral centers in the liq.-cryst. monomers produces helicoidally ordered networks, whose pitch of the mol. helix can be adjusted accurately by compn. or by polymn. temp. This fine tuning of 3-D mol. orientation within thin polymeric films makes this process very unique in the world of oriented polymers.
Controlling sophisticated motion by molecular motors is a major goal on the road to future actuat... more 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 scales to precisely defined linear, twisting and rotary motions remain particularly challenging. Here, we present the design, synthesis and functioning of liquid‐crystal network (LCN) materials with intrinsic rotary motors that allow the conversion of light energy into reversible helical motion. In this responsive system the photochemical‐driven molecular motor has a dual function operating both as chiral dopant and unidirectional rotor amplifying molecular motion into a controlled and reversible left‐ or right‐handed macroscopic twisting movement. By exploiting the dynamic chirality, directionality of motion and shape change of a single motor embedded in an LC‐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.
ABSTRACT Liquid crystal (LC) concentrations in stratified holographic polymer-dispersed liquid cr... more ABSTRACT Liquid crystal (LC) concentrations in stratified holographic polymer-dispersed liquid crystal (PDLC) films have been quantified from depth profiles obtained by time-of-flight secondary ion mass spectrometry (SIMS). The volatile nature of the LCs was hindered during SIMS analysis by capping the PDLC samples with poly(vinyl alcohol) and cooling to cryogenic temperatures. It remains difficult to gain quantitative results from SIMS analysis due to matrix effects yielding complex SIMS fingerprint spectra. With the multivariate statistical method discriminant function analysis the LC contents in the stratified holographic PDLC films were quantified. The concentration of the LC-rich layers was determined to be 32.9 ± 3.4 wt % LC, and for the polymer-rich layers it was 28.8 ± 2.7 wt % LC. The low concentration difference was supported by imaging analysis and modeling results.
In light-driven liquid-crystal network (LCN) actuators, large performance improvements are obtain... more In light-driven liquid-crystal network (LCN) actuators, large performance improvements are obtained by varying the orientation of the molecular director through the thickness of the film actuator. Experiments show that sub-millimeter bending radii are achieved using a splayed molecular orientation. Systems with a splayed or twisted nematic (TN) director profile drive greater amplitude and faster bending than uniaxial planar systems with the same chemical composition. The bending radii of these systems are predicted using a simple model including effects of light intensity, material composition and actuator thickness.
Controlled shape changes of polymerized liquid crystalline coatings is often achieved via prepatt... more Controlled shape changes of polymerized liquid crystalline coatings is often achieved via prepatterning the molecular orientation of liquid crystal (LC) monomers at the stage of preparation. In this work, using the so-called hybrid alignment of the LC, we produce surface structures of positive Gaussian curvature of coatings without complex techniques such as photoalignment. A mixture of LC monomers coated onto a glass plate with planar alignment of the director is exposed to air, which promotes vertical alignment. The competing planar and homeotropic boundary conditions result in a) thickness dependent director and b) spontaneous formation of spindle-like regions, limited by disclination loops, that are called the reverse tilt domains (RTDs). The disclination separates different director configurations inside and outside the RTD. The RTDs produce relatively big protrusions (100 − 600 nm) of the LC network coating. Actuation of the coating by heat increases the amplitude of RTD protrusions.
UV-curable polyetherurethane acrylates and poly- (dimethyl-co-methylphenyl siloxane) acrylates ha... more UV-curable polyetherurethane acrylates and poly- (dimethyl-co-methylphenyl siloxane) acrylates have been investigated for the primary buffer coating of optical fibers. Curing behavior, Emodulus, glass transition temperature and refractive index have been studied in relation to the molecular structure of both acrylate types. The benefits of the appropriate composition with respect to fiber drawing speed and performance are ultrafast curing, low operation
ABSTRACT Inkjet printing and spin-coating have been used to prepare patterns using a silver-conta... more ABSTRACT Inkjet printing and spin-coating have been used to prepare patterns using a silver-containing metallo-organic decomposition ink. The patterned ink was reduced to silver by exposure to UV light and subsequent treatment with hydroquinone solution. This process, which took less than a minute, was performed at room temperature, which allowed low glass transition temperature polymeric substrates, such as PET, to be used. The conductivity of the silver patterns was found to be 10% that of bulk silver. The mechanical stability was also measured, with a linear increase in resistance seen for increasing strain, and no significant change in resistance seen after 12 000 cyclic deformations.
A review with 35 refs. on various possibilities of making structured, oriented polymer films by i... more A review with 35 refs. on various possibilities of making structured, oriented polymer films by in situ photopolymn. of pre-ordered liq.-cryst. monomers. Formation of uniaxially oriented films and their basic process parameters and the formation of superstructures with high degrees of director control are discussed. Photoinitiated polymn. of pre-oriented mesogenic polyfunctional monomers yields films of densely crosslinked polymers with a monodomain liq.-cryst. mol. order. The morphol. of the monomer mesogenic phase is fixed by the rapid photocrosslinking, which enables the formation of either nematic or one of the various smectic structures, depending on the phase behavior of the monomers. The desired macroscopic mol. order in the monomeric state can be accomplished by using techniques such as external fields or surface-induced orientation. Surface structures are also produced by replication polymn., and combinations of these techniques enable the modulation of the orientational director in the plane of the films and also into the third dimension perpendicular to the film surface. Photocrosslinking enables lithog. techniques to fix the director selectively by local polymn., before permanently fixing the total structure. The introduction of chiral centers in the liq.-cryst. monomers produces helicoidally ordered networks, whose pitch of the mol. helix can be adjusted accurately by compn. or by polymn. temp. This fine tuning of 3-D mol. orientation within thin polymeric films makes this process very unique in the world of oriented polymers.
Controlling sophisticated motion by molecular motors is a major goal on the road to future actuat... more 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 scales to precisely defined linear, twisting and rotary motions remain particularly challenging. Here, we present the design, synthesis and functioning of liquid‐crystal network (LCN) materials with intrinsic rotary motors that allow the conversion of light energy into reversible helical motion. In this responsive system the photochemical‐driven molecular motor has a dual function operating both as chiral dopant and unidirectional rotor amplifying molecular motion into a controlled and reversible left‐ or right‐handed macroscopic twisting movement. By exploiting the dynamic chirality, directionality of motion and shape change of a single motor embedded in an LC‐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.
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Papers by Dick Broer