Jerneja Pavlin

Liquid crystals: a new topic in physics for undergraduates

This paper presents a teaching module about liquid crystals. Since liquid crystals are linked to everyday student experiences and are also a topic of current scientific research, they are an excellent candidate for a modern topic to be introduced into education. We show that liquid crystals can provide a pathway through several fields of physics such as thermodynamics, optics and electromagnetism. We discuss what students should learn about liquid crystals and what physical concepts they should know before considering them. In the presentation of the teaching module, which consists of a lecture and experimental work in a chemistry and physics laboratory, we focus on experiments on phase transitions, polarization of light, double refraction and colours. A pilot evaluation of the module was performed among pre-service primary school teachers who have no special preference for natural sciences. The evaluation shows that the module is very efficient in transferring knowledge. A prior study showed that the informally obtained pre-knowledge on liquid crystals of the first-year students from several different fields of study was negligible. Since social science students are the least interested in natural sciences, it can be expected that students in any study programme will on average achieve at least as good qualitative knowledge of phenomena related to liquid crystals as the group involved in the pilot study.

How to Teach Liquid Crystals

We present a teaching unit on liquid crystals. The unit has already been implemented into the university undergraduate pedagogical study programs for future teachers of Physics and Chemistry, preschool teachers and teachers at the lower grade of the elementary school at Faculty of Education, University of Ljubljana. The unit develops students’ knowledge on the existence of more than three phases of matter and the existence and properties of anisotropic materials, focusing on the biaxiality and birefringence. The unit is multidisciplinary since students perform the experiments with the MBBA nematic liquid crystal which they synthesize themselves. Our final goal is to implement the teaching unit to the high school curriculum (for students 14–18 years old).

Direction dependence of the extraordinary refraction index in uniaxial nematic liquid crystals

This paper presents a straightforward experiment that directly and illustratively demonstrates double refraction. For this purpose, two liquid crystalline cells were designed to enable qualitative and quantitative measurements of the extraordinary refractive index direction dependence in a uniaxial nematic liquid crystal.

A Mechanical Model for Phase Transitions in Smectics

A mechanical model is a simple device made out of helical springs. Using the mechanical model one can visualize the difference between the first and the second order phase transitions. The analogy between the mechanical model and phase transitions in liquid crystals will be discussed. The parameters of the simple device (length, frequency, amplitude, tilt, etc.) can serve as an analogy for the parameters used in theories of phase transitions. The simple mechanical model is also convenient for the presentation and visualization of the dynamics near SmA-SmC phase transition in liquid crystals.

Teaching Liquid Crystals with a Wood Model

The uniaxial symmetry in the liquid crystalline phase leads to anisotropy in many physical properties. A simple look on a piece of wood reveals that also its structure is anisotropic. It has also strong anisotropic dielectric properties in the microwave range, like liquid crystals in the visible range. Therefore the wood can serve as a model for demonstration of anisotropic optical properties in liquid crystals. Experiments for more illustrative explanation of the anisotropic properties are presented. As wood is transparent for microwaves, many anisotropic properties can be illustrated experimentally, using a simple school microwave kit.

Hydrogels in the Classroom

Hydrogels are commonly used and novel smart materials . They are superabsorbent polymers with interesting properties. Hydrogels can also motivate students for playing and learning science because they reflect the trends in current research. Literature review yielded no results about students’ conceptions of hydrogels. Therefore we decided to explore students’ knowledge about hydrogels, acquired through informal learning process. The paper first presents the description of hydrogels , list of experiments with hydrogels and describes the prior research about hydrogels in some detail. The results of the study, which included 104 1st year pre-service primary school teachers from Faculty of Education, University of Ljubljana, are then presented. On February 2015 students filled in a paper-pencil questionnaire about hydrogels (QH) with 26 items. Results show that informal knowledge about hydrogels is limited, since students on average achieved 8 % of possible points on the QH. Results have further influenced the design of a pilot teaching module about hydrogels.