Localization of n-alcohols and structural effects in aqueous solutions of sodium dodecyl sulfate

Small-angle neutron Mattering measurements OD sodium dodecyl sulfate aqueous solutions have been performed in the presence of n-alcohols, from methanol to octanol, at different alcohol concentrations. By modeling the experimental intensities, it was possible to obtain structural information and to derive simultaneously the distribution of the alcohols between the aqueous and the micellar phases. It was found that short chain alcohols tend to remain in the aqueous phase and, by altering the solvent properties, induce a decrease in the aggregation number of sodium dodecyl sulfate micelles. On the other hand, alcohols with longer hydrocarbon chains were found to be present in both phases thoug…

Identification Techniques I

Infrared (IR) and Raman spectroscopy have a high potential for characterisation of material. Extensive series of wet chemical analysis may be substituted by a single spectroscopic measurement followed by detailed chemometric data evaluation. Topics of this chapter are: (i) basics of IR and Raman spectroscopy, (ii) the registration of “correct” spectra, and (iii) spectra evaluation. Dedicated applications in the area of conservation science are collected in separate chapters. The infrared (IR) spectrum is often called the fingerprint of a substance. An IR spectrum identifies a substance like a human fingerprint. Due to their origin the features of an IR spectrum are bands, not peaks. They in…

Effect of chain stiffness on the phase behavior of model polymer and surfactant solutions by GCMC simulations

Computational Studies of POSS Based Materials

Visualizing Solubilization by a Realistic Particle Model in Chemistry Education

An application for the visualization of the mixing process of two different types of structureless interacting particles is presented. The application allows to demonstrate on a qualitative basis, as well as by quantitatively monitoring the time evolution of the fractions of aggregates of different sizes, that the formation of a homogeneous mixture is the result of favorable solute-solvent interactions as well as by temperature. It is suggested that, along with the use of suitable macroscopic examples, visualizations by the present application are useful in elucidating concepts related to miscibility/solubility. The application is based on a two-dimensional realistic dynamic model where ato…

Model Random Copolymer Solutions by Monte Carlo simulations

Effect of stiffness on the phase behavior of cubic lattice chains

Gran canonica Monte Carlo (GCMC) simulazioni assistite da tecniche di riponderazione istogramma sono stati utilizzati per studiare l'effetto della flessibilità catena sul comportamento di soluzione fase di cubi catene reticolari corti con 4-32 segmenti. Ciò è stato fatto variando un parametro di rigidità gradualmente fino alla media calcolata end-to-end distanza avvicinato la lunghezza totale. Per entrambe le catene flessibili e rigide si è riscontrato che la temperatura critica, ottenuta tramite mista analisi dei campi di dimensioni finite, aumentata lunghezza della catena e la densità critica trasferisce a valori più bassi, in accordo con le osservazioni sperimentali. Il estrapolato lungh…

Analysis of small-angle scattering patterns from a commercial Al-Li alloy by means of a model incorporating a repulsive step potential

Abstract Small-angle X-ray scattering measurements are reported for a commercial Al-8·49%Li-51% Cu (atomic composition) alloy solution treated at 520°C and thermally aged for several times at several temperatures. Data have been analysed by means of a model of ellipsoidal precipitate particles previously proposed by some of us and by a modification of this model where, in the interparticle interference term, allowance is made for interactions between the precipitate particles at longer range than previously. This was achieved by the introduction, in addition to the hard-sphere interaction potential, of a potential step. Our fits indicate that the precipitate particles interact through a rep…

Studi computazionali su fenomeni di auto-aggregazione di copolimeri-modello in soluzione

Le scienze per crescere - Edizione per progetti

The Uniqueness of Teaching and Learning Chemistry

Unfortunately, the current perception of Chemistry held by many students and the general public alike appears to be in stark contrast to its true nature. Although chemistry is ubiquitous in all aspects of our daily lives it continues to be perceived as highly theoretical and of little relevance. A clearer understanding of the fundamental Nature of Chemistry will be needed if students are to recognize its true importance and character. It is not possible to fully understand, and as a consequence accept on an intuitive basis, the 'mystery' and fascinations arising from the transformation of matter, without first adopting a convincing sub-microscopic view, able to connect observed macroscopic …

Monte Carlo simulations of aggregation phenomena in model polymer and surfactant solutions

