Nadejda B. Matsko

Interactions Between Components

Interactions can be of different kinds, e.g. interaction of polymer chains with the surface of the filler, interactions of external species with the surface (e.g. adsorption on the surface), interactions of particles surface with stimulants like temperature, sonication, salt, solvent etc., or interactions between two inorganic species etc. (also termed as decoration of one inorganic surface with the particles of other). Such information can help to predict the behavior of the materials, their aggregation tendency etc. The characterizations of such interactions can be achieved either by analyzing the effect of such expected interactions on the morphology or by actual visualization of the morphology of the components. Though such evaluations generate information on the interaction between the components, however, the nature of interaction (chemical or physical) is not possible to be obtained. Various systems dealing with above mentioned interactions between the different components and substrates are described in the following sections.

Visualization of Organic–Inorganic Nanostructures in Liquid

The characterization of colloidal systems like pharmaceutical or hydrated chemical formulations by microscopic techniques is essential to obtain reliable data about the actual morphology of the system. Since the size range of colloidal drug delivery systems has long ago reached the lower end of the nanometer scale, classical light microscopy has been replaced by electron microscopy techniques which provide sufficient resolution for the visualisation of nano-sized structures. Indeed, the superior resolution and methodological versatility of electron microscopy has rendered this technique an indispensable tool for the analysis of nanoemulsions. Microscopic analysis of these lipid-based drug delivery systems with particle sizes in the lower submicron range provides critical information about the size, shape and internal structure of the emulsion droplets. Moreover, surfactant aggregates such as liposomes or multilamellar structures which remain unnoticed during particle size measurements can be detected in this fashion. This chapter provides a brief overview about both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques which have been employed to characterise colloidal solutions. Of special interest are sophisticated cryo techniques of sample preparation for both TEM and SEM which deliver high-quality images of pharmaceutical formulations in their natural state. An overview about the instrumentation and sample preparation for all presented methods is given. Important practical aspects, sources of error and common artefacts as well as recent methodological advances are discussed. Selected examples of electron microscopic studies of nanoemulsions are presented to illustrate the potential of this technique to reveal detailed and specific information.

Structure of the Biological Membrane (Detection of the Membrane Components In Vivo)

The ultrastructure of biological membrane is one of the hottest topics in cell biology. These organelle are involved in a variety of cellular processes such as cell adhesion, ion conductivity and cell signaling and serve as the attachment surface for several extracellular structures, including the cell wall, glycocalyx, and intracellular cytoskeleton. The aim of this chapter is to provide a brief overview about microscopical techniques which are suitable for the ultrastructural characterization of different kind of cellular membranes at the level of individual macromolecule. Important practical aspects concerning sample preparation, sources of error and common artefacts as well as recent methodological advances are discussed.

Tomography of the Hydrated Materials

The preservation of native structures of soft polymers and biological organisms during sample preparation and microscopic study is the ultimate requirement for comprehensive analyses at the level of individual macromolecules. A combination of low temperature techniques such as cryo sectioning [cryoultramicrotomy and cryo focus ion beam (FIB) milling], followed by high-resolution cryo microscopy study (cryo transmission electron microscopy, cryo TEM), has proved to be the most powerful approach available so far for ultrastructural investigation of the bulk of soft materials.

Nano to Micro and Macro Characterization

The commercial applications of materials often involve the structuring of nanoparticles into micro or macro structures. For example, the polymer particles are generally structured to form monoliths which can then be used as chromatography columns. Similarly, inorganic nanoparticles are fused together to form macroporous networks which can be used as catalyst supports or high strength and low density metallic foams. Organic particles also form continuous films on the substrates on which they are applied or coated. Characterization of such structures for their porosity, surface roughness, uniformity as well as stability is required as these characteristics drive the applications of these networks. A number of examples describing these features are presented in the following sections.

Introduction to Microscopy Techniques

The answer to this question is quite obvious: in order to obtain the comprehensive impression about surrounding objects, one needs both of these sensation systems. Importantly, the information obtained visually and tactilely is not the same since different detection mechanisms are applied. This example provides a perception of diversity and similarity between detection mechanisms of three main high resolution microscopy techniques (transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM)) and human visual and tactile sensation systems.

Chapter 6:Microstructure and Properties of Compatibilized Polyethylene–Graphene Oxide Nanocomposites

Polyolefins are important among commodity plastics owing to their use in a variety of applications. Especially, high density polyethylene (HDPE) has wide range of properties including low cost, ease of recycling, good processability, non-toxicity, biocompatibility, and good chemical resistance. The ...

Morphology in Organic–Inorganic Composites

Polymeric materials are generally reinforced with inorganic fillers in order to reduce cost or to enhance mechanical, thermal, rheological and barrier properties. The fillers used have different geometrical dimensions and thus affect the polymer properties differently. For example, silica (and calcium carbonate) particles are generally spherical (aspect ratio near to 1) and enhance the strength of the polymeric materials. On the other hand, clay and graphene particles are platy in nature and enhance the mechanical, barrier and electrical properties of the polymers. Fibers or nanotubes have the highest aspect ratio and enhance the longitudinal strength as well as electrical properties of the polymer materials. Most common factor affecting the filler performance is the dispersion and distribution of the filler particles in the polymer matrix. Good dispersion and distribution of the filler particles is mandatory to achieve efficient interface between the organic inorganic components. Various microscopy techniques constitute most powerful methods to characterize the morphology of the organic–inorganic materials as described by the diverse examples presented in the following sections. The characterization of nanocomposites also poses additional challenges owing to the large number of nano-sized particles. The microscopic characterization also acts as a quality control tool as the poorly dispersed systems can be improved by changing the process parameters. Apart from characterization of the distribution and dispersion of filler particles, microscopy techniques also provide information on the alignment of the platy and fibrous particles.

Confirmation of Surface Reactions

Chemical reactions are carried out on the surface of various substrates in order to generate specific functionalities or to change the surface properties of these substrates. For example, polymeric brushes are grafted on the surface of clay platelets in order to synthesize exfoliated nanocomposites. Similarly, the brushes are also grafted from the surface of polymer particles in order to generate surface properties directing their various applications. It is thus of requirement to confirm the surface reaction.

Surface and Volume Characterization

Both surface and volume morphology of the systems is required to be characterized as the resulting surface and bulk properties of the materials drive their applications. The control on the morphology and its tuning according to the requirement is another characteristic which is generally optimized by microscopic characterizations. These analyses can lead to vital information like surface smoothness/hardness (which in turn affects the wetting and adsorption characteristics of the surface), surface morphology (like strawberry, moon crater, hemispherical morphology etc.), particle size and its distribution, porosity of the particles, interactions between the components, defects present in the bulk of the sample, overall stability/dispersion of the filler phase in the polymer matrix, structure of the monoliths etc. The following sections demonstrate these analyses for a wide range of systems. Apart from organic and organic–inorganic systems, a brief discussion on the surface and volume characterization of inorganic particles has also been presented.