Herein, a highly mechano-actuated light-responsive main-chain liquid crystal elastomer (LCE) was prepared using the two-stage thiol−acrylate Michael addition−photopolymerization (TAMAP) method with a reactive mesogenic mixture. This reactive mixture included a newly synthesized azobenzenecontaining diacrylate reactive mesogen 4,4′-di(4-(acrylolylhexyloxy) benzoyloxy) azobenzene (D6OA), which exhibited a long mesogenic structure around the azobenzene bond. The monodomain main-chain azobenzene-containing LCE (M azo-LCE) film was prepared by mechanical drawing and visible-light curing the polydomain azo-LCE (P azo-LCE) film synthesized using the TAMAP method. M azo-LCE film showed approximately 30% contraction in length because of the trans-to-cis isomerization caused by ultraviolet (UV) irradiation, but it did not exhibit response to visible light because the long mesogenic structure of D6OA has a high energy barrier with respect to the cis-to-trans isomerization caused by visible light. However, the simple mechanical drawing of the M azo-LCE film induced the cis-to-trans isomerization. The alternating UV irradiation and mechanical drawing resulted in reversible trans-to-cis and cis-to-trans isomerizations for more than 10 cycles. The cis-to-trans/trans-to-cis isomerization and structural changes during UV irradiation and mechanical drawing were investigated via Raman spectroscopy and wide-and small-angle X-ray scatterings using a synchrotron radiation source. The azobenzene-containing chains in the layer were changed such that the staggered chains with extended trans isomers in the tilted layer (smectic C) were transformed into the chains with kinked cis isomers in the parallel-packed layer via UV irradiation, which were back to the original staggered extended chains with extended trans isomers in the tilted layer through mechanical drawing. The cisto-trans isomerization via mechanical drawing can be attributed to the location of the azobenzene linkage in the main-chain backbone, but this has been rarely reported. The high actuation and simple recovery of the main-chain M azo-LCEs provide many application possibilities in various fields such as robotics, prosthetics, microfluids, data storage, and surface relief gratings.

The New York State Department of Transportation initiated a fiber-reinforced polymer (FRP) Column Wrap Demonstration Project in March 1998. The purpose of this project is to investigate the effectiveness and efficiency of preserving deteriorated concrete with FRP, its possible detrimental effects, and its viability as an alternative for concrete column repair and rehabilitation without regard to seismic considerations. To the authors’ knowledge, this is the first FRP column wrap demonstration project of its kind to involve most of the FRP wrap suppliers in the United States. A 5-year condition-monitoring program was established to monitor the performance of FRP wrapping in preserving the concrete columns. A baseline condition of the piers was established through testing, including concrete cores for compressive strength, chlorides, pH, and freeze-thaw resistance; hammer soundings; and a tight-grid survey of electric potentials. Concrete spalls were repaired; however, delaminations were not. To monitor corrosion of the column reinforcing steel, corrosion probes using linear polarization technology were embedded in the concrete. Initial corrosion readings were collected before wrapping, enhancing the observed baseline condition data. In addition, concrete humidity and temperature probes were installed through the FRP wraps, and strain gauges were mounted on the FRP wraps. Data will be collected at 3-month intervals for 4 or 5 years. The wraps will be removed after monitoring, and a complete column testing program will be implemented at that time.

Shape-persistent cis-isomer-stable azobenzene-functionalized liquid crystal elastomers (azo-LCEs) were prepared using an azobenzene crosslinker with two methyl substitutions at the ortho positions of azobenzene [4,4′-di(4-(acrylolylhexyloxy) benzoyloxy)-2,6-dimethylazobenzene (DADO)] via thiol−acrylate Michael addition photopolymerization. Ultraviolet−visible (UV− vis) and nuclear magnetic resonance (NMR) spectroscopies revealed that the methyl substituents on DADO rocked its cis conformation under UV irradiation and significantly delayed the visible (laser)-light-induced cis-to-trans isomerization. Raman spectroscopy and small-/wide-angle X-ray scattering analyses indicated that the cis-isomers in DADO-linkage-containing monodomain azo-LCE (azo-MLCE DADO ) were not readily converted to the trans conformation under visible (laser)-light irradiation but transformed easily upon mechanical drawing. The azo-MLCE DADO film exhibited a low-plateau modulus and high elongation because of the weak intermolecular interactions caused by its bulky methyl substituents, leading to considerable UV-irradiationinduced contraction (up to 50%) and suspended weight-induced recovery to its original length. These cis-stable azo-MLCE DADO films can be used in shape-persistent actuators in soft robotics, haptics, and biomedical device fabrication.

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