Prefazione - Scienza inForma. La Forma nella Scienza

Preliminary studies on nanocomposite based on high quality Silicon Carbide nanofibers

Nanocomposites are nowadays the most promising new materials due to their unique properties (such as high mechanical strength, chemical and thermal resistance). The nanocomposite matrix is blended with a nanostructured filler. In this study, Silicon Carbide nanofibers (NFSiC) and their bundles were tested as a reinforcement of two epoxy resins: EPIKOTE 828 and EL 20. PAP-4 (33 phr) and P-900 (40 phr) were used as hardeners in the two cases, respectively. Several samples were prepared in the range between 0.1 and 5 % wt for both types of resins and fillers (NFSiC and NFSiC bundles). Mechanical and electrical properties were tested. The fillers were obtained using a new simple, fast, low-cost…

Small-Angle Scattering from Phase-Separated Metallic Alloys: From Experiment to Phase Diagrams

In this paper, phase-separated metallic alloys are described in terms of concentration fluctuations. As a consequence, Small Angle Scattering equations which allow to calculate the entire scattering curve by incorporating particle-particle interference effects on the basis of the Percus-Yevick formalism, are obtained. It is shown that, for Aluminium-Lithium alloys, satisfactory fits of the experimental data can be obtained if it is assumed that Li rich elliptical monodisperse precipitate particles approach each other at average distances which are larger than the sum of the hard-sphere particle radii. It is also shown that a possible ambiguity of this model, within the Percus-Yevick formali…

Sistemi complessi e didattica delle scienze

Computer Simulations Study of the Phase Behavior of Polymer and Surfactant Solutions: from Flexible to Rigid Chains

Effect of Stiffness on the Micellization Behavior of Model H4T4 Surfactant Chains

The micellization behavior of a series of model surfactants, all with four head and tail groups (H4T4) but with different degrees of chain stiffness, was studied using grand canonical Monte Carlo simulations on a cubic lattice. The critical micelle concentration, micellar size, and thermodynamics of micellization were examined. In all cases investigated, the critical micelle concentration was found to increase with increasing temperature as observed for nonionic surfactants in apolar or slightly polar solvents. At a fixed reduced temperature and increasing chain stiffness, in agreement with previous observations, it was found that the critical micelle concentration decreased and the average…

Chimica e licei

Nutrirsi di Scienza

Virtual Reality visualizations of complex molecular structures in chemistry education. The β-CD-ASA example

SPAIS. Quali conoscenze per comprendere l'innovazione?

Le NeuroScienze

Sistemi complessi. I docenti di discipline scientifiche a confronto. L’esperienza di SPAIS 2008.

Apprendimento basato sull'indagine dei fenomeni termici di dissoluzione

Aggregation behavior of tethered POSS nanocubes by Monte Carlo simulations

Realistic Implementation of the Particle Model for the Visualization of Nanoparticle Precipitation and Growth

An application for visualizing the aggregation of structureless atoms is presented. The application allows us to demonstrate on a qualitative basis, as well as by quantitatively monitoring the aggregate surface/volume ratio, that the enhanced reactivity of nanoparticles can be connected with their large specific surface. It is suggested that, along with the use of geometric analogies, this bottom-up approach can be effective in discussing the enhanced reactivity proprieties of nanoparticles. The application is based on a two-dimensional realistic dynamic model where atoms move because of their thermal and interaction potential energies, and the trajectories are determined by solving numeric…

LA SCUOLA SPAIS: RICERCA SCIENTIFICA E DIDATTICA DELLE SCIENZE IN UN CONTESTO MULTIDISCIPLINARE

SPAIS si pone come obiettivo l’individuazione e il conseguente approfondimento delle conoscenze di base che sono necessarie nel campo della chimica, della fisica e delle scienze biologiche e naturali per comprendere e comunicare i contenuti fondamentali della moderna ricerca scientifica e tecnologica. L’edizione 2013 sul tema “ScientificaMente – le Neuroscienze” viene qui presentata evidenziandone particolarmente le implicazioni nella didattica della Chimica

Determination of the Composition of Mixed Hydrogenated and Fluorinated Micelles by Small Angle Neutron Scattering

Molecular association of cryptand 221D in NaCl-water solutions. A small-angle neutron scattering study

