Effects Of Soft Materials Research Articles

Poynting and reverse Poynting effects in soft materials.

In 1909, J. H. Poynting conducted a series of experiments on metal wires and found that loaded wires lengthen when twisted. Thus to maintain a constant length in such experiments, a compressive axial force would need to be applied at the ends of the specimen. This is the classical (positive) Poynting effect. Another example of such an effect arises when a soft material specimen is being axially sheared or rotated between two platens. The necessity to apply a normal force in order to maintain the relative distance between the platens is also often referred to as a Poynting-type effect. Both effects are inherently nonlinear phenomena. In recent papers, experimental data on the Poynting effect in soft solids have been reported. The seminal paper by Janmey et al. describes shearing experiments on hydrogels, impregnated with scleroproteins such as collagen and fibrin. It was shown that positive and negative (reverse) Poynting effects could occur. In this and subsequent papers by several authors, the microstructure of reinforced biogels involving semi-flexible filaments embedded in a soft matrix was exploited to examine the character of the normal stresses. The purpose of the present paper is to describe and review an alternative approach using the macroscopic phenomenological theory of hyperelasticity based on nonlinear continuum mechanics. Our aim is to demonstrate that such a theory can be used in a very transparent way to predict the occurrence of both positive and negative Poynting effects in anisotropic soft fibrous materials. It will be seen that material anisotropy plays a key role in the analysis.

Electrocaloric and elastocaloric effects in soft materials.

Materials with large caloric effect have the promise of realizing solid-state refrigeration which has potential to be more efficient and environmentally friendly compared with current cooling technologies. Recently, the focus of caloric effects investigations has shifted towards soft materials. An overview of recent direct measurements of the large electrocaloric effect (ECE) in a composite mixture of a liquid crystal and nanoparticles (NPs) and large elastocaloric (eC) effect in main-chain liquid crystal elastomers is given. In mixtures of 12CB liquid crystal with functionalized CdSSe NPs, an ECE exceeding 5 K was found in the vicinity of the isotropic to smectic A phase transition. It is shown that the NPs smear the isotropic to smectic coexistence range in which a large ECE is observed due to latent heat enhancement. NPs acting as traps for ions reduce the moving-ion density and consequently the Joule heating. Direct eC measurements indicate that the significant eC response can be found in main-chain liquid crystalline elastomers, but at a fraction of the stress field in contrast to other eC materials. Both soft materials could play a significant role as active cooling elements or parts of thermal diodes in development of new cooling devices.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

The use of materials patterned on a nano- and micro-metric scale in cellular engineering

Biological cells form distinct groupings in tissue depending on their function. This is as essential in the regrowth of damaged tissue as it is in the development of the mature animal from its egg. For a number of years we have been exploring the effect of surfaces patterned with a topographic relief pattern and with patterns of bound active bio-molecules. The response of cells to micron-sized features, the response of cells to nano-metric features and the effects of soft materials are discussed.

Effect of Soft Material on Insulating Impact Pressure into Explosive

Effect of Soft Material on Insulating Impact Pressure into Explosive