Exploring the Gel State: Optical Determination of Gelation Times and Transport Properties of Gels with an Inexpensive 3D-Printed Spectrophotometer

Abstract

The study of gels and their properties is a compelling topic both technologically and scientifically, and should therefore be emphasized in chemistry and material science syllabuses. In the present laboratory experiment, we propose two experiences, aimed at introducing gelation and gel transport properties using silica gels made from sodium silicate and sodium citrate buffer. In particular, gelation times are used to teach kinetics and optical properties to first and second year General Chemistry students. Gelation times are determined by measuring the increment in scattering intensity with a 3D-printed spectrophotometer. The gel transport properties are presented to further exemplify Fickian and non-Fickian behavior through ionic dyes diffusing in gels. A qualitative description is obtained from charge interactions, and a quantitative description utilizing the diffusion coefficient is achieved by analyzing absorbance profiles. These tasks were designed to encourage students to work with unusual topics in a holistic way, approaching new materials, properties, and DIY equipment. Blueprints for the spectrophotometer, resources for instructors, and a detailed students' guide are provided together with a short report model to promote critical discussion of the observations.

Gradual hydrophobization of silica aerogel for controlled drug release

“…Also, the shift in transmittance in the doped gel occurred earlier than in the blank gel, assisting the determination of its faster gelation, as proposed in the elegant work by Calcabrini and Onna. 48 …”

“…The strong dependence on the wavelength indicates that the rise in opaqueness is mainly due to the Rayleigh scattering component, resulting from interaction with refractive coefficient boundaries of regimes considerably smaller than the wavelength. 48 The higher scattering of the doped gel means that the CH-G 2 causes formation of larger silica elementary particles, as larger particle diameters lead to stronger Rayleigh scattering (following a power rule of d 6 ). This may be the reason that these gels showed no visible shrinking during supercritical drying, with a nal bulk density of 57 AE 2 mg mL À1 for the doped aerogel, denoted CH-G 2 @SiO 2 (Fig.…”

“…Also, the shi in transmittance in the doped gel occurred earlier than in the blank gel, assisting the determination of its faster gelation, as proposed in the elegant work by Calcabrini and Onna. 48 To increase the loading of chlorhexidine, another entrapment method was used that included an anion exchange during the hydrogel stage. The CH-G 2 doped hydrogels were transferred to an NaCl bath and the gluconate anion was exchanged with the chloride, resulting in precipitation of the less soluble chlorhexidine dihydrochloride (CH-Cl 2 ).…”

Introduction to Machine Learning for Chemists: An Undergraduate Course Using Python Notebooks for Visualization, Data Processing, Data Analysis, and Data Modeling

“…In the classroom, computational methods are usually applied for chemical system simulations, such as DFT calculations or molecular dynamics simulations, to predict or interpret experimental results, or for data analysis from experimental results. Examples of these trends for teaching have been published in this journal [8][9][10][11][12][13]. Also, two remarkable courses for teaching computational skills to chemistry students by Weiss [14,15] and Menke [16] can be found.…”

Modelagem Tridimensional: Reflexões De Futuros Professores De Química Para O Ensino E Aprendizagem Da Interação Enzima-Substrato

“…No entanto, a construção e o uso de modelos 3D impressos para o ensino e a aprendizagem de Ciências ainda é um tema pouco discutido em pesquisas brasileiras. Por outro lado, no contexto internacional a impressora 3D têm sido uma ferramenta amplamente utilizada em diferentes áreas, como a medicina, a odontologia, a topografia, e o ensino de ciências em particular (Scalfani & Vaid, 2014;Kaliakin, Zaari & Varganov, 2015;Meyer, 2015;Smiar & Mendez, 2016;Cataldo, Griffith, & Fogarty, 2018;Calcabrini & Onna, 2019;Kondinski & Parac-Vogt, 2019). Estes autores reportam benefícios do uso da impressão tridimensional como uma estratégia inovadora e eficaz para o ensino e a aprendizagem de diversos conceitos científicos.…”