Effect of Sugars on Gelation Kinetics of Gelatin Gels

We investigate the rheological behavior of aqueous solutions containing animal gelatin, sugars and polyols. The aim is to study how the gelation kinetics, transition temperatures and gel strengths of an aqueous gelatin solution can be affected by the progressive addition of co-solutes. Aqueous solutions with a fixed mass percentage of gelatin of 6.8 wt% were prepared at various concentrations of sugars and polyols. Through Dynamic Temperature Ramp tests, performed at various ramp rates, and Dynamic Time Sweep and Dynamic Frequency Sweep tests, carried out at different temperatures, it was possible both to evaluate the transition temperatures and to monitor the gelation kinetics of the samples. It was found that the contribution of co-solutes positively affects both the gelation process and the thermal stability of the aqueous gelatin solution by reducing the gelation time and improving the mechanical properties of the gel in terms of network elasticity

Generation of well relaxed all atom models of stereoregular polymers: a validation of hybrid particle-field molecular dynamics for polypropylene melts of different tacticities

The tacticity of vinyl polymer chains strongly affects the physical properties of polymeric materials, as example the chain conformations and stiffness. In the present work we tested how the hybrid Particle-Field Molecular Dynamics (PF-MD) technique is capable to describe conformational differences of polymer chains as function of the tacticity. In particular, we focus on tacticity effect of atactic, isotactic, and syndiotactic polypropylene (PP) homopolymer melts. We found that PF-MD simulations exhibit dependence of Flory's Characteristic Ratio from the fraction of racemo diads along the PP chains in qualitative agreement with Small Angle Neutron Scattering (SANS) experiments and theoretical previsions. Finally, we calculated and compared the packing length parameter on very high stereoregular syndiotactic PP systems with rheological measurements. A qualitative agreement between the calculated and experimental packing length is found.Solid state NMR/Biophysical Organic Chemistr

Rheometry

Rheology is the science that studies the flow and deformation of soft, complex matter. Its aim is to understand, model, and predict the behavior of such systems. One of the main outcomes of rheology is the elaboration of constitutive equations, that is, relationships between the stress state in a material and the applied deformation history. They are characterized by the presence of the so-called material functions, which are the physical parameters that quantitatively describe the rheological behavior. An official, very complete nomenclature of rheological material functions is provided by the American Society of Rheology.1 Throughout this document, the symbols adopted in the nomenclature cited in the preceding text are used. Rheometry is the experimental, metrological counterpart of rheology. Its main objective is to measure the material functions studied by rheology. This is accomplished by the use of specific apparatuses, the rheometers, where materials undergo specific stress or deformation histories. Here, the main aspects of rheometry are presented and discussed. In order to better understand the present state of rheometry, some historical perspective must be briefly put forward. Modern rheometry was born with the study of non-Newtonian fluids, whose viscosity is a function of the velocity gradient. During the course of the last century, rheology became involved with increasingly complex materials such as viscoelastic liquids, viscoelastic solids, gels, and many others. Most of such materials, which can be classified under the term soft matter, can display either a liquidlike or solid-like behavior, depending on the deformation history and the type and intensity of the applied external fields (forces, magnetic, and electric fields). Correspondingly, rheometry techniques have become more and more sophisticated. In this document, many relevant issues related, but not central, to rheometry will not be considered. One example is the problem of environmental control, especially temperature control. For more in-depth information on such issues, it is suggested to refer to some of the further readings listed at the end of this article

Linear vicoelastic rheology as a tool for the investigation of the chemical architecture of syndiotactic polypropylene

In this work we studied the rheology of a series of syndiotactic polypropylenes (sPP) of varying degree of tacticity. The linear viscoelastic properties of the different polymer samples were measured in the melt state. Experiments allowed the determination of the sPP plateau modulus and, as a consequence, of the molecular weight between entanglements. The experimental results show a well defined correlation between the molecular weight between entanglements and the degree of tacticity of sP