Molecules of 5-Decyl-4,7,13,16,21-pentaoxa-1,10-diaza-bicyclo-[8.8.5.]tricosan (221D) and its sodium complex, with both a hydrophobic and a hydrophilic portion, are expected to form aggregates in water solutions. This was confirmed by surface tension measurements. The aggregation behaviour was studied by small-angle neutron scattering at two different [NaCl]/[221D] molar ratios, such as to obtain, in one case, aggregates entirely made up of ionic monomers, and in the other, mixed micelles constituted by both ionic and non-ionic units. The variation of the aggregation number and number of aggregates indicated that, in the former case, smaller micelles were formed, as a consequence of repulsi…

Nanodispositivi e macchine molecolari

Un modello realistico per visualizzazioni dinamiche in didattica della chimica

In questo lavoro sono presentate due applicazioni per la visualizzazione dei processi di aggregazione e di solubilizzazione di particelle interagenti e prive di struttura. Le applicazioni consentono di dimostrare qualitativamente e quantitativamente, per mezzo dell'osservazione dell'evoluzione temporale del rapporto superficie/volume e della frazione di particelle aggregate, che, da un lato, il processo di crescita di nanoaggregati è accompagnato da una diminuzione del rapporto superficie/volume, dall'altro, che interazioni soluto-solvente favorevoli e temperature elevate producono soluzioni omogenee. Si propone che, insieme ad opportuni esempi macroscopici, visualizzazioni mediante le pres…

Dal Micro al Macro

.

Scienza e Arti Perdute: i Segreti degli Antichi Maestri Liutai

Lo scopo di questo lavoro è illustrare agli insegnanti la connessione tra due settori di attività apparentemente lontani: la scelta dei materiali utilizzati nella liuteria artigianale e la chimica. Il ruolo, la composizione e la classificazione delle principali vernici per liuteria sono qui descritte assieme ad una breve sintesi dello stato dell’arte. Nel lavoro, vengono presentati i principali concetti di una tecnica analitica non distruttiva abbastanza semplice (la spettroscopia di fluorescenza da raggi X) ma, probabilmente, non abbastanza nota ai non addetti ai lavori. Un caso di studio a essa correlato è inoltre presentato per evidenziare uno dei possibili contributi del chimico nello s…

Studio computazionale di materiali nanostrutturati POSS

I modelli nelle Scienze

Il contributo contiene una introduzione ai lavori presentati in occasione della XIII edizione della Scuola Permanente per l’Aggiornamento degli Insegnanti di Scienze Sperimentali - SPAIS, Agrigento, 22 – 27 Luglio 2019

VERSO UN APPRENDIMENTO AUTENTICO DELLA CHIMICA DI BASE: TRASPOSIZIONE DIDATTICA DEI RISULTATI DELLA MODERNA RICERCA SCIENTIFICA.

In questo lavoro viene presentata una proposta riguardante l'uso dei risultati della moderna ricerca in campo chimico per introdurre i concetti fondanti della disciplina nella pratica didattica della Chimica di base nella Scuola Secondaria di Secondo Grado. Con questo approccio, i concetti di base dovrebbero risultare meno astratti e il mondo della ricerca più accessibile.

Cultural Heritage and the Image of Chemistry

Application of the small-angle neutron scattering technique to the study of solubilization mechanisms of organic molecules by micellar systems

Abstract We present the possible contribution of the small-angle neutron scattering (SANS) technique to the molecular interpretation of the solubilization phenomena in simple micellar systems. We show for a few ternary micellar systems, that an appropriate analysis of SANS experimental data can provide information on modifications induced on micellar dimension, shape, number of monomer, and charge and on the partition coefficient of the additive and its localization inside the micellar aggregate. The influence of n -alcohols on the thermodynamics and on the structure of sodium dodecyl sulphate (SDS) aqueous solution has been extensively investigated, so the agreement between the results obt…

Progetto di Istituzione della Scuola di Didattica Chimica e di Ricerca Educativa “Ulderico Segre”

Prefazione - Messaggi di Scienza

Ricerca e Innovazione Responsabili in didattica. Il progetto IRRESISTIBLE

Formazione di complessi di inclusione della beta-ciclodestrina. Una dimostrazione colorimetrica

