On the Use of Quantum Chemistry for the Determination of Propagation, Copolymerization, and Secondary Reaction Kinetics in Free Radical Polymerization

Throughout the last 25 years, computational chemistry based on quantum mechanics has been applied to the investigation of reaction kinetics in free radical polymerization (FRP) with growing interest. Nowadays, quantum chemistry (QC) can be considered a powerful and cost-effective tool for the kinetic characterization of many individual reactions in FRP, especially those that cannot yet be fully analyzed through experiments. The recent focus on copolymers and systems where secondary reactions play a major role has emphasized this feature due to the increased complexity of these kinetic schemes. QC calculations are well-suited to support and guide the experimental investigation of FRP kinetics as well as to deepen the understanding of polymerization mechanisms. This paper is intended to provide an overview of the most relevant QC results obtained so far from the investigation of FRP. A comparison between computational results and experimental data is given, whenever possible, to emphasize the performances of the two approaches in the prediction of kinetic data. This work provides a comprehensive database of reaction rate parameters of FRP to assist in the development of advanced models of polymerization and experimental studies on the topic

Aqueous Free-Radical Polymerization of Non-Ionized and Fully Ionized Methacrylic Acid

Water-soluble, carboxylic acid monomers are known to exhibit peculiar kinetics when polymerized in aqueous solution. Namely, their free-radical polymerization rate is affected by several parameters such as monomer concentration, ionic strength, and pH. Focusing on methacrylic acid (MAA), even though this monomer has been largely addressed, a systematic investigation of the effects of the above-mentioned parameters on its polymerization rate is missing, in particular in the fully ionized case. In this work, the kinetics of non-ionized and fully ionized MAA are characterized by in-situ nuclear magnetic resonance (NMR). Such accurate monitoring of the reaction rate enables the identification of relevant but substantially different effects of the monomer and electrolyte concentration on polymerization rate in the two ionization cases. For non-ionized MAA, the development of a kinetic model based on literature rate coefficients allows us to nicely simulate the experimental data of conversion versus time at a high monomer concentration. For fully ionized MAA, a novel propagation rate law accounting for the electrostatic interactions is proposed: the corresponding model is capable of predicting reasonably well the electrolyte concentration effect on polymerization rate. Nevertheless, further kinetic information in a wider range of monomer concentrations would be welcome to increase the reliability of the model predictions

Interferometric length metrology for the dimensional control of ultra-stable Ring Laser Gyroscopes

We present the experimental test of a method for controlling the absolute length of the diagonals of square ring laser gyroscopes. The purpose is to actively stabilize the ring cavity geometry and to enhance the rotation sensor stability in order to reach the requirements for the detection of the relativistic Lense-Thirring effect with a ground-based array of optical gyroscopes. The test apparatus consists of two optical cavities 1.32 m in length, reproducing the features of the ring cavity diagonal resonators of large frame He-Ne ring laser gyroscopes. The proposed measurement technique is based on the use of a single diode laser, injection locked to a frequency stabilized He-Ne/Iodine frequency standard, and a single electro-optic modulator. The laser is modulated with a combination of three frequencies allowing to lock the two cavities to the same resonance frequency and, at the same time, to determine the cavity Free Spectral Range (FSR). We obtain a stable lock of the two cavities to the same optical frequency reference, providing a length stabilization at the level of 1 part in $10^{11}$, and the determination of the two FSRs with a relative precision of 0.2 ppm. This is equivalent to an error of 500 nm on the absolute length difference between the two cavities

16s rrna sequencing analysis of the gut microbiota in broiler chickens prophylactically administered with antimicrobial agents

In poultry production, gut microbiota (GM) plays a pivotal role and influences different host functions related to the efficiency of production performances. Antimicrobial (AM) use is one of the main factors affecting GM composition and functions. Although several studies have focused their attention on the role of AMs as growth promoters in the modulation of GM in broilers, the consequences of higher AM concentrations administered during prophylactic treatments need to be better elucidated. For this purpose, 16S rRNA gene sequencing was performed to evaluate the impact of different prophylactic AM protocols on the composition and diversity of the broiler GM. Diversity analysis has shown that AM treatment significantly affects alpha diversity in ileum and beta diversity in both ileum and caecum. In ileal samples, the Enterobacteriaceae family has been shown to be particularly affected by AM treatments. AMs have been demonstrated to affect GM composition in broiler. These findings indicate that withdrawal periods were not enough for the restoral of the original GM. Further studies are needed for a better elucidation of the negative effects caused by an altered GM in broilers

