Técnicas preparación muestras

Presentación del tema: "Técnicas preparación muestras"— Transcripción de la presentación:

1 Técnicas preparación muestras
Métodos habituales Técnicas transmisión; KBr pastillas, Líquidos Espectroscopía Transformada Fourier Reflectancia Total Atenuada - ATR Reflectancia Difusa - DRIFTS Reflectancia Especular Reflexión-Absorción

2 Celda Transmisión Io Is

3 Análisis Aditivos Polímeros
Universal Film Maker Espesores Film uniformes 15, 25, , 250 mm Ambiente a 300 OC 5% precisión espesor 4

4 Reflectancia Total Atenuada ATR
Onda evanescente Capacidad penetración de unas pocas Micras Elemento Reflexión Interno

5 ARK Reflectancia Total Atenuada Kit

6 Capacidad Penetración
Indices de refracción de IRE y Muestra Angulo de incidencia Longitud de onda radiación dp = l / 2 p no (sin2Q - n2/no2)

7 Capacidad de Penetración
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 4000 3000 2000 1000 Penetration Depth (mm) Wavenumbers (cm-1) ZnSe Ge Indice refracción muestra = 1.4

8 Profundidad Penetración
ZnSe (45o) Hexano RI = 2.4 Ge (45o) Hexano RI = 4.0 Si (45o) Hexano RI = 3.4 0.0 0.2 0.4 0.6 0.8 1.0 Absorbance 2700 2800 2900 3000 3100 3200 Spectra-Tech Baseline H-ATR Accessory Wavenumbers (cm-1)

9 Reflectancia Difusa Reflectancia Especular Reflectancia Difusa

10 Teoría de la Reflectancia Difusa
Diferentes procesos simultáneamente refracción, transmisión, reflexión, difracción y dispersión Teoría de Kubelka-Munk D.R. = (1-R )2/2R 8

11 Ventajas DRIFTS Preparación mínima muestra
Posibilidad análisis mayoría materiales no reflectores, incluyendo materiales muy opacos o poco absorbentes Análisis de superficies irregulars y materiales duros Alta sensibilidad (pocos ppm) This slide is self-explanatory. It shows the Gemini in the diffuse mode, and lists all of the relative features. 39

12 Análisis Agentes Espesantes Fibras por DRIFTS
Agentes comunes, como PVA y almidón, se añaden para proteger fibras sintéticas Mezclas de PVA y almidón se analizan por DRIFT TQ software se usa para determinar la cantidad de PVA añadido This example shows diffuse reflectance, the Gemini accessory, and TurboQuant software. When weaving yarns to make fabrics on a loom, the actual weaving process itself can damage the yarns. The abrasive forces encountered in weaving can damage the fibers. In order to protect the yarns, sizing ingredients are added. These sizing ingredients coat the fibers and protect them. These sizing ingredients are then removed prior to bleaching, dyeing, etc. For some synthetic fibers, a good sizing combination had been a mixture of PVA and starch. It is very important the the relative concentration of each remain constant, and that the mixture is evenly applied to the fibers. If there are inconsistencies, the weaving will be uneven. Therefore, a quick method must be developed in order to monitor the concentrations of the sizing ingredients. 37

13 Reflectancia Difusa/ Gemini
Muestras analizadas, 128 barridos, 8 cm-1 resolución 2.5% PVA 12.5% PVA 0.8 1.0 1.2 1.4 1.6 1.8 Diffuse Reflectance 1000 1500 2000 2500 3000 3500 4000 Wavenumbers (cm-1) Here are two diffuse reflectance spectra obtained on the Gemini. The difference in the PVA concentration is 2.5% for one, and 12.5% for the other. These samples were analyzed neat (no KBr dilution necessary). I collected 128 scans at a spectral resolution of 8 cm-1. Kubelka-Munk corrections were unnecessary, because we are not going to compare the data to transmission data. An automatic baseline correction was the only process applied to the spectra. We can see that there are some small differences, but TurboQuant is definitely needed to accentuate the differences and enable us to accurately predict the amount of PVA present. 40

14 Análisis de Películas por Reflectancia Especular
Q1 Q1 = Reflectance spectroscopy very thin films pose a unique problem to the IR spectroscopist. Reflectance Absorbance Spectroscopy (RAS) using near normal incident light can be used successfully for film samples on reflective surfaces which are thicker than ¼ incident radiation wavelength typically m thick films. Incident radiation passes through the sample at a given angle and reflects off the substrate at a complementary angle passing through the sample again before being collected at the detector. The RAS pathlength is greater than the transmission pathlength due to this double pass. But what about very thin films 1m to as little as 10 angstroms, where there isn’t enough pathlength to get any data? If the sample is on a metal reflective surface use of a Grazing Angle incident radiation can be the solution. Angulo incidencia próximo normal Angulo incidencia Grazing

15 Análisis monocapas por Reflectancia Angulo Grazing
¿Cuales son sus usos? Analiza films muy delgados (20 angstroms mm) incluyendo monocapas moleculares Determina espesores de films Realiza estudios de orientación molecular en films monocapa Grazing angle measurements are commonly used to measure ultra-thin films from 20angstroms to a micron. Even monolayers can be analyzed with grazing angle when they are on reflective metal surfaces. Grazing angle can be used in qualitative analysis of these films, to measure thickness and study molecular orientation.

16 Análisis monocapa por Reflectancia Especular
80o ángulo de incidencia fijo sin ajustes espejos Ópticas recubierta oro para reflexión máxima Posicionamiento horizontal FT - 80 The analysis of our monolayer sample was conducted on a Spectra-Tech FT-80 Grazing angle accessory with ZnSe wire grid polarizer (not shown).