Un percorso didattico sul legame chimico in un contesto autentico

La solubilità

La Scuola Permanente per l'Aggiornamento degli Insegnanti di Scienze Sperimentali (SPAIS) Dieci anni di attività

Preparazione assistita da microonde di nanoplacchette di grafene in miscela acqua/liquido ionico

Nanotechnology for Solar Energy Conversion

Nel presente lavoro è descritto un modulo didattico sviluppato, nell’ambito del progetto europeo IRRESISTIBLE, dall’unità di Palermo sul tema dell’applicazione delle nanoscienze allo sfruttamento dell’energia solare. L’attività è stata rivolta ad alunni del biennio dell’Istituto Tecnico, nell’ambito delle discipline Scienze Chimiche Integrate e Scienze e Tecnologie Applicate Chimca e ad alunni dell’ultimo anno del Liceo Scientifico, nell’ambito della disciplina Fisica. Tra le varie attività , anche sperimentali, è stata realizzata una cella DSSC che, insieme ad altro materiale di comunicazione preparato dagli stessi studenti, è stata presentata alla mostra scientifica Esperienza inSegna e a…

A New Procedure for the Lightning Experiment: Mn2O7 and Ethanol

Formation of Mn2O7 and its reaction with ethanol is commonly referred to as “underwater lightnings”. Classic procedures are reviewed, along with their weak points, and physical and chemical properties of dimanganese heptaoxide are shown. A new improved approach is finally presented, safer and easier, and suited for lecturehall activities.

Elucidating the Influence of the Activation Energy on Reaction Rates by Simulations Based on a Simple Particle Model

An application for visualizing the dynamic properties of an equimolar binary mixture of isotropic reactive particles is presented. By introducing a user selectable choice for the activation energy, the application is useful to demonstrate qualitatively that the reaction rate depends on the above choice and on temperature. The application is based on a 2D realistic dynamic model where atoms move because of their thermal energies and the trajectories are determined by solving numerically Newton’s laws according to a Molecular Dynamics (MD) scheme. Collisions are monitored as time progresses, and every time the collision energy is larger than the selected activation energy, a reactive event oc…

Una nuova formazione bidisciplinare degli insegnanti di Scienze Sperimentali

VERSO UN APPRENDIMENTO AUTENTICO DELLA CHIMICA DI BASE: UN PERCORSO DIDATTICO SUL LEGAME CHIMICO

Effect of chain stiffness on the phase behavior of model polymer and surfactant solutions by GCMC simulations

IMPATTO DELLA CHIMICA NELLA VITA QUOTIDIANA: UN PROGETTO DEL NETWORK EC2E2N 2

Il progetto si pone come obiettivo la realizzazione di “Studi di Caso”, esemplificativi in aree in cui la Chimica ha un ruolo determinante e che dimostrino l’impatto di questa scienza nella vita quotidiana. Gli esempi scelti, dovranno essere specifici, attraenti e interessanti anche per un pubblico privo di basi scientifiche. Inoltre, si realizzeranno un certo numero di quesiti online, attraverso i quali il pubblico potrà anche valutare la propria consapevolezza di tale impatto.

Small Angle Neutron Scattering from Systems of Interacting Particles. Modelling High Density Micellar Fluids

The need for analytical solutions of the scattering equation for complex situations (polydisperse samples, scattering from non centrosymmetrical particles, etc.) has somehow escaped the attention of the workers in the Small Angle Scattering field, although it is clear that, at the level of sophistication today available for the experiments, a more rigorous approach is necessary. For quite a few years our group has been actively engaged in SANS research and has occasionally devoted its attention to develop alternative ways of data analysis based on more rigorous solutions of the scattering equation.

The Small Angle Scattering technique: an effective tool in the structural investigation of archaeologically relevant specimens

An overview of application of Small Angle X-ray Scattering (SAXS) techniques to topics of interest in the field of Cultural Heritage is presented. The basic concepts of the technique, a description of sources and laboratory instrumentation and some models and methods for data analysis are discussed. Applications of SAXS to various kinds of materials are reported to obtain information on the structure useful to shed light in some subjects such as preparation, physical treatment, traceability and degradation of materials.

