Variety of fiber orientation tensors

Fiber orientation tensors are established descriptors of fiber orientation states in (thermo-)mechanical material models for fiber-reinforced composites. In this paper, the variety of fourth-order orientation tensors is analyzed and specified by parameterizations and admissible parameter ranges. The combination of parameterizations and admissible parameter ranges allows for studies on the mechanical response of different fiber architectures. Linear invariant decomposition with focus on index symmetry leads to a novel compact hierarchical parameterization, which highlights the central role of the isotropic state. Deviation from the isotropic state is given by a triclinic harmonic tensor with simplified structure in the orientation coordinate system, which is spanned by the second-order orientation tensor. Material symmetries reduce the number of independent parameters. The requirement of positive-semi-definiteness defines admissible ranges of independent parameters. Admissible parameter ranges for transversely isotropic and planar cases are given in a compact closed form and the orthotropic variety is visualized and discussed in detail. Sets of discrete unit vectors, leading to selected orientation states, are given.

Desynchronized liquid crystalline network actuators with deformation reversal capability

Liquid crystalline network (LCN) actuator normally deforms upon thermally or optically induced order-disorder phase transition, switching once between two shapes (shape 1 in LC phase and shape 2 in isotropic state) for each stimulation on/off cycle. Herein, we report an LCN actuator that deforms from shape 1 to shape 2 and then reverses the deformation direction to form shape 3 on heating or under light only, thus completing the shape switch twice for one stimulation on/off cycle. The deformation reversal capability is obtained with a monolithic LCN actuator whose two sides are made to start deforming at different temperatures and exerting different reversible strains, by means of asymmetrical crosslinking and/or asymmetrical stretching. This desynchronized actuation strategy offers possibilities in developing light-fueled LCN soft robots. In particular, the multi-stage bidirectional shape change enables multimodal, light-driven locomotion from the same LCN actuator by simply varying the light on/off times.

Об изотропных точках в примесных кристаллах K-=SUB=-2-=/SUB=-SO-=SUB=-4-=/SUB=-

The temperature, spectral and pressure dependences of the birefringence Δni of potassium sulfate crystals doped with 1.7% of copper have been studied. The introduction of the impurity is found to change the absolute value of Δni and lead to an increase in the temperature dependence of Δnі(Т). It is shown that the isotropic points appear in the doped crystal of potassium sulfate, and are shifted, compared with a pure crystal, towards low temperatures by 5 K and 11 K, respectively. It was established, that uniaxial stresses change the magnitude of the Δni absolute values, as well as the region of existence of the isotropic state. Generalized temperature-spectral-baric diagrams of the isotropic state of doped potassium sulfate crystal are constructed, making it possible to use them as a crystal-optical sensor.

Desynchronized Liquid Crystalline Network Actuators with Deformation Reversal Capability

Liquid crystalline network (LCN) actuator normally deforms upon thermally or optically induced order-disorder phase transition, switching once between two shapes (shape-1 in LC phase and shape-2 in isotropic state) for each stimulation on/off cycle. Herein, we report a novel type of LCN actuator that deforms from shape-1 to shape-2 and then reverses the deformation direction back to shape-1 or to a new shape-3 on heating or under light only, meaning that the actuator can complete the shape switch twice for one stimulation on/off cycle. The deformation reversal capability is obtained with a monolithic LCN actuator whose two sides are made to start deforming at different temperatures and exerting different reversible strains, which can be realized through asymmetrical crosslinking and/or asymmetrical stretching of the two sides in preparing the LCN actuator. This desynchronized actuation strategy offers new possibilities in developing light-fueled LCN soft robots. In particular, the multi-stage bidirectional shape change can be used to achieve multimodal, light-driven locomotion with different moving speeds from the same LCN actuator by simply varying the light on/off times to confine shape switch in a specific sub-stage.

Influence of polydispersity on the isotropic-nematic boundary in melt of semiflexible diblock copolymer

The analytical expressions have been obtained to describe the dependence of spinodal curve at which isotropic state of polydisperse melt of semiflexible diblock copolymer becomes unstable with respect to formation of nematic state on the polydispersity indices of the blocks, parameters of anisotropic interactions, and flexibility of blocks. The flexibility of blocks is taken into account within discrete worm-like chain model, lengths of blocks are assumed to be distributed by the Schulz–Zimm distribution. It is shown that increase of degree of polydispersity of blocks yields the increase of nematic spinodal temperature.