Optimization of the geometrical stability in square ring laser gyroscopes

Ultra sensitive ring laser gyroscopes are regarded as potential detectors ofthe general relativistic frame-dragging effect due to the rotation of theEarth: the project name is GINGER (Gyroscopes IN GEneral Relativity), aground-based triaxial array of ring lasers aiming at measuring the Earthrotation rate with an accuracy of 10^-14 rad/s. Such ambitious goal is nowwithin reach as large area ring lasers are very close to the necessarysensitivity and stability. However, demanding constraints on the geometricalstability of the laser optical path inside the ring cavity are required. Thuswe have started a detailed study of the geometry of an optical cavity, in orderto find a control strategy for its geometry which could meet the specificationsof the GINGER project. As the cavity perimeter has a stationary point for thesquare configuration, we identify a set of transformations on the mirrorpositions which allows us to adjust the laser beam steering to the shape of asquare. We show that the geometrical stability of a square cavity stronglyincreases by implementing a suitable system to measure the mirror distances,and that the geometry stabilization can be achieved by measuring the absolutelengths of the two diagonals and the perimeter of the ring

Deep underground rotation measurements: GINGERino ring laser gyroscope in Gran Sasso

GINGERino is a large frame laser gyroscope investigating the ground motion in the most inner part of the underground international laboratory of the Gran Sasso, in central Italy. It consists of a square ring laser with a $3.6$ m side. Several days of continuous measurements have been collected, with the apparatus running unattended. The power spectral density in the seismic bandwidth is at the level of $10^{-10} \rm{(rad/s)/\sqrt{Hz}}$. A maximum resolution of $30\,\rm{prad/s}$ is obtained with an integration time of few hundred seconds. The ring laser routinely detects seismic rotations induced by both regional earthquakes and teleseisms. A broadband seismic station is installed on the same structure of the gyroscope. First analysis of the correlation between the rotational and the translational signal are presented.Published0345027TM. Sviluppo e Trasferimento TecnologicoJCR Journa

The GINGER Project

GINGER (Gyroscopes IN General Relativity) is a project aiming at measuring the Lense-Thirring effect, at 1% level, with an experiment on earth. It is based on an array of ring-lasers, which are the most sensitive inertial sensors to measure the rotation rate of the Earth. The GINGER project is still under discussion; the experiment G-GranSasso is an R&D experiment financed by INFN Group II, it is studying the key points of GINGER and at the same time developing prototypes. In the following the signal coming out of a ring-laser and the present sensitivity are described.The prototypes GP2 and GINGERino and the preliminary results are reported. This project is inter-disciplinary since ring-lasers provide informations for the fast variation of the earth rotation rate, they are used for the rotational seismology and for top sensitivity angle metrology

Kinetics of the hydrogen abstraction ·C2H5 + alkane → C2H6 + alkyl reaction class: an application of the reaction class transition state theory

This paper presents an application of the reaction class transition state theory (RC-TST) to predict thermal rate constants for hydrogen abstraction reactions at alkane by the C2H5 radical on-the-fly. The linear energy relationship (LER), developed for acyclic alkanes, was also proven to hold for cyclic alkanes. We have derived all RCTST parameters from rate constants of 19 representative reactions, coupling with LER and the barrier height grouping (BHG) approach. Both the RC-TST/LER, where only reaction energy is needed, and the RC-TST/BHG, where no other information is needed, can predict rate constants for any reaction in this reaction class with satisfactory accuracy for combustion modeling. Our analysis indicates that less than 50% systematic errors on the average exist in the predicted rate constants using either the RC-TST/LER or RC-TST/BHG method, while in comparison with explicit rate calculations, the differences are within a factor of 2 on the average. The results also show that the RC-TST method is not sensitive to the choice of density functional theory used

Experimental and Modeling Study of Acrylamide Copolymerization with Quaternary Ammonium Salt in Aqueous Solution

The free-radical copolymerization of acrylamide with the cationic monomer DMAEA-Q in aqueous medium is investigated with special attention to its composition behavior, which reveals to be affected by the electrostatic interactions between the charges in the system. The reaction kinetics is determined by in situ 1H NMR experiments, showing a peculiar dependence of the copolymer composition upon initial monomer and electrolyte concentrations. A kinetic model simulating the evolution of copolymer composition as a function of conversion is developed, accounting for the nonconventional features of the system. Namely, a description of the electrostatic interactions based on the DLVO theory is introduced to define a functional dependence of the rate coefficients on the ionic strength. Secondary reactions are also included due to the acrylic nature of both monomers. The proposed model is applied to estimate the corresponding reactivity ratios and proves to exhibit the correct functionality with respect to monomer concentration and ionic strength. (Figure Presented)