Ce:Y3Al5O12−Poly(methyl methacrylate) Composite for White-Light-Emitting Diodes

A Ce:YAG-poly(methyl methacrylate) (PMMA) composite was prepared by using the melt compounding method. The structure and morphology were investigated by X-ray diffractometry, transmission electron microscopy, and small-angle X-ray scattering. The optical properties (emission, excitation, and fluorescence decay rate) of the composite were studied by using photoluminescence spectroscopy. The polymer–filler interactions were studied using 13C cross-polarization magic-angle spinning NMR spectroscopy (13C{1H} CP-MAS NMR). The results indicated that Ce:YAG particles are well-dispersed in the PMMA matrix without loss of their luminescence properties or significant spectral shift, thus suggesting t…

Diossido di titanio e alcune sue applicazioni. Spunti didattici

Il diossido di titanio, TiO2, ampiamente utilizzato come pigmento di colore bianco, è uno dei materiali più studiati nell’ambito della ricerca per le sue proprietà fotocatalitiche. Esso, infatti, contribuisce alla fotodegradazione di sostanze inquinanti, motivo per cui è utilizzato nel settore della purificazione dell’aria e dell’acqua e per la realizzazione di vetri autopulenti, disponibili commercialmente. Nel presente lavoro viene suggerito un percorso didattico con l’obiettivo di mettere in evidenza le proprietà fotocatalitiche del diossido di titanio oltre che può essere utilizzato per affrontare concetti fondamentali quali la struttura a bande dei solidi e la fotocatalisi. Il percorso…

On the nature of phase separation in a commercial aluminium-lithium alloy

Abstract The formation of lithium-rich precipitate particles, known as δ′ phase, is responsible for the particularly desirable mechanical properties which make aluminium-lithium alloys interesting for different industrial applications. The structure and the kinetics of the phase separation process are conveniently studied by small-angle X-ray scattering, though uncertainties remain on the actual shape of the phase diagram of the system, particularly in the region of interest. In this paper are reported small-angle X-ray scattering measurements on a commercial AlLi (8.49% Li atoms) both in the region of formation of the precipitate and during its successive growth. Modelling of the experime…

Computational studies of POSS - based materials

Un modello realistico per visualizzazioni in didattica

In this work, two applications for the visualization of the aggregation and the solubilization of structureless interacting particles are presented. The applications allow to demonstrate on a qualitative basis as well as by quantitatively monitoring the time evolution of the surface/volume ratio and of the fractions of aggregated particles, that, on the one hand, the growth of nanoaggregates implies a decrease of their surface/volume ratio and, on the other, that the formation of homogeneous mixtures is the result of favorable solute-solvent interactions as well as of temperature. It is suggested that, along with the use of suitable macroscopic examples, visualizations by the present applic…

Small angle scattering study of the structure of isotactic polypropylene-hydrogenated oligo(cyclopentadiene) blends

Abstract Blends of isotactic polypropylene ( i PP) and hydrogenated oligo cyclopentadiene (HOCP) have been studied by means of small angle X-ray scattering in the temperature range 70–160°C. The structure of blends containing less than 25% HOCP is very similar to the one of plain i PP, i.e. lamellae whose thickness increases by increasing the temperature. Blends containing more than 25% HOCP are characterized by two kinds of lamellae formed by layers of i PP and amorphous material rich in i PP and in HOCP, respectively. The crystallizable i PP present in both phases crystallizes from the melt, in analogy to what happens in HDPE/HOCP blends and in agreement with the values of the crystallini…

Scienza inForma. La Forma nella Scienza

SPAIS 2017 si propone di approfondire l’analisi dell’importanza della forma in vari campi del sapere scientifico: dalla forma delle molecole in relazione alle loro proprietà, gli aggregati supramolecolari e, via via su scale dimensionali sempre più grandi, alla forma degli organismi, della Terra e dell’Universo. Come sempre proporrà anche stimolanti “contaminazioni” fra Scienze, Storia, Filosofia e Arte.

I Modelli nelle Scienze

Il volume raccoglie i contributi presentati in occasione della XIII edizione della Scuola Permanente per l’Aggiornamento degli Insegnanti di Scienze Sperimentali - SPAIS, Agrigento, 22 – 27 Luglio 2019. Il tema riguardante i modelli scientifici è di particolare interesse in tutte le Scienze e particolare attenzione è stata rivolta ad argomenti di carattere interdisciplinare.