Hydrogels are widely studied for chemical sensors. However, they are known to adsorb organic compound and metal ions. The adsorption abilities of hydrogels against organic compounds and metal ions will negatively affect the performance of a hydrogel based chemical sensor. To clarify the effect of hydrophobic pollution on swelling behavior of temperature-sensitive gel, the temperature-responses of spherical N,N-diethylacrylamide (DEAA) gel in phenol solution were evaluated using the collective polymer diffusion constant. Phenol was selected as a model hydrophobic pollution. The equilibrium radius of DEAA gel changed discontinuously at about 874 g/m³ phenol solution, and the collective polymer diffusion constant decreased sharply between 874 and 916 g/m³, suggesting a “critical slowing down”. The phenol concentration difference E_C was successfully used to correlate phenol concentration with the collective polymer diffusion constant. The correlation will be useful as an estimation of hydrogel response reduction associated with hydrophobic pollution. Full article

Stimuli-responsive hydrogels can be used to convert miniature pressure sensors into novel chemomechanical sensors via confinement of the hydrogel sample between a porous membrane and a piezoresistive diaphragm. Chemomechanical sensors could prove beneficial in a variety of applications, including continuous monitoring of bioreactors and biomedical systems. In this study, one hydrogel composition with a high sensitivity to changes in pH was tested in two different chemomechanical sensors in order to compare the data obtained from each sensor design. In the first and older chemomechanical sensor design, a prefabricated hydrogel sample is loaded into the sensor chamber using a screw-on cap. In the newer sensor design, a thinner hydrogel is synthesized in situ and is held in place by a silicon boss that is mechanically connected to a piezoresistive diaphragm. The newer design results in a decreased chemomechanical sensor response time (by 60 times), and maintains a high sensitivity to changes in environmental stimuli. Full article

We present a new electrochemical sensor for Flunitrazepam using disposable and economic Screen Printed Graphene Electrodes. It was found that the electrochemical response of this sensor was improved compared to Screen Printed Graphite Electrodes and displayed an excellent analytical performance for the detection of Flunitrazepam. Those characteristics could be attributed to the high Flunitrazepam loading capacity on the electrode surface and the outstanding electric conductivity of graphene. The methodology is shown to be useful for quantifying low levels of Flunitrazepam in a buffer solution. The protocol is also shown to be applicable for the sensing of Flunitrazepam in an alcoholic beverage e.g., Gordon’s Gin & Tonic. Full article

The structure and material properties of polymer networks can depend sensitively on changes in the environment. There is a great deal of progress in the development of stimuli-responsive hydrogels for applications like sensors, self-repairing materials or actuators. Biocompatible, smart hydrogels can be used for applications, such as controlled drug delivery and release, or for artificial muscles. Numerical studies have been performed on different length scales and levels of details. Macroscopic theories that describe the network systems with the help of continuous fields are suited to study effects like the stimuli-induced deformation of hydrogels on large scales. In this article, we discuss various macroscopic approaches and describe, in more detail, our phase field model, which allows the calculation of the hydrogel dynamics with the help of a free energy that considers physical and chemical impacts. On a mesoscopic level, polymer systems can be modeled with the help of the self-consistent field theory, which includes the interactions, connectivity, and the entropy of the polymer chains, and does not depend on constitutive equations. We present our recent extension of the method that allows the study of the formation of nano domains in reversibly crosslinked block copolymer networks. Molecular simulations of polymer networks allow the investigation of the behavior of specific systems on a microscopic scale. As an example for microscopic modeling of stimuli sensitive polymer networks, we present our Monte Carlo simulations of a filament network system with crosslinkers. Full article