Surface characterization microscopical methods

A new alternative to solve this problem is atomic force microscopy (AFM) which is an emerging surface characterization tool in a wide variety of materials science fields. The method is relatively easy and offers a subnanometer or atomic resolution with little sample preparation required. The basic principle involved is to utilize a cantilever with a spring constant weaker than the equivalent spring between atoms. This way the sharp tip of the cantilever, which is microfabricated from silicon, silicon oxide or silicon nitride using photolithography, mechanically scans over a sample surface to image its topography. Typical lateral dimensions of the cantilever are on the order of 100 pm and the thickness on the order of 1 pm. Cantilever deflections on the order of 0.01 nm can be measured in modem atomic force microscopes. 

Microscopic methods. While microscopic methods provide direct visual information on membrane morphology as discussed earlier, determination of pore size, especially meaningful pore size distribution, by this type of methods is tedious and difficult. Advances have been made on the electron microscopy techniques to visualize membrane surface pores. For example, Merin and Cheryan [1980] have developed a replica-TEM technique to observe membrane surface pores. Nevertheless, microscopic methods have remained primarily as a surface morphology characterization tool and not as a pore size determination scheme. 

Bulk characterization yields information on the macroscopic properties of the biomaterial such as thermal, mechanical, solubility, optical, and dielectric properties. Surface characterization yields morphological information that is critical for interfacing the implant or drug delivery device with the host tissue. This could be achieved by microscopic and spectfoscopic methods. Next in the hierarchy is the characterization of processes such as biodegradation mechanism and kinetics under biomimetic in vitro conditions. Cases of implanted device failure need to be assessed by systematic interrogation of explanted medical devices. After knowing the basic characteristics of the biomaterial, real-time investigation of in vivo processes plays a major role in the successful journey of an implant. 

Various characterization methods both in vitro and in vivo can provide information to understand, predict, and improve the performance of drug delivery systems. Selection of methods depends on the material properties and their applications. Viscoelastic properties can be measured using both DMA and oscillatory shear rheometry. DSC is a most useful method of measuring thermal transitions. Various microscopic methods are available to obtain the microstrac-ture and shape of the materials. Amorphous and crystaUine materials have different packing patterns of molecules, and these properties can be determined from XRD or density measurements. Surface properties such as surface elemental composition and material porosity can be obtained from various spectroscopic methods as well as from BET measurements. The biocompatibility of the material can be determined from both in vitro and in vivo assays. In vitro dissolution testing can be utilized to correlate with the in vivo performance of polymeric drug delivery systems. All these characterization methods can provide valuable information... 

Surface Characterization. Several analytical methods were used in characterizing the modified polymer surfaces. Energy Dispersive X-ray (EDX) spectra and electron micrographs of the surfaces were obtained using a JEOL JSM-IC848 scanning electron microscope in order to confirm the presence of phosphorus and chlorine. 

Recently, the investigation of polymer brushes has been focused on the synthesis of new tethered polymer systems primarily through surface-initiated polymerization (SIP). Previously, the term polymer brushes has been limited to the investigation of block copolymers (qv) or end-functional linear polymers that have been physically or chemically adsorbed to surfaces, respectively (3,4). Recent synthetic efforts using different polymerization mechanisms have resulted in the discovery of many novel properties of polymer brushes. This has been aided no less than the use of innovative and unique surface-sensitive analysis methods as applied to flat substrates and particles. The study of polymer brushes has benefited from improved dielectric, optical, spectroscopic, and microscopic characterization methods. Understanding the chemistry of these grafting reactions and how... 

The interphase can be studied by microscopic, spectroscopic, and thermodynamic ) techniques. The objective of this chapter is to review selected results of some of the microscopic and spectroscopic techniques, listed in Table 1, used to study polymer/metal adhesion. Baun<4) categorized fifty-four surface characterization methods useful in analyzing six aspects of adhesion. Information expected from a microscopic and spectroscopic analysis of adhesion is depicted in Figure 1. 

A popular straightforward characterization method is microscopy. Although they cannot be used easily in all cases, microscopic techniques can be used not only for the optical observation of various surfaces and particles but also for the precise estimation of the dimensions of colloidal particles. We need to use (for colloidal particles) the advanced electron microscopic (SEM or TEM) or probe microscopic methods (STM and AFM) as the simple optical microscope cannot be used for colloids due to its low resolution, which at best can cover the upper limit of colloidal dimensions (a few micrometres). 

TABLE 32.3 Microscopical Methods Used in Membrane Surface Characterization... 

Direct information on membrane porous structure and sublayer structure is obtained with microscopical methods. The most commonly applied methods are SEM and AFM because the resolution of the microscopes is good enough for characterization of ultra- and nano-hltration membranes and even RO membranes. In rough surface characterization conventional optical microscopy can also be used. The resolution of CSLM is sufficient only for characterization of microhltration membranes. However, the advantage of CSLM is that information on the membrane bulk structure can be obtained without physical sample cross sectioning. 

Microscopic instruments such as scanning electron microscopy (SEM) and field emission SEM (EESEM) are useful for direct observation on the morphology of membrane surface and cross section (Table 15.3i). Use of microscopic methods for characterizing membrane pores provides information on pore geometry, which is difficult to obtain by other characterization techniques. Resolution of SEM and EESEM can be down to 1 nm [178], Therefore, the size, shape, and distribution of pores on ME and UF membranes can be visualized under SEM and FESEM. 

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