| Popis: |
Liquid crystal networks change their dimensions when the degree of order is altered. Upon decreasing order, e.g. as a result of temperature increase, the linear dimension decreases in the direction along the director and increases orthogonal to that. When the director changes as a function of position, the local dimensional changes cause stresses that effect in deformation of the sample. In the case of thin films with a twisted molecular orientation over their cross-section a change in the order parameter results in a double, saddle-like, bending of the film as the linear expansion is different for both in-plane axes. For geometric reasons this bending is uncontrolled and irregular. When the linear expansion is chosen to be different along one in-plane axis, but is kept the same for the other axis, the deformation becomes orderly and controlled. Therefore, films of liquid crystal networks with a splayed molecular alignment over their cross-section provide a well-controlled bending deformation as a function of a changing order parameter. In a liquid crystal network the order parameter can be modulated by temperature. The direction- and order parameter dependent linear expansion than comes on top of the volume expansion as caused by induced thermal molecular motions and decreased secondary molecular forces. Besides by temperature the order parameter can also be modulated by light in the presence of photo-sensitive moieties in the liquid crystal network. The deformation behavior is anticipated to be of relevance for polymer based MEMS technology. |
