Experimental Methods in Polymer Science

Modern Methods in Polymer Research and Technology

Toyoichi Tanaka

• Publisher: Academic Press
• Year: 2012
• Print ISBN: 9780126832655
• eBook ISBN: 9780080506128
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

Successful characterization of polymer systems is one of the most important objectives of today's experimental research of polymers. Considering the tremendous scientific, technological, and economic importance of polymeric materials, not only for today's applications but for the industry of the 21st century, it is impossible to overestimate the usefulness of experimental techniques in this field. Since the chemical, pharmaceutical, medical, and agricultural industries, as well as many others, depend on this progress to an enormous degree, it is critical to be as efficient, precise, and cost-effective in our empirical understanding of the performance of polymer systems as possible. This presupposes our proficiency with, and understanding of, the most widely used experimental methods and techniques.This book is designed to fulfill the requirements of scientists and engineers who wish to be able to carry out experimental research in polymers using modern methods. Each chapter describes the principle of the respective method, as well as the detailed procedures of experiments with examples of actual applications. Thus, readers will be able to apply the concepts as described in the book to their own experiments. - Addresses the most important practical techniques for experimental research in the growing field of polymer science - The first well-documented presentation of the experimental methods in one consolidated source - Covers principles, practical techniques, and actual examples - Can be used as a handbook or lab manual for both students and researchers - Presents ideas and methods from an international perspective - Techniques addressed in this volume include: - Light Scattering - Neutron Scattering and X-Ray Scattering - Fluorescence Spectroscopy - NMR on Polymers - Rheology - Gel Experiments

Chapter 1

Light Scattering

C. Wu, Department of Chemistry; The Chinese University of Hong Kong; Shatin, N. T. Hong Kong; The Open Laboratory of Bond-Selective Chemistry; Department of Chemical Physics; University of Science and Technology of China; Hefei, Anhui, China

B. Chu, Department of Chemistry; State University of New York at Stony Brook; Stony Brook, New York; Department of Materials Science and Engineering; State University of New York at Stony Brook; Stony Brook, New York

1.1 Introduction

When a monochromatic, coherent beam of light is incident on a dilute solution of macromolecules or suspension of colloidal particles and the solvent refractive index is different from that of the solute (macromolecules or colloidal particles), the incident light is scattered by each illuminated macromolecule or colloidal particle in all directions. The scattered light waves from different macromolecules or particles mutually interfere, or combine, at a distant, fast detector (e.g., a photo-multiplier tube) and produce a net scattered intensity I(t) or photon counts n(t) that are not uniform on the scattering (or detection) plane. If all the macromolecules or particles are stationary, the scattered light intensity at each direction would be a constant (i.e., independent of time). However, in reality, all the scatterers in solution are undergoing constant Brownian motions, and this fact leads to fluctuations of the scattered intensity pattern on the detection plane and the fluctuations in l(t) if the detection area is sufficiently small. The fluctuation rates can be related to different relaxation processes such as translational and rotational diffusions as well as internal motions of the macromolecules. The faster the relaxation process, the faster the intensity fluctuations will be.

In a broad definition, laser light scattering (LLS) could be classified as inelastic (e.g., Raman, fluorescence, and phosphorescence) and elastic (no absorption) light scattering. However, in polymer and colloid science, light scattering is normally referred to in terms of static (elastic) or dynamic (quasi-elastic) measurements, or both, of the scattered light [1]. Static LLS as a classic and absolute analytical method measures the time-average scattered intensity, and it has been widely used to characterize synthetic and natural macromolecules [2]. On the other hand, dynamic LLS measures the intensity fluctuations instead of the average light intensity (this is where the word dynamic comes from), and its essence may be explained as follows: When the incident light is scattered by a moving macromolecule or particle, the detected frequency of the scattered light will be slightly higher or lower than that of the original incident light owing to the Doppler effect, depending on whether the particle moves towards or away from the detector. Thus, the frequency distribution of the scattered light is slightly broader than that of the incident light. This is why dynamic LLS is also called quasi-elastic light scattering (QELS). The frequency broadening (≈10⁵−10⁷ Hz) is so small in comparison with the incident light frequency (≈10¹⁵ Hz) that it is very difficult, if not impossible, to detect the broadening directly in the frequency domain. However, it can be effectively recorded in the time domain via a time correlation function. Thus, dynamic light scattering is sometimes known as intensity fluctuation spectroscopy. If we use digital photons to measure the intensity fluctuations, the term photon correlation spectroscopy (PCS) is then used to refer to the technique described here.

In the last two decades, thanks to the advance of stable laser, ultrafast electronics and personal computers, LLS, especially dynamic LLS, has evolved from a very special instrument for physicists and physical chemists to a routine analytical tool in polymer laboratories or even to a daily quality-control device in production lines. Commercially available research-grade LLS instruments are normally capable of making static and dynamic measurements simultaneously for studies of colloidal particles in suspension or macromolecules in solution as well as in gels and viscous media.

1.1.1 ENERGY TRANSFE...

Table of contents

• Cover image
• Title page
• Table of Contents
• Series in Polymers, Interfaces, and Biomaterials
• Copyright
• Contributors
• Preface by Series Editor
• Preface by Editor
• Chapter 1: Light Scattering
• Chapter 2: Neutron Scattering
• Chapter 3: Fluorescence Spectroscopy
• Chapter 4: NMR Spectroscopy in Polymer Science
• Chapter 5: Mechanical Spectroscopy of Polymers
• Chapter 6: Polymer Hydrogel Phase Transitions
• Index